Development and characterization of sulfonated-unmodiftied and sulfonated-aminated PSU Udel® blend membranes

In the presented work, PSU Udel(R) which is a chemically and thermally stable arylene main-chain polymer was modified via the metalation-sulfochlorination (-esterification, -sulfonamide formation) and the metalation/amination route. The aminated PSU was stepwise alkylated to yield PSU with (a) -secondary and (b) tertiary amino groups. PSU(SO2X) (X=Cl, OCH3, NHC3H7) was hydrolysed with hot water or hot diluted sulfuric acid. From the modified polymers membranes were formed by blending the polymers as follows: (a) unmodified PSU/sulfochlorinated PSU; (b) PSU/PSU-SO2OCH3; (c) PSU/PSU-SO2NHC3H7. At these blends only physical crosslinking between the polymers occurs by entanglement of the blend components. (d) Li-sulfonated PSU/aminated PSU (PSU-NH2). (e) Li-sulfonated PSU/monomethylaminated PSU (PSU-NH(CH3). (f) Li-sulfonated PSU/di-methylaminated PSU (PSU-N(CH3)(2)). At the blend membranes (d)-(f) specific interactions between the polymer components occur by hydrogen bridges and after acidic post-treatment (see below) -polysalt formation by proton transfer from the SO3H to the amino group. The PSU/nonionic sulfonic acid precursor membranes were subsequently hydrolyzed to yield PSU/PSU-SO3H blend membranes. It was observed that the membranes containing PSU-SO2NHC3H7 could be hydrolyzed only to a small extent to the sulfonic acid tinder the applied hydrolysis conditions. The blend membranes (d)-(f) were post-treated in 10% HCl to obtain the H+ form of the membranes. The ion-exchange capacity of the blends was adjusted by variation of the substitution degree of the modified polymers and by variation of the blend composition. The membrane-blends were characterized by impedance spectroscopy, thermogravimetry and by transmission and scanning electron microscopy. From the investigations it can be concluded that it is advantageous for the mechanical stability of the blends when there is not only entanglement between the polymeric chains of the blend components (as it is the case for the blend membranes (a)-(c)). The swelling degree of the acid-base blends (d)-(f) is lower than the swelling degree of the blends (a)-(c) at the same ion-exchange capacity, leading to better mechanical stability of the acid/base blend membranes (d)-(f). (C) 2001 Elsevier Science B.V. All rights reserved.