Patent Publication Number: US-10758456-B2

Title: Redox polymerizable composition with photolabile transition metal complexes

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage filing under 35 U.S.C. 371 of PCT/US2016/055619, filed Oct. 6, 2016, which claims the benefit of U.S. Application No. 62/251,931, filed Nov. 6, 2015, the disclosure of which is incorporated by reference in its/their entirety herein. 
    
    
     BACKGROUND 
     Redox reactions represent an important method for initiating the curing of acrylate, methacrylate and other vinyl-based resin, including adhesive and dental formulations. Redox-initiated curing often has advantages over photoinitiated curing, including improved depth of cure and a slower accumulation of stress during the initial stages of curing. 
     A significant challenge in the use of redox initiating systems is finding an optimal balance between stability and reactivity. The reactivity of the redox system needs to be sufficiently high to achieve full curing and obtain the desired physical properties within a short period of time. However, if the reactivity is too great, problems such as premature curing, accumulation of stress, and poor shelf stability of the formulation can be encountered. 
     SUMMARY 
     The present disclosure provides a method to overcome these problems by creating an “on demand” redox-initiated cure, in which the transition metal complex of the redox cure initiator system has latent activity while the formulation is stored and delivered, but then can be triggered when required. 
     The present disclosure provides a redox initiator system for initiating polymerization comprising an oxidizing agent, a reducing agent, and photolabile transition metal complex that participates in a redox cycle. On exposure to actinic radiation, such as UV, the transition metal complex photolyzes, releasing the transition metal and initiating the redox-initiated polymerization. Advantageously, polymerization of the instant compositions may be initiated by exposure to actinic radiation, but continued irradiation is not required. When the redox initiator system is combined with polymerizable monomers to form a polymerizable composition, the polymerization may be initiated, then the composition builds molecular weight and physical properties as the composition continues to cure in the absence of light. 
     In one aspect, this disclosure provides a polymerizable composition comprising one or more ethylenically-unsaturated polymerizable monomers or oligomers and an initiator system that participates in a redox cycle. 
     In another aspect, this disclosure provides a polymerizable dental composition comprising a polymerizable dental resin and the initiator system that participates in a redox cycle. 
    
    
     DETAILED DESCRIPTION 
     The chemically polymerizable compositions comprise a polymerizable component (an ethylenically unsaturated polymerizable component, including monomers and oligomers) and a redox initiator system that includes the photolabile transition metal complex, an oxidizing agent, and a reducing agent. 
     The photolabile transition metal complex is of the general formula: 
                         
wherein
 
R Photo  is a photolabile group;
 
M +  is a transition metal that participates in a redox cycle;
 
each X 1  and X 2  is independently selected from —N—, —S—, and —O—;
 
each X 3  and X 4  is independently selected from the group consisting of —NR 1 —, and —S—;
 
each R 1  is independently selected from the group consisting of: H, alkyl, cycloalkyl, heterocycloalkyl, arylalkyl, heteroarylalkyl, alkoxy, halo, formyl, hydroxyl, acyl, aryloxy, alkylthio, amino, alkylamino, arylalkylamino, disubstituted amino, acylamino, acyloxy, ester, amide, and carboxyalkyl;
 
each adjacent pair of R 1  and R 2  can independently form a heterocycloalkyl or heteroaryl group with respective heteroatom X 3  or X 4 ;
 
each of R 2 , R 3 , R 4 , R 5 , R 6 , and R 7  is independently selected from the group consisting of: H, alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkylalkyl, cycloalkylalkenyl, cycloalkylalkynyl, heterocyclo, heterocycloalkyl, heterocycloalkenyl, heterocycloalkynyl, aryl, arylalkyl, arylalkenyl, arylalkynyl, heteroaryl, heteroarylalkyl, heteroarylalkenyl, heteroarylalkynyl, alkoxy, halo, mercapto, azido, cyano, formyl, carboxylic acid, carboxyalkyl, hydroxyl, nitro, acyl, aryloxy, alkylthio, amino, alkylamino, arylalkylamino, disubstituted amino, acylamino, acyloxy, ester, amide, sulfoxyl, sulfonyl, sulfonate, sulfonic acid, sulfonamide, urea, alkoxylacylamino, and aminoacyloxy;
 
with the proviso that R 3  is absent when R 1  and R 2  form a heteroaryl group with respective heteroatom X 3  or X 4 ;
 
R 4  and R 5  can together form oxo; or R 6  and R 7  can together form oxo;
 
x is from 1 to 2; and y is from 1 to 3; or a salt thereof.
 
     In some preferred embodiments, the photolabile transition metal complex is of the formula: 
     
       
         
         
             
             
         
       
     
     Wherein 
     R Photo  is a photolabile group; 
     M +  is a transition metal that participates in a redox cycle; 
     each X 1  and X 2  is independently selected from —N—, —S—, and —O—; 
     each X 3  and X 4  is independently selected from the group consisting of —NR 1 —, and —S—; 
     each R 1  is independently selected from the group consisting of: H, alkyl, cycloalkylalkyl, heterocycloalkyl, arylalkyl, heteroarylalkyl, alkoxy, halo, formyl, hydroxyl, acyl, aryloxy, alkylthio, amino, alkylamino, arylalkylamino, disubstituted amino, acylamino, acyloxy, ester, amide, and carboxyalkyl;
 
each of R 2 , R 3 , R 4 , R 5 , R 6 , and R 7  is independently selected from the group consisting of:
         H, alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkylalkyl, cycloalkylalkenyl, cycloalkylalkynyl, heterocyclo, heterocycloalkyl, heterocycloalkenyl, heterocycloalkynyl, aryl, arylalkyl, arylalkenyl, arylalkynyl, heteroaryl, heteroarylalkyl, heteroarylalkenyl, heteroarylalkynyl, alkoxy, halo, mercapto, azido, cyano, formyl, carboxylic acid, carboxyalkyl, hydroxyl, nitro, acyl, aryloxy, alkylthio, amino, alkylamino, arylalkylamino, disubstituted amino, acylamino, acyloxy, ester, amide, sulfoxyl, sulfonyl, sulfonate, sulfonic acid, sulfonamide, urea, alkoxylacylamino, and aminoacyloxy;
 
R 4  and R 5  can together form oxo; or R 6  and R 7  can together form oxo;
 
R 8  and R 9  are independently a hydrocarbyl group when taken with X 3  and X 4  respectively for a heterocyclic group or a heteroaromatic group, with the proviso that R 3  is absent when R 1  and R 2  form a heteroaryl group with respective heteroatom X 3 — or X 4 ;
 
x is from 1 to 2; and y is from 1 to 3; or a salt thereof.
       

     Any known photolabile group that may be irradiated and which cleaves or fragments to release the transition metal may be used. Reference may be made to Petr Klan et al., Photoremovable Protecting Groups in Chemistry and Biology: Reaction Mechanisms and Efficiency, Chem. Reviews, 2013, vol. 113, pp 119-191 and Jacob Wirz et al., Photoremovable Protecting Groups: Reaction Mechanisms and Applications, Photochem. Photobiol. Sci., 2002, Vol. 1, pp. 441-458. 
     With reference to Formulas I and II, useful photolabile groups “R Photo ” include, but are not limited to, phenacyl groups, 2-alkylphenacyl groups, ethylene-bridged phenacyl groups, p-hydroxyphenacyl groups, benzoin groups, o-nitrobenzyl groups, o-nitro-2-phenethylloxycarbonyl groups, coumarin-4-yl methyl groups, benzyl groups, o-hydroxylbenzyl groups, o-hydroxynapthyl groups, 2,5-dihydroxyl benzyl groups, 9-phenylthioxanthyl, 9-phenylxanthyl groups, anthraquinon-2-yl groups, 8-halo-7-hydroxyquinoline2-yl methyl groups, pivaloylglycol groups. 
     In some preferred embodiments, the transition metal complex may be represented by Formula III: 
                         
where R Photo  is a photolabile group;
 
M +  is a transition metal that participates in a redox cycle;
 
the bracketed carbonyl oxygen may be present or absent, and if absent is defined for R 4  and R 5  supra, and are preferably H; and
 
R hetero  is selected from pyridine, imidazole and thiophene rings.
 
     Useful photolabile groups include the following. It will be understood that the pyridine groups are illustrated for simplicity for the —R 1 —R 2 —X 3 — or —R 1 —R 2 —X 4 — or group of Formula I, or the —R 8 —X 3 — or the R 9 —X 4 — groups of Formula II, and are not intended to limit the scope or interpretation of the compounds of Formulas I or II. Further, the aromatic groups, particularly the phenyl groups, may be further substituted by alkyl, aryl, halide, or hydroxy groups. The transition metal, shown as M + , is also not shown for simplicity. The illustrated phenyl groups may further be substituted for napthyl, biphenyl, phenanthrenyl or anthracenyl groups. The mode of photocleavage is illustrated by the ˜. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Useful transition metals, M + , include the catalytically active valence states of Cu, Fe, Ru, Cr, Mo, Pd, Ni, Pt, Mn, Rh, Re, Co, V, Au, Nb and Ag. Preferred low valent metals include Cu(II), Fe(II), Co(II), Pt(II) and Ru(II). Other valent states of these same metals may be used, and the catalytically active valence states generated in situ. 
     The compounds of Formulas I-III may be prepared as described in U.S. Pat. No. 8,440,827 (Franz et al.), incorporated herein by reference. 
     The molar proportion of photolabile transition metal complex (of Formulas I-III) relative to oxidizing agent (or reducing agent) is generally that which is effective to polymerize the selected polymerizable component(s), but may be from 1:1000 to 1:5, preferably from 1:500 to 1:25, more preferably from 1:250 to 1:50, and most preferably from 1:200 to 1:75. The oxidant and reductant of the redox initiator system are used in approximately equimolar amount. Generally the mole ratio of the oxidant and reductant is from 1:1.5 to 1.5:1, preferably 1:1.1 to 1.1 to 1. 
     Useful reducing agents include ascorbic acid, ascorbic acid derivatives, and metal complexed ascorbic acid compounds as described in U.S. Pat. No. 5,501,727 (Wang et al.); amines, especially tertiary amines, such as 4-tert-butyl dimethylaniline; aromatic sulfinic salts, such as p-toluenesulfinic salts and benzenesulfinic salts; thioureas, such as 1-ethyl-2-thiourea, tetraethyl thiourea, tetramethyl thiourea, 1,1-dibutyl thiourea, and 1,3-dibutyl thiourea; barbituric acid and 1-benzyl-5-phenyl barbituric acid; beta-diketones, including dimedone, 2-methylcyclohexane-1,3-dione, 2-methylcyclopentane-1,3-dione, and 3-methyl-2,4-pentanedione; beta-diesters, including 2,2-dimethyl-1,3-dioxane-4,6-dione,2,2,5-trimethyl-1,3-dioxane-4,6-dione, 2,2-dimethyl-5-phenyl-1,3-dioxane-4,6-dione, and dimethyl malonate, and mixtures thereof. Other secondary reducing agents may include cobalt (II) chloride, ferrous chloride, ferrous sulfate, hydrazine, hydroxylamine (depending on the choice of oxidizing agent), salts of a dithionite or sulfite anion, and mixtures thereof. Preferably, the reducing agent is an ascorbic acid derivative. 
     Suitable oxidizing agents will also be familiar to those skilled in the art, and include but are not limited to persulfuric acid and salts thereof, such as sodium, potassium, ammonium, cesium, and alkyl ammonium salts. Preferable oxidizing agents include peroxides such as benzoyl peroxides, hydroperoxides such as cumyl hydroperoxide, t-butyl hydroperoxide, and amyl hydroperoxide, as well as salts of transition metals such as cobalt (III) chloride and ferric chloride, cerium (IV) sulfate, perboric acid and salts thereof, permanganic acid and salts thereof, perphosphoric acid and salts thereof, and mixtures thereof. 
     The reducing and oxidizing agents are present in amounts sufficient to permit an adequate free radical reaction rate. This can be evaluated by combining all of the ingredients of the polymerizable composition except for the optional filler, and observing whether or not a hardened mass is obtained. 
     Preferably, the reducing agent is present in an amount of at least 0.01% by weight, and more preferably at least 0.1% by weight, based on the total weight of the polymerizable components of the polymerizable composition. Preferably, the reducing agent is present in an amount of no greater than 10% by weight, and more preferably no greater than 5% by weight, based on the total weight (including water) of the polymerizable components of the polymerizable composition. 
     Preferably, the oxidizing agent is present in an amount of at least 0.01% by weight, and more preferably at least 0.10% by weight, based on the total weight of the polymerizable components of the polymerizable composition. Preferably, the oxidizing agent is present in an amount of no greater than 10% by weight, and more preferably no greater than 5% by weight, based on the total weight of the polymerizable components of the polymerizable composition. 
     In general, the oxidizing agent and reducing agent are chosen so they are not directly reactive, and require the presence of the transition metal to effect the redox cycle, as is known in the art. The components of the polymerizable composition may be segregated to prevent premature reactions. In particular it is desirable to segregate the transition metal complex and the reducing agent, prior to reaction. In particular, it is beneficial to have a “two-part” system in which the polymerizable monomers, the oxidizing agent and the transition metal complex is in the first mixture, and the reducing agent and any filler or other additives are in a second mixture. 
     The present disclosure further provides a polymerizable composition comprising the redox initiator system (including labile transition metal complex, oxidant and reductant), and at least one polymerizable monomer, such as vinyl monomers, and (meth)acryloyl monomers (including acrylate esters, amides, and acids to produce (meth)acrylate homo- and copolymers). The redox initiator system is present in the composition in amounts, from about 0.1 to about 10 parts by weight, preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the polymerizable component of the polymerizable composition. 
     In some embodiments, the polymerizable composition comprises the redox initiator system and one or more vinyl monomers. Vinyl monomers useful in the polymerizable composition include vinyl ethers (e.g. methyl vinyl ether, ethyl vinyl ether), vinyl esters (e.g., vinyl acetate and vinyl propionate), styrene, substituted styrene (e.g., α-methyl styrene), vinyl halide, divinylbenzene, alkenes (e.g. propylene, isomers of butylene, pentene, hexene up to dodecene, isoprene, butadiene) and mixtures thereof. 
     In some embodiments the polymerizable composition comprises one or more (meth)acrylate ester monomer(s). (Meth)acrylate ester monomer useful in preparing (meth)acrylate (co)polymers are monomeric (meth)acrylic ester of a non-tertiary alcohol, which alcohol contains from 1 to 14 carbon atoms and preferably an average of from 4 to 12 carbon atoms. 
     Examples of monomers suitable for use as the (meth)acrylate ester monomer include the esters of either acrylic acid or methacrylic acid with non-tertiary alcohols such as ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 1-hexanol, 2-hexanol, 2-methyl-1-pentanol, 3-methyl-1-pentanol, 2-ethyl-1-butanol, 3,5,5-trimethyl-1-hexanol, 3-heptanol, 1-octanol, 2-octanol, isooctylalcohol, 2-ethyl-1-hexanol, 1-decanol, 2-propylheptanol, 1-dodecanol, 1-tridecanol, 1-tetradecanol, citronellol, dihydrocitronellol, and the like. In some embodiments, the preferred (meth)acrylate ester monomer is the ester of (meth)acrylic acid with butyl alcohol or isooctyl alcohol, or a combination thereof, although combinations of two or more different (meth)acrylate ester monomer are suitable. In some embodiments, the preferred (meth)acrylate ester monomer is the ester of (meth)acrylic acid with an alcohol derived from a renewable source, such as 2-octanol, citronellol, or dihydrocitronellol. 
     In some embodiments it is desirable for the (meth)acrylic acid ester monomer to include a high T g  monomer. The homopolymers of these high T g  monomers have a T g  of at least 25° C., and preferably at least 50° C. Examples of suitable monomers useful in the present invention include, but are not limited to, t-butyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, s-butyl methacrylate, t-butyl methacrylate, stearyl methacrylate, phenyl methacrylate, cyclohexyl methacrylate, isobornyl acrylate, isobornyl methacrylate, benzyl methacrylate, 3,3,5 trimethylcyclohexyl acrylate, cyclohexyl acrylate, N-octyl acrylamide, and propyl methacrylate or combinations. 
     The (meth)acrylate ester monomer is present in an amount of up to 100 parts by weight, preferably 85 to 99.5 parts by weight based on 100 parts total monomer content used to prepare the polymer, exclusive of the amount of multifunctional (meth)acrylates. Preferably (meth)acrylate ester monomer is present in an amount of 90 to 95 parts by weight based on 100 parts total monomer content. When high T g  monomers are included, the copolymer may include up to 50 parts by weight, preferably up to 20 parts by weight of the (meth)acrylate ester monomer component. 
     The polymerizable composition may comprise an acid functional monomer, where the acid functional group may be an acid per se, such as a carboxylic acid, or a portion may be a salt thereof, such as an alkali metal carboxylate. Useful acid functional monomers include, but are not limited to, those selected from ethylenically unsaturated carboxylic acids, ethylenically unsaturated sulfonic acids, ethylenically unsaturated phosphonic or phosphoric acids, and mixtures thereof. Examples of such compounds include those selected from acrylic acid, methacrylic acid, itaconic acid, fumaric acid, crotonic acid, citraconic acid, maleic acid, oleic acid, β-carboxyethyl (meth)acrylate, 2-sulfoethyl methacrylate, styrene sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, vinylphosphonic acid, and mixtures thereof. 
     Due to their availability, acid functional monomers of the acid functional copolymer are generally selected from ethylenically unsaturated carboxylic acids, i.e. (meth)acrylic acids. When even stronger acids are desired, acidic monomers include the ethylenically unsaturated sulfonic acids and ethylenically unsaturated phosphonic acids. The acid functional monomer is generally used in amounts of 0.5 to 15 parts by weight, preferably 1 to 15 parts by weight, most preferably 5 to 10 parts by weight, based on 100 parts by weight total monomer. 
     The polymerizable composition may comprise a polar monomer. The polar monomers useful in preparing the copolymer are both somewhat oil soluble and water soluble, resulting in a distribution of the polar monomer between the aqueous and oil phases in an emulsion polymerization. As used herein the term “polar monomers” are exclusive of acid functional monomers. 
     Representative examples of suitable polar monomers include but are not limited to 2-hydroxyethyl (meth)acrylate; N-vinylpyrrolidone; N-vinylcaprolactam; acrylamide; mono- or di-N-alkyl substituted acrylamide; t-butyl acrylamide; dimethylaminoethyl acrylamide; N-octyl acrylamide; tetrahydrofurfuryl (meth)acrylate, poly(alkoxyalkyl) (meth)acrylates including 2-(2-ethoxyethoxy)ethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-methoxyethoxyethyl (meth)acrylate, 2-methoxyethyl methacrylate, polyethylene glycol mono(meth)acrylates; alkyl vinyl ethers, including vinyl methyl ether; and mixtures thereof. Preferred polar monomers include those selected from the group consisting of tetrahydrofurfuryl (meth)acrylate, 2-hydroxyethyl (meth)acrylate and N-vinylpyrrolidinone. The polar monomer may be present in amounts of 0 to 10 parts by weight, preferably 0.5 to 5 parts by weight, based on 100 parts by weight total monomer. 
     The polymerizable composition may further comprise a vinyl monomer when preparing acrylic copolymers. When used, vinyl monomers useful in the (meth)acrylate polymer include vinyl esters (e.g., vinyl acetate and vinyl propionate), styrene, substituted styrene (e.g., α-methyl styrene), vinyl halide, divinylbenzene, and mixtures thereof. As used herein vinyl monomers are exclusive of acid functional monomers, acrylate ester monomers and polar monomers. Such vinyl monomers are generally used at 0 to 5 parts by weight, preferably 1 to 5 parts by weight, based on 100 parts by weight total monomer when preparing acrylic copolymers. 
     A multifunctional (meth)acrylate may be incorporated into the blend of polymerizable monomers. Examples of useful multifunctional (meth)acrylates include, but are not limited to, di(meth)acrylates, tri(meth)acrylates, and tetra(meth)acrylates, such as 1,6-hexanediol di(meth)acrylate, poly(ethylene glycol) di(meth)acrylates, polybutadiene di(meth)acrylate, polyurethane di(meth)acrylates, and propoxylated glycerin tri(meth)acrylate, and mixtures thereof. The amount and identity of multifunctional (meth)acrylate is tailored depending upon application of the adhesive composition, for example, adhesives, hardcoats or dental resins. 
     Typically, the multifunctional (meth)acrylate is present in amounts up to 100 parts, preferably 0.1 to 100 parts, based 100 parts by weight of remaining polymerizable monofunctional monomers. In some embodiments the multifunctional (meth)acrylate is used in amounts of greater than 50 parts by weight, based on the 100 parts by weight of remaining polymerizable monomers. In some embodiments, the multifunctional (meth)acrylate may be present in amounts from 0.01 to 5 parts, preferably 0.05 to 1 parts, based on 100 parts total monomers of the polymerizable composition for adhesive applications, and greater amounts for hardcoats or dental resins, as described herein. 
     In such embodiments, an acrylic copolymer may be prepared from a polymerizable composition comprising:
         i. up to 100 parts by weight, preferably 85 to 99.5 parts by weight of an (meth)acrylic acid ester;   ii. 0 to 15 parts by weight, preferably 0.5 to 15 parts by weight of an acid functional ethylenically unsaturated monomer;   iii. 0 to 15 parts by weight of a non-acid functional, ethylenically unsaturated polar monomer;   iv. 0 to 5 parts by weight vinyl monomer;   v. 0 to 100 parts by weight of a multifunctional (meth)acrylate, preferably 50 to 100 parts by weight, relative to i-iv;
 
