Free radical copolymerization V. Rate constants of propagation and termination for a styrene/methyl methacrylate/toluene system

Abstract

The free-radical copolymerization of styrene and methyl methacrylate at 40°C in the presence of 50 wt% of toluene was critically examined by studying both the steady-state and nonsteady-state polymerizations and thus evaluating the rate constants of propagation and termination individually as a function of monomer composition. The results closely agree with those for the corresponding bulk system, establishing that the propagation step of this system, which the terminal model fails to describe, obeys the penultimate model rather than other alternatives which include the solvent fraction as one of the model parameters. Numerically, the experimental values of propagation constant are reproduced with sufficient accuracy by assuming that the homo-propagation rates decrease by a factor about 0.3, when the penultimate units are replaced by the foreign monomers. There is detected no apparent penultimate-unit effect on the composition curve in the solution as well as in bulk. The termination rate constants in the solution agree, within experimental error, with those in the bulk, showing no particular preference for the cross-termination reactions. © 1987 The Society of Polymer Science, Japan. All rights reserved.