Chemical modification of poly(2,6-dimethyl-1,4-phenylene oxide) by bromination-alkynylation

Preparation of Poly(phenylene oxide-gstyrenesulfonic acid) and their Characterization for DMFC Membrane

Well-defined poly(2,6-dimethyl-4,4′-phenylene oxide)-g-poly(styrenesulfonic acid) (PPO-g-PSSA) graft copolymer was synthesized via living radical polymerization. For the graft copolymer, poly(2,6-dimethylphenylene oxide) (PPO) was brominated first, and the brominated PPO (PPO-Br) was used as a macroinitiator in the atom transfer radical polymerization (ATRP) of styrenesulfonic acid sodium salt. The number of grafts per PPO chain and the molecular weight of the graft were controlled by adjusting the degree of bromination, and conversion in ATRP, respectively. The graft copolymers obtained were transformed into proton exchange membranes for direct methanol fuel cell (DMFC) application. The performance of the membranes was measured in terms of water uptake, proton conductivity, methanol permeability, and thermal stability. The water uptake, ion exchange capacity (IEC), and proton conductivity of the membranes increased with PSSA block content. Very low methanol permeability and good proton conductivity were observed by adjusting grafting frequency and PSSA block content.

Ion pair reinforced semi-interpenetrating polymer network for direct methanol fuel cell applications

This paper describes the synthesis of ion-pair-reinforced semi-interpenetrating polymer networks (SIPNs) as proton exchange membranes (PEMs) for the direct methanol fuel cells (DMFCs). Specifically, sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO), a linear polymer proton source, was immobilized in a brominated PPO (BPPO) network covalently cross-linked by ethylenediamine (EDA). The immobilization of SPPO in the SIPN network was accomplished not only by the usual means of mechanical interlocking but also by ion pair formation between the sulfonic acid groups of SPPO and the amine moieties formed during the cross-linking reaction of BPPO with EDA. Through the ion pair interactions, the immobilization of SPPO polymer in the BPPO network was made more effective, resulting in a greater uniformity of sulfonic acid cluster distribution in the membrane. The hydrophilic amine-containing cross-links also compensated for some of the decrease in proton conductivity caused by ion pair formation. The SIPN membranes prepared as such showed good proton conductivity, low methanol permeability, good mechanical properties, and dimensional stability. Consequently, the PPO based SIPN membranes were able to deliver a higher maximum power density than Nafion, demonstrating the potential of the SIPN structure for PEM designs.