and
   vi. the redox initiator system (including the photolabile complex, oxidant and reductant) in amounts from about 0.1 weight percent to about 5.0 weight percent, relative to 100 parts total monomer i-v.       

     The curable composition may also include other additives. Examples of suitable additives include tackifiers (e.g., rosin esters, terpenes, phenols, and aliphatic, aromatic, or mixtures of aliphatic and aromatic synthetic hydrocarbon resins), surfactants, plasticizers (other than physical blowing agents), nucleating agents (e.g., talc, silica, or TiO 2 ), pigments, dyes, reinforcing agents, solid fillers, stabilizers (e.g., UV stabilizers), and combinations thereof. The additives may be added in amounts sufficient to obtain the desired properties for the cured composition being produced. The desired properties are largely dictated by the intended application of the resultant polymeric article. 
     Adjuvants may optionally be added to the compositions such as colorants, abrasive granules, anti-oxidant stabilizers, thermal degradation stabilizers, light stabilizers, conductive particles, tackifiers, flow agents, bodying agents, flatting agents, inert fillers, binders, blowing agents, fungicides, bactericides, surfactants, plasticizers, rubber tougheners and other additives known to those skilled in the art. They also can be substantially unreactive, such as fillers, both inorganic and organic. These adjuvants, if present, are added in an amount effective for their intended purpose. 
     In some embodiments, a toughening agent may be used. The toughening agents which are useful in the present invention are polymeric compounds having both a rubbery phase and a thermoplastic phase such as: graft polymers having a polymerized, diene, rubbery core and a polyacrylate, polymethacrylate shell; graft polymers having a rubbery, polyacrylate core with a polyacrylate or polymethacrylate shell; and elastomeric particles polymerized in situ in the epoxide from free radical polymerizable monomers and a copolymerizable polymeric stabilizer. 
     Examples of useful toughening agents of the first type include graft copolymers having a polymerized, diene, rubbery backbone or core to which is grafted a shell of an acrylic acid ester or methacrylic acid ester, monovinyl aromatic hydrocarbon, or a mixture thereof, such as disclosed in U.S. Pat. No. 3,496,250 (Czerwinski), incorporated herein by reference. Preferable rubbery backbones comprise polymerized butadiene or a polymerized mixture of butadiene and styrene. Preferable shells comprising polymerized methacrylic acid esters are lower alkyl (C 1 -C 4 ) substituted methacrylates. Preferable monovinyl aromatic hydrocarbons are styrene, alphamethylstyrene, vinyltoluene, vinylxylene, ethylvinylbenzene, isopropylstyrene, chlorostyrene, dichlorostyrene, and ethylchlorostyrene. It is important that the graft copolymer contain no functional groups that would poison the catalyst. 
     Examples of useful toughening agents of the second type are acrylate core-shell graft copolymers wherein the core or backbone is a polyacrylate polymer having a glass transition temperature below about 0° C., such as polybutyl acrylate or polyisooctyl acrylate to which is grafted a polymethacrylate polymer (shell) having a glass transition above about 25° C., such as polymethylmethacrylate. 
     The third class of toughening agents useful in the invention comprises elastomeric particles that have a glass transition temperature (T g ) below about 25° C. before mixing with the other components of the composition. These elastomeric particles are polymerized from free radical polymerizable monomers and a copolymerizable polymeric stabilizer that is soluble in the resins. The free radical polymerizable monomers are ethylenically unsaturated monomers or diisocyanates combined with coreactive difunctional hydrogen compounds such as diols, diamines, and alkanolamines. 
     Useful toughening agents include core/shell polymers such as methacrylate-butadiene-styrene (MBS) copolymer wherein the core is crosslinked styrene/butadiene rubber and the shell is polymethylacrylate (for example, ACRYLOID KM653 and KM680, available from Rohm and Haas, Philadelphia, Pa.), those having a core comprising polybutadiene and a shell comprising poly(methyl methacrylate) (for example, KANE ACE M511, M521, B11A, B22, B31, and M901 available from Kaneka Corporation, Houston, Tex. and CLEARSTRENGTH C223 available from ATOFINA, Philadelphia, Pa.), those having a polysiloxane core and a polyacrylate shell (for example, CLEARSTRENGTH S-2001 available from ATOFINA and GENIOPERL P22 available from Wacker-Chemie GmbH, Wacker Silicones, Munich, Germany), those having a polyacrylate core and a poly(methyl methacrylate) shell (for example, PARALOID EXL2330 available from Rohm and Haas and STAPHYLOID AC3355 and AC3395 available from Takeda Chemical Company, Osaka, Japan), those having an MBS core and a poly(methyl methacrylate) shell (for example, PARALOID EXL2691A, EXL2691, and EXL2655 available from Rohm and Haas) and the like and mixtures thereof. Preferred modifiers include the above-listed ACRYLOID and PARALOID modifiers and the like, and mixtures thereof. 
     The toughening agent is useful in an amount equal to about 1-35 parts by weight, preferably about 3-25 parts by weight, relative to 100 parts by weight of the polymerizable component of the polymerizable composition. The toughening agent adds strength to the composition after curing without reacting with the component of the curable composition or interfering with curing. 
     In some embodiments the crosslinkable composition may include filler. In some embodiments the total amount of filler is at most 50 wt. %, preferably at most 30 wt. %, and more preferably at most 10 wt. % filler. Fillers may be selected from one or more of a wide variety of materials, as known in the art, and include organic and inorganic filler. Inorganic filler particles include silica, submicron silica, zirconia, submicron zirconia, and non-vitreous microparticles of the type described in U.S. Pat. No. 4,503,169 (Randklev). 
     Filler components include nanosized silica particles, nanosized metal oxide particles, and combinations thereof. Nanofillers are also described in U.S. Pat. No. 7,090,721 (Craig et al.), U.S. Pat. No. 7,090,722 (Budd et al.), U.S. Pat. No. 7,156,911 (Kangas et al.), and U.S. Pat. No. 7,649,029 (Kolb et al.). 
     In some embodiments the filler may be surface modified. A variety of conventional methods are available for modifying the surface of nanoparticles including, e.g., adding a surface-modifying agent to nanoparticles (e.g., in the form of a powder or a colloidal dispersion) and allowing the surface-modifying agent to react with the nanoparticles. Other useful surface-modification processes are described in, e.g., U.S. Pat. No. 2,801,185 (Iler), U.S. Pat. No. 4,522,958 (Das et al.) U.S. Pat. No. 6,586,483 (Kolb et al.), each incorporated herein by reference. 
     Surface-modifying groups may be derived from surface-modifying agents. Schematically, surface-modifying agents can be represented by the formula X-Y, where the X group is capable of attaching to the surface of the particle (i.e., the silanol groups of a silica particle) and the Y group is a reactive or non-reactive functional group. A non-functional group does not react with other components in the system (e.g. the substrate). Non-reactive functional groups can be selected to render the particle relatively more polar, relatively less polar or relatively non-polar. In some embodiments the non-reactive functional group “Y” is a hydrophilic group such as an acid group (including carboxylate, sulfonate and phosphonate groups), ammonium group or poly(oxyethylene) group, or hydroxyl group. In other embodiments, “Y” may be a reactive functional groups such as an ethylenically unsaturated polymerizable group, including vinyl, allyl, vinyloxy, allyloxy, and (meth)acryloyl, that may be free-radically polymerized with the polymerizable resin or monomers. 
     Such optional surface-modifying agents may be used in amounts such that 0 to 100%, generally 1 to 90% (if present) of the surface functional groups (Si—OH groups) of the silica nanoparticles are functionalized. The number of functional groups is experimentally determined where quantities of nanoparticles are reacted with an excess of surface modifying agent so that all available reactive sites are functionalized with a surface modifying agent. Lower percentages of functionalization may then be calculated from the result. Generally, the amount of surface modifying agent is used in amount sufficient to provide up to twice the equal weight of surface modifying agent relative to the weight of inorganic nanoparticles. When used, the weight ratio of surface modifying agent to inorganic nanoparticles is preferably 2:1 to 1:10. If surface-modified silica nanoparticles are desired, it is preferred to modify the nanoparticles prior to incorporation into the coating composition. 
     The present polymerizable compositions are also useful in the preparation of hardcoats and structural or semi-structural adhesives. The term “hardcoat” or “hardcoat layer” means a layer or coating that is located on the external surface of an object, where the layer or coating has been designed to at least protect the object from abrasion. 
     The present disclosure provides hardcoat compositions comprising the redox initiator system of Formulas I and II and, a multi-functional (meth)acrylate monomer comprising two (preferably three) or more (meth)acrylate groups, and/or a multi-functional (meth)acrylate oligomer and optionally a (meth)acrylate-functional diluent. 
     In some embodiments, the polymerizable composition provides a structural and/or semi-structural adhesive composition in which the partially cured composition may be disposed between two substrates (or adherends), and subsequently fully cured to effect a structural or semi-structural bond between the substrates. “Semi-structural adhesives” are those cured adhesives that have an overlap shear strength of at least about 0.5 MPa, more preferably at least about 1.0 MPa, and most preferably at least about 1.5 MPa. Those cured adhesives having particularly high overlap shear strength, however, are referred to as structural adhesives. “Structural adhesives” are those cured adhesives that have an overlap shear strength of at least about 3.5 MPa, more preferably at least about 5 MPa, and most preferably at least about 7 MPa. 
     Useful multifunctional (meth)acrylate monomers comprise three or more (meth)acrylate groups. Multifunctional (meth)acrylate monomers are useful in the practice of the present invention because they add abrasion resistance to the hard coat layer. Preferred multifunctional (meth)acrylate monomers comprising three or more (meth)acrylate groups include trimethylol propane tri(meth)acrylate (TMPTA), pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentrithritol tri(meth)acrylate (Sartomer 355), dipentaerythritol penta(meth)acrylate (Sartomer 399), dipentaerythritol hydroxy penta(meth)acrylate (DPHPA), glyceryl propoxy tri(meth)acrylate, trimethylopropane tri(meth)acrylate, and mixtures thereof Another useful radiation-curable component of the present invention is the class of multifunctional (meth)acrylate oligomers, having two or more (meth)acrylate groups, and having an average molecular weight (Mw) in the range from about 400 to 2000. 
     Useful multifunctional (meth)acrylate oligomers include polyester (meth)acrylates, polyurethane (meth)acrylates, and (meth)acrylated epoxy (meth)acrylates. (Meth)acrylated epoxy (meth)acrylates and polyester(meth)acrylates are most preferred because they tend to have a relatively low viscosity and therefore allow a more uniform layer to be applied by the spin coating method. Specifically, preferred multifunctional (meth)acrylate oligomers include those commercially available from UCB Radcure, Inc. of Smyrna, Ga. and sold under the trade name Ebecryl (Eb): Eb40 (tetrafunctional acrylated polyester oligomer), ENO (polyester tetra-functional (meth)acrylate oligomer), Eb81 (multifunctional (meth)acrylated polyester oligomer), Eb600 (bisphenol A epoxy di(meth)acrylate), Eb605 (bisphenol A epoxy di(meth)acrylate diluted with 25% tripropylene glycol di(meth)acrylate), Eb639 (novolac polyester oligomer), Eb2047 (trifunctional acrylated polyester oligomer), Eb3500 (di-functional Bisphenol-A oligomer acrylate), Eb3604 (multi-functional polyester oligomer acrylate), Eb6602 (trifunctional aromatic urethane acrylate oligomer), Eb8301 (hexafunctional aliphatic urethane acrylate), EbW2 (difunctional aliphatic urethane acrylate oligomer), and mixtures thereof. Of these, the most preferred are, Eb 600, Eb605, Eb80, and Eb81. 
     In some embodiments, the multifunctional (meth)acrylate oligomers may comprise a reactive oligomer having pendent polymerizable groups comprising: 
     a) greater than 50 parts by weight, preferably greater than 75 parts by weight, most preferably greater than 80 parts by weight of (meth)acrylate ester monomer units; 
     b) 0.5 to 10 parts by weight, preferably 1 to 5 parts by weight, most preferably 1 to 3 parts by weight, of monomer units having a pendent, free-radically polymerizable functional groups, 
     c) 0 to 20 parts by weight of other polar monomer units, wherein the sum of the monomer units is 100 parts by weight. 
     The reactive oligomer may be redox polymerized per se, or with a multifunctional acrylate, such as hexanediol di(meth)acrylate. The monomer component may further comprise a diluent monomer, as described. The reactive oligomer having pendent polymerizable groups may be prepared as described in U.S. Pat. No. 7,598,298 (Lewandowski et al.), U.S. Pat. No. 7,342,047 (Lewandowski et al.) and U.S. Pat. No. 7,074,839 (Fansler et al.), each incorporated herein by reference. 
     The (meth)acrylate-functional diluents, also referred to herein as “reactive diluents”, are relatively low molecular weight mono- or di-functional, non-aromatic, (meth)acrylate monomers. These relatively low molecular weight reactive diluents are advantageously of a relatively low viscosity, e.g., less than about 30 centipoise (cps) at 25° C. Di-functional, non-aromatic (meth)acrylates are generally preferred over mono-functional non-aromatic (meth)acrylates because di-functional non-aromatic (meth)acrylates allow for quicker cure time. Preferred reactive diluents include 1,6-hexanediol di(meth)acrylate (HDDA from UCB Radcure, Inc. of Smyrna, Ga.), tripropylene glycol di(meth)acrylate, isobornyl (meth)acrylate (1130A, Radcure), 2(2-ethoxyethoxy) ethyl (meth)acrylate (sold under the trade name Sartomer 256 from SARTOMER Company, Inc. of Exton, Pa.), n-vinyl formamide (Sartomer 497), tetrahydrofurfuryl (meth)acrylate(Sartomer 285), polyethylene glycol di(meth)acrylate (Sartomer 344), tripropylene glycol di(meth)acrylate (Radcure), neopentyl glycol dialkoxy di(meth)acrylate, polyethyleneglycol di(meth)acrylate, and mixtures thereof. 
     In some embodiments the polymerizable composition may comprise: 
     20-80 wt. % of multifunctional (meth)acrylate monomers and/or multifunctional (meth)acrylate oligomers, 
     0 to 25 wt. % range of (meth)acrylate diluent, (0-25 wt. %); 
     20 to 75 wt. % of silica (per se, whether or not functionalized), and 
     from about 0.1 weight percent to about 5.0 weight percent of the redox initiator, based on the total weight of the polymerizable composition. 
     In some embodiments the amount of silica, including the silica modified with conventional surface modifying agents and unmodified silica is 20-75 wt. %., preferably 50-70 wt. %. 
     Filler components include nanosized silica particles, nanosized metal oxide particles, and combinations thereof. Nanofillers are also described in U.S. Pat. No. 7,090,721 (Craig et al.), U.S. Pat. No. 7,090,722 (Budd et al.), U.S. Pat. No. 7,156,911 (Kangas et al.), and U.S. Pat. No. 7,649,029 (Kolb et al.). 
     The present polymerization may be conducted in bulk, or in a solvent. Solvents, preferably organic, can be used to assist in the dissolution of the initiator and initiator system in the polymerizable monomers, and as a processing aid. Preferably, such solvents are not reactive with components. It may be advantageous to prepare a concentrated solution of the transition metal complex in a small amount of solvent to simplify the preparation of the polymerizable composition. 
     Suitable solvents include ethers such as diethyl ether, ethyl propyl ether, dipropyl ether, methyl t-butyl ether, di-t-butyl ether, glyme (dimethoxyethane), diglyme, diethylene glycol dimethyl ether; cyclic ethers such as tetrahydrofuran and dioxane; alkanes; cycloalkanes; aromatic hydrocarbon solvents such as benzene, toluene, o-xylene, m-xylene, p-xylene; halogenated hydrocarbon solvents; acetonitrile; lactones such as butyrolactone, and valerolactones; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, and cyclohexanone; sulfones such as tetramethylene sulfone, 3-methylsulfolane, 2,4-dimethylsulfolane, butadiene sulfone, methyl sulfone, ethyl sulfone, propyl sulfone, butyl sulfone, methyl vinyl sulfone, 2-(methylsulfonyl) ethanol, and 2,2′-sulfonyldiethanol; sulfoxides such as dimethyl sulfoxide; cyclic carbonates such as propylene carbonate, ethylene carbonate and vinylene carbonate; carboxylic acid esters such as ethyl acetate, Methyl Cellosolve™ and methyl formate; and other solvents such as methylene chloride, nitromethane, acetonitrile, glycol sulfite and 1,2-dimethoxyethane (glyme), mixtures of such solvents, and supercritical solvents (such as CO 2 ). The present polymerization may also be conducted in accordance with known suspension, emulsion and precipitation polymerization processes. 
     Preferably, the monomer(s) and components of the redox initiator system are selected such that the rate of initiation is not less than 1,000 times (preferably not less than 100 times) slower than the rate of propagation and/or transfer of the generated radical group to the polymer radical. In the present application, “propagation” refers to the reaction of a polymer radical with a monomer to form a polymer-monomer adduct radicals. 
     Polymerizing may be conducted at a temperature of from −78 to 200° C., preferably from 0 to 160° C. and most preferably from 20 to 100° C. The reaction should be conducted for a length of time sufficient to convert at least 10% (preferably at least 50%, more preferably at least 75% and most preferably at least 90%) of the monomer to polymer. Typically, the reaction time will be from several minutes to 5 days, preferably from 30 minutes to 3 days, and most preferably from 1 to 24 hours. 
     Preferable the polymerizable composition comprises a “two-part” system in which the polymerizable monomers and the transition metal complex are in the first mixture, and the oxidizing agent, the reducing agent and any fillers are in a second mixture. The two parts are combined, optionally coated on a substrate, and the redox initiated by exposure to actinic radiation. 
     The polymerizable composition and the redox initiator system may be combined may be irradiated with activating UV radiation to cleave or fragment the photolabile transition metal complex, initiate the redox cycle and polymerize the polymerizable component(s). UV light sources can be of two types: 1) relatively low light intensity sources such as backlights which provide generally 10 mW/cm 2  or less (as measured in accordance with procedures approved by the United States National Institute of Standards and Technology as, for example, with a Uvimap™ UM 365 L-S radiometer manufactured by Electronic Instrumentation &amp; Technology, Inc., in Sterling, Va.) over a wavelength range of 280 to 400 nanometers and 2) relatively high light intensity sources such as medium pressure mercury lamps which provide intensities generally greater than 10 mW/cm 2 , preferably between 15 and 450 mW/cm 2 . Where actinic radiation is used to fully or partially polymerize the polymerizable composition, high intensities and short exposure times are preferred. Intensities can range from about 0.1 to about 150 mW/cm 2 , preferably from about 0.5 to about 100 mW/cm 2 , and more preferably from about 0.5 to about 50 mW/cm 2 . UV LEDs may also be used, such as a Clearstone UV LED lamp (Clearstone Technologies Inc., Hopkins, Minn. 385 nm). 
     The above-described compositions may be coated on a substrate using conventional coating techniques modified as appropriate to the particular substrate. For example, these compositions can be applied to a variety of solid substrates by methods such as roller coating, flow coating, dip coating, spin coating, spray coating, knife coating, and die coating. These various methods of coating allow the compositions to be placed on the substrate at variable thicknesses thus allowing a wider range of use of the compositions. 
     The polymerizable compositions may be coated upon a variety of flexible and inflexible substrates using conventional coating techniques to produce coated articles. Flexible substrates are defined herein as any material which is conventionally utilized as a tape backing or may be of any other flexible material. Examples include, but are not limited to plastic films such as polypropylene, polyethylene, polyvinyl chloride, polyester (polyethylene terephthalate), polycarbonate, poly(methyl methacrylate) (PMMA), cellulose acetate, cellulose triacetate, and ethyl cellulose. Foam backings may be used. 
     In some preferred embodiments, the substrate may be chosen so as to be transparent to the UV radiation used to initiate the redox cycle. The coated article may then be initiated through the thickness of the transparent substrate. In other embodiments the substrate may be opaque to the incident actinic radiation. The coated article having a layer of the polymerizable composition may be initiated before bond closure, and the polymerization will continue once initiated. 
     The present disclosure further provides curable dental compositions comprising the redox initiator system. Although various curable dental compositions have been described, industry would find advantage in compositions having improved properties such as improved working time, and reduced stress deflection and/or reduced shrinkage while maintaining sufficient mechanical properties and depth of cure. 
     As used herein, “dental composition” refers to a material, optionally comprising filler, capable of adhering or being bonded to an oral surface. A curable dental composition can be used to bond a dental article to a tooth structure, form a coating (e.g., a sealant or varnish) on a tooth surface, be used as a restorative that is placed directly into the mouth and cured in-situ, or alternatively be used to fabricate a prosthesis outside the mouth that is subsequently adhered within the mouth. 
     Curable dental compositions include, for example, adhesives (e.g., dental and/or orthodontic adhesives), cements (e.g., resin-modified glass ionomer cements, and/or orthodontic cements), primers (e.g., orthodontic primers), liners (applied to the base of a cavity to reduce tooth sensitivity), coatings such as sealants (e.g., pit and fissure), and varnishes; and resin restoratives (also referred to as direct composites) such as dental fillings, as well as crowns, bridges, and articles for dental implants. Highly filled dental compositions are also used for mill blanks, from which a crown may be milled. A composite is a highly filled paste designed to be suitable for filling substantial defects in tooth structure. Dental cements are somewhat less filled and less viscous materials than composites, and typically act as a bonding agent for additional materials, such as inlays, onlays and the like, or act as the filling material itself if applied and cured in layers. Dental cements are also used for permanently bonding dental restorations such as a crown or bridge to a tooth surface or an implant abutment. 
     As used herein: 
     “dental article” refers to an article that can be adhered (e.g., bonded) to a tooth structure or dental implant. Dental articles include, for example, crowns, bridges, veneers, inlays, onlays, fillings, orthodontic appliances and devices. 
     “orthodontic appliance” refers to any device intended to be bonded to a tooth structure, including, but not limited to, orthodontic brackets, buccal tubes, lingual retainers, orthodontic bands, bite openers, buttons, and cleats. The appliance has a base for receiving adhesive and it can be a flange made of metal, plastic, ceramic, or combinations thereof. Alternatively, the base can be a custom base formed from cured adhesive layer(s) (i.e. single or multi-layer adhesives). 
     “oral surface” refers to a soft or hard surface in the oral environment. Hard surfaces typically include tooth structure including, for example, natural and artificial tooth surfaces, bone, and the like. 
     “curable” is descriptive of a material or composition that can be polymerized or crosslinked by a free radical means such as by irradiating with actinic irradiation to induce polymerization and/or crosslinking; “hardened” refers to a material or composition that has been cured (e.g., polymerized or crosslinked). 
     “initiator” refers to something that initiates curing of a resin. An initiator may include, for example, a polymerization initiator system, a photoinitiator system, a thermal initiator and/or a redox initiator system. 
     “self-etching” composition refers to a composition that bonds to a dental structure surface without pretreating the dental structure surface with an etchant. Preferably, a self-etching composition can also function as a self-primer wherein no separate etchant or primer are used. 
     a “self-adhesive” composition refers to a composition that is capable of bonding to a dental structure surface without pretreating the dental structure surface with a primer or bonding agent. Preferably, a self-adhesive composition is also a self-etching composition wherein no separate etchant is used. 
     a “dental structure surface” refers to tooth structures (e.g., enamel, dentin, and cementum) and bone. 
     an “uncut” dental structure surface refers to a dental structure surface that has not been prepared by cutting, grinding, drilling, etc. 
     an “untreated” dental structure surface refers to a tooth or bone surface that has not been treated with an etchant, primer, or bonding agent prior to application of a self-etching adhesive or a self-adhesive composition of the present invention. 
     an “unetched” dental structure surface refers to a tooth or bone surface that has not been treated with an etchant prior to application of a self-etching adhesive or a self-adhesive composition of the present invention. 
     The total amount of the redox initiator system in the polymerizable resin portion of the unfilled curable dental composition is typically no greater than 5 wt. %. Generally, the amount of redox initiator system is from about 0.1 to 5 wt. % of the polymerizable portion of the unfilled dental composition. 
     The curable dental compositions comprise at least one ethylenically unsaturated resin monomer or oligomer in combination with the redox initiator system. In some embodiments, such as primers, the ethylenically unsaturated monomer may be monofunctional, having a single (e.g. terminal) ethylenically unsaturated group. In other embodiments, such as dental restorations the ethylenically unsaturated monomer is multifunctional. The phrase “multifunctional ethylenically unsaturated” means that the monomers each comprise at least two ethylenically unsaturated (e.g. free radically) polymerizable groups, such as (meth)acrylate groups. 
     The amount of curable resin in the dental composition is a function of the desired end use (adhesives, cements, restoratives, etc.) and can be expressed with respect to the (i.e. unfilled) polymerizable resin portion of the dental composition. For favored embodiments, wherein the composition further comprises filler, the concentration of monomer can also be expressed with respect to the total (i.e. filled) composition. When the composition is free of filler, the polymerizable resin portion is the same as the total composition. 
     In favored embodiments, such ethylenically unsaturated groups of the curable dental resin includes (meth)acryloyl such as (meth)acrylamide and (meth)acrylate. Other ethylenically unsaturated polymerizable groups include vinyl and vinyl ethers. The ethylenically unsaturated terminal polymerizable group(s) is preferably a (meth)acrylate group, particularly for compositions that are hardened by exposure to actinic (e.g. UV and visible) radiation in the presence of the redox initiator system. Further, methacrylate functionality is typically preferred over the acrylate functionality in curable dental compositions. The ethylenically unsaturated monomer may comprise various ethylenically unsaturated monomers, as known in the art, for use in dental compositions. 
     In favored embodiments, the dental composition comprises one or more dental resins having a low volume shrinkage monomer. Preferred (e.g. filled) curable dental compositions (useful for restorations such as fillings and crowns) comprise one or more low volume shrinkage resins such that the composition exhibits a Watts Shrinkage of less than about 2%, preferably no greater than 1.80%, more preferably no greater than 1.60%. In favored embodiments, the Watts Shrinkage is no greater than 1.50%, or no greater than 1.40%, or no greater than 1.30%, and in some embodiments no greater than 1.25%, or no greater than 1.20%, or no greater than 1.15%, or no greater than 1.10%. 
     Preferred low volume shrinkage monomers include isocyanurate resins, such as described in U.S.S.N. 2013/0012614 (Abuelyaman et al.); tricyclodecane resins, such as described in U.S.S.N 2011/041736 (Eckert et al.); polymerizable resins having at least one cyclic allylic sulfide moiety such as described in U.S. Pat. No. 7,888,400 (Abuelyaman et al.); methylene dithiepane silane resins as described in U.S. Pat. No. 6,794,520 (Moszner et al.); and di-, tri, and/or tetra-(meth)acryloyl-containing resins such as described in U.S. 2010/021869 (Abuelyaman et al.); each of which are incorporated herein by reference. 
     In favored embodiments, the majority of the unfilled polymerizable resin composition comprises one or more low volume shrinkage monomers (“Low shrinkage monomers”). For example, at least 50%, 60%, 70%, 80%, 90% or more of the unfilled polymerizable resin may comprise low volume shrinkage monomer(s). 
     In one embodiment, the dental composition comprises at least one isocyanurate resin. The isocyanurate resin comprises a trivalent isocyanuric acid ring as an isocyanurate core structure and at least two ethylenically unsaturated (e.g. free radically) polymerizable groups bonded to at least two of the nitrogen atoms of the isocyanurate core structure via a (e.g. divalent) linking group. The linking group is the entire chain of atoms between the nitrogen atom of the isocyanurate core structure and the terminal ethylenically unsaturated group. The ethylenically unsaturated free radically polymerizable groups are generally bonded to the core or backbone unit via a (e.g. divalent) linking group. 
     The trivalent isocyanurate core structure generally has the formula: 
     
