Influence of Pressure Conditioning on the Gas Transport Properties of Imidized Polyamic Acid Films

Abstract

ABSTRACT:The influence of pressure conditioning on the gas transport properties of various imidized polyamic acid [PAA] films was investigated. The variation of sorption and permeation caused by CO2 pressure conditioning was interpreted using dual-mode sorption and partial immobilization models. The sorption amount of CO2 at 25"C of unimidized PAA film increased markedly by pressure conditioning above 30atm of CO2 • It was found that unimidized PAA film was plasticized at 25' C at a pressure above 30 atm of CO2 and the film cooled relatively quickly to liquid N2 temperature and possibly contain a frozen microvoid or free volume between polymer segments. The sorption amount of CO2 of imidized PAA films also increased by pressure conditioning at 60 atm of CO2• This can be attributed to increase of unrelaxed volume due to pressure conditioning as shown by increase of Langmuir sorption capacity CH'· The increase in CH' of pressure conditioned films with low imide content was larger than that with high content. T.he diffusion coefficients of Henry and Langmuir modes of CO2 for imidized PAA film, D0 and DH, also increased by pressure conditoning. The increase of DH of each imidized PAA film was more marked than that of D0 • KEY WORDS Sorption / Diffusion / Polyamic Acid / Imidization / CO2 / Plasticization / Pressure Conditioning/ Langmuir Sorption Capacity Term/ It is well-known that sorption and permeation of gases in glassy polymer films are quite different from those in rubbery polymer films. This difference can be attributed to the fact that glassy polymers have unrelaxed volume or microvoid frozen in nonequilibrium state between segments. In general, the transport properties of glassy polymers have been analyzed on the basis of the dual-mode sorption 1 ·2 and partial immobilization models. 3 We reported that the nonequilibrium state varied by "thermal conditioning", e.g., quenching from above the glass transition temperature (Tg) or sub-Tg annealing. 4 -7 It was found that gas transport properties were influenced by nonequilibrium nature. Namely, gas solubility and diffusivity were enhanced by quenching from above Tg and decreased by sub-Tg annealing, reflecting that unrelaxed volume varies by thermal conditioning.

Characterization of the microvoids of a tetramethyl polycarbonate/polystyrene blend system using Xe sorption measurements and 129Xe NMR spectroscopy

“…[1][2][3] The microvoids significantly affect the gas permeation, diffusion and sorption properties of glassy polymers. [4][5][6] In other words, the gas sorption property of a glassy polymer can provide information about the microvoids. Generally, the gas sorption isotherm of a glassy polymer can be interpreted using the dual-mode sorption model, [1][2][3][4][5][6][7] which is represented by the following equation,…”