RADICAL TERMINATION AND RADICAL CONCENTRATIONS DURING THE BATCH EMULSION POLYMERIZATION OF METHYL-METHACRYLATE STUDIED BY ELECTRON-SPIN-RESONANCE SPECTROSCOPY

Electron spin resonance (ESR) spectroscopy has been employed to monitor occluded radical concentrations during the unseeded batch emulsion polymerization of methyl methacrylate. A cryogenic quenching procedure has been used to record ESR spectra periodically during the course of the reaction. The occluded radical concentration first increases, reaching a maximum at a time corresponding to almost 100% conversion and then slowly decays due to ''residual termination''. The decay period exhibits second-order kinetics and reveals a rate constant (k(t)) of 410 mol-1 dm3 s-1 at 333 K for a particle size of 72 nm. The variation of the decay profile with initiator concentration, surfactant concentration, and temperature has also been examined.