CA1082164A - Maleic acid hemi-perester initiator system for the polymerization of ethylenically unsaturated monomers - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
In the use of certain metal salts of the hemi-perester of maleic acid as catalysts for the polymerization and curing of ethylenically unsaturated monomers and of methyl methacrylate-containing syrups the addition of an activator such as sodium bisulfite provides a substantial reduction in the curing time. The process is relatively insensitive to the amount of filler used. The salts of maleic hemi-peresters, in combination with the activators, are also useful for polymerizing ethylenically unsaturated monomers.

Description

108Z~64 BACKGROU~D OF THE INVENTION
Field of Invention This invention is related to the polymerization and curing of ethylenically unsatur~ted monomers and of methyl methacrylate-containing syrups. More particularly, it is related to the improved, more rapid production of articles of polymeric methyl methacrylate, e.g., methacrylate homo-polymer and copolymers of methyl methacrylate with alpha, beta-ethylenically unsaturated compounds such as vinyl acetate, 1 styrene, alkyl acrylates, alkyl methacrylates, and the like.
Description of Prior Art In the production of articles of polymeric methyl methacrylate and, more specifically, in the curing or poly-merization of the monomers involved for producing the ; polymeric articles, the most important step is the curing of the methyl methacrylate-containing syrup. For this step it is necessary to use a catalyst or, as it is sometimes called, an initiator. As catalysts, the prior art has suggested the use of peroxy compounds such as lauroyl per-oxide and benzoyl peroxide. Recently, the use of the hemi-perester of maleic acid has been disclosed as a useful catalyst for the polymerization and curing of methyl meth-acrylate-containing syrups. However, it is known that, al-though this catalyst is quite effective, it operates rather slowly. Thus, curing times of over four hours are not uncommon in the preparation of articles of the methyl methacrylate homopolymer when curing at or near room temperature. -The rate of curing of such methyl methacrylate- -containing syrups has been increased through the use of

- 2 -~ .

metal salts of the hemi-peresters of maleic acid as dis-closed in United States Patent 3,362,942, issued January 9, 1968 to George E. Munn. However, even this catalyst re-quires 1-2 hours to complete the polymerization and curing.
When a mercaptan activator is included in the syrup, the curing rate can be further increased but the curing step : still requires 15-20 minutes for thick sheets and the activator's high cost is disadvantageous.
SUMMARY OF THE INVENTION

According to the present invention there is pro-vided an improved process and composition for preparing a methyl methacrylate polymer selected from the group con-sisting of methyl methacrylate homopolymer and copolymers of methyl methacrylate with a,~-ethylenically unsaturated compounds which includes curing a syrup containing 10-40%
by weight of methyl methacrylate polymer, having an inherent viscosity of 0.25-1.0, in monomeric methyl methacrylate, in the presence of a small amount of a metal salt of a hemi-perester of maleic acid having the formula ? r 0 H-C-C-O-: .. Me . . H-C-C-O-O-R
~ ~x ". ,.

wherein ~-Me is a metal selected from the group consisting of Group IA metals, Group IIA metals, zinc, lead, cobalt, nickel, manganese and copper;
,

- 3 -.

X i5 an integer havin~ a value of from 1 to the valence of the metal; and R is a saturated tertiary alkyl radical, wherein the improvement comprises the presence of a salt of an oxo acid of sulfur activator selected from the group consisting of bisulfite, metabisulfite, and thiosulfate salts or of the free acid and of a polar liquid~ There is further provided an improved process and composition for pre-paring polymers from syrups wherein the polymer dissolved 1~ in the monomer can be any conventional polymer including addition polymers, condensation polymers such as polyesters, and the like and the monomer or mixtures of monomers used to dissolve the polymer can be any monomer(s) in which the polymer is soluble. There is also provided an improved process and composition for polymerizing any ethylenically unsaturated monomer or mixtures of such monomers capable of copolymerization via free radical initiation. Optionally, inert additives, pigments, and fillers can also be present in the syrup.

