Abstract:
A composition for preparing polymeric articles comprising: (a) an acrylic polymerizable component such as monomeric and polymeric aliphatic acrylate and methacrylate esters having a Brookfield viscosity of about 0.1-400 poise and about 5-60% by weight of solids; (b) copper and tin polymerization promoters providing in the composition about 0.05-4 ppm of Cu +2  and about 10-300 ppm of Sn +2  ; (c) about 5×10 -6  to 1×10 -4  mole/gm of the composition of a primary mercaptan chain transfer agent; and (d) sufficient peroxyester initiator to provide about 0.02-0.3% by weight of active oxygen in the composition. The composition is highly efficient at room temperature and provides excellent optical quality polymers while permitting a wide choice of peroxyesters as the initiator.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the polymerization and curing of acrylic monomers and polymers. More particularly, it relates to the rapid production of acrylic polymers, usually from an acrylic containing syrup, with peroxyester initiators in the presence of a limited group of promoters and chain transfer agents. 
     2. Description of the Prior Art 
     U.S. Pat. No. 4,188,315 to Dudinyak is directed to the polymerization of acrylate syrups utilizing formulations which are suitable for room temperature applications, but where good optical properties are not required in the resulting acrylic polymers. Rapid room temperature cures are obtained with the use of metal salts of hemiperesters of maleic acid as the polymerization initiator in the presence of a salt of an oxo acid of sulfur activator. 
     The article by V. R. Kamath, et al., &#34;Novel Room Temperature Cure System&#34;, presented at the 37th Annual Conference, Reinforced Plastics/Composites Institute, The Society of the Plastics Industry, Inc. Session 12-B (Jan. 11-15, 1982), describes a peroxyester initiated room temperature formulation for polyester resins. The system described is not suitable for acrylic systems. 
     U.S. Pat. No. 3,487,062 to Bodycot describes a system for acrylic polymerization useful at room temperature and providing good optical properties in the acrylic end product. The peroxyester initiator is limited to t-butyl peroxy maleate in combination with stannous chloride, tertiary amine hydrochloride and a mercaptan which are also used in the system. 
     U.S. Pat. No. 4,189,451 to Dudinyak provides an acrylic polymer at room temperature with a system similar to that of Dudinyak &#39;315. 
     U.S. Pat. No. 3,775,364 to Duggins describes the polymerization of an acrylic system again utilizing a mercaptan chain transfer agent and a metal salt of a hemiperester such as monotertiary butyl peroxy maleate as a polymerization initiator. 
     SUMMARY OF THE INVENTION 
     The present invention describes a composition for preparing polymeric articles suitable for use under ambient conditions if desired and which includes four essential components: (a) a polymerizable component selected from monomeric and polymeric aliphatic acrylics having a Brookfield viscosity of about 0.1-400 poise and about 5-60% by weight of solids; (b) copper and tin polymerization promoters providing in the composition about 0.05-4 ppm of Cu +2  and about 10-300 ppm of Sn +2  ; (c) about 5×10 -6  to 1×10 -4  mole/gm of the composition of a primary mercaptan chain transfer agent; and (d) sufficient peroxyester initiator to provide about 0.02-0.3% by weight of active oxygen in the composition. 
     Where the composition contains all of the above components and the formulation is mixed and cured, an acrylic polymer product of excellent optical quality is obtained at room temperature. The formulation is very efficient in that peak temperatures are reached in a brief period of time, for example on the order of thirty minutes. Exotherms are sufficiently high in the system, resulting in low monomer residue. 
     A major advantage of the new composition and method is the wide choice of peroxyester initiators permitted. For example, the present compositions may utilize t-buty peroxy benzoate, which has significant advantages from the standpoint of cost as well as stability and relative ease of storage and handling. Also, most of these peroxyesters are available commercially as pure products. 
     DESCRIPTION OF THE INVENTION 
     The invention is broadly applicable to the formation of acrylic resins from acrylic monomers and polymers in all of their known variations. Thus, the invention is applicable to monomeric and polymeric aliphatic acrylate and methacrylate esters, both linear and cyclic. The acrylic monomers also include cyanoacrylates as well as the acrylic acids from which the esters are formed. 
     Usually the starting material to be polymerized will be provided in the form of a &#34;syrup&#34; as that term is understood in this art. A syrup is formed from an acrylic polymer in a liquid acrylic monomer. In general, some polymer content is desired in the syrup so that heat will be retained during the course of the polymerization reaction and thereby accelerate the curing time. The higher viscosity syrups, therefore, provide a more efficient system. The present invention does, however, contemplate the polymerization of acrylic monomers when the monomer is coreacted with ethylene glycol dimethacrylate without the presence of any polymer. 
     The compositions and methods of this invention are useful for coreacting a curable resin other than an acrylate with the acrylates. Any suitable curable coreactant may be used. In the preferred embodiment, a polyester containing coreactive ethylenic unsaturation is contemplated for coreaction with the selected acrylates. 
     As indicated, the present invention is advantageous in that it permits employing any one of a broad range of polyester initiators. In the preferred embodiment, the peroxyester is selected from: ##STR1## where R 1  contains up to 13 carbon atoms and is phenyl, alkyl, alkenyl or carboxylic substituted cycloalkyl; 
     R 2  is t-alkyl of 4-8 carbon atoms; and 
     R 3  contains up to 13 carbon atoms and is alkyl, alkenyl or carboxylic substituted cycloalkyl. The alkyl and alkenyl groups may be straight or branched chain. 
     The amounts of the composition to be polymerized are important. The following table summarizes the useful amounts of each component: 
     
