Photoinitiated polymerization of methyl methacrylate using Q-sized zinc oxide colloids

Abstract

The polymerization of methyl methacrylate has been shown to occur readily using Q-sized ZnO semiconductors as photoinitiators. We have examined the effects of solvent, monomer concentration, initiator concentration, light intensity, and semiconductor particle size upon the reaction rates. The reaction pathway appears to be via anionic initiation, followed by free-radical propagation steps. The holes formed upon illumination are scavenged by the solvent. Increasing the concentration of the photoinitiator increased polymer yield until a saturation value was achieved. The rate of polymerization rapidly increased with increasing monomer concentration, due to the Trommsdorf effect. The rate of polymerization was found to depend upon the square root of the incident light intensity, as predicted from simple kinetic theory. Quantum yields of polymerization decreased as particle size decreased, due to either increased surface defects or enhanced rates of competing electron-hole recombination. Under the same experimental conditions, no polymerization occurred with bulk-size ZnO particles as photoinitiators; thus Q-sized ZnO particles were more efficient photoinitiators of polymerization.