DESCRIPTION OF THE INVENTION
The rate of curing of a syrup,containing 10-40% by weight of methyl methacrylate polymer having an .
inherent viscosity of 0.25-1.0 dissolved in monomeric methyl methacrylate in the presence of a small amount, usually 0.05-5 mole percent (preferably 0.1-1 mole percent) of a metal salt of a hemi-perester of maleic acid having the formula .
- , . :

~o8z~64 - o H-C-C-O-., Me H-C-C-O-O-R x O
wherein Me is a metal, preferably selected from the group consisting of Group I-A metals (sodium, potassium, lithium, etc.), Group II-A metals (calcium, magnesium, strontium, barium, etc.), zinc, lead, cobalt, nickel, manganese, and copper;
x is an integer that has a value of 1 or more up to and including the valence of the metal; and R is a saturated tertiary alkyl radical, pre-ferably tertiary butyl, can be improved by the inclusion of an activator which can increase the rate of decomposition of the hemi-perester ; and thereby the rate of polymerization and curing. Activa~
tors have been used previously to increase rates of poly-merization. Redox initiator systems are well known in emulsion polymerization wherein oxidation-reduction steps rapidly generate free radicals capable of initiating poly- -merization reactions of ~,~- ethylenically unsaturated monomers. Activation of polymerization reactions, initiated by peroxide initiators, with tertiary amines which induce the decomposition of peroxides into free radicals, ~are also well known to those skilled in the art. Use of mercaptans ~ .

321~4 to increase the rate of polymerlzation of hemi-per~ter initiated polymerization and curing of methyl methacrylate-containing syrups has been described in United States Patent 3,362,942.
The activator of this invention is a salt of an oxo acid of sulfur or the free acid. While the exact mechan-ism of activation ls not known, it is thought that those members of this group whose anions are capable of reactlng wlth the double bond of the maleic hemi-perester are effecti~e ln increasing the rate of polymerization and cure. Among uæeful salts are included bisulfltes, thiosulfates, and meta-bi~ulfites, the latter, when dissolved ln water, are known to generate blsulfites, thought to be the actlve species which co-react wlth the heml-peresters of maleic acid. The activ~tor ls present in a weight ratio to the hemi-perester of maleic acid of from approxlmately 1:7 to 4:1, preferably from 1:7 to 1:1, and even more preferably for optimum cure ~ -rates, in a ratio of approximately 1:3 to 1:1. Most pre-ferred are the weight ratio~ of from 1:1.2 to 1:1. m e activator can be added to the syrup in the form of an aqueou~
solutlon. Increased levels of water can further increase the rate of polymerization and cure in some instances.
m e st~rting 8yrUp or polymer-in-monomer solution can be prepared by any of the methods de~cribed in British Patent No. 870,191 or U.S. Patent No. 3,154,600. Specifically, the syrup can be made by heating a small amount of a polymerization initiator in a solution in the methacrylic ester, in the optional presence of a chain transfer f ~