       
         
         
             
             
         
       
     
     The divalent linking group comprises at least one nitrogen, oxygen or sulfur atom. Such nitrogen, oxygen or sulfur atom forms a urethane, ester, thioester, ether, or thioether linkage. Ether and especially ester linkages can be beneficial over isocyanurate resin comprising urethane linkages for providing improved properties such as reduced shrinkage, and/or increased mechanical properties, e.g., diametral tensile strength (DTS). Thus, in some embodiments, the divalent linking groups of the isocyanurate resin are free of urethane linkages. In some favored embodiments, the divalent linking group comprises an ester linkage such as an aliphatic or aromatic diester linkage. 
     The isocyanurate monomer typically has the general structure: 
                         
wherein R 7  is a (hetero)hydrocarbyl group including straight chain, branched or cyclic alkylene, arylene, or alkarylene, and optionally including a heteroatom (e.g. oxygen, nitrogen, or sulfur); R 4  is hydrogen or C1-C4 alkyl; R 8  is heterohydrocarbyl group including alkylene, arylene, or alkarylene linking group comprising at least one moiety selected from urethane, ester, thioester, ether, or thioether, and combinations of such moieties; and at least one of the R 9  groups is
 
     
       
         
         
             
             
         
       
     
     R 7  is typically a straight chain, branched or cyclic alkylene, optionally including a heteroatom, having no greater than 12 carbons atoms. In some favored embodiments, R 7  has no greater than 8, 6, or 4 carbon atoms. In some favored embodiments, R 7  comprises at least one hydroxyl moiety. 
     In some embodiments, R 8  comprises an aliphatic or aromatic ester linkage such as a diester linkage. 
     In some embodiment, R 8  further comprises one or more ether moieties. Hence, the linking group may comprise a combination of ester or diester moieties and one or more ether moieties. 
     For embodiments, wherein the isocyanurate monomer is a di(meth)acrylate monomer, R 9  is hydrogen, alkyl, aryl, or alkaryl, optionally including a heteroatom. 
     The polymerizable resin portion of the curable unfilled dental composition described herein may comprise at least 10 wt. %, 15 wt. %, 20 wt. %, or 25 wt. %, multifunctional ethylenically unsaturated isocyanurate resin(s). The isocyanurate resin may comprise a single monomer or a blend of two or more isocyanurate resins. The total amount of isocyanurate resin(s) in the unfilled polymerizable resin portion of the curable dental composition is typically no greater than 90 wt. %, 85 wt. %, 80 wt. %, or 75 wt. %. 
     The filled curable dental composition described herein typically comprises at least 5 wt. %, 6 wt. %, 7 wt. %, 8 wt. %, or 9 wt. % of multifunctional ethylenically unsaturated isocyanurate resin(s). The total amount of isocyanurate resin(s) of the filled hardenable (i.e. polymerizable) dental composition is typically no greater than 20 wt. %, or 19 wt. %, or 18 wt. %, or 17 wt. %, or 16 wt. %, or 15 wt. %. 
     In another embodiment, the dental composition comprises at least one tricyclodecane resin. The tricyclodecane resin may comprise a single monomer or a blend of two or more tricyclodecane resins. The concentration of multifunctional ethylenically unsaturated tricyclodecane monomer in the (i.e. unfilled) polymerizable resin portion or filled hardenable (i.e. polymerizable) composition can be the same as just described for the multifunctional ethylenically unsaturated isocyanurate monomer. 
     Tricyclodecane monomers generally have the core structure (i.e. backbone unit (U): 
     
       
         
         
             
             
         
       
     
     The backbone unit (U) if the tricyclodecane resin typically comprises one or two spacer unit(s) (S) bonded to the backbone unit (U) via an ether linkage. At least one spacer unit (S) comprises a CH(R 10 )—OG chain, wherein each group G comprises a (meth)acrylate moiety and R 10  (comprises at least one group selected from hydrogen, alkyl, aryl, alkaryl and combinations thereof. In some embodiments, R 10  is hydrogen, methyl, phenyl, phenoxymethyl, and combinations thereof. G may be bonded to the spacer unit(s) (S) via a urethane moiety. 
     In some embodiments, the spacer unit(s) (S) typically comprise 
                         
wherein m is 1 to 3; n is 1 to 3; and R 10  is hydrogen, methyl, phenyl, phenoxymethyl.
 
     In other embodiments, the spacer unit(s) (S) typically comprise 
                         
wherein M=aryl.
 
     In some embodiments the composition comprises a multifunctional ethylenically unsaturated isocyanurate monomer and multifunctional ethylenically unsaturated tricyclodecane monomer at a weight ratio ranging from about 1.5:1 to 1:1.5. 
     In some embodiments, the curable dental composition comprises a polymerizable resin having at least one cyclic allylic sulfide moiety with at least one (meth)acryloyl moiety. 
     The cyclic allylic sulfide moiety typically comprises at least one 7- or 8-membered ring that has two heteroatoms in the ring, one of which is sulfur. Most typically both of the heteroatoms are sulfur, which may optionally be present as part of an SO, SO 2 , or S—S moiety. In other embodiments, the ring may comprise a sulfur atom plus a second, different heteroatom in the ring, such as oxygen or nitrogen. In addition, the cyclic allylic moiety may comprise multiple ring structures, i.e. may have two or more cyclic allylic sulfide moieties. The (meth)acryloyl moiety is preferably a (meth)acryloyloxy (i.e. a (meth)acrylate moiety) or a (meth)acryloylamino (i.e., a (meth)acrylamide moiety). 
     In one embodiment, the low shrinkage resin includes those represented by the formulae: 
     
       
         
         
             
             
         
       
     
     In the above formulae, each A can be independently selected from S, O, N, C (e.g., C(R 10 ) 2 , where each R 10  is independently a H or an organic group), SO, SO 2 , N-alkyl, N-acyl, NH, N-aryl, carboxyl or carbonyl group, provided that at least one X is S or a group comprising S. Preferably, each A is sulfur. 
     B is either alkylene (e.g., methylene, ethylene, etc.) optionally including a heteroatom, carbonyl, or acyl; or is absent, thereby indicating the size of the ring, typically 7- to 10-membered rings, however larger rings are also contemplated. Preferably, the ring is either a 7- or 8-membered ring with B thus being either absent or methylene, respectively. In some embodiments, B is either absent or is a C1 to C3 alkylene, optionally including a heteroatom, carbonyl, acyl, or combinations thereof. 
     X 1  is independently —O— or —NR 4 —, where R 4  is H or C1-C4 alkyl. 
     The R 11  group represents a linker selected from alkylene (typically having more than one carbon atom, i.e. excluding methylene), alkylene optionally including a heteroatom (e.g., O, N, S, S—S, SO, SO 2 ), arylene, cycloaliphatic, carbonyl, siloxane, amido (—CO—NH—), acyl (—CO—O—), urethane (—O—CO—NH—), and urea (—NH—CO—NH—) groups, and combinations thereof. In certain embodiments, R′ comprises an alkylene group, typically a methylene or longer group, that may be either straight chain or branched, and which can be either unsubstituted, or substituted with aryl, cycloalkyl, halogen, nitrile, alkoxy, alkylamino, dialkylamino, akylthio, carbonyl, acyl, acyloxy, amido, urethane group, urea group, a cyclic allylic sulfide moiety, or combinations thereof. 
     R 4  is H or C 1 -C 4  alkyl, and “a” and “b” are independently 1 to 3. 
     Optionally the cyclic allylic sulfide moiety can further be substituted on the ring with one or more groups selected from straight or branched chain alkyl, aryl, cycloalkyl, halogen, nitrile, alkoxy, alkylamino, dialkylamino, akylthio, carbonyl, acyl, acyloxy, amido, urethane group, and urea group. Preferably the selected substituents do not interfere with the hardening reaction. Preferred are cyclic allylic sulfide structures that comprise unsubstituted methylene members. 
     A typical low shrinkage monomer can comprise an 8-membered cyclic allylic sulfide moiety with two sulfur atoms in the ring and with the linker attached directly to the 3-position of the ring with an acyl group (i.e., Ring-OC(O)—). Typically the weight average molecular weight (MW) of the hybrid monomer ranges from about 400 to about 900 and in some embodiments is at least 250, more typically at least 500, and most typically at least 800. 
     The inclusion of a polymerizable compound having at least one cyclic allylic sulfide moiety can result in a synergistic combination of low volume shrinkage in combination with high diametral tensile strength. 
     In another embodiment, the dental composition comprises a low shrinkage resin that includes at least one di-, tri-, and/or tetra (meth)acryloyl-containing resins having the general formula: 
                         
wherein: each X 1  is independently —O— or —NR 4 —, where R 4  is H or C 1 -C 4  alkyl; D and E each independently represent an organic group, and R 12  represents —C(O)C(CH 3 )═CH 2 , and/or p=0 and R 12  represents H, —C(O)CH═CH 2 , or —C(O)C(CH 3 )═CH 2 , with the proviso that at least one R 12  is a (meth)acrylate; each m is 1 to 5; p and q are independently 0 or 1. Although this material is a derivative of bisphenol A, when other low volume shrinkage monomer are employed, such as the isocyanurate and/or tricyclodecane monomer, the dental composition is free of (meth)acrylate monomers derived from bisphenol A. Such resins are described in WO 2008/082881 (Abuelyaman et al.)
 
