Phase-Separated Elastomers: Novel Syntheses and CharacterizationPublic Deposited
Phase separation in segmented polymers provides distinct challenges in regard to their chemical reaction kinetics and characterization. Well studied, it has been shown that structure, phase separation and non-covalent interactions are key factors in the design of elastomeric polyurethanes. Specifically, this dissertation is focused on two areas: the synthesis of novel materials that, through these factors, have potential for use as polyurethane replacements and the novel application of fluorescence to discern aromatic interactions in phase-separated polyurethanes. In this work, two synthetic routes are employed to generate elastomers: multicomponent thiol reactions and amine-vinyl sulfone polymerizations. Using thiol-based click reactions, thiol-acrylate-epoxide hybrid polymers were produced by two simultaneous reactions at room temperature in a one-pot synthesis. Beyond good mechanical properties, some of the resulting phase-separated networks were very good shape memory polymers. Temperature and DBU catalyst loading were not found to influence the reaction-induced phase separation behavior in this system. Therefore, the spherical two-phase morphology is independent of cure conditions as thiol-acrylate reactions are much faster than thiol-epoxy reactions. Next, novel amine-vinyl sulfone networks were formed from oligomeric diamines and divinyl sulfone. Upon characterization of reaction kinetics and properties, it was found that these uncatalyzed reactions have rates that are competitive with both uncatalyzed polyurethane and non-isocyanate polyurethane reaction rates and the resulting polymers exhibited tensile properties comparable to polyurethanes and catalyzed non-isocyanate polyurethanes. Although phase separation in polyurethanes has been well studied for several decades, challenges remain in the experimental determination of aromatic interactions that exist between hard segments. Here, intrinsic fluorescence is applied to segmented polyurethanes with aromatic ring-containing hard segments to experimentally observe these interactions. Using emission spectra, the orientation and alignment of aromatic rings was characterized and quantified through monomer and excimer emission. Using excitation spectra, it can be observed that excimer formation originates from a ground-state dimer complex, which implies that the rings are specifically oriented in a sandwich-like configuration. In addition, the effects of confinement and substrate interactions are explored. Hydrogen bonding and rigidity at the substrate were observed to interfere with dynamic excimer formation, an effect that propagates some tens of nanometers into the film.
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