Copolymerization propagation kinetics of styrene and methyl methacrylate-revisited. 1. Pulsed laser polymerization study

A comprehensive set of propagation rate coefficients for styrene-methyl methacrylate bulk copolymerization has been obtained from pulsed laser polymerization experiments performed over a range of temperatures (18-57 °C). The copolymer molecular weight distributions were analyzed using size exclusion chromatography with on-line low-angle laser-light scattering (LALLS) and differential viscometry (DV) detectors. The molecular weight data obtained using these absolute detection methods were compared with data obtained by assuming the copolymer hydrodynamic volumes (HDVs) can be described by a weighted average of the homopolymer HDVs. The analyses via these three different approaches yielded virtually identical molecular weight data, validating previous work on this copolymerization system. The precision of the data obtained from LALLS and DV was worse than that obtained from the HDV-weighted approach. However, the errors in the molecular weight data from DV and LALLS analyses are believed to be a more correct representation of the true errors in the molecular weight measurement. A strategy for reducing the effect of the molecular weight errors in the kp measurements, via the selection of slow laser flashing rates, is presented.