     In another embodiment, the low shrinkage dental resin may be selected from methylene dithiepane silane resins described in U.S. Pat. No. 6,794,520 (Moszner et al.), incorporated herein by reference. Such resins have the general formula 
                         
in which R 14  is a saturated or unsaturated aliphatic or alicyclic hydrocarbon radical with 1 to 10 carbon atoms, which can be interrupted by one or more oxygen and/or sulfur atoms and can contain one or more ester, carbonyl, amide and/or urethane groups, or is an aromatic or heteroaromatic hydrocarbon radical with 6 to 18 carbon atoms, the hydrocarbon radicals being able to be substituted or unsubstituted; R 15  has one of the meanings given for R 14  or is absent; R 16  has one of the meanings given for R 14  or is absent; R 17  is equal to —(CHR 19 ) n —, —W—CO—NH—(CHR 19 ) n —, —(CHR 19 ) n , —SR 18 —, —CO—O—R 18 — or is absent, with n being equal to 1 to 4, R 19  is hydrogen, C 1  to C 10  alkyl or C 6  to C 10  aryl, R 18  has one of the meanings given for R 14  and W stands for an O or S atom or is absent; with R 18  and R 19  being able to be substituted or unsubstituted; R 20  is a hydrolyzable group; d, e, f and x each independently of each other being 1, 2 or 3; and the sum of d+x=2 to 4.
 
     The multifunctional low shrinkage resins are (e.g. highly) viscous liquids at about 25° C., yet are flowable. The viscosity as can be measured with a Haake RotoVisco RV1 device, as described in EP Application No. 10168240.9, filed Jul. 2, 2010 is typically at least 300, or 400, or 500 Pa*s and no greater than 10,000 Pascal-seconds (Pa*s). In some embodiments, the viscosity is no greater than 5000 or 2500 Pa*s. 
     The ethylenically unsaturated resins of the dental composition are typically stable liquids at about 25° C. meaning that the resins do not substantially polymerize, crystallize, or otherwise solidify when stored at room temperature (about 25° C.) for a typical shelf life of at least 30, 60, or 90 days. The viscosity of the resins typically does not change (e.g. increase) by more than 10% of the initial viscosity. 
     Particularly for dental restoration compositions, the ethylenically unsaturated resins generally have a refractive index of at least 1.50. In some embodiments, the refractive index is at least 1.51, 1.52, 1.53, or greater. The inclusion of sulfur atoms and/or the present of one or more aromatic moieties can raise the refractive index (relative to the same molecular weight resin lacking such substituents). 
     In some embodiments, the (unfilled) polymerizable resin may comprise solely one or more low shrink resins in combination with the redox initiator system. In other embodiments, the (unfilled) polymerizable resin comprises a small concentration of other monomer(s). By “other” is it meant an ethylenically unsaturated monomer such as a (meth)acrylate monomer that is not a low volume shrinkage monomer. 
     The concentration of such other monomer(s) is typically no greater than 20 wt. %, 19 wt. %, 18 wt. %, 17 wt. %, 16 wt. %, or 15 wt. % of the (unfilled) polymerizable resin portion. The concentration of such other monomers is typically no greater than 5 wt. %, 4 wt. %, 3 wt. %, or 2 wt. % of the filled polymerizable dental composition. 
     In some embodiments, the “other monomers” of the dental composition comprise a low viscosity reactive (i.e. polymerizable) diluent. Reactive diluents typically have a viscosity of no greater than 300 Pa*s and preferably no greater than 100 Pa*s, or 50 Pa*s, or 10 Pa*s. In some embodiments, the reactive diluent has a viscosity no greater than 1 or 0.5 Pa*s. Reactive diluents are typically relatively low in molecular weight, having a molecular weight less than 600 g/mole, or 550 g/mol, or 500 g/mole. Reactive diluents typically comprise one or two ethylenically unsaturated groups such as in the case of mono(meth)acrylate or di(meth)acrylate monomers. 
     In some embodiments, the reactive diluent is an isocyanurate or tricyclodecane monomer. Tricyclodecane reactive diluent may have the same generally structure as previously described. In favored embodiments, the tricyclodecane reactive diluent comprises one or two spacer unit(s) (S) being connected to the backbone unit (U) via an ether linkage; such as described in U.S. 2011/041736 (Eckert et al.); incorporated herein by reference. 
     The curable component of the curable dental composition can include a wide variety of “other” ethylenically unsaturated compounds (with or without acid functionality), epoxy-functional (meth)acrylate resins, vinyl ethers, and the like. 
     The dental compositions may include free radically polymerizable monomers, agents, and polymers having one or more ethylenically unsaturated groups. Suitable compounds contain at least one ethylenically unsaturated bond and are capable of undergoing addition polymerization. Examples of useful ethylenically unsaturated compounds include acrylic acid esters, methacrylic acid esters, hydroxy-functional acrylic acid esters, hydroxy-functional methacrylic acid esters, and combinations thereof. 
     Such free radically polymerizable compounds include mono-, di- or poly-(meth)acrylates (i.e., acrylates and methacrylates) such as, methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-hexyl (meth)acrylate, stearyl (meth)acrylate, allyl (meth)acrylate, glycerol tri(meth)acrylate, ethyleneglycol di(meth)acrylate, diethyleneglycol di(meth)acrylate, triethyleneglycol di(meth)acrylate, 1,3-propanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, 1,2,4-butanetriol tri(meth)acrylate, 1,4-cyclohexanediol di(meth)acrylate, pentaerythritol tetra(meth)acrylate, sorbitol hex(meth)acrylate, tetrahydrofurfuryl (meth)acrylate, bis[1-(2-acryloxy)]-p-ethoxyphenyldimethylmethane, bis[1-(3-acryloxy-2-hydroxy)]-p-propoxyphenyldimethylmethane, ethoxylated bisphenol A di(meth)acrylate, and trishydroxyethyl-isocyanurate tri(meth)acrylate; (meth)acrylamides (i.e., acrylamides and methacrylamides) such as (meth)acrylamide, methylene bis-(meth)acrylamide, and diacetone (meth)acrylamide; urethane (meth)acrylates; the bis-(meth)acrylates of polyethylene glycols (preferably of molecular weight 200-500); and vinyl compounds such as styrene, diallyl phthalate, divinyl succinate, divinyl adipate and divinyl phthalate. Other suitable free radically polymerizable compounds include siloxane-functional (meth)acrylates. Mixtures of two or more free radically polymerizable compounds can be used if desired. 
     The curable dental composition may also contain a monomer having hydroxyl groups and ethylenically unsaturated groups as an example of an “other monomer”. Examples of such materials include hydroxyalkyl (meth)acrylates, such as 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate; glycerol mono- or di-(meth)acrylate; trimethylolpropane mono- or di-(meth)acrylate; pentaerythritol mono-, di-, and tri-(meth)acrylate; sorbitol mono-, di-, tri-, tetra-, or penta-(meth)acrylate; and 2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane (bisGMA). Suitable ethylenically unsaturated compounds are available from a wide variety of commercial sources, such as Sigma-Aldrich, St. Louis. 
     The curable dental compositions can include at least 1 wt. %, at least 3 wt. %, or at least 5 wt. % ethylenically unsaturated compounds with hydroxyl functionality, based on the total weight of the unfilled composition. The compositions can include at most 80 wt. %, at most 70 wt. %, or at most 60 wt. % ethylenically unsaturated compounds with hydroxyl functionality. 
     The dental compositions described herein may include one or more curable components in the form of ethylenically unsaturated compounds with acid functionality as an example of an “other” monomer. When present, the polymerizable component optionally comprises an ethylenically unsaturated compound with acid functionality. Preferably, the acid functionality includes an oxyacid (i.e., an oxygen-containing acid) of carbon, sulfur, phosphorous, or boron. Such acid-functional “other” monomers contribute to the self-adhesion or self-etching of the dental compositions as described in U.S. 2005/017966 (Falsafi et al.), incorporated herein by reference. 
     As used herein, ethylenically unsaturated compounds with acid functionality is meant to include monomers, oligomers, and polymers having ethylenic unsaturation and acid and/or acid-precursor functionality. Acid-precursor functionalities include, for example, anhydrides, acid halides, and pyrophosphates. The acid functionality can include carboxylic acid functionality, phosphoric acid functionality, phosphonic acid functionality, sulfonic acid functionality, or combinations thereof. 
     Ethylenically unsaturated compounds with acid functionality include, for example, α,β-unsaturated acidic compounds such as glycerol phosphate mono(meth)acrylates, glycerol phosphate di(meth)acrylates, hydroxyethyl (meth)acrylate (e.g., HEMA) phosphates, bis((meth)acryloxyethyl) phosphate, bis((meth)acryloxypropyl) phosphate, bis((meth)acryloxy)propyloxy phosphate, (meth)acryloxyhexyl phosphate, bis((meth)acryloxyhexyl) phosphate, (meth)acryloxyoctyl phosphate, bis((meth)acryloxyoctyl) phosphate, (meth)acryloxydecyl phosphate, bis((meth)acryloxydecyl) phosphate, caprolactone methacrylate phosphate, citric acid di- or tri-methacrylates, poly(meth)acrylated oligomaleic acid, poly(meth)acrylated polymaleic acid, poly(meth)acrylated poly(meth)acrylic acid, poly(meth)acrylated polycarboxyl-polyphosphonic acid, poly(meth)acrylated polychlorophosphoric acid, poly(meth)acrylated polysulfonate, poly(meth)acrylated polyboric acid, and the like, may be used as components. Also, monomers, oligomers, and polymers of unsaturated carbonic acids such as (meth)acrylic acids, itaconic acid, aromatic (meth)acrylated acids (e.g., methacrylated trimellitic acids), and anhydrides thereof can be used. 
     The dental compositions can include an ethylenically unsaturated compound with acid functionality having at least one P—OH moiety. Such compositions are self-adhesive and are non-aqueous. For example, such compositions can include: a first compound including at least one (meth)acryloxy group and at least one —O—P(O)(OH) x  group, wherein x=1 or 2, and wherein the at least one —O—P(O)(OH) x  group and the at least one (meth)acryloxy group are linked together by a C 1 -C 4  hydrocarbon group; a second compound including at least one (meth)acryloxy group and at least one —O—P(O)(OH) x  group, wherein x=1 or 2, and wherein the at least one —O—P(O)(OH) x  group and the at least one (meth)acryloxy group are linked together by a C 5 -C 12  hydrocarbon group; an ethylenically unsaturated compound without acid functionality; an initiator system; and a filler. 
     The curable dental compositions can include at least 1 wt. %, at least 3 wt. %, or at least 5 wt. % ethylenically unsaturated compounds with acid functionality, based on the total weight of the unfilled composition. The compositions can include at most 80 wt. %, at most 70 wt. %, or at most 60 wt. % ethylenically unsaturated compounds with acid functionality. 
     The curable dental compositions may include resin-modified glass ionomer cements such as those described in U.S. Pat. No. 5,130,347 (Mitra), U.S. Pat. No. 5,154,762 (Mitra), U.S. Pat. No. 5,925,715 (Mitra et al.) and U.S. Pat. No. 5,962,550 (Akahane). Such compositions can be powder-liquid, paste-liquid or paste-paste systems. Alternatively, copolymer formulations such as those described in U.S. Pat. No. 6,126,922 (Rozzi) are contemplated. 
     The curable dental compositions include the redox cure systems that include a polymerizable component (e.g., an ethylenically unsaturated polymerizable component including monomers and oligomers) and redox agents that include an oxidizing agent, a reducing agent and the photolabile transition metal complex. 
     The photolabile transition metal complex, and the reducing and oxidizing agents react with or otherwise cooperate with one another to produce free radicals capable of initiating polymerization of the resin system (e.g., the ethylenically unsaturated component). Once initiated, this type of cure is not dependent on continued irradiation and can proceed in the absence of light. The reducing and oxidizing agents are preferably sufficiently shelf-stable and free of undesirable colorization to permit their storage and use under typical conditions. 
     Useful reducing agents include ascorbic acid, ascorbic acid derivatives, and metal complexed ascorbic acid compounds as described in U.S. Pat. No. 5,501,727 (Wang et al.); amines, especially tertiary amines, such as 4-tert-butyl dimethylaniline; aromatic sulfinic salts, such as p-toluenesulfinic salts and benzenesulfinic salts; thioureas, such as 1-ethyl-2-thiourea, tetraethyl thiourea, tetramethyl thiourea, 1,1-dibutyl thiourea, and 1,3-dibutyl thiourea; and mixtures thereof. Other secondary reducing agents may include cobalt (II) chloride, ferrous chloride, ferrous sulfate, hydrazine, hydroxylamine (depending on the choice of oxidizing agent), salts of a dithionite or sulfite anion, and mixtures thereof. Preferably, the reducing agent is an ascorbic acid derivative. 
     Suitable oxidizing agents will also be familiar to those skilled in the art, and include but are not limited to persulfuric acid and salts thereof, such as sodium, potassium, ammonium, cesium, and alkyl ammonium salts. Preferable oxidizing agents include peroxides such as benzoyl peroxides, hydroperoxides such as cumyl hydroperoxide, t-butyl hydroperoxide, and amyl hydroperoxide, as well as salts of transition metals such as cobalt (III) chloride and ferric chloride, cerium (IV) sulfate, perboric acid and salts thereof, permanganic acid and salts thereof, perphosphoric acid and salts thereof, and mixtures thereof. 
     It may be desirable to use more than one oxidizing agent or more than one reducing agent. 
     The photolabile transition metal complex is added to accelerate the rate of redox cure, improve the working time, and simplify the compounding of the dental resin so that the reaction is initiated or accelerated only upon exposure to actinic radiation that photolyzes the complex and initiates polymerization. 
     The reducing or oxidizing agents can be microencapsulated as described in U.S. Pat. No. 5,154,762 (Mitra et al.). This will generally enhance shelf stability of the polymerizable composition, and if necessary permit packaging the reducing and oxidizing agents together. For example, through appropriate selection of an encapsulant, the oxidizing and reducing agents can be combined with an acid-functional component and optional filler and kept in a storage-stable state. The redox initiator is used in an amount effective to facilitate free radical addition of the polymerizable components, and the molecular weight of the polymer and the degree of functionalization desired. The initiator system can be used in amounts from about 0.1 part by weight to about 5 parts by weight based on 100 parts total monomer. 
     The photopolymerizable compositions are typically prepared by admixing the various components of the compositions. For embodiments wherein the photopolymerizable compositions are not cured in the presence of air, the initiator system is combined under “safe light” conditions (i.e., conditions that do not cause premature hardening of the composition). Suitable inert solvents may be employed if desired when preparing the mixture. 
     Curing is effected by exposing the composition to a radiation source, preferably a UV light source. It is convenient to employ light sources that emit actinic radiation light between 320 nm and 400 nm (particularly blue light of a wavelength of 380-520 nm) such as quartz halogen lamps, tungsten-halogen lamps, mercury arcs, carbon arcs, low-, medium-, and high-pressure mercury lamps, plasma arcs, light emitting diodes, and lasers. In general, useful light sources have intensities in the range of 500-1500 mW/cm 2 . A variety of conventional lights can be used, including UV LEDs, for curing such compositions. 
     The exposure may be accomplished in several ways. Although the polymerizable composition may be continuously exposed to radiation throughout the entire hardening process (e.g., about 2 seconds to about 60 seconds), the instant initiator system allows one to expose the composition to a single dose of radiation, and then remove the radiation source, thereby allowing polymerization to occur. 
     In favored embodiments, such as when the dental composition is employed as a dental restorative (e.g. dental filling or crown) or an orthodontic cement, the dental composition typically comprises appreciable amounts of (e.g. nanoparticle) filler. The amount of such fillers is a function of the end use as further described herein. Such compositions preferably include at least 40 wt. %, more preferably at least 45 wt. %, and most preferably at least 50 wt. % filler, based on the total weight of the composition. In some embodiments the total amount of filler is at most 90 wt. %, preferably at most 80 wt. %, and more preferably at most 75 wt. % filler. 
     The filled dental composite materials typically exhibit a diametral tensile strength (DTS) of at least about 70, 75, or 80 MPa and/or a Barcol Hardness of at least about 60, or 65, or 70. The ISO 4049 depth of cure ranges from about 4 to about 5 mm and is comparable to commercially available (e.g. filled) dental compositions suitable for restorations. 
     Dental compositions suitable for use as dental adhesives can optionally also include filler in an amount of at least 1 wt. %, 2 wt. %, 3 wt. %, 4 wt. %, or 5 wt. % based on the total weight of the composition. For such embodiments, the total concentration of filler is at most 40 wt. %, preferably at most 20 wt. %, and more preferably at most 15 wt. % filler, based on the total weight of the composition. 
     Fillers may be selected from one or more of a wide variety of materials suitable for incorporation in compositions used for dental applications, such as fillers currently used in dental restorative compositions, and the like. 
     The filler can be an inorganic material. It can also be a crosslinked organic material that is insoluble in the polymerizable resin, and is optionally filled with inorganic filler. The filler is generally non-toxic and suitable for use in the mouth. The filler can be radiopaque, radiolucent, or nonradiopaque. Fillers as used in dental applications are typically ceramic in nature. 
     Suitable inorganic filler particles include quartz (i.e., silica), submicron silica, zirconia, submicron zirconia, and non-vitreous microparticles of the type described in U.S. Pat. No. 4,503,169 (Randklev). 
     The filler can also be an acid-reactive filler. Suitable acid-reactive fillers include metal oxides, glasses, and metal salts. Typical metal oxides include barium oxide, calcium oxide, magnesium oxide, and zinc oxide. Typical glasses include borate glasses, phosphate glasses, and fluoroaluminosilicate (“FAS”) glasses. The FAS glass typically contains sufficient elutable cations so that a hardened dental composition will form when the glass is mixed with the components of the hardenable composition. The glass also typically contains sufficient elutable fluoride ions so that the hardened composition will have cariostatic properties. The glass can be made from a melt containing fluoride, alumina, and other glass-forming ingredients using techniques familiar to those skilled in the FAS glassmaking art. The FAS glass typically is in the form of particles that are sufficiently finely divided so that they can conveniently be mixed with the other cement components and will perform well when the resulting mixture is used in the mouth. 
     Generally, the average particle size (typically, diameter) for the FAS glass is no greater than 12 micrometers, typically no greater than 10 micrometers, and more typically no greater than 5 micrometers as measured using, for example, a sedimentation particle size analyzer. Suitable FAS glasses will be familiar to those skilled in the art, and are available from a wide variety of commercial sources, and many are found in currently available glass ionomer cements such as those commercially available under the trade designations VITREMER, VITREBOND, RELY X LUTING CEMENT, RELY X LUTING PLUS CEMENT, PHOTAC-FIL QUICK, KETAC-MOLAR, and KETAC-FIL PLUS (3M ESPE Dental Products, St. Paul, Minn.), FUJI II LC and FUJI IX (G-C Dental Industrial Corp., Tokyo, Japan) and CHEMFIL Superior (Dentsply International, York, Pa.). Mixtures of fillers can be used if desired. 
     Other suitable fillers are disclosed in U.S. Pat. No. 6,387,981 (Zhang et al.) and U.S. Pat. No. 6,572,693 (Wu et al.) as well as PCT International Publication Nos. WO 01/30305 (Zhang et al.), U.S. Pat. No. 6,730,156 (Windisch et al.), WO 01/30307 (Zhang et al.), and WO 03/063804 (Wu et al.). Filler components described in these references include nanosized silica particles, nanosized metal oxide particles, and combinations thereof. Nanofillers are also described in U.S. Pat. No. 7,090,721 (Craig et al.), U.S. Pat. No. 7,090,722 (Budd et al.) and U.S. Pat. No. 7,156,911; and 7,649,029 (Kolb et al.). 
     Examples of suitable organic filler particles include filled or unfilled pulverized polycarbonates, polyepoxides, poly(meth)acrylates and the like. Commonly employed dental filler particles are quartz, submicron silica, and non-vitreous microparticles of the type described in U.S. Pat. No. 4,503,169 (Randklev). 
     Mixtures of these fillers can also be used, as well as combination fillers made from organic and inorganic materials. 
     Fillers may be either particulate or fibrous in nature. Particulate fillers may generally be defined as having a length to width ratio, or aspect ratio, of 20:1 or less, and more commonly 10:1 or less. Fibers can be defined as having aspect ratios greater than 20:1, or more commonly greater than 100:1. The shape of the particles can vary, ranging from spherical to ellipsoidal, or more planar such as flakes or discs. The macroscopic properties can be highly dependent on the shape of the filler particles, in particular the uniformity of the shape. 
     Micron-size particles are very effective for improving post-cure wear properties. In contrast, nanoscopic fillers are commonly used as viscosity and thixotropy modifiers. Due to their small size, high surface area, and associated hydrogen bonding, these materials are known to assemble into aggregated networks. 
     In some embodiments, the dental composition preferably comprises a nanoscopic particulate filler (i.e., a filler that comprises nanoparticles) having an average primary particle size of less than about 0.100 micrometers (i.e., microns), and more preferably less than 0.075 microns. As used herein, the term “primary particle size” refers to the size of a non-associated single particle. The average primary particle size can be determined by cutting a thin sample of hardened dental composition and measuring the particle diameter of about 50-100 particles using a transmission electron micrograph at a magnification of 300,000 and calculating the average. The filler can have a unimodal or polymodal (e.g., bimodal) particle size distribution. The nanoscopic particulate material typically has an average primary particle size of at least about 2 nanometers (nm), and preferably at least about 7 nm. Preferably, the nanoscopic particulate material has an average primary particle size of no greater than about 75 nm, and more preferably no greater than about 20 nm in size. The average surface area of such a filler is preferably at least about 20 square meters per gram (m 2 /g), more preferably, at least about 50 m 2 /g, and most preferably, at least about 100 m 2 /g. 
     In some preferred embodiments, the dental composition comprises silica nanoparticles. Suitable nano-sized silicas are commercially available from Nalco Chemical Co. (Naperville, Ill.) under the product designation NALCO COLLOIDAL SILICAS. For example, preferred silica particles can be obtained from using NALCO products 1040, 1041, 1042, 1050, 1060, 2327 and 2329. 
     Silica particles are preferably made from an aqueous colloidal dispersion of silica (i.e., a sol or aquasol). The colloidal silica is typically in the concentration of about 1 to 50 weight percent in the silica sol. Colloidal silica sols that can be used are available commercially having different colloid sizes, see Surface &amp; Colloid Science, Vol. 6, ed. Matijevic, E., Wiley Interscience, 1973. Preferred silica sols for use making the fillers are supplied as a dispersion of amorphous silica in an aqueous medium (such as the Nalco colloidal silicas made by Nalco Chemical Company) and those which are low in sodium concentration and can be acidified by admixture with a suitable acid (e.g. Ludox colloidal silica made by E.I. Dupont de Nemours &amp; Co. or Nalco 2326 from Nalco Chemical Co.). 
     Preferably, the silica particles in the sol have an average particle diameter of about 5-100 nm, more preferably 10-50 nm, and most preferably 12-40 nm. A particularly preferred silica sol is NALCO™ 1042 or 2327. 
     In some embodiments, the dental composition comprises zirconia nanoparticles. Suitable nano-sized zirconia nanoparticles can be prepared using hydrothermal technology as described in U.S. Pat. No. 7,241,437 (Davidson et al.). 
     In some embodiments, lower refractive index (e.g. silica) nanoparticles are employed in combination with high refractive index (e.g. zirconia) nanoparticles in order to index match (refractive index within 0.02) the filler to the refractive index of the polymerizable resin. 
     In some embodiments, the nanoparticles are in the form of nanoclusters, i.e. a group of two or more particles associated by relatively weak intermolecular forces that cause the particles to clump together, even when dispersed in a hardenable resin. 
     Preferred nanoclusters can comprise a substantially amorphous cluster of non-heavy (e.g. silica) particles, and amorphous heavy metal oxide (i.e. having an atomic number greater than 28) particles such as zirconia. The primary particles of the nanocluster preferably have an average diameter of less than about 100 nm. Suitable nanocluster fillers are described in U.S. Pat. No. 6,730,156 (Windisch et al.); incorporated herein by reference. 
     In some preferred embodiments, the dental composition comprises nanoparticles and/or nanoclusters surface treated with an organometallic coupling agent to enhance the bond between the filler and the resin. The organometallic coupling agent may be functionalized with reactive curing groups, such as acrylates, methacrylates, vinyl groups and the like and may comprise silane, zirconate or titanate coupling agents. Preferred coupling agents include gamma-methacryloxypropyltrimethoxysilane, gamma-mercaptopropyltriethoxysilane, gamma-aminopropyltrimethoxysilane, and the like. 
     Suitable copolymerizable or reactive organometallic compounds may have the general formulas: CH 2 ═C(R 22 )—R 21 Si(OR) n R 3-n  or CH 2 ═C(R 22 )—C═OOR 21 Si(OR) n R 3-n ; wherein R is an C 1 -C 4  alkyl, R 21  is a divalent organic heterohydrocarbyl linking group, preferably alkylene; R 22  is H or C1-C4 alkyl; and n is from 1 to 3. Preferred coupling agents include gamma-methacryloxypropyltrimethoxysilane, gamma-mercaptopropyltriethoxysilane, gamma-aminopropyltrimethoxysilane, and the like. 
     In some embodiments, the disclosure provides a universal restorative composite comprising: 
     a) 15-30 wt. % of a curable dental resin comprising at least two polymerizable, ethylenically unsaturated groups; 
     b) 70-85 wt. % of an inorganic filler, preferably a surface modified filler; 
     c) 0.1 to 5 wt. % of the redox initiator system, relative to 100 parts by weight a). 
     In some embodiments, the disclosure provides a flowable restorative (flowable) composite comprising: 
     a) 25-50 wt. % of a curable dental resin comprising at least two polymerizable, ethylenically unsaturated groups; 
     b) 30-75 wt. % of an inorganic filler, preferably a surface modified filler; 
     c) 0.1 to 5 wt. % of the redox initiator system, relative to 100 parts by weight of a), said curable composition further comprising an initiator and &lt;2% stabilizers, pigments, etc. 
     In some embodiments, the disclosure provides a resin modified glass-ionomer adhesive comprising:
         a) 10-25 wt. % of a partially (meth)acrylated poly(meth) acrylic acid, which includes acrylic acids such as itaconic acid;   b) 5-20 wt. % of a hydroxyalkyl (meth)acrylate;   c) 30-60 wt. % of fluoroaluminosilicate (FAS) acid reactive glass   d) 0-20 wt. % non-acid reactive fillers, preferably surface-treated;   e) 10-20 wt. % water; and   f) 0.1 to 5 wt. % of the redox initiator system, relative to 100 parts by weight of a)-c)   said curable composition further comprising an initiator and &lt;2% stabilizers, or pigments.       

