Patent Publication Number: US-2020291168-A1

Title: Curable urethane acrylate composition

Description:
FIELD OF INVENTION 
     The instant invention relates to a curable urethane acrylate composition. 
     BACKGROUND OF THE INVENTION 
     The thermosetting resins used in fiber reinforced composites mainly include unsaturated polyesters, vinyl esters, epoxies, phenolics, polyimides and polyurethanes. Recently, polyurethane resins have attracted broad interest as composite matrix materials. Compared with traditional unsaturated polyester, vinyl ester, and epoxy resins, polyurethane resins offer increased toughness, exceptional durability, and fast cycle time. The use of polyurethane as the resin matrix in fiber reinforced composites potentially offers various benefits: for instance in the pultrusion process, polyurethane allows the use of a higher concentration of fiberglass, or alternatively of a simpler reinforcement lay-up, with limited impact on the strength of the end product. 
     However, the high reactivity of two-component (isocyanate and polyol) polyurethane resins not only allows fast cycle time of process, but it also reduces the pot life of the resin system to typically less than 30 minutes. The short pot life of two-component polyurethane resins has limited their application in many composite fabrication processes. In some composite fabrication processes, polyurethanes are usually limited to small composite articles or articles with simple cross section, because of the short pot life of the mixed resin and the quick increase of viscosity. Composites made from polyurethane resins that combine high glass transition temperatures (Tg) higher than 60° C. and preferably higher than 70° C. with the toughness levels typical of polyurethanes, are desired. 
     SUMMARY OF THE INVENTION 
     In one broad embodiment of the present invention, there is disclosed A curable resin composition comprising, consisting of, or consisting essentially of: (1) a urethane (meth)acrylate; 
     (2) a reactive diluent comprising at least 20 percent by weight of glycols and/or polyols with terminal acrylate or methacrylate groups; and (3) a free radical-generating catalyst. 
     In an alternative embodiment, the instant invention provides a composition, in accordance with the preceding embodiment, except that the curable resin composition comprises 10 to 90 percent by weight of said urethane (meth)acrylate, 10 to 90 percent by weight of said reactive diluent, and 0.001 to 10 percent by weight of said free radical-generating catalyst, based on the total weight of the curable resin composition. 
     In an alternative embodiment, the instant invention provides a composition, in accordance with the preceding embodiment, except that the urethane (meth)acrylate is a reaction product of a polyisocyanate, a polyol, and a compound comprising a nucleophilic group and a (meth)acrylate group. 
     In an alternative embodiment, the instant invention provides a composition, in accordance with the preceding embodiment, except that the compound comprising a nucleophilic group and a (meth)acrylate group is selected from the group consisting of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxyethyl acrylamide, hydroxypropyl acrylamide, and mixtures thereof. 
     In an alternative embodiment, the instant invention provides a composition, in accordance with the preceding embodiment, except that the urethane (meth)acrylate has a free isocyanate group content in the range of from 0 to 0.1 percent by weight, based on the total weight of the urethane (meth)acrylate. 
     In an alternative embodiment, the instant invention provides a composition, in accordance with the preceding embodiment, except that the reactive diluent is selected from the group consisting of 1,4-butanediol diacrylate (BDDA), 1,6-hexanediol diacrylate (HDDA), diethylene glycol diacrylate, 1,3-butylene glycol diacrylate, neopentyl glycol diacrylate, cyclohexane dimethanol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, ethoxylated bisphenol A diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, their corresponding methacrylate analogues, and derivatives and mixtures thereof. 
     In an alternative embodiment, the instant invention provides a composition, in accordance with the preceding embodiment, except that the free radical-generating catalyst is selected from the group consisting of tert-Butyl peroxyneodecanoate, benzoyl peroxide, dicumyl peroxide, methyl ethyl ketone peroxide, lauryl peroxide, cyclohexanone peroxide, t-butyl perbenzoate, t-butyl hydroperoxide, t-butylbenzene hydroperoxide, cumene hydroperoxide, t-butyl peroctoate, azobis-isobutyronitrile, 2-tbutylazo-2-cyano-4-methylpentane, and 4-t-butylazo-4-cyano-valeric acid. 
     In an alternative embodiment, the instant invention provides a composition, in accordance with the preceding embodiment, except that the curable resin composition is prepared by mixing said urethane (meth)acrylate and said reactive diluent to form a mixture and subsequently adding said free radical catalyst to the mixture. 
