Abstract
Two series of disulfonated iptycene-based poly(arylene ether sulfone) random copolymers, i.e., TRP-BP (triptycene-based) and PENT-BP (pentiptycene-based), were synthesized via condensation polymerization from disulfonated monomer and comonomers to prepare proton exchange membranes (PEMs) for potential applications in electrochemical devices such as fuel cell. To investigate the effect of iptycene units on membrane performance, these copolymers were systematically varied in composition (i.e., iptycene content) and the degree of sulfonation (i.e., 30–50%), which were characterized comprehensively in terms of water uptake, swelling ratio, oxidative stability, thermal and mechanical properties, and proton conductivity at various temperatures. Comparing to copolymers without iptycene units, TRP-BP and PENT-BP ionomers showed greatly enhanced thermal and oxidative stabilities due to strong intra- and inter-molecular supramolecular interactions induced by hierarchical iptycene units. In addition, the introduction of iptycene units in general provides PEMs with exceptional dimensional stability of low volume swelling ratio at high water uptakes, which is ascribed to the supramolecularly interlocked structure as well as high fractional free volume of iptycene-based polymers. It is demonstrated that the combination of high proton conductivity and good membrane dimension stability is the result of the synergistic effects of multiple factors including free volume (iptycene content), sulfonation degree, hydrophobicity, and swelling behavior (supramolecular interactions).
Highlights
With the increasing world population and limited fossil energy sources, clean, and sustainable energy has become a hot topic (Dincer, 2000; Omer, 2008; Chu and Majumdar, 2012)
It should be noted that the molar content of TRP or PENT in the copolymers was limited due to the relatively low reactivity between TRP/PENT and SDCDPS as well as the low solubility of pentiptycene-based polymers, which prevented the formation of polymers with sufficiently high molecular weight for film casting
The relatively lower intrinsic viscosity (IV) values of TRP/PENT-BP series compared to the BPSH series indicating lower molecular weight than BPSH series due to lower reactivity of TRP and PENT series caused by the steric hindrance and poor solubility
Summary
With the increasing world population and limited fossil energy sources, clean, and sustainable energy has become a hot topic (Dincer, 2000; Omer, 2008; Chu and Majumdar, 2012). At given degree of sulfonation, the dry membrane densities of iptycene-containing copolymers, both TRP-BP series and PENT-BP series were all lower than BPSH series without iptycene moieties.
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