Unconventional radical miniemulsion polymerization
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Conventional free-radical miniemulsion polymerization has been well studied since early 1970s. Conventional free-radical miniemulsion polymerizations have inherent limitations associated with uncontrolled free-radical polymerization mechanism. The goal of this work is to develop a variety of unconventional miniemulsion polymerization techniques by applying new polymerization techniques (typically in solution or bulk) to miniemulsion systems to overcome their inherent limitations and extend the application of free-radical miniemulsion polymerization. This work focused on the exploration of kinetic and mechanistic aspects of unconventional miniemulsion polymerizations. First, enzyme initiated free-radical miniemulsion polymerization, in contrast with those conventional chemical initiated miniemulsion polymerization, is demonstrated for the first time as an answer to the challenges associated with using the hydrophobic of vinyl monomers in aqueous enzymatic reactions. A procedure for enzyme initiated free-radical miniemulsion polymerization was formulated and stable poly(styrene) latexes were successfully synthesized. The kinetics of enzyme initiated free-radical miniemulsion polymerization and the effect of reaction conditions on the polymerization was elucidated. Second, RAFT miniemulsion polymerization of hydrophobic monomers was performed in CSTR trains and the transient states, previously identified by others in our group, were elucidated. Next, RAFT miniemulsion polymerization of a partially water soluble monomer was studied. RAFT miniemulsion polymerizations of gamma-methyl-alpha-methylene-gamma-butyrolactone, a partially water soluble lactone monomer derived from renewable sources, was successfully formulated. Homogeneous nucleation was found to play an important role in the free-radical "miniemulsion" homopolymerization of MeMBL. By using styrene as a comonomer, the RAFT miniemulsion polymerizations of MeMBL and styrene were well controlled and narrowly distributed copolymers of MeMBL/styrene were produced. Following the study of the partially water monomer, RAFT inverse miniemulsion polymerization was proposed for the polymerization of hydrophilic monomers. The kinetics of RAFT inverse miniemulsion polymerization of acrylamide exhibited the typical behavior of controlled polymerizations up to high conversions. The effects of reaction parameters on the polymerization rate and particle size were investigated. The dominant locus of radical generation for particle nucleation and the fate of desorbed monomeric radicals in inverse miniemulsion polymerizations were evaluated. Finally in this work, conclusions and implications are presented and ideas for future work are suggested.