     Preferably the fluoroaluminosilicate is a silane methacrylate surface-treated fluoroaluminosilicate. 
     In some embodiments, the disclosure provides a dental adhesive comprising: 
     a) 30-80 wt. % mono (meth)acrylate monomers; 
     b) 1-10 wt. % polyfunctional (meth)acrylate monomers; 
     c) 5-60 wt. % monomers having an acid-functional group (including phosphate, phosphonate, carboxylate, sulfonic acids) 
     d) 0-10, preferably 1-10 wt. % poly(meth)acrylic acid methacrylate monomers; 
     e) 0.1 to 5 wt. % of the redox initiator system, relative to 100 parts by weight of a) to d) 
     f) 0-30 wt. % inorganic filler, preferably surface modified, relative to 100 parts by weight of a) to d); 
     g) 0 to 25 wt. % solvent relative to 100 parts by weight of a) to d); 
     h) 0 to 25 wt. % water relative to 100 parts by weight of a) to d); and 
     &lt;2% stabilizers, pigments. 
     In some embodiments, the dental compositions can have an initial color different than the cured dental structures. Color can be imparted to the composition through the use of a photobleachable or thermochromic dye. As used herein, “photobleachable” refers to loss of color upon exposure to actinic radiation. The composition can include at least 0.001 wt. % photobleachable or thermochromic dye, and typically at least 0.002 wt. % photobleachable or thermochromic dye, based on the total weight of the composition. The composition typically includes at most 1 wt. % photobleachable or thermochromic dye, and more typically at most 0.1 wt. % photobleachable or thermochromic dye, based on the total weight of the composition. The amount of photobleachable and/or thermochromic dye may vary depending on its extinction coefficient, the ability of the human eye to discern the initial color, and the desired color change. Suitable thermochromic dyes are disclosed, for example, in U.S. Pat. No. 6,670,436 (Burgath et al.). 
     For embodiments including a photobleachable dye, the color formation and bleaching characteristics of the photobleachable dye varies depending on a variety of factors including, for example, acid strength, dielectric constant, polarity, amount of oxygen, and moisture content in the atmosphere. However, the bleaching properties of the dye can be readily determined by irradiating the composition and evaluating the change in color. The photobleachable dye is generally at least partially soluble in a hardenable resin. 
     Photobleachable dyes include, for example, Rose Bengal, Methylene Violet, Methylene Blue, Fluorescein, Eosin Yellow, Eosin Y, Ethyl Eosin, Eosin Bluish, Eosin B, Erythrosin B, Erythrosin Yellowish Blend, Toluidine Blue, 4′,5′-Dibromofluorescein, and combinations thereof. 
     The color change can be initiated by actinic radiation such as provided by a dental curing light which emits visible or near infrared (IR) light for a sufficient amount of time. The mechanism that initiates the color change in the compositions may be separate from or substantially simultaneous with the hardening mechanism that hardens the resin. For example, a composition may harden when polymerization is initiated chemically (e.g., redox initiation) or thermally, and the color change from an initial color to a final color may occur subsequent to the hardening process upon exposure to actinic radiation. 
     Optionally, compositions may contain solvents (e.g., alcohols (e.g., propanol, ethanol), ketones (e.g., acetone, methyl ethyl ketone), esters (e.g., ethyl acetate), other nonaqueous solvents (e.g., dimethylformamide, dimethylacetamide, dimethylsulfoxide, 1-methyl-2-pyrrolidinone)), and water. 
     If desired, the compositions can contain additives such as indicators, dyes, pigments, inhibitors, accelerators, viscosity modifiers, wetting agents, buffering agents, radical and cationic stabilizers (for example BHT,), and other similar ingredients that will be apparent to those skilled in the art. 
     Additionally, medicaments or other therapeutic substances can be optionally added to the dental compositions. Examples include, but are not limited to, fluoride sources, whitening agents, anticaries agents (e.g., xylitol), calcium sources, phosphorus sources, remineralizing agents (e.g., calcium phosphate compounds), enzymes, breath fresheners, anesthetics, clotting agents, acid neutralizers, chemotherapeutic agents, immune response modifiers, thixotropes, polyols, anti-inflammatory agents, antimicrobial agents, antifungal agents, agents for treating xerostomia, desensitizers, and the like, of the type often used in dental compositions. Combinations of any of the above additives may also be employed. The selection and amount of any one such additive can be selected by one of skill in the art to accomplish the desired result without undue experimentation. 
     The curable dental composition can be used to treat an oral surface such as tooth, as known in the art. In some embodiments, the compositions can be hardened by curing after applying the dental composition. For example, when the curable dental composition is used as a restorative such as a dental filling, the method generally comprises applying the curable composition to an oral surface (e.g. cavity); and curing the composition. In some embodiments, a dental adhesive may be applied prior to application of the curable dental restoration material described herein. Dental adhesives are also typically hardened by curing concurrently with curing the highly filled dental restoration composition. The method of treating an oral surface may comprise providing a dental article and adhering the dental article to an oral (e.g. tooth) surface. 
     In other embodiments, the compositions can be cured into dental articles prior to applying. For example, a dental article such as a crown may be pre-formed from the curable dental composition described herein. Dental composite (e.g. crowns) articles can be made from the curable composition described herein by casting the curable composition in contact with a mold and curing the composition. Alternatively, dental composites or articles (e.g. crowns) can be made by first curing the composition forming a mill blank and then mechanically milling the composition into the desired article. 
     Another method of treating a tooth surface comprises providing a dental composition as described herein wherein the composition is in the form of a (partially cured) curable, self-supporting, malleable structure having a first semi-finished shape; placing the curable dental composition on a tooth surface in the mouth of a subject; customizing the shape of the curable dental composition; and hardening the curable dental composition. The customization can occur in the patient&#39;s mouth or on a model outside the patient mouth such as described in U.S. Pat. No. 7,674,850 (Karim et al.); incorporated herein by reference. 
     EXAMPLES 
     Amounts of materials are by weight or weight percent (“wt. %”), unless designated otherwise. 
     Materials Utilized: 
     Acetone (EMD Millipore Corporation, Billerica, Mass.) 
     Aluminum Oxide, powder, &lt;/=10 □m avg. particle size (Sigma-Aldrich, St. Louis, Mo.) 
     3-Amino-3-(2-nitrophenyl)propionic acid, 98% (Alfa Aesar, Ward Hill, Mass.) 
     Ammonium Chloride (EMD Chemicals, Inc. Gibbstown, N.J.) 
     BENZOFLEX 9-88, plasticizer (Eastman Chemical Co., Kingsport, Tenn.) 
     Benzyltributyl ammonium chloride (Sigma-Aldrich, St. Louis, Mo.) 
     BisGMA: 2,2-Bis[4-hydroxy-3-methacryloyloxy)propoxyphenyl]propane (Sigma-Aldrich, St. Louis, Mo.) 
     CAB-O-SIL TS720 (Cabot Corporation, Billerica, Mass.) 
     CDCl 3 : Deuterochloroform (Cambridge Isotope Laboratories, Andover, Mass.) 
     CH 2 Cl 2 : Dichloromethane (EMD Millipore Corporation, Billerica, Mass.) 
     CHP: Cumene hydroperoxide, 80% Tech. grade (Alfa Aesar, Heysham, England) 
     Copper (II) acetate (Sigma-Aldrich, St. Louis, Mo.) 
     Copper (II) chloride dihydrate (Alfa Aesar, Heysham, England) 
     Cobalt (II) chloride hexahydrate (Alfa Aesar, Ward Hill, Mass.) 
     CSA: 10-Camphorsulfonic acid (Aldrich Chemical Co., Milwaukee, Wis.) 
     1,1-Dimethoxycyclohexane (Sigma-Aldrich, St. Louis, Mo.) 
     2,2-Dimethoxypropane (Sigma-Aldrich, St. Louis, Mo.) 
     DMF: Dimethylformamide (EMD Millipore Corporation, Billerica, Mass.) 
     d 6 -DMSO: Dimethylsulfoxide-d 6  (Cambridge Isotope Laboratories, Andover, Mass.) 
     DVB: Divinylbenzene, 80% technical grade (Sigma-Aldrich, St. Louis, Mo.) 
     EtOAc: Ethyl acetate (VWR International, Radnor, Pa.) 
     EtOH: Ethanol (EMD Chemicals, Gibbstown, N.J.) 
     HDDA: Hexanediol diacrylate, Sartomer SR238B (Warrington, Pa.) 
     HDK H-2000 Hydrophobic pyrogenic silica (Wacker Silicones. Wacker Chemical Corp., Adrian, Mich.) 
     HEMA: 2-Hydroxyethyl methacrylate (Sigma-Aldrich, St. Louis, Mo.) 
     Hexane (EMD Millipore Corporation, Billerica, Mass.) 
     Iron (II) chloride tetrahydrate (Alfa Aesar, Ward Hill, Mass.) 
     L-Ascorbic acid (Alfa Aesar, Ward Hill, Mass.) 
     MeOH: Methanol (EMD Millipore Corporation, Billerica, Mass.) 
     MgSO 4 : Magnesium sulfate, anhydrous (EMD Chemicals, Inc. Gibbstown, N.J.) 
     N-methyl morpholine (Aldrich, Milwaukee, Wis.) 
     2-Picolyl chloride hydrochloride (Sigma-Aldrich, St. Louis, Mo.) 
     PyBOP: benzotriazol-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate (Oakwood Chemical, West Columbia, S.C.) 
     SARTOMER SR203: Tetrahydrofuryl methacrylate (Sartomer, Warrington, Pa.) 
     SARTOMER SR541: Ethoxylated(6) Bisphenol A dimethacrylate (Sartomer, Warrington, Pa.) 
     TEGDMA: Tetraethylene glycol dimethacrylate (Sigma-Aldrich, St. Louis, Mo.) 
     2-Thiopheneethylamine (Aldrich, Milwaukee, Wis.) 
     2-Thiophenemethylamine (Aldrich, Milwaukee, Wis.) 
     Triethylamine (EMD Chemicals Inc., Gibbstown, N.J.) 
     VTBN: 1300X33 VTBNX (Emerald Performance Materials, Akron, Ohio); methacrylate-functional butadiene-acrylonitrile liquid rubber 
     Z250: Filtek™ Z250 S/T Universal Restorative (3M ESPE) 
     Test Methods 
     Barcol Hardness Test Method 
     “Barcol hardness” of test samples was determined according to the following procedure. Uncured composite samples were placed in a TEFLON mold (4 mm thickness with a 7 mm diameter circular hole in the center) sandwiched between a sheet of polyester (PET) film and a glass slide and irradiated with an OMNICURE LX-400 LED lamp (Lumen Dynamics, Mississauga, Ontario, Canada) at 365 nm for 10 seconds, then allowed to cure in either a 37° C./95% RH chamber, or at ambient temperature, as specified. Following the specified time lengths, the PET film was removed and the hardness of samples at both the top and the bottom of the mold were measured using a Barber-Coleman IMPRESSOR (a hand-held portable hardness tester; MODEL GYZJ 934-1, obtained from Barber-Coleman Company, Industrial Instruments Division, Lovas Park, Ind.) equipped with an indenter. The reported “Top Barcol” and “Bottom Barcol” values were means from triplicate measurement, with standard deviations listed in parentheses. 
     Flexural Strength/Flexural Modulus Test Method 
     Paste samples were extruded into 2 mm×2 mm×25 mm quartz glass molds to form test bars. All test bars were cured for 30 minutes in a 37° C./95% RH chamber, then stored in water at 37° C. for 24 h. Irradiated samples were irradiated with an OMNICURE LX400 LED lamp (Lumen Dynamics, Mississauga, Ontario, Canada) at 365 nm for 10 seconds prior to curing as above. Flexural strength and flexural modulus of the bars was measured on an INSTRON tester (INSTRON 4505 or INSTRON 1123, Instron Corp., Canton, Mass.) according to ANSI/ADA (American National Standard/American Dental Association) specification No. 27 (1993) at a crosshead speed of 0.75 mm/minute. The results were reported in megapascals (MPa). The resulting flexural strength and flexural modulus values were reported as means from a minimum of five measurements, with standard deviations listed in parentheses. 
     Preparative Examples 
     Preparative Example 1 (PE-1): Copper Complex 
     This copper metal complex designated was prepared according to Ciesienski, K. L.; Haas, K. L.; Dickens, M. G.; Tesema, Y. T.; Franz, K. J. “A Photolabile Ligand for Light-Activated Release of Caged Copper” J. Am. Chem. Soc. 2008, vol. 130, pages 12246-12247. 
     