     In an alternative embodiment, the instant invention provides a filament winding process, a pultrusion process, and a cured-in-place pipe process incorporating the curable resin composition of the above-disclosed embodiments. 
     In addition to the ingredients described in the inventive compositions as per previous embodiments, other ingredients may be also included to adjust the reactivity or the processability or any other feature of the composition: this includes ingredients such as activators, inhibitors, internal mold release agents, fillers, thixotropic agents, and other additives as well known to those skilled in the art. 
     The instant invention also discloses composites prepared from the curable resin composition. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The instant invention is a curable resin composition. The instant invention is a curable resin composition comprising (1) a urethane methacrylate, (2) a reactive diluent; and (3) a free radical-generating catalyst. 
     The urethane (meth)acrylate can be synthesized through the reaction of polyisocyanates, polyols, and a compound containing both a nucleophilic group and a (meth)acrylate group. 
     The polyisocyanates used are typically aromatic, aliphatic, and cycloaliphatic polyisocyanates with a number average molar mass below 800 g/mol. Examples of suitable compounds include, but are not limited to diisocyanates from the group of toluene 2,4-/2,6-diisocyanate (TDI), methylenediphenyl diisocyanate (MDI), triisocyanatononane (TIN), naphthyl diisocyanate (NDI), 4,4′-diisocyanatodicyclohexylmethane, 3-isocyanatomethyl-3,3,5-trimethylcyclohexyl isocyanate (isophorone diisocyanate (IIPDI)), tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), 2-methylpentamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate (THDI), dodecamethylene diisocyanate, 1,4-diisocyanatocyclohexane, 4,4′-diisocyanato-3,3′-dimethyldicyclohexylmethane, 4,4′-diisocyanato-2,2-dicyclohexylpropane, 3-isocyanatomethyl-1-methyl-1-isocyanatocyclohexane (MCI), 1,3-diisooctylcyanato-4-methylcyclohexane, 1,3-diisocyanato-2-methylcyclohexane, tetramethylxylylenediisocyanate (TMXDI), 4,6′-xylene diisocyanate (XDI), para-phenylene diisocyanate (PPDI), 3,3′-tolidene 4,4′-diisocyanate (TODI), 3,3′-dimethyl-diphenylmethane 4,4′-diisocyanate (DDI), their adducts, their polymeric forms, and also mixtures thereof. Examples of commercial isocyanates suitable for the scope of this invention, are the aromatic isocyanates available from The Dow Chemical Company under the trademark Voranate T-80, Isonate M125, Voranate M2940, or the aliphatic isocyanates available from Evonik and Bayer respectively under the trademarks Vestanat IPDI and Desmodur W. Prior to reaction with the compound containing both a nucleophilic group and a (meth)acrylate group, these isocyanates may optionally be “chain extended” by reaction with a polyol. The polyols used may feature various chain lengths and functionalities in relation to the desired performance level of the resulting polymer. This also includes combinations of polyols that include at least two polyols having different equivalent weights, wherein the short-chain average equivalent weight is from 50 to 2000, preferably from 100 to 1000, and the long chain average equivalent weight is from 2000 to 20,000, preferably from 2000 to 10000. The polyol can be selected from polyether polyols and polyester polyols. Preferably the polyols have a functionality of 2.0 or greater. Examples include polyether polyols such as Voranol 8000LM, Voranol 4000LM, Polyglycol P2000, Voranol 1010L, Polyglycol P425, TPG, Voranol 230-660 and mixtures thereof: also included are polyester polyols such as those available from Stepan Company under the trademark Stepanpol, or those available from COIM under the trademarks Isoexter and Diexter, or those available from Invista under the trademark Terate. 
     The polyurethane with free terminal isocyanate groups is capped with a compound containing the nucleophilic group (eg. hydroxyl, amino, or mercapto) and ethylenically unsaturated functionalities derived from (meth)acrylate. Preferred examples include 2-hydroxyethyl methacrylate (HEMA), 2-hydroxypropyl methacrylate (HPMA), 2-hydroxyethyl acrylate (HEA), 2-hydroxypropyl acrylate (HPA) and related compounds. These compounds may also form part of the reactive diluent composition in the final curable resin. 
