Propagation and termination kinetics in high conversion free radical co-polymerization of styrene/divinylbenzene investigated by electron spin resonance and Fourier-transform near-infrared spectroscopy

Abstract

The bulk co-polymerization of styrene (St) and divinylbenzene (DVB; 0–0.20 M) has been monitored by electron spin resonance and FT near infrared spectroscopy to high conversion at 70 °C. The molecular weight and polydispersity started to increase at lower conversion than the radical concentration and the rate of polymerization, indicating that a significant fraction of pendant unsaturations had reacted at the onset of the gel-effect. The propagation rate coefficient ( k p) remained approximately constant until 80% conversion for all DVB contents, where it fell dramatically. The values of k t exhibited an initial plateau region, then decreased by approximately two orders of magnitude between approximately 20 and 60% conversion. The decrease was more significant, and the onset of the decrease occurred at lower conversion, with increasing DVB content. At very high conversion levels (>80%), both k p and k t decreased with increasing DVB content at a given conversion, consistent with reaction diffusion being the dominant termination mechanism.