Modeling of living free-radical polymerization processes. I. Batch, semibatch, and continuous tank reactors

A comprehensive mathematical model is developed for living free-radical polymerization carried out in tank reactors and provides a tool for the study of process development and design issues. The model is validated using experimental data for nitroxide-mediated styrene polymerization and atom transfer radical copolymerization of styrene and n-butyl acrylate. Simulations show that the presence of reversible capping reactions between growing and dormant polymer chains should boost initiation efficiency when using free nitroxide in conjunction with conventional initiator and also increase the effectiveness of thermal initiation. A study shows the effects of the value of the capping equilibrium constant and capping reaction rate constants for both nitroxide-mediated styrene polymerization (using alkoxyamine as polymer chain seeds) and atom transfer radical polymerization of n-butyl acrylate (using methyl 2-bromopropionate as chain extension seeds), Also the effect of introducing additional conventional initiator into atom transfer radical polymerization of n-butyl acrylate is studied. It is found that the characteristics of long chain growth are determined by file fast exchange of radicals between growing and dormant polymer chains. Polymerization results in batch, semibatch, and a series of continuous tank reactors are analyzed. The simulations, also show that a semibatch reactor is most flexible for the preparation of polymers with controlled architecture. For continuous tank reactors, the residence time distribution has a significant effect on the development of chain architecture. (C) 2002 Wiley Periodicals, Inc.