     Urethane (meth)acrylates utilized in this invention are prepared by two-step reactions. In the first step, the polyurethane oligomers are prepared by reacting an organic polyisocyanate with a mixture of polyols in an equivalent ratio of NCO:OH from 1.4:1 to 3.0:1, using standard procedures, to yield an isocyanate-terminated prepolymer with controlled molecular weight. Any and all ranges between 1.4:1 and 3.0:1 are included herein and disclosed herein, for example, the NCO/OH ratio can range from about 1.4:1 to about 2.3:1. In the second step, polyurethane oligomers with free terminal isocyanate groups are capped with a compound containing the nucleophilic group (e.g. hydroxyl, amino or mercapto) and ethylenically unsaturated functionalities derived from (meth)acrylate by using methods well-known in the art. The functionalized (meth)acrylate component may be provided in a stoichiometric excess with respect to the isocyanate component. The excess functionalized (meth)acrylate component functions as a reactive diluent, which lowers the viscosity of the urethane acrylate composition and cross-links with the urethane (meth)acrylate adduct during formation of the polymer. The percent of free NCO in the final urethane (meth)acrylate is generally in the range of from 0 to 0.1 percent. Any and all ranges between 0 and 0.1 percent are included herein and disclosed herein, for example, the percent of free NCO in the final urethane acrylate can be in the range of from 0 to 0.001%. Alternatively, the urethane (meth)acrylates may be prepared by the so called “reverse process”, in which the isocyanate is reacted first with the compound containing the nucleophilic group (e.g. hydroxyl, amino or mercapto) and ethylenically unsaturated functionalities derived from (meth)acrylate, and then with the polyols, as disclosed in U.S. Pat. No. 4,246,391. Alternatively, a “one step process” may be adopted, in which the isocyanate is reacted simultaneously with a mixture of the polyol and the compound containing the nucleophilic group (e.g. hydroxyl, amino or mercapto) and ethylenically unsaturated functionalities derived from (meth)acrylate. 
     In some embodiments, a urethane catalyst can be used to accelerate the reaction. Examples of urethane catalysts include, but are not limited to tertiary amines and metal compounds such as stannous octoate and dibutyltin dilaurate. The urethane catalyst is employed in an amount in the range of from 10 to 1000 ppm based on the total weight of the urethane (meth)acrylate, preferably from 50 to 400 ppm. 
     Additionally, in some embodiments, an inhibitor can be added to avoid the free radical polymerization of (meth)acrylates during storage. Preferred inhibitors include (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (TEMPO), Mono Methyl Ether of Hydroquinone (MEHQ), dihydroxybenzenes, benzoquinones, hindered phenols, and hindered phenols based on triazine derivatives. The preferred percentage of inhibitor is 50 to 10000 ppm, preferably 100 to 1000 ppm, based on the total weight of the curable resin. 
     Commercially available urethane (meth)acrylates can also be used. These include, but are not limited to CN 1963, CN9167, CN 945A60, CN 945A70 CN 944B85, CN 945B85, CN 934, CN 934X50, CN 966A80, CN 966H90, CN 966J75, CN 968, CN 981, CN 981A75, CN 981B88, CN 982A75, CN 982B88, CN 982E75, CN 982P90, CN 983B88, CN 985B88, CN 970A60, CN 970E60, CN 971A80, CN 972, CN 973A80, CN 977C70, CN 975, CN 978, all available from Sartomer. Mixtures thereof can also be used. 
     The weight ratio of low molecular weight urethane (meth)acrylate (50-2000) and high molecular weight urethane (meth)acrylate (2000-20,000) generally ranges from 1:100 to 100:1, preferably from 1:10 to 10:1. All individual values and subranges from 0.1:1 to 100:1 are included herein and disclosed herein; for example, the weight ratio of low molecular weight urethane (meth)acrylate and high molecular weight urethane (meth)acrylate can be from 0.1:10 to 25:1; or in the alternative, the weight ratio of low molecular weight urethane (meth)acrylate and high molecular weight urethane (meth)acrylate can be from 1:10 to 10:1. 
     The curable resin composition may comprise 1 to 99 percent by weight of urethane (meth)acrylate, preferably 10 to 90 percent by weight of urethane (meth)acrylate. All individual values and subranges from 1 to 99 weight percent are included herein and disclosed herein; for example, the weight percent of urethane (meth)acrylate can be from a lower limit of 1, 5, 10, 15, 25, 30, 35, 40, 50, or 55 weight percent to an upper limit of 60, 65, 70, 75, 80, 85, 90, or 99 weight percent. For example, the curable resin composition may comprise 1 to 99 percent by weight of urethane (meth)acrylate; or in the alternative, the curable resin composition may comprise 30 to 80 percent by weight of urethane (meth)acrylate; or in the alternative, the curable resin composition may comprise 40 to 65 percent by weight of urethane (meth)acrylate. 
