Penultimate unit effects in free-radical copolymerization. number-average degree of polymerization and copolymerization rate in styrene/methyl methacrylate/toluene system

Abstract

Recently, Fukuda et al. showed from the measurements of absolute rate constants that in the free-radical copolymerization the propagation step obeys the penultimate model and the termination step is diffusion-controlled. Also Fukuda et al. proposed the “radical stabilization energy model” in the free radical copolymerization. To examine this copolymerization model, relationships between feed monomer composition f1 and number-average degree of polymerization Xn and between f1 and copolymerization rate Rp were investigated for the copolymerization of styrene and methyl methacrylate in toluene at 40°C. The composition of the copolymer F1 was determined by 1H NMR. The number-average molecular weight of the copolymer Mn was measured to calculate Xn by osmometry and size exclusion chromatography (SEC). By the so-called terminal model (the Mayo–Lewis model), the copolymer composition data was well described while the data of Xn and Rp Were not described. Alternatively, the model proposed by Fukuda et al. described well the composition data, the Xn data and the Rp data. © 1995, The Society of Polymer Science, Japan. All rights reserved.