       
         
         
             
             
         
       
     
     Preparative Example 2 (PE-2): Copper Complex 
     This copper metal complex was prepared according to Ciesienski, K. L.; Haas, K. L.; Franz, K. J. “Development of Next-generation Photolabile Cages with Improved Copper Binding Properties” Dalton Trans. 2010, vol. 39, pages 9538-9546. 
     
       
         
         
             
             
         
       
     
     Preparative Example 3 (PE-3): Copper Complex 
     This copper metal complex was prepared according to Ciesienski, K. L.; Haas, K. L.; Franz, K. J. “Development of Next-generation Photolabile Cages with Improved Copper Binding Properties” Dalton Trans. 2010, vol. 39, pages 9538-9546. 
     
       
         
         
             
             
         
       
     
     Preparative Example 4 (PE-4): Copper Complex 
     A slurry of 3-amino-3-(2-nitrophenyl)propionic acid (30.0 mmol, 6.31 g) and N-methyl morpholine (60.0 mmol, 6.07 g) in DMF (100 mL) was heated at 70° C. with a heating mantle under nitrogen atmosphere. A solution of 2-picolyl chloride hydrochloride (30.0 mmol, 5.34 g) in DMF (20 mL) was added via pipette. The resultant solution was heated 70° C. overnight. Following addition of H 2 O (200 mL), the reaction mixture was extracted with EtOAc (4×75 mL). The combined organic layers were then extracted with 1N aq. NaOH (2×75 mL). The combined 1N aq. NaOH layers were acidified to pH ˜3 via addition of conc. HCl, then extracted with EtOAc (3×75 mL). These combined EtOAc layers were washed with H 2 O (2×) and sat. aq. NaCl (lx), dried over MgSO 4 , filtered, and concentrated to a light tan oil under reduced pressure. This material foams under vacuum to afford the desired amide product (5.86 g, 62% yield), which was revealed by  1 H NMR to be sufficiently clean to carry forward without additional purification. To a solution of this amide (18.6 mmol, 5.86 g), 2-thiophenemethylamine (18.6 mmol, 2.10 g), and N-methyl morpholine (18.6 mmol, 1.88 g) in CH 2 Cl 2  (150 mL) was added PyBOP (18.6 mmol, 9.67 g). The resultant reaction mixture was heated at reflux with a heating mantle while stirring under nitrogen atmosphere overnight. The reaction mixture was then washed with H 2 O (2×) and sat. aq. NaCl (lx), dried over MgSO 4 , filtered, and concentrated to an orange oil. This crude reaction product was purified via silica gel flash chromatography (ramp eluent from 1:1 hexane/EtOAc to 2:3 hexane/EtOAc) to afford a yellow solid. This solid was further purified via trituration with a hexane/EtOAc mixture to afford the ligand as a white solid (3.51 g, 46% yield).  1 H NMR (CDCl 3 , 500 MHz) shows this to be clean material and consistent with the reported structure. A portion of this ligand (1.7 mmol, 0.70 g) was added to EtOH (40 mL). Copper (II) chloride dihydrate (1.7 mmol, 0.29 g) was then added, and the resultant mixture rapidly becomes a homogeneous blue solution. The solution was heated at reflux with stirring overnight. The EtOH was then removed under reduced pressure, and MeOH was added to the residue. The mixture was filtered through a short plug of aluminum oxide. The blue colored filtrate was concentrated and dried under vacuum to afford the desired copper metal complex (PE-4) as a greenish-brown solid (0.91 g). 
     
       
         
         
             
             
         
       
     
     Preparative Example 5 (PE-5): Copper Complex 
     A slurry of 3-amino-3-(2-nitrophenyl)propionic acid (20.0 mmol, 4.20 g) and N-methyl morpholine (40.0 mmol, 4.05 g) in DMF (100 mL) was heated 70° C. with a heating mantle under nitrogen atmosphere. A solution of 2-picolyl chloride hydrochloride (20.0 mmol, 3.56 g) in DMF (20 mL) was added via pipette. The resultant solution was heated at 70° C. overnight. Following addition of H 2 O (200 mL), the reaction mixture was extracted with EtOAc (4×75 mL). The combined organic layers were then extracted with 1N aq. NaOH (2×75 mL). The combined 1N aq. NaOH layers were acidified to pH ˜3 via addition of conc. HCl, then extracted with EtOAc (3×75 mL). These combined EtOAc layers were washed with H 2 O (2×) and sat. aq. NaCl (lx), dried over MgSO 4 , filtered, and concentrated under reduced pressure to provide a light tan oil. This material foams under vacuum to afford the desired amide product (3.79 g, 60% yield), which was revealed by  1 H NMR to be sufficiently clean to carry forward without additional purification. To a solution of this amide (7.29 mmol, 2.30 g), 2-thiopheneethylamine (7.29 mmol, 0.93 g), and N-methyl morpholine (7.29 mmol, 0.74 g) in CH 2 Cl 2  (80 mL) was added PyBOP (7.29 mmol, 3.79 g). The resultant reaction mixture was heated at reflux with a heating mantle while stirring under nitrogen atmosphere overnight. The reaction mixture was then washed with H 2 O (2×) and sat. aq. NaCl (1×), dried over MgSO 4 , filtered, and concentrated to an orange oil. This crude reaction product was purified via silica gel flash chromatography (1:1 hexane/EtOAc eluent) to afford a yellow solid. This solid was further purified via trituration with a hexane/EtOAc mixture to afford the ligand as a white solid (0.85 g, 28% yield).  1 H  1  NMR (CDCl 3 , 500 MHz) shows this to be clean material and consistent with the reported structure. A portion of this ligand (1.0 mmol, 0.42 g) was added to EtOH (40 mL). Copper (II) chloride dihydrate (1.0 mmol, 0.17 g) was then added, and the resultant mixture rapidly becomes a homogeneous blue solution. The solution was heated at reflux with stirring overnight. The EtOH was then removed under reduced pressure, and MeOH was added to the residue. The mixture was filtered through a short plug of aluminum oxide. The blue colored filtrate was concentrated and dried under vacuum to afford the desired copper metal complex (PE-5) as a greenish-brown solid (0.54 g). 
     
       
         
         
             
             
         
       
     
     Preparative Example 6 (PE-6): Iron Complex 
     The ligand for this complex was prepared as reported in Ciesienski, K. L.; Haas, K. L.; Dickens, M. G.; Tesema, Y. T.; Franz, K. J. “A Photolabile Ligand for Light-Activated Release of Caged Copper” J. Am. Chem. Soc. 2008, vol. 130, pages 12246-12247. This ligand (1.00 g, 2.47 mmol) was added to 100 mL EtOH and heated at gentle reflux. Iron (II) chloride tetrahydrate (0.49 g, 2.47 mmol), was added, resulting in an immediate formation of a dark red solution. After heating overnight, the EtOH was removed under reduced pressure, and the resultant red solid was dissolved in MeOH. The mixture was filtered through a plug of alumina to remove residual solids. The filtrate was concentrated and dried under vacuum, providing the iron complex (PE-6) as a red-brown solid (1.10 g). 
     
       
         
         
             
             
         
       
     
     Preparative Example 7 (PE-7): Iron Complex 
     The ligand for this complex was prepared according to Ciesienski, K. L.; Haas, K. L.; Franz, K. J. “Development of Next-generation Photolabile Cages with Improved Copper Binding Properties” Dalton Trans. 2010, vol. 39, pages 9538-9546. This ligand (0.95 g, 2.33 mmol) was dissolved in 100 ml EtOH. Iron (II) chloride tetrahydrate (0.46 g, 2.33 mmol) was added, resulting in the formation of a red solution which was heated at reflux overnight. The EtOH was removed under reduced pressure, and the residue was filtered through a plug of aluminum oxide, eluting with methanol. The filtrate was concentrated and dried under vacuum to afford the iron complex (PE-7) as a red-brown solid (0.92 g). 
     
       
         
         
             
             
         
       
     
     Preparative Example 8 (PE-8): Cobalt Complex 
     The ligand for this complex was prepared according to Ciesienski, K. L.; Haas, K. L.; Dickens, M. G.; Tesema, Y. T.; Franz, K. J. “A Photolabile Ligand for Light-Activated Release of Caged Copper” J. Am. Chem. Soc. 2008, vol. 130, pages 12246-12247. This ligand (1.24 g, 3.06 mmol) was dissolved in 75 ml EtOH. Cobalt (II) chloride hexahydrate (0.73 g, 3.06 mmol) was added, resulting in the formation of a bright blue slurry which was heated at reflux overnight. The EtOH was removed under reduced pressure, and the residue was filtered through a plug of aluminum oxide, eluting with methanol. The filtrate was concentrated and dried under vacuum to afford the cobalt complex (PE-8) as a blue solid (0.72 g). 
     
       
         
         
             
             
         
       
     
     Preparative Example 9 (PE-9): Synthesis of Cyc-AA 
     To a suspension of L-ascorbic acid (10.0 g, 56.8 mmol) in 100 mL acetone was added 1,1-dimethoxycyclohexane (13.9 g, 96.6 mmol) and 10-camphorsulfonic acid (0.66 g, 2.84 mmol). The resultant mixture was allowed to stir at room temperature under nitrogen atmosphere, and slowly became a clear, nearly colorless solution. After 48 hours, the solution had become pale yellow in color. Approximately 0.4 g of triethylamine was added, which resulted in the solution becoming nearly colorless again. The solvents were removed under reduced pressure to afford a white solid which was triturated with a 9:1 hexane/EtOAc mixture. The precipitate was collected via filtration and dried under vacuum to afford the product as a white solid (13.0 g, 89% yield).  1 H NMR signals were consistent with the desired product. 
     
       
         
         
             
             
         
       
     
     Preparative Example 10 (PE-10): Synthesis of 5,6-O-Isopropylidene-L-Ascorbic Acid (p-AA) 
     This material was prepared according to literature precedence (Bioorg. Med. Chem. 2003, vol. 11, 827). To a suspension of L-ascorbic acid (20.0 g, 114 mmol) in acetone (200 mL) was added 2,2-dimethoxypropane (20.4 g, 196 mmol) and 10-camphorsulfonic acid (1.32 g, 5.68 mmol). The resultant mixture was allowed to stir overnight at room temperature. To the resultant slurry was added approximately 0.6 g triethylamine. A portion of hexane was added to the mixture, and the white precipitate was collected via vacuum filtration, washing with additional hexane. The material was dried under vacuum to afford the desired product (21.0 g, 86% yield).  1 H NMR (d 6 -DMSO, 500 MHz) was consistent with the desired product. 
     
       
         
         
             
             
         
       
     
     Examples of Two-Part Methacrylate-Based Formulations 
     Examples of two-part formulations were provided that included a polymerizable methacrylate-based monomer. 
     Example 1 (EX-1): Two-Part Formulation Using the PE-1 Copper Complex 
     A representative two-part dental composite formulation was prepared as follows. A “Mixture-A” paste included a 1:1 mixture of BisGMA and TEGDMA as polymerizable methacrylate-based monomers, 5,6-O-isopropylidene-L-ascorbic acid (p-AA), HDK H-2000 fumed silica as a flow agent, and Z250 as filler material, according to the amounts listed in Table 1. A “Mixture-B” paste included a 1:1 mixture of BisGMA and TEGDMA, a 2 wt. % solution of PE-1 Copper Complex dissolved in 1:1 BisGMA/TEGDMA, cumene hydroperoxide (CHP), HDK H-2000 fumed silica, and Z250 filler, according to the amounts listed in Table 1. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Material 
                 Wt. % 
                 mass (g) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 Mixture-A 
               
            
           
           
               
               
               
               
            
               
                   
                 BisGMA 
                 19.5 
                 1.95 
               
               
                   
                 TEGDMA 
                 19.5 
                 1.95 
               
               
                   
                 — 
                 — 
                 — 
               
               
                   
                 p-AA 
                 0.5 
                 0.05 
               
               
                   
                 HDK H-2000 
                 2.0 
                 0.20 
               
               
                   
                 Z250 filler 
                 58.5 
                 5.85 
               
               
                   
                 Total 
                 100.0 
                 10.00 
               
            
           
           
               
            
               
                 Mixture-B 
               
            
           
           
               
               
               
               
            
               
                   
                 BisGMA 
                 18.95 
                 1.90 
               
               
                   
                 TEGDMA 
                 18.95 
                 1.90 
               
               
                   
                 Cu cage soln* 
                 0.10 
                 0.01 
               
               
                   
                 CHP 
                 1.00 
                 0.10 
               
               
                   
                 HDK H-2000 
                 2.00 
                 0.20 
               
               
                   
                 Z250 filler 
                 59.00 
                 5.90 
               
               
                   
                 Total 
                 100.00 
                 10.00 
               
               
                   
                   
               
               
                   
                 *The “Cu cage soln” of EX-1 was prepared as a 2 wt. % solution of PE-1 Cu complex in 1:1 BisGMA/TEGDMA; thus the Mixture-B paste was 0.002 wt. % PE-1 Cu complex 
               
            
           
         
       
     
     To perform curing experiments with the EX-1 two-part formulation, 60 mg portions of each of the Mixture-A and Mixture-B parts of EX-1 were weighed out onto a mixing pad and hand mixed together for 20 seconds. At time=30 seconds, the mixture was irradiated with an LX-400 LED lamp (Lumen Dynamics, Mississauga, Ontario, Canada) held 2 cm from the mixture for the specified time at the specified wavelength, as summarized in Table 2. A dental probe was then used to evaluate the cure of the material. Working time was defined as the elapsed time until the first solid chunk of cured material could be detected, and full cure was defined as the elapsed time until the entire sample had cured to a solid. Results were as summarized in Table 2. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 2* 
               
             
            
               
                   
                   
               
               
                   
                 365 nm 
                 385 nm 
                 400 nm 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Irradiation 
                   
                 full 
                   
                 full 
                 work 
                 full 
               
               
                 time, 
                 work time, 
                 cure, 
                 work time, 
                 cure, 
                 time, 
                 cure, 
               
               
                 seconds 
                 minutes 
                 minutes 
                 minutes 
                 minutes 
                 minutes 
                 minutes 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 0 
                 5.25 
                 6.50 
                 5.25 
                 6.50 
                 5.25 
                 6.50 
               
               
                 5.0 
                 4.00 
                 5.50 
                 4.25 
                 5.50 
                 4.75 
                 5.75 
               
               
                 7.5 
                 2.25 
                 4.25 
                 3.25 
                 4.75 
                 4.50 
                 5.25 
               
               
                 10 
                 1.00 
                 3.75 
                 1.50 
                 4.25 
                 4.25 
                 5.00 
               
               
                   
               
               
                 *Work time = time until the first amount of cured material could be detected; Full cure = time until the entire paste sample became hardened. 
               
