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

Abstract

Photopolymerization of methyl methacrylate in bulk and in solution at 40 °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 kp2/kt was 1.27 × 10−2 1/mol/sec. The kinetic data indicated that polymerization followed a radical mechanism. The initiator order was found to be 0.25, indicating significant deviation from the square root dependence for normal free radical kinetics. The non-ideality in the kinetics can be explained on the basis of significant initiator-dependent termination through primary radicals or degradative initiator transfer. The observed monomer order was significantly less than unity (i.e. nonideal behavior) for use of carbon tetrachloride, chloroform, methylethyl ketone and acetic acid as diluents, but it was unity (i.e. ideal behavior) for use of benzene as the diluent. Solvents other than benzene contributed to enhancement of rate of polymerization by influencing the radical generation step. End-group analysis indicated the incorporation of DMA and MCAA moieties as end-groups in the polymers. Copyright © 1999 John Wiley & Sons, Ltd.