On the influence of the proportion of PEO in thermally controlled phase segregation of copoly(ether-imide)s for gas separation

A complete series of aliphatic aromatic copoly(etherimide)s, based on an aromatic dianhydride (BPDA), an aromatic diamine (ODA) and a diamino terminated poly(ethylene oxide) (PEO2000) of 2000 g/mol molecular weight, using different PEO contents, has been synthesized. Cast films of these copolymers have been thermally treated and characterized by FTIR-ATR, DSC, TGA and SAXS. It has been found that there is a direct relationship between phase segregation and permeability for increasing treatment temperatures. Results show that permeability is higher when PEO content increases in the copolymer. Selectivity for O2/N2 and CO2/CH4 gas pairs follows the same tendency, while those for CO2/N2, and CH4/N2 give higher selectivities for intermediate (30–40%) PEO contents. Especially promising are the results for these two pairs of gases because materials with high permeability with high selectivity can be obtained. The Maxwell model has been applied to predict permeability (for CO2, CH4, O2 and N2) from known data for pure BPDA–ODA and neat PEO and it has been found that assuming PEO as the dispersed phase, the use of this equation is adequate for percentages up to approximately a 40% over which we should assume that it is the aromatic part of the copolymer which plays the role of dispersed phase.