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Predicting Mw and Branching Levels for Self-Condensing Vinyl Copolymerization in a CSTR

A continuous stirred-tank reactor (CSTR) model is developed for the production of arborescent polyisobutylene via carbocationic copolymerization of isobutylene and an inimer using multi-dimensional method of moments. An inimer is a molecule that contains a functional initiating group and vinyl monomeric group (Initiator-Monomer) forming a T-shaped branching point. The model is used to predict dynamic changes in average branching level (Br) and number-average and weight-average molecular weights (Mn and Mw). Simulations of this self-condensing vinyl copolymerization (SCVCP) show a tendency toward higher polydispersity and higher Br compared to batch reactor simulations conducted using the same recipes and residence times. At high inimer feed concentration and/or long residence time, the model predicts that a CSTR does not reach steady-state operation due to Mw increasing toward infinity. There is only a narrow operating range in which the inimer feed concentration can be adjusted to achieve a desired steadystate Mw. If SCVCP is to be conducted in a CSTR, it will be important to ensure that residence times and inimer feed concentrations are selected within the permissible stable operating window.