     The reactive diluent is a liquid reaction medium containing at least one ethylenic double bond. The reactive diluent is curable by polymerization in the presence of a free radical catalyst. In an embodiment, the reactive diluent does not contain styrene. The scope of this invention includes the use of reactive diluents that are glycols and/or polyols with terminal acrylate or methacrylate groups, thus carrying two or more ethylenic double bonds: such ingredients comprise at least 20% by weight of the total reactive diluent composition. Examples of glycols and/or polyols with terminal acrylate or methacrylate groups include 1,4-butanediol diacrylate (BDDA), 1,6-hexanediol diacrylate (HDDA), diethylene glycol diacrylate, 1,3-butylene glycol diacrylate, neopentyl glycol diacrylate, cyclohexane dimethanol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, ethoxylated or propoxylated bisphenol A diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, ethoxylated or propoxylated glycerine triacrylate, poly tetramethylene glycol diacrylate, ethoxylated or propoxylated trimethylolpropane triacrylate, ethoxylated or propoxylated pentaerythritol tetraacrylate, their corresponding methacrylate analogues, and derivatives and mixtures thereof. As mentioned previously, at least 20 percent by weight (based on the total amount) of the reactive diluent) is comprised of glycols and/or polyether polyols with terminal acrylate or methacrylate groups, namely molecules carrying at least 2 ethylenic double bonds. Any and all ranges greater than 20 percent are included herein and disclosed herein; for example, at least 50% of the reactive diluent is comprised of glycols and/or polyether polyols with terminal acrylate or methacrylate groups; or in the alternative, at least 80 of the reactive diluent is comprised of glycols and/or polyether polyols with terminal acrylate or methacrylate groups. 
     The remaining 80 percent or less by weight of the total reactive diluent composition includes mono-functional radical polymerizable monomers carrying one acrylate-reactive unsaturated functional group selected from the group of vinyl, allyl, cyclic allyl, cyclic vinyl, acrylic, functionalized and non-functionalized acrylic, acrylamides, acrylonitrile, and combinations thereof. 
     Specific examples include vinyl toluene, divinyl benzene, allylic derivatives such as diallyl phthalate, and (meth)acrylates such as methyl methacrylate, tert-butyl methacrylate, iso-butyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxyethyl acrylamide, hydroxypropyl acrylamide, and mixtures thereof. Also included, though less preferred, is styrene. 
     When used, the reactive diluent is preferably added in an amount of about 20 to 80% of the total weight of urethane (meth)acrylate+reactive diluent, and 30 to 70 weight % is preferable. Alternatively, a non-reactive diluent, as is known in the art, may also be used: the non-reactive diluent may for instance be a plasticizer such as phthalate, and is preferably added in an amount of from 5 to 10 parts by weight based on the total weight of the urethane acrylate composition. 
     The curable resin composition may comprise 1 to 99 percent by weight of reactive diluents. All individual values and subranges from 1 to 99 weight percent are included herein and disclosed herein; for example, the weight percent of reactive diluents can be from a lower limit of 1, 5, 10, 15, 25, 30, 35, 40, 50, or 55 weight percent to an upper limit of 60, 65, 70, 75, 80, 85, 90, or 99 weight percent. For example, the curable resin composition may comprise 1 to 99 percent by weight of reactive diluent; or in the alternative, the curable resin composition may comprise 10 to 90 percent by weight of reactive diluent; or in the alternative, the curable resin composition may comprise 35 to 60 percent by weight of reactive diluent. In an embodiment, the curable resin composition may comprise from 10 to 90 percent by weight of reactive diluents, the rest consisting mainly of the urethane (meth)acrylate. 
     Suitable free radical-generating catalysts include peroxide or azo type compounds. Examples of peroxide catalysts include organo peroxides and hydroperoxides such as tert-Butyl peroxyneodecanoate, benzoyl peroxide, dicumyl peroxide, methyl ethyl ketone peroxide, lauryl peroxide, cyclohexanone peroxide, t-butyl perbenzoate, t-butyl hydroperoxide, t-butylbenzene hydroperoxide, cumene hydroperoxide, t-butyl peroctoate, and the like. Examples of azo compounds include azobis-isobutyronitrile, 2-tbutylazo-2-cyano-4-methylpentane, and 4-t-butylazo-4-cyano-valeric acid. Without intending to be bound or limited by any particular theory, it is believed that the free radical-generating catalyst serves as a source of free radicals, which may be released upon heating or through an interaction with an accelerator, described in further detail below. Combinations of different peroxides may be advantageously used: for instance, peroxides which release free radicals upon heating to a certain temperature may be combined with peroxides that release radicals upon heating to a higher temperature. Examples of suitable commercial peroxides are available from Akzo Nobel under the trademark Trigonox and Perkadox. 