agent,at a suitable pressure and temperature. Heating is continued until the solution reaches a predetermined viscosity. Thereafter, the hot solution is quenched by the addition of cold monomer containing a polymerization inhibitor. More specifically, a syrup having a viscosity of 0.5-50 poises at 25C can be produced from methyl meth-acrylate by heating the monomeric methyl methacrylate in a jacketed kettle at a temperature of 50-150C under refluxing conditions. Atmospheric pressure is used and the refluxing lC material is stirred. Heating is conducted in the presence of a very small amount of initiator When a bulk viscosity in the range of 0.5-50 poises and an inherent vis-cosity of 0.25-1.0 is attained and the initiator content has been reduced substantially to zero, i.e., below 20 parts per million, the polymerization is stopped by cooling in any suitable manner. One method of cooling in-volves adding 1-10~ by weight of cold methyl methacrylate containing sufficient hydroquinone or other polymerization inhibitor to inhibit further polymerization of the methyl methacrylate.
For the purpose of the present invention, a final solution contains 10~0~ by weight of the methyl methacrylate polymer dissolved in the methyl methacrylate monomer. The polymer has an inherent viscosity of 0.25-1.0 determined at 20~C using a solution of 0.50 gram of the polymer per l00 milliliters of chloroform in accordance with the method described in F. W. Billmeyer, Textbook of Polymer Chemistry, Interscience Publishing Inc. (1957), p. 128. As mentioned pre-viously, the polymer can also be a copolymer involving a major ~ortion of the methyl methacrylate monomer with such monomers as vinyl acetate, styrene, methyl acrylate, ethyl acrylate, ~ 082164 butyl acrylate, cyclohexyl acrylate~ 2-ethylhexyl acrylate, acrylonitrile, ethyl methacrylate, butyl methac~ylate, cyclo-hexyl methacrylate, 2-ethylhexyl methacrylate, methacrylo-nitri:!e, and the like~
Furthermore, the polymer c~n be any conventional polymer such as addition polymers and conden-sation polymers. Among the addition polymers are included acrylic and methacrylic homo- and copolymers with ethyleni-cally unsaturated monomers or mixtures of such monomers wherein methyl methacrylate is n,ot the major portion of the polymer;
homo- and copolymers of ethylenically unsaturated monomers wherein the unsaturated monomer is at least one of styrene, substituted styrenes such as alpha-methylstyrene, ring-sub-stituted styrenes, and the like; vinyl esters such as vinyl acetate, vinyl propionate, and the like; alpha-olefins such as ethylene, propylene, l-butene, l-octene, and the like, vinyl chloride, vinylidene chloride; conjugated dienes such as 1,3-butadiene; olefins containing fluorine such as vinyl fluoride, trichlorofluoroethylene, tetrafluoroethylene, hexafluoropropylene; vinyl and allyl ethers; and mono- and di- esters of alpha,beta-ethylenically unsaturated dicarboxylic acids such as mono- and dialkyl maleates ! mono- and dialkyl -fumarates, mono- and dialkyl itaconates, The choice of these monomers can be dictated by the intended end use of the polymers obtained in this invention as long as the monomer or monomers are capable of homo- and or copolymerization via free radical initiation.
Among the condensation polymers that can be utilized with the maleic acid perester-oxo acid of sulfur activator , system of this lnvention are polyesters and polyether~ w~ll kn~wn to tho~e ~killed in the art. m e dlols utilized in preparing the polye~ters can be allphatic or aromatic.
Suitable diol~ include: ethylene elYcol; propyleno-1,2-glycol;
propylene-1,3-glycol; butylene-1,3-dlol; butylene-1,4-dlol;
butylene-2,3-diol; neopentylglycol; 2,2-dlethylpropane-1,3-dlol; 2-methyl-2-propylpropane-1,3-diol; decamethylene glycol;
dodecamethylene glycol, monoethyl ether o~ glycerine;
alpha,beta-allyl ether~ o~ glycerol, and the llke.
m e d~carboxylic acids utllized in prep~ring the polyesters can be aliphatic, cycloaliphatlc, both ~aturated and unsaturated or aromatlc. Sultable dlcarboxyl~c acld~ lnclude:
malonic, succlnic, glutaric, adipic, pimel~C, ~uberlc, azelalc, sebacic, brassylic, malelc, ~umarlc, dilinolelc, dlphenic, tetrachlorophthalic, lsophthalic, terephthalic, orthophthallc acids, cyclohexane 1,2-dicarboxylic acld, p-phenglene diace~lc, naphthale~e dicarboxylic acid, dihydromuconlc acld, beta-methyl adipic acid, trimethyl adipic acid, ethylether-2,2'-dicarboxylic acld, and the like.
If deslred, one can use anhydrldee of the above dicarboxylic aclas ~uch a~ phthallc anhydride, tetrahydro-phthalic anhydride and the like. If desired, one can al80 use acld chlorides of the abo~e dlcarboxylic acid~.
Among the polyether~ are lncluded polyethylene gl~col and polypropylene glycol.
Naturally occurrlng polymer~ such as the celluloslc~
and thelr derlvatives can also be utilized in this invent~on.

