Particles with a copolymer soft core of poly(n-butyl acrylate)/poly(methyl methacrylate) (PBA/PMMA) and a homopolymer hard shell of PMMA were characterized using transmission electron microscopy and solid-state NMR spectroscopy. Two synthesis parameters were investigated: (1) the phase ratio of the core and the shell and (2) the compatibility of the two phases. A series of core-to-shell ratios from 100/0 to 25/75 were synthesized and characterized. The compatibility between the phases was changed (1) by using acrylic acid in either the core and the shell or in both, (2) by synthesizing a homopolymer or a copolymer core or (3) by introducing crosslinking points in the core. The combination of transmission electron microscopy and solid-state NMR spectroscopy allows quantitative determination of the extent of coverage of the core by the shell polymer and the interphase thickness; both were found to depend on the shell content and the compatibility of the phases.

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A thermodynamic analysis and a mathematical model were developed to describe the free energy changes corresponding to various possible morphologies in composite latex particles. Two experimental composite latex systems were used to verify and establish limitations of the model. The,two latex systems were based on polystyrene/poly(methyl methacrylate), one prepared by conventional seeded emulsion polymerization and the second system by direct emulsification of a solution of a blend of the two polymers. The influence of several experimental parameters on latex particle morphology was investigated. These included monomer/polymer ratio, surfactant type, and initiator type in the seeded emulsion polymerization system. The influence of local viscosity, shear effects, and molecular weights of polymers were investigated in the artificial latex system.

SYNOPSISSemi-interpenetrating networks have been synthesized from vernonia oil-sebacic acid polyester network and poly (ethylene terephthalate) ( P E T ) . Bond interchange reactions during mixing of the two materials led to the formation of a miscible copolymer mixture, in which the vernonia oil was then cross-linked with sebacic acid. The materials were phase-separated, exhibiting two glass transitions, when the network was synthesized at 160°C, below the crystallization temperature of PET; however, a single stable glass transition ( T,) results after the material is heated to above the melting temperature of PET and cooled. When the vernonia polyester network was completely formed at 250°C, above the crystallization temperature of PET, noncrystalline, single-T, material was created. The two-phase semi-IPNs were much tougher than were their constituent materials, with the 50% semi-IPN over 15 times tougher than the PET from which it was made and over 50 times tougher than the neat vernonia oil elastomer, with tensile energy to break of 1780 kJ/m3. The single-T, material was nearly 2.5 times as tough as the two-phase material, with energy to break of 4400 kJ/m3. The microstructure of the two-phase 50% semi-IPN was investigated by transmission electron microscopy, which showed regularly shaped spherulites of 10-20 pm in diameter, as compared to irregularly shaped spherulites observed in a similar 50/50 castor oil urethane/PET semi-IPN, in which the network formed simultaneously with PET crystallization. Scanning electron microscopy of the semi-IPN fracture surfaces showed microscopic fibrils several hundred nanometers in diameter in both the two-phase and single-T, materials, although only the two-phase semi-IPN had a macroscopically rough surface.

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