Amphiphilic Block-Random Copolymers as Stabilizers in Emulsion Polymerization
Emulsion Polymerization , Block Copolymers , Reactive Surfactant , Block-Random Copolymers
The objective of this thesis is to explore block-random copolymers of styrene and acrylic acid, PS-b-(PS-r-PAA), as stabilizers in emulsion polymerization. Small molecule surfactants are typically used to stabilize emulsion polymerizations, but they are detrimental to performance properties of the final products and can leach into the environment. Various replacements have been explored, and this thesis adds to that toolbox. First, a variety of PS-b-(PS-r-PAA) are synthesized and studied both in aqueous dispersion and as stabilizers in emulsion polymerizations of styrene. This study uncovered unique properties of the block-random copolymers in dispersion and as stabilizers and prompted further investigation to the mechanisms in emulsion polymerization. Second, the nucleation mechanism in emulsion polymerizations stabilized by block-random copolymers is investigated, resulting in the description of a seeded-coagulative nucleation mechanism and model. Both a mathematical and qualitative description of the process is presented. Next, PS-b-(PS-r-PAA) are studied in aqueous environments to elucidate the behaviour of block-random copolymers in the absence of emulsion polymerization. This study showed that self assembly and surface activity can be tuned with pH and ionic strength. The nature of the aggregates is discussed in the context of emulsion polymerization, showing that the seeded-coagulative nucleation mechanism is likely a result of the unique conformations of PS-b-(PS-r-PAA) aggregates. Finally, a zwitterionic surfactant bearing polymerizable functionality is explored in emulsion polymerization as another means to replacing typical small-molecule surfactants. The surfactant covalently binds to polymer particles because of its polymerizability and provides stability in both acidic and basic conditions owing to its zwitterionic nature. In this thesis, the overarching goal of replacing small molecule surfactants in emulsion polymerizations is explored using PS-b-(PS-r-PAA) and a reactive surfactant.