Preparation of thin cation-exchange membranes using glow discharge plasma polymerization and its reactions

Thin cation-exchange films with Fixed sulfonic acid groups were prepared by plasma polymerization followed by hydrolysis of sulfonyl halide groups usi ng benzenesulfonyl fluoride and benzenesulfonyl chloride as starting materi als. For benzenesulfonyl fluoride, sulfonyl fluoride groups were introduced into the plasma-formed polymers, whereas benzenesulfonyl chloride tended t o decompose during plasma polymerization. The difference between the reacti on in the glow discharge plasma of benzenesulfonyl fluoride and that of ben zenesulfonyl chloride is discussed based on results obtained by in situ mas s spectrometry and molecular orbital calculations. For benzenesulfonyl fluo ride, the parent ion ([C6H5SO2F](+.)) is the major species which introduces the sulfonic fluoride groups into the plasma polymer because S-F bond clea vage is difficult. However, the parent ion of benzenesulfonyl chloride is u nstable in the glow discharge plasma, and cleavage of the S-C1 bond is faci le and produces Ci radicals. The plasma polymer formed at 3.5 W using benze nesulfonyl fluoride exhibits a cation-exchange capacity of 1.3 mequiv g(-1) after hydrolysis, which is comparable to the capacities of commercially av ailable cation-exchange membranes. (C) 2000 The Electrochemical Society. S0 013-4651 (99)05-046-6. All rights reserved.