The effect of crosslinked networks with poly(ethylene glycol) on sulfonated polyimide for polymer electrolyte membrane fuel cell

Abstract

To investigate the effect of crosslinking by a hydrophilic group on a sulfonated polyimide electrolyte membrane, sulfonated polyimide end-capped with maleic anhydride was synthesized using 1,4,5,8-naphthalenetetracarboxylic dianhydride, 4,4 0diaminobiphenyl, 2,2 0 -disulfonic acid, 2-bis [4-(4-aminophenoxy)phenyl] hexafluropropane and maleic anhydride. The sulfonated polyimides end-capped with maleic anhydride were self-crosslinked or crosslinked with poly(ethylene glycol) diacrylate. A series of the crosslinked sulfonated polyimides having various ratios of sulfonated polyimide and poly(ethylene glycol) diacrylate were prepared and compared with uncrosslinked and self-crosslinked sulfonated polyimides. The synthesized sulfonated polyimide films were characterized for FTIR spectrum, thermal stability, ion exchange capacity, water uptake, hydrolytic stability, morphological structure, and proton conductivity. The formation of sulfonated polyimide was confirmed in FTIR spectrum. Thermal stability was good for all the sulfonated polyimides that exhibited a three-step degradation pattern. Ion exchange capacity was the same for both the uncrosslinked and the self-crosslinked sulfonated polyimides (1.30 mEq/g). When the crosslinked sulfonated polyimides with poly(ethylene glycol) were compared, the ion exchange capacity was decreased as 1.27 > 1.25 > 1.23 mEq/g and water uptake was increased as 23.8 < 24.0 < 24.3% with the increase in poly(ethylene glycol) diacrylate content. All the crosslinked sulfonated polyimides with poly(ethylene glycol) diacrylate were stable for over 200 h at 80 8C in deionized water. Morphological structure and mean intermolecular distance were obtained by WAXD. Proton conductivities were measured at 30, 50, 70 , and 90 8C. The proton conductivity of the crosslinked sulfonated polyimides with poly(ethylene glycol) diacrylate increased with the increase in poly(ethylene glycol) diacrylate content despite the fact that the ion exchange capacity was decreased.

Water Soluble Polymers as Proton Exchange Membranes for Fuel Cells

“…Polymers 2012, 4 920 stability without compromising proton conductivity or brittleness [47][48][49][50]. Compared to using rigid arylene polymers as crosslinkers, the crosslinked membranes with PEG become more flexible and show a greatly reduced water uptake and swelling ratio with only a slightly sacrifice in proton conductivity [51].…”

“…The numerous crosslinked membranes that have been designed with a view to meeting these requirements include common chemical networks (a polymer comprising only one network without a linear polymer entrapped within the network polymer) [121][122][123][124], interpenetrating polymer networks (IPNs) [68,125] and semi-IPNs [126][127][128]: an illustrated common polymer network and the associated IUPAC polymer network definition are shown in Figure 6 [129]. A possible drawback to the use of cross-linked polymers is that the crosslinking might hinder the mobility of ions and hence lower the final conductivity.…”

“…PEG is generally used as a crosslinker and has been introduced into several sulfonated polymer matrices, such as sulfonated polyimide (SPI) [47], poly [(maleic anhydride)-alt-styrene-co-(2-acrylamido-2-methyl-1-propanesulfonic acid)] (PMA-alt-PS)-co-PAMPS [48], sulfonated poly (arylene ether ketone) (SPAEK) [51] and sulfonated poly (ether ether ketone) (SPEEK) [50], to improve the membrane's mechanical and hydrolytic stabilities while reducing methanol crossover without compromising proton conductivity and brittleness. (Figure 8 and Table 4; 11-14) Thus, Yang et al [47] prepared a series of crosslinked SPI/PEG membranes with various ratios of maleic anhydride SPI and PEG diacrylate as PEMs (Table 4; 11). Their results showed that the water uptake (from 23.8 to 24.3%) and the proton conductivity increased with increasing contents of PEG (from 0 to 25 wt%) despite a decrease in the ion exchange capacity (IEC) (from 1.27 to 1.23 meq•g −1 ) and an increase in the crosslinking density.…”

Synthesis and properties of novel multiblock copolyimides consisting of benzimidazole-groups-containing sulfonated polyimide hydrophilic blocks and non-sulfonated polyimide hydrophobic blocks as proton exchange membranes

“…However, high IEC often causes excess swelling or even dissolution of the membranes. To reduce swelling ratio while maintaining high IECs, many approaches have been proposed such as ionic cross-linking [19][20][21], covalent cross-linking [14,[22][23][24][25][26][27][28][29], preparation of composite membranes [30][31][32][33] and block copolymerization [34][35][36][37][38][39][40][41][42][43]. It has been recognized that the existence of ionic channels in PEMs can facilitate proton transport resulting in high proton conductivity.…”

Physical and mechanical properties of sulfonated aromatic copolyimide membranes

“…The stability of polyimide film in water mainly depends on the sulfonation content and polymer chain flexibility [17]. In other word, the stability in water is directly proportional to flexibility of monomers (polymer chain), due to better standing on bending operation in mechanical test [18].…”