     The curable resin composition may comprise 0.001 to 10 percent by weight of a free radical-generating catalyst. All individual values and subranges from 0.001 to 10 weight percent are included herein and disclosed herein; for example, the weight percent of the free radical-generating catalyst can be from a lower limit of 0.001, 0.05, 0.1, or 0.5 weight percent to an upper limit of 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.4, 5, 6, 7, 8, 9, or 10 weight percent. For example, the curable resin composition may comprise 0.001 to 10 percent by weight of free radical-generating catalyst; or in the alternative, the curable resin composition may comprise 0.05 to 2 percent by weight of free radical-generating catalyst; or in the alternative, the curable resin composition may comprise 0.1 to 1 percent by weight of free radical-generating catalyst, or in the alternative, the curable resin composition may comprise from 0.1 to 5 percent by weight of free radical-generating catalyst. 
     The curable resin composition may include other ingredients, such as activators: these are metal carboxylates capable of increasing the effectiveness of the free radical-generating catalyst, consequently improving the degree of polymerization of the curable resin. Examples of activators include metal carboxylates, and cobalt salts such as cobalt naphtenate, and they may be used at a level of about 0.01 to 1% by weight of the curable resin composition. Accelerators represent another ingredient that can effectively increase the speed and completeness of the radical polymerization of the curable resin. The accelerator may be selected from the group of anilines, amines, amides, pyridines, and combinations thereof. Another example of an accelerator, not selected from the group of anilines, amines, amides, and pyridines is acetylacetone. In various embodiments, the accelerator, if included, includes a dimethyl toluidine or a dialkyl aniline. In various other embodiments, the accelerator, if included, includes N,N-dimethyl-p-toluidine, N,N-diethylaniline, N,N-dimethylaniline, and combinations thereof. If present, the accelerator is generally present in an amount of from 0.01 to 0.5 by weight of the curable resin composition. The curable resin composition may also include a gel time retarder. Addition of a gel time retarder decreases the gel time of the urethane acrylate composition. If included, the gel time retarder is generally selected from the group of diones, naphthenates, styrenes, and combinations thereof. In various embodiments, if included, the gel time retarder includes 2,4-pentanedione. In various other embodiments, if included, the gel time retarder is included in an amount of from 0.01 to 0.3 by weight of the resin system. 
     It should be noted that the free radical catalyst system, namely the peroxides or azo compounds plus the other ingredients directly associated with the speed of radical polymerization (activators, accelerators, retarders) are preferably added to the rest of the curable resin, comprising the urethane acrylate and the reactive diluent, preferably shortly before the curable resin undergoes polymerization: in fact the free radical-generating catalyst system may have a negative impact on the storage stability of the curable resin. 
     Other ingredients may be also included in the curable resin, some of these preferably shortly before the curable resin undergoes polymerization, to avoid possible negative impact on the storage stability of the curable resin. Thus, internal mold release agents may be included to facilitate the release of the polymerized composite article from the mold in which it has been prepared: the amount may range from about 0.1% to about 5% by weight of the curable resin composition, and examples of suitable products are the internal mold release agents for composite applications available from Axel or from Wurtz. 
     Other types of ingredients that may be included in the curable resin are fillers, which may be used for a number of different reasons, such as to provide pigmentation, flame retardance, insulation, thixotropicity, aid with dimensional stability and physical properties, and reduced cost of the composite structure. Suitable fillers for the urethane acrylate layer include reactive and non-reactive conventional organic and inorganic fillers. Examples include, but are not limited to, inorganic fillers, such as calcium carbonate, silicate minerals, for example, both hollow and solid glass beads, phyllosilicates such as antigorite, serpentine, hornblends, amphiboles, chrysotile, and talc; metal oxides and hydroxides, such as aluminum oxides, aluminium hydroxide, titanium oxides and iron oxides; metal salts, such as chalk, barite and inorganic pigments, such as cadmium sulfide, zinc sulfide and glass, inter alia; kaolin (china clay), and aluminum silicate and co-precipitates of barium sulfate and aluminum silicate. Examples of suitable organic fillers include, but are not limited to, carbon black and melamine Thixotropic agents that are useful in this invention include fumed silica, organoclays, inorganic clays and precipitated silica. The amount of filler used for the purposes of this invention, will depend of the type of filler and reason for its presence in the system: thus, the thixotropic agents are often used at levels of up to about 2 percent by weight, while fillers that have a flame retardant action such as aluminium hydroxide, may be used in much larger amounts, in an amount that is in fact comparable or even larger than the amount of curable resin, comprising the urethane acrylate plus the reactive diluent. 