         ______________________________________Ingredient     Useful Range   Optimum Level______________________________________MMA* Syrup     0.1-400 poise  &gt;10 poise     5-60% solids   &gt;10% solidsCu.sup.+2 0.05-4 ppm     1-2 ppmSn.sup.+2 10-300 ppm     100-200 ppmmercaptan 5 × 10.sup.-6 -1 × 10.sup.-4                    2.5 × 10.sup.-5 -5 × 10.sup.-5     mole/gm        mole/gmperoxyester     0.02-0.3 A.O.**                    &gt;0.07 A.O.______________________________________ *MMA = methyl methacrylate **A.O. = active oxygen 
    
     With respect to the mercaptan used in the present invention, the only requirement is that it be a primary mercaptan. Particularly satisfactory results have been obtained with laurylmercaptan but any of the other mercaptans described in prior literature could also be utilized. The following work will illustrate the invention. 
    
    
     EXPERIMENTAL 
     Polymerization Runs 
     All runs were made in 30 ml glass vials (3×6.3 cm) with polyethylene snap caps, and monitored with a type J thermocouple on line to a Rustrak (model 2155A) X-Y potentiometer. A sample size of 10 gms (syrup) was used for all samples and the ingredients were mixed in the vials with a stainless steel spatula. 
     Promoter Formulations 
     The 0.005% Cu +2  and 0.53% Sn +2  solution was made as follows: 
     0.75 gms aliquot of 33% SnCl 2 .2H 2  O in methanol was added to 24 gms of MMA along with 0.014 gms (1 drop) of copper naphthenate (8%). This mixture was then mixed and stored in an amber bottle. The 0.009% Cu +2  and 1.05% Sn +2  solution was made up as described above except 0.03 gms (2 drops) of 8% copper naphthenate and 1.5 gms of 33% SnCl 2 .2H 2  O were added to 24 gms of MMA. The other metal solutions were made up in MMA except the iron solutions, which were made up in methanol/MMA (1/5). 
     Acrylic Syrup 
     A 3 kg bottle of MMA (Baker) that was autolytically polymerized to 11.5% solids and 50 poise was used for most runs. Other syrups were made from a 40% solids (Elvacite® acrylic resin) in MMA (Baker). All viscosities of resins were determined on a Brookfield Synchro-Lectric viscometer (model HAF). 
     
