By removing anhydride groups from crosslinked copolyimide membranes at 430 degrees C, partially pyrolysed membranes were obtained and gas separation properties were evaluated and related to the content of labile groups. The spaces occupied by the linking anhydride groups prevailed as micropores, which greatly improved the gas transport properties. The release of the labile groups was confirmed by TGA and FT-IR spectroscopy which permitted us to establish that polymer main chains did not suffer any substantial change during the pyrolytic treatment. During the heating step new cross-linking points are created, no Tg below 450 degrees C could be observed and the process prevents the collapse of micropores. The pyrolysed membrane obtained from the precursor with the lowest content of anhydride groups showed the highest permeability values: 101, 25, 17 and 446 barrers to O-2, N-2, CH4 and CO2 respectively, and a selectivity to CO2/CH4 of 26, good enough to place this membrane close to Robeson's new upper bound (2008), while the crosslinked precursor membrane fell below Robeson's old upper bound (1991). (c) 2012 Elsevier Ltd. All rights reserved.

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-PEO-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 N-2) 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 does not depend on the PEO length in the copolymer. Remarkable are the results for the CO2/N-2 gas pair, with selectivity-versus-permeability very near to the Robeson's upper bound at 30 degrees C and even in closer proximity to the corresponding trade off line for higher permeation temperatures. (C) 2013 Elsevier Ltd. All rights reserved.

Two novel copolyimides bearing bulky pendent groups have been prepared by chemical modification of a copolyimide precursor containing carboxylic acid groups. The incorporation of the bulky groups was achieved by esterification of the copolyimide containing carboxylic acid groups with 4-tert-butylbenzyl alcohol. By controlling the carboxylic acid/alcohol ratio, two different degrees of modification were obtained The actual composition of the modified polymer was estimated by H-1 NMR. They showed better solubility than the copolyimide precursor where 100% modification yielded the copolyimide with the highest solubility properties. Thermal analyses indicated that the incorporation bulky pendent groups has a moderate effect on decreasing the thermal degradation temperature and the glass transition temperature. (C) 2007 Published by Elsevier Ltd.

A series of aromatic polyimides has been obtained by the reaction of two dianhydrides, the commercial 2,2'-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and another having a 5'-tert-butyl-m-terphenyl moiety (BTPDA), with several diamines, including two that have a cardo structure (derived from 9H-fluorene), one of them bearing methyl groups ortho to the amino functionalities (TMeCardo). The solubility, and also the thermal, mechanical, and gas separation properties of the corresponding polyimide membranes were evaluated and compared in order to explore the effect of the different groups in the polyimide backbone. The novel polyimides, which were derived from BTPDA and the cardo diamines, showed high thermal stability, excellent solubility in organic solvents and good gas separation properties, especially the polyimide that bore the ortho methyl substituents. The behavior was especially good for the pair O-2/N-2, where the TMeCardo polymer overpassed the Robeson upper bound.