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KEY WORDSPlasticization / CO2 / Glassy Polymer / Glass Transition Temperature / It is well-known that sorption of vapors and liquids in polymers can cause significant plasticization resulting in substantial decrease in the glass transition temperature ( Tg). 1 -4 Such effect is slight in the sorption of gases in polymers since the solubility level is quite low. However condensable gases like CO 2 with high critical temperature are, in general, considerably soluble, particularly in glassy polymers. Correspondingly, it has been reported that glassy polymers are plasticized by sorbed CO 2 at high pressure. Physical properties such as gas sorption and permeation are markedly influenced by the plasticization of glassy polymer by sorbed CO 2 . 5 -12 Investigations on the plasticization of glassy polymer at high CO 2 pressure have been carried out. 13 -17 It is of interest as to how much Tg may be reduced by sorbed CO 2 . However, it is difficult to determine Tg of glassy polymers at CO2 high pressure and only a few studies have been reported by Wonders et al. They showed that Tg of polycarbonate sorbed at 6.8 atm was 8~ 9"C lower than that in the absence of CO2 using a special differential thermal analyzer. 14 Wang et al. have also reported that the re-• To whom all correspondence should be addressed.Polym. J., Vol. 22, No. I, 1990 duction of Tg of polystyrene in the presence of CO 2 was estimated by the change in mechanical relaxation behavior. 15 Chiou et al. have furthermore reported in detail that the variation of Tg of various glassy polymers caused by sorbed CO 2 at the pressure range up to 25 atm was determined using a differential scanning calorimeter (DSC) . 16 How ever there are few investigations on the variation of Tg of glassy polymers having relatively high Tg at higher CO 2 pressure.Here we report on the variation of Tg of various engineering plastics having relative high Tg by CO 2 sorbed under 60 atm at 25' C and a skillful method to determine Tg of glassy polymers using DSC in the range up to 60 atm.The determination of Tg of various glassy polymers using DSC (SSC-560, Seiko Electronics Co., Ltd.) was carried out as follows. A glassy polymer film and dry ice (CO 2 ) were placed in a pressure-sealable aluminium pan which was sealed completely by an aluminium lid. The CO 2 pressure in the pan was controlled by the amount of dry ice. To evaluate the CO 2 pressure in the pan, the van der Waals equation, which can express satisfactory real 77

We examined the influence of polyaniline (PAn)'s unit sequence and doping with low molecular weight dopants or polymer dopants on permeation property. It was found that CO2 permeability was increased by the formation of a quinonediimine unit in PAn with the oxidation. CO2 sorption amount of PAn was decreased by oxidation. The increase of CO2 permeability with oxidation, therefore, resulted from the increase of diffusivity, which was attributable to morphological variation by the increase of a quinonediimine unit. The permselectivity of PAn films was found to be remarkably improved by doping. In particular, the selectivity value of the PAn film doped with polyvinyl sulphonic acid as a polymer dopant went up to over 2,000. This remarkable increase of selectivity was found to result in the increase of selectivity, depending on diffusivity. It was also found that the permselectivity of the PAn film doped by polymer dopants was surpassed, as compared with that doped by low molecular dopants. © 1995 John Wiley & Sons, Inc.

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ABSTRACT:To elucidate the mechanism of gas sorption in polymer blends in glassy and rubbery states, CO2 sorption· of polystyrene [PS] (T. 75°C), pol;y(vinylmethylether) [PVME] (T. -26°C), and their blends was studied at 25°C and the influence of the single-phase or separated-phase of their blends on sorption properties was also investigated. The solubility in the rubbery polymer blends obeyed Henry's law and that in the glassy blends were described well by the dual-mode sorption model _which consists of two contributions of Henry's law mode and Langmuir mode sorption applied often to glassy polymer-gas systems. The dual-mode sorption parameters were obtained by a curve fitting of experimental data to the theoretical curve. The value of Henry's law constant k0 of the single-phase polymer blends deviated negatively from semilogarithmic additivity. The k0 of the phase-separated blends was slightly higher than that of single-phase blends and was smaller than the semilogarithmic additivity, reflecting that the single-phase blends did not separate completely to the pure polymer phases of PS and PVME but to two mixed phases. The Langmuir sorption capacity term CH' of single-phase or phase-separated blends was proportional to (T. -25°C) of each phase, irrespective of the single-phase or separated-phase and the CH' became zero at the temperature above the T •.

Sorption and permeation of CO2 in various annealed polyimide (PI) films were investigated. Dual‐mode sorption and partial immobilization models were used to analyze the data. Sorption of CO2 in PI film quenched from above the glass transition temperature (Tg) is greater than in film as received. In fact, sorption is decreased over the entire pressure range by cooling the film slowly. These changes in sorption of CO2 can be attributed to a change in the Langmuir sorption capacity C′H by annealing, since the other dual‐mode sorption parameters, kD and b, are almost independent of annealing. The value of C′H is increased by quenching, and decreased by slow cooling from above Tg. The two diffusion coefficients DD and DH according to the Henry and Langmuir modes, respectively, for CO2 also depend markedly on annealing. Diffusion coefficients of quenched PI films are increased and those of film cooled slowly are decreased compared with values for PI film as received. The change in DH is larger than that in DD. The permeability coefficient of quenched PI films at 100 cmHg is about 1.7 times that of PI film as received. The film structure formed by quenching can enhance permselectivity.