                       TABLE 1______________________________________Peroxides Used in Room Temperature Experiments                         %Peroxides          Abbreviation                         Purity  MW______________________________________1.  di-2-ethylhexyl    2EHP       96.0  346.3    peroxydicarbonate2.  t-butyl perneodecanoate                  TBPN       75.9  244.43.  t-butylperpivalate TBPP       77.0  174.24.  diacetyl peroxide  --         18.0  118.15.  benzoyl peroxide   BPO        98.0  242.26.  t-butylperoxy 2-ethyl hexanoate                  TBPEH      96.4  216.37.  t-butylperoxy 2-ethyl hexyl                  TBPEHC     78.5  246.2    carbonate8.  methylethyl ketone peroxide                  MEKP        9.0%                             A.O.9.  cumene hydroperoxide                  CHP        85.0  146.110. 1,1-bis(t-butylperoxy)                  11TBPH     98.0  260.4    cyclohexane11. 2,5-dimethyl-2,5-bis(t-butyl                  25TBH      98.0  290.4    peroxy) hexane12. t-butyl peroxybenzoate                  TBPB       98.0  194.213. 2,5-dimethyl-2,5-bis(2-ethyl                  25TBPEHH   92.0  430.6    hexanoyl peroxy)hexane14. 2,5-dimethyl-2,5-bis(benzoyl                  25TBPBH    78.8  386.4    peroxy)hexane15. t-butylperoxy crotonate                  TBPC       62.3  158.216. bis-(t-butylperoxy) thio-                  TBPTP      97.0  322.3    dipropionate17. t-amyl peroxy 2-ethylhexanoate                  TAPEH      76.4  230.318. t-butyl peroxytetrahydro                  TBPTA      91.3  242.3    phthalic acid______________________________________ 
    
     
                                           TABLE 2__________________________________________________________________________Peroxides as Room Temperature InitiatorsFormulation, parts by weightMMA syrup (11.5% solids, 50 poise)                         1000.005% Cu.sup.+2 (from 8% Cu.Naphthenate in MMA)                         20.53% Sn.sup.+2 (1% SnCl.sub.2.2H.sub.2 O in MMA)                         2Laurylmercaptan               1Peroxide (used at purity of Table 1)                         2                           Time (hrs)                                  Peak                           to Peak                                  ExothermPeroxide          % A.O.                  Type     Exotherm                                  Temp. (°C.)__________________________________________________________________________  diacetyl peroxide             .048 diacyl peroxide                           gelled                           overnight  benzoyl peroxide             .132 aromatic diacyl                           gelled                  peroxide overnight  methylethyl ketone             .180 MEK peroxide                           gelled  peroxide                      w/in 48 hrs.  cumene hydroperoxide             .186 hydroperoxide                           gelled                           overnight  1,1-bis(t-butyl .241 peroxyketal                           gelled  peroxy) cyclohexane           w/in 48 hrs.  2,5-dimethyl-2,5-bis             .216 dialkyl peroxide                           gelled  (t-butylperoxy)hexane         w/in 48 hrs.  di-2-ethylhexyl .042 peroxy   gelled  peroxydicarbonate    dicarbonate                           overnight  t-butylperoxy 2-ethyl             .130 percarbonic                           0.60   110  hexyl carbonate      ester  t-butylperoxy 2-ethyl             .148 peroxy ester                           0.60   120  hexanoate10.  t-butylperoxy benzoate             .161 peroxy ester                           0.40   110  t-butylperoxy   .099 peroxy ester                           0.60   102  neodecanoate  t-butylperoxy pivalate             .142 peroxy ester                           0.35   120  2,5-dimethyl-2,5-bis             .133 diperoxyester                           0.50   105  (2-ethylhexanoyl peroxy)hexane  2,5-dimethyl-2,5-bis             .127 diperoxyester                           0.50   105  (benzoyl peroxy)hexane  t-butylperoxy   .126 peroxyester                           0.50   130  crotonate  bis-(t-butylperoxy)             .194 diperoxyester                           2.25    50  thiodipropionate*  t-amyl peroxy   .106 peroxyester                           0.30   130  2-ethylhexanoate  t-butyl peroxytetra-             .121 peroxyester acid                           0.70    80  hydrophthalic acid__________________________________________________________________________ *This system appears to require laurylmercaptan. 
    
