Synthesis and Modelling of High Tg Copolymers Through Suspension Copolymerization with Bifunctional Initiators

Abstract

<p>In this thesis, the copolymerization theory has been extended to account for the unique phenomenon of multiple initiation/propagation/termination cycles, experienced by copolymer chains in free radical copolymerization with bifunctional initiators. A comprehensive model for the most general free radical copolymerization scheme, involving simultaneous and competitive statistical and donor-acceptor propagation mechanisms, has been developed. The effects of multiple chain recombination during bifunctionally initiated batch free radical copolymerization, on copolymer microstructure and compositional drift, have been evaluated. As a result, the concepts of effective instantaneous copolymer composition, and number of segments per copolymer chain have been introduced as an addition to the copolymerization theory.</p> <p>The ability to control the segment composition of the multi-segment copolymers formed during bifunctionally initiated free radical copolymerization, has been the basis for the design and synthesis of four different high T₀ engineering copolymers. Styrene/α-methylstyrene (T₀-115°C), styrene/N-phenylmaleimide (T₀-215°C), and α-methylstyrene/N-phenylmaleimide copolymers (T₀-260°C), as well as styrene/α-methylstyrene/n-phenylmaleimide terpolymers (T₀-220ºC), have been synthesized in bulk and suspension, and fully characterized. The performance of these four copolymer systems in suspension polymerization with bifunctional initiators has been evaluated at pilot plant scale, to assess the technical feasibility for their commercial production.</p> <p>In addition, a novel route for the synthesis of suspension expandable polystyrene with bifunctional initiators, in a highly productive simultaneous polymerization/impregnation stage, has been developed and fully tested in pilot plant scale.</p> <p>From the comprehensive kinetic and micro-structure models proposed in this thesis, two computer simulation programs (BIPEN and BICOP), have been developed. Both programs, predicting the most important phenomena of the polymerization processes studied herein, have been used as a product design tool, throughout this thesis, with very good results.</p>