Effects of packing density on the gas-transport properties of poly(phenolphthalein phthalate)s

The gas transport and other pertinent properties of three aromatic polyesters, made by reacting phenolphthalein with terephthaloyl chloride (PPha‐tere), 50:50 terephthaloyl and isophthaloyl chlorides (PPha‐50:50), and isophthaloyl chloride (PPha‐iso), are reported. The glass transition temperatures of PPha‐tere, PPha‐50:50, and PPha‐iso are 299, 279, and 249°C, respectively. Unexpectedly, the densities are 1.297, 1.298, and 1.304 g/cm3 in the same order; PPha‐iso, therefore, has a higher packing density than PPha‐tere. The permeability of PPha‐tere to CO2, CH4, N2, and O2 is roughly 25% higher than that of PPha‐50:50, and roughly 100% higher than that of PPha‐iso. PPha‐tere is roughly five times as permeable as polysulfone but has slightly higher permselectivities for the above gases. On the other hand, the solubilities of each gas in these three aromatic polyesters are roughly the same, suggesting that the higher permeability of PPha‐tere is the result of a much larger gas diffusivity in the polymer. It is shown here that the significant difference in gas‐diffusivity is a manifestation of the effects of packing density on the transport properties of glassy polymers.