High‐Temperature Propagation and Termination Kinetics of Styrene to High Conversion Investigated by Electron Paramagnetic Resonance Spectroscopy

Summary: The free radical bulk polymerization of styrene at 120 °C 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.Termination rate coefficient ( k t ) versus conversion for bulk free radical polymerization of St initiated by TBP at 120 °C. [TBP] = 0.15 (○), 0.10 (▴) and 0.05 M ().