Photopolymers (I): Photoinitiating role of monochloroacetic acid in the synthesis of poly(methyl methacrylate)

Photopolymerization of methyl methacrylate in bulk and in solution at 40 de grees C using monochloroacetic acid dimethyl aniline (MCAA-DMA) combination as photoinitiator was studied kinetically. The apparent activation Energy was found to be 4.39 kcal/mol (18.37 kJ/mol) while the kinetic parameter k( p)(2)/k(t) was 1.27 x 10(-2) 1/mol/sec. The kinetic data indicated that pol ymerization followed a radical mechanism. The initiator order was found to be 0.25, indicating significant deviation from the square root dependence f or normal free radical kinetics. The nonideality in the kinetics can be exp lained on the basis of significant initiator-dependent termination through primary radicals or degradative initiator transfer. The observed monomer or der was significantly less than unity (i.e. nonideal behavior) for use of c arbon tetrachloride, chloroform, methylethyl ketone and acetic acid as dilu ents, but it was unity (i.e. ideal behavior)for use of benzene as the dilue nt. Solvents other than benzene contributed to enhancement of rate of polym erization by influencing the radical generation step. End-group analysis in dicated the incorporation of DMA and MCAA moieties as end-groups in the pol ymers. Copyright (C) 1999 John Wiley & Sons, Ltd.