Differences in the Synthetic Method Affected Copolymer Sequence and Membrane Properties of Sulfonated Polymers

The versatility of the synthesis of sulfonated aromatic polymers using NiBr 2 was investigated. The copolymerization of sulfo-dichlorobenzene protected with a neopentyl group was carried out with chlorine-terminated oligomer (1) or three different comonomers (2, 3, 4). The copolymerization proceeded well to obtain high molecular weight copolymers (M-n = 4.83-60.1 kDa, M-W = 24.9-133 kDa) and provided flexible membranes, comparable to those obtained with Ni(0) as a polymerization promoter. (HNMR)-H-1 spectra suggested differences in the comonomer sequence between the copolymers synthesized with Ni(II) and Ni(0). The sequence was quantified as a randomness of sulfophenylene (SP) unit and correlated with the membrane properties. The randomness of SP unit in the sulfonated polyphenylene copolymer (SPP-QP) did not affect the phase-separated morphology under the thy-state as suggested by TEM images. SAXS analysis under humidified conditions revealed that the SPP-QP with lower randomness of SP unit formed higher periodicity in the self-assembling structures (i.e., the uniform-sized ionic clusters). The increase of the randomness of SP unit from 19% to 47% in SPP-QP caused decrease of the proton conductivity (at 80 degrees C and 20% RH) by a factor of 1/1.7 and decrease of the elongation (at 80 degrees C and 60% RH) by a factor of 1/27. Similar tendency was observed for other series of the sulfonated copolymer membranes.