Preparation And Modification Of Proton Exchange Membranes Based On Side-chain-type Sulfonated Poly(Arylene Ether Sulfone)s

Currently, perfluorinated polymer membranes have been widely used as polymer electrolyte membrane in fuel cells for their excellent chemical and physical stability, high proton conductivity under low humidity, for example, Nafion and Flemion series. However, they are also limited by some shortcomings such as low operating temperature (0-80℃), high cost and high fuel permeability. To overcome these drawbacks, many low-cost, high-efficiency aromatic proton exchange membranes have been developed.This paper dedicates to developing new side-chain-type proton exchange membrane materials, combining with crosslinking and blending modifications. The structure-property relationship for the prepared membranes are investigated in details, including proton conductivity, water uptake, dimensional changes, hydrolytic stability and mechanical strength.First, a series of novel side-chain-type sulfonated poly(ether sulfone)s (SPES-NDS) copolymers were successfully synthesized by nucleophilic substitution reaction from 4,4’-sulfonyldiphenol, decafluorobiphenyl and 2-naphthol-6,8-disulfonic acid di-potassium salt. The as-prepared membranes with ion exchange membrane (IEC) of 1.22-2.07 mmol/g showed very low water uptake (27-58%) and good dimensional stability. The membrane of SPES-NDS60 (1.68 mmol/g) displayed water uptake of 40% and its proton conductivity reached 124 mS/cm in water at 60 ℃. The membranes with IEC<1.68 mmol/g exhibited excellent hydrolytic stability, suggesting its good potentials for fuel cell applications.Secondly, a series of blend membranes with various mass ratios were successfully prepared from SPES-NDSx and sulfonated polyimide (SPI). The results showed that by the introduction of SPI, the dimensional stability and mechanical properties of the blend membranes had been greatly improved, as well as the hydrolytic stability. After the treatment in water at 140℃ for 24h, all the blend membranes still kept excellent water stability, their weight losses were controlled within 6%. Although the proton conductivities of the blend membranes decreased with the increasing of SPI, the whole SPES-NDS70/SPI series have shown proton conductivities higher than Nafion112.Finally, a series of graft-crosslinking sulfonated poly(aryl ether sulfone) proton exchange membranes (bSPAES) with various sulfonation and crosslinking degrees were successfully prepared. In the bSPAES, the non-sulfonated polymer was used as the main chain, while the sulfonated polyoligomer was used as the side chain and crosslinking reagent simultaneously. All the bSPAES membranes exhibited excellent dimensional stability and hydrolytic stability due to the side chain and the crosslinking structure. Meanwhile, bSPAES membranes showed relatively high conductivities under lower IEC levels, wherein, bSPAES-5/5 exhibited equivalent conductivity to Nafion112 over the entire temperature range, and showed better dimensional stability than Nafion112 at the same time.