Mathematical Modeling of Atom Transfer Radical Polymerization
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Atom transfer radical polymerization is a new and important living polymerization mechanism because it can produce many different polymers with controlled microstructures and novel properties. The commercialization of these new polymers will require detailed polymer reaction engineering investigations. Mathematical models are essential in this stage because they can summarize our knowledge on polymers made by ATRP and help us to find the optimum conditions for their synthesis. This thesis studies the polymerization kinetics of ATRP with mathematical models based on our own experimental work and experimental data published by other researchers. ATRP with both monofunctional and bifunctional initiators are considered. This is one of very few studies combining detailed mathematical models for polymerization kinetics and polymer microstructure and experimental results in the area of ATRP. Fundamental mathematical models were used to study the main features of ATRP. Population balances and the method of moments were used to predict polymer average properties, while Monte Carlo models were used to predict the complete microstructural distributions. This type of comparison between different modeling techniques is seldom done in the literature, even for other polymerization techniques, and can lead to a better understanding of polymerization mechanisms and mathematical modeling techniques. Since the discovery of ATRP, approximately ten years ago, little attention has been given to bifunctional initiators. This thesis tries to extend our knowledge on this important class of initiators. Comparison between monofunctional and bifunctional initiators, both through mathematical modeling and experimentally, showed that bifunctional initiators have some advantages over monofunctional initiators for ATRP. Polymers made with bifunctional initiators have narrow molecular weight distributions, higher molecular weight averages, and higher monomer conversion for the same polymerization time. In addition to homopolymerization studies, this thesis presents mathematical models for copolymerization with ATRP and for processes combining ATRP and coordination polymerization. These models describe the detailed microstructures of these copolymers and permit a better understanding of ATRP with its advantages and pitfalls. An interesting conclusion from these modeling studies in atom transfer radical copolymerization is that the Mayo-Lewis terminal model is applicable to ATRP and that the copolymer composition in ATRP is independent of the equilibrium constants (activation and deactivation). In order to develop and validate these mathematical models, we collected experimental data in our own laboratories and also used experimental data available in the literature. Our experimental work focused on the homopolymerization and copolymerization of styrene, because of the commercial importance of this monomer and also due to the relative simplicity of its polymerization. Experimental data collected from the literature covered the following systems: bulk homopolymerization of styrene, solution polymerization of styrene, solution polymerization of methyl methacrylate, bulk polymerization of n-butyl acrylate, bulk copolymerization of styrene and n-butyl acrylate. Different characterization techniques were used to determine polymer properties. Molecular weight and molecular weight distribution were measured using gel permeation chromatography (GPC); copolymer chemical composition was determined with nuclear magnetic resonance (NMR) and Fourier-transform infrared (FTIR). We have also done copolymerization with styrene and acrylonitrile (SAN) because it is one of the least understood ATRP system and also because its potential industrial importance. The ability to synthesize polymers with novel molecular architectures is one of the advantages of living polymerization techniques. In this thesis, we used ATRP to produce amphiphilic copolymers composed of polystyrene and polyethylene glycol methacrylate macromonomers. We have shown that ATRP can produce these very interesting polymers with two different types of macroinitiators.