High-temperature propagation and termination kinetics of styrene to high conversion investigated by electron paramagnetic resonance spectroscopy

摘要

The free radical bulk polymerization of styrene at 120 degreesC has been investigated over almost the entire conversion range using electron paramagnetic resonance spectroscopy, Fourier-transform near-infrared spectroscopy and gel permeation chromatography. The free radical concentration went through a sharp maximum that coincided with the peak in the rate of polymerization during the gel effect, and shifted to higher conversion with increasing initiator concentration. The termination rate coefficient (k(t)), decoupled from the initiator efficiency (f) by use of the instantaneous degree of polymerization, remained close to constant up to as high as approximately 80 conversion, at which a dramatic decrease occurred. Both the propagation rate coefficient (k(p)) and f fell orders of magnitude near 80 conversion in spite of the temperature being above the glass transition temperature of the system. The value of k(p) increased with the initiator concentration at a given conversion in the highest (diffusion-controlled) conversion range.