Oxidative polymerization of diphenyl disulfide under molten conditions at moderately elevated temperatures gave poly(1,4-phenylene sulfide) (PPS), using a vanadyl complex strong acid catalyst with oxygen as the ultimate oxidant. Origin of the selectivity of the sulfonium electrophile for the formation of the 1,4-thiophenylene chain, characterized by the presence of a disulfide bond at the chain end, was determined by the behavior of polymerization and structural analysis of the product together with a computational calculation, which revealed a unique chain growth-type polycondensation process.