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.

No abstract

No abstract

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.

The vapor-liquid equilibria of HCFC 142b, HFC 134a, HFC 125 and isopropanol in polystyrene were determined in a closed high pressure vessel at temperatures up to 220°C. Complete solubility maps are presented for each blowing agent, including conditions for phase separation in the polystyrene phase. In order of decreasing solubility, the blowing agents rank isopropanol > HCFC 142b > HFC 134a > HFC 125. In the cases of isopropanol and HFC 134a, some solubility results obtained by the vapor pressure method and those using a high-pressure electrobalance are compared.

The solubility of CO, in PETG, a glycol-modifled PET, was measured at different tempentures and over a broad pressure range, and diffusion coefficients were derived at the corresponding conditions. The solubility of CO, is quite high. For example, almost 15 wt% CO, can be dissolved in PETG at 35°C and 6.0 MPa. Consequently, CO, is a god blowing agent for PETG. Cellular foams in the density range of about 0.04 to 1.2 g/cm3 and cell diameters in the range of about 10 to 150 pm were produced. The foam density and the cell size were found to depend on the foaming temperature and time, with larger cells obtained at higher temperatures or when the sample was foamed for a longer time. The foam density decreased with an increase in the foaming temperature to about 90°C beyond which the density tended to increase slightly due to the cell collapse or coalescence. The density reduction also depended on the pressure at which the polymer was saturated with CO,; the higher the saturating pressure at a given temperature, the greater the density reduction.

No abstract