| For the modeling of carbocationic polymerization systems, accurate values for the propagation rate constants as well reactivity ratios for the respective comonomers should be identified. This thesis reports on reaction schemes and kinetic models for two different carbocationic polymerization systems, isobutylene (IB) polymerization and trimethylstyrene (TMS) polymerization. On the basis of these models, we seek to explain the discrepancy in the values reported for the rate constants for propagation measured by two differing approaches. Furthermore, a method has been developed utilizing real-time FTIR for accurately calculating reactivity ratio values.; The kinetics of IB polymerization are governed by dormant-active equilibria. A kinetic model based on a previously proposed mechanism, involving a pre-equilibrium step has been constructed. The kinetic model yielded good agreement with experimental data, with the exception of Mw values that slightly diverged from the theoretically predicted 'Mw - Mn = constant' relationship. This may indicate the occurrence of a minor side reaction. This model reconciles the discrepancy between rate constants published for carbocationic IB polymerization and accounts for shifting TiCl4 orders. When the kinetics of IB and Styrene (St) homopolymerization were compared, it was found that St polymerization too displayed similar behavior as IB, i.e. shifting TiCl4 order. The rate of initiation was found to be first order in TiCl4 in both systems. While initiation is instantaneous in IB polymerization at [TiCl 4]0 (co-initiator) ≥ [TMPCl]0 (initiator), it is slow in St polymerization. Kinetic derivation showed that initiating efficiency is monomer concentration dependant i.e. at lower monomer concentrations, initiator efficiency is low, but at higher monomer concentration it increases. Optimized conditions led to living carbocationic St polymerization producing high molecular weight polystyrene (PS) with 100% initiating efficiency.; A mechanism involving a pre-equilibrium was also suggested for TMS polymerization. It was found that the model without pre-equilibrium was very suitable to explain the lower values of the propagation rate constant. (Abstract shortened by UMI.)... |