_ g _ 6~

me monomer or mixtures of monomers used to prepare syrups of the polymers can be any of the monomers mentloned above prov~ded that the monomer(s) i~ capable of substantlally dissolving the polymer and i8 capable o~ homopolymerlzlng or copolgmerizing with any other monomer pre~ent. Pre~erably, the syrups ~o prepared contaln 10-40% by weight of a polymer, ~ubstantially dis~olved in the monomer(s). Pre~erably, the syrups of the polymers contain, as the polgmerlc components, addition polymers, such as polgmethyl methacrylate and copolymers of methyl methacrylate with alpha,beta-ethyleni-cally unsaturated compounds, and polye~ters and, as the monomeric component~, alpha,beta-un~aturated monomer~ or ~ixtures thereo~, such as those selected from the group:
esters of acryllc and methacrylic acid and ~tyrene. In ca~e of very hlgh molecular weight polgmer~, syrups can be pre-pared at polgmer concentratlons as low as 1%.
The s~rup can also contain a cro~slinking agent, added to the 8yrup in an amount of up to 20% by welght upon completion of quenching. Any suitable poly-unsaturated cross}lnking agent can be u~ed, e.e., ethylene dimeth-acrylate, propylene dlmethacrylate, polyethylene glycol dimethacrylate, trlmethylolpropane triacrylate, pentaery-thrltol tetramethacrylate, divinyl benzene, triallyl cyanurate, and diallyl phthalate. 1~ de~ired, a portion, ~.e., up to about 2% o~ the cro~slinking agent can be added to the ~yrup prlor to quenching.
me malelc acid pere~ter salt-oxo acid o~ sul~ur actlvator syatem of this lnvention, in the pr~sence of a polar liquid such as water, 18 al~o capable of inltiatlng the 108Z~64 polymerization of ethylenically unsaturated monomers or mix-tures of such monomers. Among the monomers which can be polymerized with this system are included acrylic and methacrylic acids, their esters, substituted and unsubstituted amides, nitriles; styrene, substituted styrenes such as alpha-methlystyrene, ring-substituted styrenes, and the like;
vinyl esters such as vinyl acetate, vinyl propionate, and the like; alpha-olefins such as ethylene, propylene, l-butene, l-octene, and the like, vinyl chloride, vinylidene chloride; con~u~ated dienes such as 1,3-butadiene; olefins containing fluorine such as vinyl fluoride, trichlorofluoro-ethylene, tetrafluoroethylene, hexafluoropropylene; vinyl and alkyl ethers; and mono- and di- esters of alpha,beta-ethyleni-cally unsaturated dicarboxylic acids such as mono- and dialkyl maleates, mono- and dialkyl fumarates, mono- and dialkyl itaconates, and mixtures thereof as long as such monomers or mixtures of monomers are capable of homo- and copolymerization. The initiator system of this invention is capable of initiating a polymerization reaction at or near room temperature.
Specifically, the process of this invention involves adding to the polymer-in-monomer solution or to the monomerts) the hemi-perester of maleic acid, e.g., monotertiary-butyl peroxymaleate,sometimes referred to as t-butyl permaleic acid,in combination with a basic compound of the desired metal. As such basic compounds, one can use any metal com-pound that will react with the acid substituent of the hemi-perester to form the metal salt of the hemi-perester. Such basic compounds include but are not limited to the oxides or hydroxides of the metals; the carbonates of sodium, 3C potassium or zinc; the acetates of sodium, potassium, copper, 108Z~,4 strontium, magnesium, lead, cobalt, manganese; the octoates of calcium, zinc, magnesium; the ~cid phthalates, bicarbonates, benzoates, phosphates, sulfides, methacrylates, etc. of sodium and potassium or mixtures thereof. Conveniently, the activator can be the last ingredient to be added. A
very useful mode of conducting the process involves the dissolution of the hemi-perester in one portion of the syrup and the suspension of the basic compound in another portion of the syrup.
The polymerization and/or curing is accomplished in any case autogenically by merely exposing the monomers or the syrup containing the metal salt of the hemi-perester of maleic acid and an activator to a temperature of 15-40C.
Although elevated temperatures and higher pressures may be used, they are not necessary.
Utilization of the activator of this invention increases the rate of cure of a syrup when compared to mercaptan containing activators. In a typical curing experiment, utilizing sodium bisulfite activator, curing, as measured by the length of time required for the exothermic reaction to peak, was obtained in 7.5 minutes. In a control experiment, utilizing the diester of ethylene glycol and mercaptoacetic acid, curing was obtained in 14 minutes.
Alternatively, the advantage of the activator of this inven-tion can be seen in the ability to obtain the same rate of cure possible with prior art activator but needing only diminished amounts of the hemi-perester.
The syrup can be mixed with as much as 85% by weight of an inert additive without adversely affecting the improvements obtained by the process of this invention. Such additives include glass fibers, .

108Z16~

powdered metals, inert particles, pigments, alumina, alumina trihydrate, calcium carbonate, natural and synthetic fibers and any other toughening, filling, coloring or strengthening materials. Such fillers can be any of those that do not interfere with the polymerization of the acrylic resin.
The syrups of the present invention including the metal salt of the hemi-perester of maleic acid and an activator can be used to fabricate all types of polymeric articles. Thus, the syrup can be poured on a corrugated surface to produce sheets. The syrups can be poured into molds or over fabrics, metals or layers of glass to provide useful products. The syrup can also be used as a laminating layer for wood and other plastics.
A preferred hemi-perester for forming the metal salt thereof is monotertiary-butyl peroxymaleate. However, other useful hemi-peresters include those where the saturated tertiary alkyl of the hemi-perester is t-amyl, l-methylcyclo-hexyl and p-menthyl. The metal salt of the hemi-perester is usualiy present in an amount greater than 0.05 mo;e percent based on the syrup in order to ohtain the advantages of the present invention. The upper limit of 5 mole percent is merely to indicate that no additional advantage seems to be obtained by adding more than that percentage of the salt.
:~

~08Z164 In the following Examples illustrating the invention, all parts are by weight unless otherwise indicated.