     Other additives having specific functions, as known in the industry, may also be included in the curable resin composition: examples include but are not limited to, air release agents, adhesion promoters, leveling agents, wetting agents, UV absorbers and light stabilizers. 
     In production of the curable resin composition, the method for producing such a composition includes blending or mixing urethane (meth)acrylates and reactive diluents first for long time storage (generally more than one month) and then adding the free radical-generating catalyst. 
     The polymerization and curing of the urethane acrylate resin is effected, using well-known procedures in the art, preferably in the presence of a polymerization catalyst. The resin composition may be thermally cured or light-cured. As for thermal curing, the curing temperature is dependent on the particular catalyst used. In one embodiment, the curable resin composition can be cured from 25° C. to 200° C., and in another embodiment, the curable resin composition can be cured from 70° C. to 150° C. As for light curing, the light source is dependent on the particular photoinitiator catalyst used. The light source can be visible light or UV light. 
     The curable resin composition contains urethane groups which provide toughness to the resin and improved adhesion to substrates and or fibers without dealing with isocyanate groups that are present in urethane resins. They provide the performance of high-end composite resins such as epoxy and polyurethanes with a reactivity that is commonly found in polyester and vinyl ester resins. These compositions can be used in pultrusion, filament winding, closed mold infusion, and cured-in-place pipe applications. They can be used with glass fibers as well as carbon fibers. A cured article prepared from the curable resin composition can be used to produce composites, coatings, adhesives, inks, encapsulations, or castings. The composites can be used in applications such as, for example, wind turbines, boat hulls, truck bed covers, automobile trim and exterior panels, pipe, tanks, window liners, seawalls, composite ladders and the like. 
     EXAMPLES 
     The present invention will now be explained in further detail by showing Inventive Examples, and Comparative Examples, but the scope of the present invention is not, of course, limited to these Examples. 
     Materials 
     Isonate OP50 is a 50:50 weight % mixture of 4,4′-MDI and 2,4′-MDI available from The Dow Chemical Company (TDCC) 
     Voranol P1010 is a polypropylene oxide diol with molecular weight about 1000 from TDCC 
     Voranol P2000 is a polypropylene oxide diol with molecular weight about 2000 from TDCC 
     TPG is tri propylene glycol, from TDCC 
     Dabco T12 is dibutyl tin dilaurate, a urethane catalyst available from Air Products and Chemicals 
     ROCRYL™ 400 Hydroxyethyl methacrylate (HEMA) available from TDCC 
     Ethylene glycol dimethacrylate and DEG dimethacrylate, available from Evonik 
     Trimethylolpropane triacrylate available from Sartomer under the name SR351 
     Tri ethylene glycol dimethacrylate available from BASF 
     PEG dimethacrylate MW 550 available from Sigma Aldrich 
     PPG dimethacrylate MW 550 available from Sigma Aldrich 
     Trigonox 23 (tert-Butyl peroxyneodecanoate) is obtained from AkzoNobel 
     Procedures 
     Plaque Preparation of Urethane Acrylate 
     The mold was made from “U”-shaped, 4 mm thick aluminum spacers positioned between two thick heavy metal plates. The mold was coated with a proprietary release agent. A rubber tubing was used for gasket material following the inside dimensions of the spacer. Once assembled, the mold was clamped together with multiple screws. The open end of the “U”-shaped spacer faced upward. The internal volume of the mold was 10 cm×20 cm×0.4 cm. After the mold was filled with the curable resin, it was placed in an oven for thermal curing: the plaque was cured at 100° C. for 1-2 hours. 
     Dynamic Mechanical Thermal Analysis 
     Glass transition temperature (Tg) was determined by Dynamic Mechanical Thermal Analysis (DMTA), using a TA instrument Rheometer. Rectangular samples were placed in solid state fixtures and subjected to an oscillating torsional load. The samples were thermally ramped from about −60° C. to about 200° C. at a rate of 3° C./minute and 1 Hertz (Hz) frequency. 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE I 
               
