High-Conversion Free-Radical Bulk Polymerization of Styrene:  Termination Kinetics Studied by Electron Spin Resonance, Fourier Transform Near-Infrared Spectroscopy, and Gel Permeation Chromatography

The free-radical bulk polymerization of styrene initiated by dimethyl 2,2‘-azobisisobutyrate at 70 °C has been studied employing the techniques of Fourier transform near-infrared spectroscopy, electron spin resonance spectroscopy and gel permeation chromatography. The initiator efficiency (f) as a function of monomer conversion was estimated via an equation relating the instantaneous and the cumulative number average degrees of polymerization. The result was subsequently employed to calculate the conversion dependence of the termination rate coefficient (k t) from zero to the limiting conversion for different initiator concentrations. Over the course of the reaction, k t decreases by 5 orders of magnitude (107−102 M-1 s-1). At conversion levels approaching the limiting value, k t shows a marked dependence on initiator concentration; higher initiator concentration shifts the k t vs conversion curves toward higher conversion levels. The reaction diffusion constant was found to decrease with increasing conversion in the high-conversion regime.