     
                       TABLE 3______________________________________Effect of Peroxyester Concentrationon Cure RateFormulation, parts by weightMMA syrup (11.5% solids, 50 poise)                     1000.009% Cu.sup.+2 (from 8% Cu.Naphthenate in MMA)                     11.05% Sn.sup.+2 (2% SnCl.sub.2.2H.sub.2 O in MMA)                     1Laurylmercaptan           1                            Time  Peak                   (hrs) to Exo-            Parts           Peak  therm            by              Exo-  Temp.Peroxide         wt.    % A.O.   therm (°C.)______________________________________1.a. t-butyl peroxybenzoate                0      0      none  noneb.   t-butylperoxy 2-ethyl-                0      0      none  nonehexanoate2.a. t-butyl peroxybenzoate                0.5    .040   2.5    65b.   t-butylperoxy 2-ethyl-                0.5    .036   3.6    50hexanoate3.a. t-butyl peroxybenzoate                1.0    .081   1.0   100b.   t-butylperoxy 2-ethyl-                1.0    .071   1.0   105hexanoate4.a. t-butyl peroxybenzoate                2.0    .161   0.6   120b.   t-butylperoxy 2-ethyl-                2.0    .143   0.4   110hexanoate5.a. t-butyl peroxybenzoate                3.0    .242    .7    90b.   t-butylperoxy 2-ethyl-                3.0    .214    .7   110hexanoate______________________________________ 
    
     
                                           TABLE 4__________________________________________________________________________Metal Ions as PromotersFormulation, parts by weightMMA syrup (11.5% solids, 50 poise)                    1001.0% SnCl.sub.2.2H.sub.2 O in MMA (0.53% Sn.sup.+2)                    1Laurylmercaptan          0.5ethylene glycol dimethacrylate                    1t-butyl peroxybenzoate   2                Metal                Ion, Time (hrs)                           Peak            Parts                Approx.                     to Peak                           Exotherm% Metal Ion  Type      by wt.                ppm  Exotherm                           Temp. (°C.)__________________________________________________________________________0.005% Cu.sup.+2  8% Cu Naphthenate            0        none  none0.005% Cu.sup.+2  8% Cu Naphthenate            0.1 0.05 4.3   400.005% Cu.sup.+2  8% Cu Naphthenate            0.5 0.25 2.5   530.005% Cu.sup.+2  8% Cu Naphthenate            1.0 0.5  2.8   580.005% Cu.sup.+2  8% Cu Naphthenate            2.0 1    1.6   980.005% Cu.sup.+2  8% Cu Naphthenate            3.0 1.5  1.8   980.005% Cu.sup.+2  8% Cu Naphthenate            4.0 2.0  1.7   1100.005% Cu.sup.+2  Cu(acac)* 1.0 0.5  2.5   650.005% Co.sup.+2  Co(acac)  1.0 0.5  none  none0.006% Mn.sup.+2  Mn(acac)  1.0 0.6  none  none0.003% V.sup.+2  V(acac)   1.0 0.3  none  none0.005% Ce.sup.+3  Ce(acac)  1.0 0.5  none  none0.005% Fe.sup.+3  Fe Cl.sub.3.6H.sub.2 O            1.0 0.5  gelled                     overnight0.005% Fe.sup.+3  Fe Cl.sub.3            2.0 1    gelled                     overnight0.005% Fe.sup.+2  Fe Cl.sub.2.4H.sub.2 O            2.0 1    gelled                     overnight__________________________________________________________________________ *acac = acetylacetonate 
    
