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synopsisThe exotherm for the polymerization of methyl methacrylate was monitored by a simple thermal technique to gain useful information about the effect of several factors on the polymerization rate and the degree of completion. All reactions were begun at room temperature (24OC) and no external heating was provided. Initiation was by decomposition of benzoyl peroxide (and mixtures with lauroyl peroxide) catalyzed by the accelerator N,N-dimethyl-p-toluidine. Specific factors examined were peroxide and accelerator levels, sample size, peroxide combinations, and crosslinking agents. The results are discussed in terms of the stoichiometry of the initiator system; the balance of heat generation, heat capacity, and heat loss; and the autoacceleration effect. INTRODUCTIONFrequently polymers are formed into specific shapes by a procedure wherein a monomer or prepolymer is polymerized in place, which is sometimes referred to as casting. Examples include various coatings, fiber glass constructions, embedding techniques, etc. A number of complex initiator formulations are employed for each monomer system and their selection is based on use experience. Often in this procedure the polymerization must start at ambient temperature or a little above, although owing to the exothermic reaction it will subsequently rise well above this level. The reaction occurs under very complex and varying conditions as opposed t o the rather well-controlled conditions that prevail in most commercial reactors where large quantities of polymers of consistent quality are made. Kinetic data for the latter may be obtained and expressed in a fundamental fashion and are often utilized quantitatively. Kinetic data would also be valuable for casting procedures; however, there is little chance of obtaining fundamental data nor of using it quantitatively since the complex features are an inherent part of the process and must be preserved. There is a considerable need, however, for data of some type t o assist in the decisionmaking process where the types and levels of initiators, accelerators, and other agents are selected.This study was undertaken because of a need for this type information in connection with our work on developing polymeric surface treatments for PAUL, FOWLER, AND HOUSTONconcrete, concrete crack repair systems, and other technology associated with the concept of impregnating thc pores of concrete with liquid monomers with subsequent conversion t oWe have developed a simple thermal analysis technique t o follow the exotherm of the polymerization reaction which allows rather rapid screening of various systems. Some results of gencral interest are reported here. The monomer employed was methyl methacrylate, MAIA, with benzoyl and lauroyl peroxide as initiators in conjunction with the accelerator N,N-dimethyl-p-toluidine.