Segmental dynamics during the thermal polymerization of styrene: a kinetic fluorescence anisotropy decay study

Abstract

The segmental dynamics of anthracene-labelled polystyrene chains is studied during the thermal polymerization process of styrene by means of fluorescence anisotropy decay. The characteristic time of conformational jumps starts to increase drastically after a conversion rate of ca. 15 wt%, due to the direct steric interaction between different chains. The shape of the orientation autocorrelation function remains rather independent of the polymer concentration. It is well described by the process of ‘diffusive conformational jumps’. The corresponding ‘distribution of relaxation times’ is significantly narrower than the one observed in depolarized Rayleigh scattering, indicating that multimolecular interactions affect this latter technique significantly. The variation of the correlation times as a function of the concentration is in agreement with the free-volume models for concentrated solutions proposed by Fujita and Mashimo. However, the large difference between the concentration dependence of the conformational jump rate of the polymer chain and that of the reorientation time of styrene monomers rules out the idea of a single ‘local viscosity’ valid for all the species in the mixture.