When treated with compressed CO2, syndiotactic polystyrene (sPS) undergoes a number of solid-solid transitions that do not occur on treatment with liquid solvents. For example, planar mesophase f , R f , and γ f transitions can be brought about under appropriate conditions of temperature and CO2 pressure. In addition, the transitions of glassy sPS to the planar mesomorphic and to the R form, and the γ f R transition occur at temperatures lower than when the same transitions are effected under ambient pressure. The dissolved CO2 lowers the glass transition and the cold crystallization temperatures of sPS at the rate of -0.92 and -0.58°C/atm, respectively. Crystallization kinetics from the sPS-CO2 solution follow the Avrami equation, but the value of the exponent n is lower than when crystallization is conducted under ambient pressure.

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A magnetic suspension balance was used to measure solubility of CO2 in PMMA in the temperature range 0 to 167°C and at pressures to 61.2 atm. CO2 dissolves to considerable extent in PMMA, reaching a value of about 30 wt% at 0°C and 34 atm. Diffusion coefficients, derived from the sorption kinetics, were analyzed to extract glass transition temperature of the PMMA-CO2 system over the pressure range of 0 to about 60 atm. The results confirm the existence of retrograde vitrification in this system previously observed by creep compliance and high-pressure thermal analysis techniques. A fundamental understanding of the polymer-gas interactions has led to the development of novel, sub-micron cellular structures.

Free radical melt grafting of glycidyl methacrylate (GMA) onto polypropylene (PP) was studied. The extent of GMA grafting and the molecular weight of the functionalized PP copolymers were controlled by carefully manipulating various reaction factors, such as monomer concentration, initiator concentration, reaction temperature, and molecular weight of the starting PP homopolymer. The use of a second monomer, styrene, in the grafting process helped to increase GMA grafting further and reduce chain scission. The GMA modified PP copolymer was found to be able to reactively compatibilize PP/acrylonitrile‐co‐butadiene‐co‐acrylic acid rubber (NBR) blends. Up to an eight‐fold increase in the impact energy of the PP/NBR blend was obtained. The compatibilizing capacities of the reactive copolymers, in terms of impact energy improvement of the PP/NBR blend, were found not to be exclusively dependent on the total concentration of reactive functionalities in the matrix of the blend. The characteristics of the reactive copolymers, i.e., the extent of functionalization and the molecular weight, were found to have significant influences on the compatibilizing capacity. A large amount of moderately functionalized copolymer offers better compatibilization performance than a small amount of highly functionalized copolymer. A significant drop in impact energy was observed with declining molecular weight of the copolymer.