               
                   
               
               
                 Run 
                 A 
                 B 
                 C 
                 D 
                 E 
                 F 
                 G 
                 H 
                 I 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Urethane acrylate 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Isonate OP 50 
                 19 
                 26.25 
                 32 
                   
                   
                   
                   
                   
                   
               
               
                 Voranol P1010 
                 51 
                 51 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Voranol P2000 
                   
                   
                 18 
                   
                   
                   
                   
                   
                   
               
               
                 TPG 
                   
                   
                 9.33 
                   
                   
                   
                   
                   
                   
               
               
                 Catalyst (Dabco T12)  
                 0.02 
                 0.02 
                 0.01 
                   
                   
                   
                   
                   
                   
               
               
                 Hydroxy ethyl meta acrylate 
                 14.3 
                 14.3 
                 18.2 
                   
                   
                   
                   
                   
                   
               
               
                 Reactive diluent 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Hydroxy ethyl meta acrylate 
                 70 
                 10 
                 15 
                 20 
                   
                   
                 35 
                 25 
                 25 
               
               
                 Triethylene glycol Dimethacrylate 
                   
                 60 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Diethylene glycol dimethacrylate 
                   
                   
                 44 
                 22 
                 22 
                 22 
                   
                   
                   
               
               
                 Ethylene glycol dimethacrylate 
                   
                   
                   
                 47.5 
                 47.5 
                   
                   
                   
                   
               
               
                 PEG dimethacrylate MW 550 
                   
                   
                   
                   
                   
                   
                   
                   
                 65 
               
               
                 SR351 (Trimetilolpropane  
                   
                   
                   
                   
                   
                   
                   
                 10 
                 10 
               
               
                 triacrylate) 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 PPG dimethacrylate MW 550 
                   
                   
                   
                 20 
                 40 
                 87.5 
                 65 
                 65 
                   
               
               
                 Percent reactive diluent 
                 45.36 
                 43.32 
                 43.21  
                 100 
                 100 
                 100 
                 100 
                 100 
                 100 
               
               
                 Physical mechanical Tests (Norm) 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Tensile Str. - Mpa (ISO 527-2) 
                 25 
                 18 
                 35.5 
                 NA 
                 NA 
                 NA 
                 12.5  
                 10.8 
                 13.4 
               
