A PULSED-LASER STUDY OF PENULTIMATE COPOLYMERIZATION PROPAGATION KINETICS FOR METHYL-METHACRYLATE N-BUTYL ACRYLATE

The PLP/MWD technique, based upon analysis of the molecular weight dis tribution (MWD) of a polymer produced by pulsed-laser polymerization ( PLP), has proven to be a powerful probe for the examination of free-ra dical homopolymerization kinetics. The same method is applicable to th e study of copolymerization propagation kinetics provided that proper calibrations are established for the measurement of copolymer MWDs, as illustrated by an examination of the methyl methacrylate (MMA)/n-buty l acrylate (nBA) system. Statistical analysis indicates that although MMA/nBA copolymer composition is well described by the terminal model, propagation kinetics are not. Like many other systems recently examin ed, the data are well represented by the ''implicit penultimate unit e ffect'' model of Fukuda and co-workers. However, whereas previous syst ems studied have propagation rates that are lower than those predicted by the terminal model, it is found that the propagation rate of MMA/n BA is greater than the terminal model predictions. The implications of these results to theoretical interpretations of the penultimate model are discussed.