            
           
         
       
     
     Example 2 (EX-2): Two-Part Formulation Using the PE-4 Copper Complex 
     A two-part formulation was prepared according to the method described in Example 1, except that the PE-4 Copper complex material was used in place of the PE-1 Copper complex material, and using the amounts as summarized in Table 3. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Material 
                 Wt. % 
                 mass (g) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 Mixture-A 
               
            
           
           
               
               
               
               
            
               
                   
                 BisGMA 
                 19.5 
                 1.95 
               
               
                   
                 TEGDMA 
                 19.5 
                 1.95 
               
               
                   
                 — 
                 — 
                 — 
               
               
                   
                 p-AA 
                 0.5 
                 0.05 
               
               
                   
                 HDK H-2000 
                 2.0 
                 0.20 
               
               
                   
                 Z250 filler 
                 58.5 
                 5.85 
               
               
                   
                 Total 
                 100.0 
                 10.00 
               
            
           
           
               
            
               
                 Mixture-B 
               
            
           
           
               
               
               
               
            
               
                   
                 BisGMA 
                 18.95 
                 1.90 
               
               
                   
                 TEGDMA 
                 18.95 
                 1.90 
               
               
                   
                 Cu cage soln* 
                 0.10 
                 0.01 
               
               
                   
                 CHP 
                 1.00 
                 0.10 
               
               
                   
                 HDK H-2000 
                 2.00 
                 0.20 
               
               
                   
                 Z250 filler 
                 59.00 
                 5.90 
               
               
                   
                 Total 
                 100.00 
                 10.00 
               
               
                   
                   
               
               
                   
                 *The “Cu cage soln” of EX-2 was prepared as a 2 wt. % solution of PE-4 Cu complex in 1:1 BisGMA/TEGDMA; thus the Mixture-B paste was 0.002 wt. % PE-4 Cu complex 
               
            
           
         
       
     
     To perform curing experiments with the EX-2 two-part formulation, 60 mg portions of each of the Mixture-A and Mixture-B parts of EX-2 were weighed out onto a mixing pad and hand mixed together for 20 seconds. At time=30 seconds, the mixture was irradiated with an LX-400 LED lamp (Lumen Dynamics, Mississauga, Ontario, Canada) held 2 cm from the mixture for the specified time at the specified wavelength (365 nm, 385 nm, or 400 nm), as summarized in Table 4. A dental probe was then used to evaluate the cure of the material. Working time was defined as the elapsed time until the first solid chunk of cured material could be detected, and full cure was defined as the elapsed time until the entire sample had cured to a solid. Results were as summarized in Table 4. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 4* 
               
             
            
               
                   
                   
               
               
                   
                 365 nm 
                 385 nm 
                 400 nm 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Irradiation 
                   
                 full 
                   
                 full 
                 work 
                 full 
               
               
                 time, 
                 work time, 
                 cure, 
                 work time, 
                 cure, 
                 time, 
                 cure, 
               
               
                 seconds 
                 minutes 
                 minutes 
                 minutes 
                 minutes 
                 minutes 
                 minutes 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 0 
                 6.50 
                 7.75 
                 6.50 
                 7.75 
                 6.50 
                 7.75 
               
               
                 5.0 
                 5.25 
                 7.00 
                 5.50 
                 7.00 
                 6.25 
                 7.50 
               
               
                 7.5 
                 3.00 
                 4.75 
                 3.75 
                 5.50 
                 6.00 
                 7.00 
               
               
                 10 
                 1.00 
                 3.25 
                 2.25 
                 4.00 
                 5.00 
                 6.50 
               
               
                   
               
               
                 *Work time = time until the first amount of cured material could be detected; Full cure = time until the entire paste sample became hardened. 
               
            
           
         
       
     
     Example 3 (EX-3): Two-Part Formulation Using the PE-3 Copper Complex 
     A two-part formulation was prepared according to the method described in EX-1, except that the PE-3 Copper complex material was used in place of the PE-1 Copper complex material, using the amounts as summarized in Table 5. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 5 
               
               
                   
                   
               
               
                   
                 Material 
                 Wt. % 
                 mass (g) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 Mixture-A 
               
            
           
           
               
               
               
               
            
               
                   
                 BisGMA 
                 19.5 
                 1.95 
               
               
                   
                 TEGDMA 
                 19.5 
                 1.95 
               
               
                   
                 — 
                 — 
                 — 
               
               
                   
                 p-AA 
                 0.5 
                 0.05 
               
               
                   
                 HDK H-2000 
                 2.0 
                 0.20 
               
               
                   
                 Z250 filler 
                 58.5 
                 5.85 
               
               
                   
                 Total 
                 100.0 
                 10.00 
               
            
           
           
               
            
               
                 Mixture-B 
               
            
           
           
               
               
               
               
            
               
                   
                 BisGMA 
                 18.95 
                 1.90 
               
               
                   
                 TEGDMA 
                 18.95 
                 1.90 
               
               
                   
                 Cu cage soln* 
                 0.10 
                 0.01 
               
               
                   
                 CHP 
                 1.00 
                 0.10 
               
               
                   
                 HDK H-2000 
                 2.00 
                 0.20 
               
               
                   
                 Z250 filler 
                 59.00 
                 5.90 
               
               
                   
                 Total 
                 100.00 
                 10.00 
               
               
                   
                   
               
               
                   
                 *The “Cu cage soln” of EX-3 was prepared as a 2 wt. % solution of PE-3 Copper complex in 1:1 BisGMA/TEGDMA; thus the Mixture-B paste was 0.002 wt. % PE-3 Copper complex 
               
            
           
         
       
     
     To perform curing experiments with the EX-3 two-part formulation, 60 mg portions of each of the Mixture-A and Mixture-B parts of EX-3 were weighed out onto a mixing pad and hand mixed together for 20 seconds. At time=30 seconds, the mixture was irradiated with an LX-400 LED lamp (Lumen Dynamics, Mississauga, Ontario, Canada) held 2 cm from the mixture for the specified time at the specified wavelength (365 nm, 385 nm, or 400 nm), as summarized in Table 6. A dental probe was then used to evaluate the cure of the material. Working time was defined as the elapsed time until the first solid chunk of cured material can be detected, and full cure was defined as the elapsed time until the entire sample had cured to a solid. Results were as summarized in Table 6. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 6* 
               
             
            
               
                   
                   
               
               
                   
                 365 nm 
                 385 nm 
                 400 nm 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Irradiation 
                   
                 full 
                   
                 full 
                 work 
                 full 
               
               
                 time, 
                 work time, 
                 cure, 
                 work time, 
                 cure, 
                 time, 
                 cure, 
               
               
                 seconds 
                 minutes 
                 minutes 
                 minutes 
                 minutes 
                 minutes 
                 minutes 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 0 
                 7.50 
                 12.00 
                 7.50 
                 12.00 
                 7.50 
                 12.00 
               
               
                 5.0 
                 1.50 
                 3.25 
                 2.75 
                 3.75 
                 4.25 
                 5.50 
               
               
                 7.5 
                 0.75 
                 1.50 
                 1.25 
                 2.50 
                 3.50 
                 4.50 
               
               
                 10 
                 &lt;0.75 
                 1.00 
                 0.75 
                 1.50 
                 2.75 
                 3.50 
               
               
                   
               
               
                 *Work time = time until the first amount of cured material could be detected; Full cure = time until the entire paste sample became hardened. 
               
            
           
         
       
     
     Example 4 (EX-4): Two-Part Formulation Using the PE-6 Iron Complex 
     For experiments containing this PE-6 iron complex, a “Mixture-A” paste included a 1:1 mixture of BisGMA and TEGDMA, 5,6-O-isopropylidene-L-ascorbic acid (p-AA), cumene hydroperoxide (CHP), HDK H-2000 fumed silica, and Z250 filler in the amounts listed in Table 7. “Mixture-B” paste included a 1:1 mixture of BisGMA and TEGDMA as polymerizable methacrylate-based monomers, a 2 wt. % solution of the PE-6 iron complex dissolved in 1:1 BisGMA/TEGDMA, a 20 wt. % solution of ammonium chloride dissolved in 2-hydroxyethyl methacrylate (HEMA), HDK H-2000 fumed silica as a flow agent, and Z250 as filler material in the amounts listed in Table 7. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 7 
               
               
                   
                   
               
               
                   
                 Material 
                 Wt. % 
                 mass (g) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 Mixture-A 
               
            
           
           
               
               
               
               
            
               
                   
                 BisGMA 
                 20.00 
                 2.00 
               
               
                   
                 TEGDMA 
                 20.00 
                 2.00 
               
               
                   
                 p-AA 
                 0.50 
                 0.05 
               
               
                   
                 CHP 
                 2.00 
                 0.20 
               
               
                   
                 HDK H-2000 
                 1.00 
                 0.10 
               
               
                   
                 Z250 filler 
                 56.50 
                 5.65 
               
               
                   
                 Total 
                 100.00 
                 10.00 
               
            
           
           
               
            
               
                 Mixture-B 
               
            
           
           
               
               
               
               
            
               
                   
                 BisGMA 
                 18.00 
                 1.80 
               
               
                   
                 TEGDMA 
                 18.00 
                 1.80 
               
               
                   
                 Fe cage soln* 
                 2.00 
                 0.20 
               
               
                   
                 Am. Cl soln** 
                 5.00 
                 0.50 
               
               
                   
                 HDK H-2000 
                 1.00 
                 0.10 
               
               
                   
                 Z250 filler 
                 56.00 
                 5.60 
               
               
                   
                 Total 
                 100.00 
                 10.00 
               
               
                   
                   
               
               
                   
                 *The “Fe cage soln” of EX-4 was prepared as a 2 wt. % solution of PE-6 iron complex in 1:1 BisGMA/TEGDMA; thus the Mixture-B paste was 0.04 wt. % PE-6 iron complex. 
               
               
                   
                 **The “Am. Cl. soln” was 20 wt. % benzyltributyl ammonium chloride in HEMA. 
               
            
           
         
       
     
     To perform curing experiments with the EX-4 two-part formulation, 60 mg portions of each of the Mixture-A and Mixture-B parts of EX-4 were then weighed out onto a mixing pad and hand mixed together for 20 seconds. At time=30 seconds, the mixture was then irradiated either with an LX-400 LED lamp (Lumen Dynamics, Mississauga, Ontario, Canada) held 2 cm from the mixture for the specified time at the specified wavelength (365 nm, 385 nm, or 400 nm), or in the case of 450 nm irradiation, with an ELIPAR S10 LED Curing Light (3M ESPE, St. Paul, Minn.) held &lt;1 cm from the sample. The sample was then placed in a 37° C. chamber. A dental probe was then used to evaluate the cure of the material. Working time was defined as the elapsed time until the first solid chunk of cured material can be detected, and full cure was defined as the elapsed time until the entire sample had cured to a solid. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 8* 
               
               
                   
               
               
                 Irradiation 
                 365 nm 
                 385 nm 
                 400 nm 
                 450 nm 
               
               
                 time, 
                 full cure, 
                 full cure, 
                 full cure, 
                 full cure, 
               
               
                 seconds 
                 minutes 
                 minutes 
                 minutes 
                 minutes 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 0 
                 10.0 
                 10.0 
                 10.0 
                 10.0 
               
               
                 2.0 
                 3.5 
                 4.0 
                 5.5 
                 6.0 
               
               
                 4.0 
                 2.5 
                 3.0 
                 4.5 
                 5.5 
               
               
                 6.0 
                 1.0 
                 2.0 
                 3.5 
                 5.0 
               
               
                   
               
               
                 *Full cure = time until the entire paste sample became hardened. 
               
            
           
         
       
     
     Comparative Example 1 (CE-1): Two-Part Formulation Using Cu(OAc) 2    
     A comparative example of a two-part formulation was prepared according to the method used for EX-1, except that copper (II) acetate was the copper source, with amounts as summarized in Table 9. 
     
       
         
           
               
               
             
               
                 TABLE 9 
               
             
            
               
                   
               
               
                 Mixture-A 
                 Mixture-B 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 mass 
                   
                   
                 mass 
               
               
                 Material 
                 Wt. % 
                 (g) 
                 Material 
                 Wt. % 
                 (g) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 BisGMA 
                 19.5 
                 11.7 
                 BisGMA 
                 18.95 
                 3.79 
               
               
                 TEGDMA 
                 19.5 
                 11.7 
                 TEGDMA 
                 18.95 
                 3.79 
               
               
                 — 
                 — 
                 — 
                 Cu(OAc) 2  soln* 
                 0.60 
                 0.12 
               
               
                 p-AA 
                 0.5 
                 0.3 
                 CHP 
                 1.00 
                 0.20 
               
               
                 HDK H-2000 
                 2.0 
                 1.2 
                 HDK H-2000 
                 2.00 
                 0.40 
               
               
                 Z250 filler 
                 58.5 
                 35.1 
                 Z250 filler 
                 59.00 
                 11.70 
               
               
                 Total 
                 100.0 
                 60.0 
                 Total 
                 100.00 
                 20.00 
               
               
                   
               
               
                 *The “Cu(OAc) 2  soln” of CE-1 was prepared as a 1.7 wt. % solution of Cu(OAc) 2  in 1:1 BisGMA/TEGDMA; thus the Mixture-B paste was 0.0102 wt. % Cu(OAc) 2   
               
            
           
         
       
     
     Barcol hardness values of test samples from CE-1, EX-1, and EX-3 were determined according to the “Barcol Hardness Test Method” described above, using a 37° C./95% RH chamber for treatment during the curing time. The “Top Barcol” and “Bottom Barcol” values reported in Table 10 were means from triplicate measurement, with standard deviations listed in parentheses. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 10 
               
               
                   
               
               
                 Two-part 
                 Irradiation 
                 Curing 
                 Top 
                 Bottom 
               
               
                 formulation 
                 (10 seconds at 365 nm) 
                 time 
                 Barcol 
                 Barcol 
               
               
                   
               
             
            
               
                 CE-1 
                 No 
                 15 min 
                 30.0 (0.8) 
                 29.3 (0.5) 
               
               
                   
                   
                 30 min 
                 47.0 (1.4) 
                 50.0 (1.6) 
               
               
                   
                   
                 45 min 
                 57.7 (0.5) 
                 59.3 (0.9) 
               
               
                   
                   
                 60 min 
                 63.3 (1.3) 
                 61.7 (0.5) 
               
               
                 EX-1 
                 No 
                 15 min 
                 28.0 (0.0) 
                 30.0 (1.6) 
               
               
                   
                   
                 30 min 
                 42.0 (0.0) 
                 42.7 (0.5) 
               
               
                   
                   
                 45 min 
                 48.0 (0.8) 
                 49.3 (0.5) 
               
               
                   
                   
                 60 min 
                 53.3 (0.9) 
                 55.3 (0.9) 
               
               
                   
                 Yes 
                 15 min 
                 40.0 (1.6) 
                 41.7 (0.5) 
               
               
                   
                   
                 30 min 
                 49.3 (0.9) 
                 50.7 (0.9) 
               
               
                   
                   
                 45 min 
                 54.7 (0.9) 
                 55.0 (0.8) 
               
               
                   
                   
                 60 min 
                 57.3 (0.9) 
                 57.3 (0.5) 
               
               
                 EX-3 
                 No 
                 10 min 
                 0 
                 0 
               
               
                   
                   
                 20 min 
                 0 
                 0 
               
               
                   
                   
                 30 min 
                  5.3 (0.6) 
                  5.3 (0.6) 
               
               
                   
                   
                 40 min 
                  9.7 (0.6) 
                  9.3 (0.6) 
               
               
                   
                   
                 60 min 
                 22.7 (1.2) 
                 23.0 (1.0) 
               
               
                   
                   
                 90 min 
                 48.0 (1.0) 
                 47.3 (1.2) 
               
               
                   
                 Yes 
                 10 min 
                 0 
                 0 
               
               
                   
                   
                 20 min 
                 11.3 (1.2) 
                 10.3 (1.5) 
               
               
                   
                   
                 30 min 
                 22.7 (0.6) 
                 23.0 (1.0) 
               
               
                   
                   
                 40 min 
                 31.0 (1.0) 
                 33.7 (1.2) 
               
               
                   
                   
                 60 min 
                 40.0 (1.0) 
                 39.7 (0.6) 
               
               
                   
                   
                 90 min 
                 55.0 (1.0) 
                 56.3 (0.6) 
               
               
                   
               
            
           
         
       
     
     Flexural strength and flexural modulus values of test samples from CE-1, EX-1, and EX-3 were determined according to the “Flexural Strength/Flexural Modulus Test Method” described above. The resulting flexural strength and flexural modulus values (in MPa) listed in Table 11 were means from a minimum of five measurements, with standard deviations (in MPa) listed in parentheses. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 11 
               
               
                   
               
               
                   
                   
                   
                 Flexural 
               
               
                 Two-part 
                 Irradiation 
                 Flexural strength, 
                 modulus, 
               
               
                 formulation 
                 (10 seconds at 365 nm) 
                 MPa 
                 MPa 
               
               
                   
               
             
            
               
                 CE-1 
                 No 
                 98.6 (11.7) 
                 6.11 (0.4) 
               
               
                 EX-1 
                 No 
                 83.9 (12.2) 
                 5.36 (0.4) 
               
               
                   
                 Yes 
                 108.0 (12.0)  
                 5.40 (0.4) 
               
               
                 EX-3 
                 No 
                 63.5 (13.9) 
                 3.60 (0.4) 
               
               
                   
                 Yes 
                 88.6 (14.8) 
                 4.62 (0.8) 
               
               
                   
               
            
           
         
       
     
     Examples of Two-Part Acrylate-Based Formulations 
     Examples of two-part formulations were provided that included a polymerizable acrylate-based monomer. 
     Example 5 (EX-5): Two-Part Formulation Using the PE-1 Copper Complex 
     A representative two-part formulation was prepared as follows. A “Mixture-A” paste included SARTOMER SR238B (hexanediol diacrylate, HDDA) as a polymerizable acrylate-based monomer, 5,6-O-isopropylidene-L-ascorbic acid (p-AA), HDK H-2000 fumed silica as a flow agent, and Z250 as filler material in the amounts listed in Table 13. A “Mixture-B” paste included SARTOMER SR238B (hexanediol diacrylate, HDDA), a 2 wt. % solution of the PE-1 copper (II) cage complex dissolved in 1:1 BisGMA/TEGDMA, cumene hydroperoxide (CHP), HDK H-2000 fumed silica, and Z250 filler in the amounts listed in Table 12. 
     
       
         
           
               
               
             
               
                 TABLE 12 
               
             
            
               
                   
               
               
                 Mixture-A 
                 Mixture-B 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 mass 
                   
                   
                 mass 
               
               
                 Material 
                 Wt. % 
                 (g) 
                 Material 
                 Wt. % 
                 (g) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 HDDA 
                 37.5 
                 3.75 
                 HDDA 
                 36.50 
                 7.30 
               
               
                 p-AA 
                 0.5 
                 0.05 
                 Cu cage soln* 
                 0.15 
                 0.03 
               
               
                 — 
                 — 
                 — 
                 CHP 
                 1.00 
                 0.20 
               
               
                 HDK H-2000 
                 4.0 
                 0.40 
                 HDK H-2000 
                 4.00 
                 0.80 
               
               
                 Z250 filler 
                 58.0 
                 5.80 
                 Z250 filler 
                 58.35 
                 11.67 
               
               
                 Total 
                 100.0 
                 10.00 
                 Total 
                 100.00 
                 20.00 
               
               
                   
               
               
                 *The “Cu cage soln” of Example 5 was prepared as a 2 wt. % solution of PE-1 Cu complex in 1:1 BisGMA/TEGDMA; thus the Mixture-B paste was 0.003 wt. % PE-1 Cu complex. 
               