               
                 Tensile Mod. - Mpa (ISO 527-2) 
                 640 
                 540 
                 1902 
                 NA 
                 NA 
                 NA 
                 400 
                 474 
                 607 
               
               
                 DMTA 3-point bending-Tg ° C.  
                 107 
                 110 
                 134 
                 NA 
                 NA 
                 NA 
                 52 
                 NA 
                 65 
               
               
                 % weight increase after 3 days at  
                 4% 
                 1% 
                 1% 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
                 NA 
               
               
                 70° C., 90% relative humidity,  
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 followed by 1 day conditioning at  
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 room temp and 50% humidity 
               
               
                   
               
            
           
         
       
     
     Curable Resins Preparation 
     The formulations of Table I, above, were prepared according to a multi step process, consisting of the reaction between the isocyanate and the polyol and the capping agent (in the experiments, HEMA) to obtain the urethane acrylate that was further combined with various reactive diluents as described in Table I. A catalyst (Dabco T12) was also used to accelerate the reaction between isocyanate and hydroxyl groups. The various curable resins were stabilized by including also about 0.05-0.1% MEHQ (Mono Methyl Ether of Hydroquinone), which was in certain cases already included in some of the ingredients: for example, the Rocryl 400 used in these experiments was already stabilized with about 200 ppm MEHQ. 
     All formulations were cured by adding about 1 Trigonox 23, mixing, degassing, pouring the liquid resin in the mold, and then placing the mold in the oven. 
     Formulations A, B, C, contain the same amount of reactive diluent, about 43%, except recipe A, which contains slightly more. Formulation A represents the comparative formulation, that uses HEMA as reactive diluent. Formulations B and C represent inventive examples. The physical mechanical testing results show that formulation A matches the inventive examples on key performance aspects such as Tg or modulus. However formulation A misses an important performance aspect, the water pick up test, showing that formulation A has a rather high water pick up value. 
     Formulation C shows how the inventive technology can result in an even more attractive combination of properties when the urethane acrylate is based on a combination of long chain and short chain polyether polyol. 
     Formulations D to I are only based on combinations of reactive diluents, without the urethane acrylate component. Some of these recipes result in a polymer that is too brittle and that therefore cannot be tested while others result in a polymer with a low level of performance, such as low Tg or low modulus. This demonstrates that while combinations of urethane acrylates and reactive diluents can provide a good overall balance of properties, using only the reactive diluents cannot deliver the desired level of polymer performance. 
     Table II reports some additional formulations, together with some test results, in particular the Tg and the water pick up. While the Tg values are similar for the three formulations, the comparative recipe 1a is showing relatively high values of water pick up, due to the large amount of hydroxyacrylate diluent in formulation. On the other hand, the inventive recipes 2a and 3a, show much better performance in terms of water pick up. 
     
       
         
           
               
               
               
               
             
               
                 TABLE II 
               
               
                   
               
               
                 Run 
                 1a 
                 2a 
                 3a 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Urethane acrylate 
                   
                   
                   
               
               
                 Isonate OP 50 
                 26.25 
                 26.25 
                 26.25 
               
               
                 Voranol P1010 
                 51.00 
                 51.00 
                 51.00 
               
               
                 Catalisi (Dabco T12) 
                 0.02 
                 0.02 
                 0.02 
               
               
                 Hydroxy ethyl meta acrylate 
                 14.30 
                 14.30 
                 14.30 
               
               
                 Reactive diluent 
               
               
                 Hydroxy ethyl meta acrylate 
                 70.00 
                 20.00 
                 5.00 
               
               
                 Ethylene glycol dimethacrylate 
                   
                 20.00 
                 25.00 
               
               
                 Tripropylene glycol diacrylate 
                   
                 30.00 
                 40.00 
               
               
                 Percent reactive diluent 
                 43.32 
                 43.32 
                 43.32 
               
               
                 Physical mechanical Tests (Norm) 
               
               
                 DMTA 3-point bending - Tg ° C. 
                 105 
                 100 
                 95 
               
               
                 % weight increase after 3 days at 70° C., 
                 5.0 
                 2.0 
                 1.5 
               
               
                 90% relative humidity, followed 
               
               
                 by 1 day conditioning at room temp 
               
               
                 and 50% humidity