Phase Behavior of ternary polymer blends: asymmetry, segregation strength, and coexisting phases

Abstract

The bicontinuous microemulsion phase, found in ternary polymer blends containing immiscible A and B homopolymers and an amphiphilic A-B diblock copolymer, has attracted interest due to its combination of properties that make it attractive for use as a template for nanoporous materials. While recent work has demonstrated that a variety of materials can be templated from a single blend system, future work may demand incorporation of a variety of polymers into microemulsion-forming blends. Such systems fall beyond the currently understood model phase behavior for ternary blends. In this thesis, the effect of well-controlled nonidealities and other extensions of ternary blend phase behavior are described. Systems were designed to investigate the influence of conformational asymmetry – a difference in the radius of gyration per molar volume of two polymers – on blend phase behavior. Previous work suggested that the influence was significant, and resulted in a broad region of a hexagonally symmetric phase in the vicinity of the microemulsion. This behavior could inhibit the process of capturing of microemulsion for templating purposes, so it is important to understand conformational asymmetry’s influence. A related series of systems was designed to investigate the effect of increased segregation strength by using amphiphilic diblocks of varying molecular weight. Finally, a previous study incorporating an ABA triblock, C homopolymer, and ABABA–C amphiphilic hexablock was expanded to incorporate ordered components, allowing for hierarchical microphase separation. This study demonstrates that model ternary blend phase behavior can be extended to systems containing more complex linear polymer architectures. Additionally, two phenomena observed in these systems were investigated in detail. First, light scattering was observed in the vicinity of the order-disorder transition of blends; this scattering is a result of coexisting ordered and disordered phases. Finally, catalytic hydrogen-deuterium exchange on polyolefins was investigated. The reaction conditions described provide a facile method of preparing isotopically labeled chains and give insight into the mechanism of exchange.