Influence of the PEO length in gas separation properties of segregating aromaticaliphatic copoly(ether-imide)s

Abstract

A complete series of aliphatic-aromatic copoly(ether-imide)s has been synthesized in this work. All these copoly(ether-imide)s had the same structure, BPDA-PEOX-ODA, but different lengths of PEO in the final polymer. These copolymers have been thermally treated and characterized by several techniques. A direct relationship between the temperature of treatment, the improvement of phase segregation, and permeability has been demonstrated. The Maxwell model has been applied to predict permeability (for CO2, CH4 and N2) and it has been found that when the segregated PEO can be considered to be amorphous – it is at high temperatures when crystallinity disappears – the model fits reasonably well. This confirms that the aliphatic and aromatic portions of the copolymer behave approximately as a bi-phase of disperse domains within a continuous matrix. Results show that permeability is higher when the PEO chains are longer – when there is no crystallinity, or any kind of internal bonds, distorting the results – while selectivity doesn´t depend on the PEO length in the copolymer. Remarkable are the results for the CO2/N2 gas pair, with selectivity-versus-permeability very near to the Robeson‘s upper bound at 30 ºC and even in closer proximity to the corresponding trade off line for higher permeation temperatures.