     
                       TABLE 5______________________________________Sn.sup.+2 as a PromoterFormulation, parts by weightMMA Syrup (11.5% solids, 50 poise)                     1000.005% Cu.sup.+2 (from 8% Cu.Naphthenate in MMA)                     1Laurylmercaptan           1ethylene glycol dimethacrylate                     1t-butyl peroxybenzoate    21% SnCl.sub.2.2H.sub.2 O in MMA (0.53% Sn.sup.+2)Parts                Time (hrs)by Weight Conc. Sn.sup.+2                to Peak   Peak Exotherm0.53% Sn.sup.+2     Approx. ppm                Exotherm  Temperature (°C.)______________________________________1.  0          0         none    none2.  0.5        25        3.0     353.  1.0        50        2.2     704.  2.0       100        1.0     955.  3.0       150         .8     956.  4.0       200         .9     707.  6.0       300         .9     60______________________________________ 
    
     
                       TABLE 6______________________________________Mercaptan as Promoter/Chain Transfer AgentFormulation, parts by weightMMA syrup (11.5% solids, 50 poise)                     1000.005% Cu.sup.+2 (from 8% Cu.Naphthenate in MMA)                     11.0% SnCl.sub.2.2H.sub.2 O in MMA (0.53% Sn.sup.+2)                     1t-butyl peroxybenzoate    2ethylene glycol dimethacrylate                     1                              Peak                    Time      Exotherm            Parts   (hrs.) to Temp.Mercaptan        by wt.  Exotherm  (°C.)______________________________________Laurylmercaptan  0       none      noneLaurylmercaptan  0.1     2.4       50Laurylmercaptan  0.5     2.8       58Laurylmercaptan  1.0     2.2       70Laurylmercaptan  2.0     2.0       50Lauryl-3-mercapto propionate            0.5     2.0       702-mercapto ethanol            0.5     2.5       552-mercapto benzothiozole            0.6     none      none______________________________________ 
    
     
                       TABLE 7______________________________________Effect of Syrup Viscosity and % Solidson the Cure RateFormulation, parts by weightMMA syrup                 1000.009% Cu.sup.+2 (from 8% Cu.Naphthenate in MMA)                     11.05% Sn.sup.+2 (2% SnCl.sub.2.2H.sub.2 O in MMA)                     1Laurylmercaptan           1Syrup              Time (hrs.) Peak Exotherm% Solids  Viscosity              Peak Exotherm                          Temperature (°C.)______________________________________1.   40*      300 poise                  0.3       1002.   30*      9.2 poise                  0.5       1003.   20*      0.13 poise                  1.8        704.   11.5     50 poise 0.6       120______________________________________ *DuPont, Elvacite ® acrylic resin (grade 2010) 
    
     
                       TABLE 8______________________________________Effect of Different Monomerson the Cure RateFormulation, parts by weightMonomer or syrup          1000.009% Cu.sup.+2 (from 8% Cu.Naphthanate in MMA)                     11.05% Sn.sup.+2 (2% SnCl.sub.2.2H.sub.2 O in MMA)                     1Laurylmercaptan           1t-butyl peroxybenzoate    2                        Time    Peak                        (hrs) to                                Exo-                        Peak    therm              % Solids  Exo-    Temp.Monomer            as PMMA*  therm   (°C.)______________________________________1.  ethylacrylate      30        0.06  2002.  ethylacrylate      0         0.10  2003.  ethylene glycol    0         0.05  200    dimethacrylate4.  allyl diglycol carbonate                  0         no rxn.                                  --5.  allyl diglycol carbonate/                  0         0.06  200    ethylene glycol dimethacrylate    (50:50)6.  allyl diglycol carbonate/                  0         0.3**  38    ethylene glycol dimethacrylate    (90:10)7.  styrene            0         no rxn.                                  --8.  MMA/ethylene glycol                  0         1.25  130    dimethacrylate (90:10)9.  styrene/ethylene glycol                  0         no rxn.                                  --    dimethacrylate (80:20)10. methacrylic acid   0         0.05  20011. general purpose orthophthalic                  NA        0.08  150    unsaturated polyester resin/    ethylene glycol dimethacrylate    (85:15)12. acrylonitrile      0         0.08  12013. MMA/acrylonitrile (75/25)                  12        0.10  100______________________________________ *DuPont, Elvacite ® acrylic resin (grade 2010) **Resulted in a hazy gell which became clear after post curing.