            
           
         
       
     
     To perform curing experiments with the EX-5 two-part formulation, 60 mg portions of each of the Mixture-A and Mixture-B parts of EX-5 were weighed out onto a mixing pad and hand mixed together for 20 seconds. At time=30 seconds, the mixture was irradiated either with an LX-400 LED lamp (Lumen Dynamics, Mississauga, Ontario, Canada) held 2 cm from the mixture for the specified time at the specified wavelength, as summarized in Table 13, or in the case of 450 nm with an ELIPAR S10 LED Curing Light (3M ESPE, St. Paul, Minn.) held &lt;1 cm from the mixture. A dental probe was then used to evaluate the cure of the material. Working time was defined as the elapsed time until the first solid chunk of cured material could be detected, and full cure was defined as the elapsed time until the entire sample had cured to a solid. Results were as summarized in Table 13. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 13* 
               
             
            
               
                   
                   
               
               
                   
                 365 nm 
                 385 nm 
                 400 nm 
                 450 nm 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Irradiation 
                 work 
                 full 
                 work 
                 full 
                 work 
                 full 
                 work 
                 full 
               
               
                 time, 
                 time, 
                 cure, 
                 time, 
                 cure, 
                 time, 
                 cure, 
                 time, 
                 cure, 
               
               
                 seconds 
                 minutes 
                 minutes 
                 minutes 
                 minutes 
                 minutes 
                 minutes 
                 minutes 
                 minutes 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 0 
                 5.50 
                 8.00 
                 5.50 
                 8.00 
                 5.50 
                 8.00 
                 5.50 
                 8.00 
               
               
                 5.0 
                 3.50 
                 4.50 
                 4.50 
                 6.00 
                 5.25 
                 7.00 
                 5.00 
                 6.00 
               
               
                 10.0 
                 2.00 
                 3.00 
                 4.00 
                 5.75 
                 4.50 
                 6.00 
                 4.00 
                 4.50 
               
               
                 15.0 
                 &lt;0.75 
                 0.75 
                 2.25 
                 4.00 
                 4.00 
                 5.75 
                 3.50 
                 4.00 
               
               
                   
               
               
                 *Work time = time until the first amount of cured material could be detected; Full cure = time until the entire paste sample became hardened. 
               
            
           
         
       
     
     Comparative Example 2 (CE-2): Two-Part Formulation Using Cu(OAc) 2    
     A comparative example of a two-part formulation was prepared according to the method used for EX-5, except that copper (II) acetate was the copper source, with amounts as summarized in Table 14. 
     
       
         
           
               
               
             
               
                 TABLE 14 
               
             
            
               
                   
               
               
                 Mixture-A 
                 Mixture-B 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 mass 
                   
                   
                 mass 
               
               
                 Material 
                 Wt. % 
                 (g) 
                 Material 
                 Wt. % 
                 (g) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 HDDA 
                 37.5 
                 3.75 
                 HDDA 
                 36.50 
                 7.30 
               
               
                 p-AA 
                 0.5 
                 0.05 
                 Cu(OAc) 2  soln* 
                 0.15 
                 0.03 
               
               
                 — 
                 — 
                 — 
                 CHP 
                 1.00 
                 0.20 
               
               
                 HDK H-2000 
                 4.0 
                 0.40 
                 HDK H-2000 
                 4.00 
                 0.80 
               
               
                 Z250 filler 
                 58.0 
                 5.80 
                 Z250 filler 
                 58.35 
                 11.67 
               
               
                 Total 
                 100.0 
                 10.00 
                 Total 
                 100.00 
                 20.00 
               
               
                   
               
               
                 *The “Cu(OAc) 2  soln” of CE-2 was prepared as a 1.7 wt. % solution of Cu(OAc) 2  in 1:1 BisGMA/TEGDMA; thus the Mixture-B paste was 0.0026 wt. % Cu(OAc) 2   
               
            
           
         
       
     
     Barcol hardness values of test samples from CE-2 and EX-5 were determined according to the “Barcol Hardness Test Method” described above, using ambient temperature during the curing time. The “Top Barcol” and “Bottom Barcol” values reported in Table 15 were means from triplicate measurement, with standard deviations listed in parentheses. 
                                     TABLE 15               Two-part   Irradiation   Curing   Top   Bottom       formulation   (10 seconds at 365 nm)   time   Barcol   Barcol                  CE-2   No    5 min   0   0               10 min   47.3 (0.3)   47.0 (1.0)               15 min   65.0 (0.0)   65.0 (1.0)               20 min   65.0 (1.0)   65.7 (0.6)       EX-5   No    5 min   0   0               10 min   53.3 (1.2)   53.0 (1.0)               15 min   66.3 (0.6)   66.0 (0.0)               20 min   65.7 (0.6)   66.7 (0.6)           Yes    5 min   37.7 (0.6)   37.0 (1.0)               10 min   65.0 (1.0)   64.3 (0.6)               15 min   66.3 (0.6)   67.0 (0.0)               20 min   66.3 (1.2)   67.0 (1.0)                    
Curing Experiments with Vinyl-Based Formulations
 
     An example of a one-part formulation was provided that included a polymerizable vinyl-based monomer. 
     Example 6 (EX-6): One-Part Formulation Using the PE-1 Copper Complex 
     A representative formulation was prepared which included divinylbenzene (DVB) as the polymerizable vinyl-based monomer, ethyl acetate (EtOAc), cyclohexyl ketal-protected ascorbic acid (cyc-AA), cumene hydroperoxide (CHP), and a 1.7 wt. % solution of the PE-1 copper complex in ethyl acetate, according to the amounts in Table 16. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 16 
               
               
                   
                   
               
               
                   
                 Material 
                 Wt. % 
                 mass (g) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 DVB 
                 49.0 
                 44.10 
               
               
                   
                 EtOAc 
                 49.0 
                 44.10 
               
               
                   
                 cyc-AA 
                 0.5 
                 0.45 
               
               
                   
                 CHP 
                 1.0 
                 0.90 
               
               
                   
                 Cu cage soln* 
                 0.5 
                 0.45 
               
               
                   
                 Total 
                 100.0 
                 90.00 
               
               
                   
                   
               
               
                   
                 *The “Cu cage soln” of Example 6 was prepared as a 1.7 wt. % solution of PE-1 Cu complex in 1:1 BisGMA/TEGDMA; thus the resin was 0.0085 wt. % PE-1 Cu complex. 
               
            
           
         
       
     
     To perform curing experiments, nitrogen was bubbled through the EX-6 formulation for several minutes, then 6.0 gram samples were placed in 20 mL glass vials which were flushed with nitrogen, and then capped with a screw-top cap. The samples were then irradiated through the bottom of the vial using an LX400 LED lamp (Lumen Dynamics, Mississauga, Ontario, Canada) at 365 nm for 5×1 minute. Afterwards, at the times specified in Table 17, any polymerized material was collected by vacuum filtration. The collected precipitate was then ground to a fine powder, stirred with ethyl acetate for 30 min, collected again via vacuum filtration, dried under vacuum, and weighed. The amounts of polymerized material collected and corresponding percent conversion values were as summarized in Table 17. 
                                 TABLE 17                          UV irradiation   No UV irradiation                                 Time,   poly(DVB),       poly(DVB),           hours   grams   % conversion   grams   % conversion                                         0   0   0   0   0       8   0.74   25.2   0   0       16   1.24   42.2   0   0       24   1.58   53.7   0.30   10.2       40   1.92   65.3   1.10   37.4       48   1.96   66.7   1.40   47.6       64   2.16   73.5   1.71   58.2       70   2.21   75.2   1.81   61.6                    
Additional Curing Experiments with Methacrylate-Based Formulation
 
     Example 7 (EX-7): Two-Part Formulation Using the PE-1 Copper Complex 
     A representative two-part formulation was prepared as shown below. A “Mixture-A” paste included SARTOMER SR203 (THF methacrylate) and a solution of the PE-1 copper complex dissolved in a 1:1 mixture of BisGMA/TEGDMA, in amounts according to Table 18. A “Mixture-B” paste included BENZOFLEX 9-88, CAB-O-SIL TS720 fumed silica, isopropylidene-protected ascorbic acid (p-AA), and cumene hydroperoxide (CHP), in amounts according to Table 18. 
     
       
         
           
               
               
             
               
                 TABLE 18 
               
             
            
               
                   
               
               
                 Mixture-A 
                 Mixture-B 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 mass, 
                   
                 Wt. 
                 mass, 
               
               
                 Material 
                 Wt. % 
                 grams 
                 Material 
                 % 
                 grams 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 SR203 
                 98.8 
                 19.75 
                 BENZOFLEX 9-88 
                 89.0 
                 4.45 
               
               
                 Cu cage soln* 
                 1.2 
                 0.25 
                 CAB-O-SIL TS720 
                 1.8 
                 0.09 
               
               
                 — 
                 — 
                 — 
                 p-AA 
                 7.4 
                 0.37 
               
               
                 — 
                 — 
                 — 
                 CHP 
                 1.8 
                 0.09 
               
               
                 Total 
                 100.0 
                 20.00 
                 Total 
                 100.0 
                 5.00 
               
               
                   
               
               
                 *The “Cu cage soln” of EX-7 was prepared as a 2 wt. % solution of PE-1 Cu complex in 1:1 BisGMA/TEGDMA; thus the Mixture-A resin was 0.024 wt. % PE-1 Cu complex 
               
            
           
         
       
     
     To perform curing experiments with the EX-7 two-part formulation, 0.25 mL of Mixture-B was added to 2.00 g of Mixture-A in an 8-mL glass vial and shaking briefly to mix. The vial was then irradiated with an LX-400 LED lamp (Lumen Dynamics, Mississauga, Ontario, Canada) held within 1 cm of the glass vial for the specified time at the specified wavelength. Working time was defined as the point at which the material was fully solidified and was no longer able to flow. Irradiation and working times were as summarized in Table 19. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 19 
               
               
                   
                   
               
               
                   
                 Irradiation at 365 nm, 
                 Work time, 
               
               
                   
                 seconds 
                 minutes 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 0 
                 9.0 
               
               
                   
                 30 
                 6.0 
               
               
                   
                 60 
                 4.5 
               
               
                   
                   
               
            
           
         
       
     
     Example 8 (EX-8): Two-Part Formulation Using the PE-3 Copper Complex 
     A representative two-part formulation was prepared as shown below. A “Mixture-A” paste included SARTOMER SR203 (THF methacrylate) and a solution of the PE-3 copper complex dissolved in a 1:1 mixture of BisGMA/TEGDMA in amounts according to Table 20. A “Mixture-B” paste included BENZOFLEX 9-88, CAB-O-SIL TS720 fumed silica, isopropylidene-protected ascorbic acid (p-AA), and cumene hydroperoxide (CHP) in amounts according to Table 20. 
     
       
         
           
               
               
             
               
                 TABLE 20 
               
             
            
               
                   
               
               
                 Mixture-A 
                 Mixture-B 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 mass, 
                   
                 Wt. 
                 mass, 
               
               
                 Material 
                 Wt. % 
                 grams 
                 Material 
                 % 
                 grams 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 SR203 
                 98.8 
                 19.75 
                 BENZOFLEX 9-88 
                 89.0 
                 4.45 
               
               
                 Cu cage soln* 
                 1.2 
                 0.25 
                 Cab-o-Sil TS720 
                 1.8 
                 0.09 
               
               
                 — 
                 — 
                 — 
                 p-AA 
                 7.4 
                 0.37 
               
               
                 — 
                 — 
                 — 
                 CHP 
                 1.8 
                 0.09 
               
               
                 Total 
                 100.0 
                 20.00 
                 Total 
                 100.0 
                 5.00 
               
               
                   
               
               
                 *The “Cu cage soln” of EX-8 was prepared as a 2 wt. % solution of PE-3 Cu complex in 1:1 BisGMA/TEGDMA; thus the Mixture-A resin was 0.024 wt. % PE-3 Cu complex 
               
            
           
         
       
     
     To perform curing experiments with the EX-8 two-part formulation, 0.25 mL of Mixture-B was added to 2.00 g of Mixture-A in an 8-mL glass vial and shaking briefly to mix. The vial was then irradiated with an LX-400 LED lamp held within 1 cm of the glass vial for the specified time at the specified wavelength. Working time was defined as the point at which the material was fully solidified and no longer able to flow. Irradiation and working times were as summarized in Table 21. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 21 
               
               
                   
                   
               
               
                   
                 Irradiation at 365 nm, 
                 Work time, 
               
               
                   
                 seconds 
                 minutes 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 0 
                 6.50 
               
               
                   
                 15 
                 5.75 
               
               
                   
                 30 
                 4.75 
               
               
                   
                 60 
                 4.25 
               
               
                   
                   
               
            
           
         
       
     
     Example 9 (EX-9): Two-Part Formulation Using the PE-1 Copper Complex 
     A representative two-part structural adhesive formulation was prepared as shown below. A “Mixture-A” paste included 15 wt. % VTBN in SARTOMER SR203, SARTOMER SR541, CAB-O-SIL TS720 fumed silica, and the PE-1 copper complex dissolved in a 1:1 mixture of BisGMA/TEGDMA, in the amounts listed in Table 22. 5-mil spacer beads (E-Spheres SL300 Ceramic Microspheres obtained from Envirospheres PTY Ltd., Lindfield NSW, Australia) were also added to Mixture-A in an amount of 0.5 parts by weight relative to a total 100 parts by weight of the other Mixture-A components. A “Mixture-B” paste included isopropylidene-protected ascorbic acid (p-AA), BENZOFLEX 9-88, cumene hydroperoxide (CHP), and CAB-O-SIL TS720 fumed silica, in the amounts listed in Table 22. 
     
       
         
           
               
               
             
               
                 TABLE 22 
               
             
            
               
                   
               
               
                 Mixture-A 
                 Mixture-B 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Wt.  
                 mass, 
                   
                 Wt. 
                 mass, 
               
               
                 Material 
                 % 
                 grams 
                 Material 
                 % 
                 grams 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 15 wt. % VTBN 
                 79.6 
                 7.96 
                 BENZOFLEX 
                 89.0 
                 4.45 
               
               
                 in SR203 
                   
                   
                 9-88 
               
               
                 SR541 
                 14.7 
                 1.47 
                 CAB-O-SIL 
                 1.8 
                 0.09 
               
               
                   
                   
                   
                 TS720 
               
               
                 Cu cage solution* 
                 0.17 
                 0.02 
                 p-AA 
                 7.4 
                 0.37 
               
               
                 CAB-O-SIL 
                 5.50 
                 0.55 
                 CHP 
                 1.8 
                 0.09 
               
               
                 TS720 
                   
                   
                   
                   
                   
               
               
                 Total 
                 100.0 
                 10.00 
                 Total 
                 100.0 
                 5.00 
               
               
                   
               
               
                 *The “Cu cage solution” was prepared as a 2 wt. % solution of PE-1 Cu complex in 1:1 BisGMA/TEGDMA; thus the Mixture-A paste was 0.0034 wt. % PE-1 Cu complex. 
               
            
           
         
       
     
     Comparative Example 3 (CE-3): Two-Part Formulation Using Cu(OAc) 2    
     A comparative example of a two-part formulation was prepared according to the method used for EX-9, except that copper (II) acetate was the copper source, with amounts as summarized in Table 23. 
     
       
         
           
               
               
             
               
                 TABLE 23 
               
             
            
               
                   
               
               
                 Mixture-A 
                 Mixture-B 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                 mass, 
                   
                   
                 mass, 
               
               
                 Material 
                 Wt. % 
                 grams 
                 Material 
                 Wt. % 
                 grams 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 15 wt. % VTBN 
                 79.6 
                 7.96 
                 BENZOFLEX 
                 89.0 
                 4.45 
               
               
                 in SR203 
                   
                   
                 9-88 
               
               
                 SR541 
                 14.7 
                 1.47 
                 CAB-O-SIL 
                 1.8 
                 0.09 
               
               
                   
                   
                   
                 TS720 
               
               
                 Cu(OAc) 2    
                 0.17 
                 0.02 
                 p-AA 
                 7.4 
                 0.37 
               
               
                 solution* 
               
               
                 CAB-O-SIL 
                 5.50 
                 0.55 
                 CHP 
                 1.8 
                 0.09 
               
               
                 TS720 
                   
                   
                   
                   
                   
               
               
                 Total 
                 100.0 
                 10.00 
                 Total 
                 100.0 
                 5.00 
               
               
                   
               
               
                 *The “Cu(OAc) 2  solution” was prepared as a 2 wt. % solution of Cu(OAc) 2  in 1:1 BisGMA/TEGDMA; thus the Mixture-A paste was 0.0034 wt. % Cu(OAc) 2 . 
               
            
           
         
       
     
     For curing experiments using either CE-3 or EX-9, an 8:1 ratio of the corresponding Mixture-A paste and Mixture-B paste was weighed out and hand mixed, then spread onto hand-roughened aluminum shims (scrubbed with 3M SCOTCH-BRITE GENERAL PURPOSE HAND PADS #7447, obtained from 3M Co., St. Paul, Minn.). Irradiated samples (i.e. samples utilizing the formulations with the copper cage complex; the control sample CE-3 was not irradiated) were passed through a fusion processor (2 J/cm 2  D-bulb, obtained from Heraeus Noblelight America, Gaithersburg, Md.) and clamped shut with 0.5 inch (˜1.3 cm) overlap. Samples containing the copper (II) acetate were not irradiated prior to clamping shut with 0.5 inch (˜1.3 cm) overlap. All samples were allowed to sit at room temperature for 24 hours prior to overlap shear testing. A dynamic overlap shear test was performed at ambient temperature using an MTS SINTECH TENSILE TESTER (obtained from MTS Systems, Eden Prairie, Minn.). Test specimens were loaded into the grips and the crosshead was operated at 0.1 inch (˜2.5 mm) per minute, loading the specimen to failure. Samples were run in triplicate and results were reported as the averages. Stress at break was recorded in units of pounds per square inch (“psi”), which was also converted to units of megapascal (“MPa”); and peak load was recorded in units of pound force (“lbf”), which was also converted to Newtons (“N”). Results were as listed in Table 24. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 24 
               
               
                   
                   
               
               
                   
                   
                 Peak stress, psi 
                   
               
               
                   
                 Sample 
                 (MPa) 
                 Peak load, lbf (N) 
               
               
                   
                   
               
             
            
               
                   
                 CE-3 
                 1159.3 (7.99) 
                 579.6 (2578) 
               
               
                   
                 EX-9 
                 1057.9 (7.29) 
                 528.9 (2353) 
               
               
                   
                   
               
            
           
         
       
     
     The samples which utilized the irradiated copper cage complex exhibited adhesion that was essentially equivalent to the control samples utilizing the copper (II) acetate, demonstrating the viability of the photo-triggered redox cure for adhesive material.