Tailoring Polymer Chain Structures By Semibatch RAFT Miniemulsion Polymerization

A recent trend in the chemical industry is the production of specialized chemicals possessing a diversity of properties for a variety of niche markets. For polymers, properties are governed to a large extent by chain structure. Therefore, precise control over chain structure is key to producing value-added products making this an important research area in polymer product engineering.The thesis project described herein developed a digital synthesis technology for precise preparation of polymer chain structures in heterogeneous systems. The technology is based on principles of chemical reaction engineering but also draws on concepts from numerical control manufacturing utilized in mechanical fields and incorporates characteristics of heterogeneous controlled/living radical polymerization, specifically reversible addition-fragmentation chain transfer (RAFT) miniemulsion polymerization. The kinetics of RAFT miniemulsion copolymerizations without/with branching were both investigated and corresponding kinetic models were developed. The batch models were combined with the semibatch reactor model, and the digital synthesis technology was then devised for precise control of polymer chain structures by model-based monomer feeding strategy via semibatch RAFT miniemulsion copolymerization.The works in the thesis include:(1) For the RAFT miniemulsion copolymerization of styrene (St) and butyl acrylate (BA), the effects of different monomer mole ratios on copolymer composition, polymerization rate, molecular weight and molecular weight distribution and particle size were investigated, along with the number of polymer particles and the average number of propagating radicals per particle. With the utilization of an implicit penultimate model and the consideration of droplet nucleation which was assumed to contribute to particle generation, a kinetic model for RAFT miniemulsion copolymerization was developed. The agreements between model simulation and experimental data were good.(2) The batch RAFT miniemulsion copolymerization model was combined with the semibatch reactor model to produce a semibatch RAFT minimeulsion copolymerization model. The model was used to control comonomer feed rate for producing targeted copolymer composition distributions (CCDs). A series of St/BA copolymers with predesigned uniform and linear gradient CCDs were successfully produced.(3) The influence of both the branching and RAFT agent concentrations on branch formation were investigated in RAFT miniemulsion copolymerization of St and triethylene glycol dimethacrylate (TEGDMA). The confined space of polymer particles promoted formation of branches. Given that droplet nucleation contributes to particle generation and the consideration of particle-droplet coalescences and diffusion-controlled reactions, a kinetic model for RAFT miniemulsion copolymerization with branching was’ developed, and the agreement between model simulation and experimental data were found to be good.(4) Based on the batch kinetic model for RAFT miniemulsion copolymerization with branching, a semibatch RAFT miniemulsion branching copolymerization was developed that controls comonomer feeding rate to generate targeted branching density distributions (BDDs). A series of hyperbranched polystyrenes with different uniform BDDs were successfully produced to demonstrate the effectiveness of the approach for controlling BDD.The following were the key innovations of this thesis work:(1) A novel programmed synthesis technology has been developed for precise control of polymer chain structures in heterogeneous controlled/living radical polymerization systems, which provides an innovative methodology for the design and control of polymer products.(2) Kinetics models for RAFT miniemulsion copolymerization without/with branching were developed and shown to be in agreement with experiment results.(3) A series of polystyrenes with predesigned CCDs and BDDs were successfully produced by semibatch RAFT miniemulsion polymerization. These species are useful for the systematic study of polymer structure-property relationships.