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Evolution of phase behavior and dynamics in reactive polymer blends
Polyurethane-based materials are the basis for a large number of commercially important materials such as foams, adhesives and coatings. Blends of polymers, fillers, surfactants, flow modifiers, crosslinkers, chain extenders and reactive isocyanates are used to prepare these materials. However, polymer blends are not typically thermodynamically stable, forming phase-separated morphologies. Formation of specific morphologies is responsible for the performance of many materials but despite the wide range of applications for polyurethanes, the relationship between phase behavior, chemical reaction and morphology is not well understood. This work is focused on understanding the influence of the reaction products formed in a model ternary reactive polyurethane based polymer blend on the evolution of blend miscibility and morphology. The ternary blend systems are composed of polypropylene glycol, an aliphatic polyester diol and an acrylic co-polymer, a system simple enough to conduct fundamental studies and complex enough to represent commercial systems. The effects of the polyester chemical structure, specific interactions from urethane groups and polyether molecular weight on ternary blend miscibility and the relationship between the ternary blend miscibility in the melt and morphology are given principal emphasis. It was found that the length of the methylene segments in the aliphatic polyesters dramatically changes the miscibility of the ternary blends in the melt. A thermodynamic treatment based on a modified Flory lattice model was used to describe the free energy of mixing for the polymer blends and calculate phase diagrams for ternary blends containing different polyurethane reaction products. When reactions are initiated strongly interacting urethane groups are generated and modify the enthalpic interactions present. Interacting groups generally improve polymer blend miscibility. The polyurethane reaction also increases the molecular weight of the starting materials, which has a deleterious effect on blend miscibility. The miscibility of ternary polymer blends is found to be sensitive to the balance of the competitive enthalpic and entropic contributions. As a result of this competition, the miscibility of the binary and ternary polymer blend systems can oscillate as chemical reaction proceeds.
Duffy, Daniel J, "Evolution of phase behavior and dynamics in reactive polymer blends" (2003). Doctoral Dissertations Available from Proquest. AAI3110481.