A syrup of 18% methyl methacrylate homopolymer in methyl methacrylate monomer, the polymer having a viscosity of about 50 centipoises, is prepared by partial polymerization in si~u substantially in the manner described in Example I of U.S. Patent 3,154,600, but without the use of the mercaptoacetic acid.
To 35 parts of this syrup are added 65 parts of alumina trihydrate, 0.30 part of a 30% paste of calcium hydroxide in the syrup, 0.80 part of a 25% solution of mono-tertiary-butyl peroxymaleate in a 1:2 by weight solution of methanol and methyl methacrylate, and 0.5 part of a 33%
aqueous solution of sodium metabisulfite corresponding to bisulfite: hemi-perester ratio of 1:1.4. Prior to the addition of the last ingredient, the mixture is heated to 30C. The final mix is cast in 2.5 inch diameter dishes to have a thickness of 0.75 inch. Curing is obtained in 7.5 minutes. The cured sheet is translucent and shows no blushing (whitening) after immersion in 70C water for 16 hours.

EXAMPLES 2-?
To 101.1 part-portions of the mixture as prepared in Example 1 prior to the addition of the activator, pre- -heated to 30C are added, respectively, 0.4, 0.6, 0.2~ 0.1, 0.7, and 0.3 part of a 33% aqueous solution of sodium bisulfite.
Cast as above, the following curing times are observed as ; shown in Table 1:

,.
, .
, ~, . ' ' ' ',. ' ' , . ' , ~,, . , . : ~:

TABLE I
-Ratio Example Sodium bisulfite: tert-butyl Cure Time Deroxvmaleate (minutes) 1 1:1.4 7.5 2 1:1.2 8.6 3 1:1 7-5

4 1:3 13.5 1:6 28 6 1:0.94 28 7 1:2 12.5 .

Utilizing 101.1 parts of the mixture as prepared ; in Example 1, prior to the addition of the activator, the following additional ingredients are added: water, 0.1 part; ~:
zinc octoate, 0.1 part; and the diester of ethylene glycol :
and mercaptoacetic acid, 0.1 part. Curing time in this con- i~
trol experiment is 14 minutes.

Claims (17)

The embodiments of the invention in which an exclusive property or prlvilege is claimed are defined as follows:

1. An initiator system for ethylenically unsaturated monomers consisting essentially of (A) a metal salt of a hemi-perester of maleic acid having the formula wherein Me is a metal selected from the group consisting of Group IA metals, Group IIA metals, zinc, lead, cobalt, nickel, manganese and copper;
x is an integer having a value from 1 to the valence of the metal; and R is a saturated tertiary alkyl radical;
(B) a salt of an oxo acid of sulfur activator selected from the group consisting of bisul-fite, metabisulfite and thiosulfate salts or the free acid; and (C) a polar liquid;
said salt of an oxo acid of sulfur or the free acid activator being present in a ratio to said salt of hemi-perester of maleic acid of from approximately 1:7 to approximately 4:1 by weight.

2. The initiator system of Claim 1 wherein the polar liquid is water.

3. In an improved mixture for preparing polymers consisting of a syrup containing 1-40% by weight of a polymer substantially dissolved in an ethylenically unsaturated monomer or mixtures thereof, and 0.05-5 mole per cent of a metal salt of a hemi-perester of maleic acid having the for-mula wherein Me is a metal selected from the group consisting of Group IA metals, Group IIA metals, zinc, lead, cobalt, nickel, manganese and copper;
x is an integer having a value of from 1 to the valence of the metal; and R is a saturated tertiary alkyl radical the improvement comprislng the presence of a salt of an oxo acid of sulfur activator selected from the group consisting of bisulfite, metabisulfite and thiosulfate salts or the free acid and the presence of a polar liquid; said salt of an oxo acid of sulfur or the free acid activator being present in a ratio to said salt of hemi-perester of maleic acid of from approximately 1:7 to approximately 4:1 by weight.

4. The improved mixture of Claim 3 containing in said syrup 10-40% by weight of said polymer.

5. The improved mixture of Claim 4 wherein said polymer component of said syrup is an addition polymer or a condensation polymer.

