Advances in the design of co-poly(ether-imide) membranes for CO2 separations. Influence of aromatic rigidity on crystallinity, phase segregation and gas transport

Abstract

In our previous works, it was observed a clear relationship between the structure and the properties for different copoly(ether-imide)s, besides a good relation was found between SAXS characterization and permeability results. Here, a series of aliphatic aromatic copoly( ether-imide)s, based on an aromatic diamine (ODA), a diamine terminated poly(ethylene oxide) (PEO2000) of a molecular weight of 2000 g/mol and different aromatic dianhydrides (BPDA, BKDA (or BTDA) and PMDA) has been synthesized and characterized. The permeability for O2, N2, CO2 and CH4, increased with the rigidity of the monomers (BKDA < BPDA < PMDA), with the amount of PEO2000 in the copolymers, as well as with the increase in the temperature of treatment of the films. In this case, it was observed that when the proportion of PEO in the copolymer exceeded 50%, the permeability was similar for all samples, and the aromatic portion had no significant influence. Attending to glass transition temperature, Tg, of the aliphatic part, to its melting temperature, Tm, and to its crystallinity, segregation was better for more rigid dianhydrides at lower temperatures of treatment. Higher dianhydride rigidity produced better mechanical properties that were good but decreased a little bit when the percentage of PEO in the samples increased. Good permselectivity compromises were attained for the CO2/N2 separation. This work gives indications on how to design advanced materials for this separation with the increasing possibilities of controlled structure and properties.