Polymer-Polymer Interactions, Phase Behavior, and Interfaces

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9726484 Paul The rational development of multicomponent polymer blends (or alloys) requires an understanding of the polymer-polymer interactions involved and how to control them in order to generate materials with useful mechanical properties, obtain optically clear mixtures. (miscibility), disperse impact modifiers in a brittle matrix, reactively compatibilize immiscible mixtures, etc. This proposal outlines a program for obtaining quantitative information on the interactions between pairs of a number of important polymer repeat units. The methodology involves experimental observations of the phase behavior of blend systems that are analyzed in terms of appropriate theories of mixing combined with a mean field binary interaction model. The experimental methods involve copolymer composition mapping, the critical molecular weight method, quantitative analysis of phase diagrams, light scattering, and neutron reflectivity. Specific objectives involve (a) comparison of interactions of acrylate and methaclylate monomer units having various pendant groups with other polymers, (b) effect of bromine atoms in the repeat unit on interactions with other polymers, (c) development of reactive copolymers that are miscible with styrene/acrylonitrile copolymers (SAN) for use in reactive compatibilization of engineering thermoplastics with ABS materials, and (d) comparison of polymer-polymer interfacial thicknesses measured by neutron reflectivity with those predicted from theory using interaction energies determined in this program. The neutron reflectivity studies will be performed on pairs of commercially important polymers like polycarbonate, poly(phenylene ether), etc. with copolymers, e.g., styrene with acrylonitrile, maleic anhydride, etc. The experiments will be done in collaboration with the National Institute of Standards and Technology and industry. In addition, the research will make a systematic study of the kinetics of phase separation of selected blends using a recently constructed light scattering apparatus. This will provide accurate assessment of spinodal temperature-composition curves for use in evaluation of interaction energies as well as information about polymer-polymer diffusion coefficients. %%% The results of this fundamental research will be quantitative information about interactions between polymer repeat unit pairs for use in designing homogeneous or phase separated polymer blends (or alloys) that either are or may be of technological importance. This research will provide a valuable educational experience for students at all levels including postgraduate, PhD, undergraduate, and high school. ***