6. The improved mixture of Claim 3 wherein said ethylenically unsaturated monomer is selected from the group:
acrylic acid, methacrylic acld, esters, amides and nitriles of acrylic and methacrylic acids, styrene, alphamethyl-styrene, ring-substituted styrenes, vinyl esters, alpha-olefins, conjugated dienes, vinyl chloride, vinylidene chloride, vinyl fluoride, tetrafluoroethylene, hexafluoro-propylene, trichlorofluoroethylene, and mono- and dialkyl esters of maleic, fumaric, and itaconic acids, with the proviso that said monomers or mixtures of monomers are capable of homopolymerization or copolymerization.

7. The improved mixture of Claim 5 wherein said activator is an aqueous solution of sodium bisulfite or sodium metabisulfite.

8. In an improved process for preparing a methyl methacrylate polymer selected from the group consisting of methyl methacrylate homopolymer and copolymers of methyl methacrylate with .alpha.,.beta. ethylenically unsaturated compounds which includes curing a syrup containing 10-40% by weight of methyl methacrylate polymer, having an inherent viscosity of 0.25-1.0, in monomeric methyl methacrylate, in the presence of 0.05-5 mole per cent of a metal salt of a hemi-perester of malelc acid having the formula wherein Me is a metal selected from the group consisting of Group IA metals, Group IIA metals, zinc, lead, cobalt, nickel, manganese and copper;
x is an integer having a value from 1 to the valence of the metal; and R is a saturated tertiary alkyl radical the improvement comprising the presence of a salt of an oxo acid of sulfur activator selected from the group con-sisting of bisulfite, metabisulfite and thiosulfate salts and the presence of a polar liquid; said salt of an oxo acid of sulfur or the free acid activator being present in a ratio to said salt of hemi-perester of malelc acid of from approxi-mately 1:7 to approximately 4:1 by weight.

9. The process of Claim 8 wherein there is also present up to 85% by weight of the total of an inert additive.

10. The process of Claim 9 wherein said inert additive is alumina trihydrate.

11. In an improved mixture for preparing methyl methacrylate polymers selected from the group consisting of methyl methacrylate homopolymer and copolymers of methyl methacrylate with .alpha.,.beta.ethylenically unsaturated compounds consisting essentially of a syrup containing 10-40% by weight of methyl methacrylate polymer, having an inherent viscosity of 0.25-1.0, in monomeric methyl methacrylate, and 0.05-5 mole per cent of a metal salt of a hemi-perester of maleic acid having the formula wherein Me is a metal selected from the group consisting of Group IA metals, Group IIA metals, zinc, lead, cobalt, nickel, manganese and copper;
X is an integer having a value of from 1 to the valence of the metal; and R is a saturated tertiary alkyl radical the improvement comprising the presence of a salt of an oxo acid of sulfur activator selected from the group consisting of bisulfite, metabisulfite and thiosulfate salts and the presence of a polar liquid; said salt of an oxo acid of sulfur or the free acid activator being present in a ratio to said salt of hemi-perester of maleic acid of from approxi-mately 1:7 to approximately 4:1 by weight.

12. The mixture of Claim 11 wherein there is also present up to 85% by weight of the total of an inert additive.

13. The mixture of Claim 12 wherein said inert additive is alumina trihydrate.

14. The mixture of Claim 11 wherein said acti-vator is an aqueous solution of sodium bisulfite or sodium metabisulfite.

15. In an improved mixture for preparing polymers consisting essentially of a syrup containing 10-40% by weight of a polyester substantially dissolved in an alpha,beta-ethylenically unsaturated compound or mixtures thereof, and 0.05-5 mole per cent of a metal salt of a hemi-perester of maleic acid having the formula wherein Me is a metal selected from the group consisting of Group IA metals, Group IIA metals, zinc, lead, cobalt, nlckel, manganese and copper;
x is an integer having a value of from 1 to the valence of the metal; and R is a saturated tertiary alkyl radical the improvement comprising the presence of a salt of an oxo acid of sulfur activator selected from the group consisting of bisulfite, metabisulfite and thiosulfate salts or the free acid and the presence of a polar liquid; said salt of an oxo acid of sulfur or the free acid activator being present in a ratio to said salt of hemi-perester of maleic acid of from approximately 1:7 to approximately 4:1 by weight.

16. The mixture of Claim 15 wherein there is also present up to 85% by weight of the total of an inert additive.

17. The mixture of Claim 16 wherein said inert additive is alumina trihydrate.