Air void control composition for carbonyl-containing monomer polymerization
The invention relates to the use of low levels of glycols and short chain diols to control air void formation in any polymerization reaction having carbonyl-containing monomers, and preferably carboxylic acid ester monomers, at a level of at least 10% of total monomer, where the monomer has a peak polymerization exotherm temperature of greater than the boiling point of the monomer. The glycols and short chain diols are used in the polymization mixture at levels of 0.5 to 10 weight percent, based on the carboxylic acid ester-containing monomer. It is believed the glycols and short chain diols hydrogen bond with the —(C═O)O— containing monomer to increase the monomer boiling point, and decrease or even eliminate the formation of air voids due to monomer boiling. The invention is especially useful in polymerization of methyl methacrylate polymers and copolymers, either neat, or as a polymer composite system.
1. A polymerization reaction mixture comprising:
a) an exotherm control additive comprising 4 to 10 weight percent of one or more aliphatic glycols and short chain diols having from 2 to 6 carbon atoms, said percentage based on the weight of monomer mixture in the reaction mixture;
b) a monomer mixture, wherein said monomer mixture comprises at least 10 weight percent of carbonyl-group-containing monomer; and
c) 1 to 80 weight percent of (meth)acrylic polymer,
wherein the polymerization reaction mixture is in the form of a (meth)acrylic syrup having a dynamic viscosity at 25° C. of between 50 mPa·s and 10,000 mPa·s.
2. The polymerization reaction mixture of claim 1 , wherein said monomer mixture comprises at least 90 weight percent of one or more (meth)acrylic monomers.
3. The polymerization reaction mixture of claim 2 , wherein said (meth)acrylic monomers comprise at least 51 percent by weight of methyl methacrylate monomer, and from 0 to 49 weight percent of C 1-8 alkyl acrylates.
4. The polymerization reaction mixture of claim 1 , wherein said aliphatic glycols and short chain diols are selected from the group consisting of 1,2-propylene glycol, 1,3-propylene glycol, diethylene glycol, TRITON X-100 (C 14 H 22 O(C 2 H 4 O) n ), oligoethylene glycols of structure H—(O—CH 2 —CH 2 ) n —OH, where n=2 to 50, and polyethylene glycols having repeating units of from 51 to 200, glycerol, 1,3-butanediol, and 1,4-butane diol.
5. The polymerization reaction mixture of claim 1 , wherein said (meth)acrylic polymer comprises polymethyl methacrylate.
6. The polymerization reaction mixture of claim 1 , wherein said reaction mixture further comprises one or more additional exotherm control additives selected from the group consisting of:
(i) up to 20 weight percent of an additive selected from the group consisting of glycols, diols, chain transfer agents and aliphatic short chain fatty esters, based on the total weight of the monomer mixture, and
(ii) from 100 to 5000 ppm of an additive selected from the group consisting of aliphatic primary and secondary amines, based on the total weight of the monomer mixture.
7. The polymerization reaction mixture of claim 1 , wherein the exotherm control additive comprises one or more aliphatic glycols and short chain diols having from 3 to 4 carbon atoms.