GAS-INDUCED PLASTICIZATION AND THE PERMSELECTIVITY OF POLY(TETRABROMOPHENOLPHTHALEIN TEREPHTHALATE) TO A MIXTURE OF CARBON-DIOXIDE AND METHANE

A high glass transition temperature (T(g) = 319-degrees-C), rigid-chain polymer, poly(tetrabromophenolphthalein terephthalate) (TBrPPha-tere), was synthesized and characterized by IR, H-1 NMR, intrinsic viscosity, GPC, DSC, and density measurements. Its permeability to pure carbon dioxide, pure methane, pure ethane, and a mixture of carbon dioxide and methane (32.3 mol % CO2) at 35-degrees-C was investigated. Despite its rigid backbone, TBrPPha-tere's permeability to either pure carbon dioxide or pure ethane showed a minimum at approximately 10 atm when measured as a function of the gas pressure. The normalized diffusion coefficient, D(c)/D(c = 0), of ethane increased more than 60 times over a small concentration range (approximately 3.5 wt %), reflecting the effects of "gas-induced plasticization". Moreover, the mixed-gas permeabilities of carbon dioxide were much less than the corresponding pure-gas values at the same partial pressures. There also was not an upturn in the mixed-gas CO2 permeability when the partial pressure of carbon dioxide was raised up to 15 atm. In contrast, the mixed-gas permeability of methane increased with methane partial pressure and surpassed its pure-gas value at the same partial pressure. The limitations of models based on Fick's first law for describing these mixed-gas permeability data are also addressed.