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

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 (kp) remained approximately constant until 80% conversion for all DVB contents, where it fell dramatically. The values of kt 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 kp and kt decreased with increasing DVB content at a given conversion, consistent with reaction diffusion being the dominant termination mechanism.