FREE-RADICAL COPOLYMERIZATION - AN NMR INVESTIGATION OF CURRENT KINETIC-MODELS

The ability of terminal model kinetics to predict copolymer microstructure was tested for the styrene-methyl methacrylate system copolymerized at 40-degrees-C at various fractions of monomers. Carbon-13 NMR studies (in the accompanying paper) showed that previous peak assignments of the spectra of statistical styrene-methyl methacrylate copolymers were incorrect. The peak areas obtained for all copolymers were described in terms of triad sequences and were also adequately predicted by the terminal model utilizing reactivity ratios calculated from a nonlinear least squares fit to the copolymer composition data determined by H-1 NMR. The nonterminal model behavior of the kinetics of the rate of polymerization described elsewhere can be successfully modeled by the 'restricted'' penultimate model of Fukuda et al. We show that all current data can also be explained by various ''bootstrap'' or monomer-polymer complex models. Further model discrimination awaits new independent experimental results.