STUDIES ON THE STEP-GROWTH POLYMERIZATION OF AROMATIC POLYCARBONATES
Choi, Kyu Y.
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Bisphenol A polycarbonate (BAPC) is a versatile engineering polymer that has a broad spectrum of applications. In this dissertation, theoretical and experimental studies of step-growth polymerization of BAPC are presented to gain better understandings in both solid-state polymerization (SSP) and melt copolymerization systems. The reactive end group mole ratio in the prepolymer is one of the most important parameters in the AA-BB type polycondensation system. However, it often deviates from the stoichiometric ratio due to the loss of diphenyl carbonate during the melt transesterification process, limiting the molecular weight increase in a subsequent SSP process. In this work, a new back calculation method has been developed to estimate the initial mole ratio of reactive end groups for the melt transesterification using the data of prepolymer's molecular weight and end group mole ratio. An end group model and a molecular species model have been developed to describe the reaction kinetics of SSP in a single polymer particle. A single particle model is combined with a dynamic moving packed bed reactor model to investigate the steady-state and dynamic behaviors of a continuous polymerization reactor process. The model simulations show that any temperature nonuniformity in the reactor caused by poor heat transfer from the purge gas or the reactor walls leads to a slow increase in the polymer molecular weight averages and molecular weight distribution. A new method has been developed to calculate the sequence length distributions for condensation terpolymers and applied to calculating the time evolution of sequence length distributions for a semibatch melt copolymerization process. Finally, the crystalline structures of BAPC have been investigated using scanning electron microscopy. We observed that BAPC crystallization occurs readily by solvent-induced crystallization technique when the polymer is deposited as a thin film onto a substrate surface. When acetone is used as a swelling agent, the polycarbonate crystals grow to three dimensionally structured spherulites that have been rarely reported in the literature.