GAS-TRANSPORT PROPERTIES OF A SERIES OF POLY(ETHER KETONE) POLYMERS

The gas sorption and transport properties of a series of poly(aryl ether ketone) materials are reported. In this series, the isopropylidene groups (-C(CH3)2-) in the backbone are systematically replaced with a hexafluoroisopropylidene group (-C(CF3)2-). Dynamic mechanical analysis and differential scanning calorimetry were used to show that the substitution of -C(CF3)2- for -C(CH3)2- units results in a stiffer polymer chain. Free-volume calculations show that the substitution opens up the polymer structure and leads to an increase in diffusion coefficients. Methane and carbon dioxide sorption measurements were made to examine the solubility and diffusivity contributions to the permeability. The permeability increases as -C(CF3)2- units replace the -C(CH3)2- groups and, in general, it is the increase in diffusivity that accounts for the permeability increase. Along with the increase in permeability is an increase in the selectivity for gas pairs like helium/methane and carbon dioxide/methane. This simultaneous increase in permselectivity and permeability when -C(CF3)2- units replace -C(CH3)2- units seems to be a general trend, as it has been observed for polycarbonate and polysulphone materials as well.