The mechanism of polymerization reaction of 2,5-bis(tetrahydrothiopheniomethyl)furan dichloride was studied kinetically. The reaction proceeds by the (E1cb)(irr) mechanism to afford a 2,5-dihydrofuran intermediate M, which undergoes a free radical polymerization reaction. Comparison of the kinetic results reveals that the rate of elimination reaction increases, whereas that for the subsequent polymerization reaction decreases as the aromatic moiety of the bis(sulfonium) salts is changed from phenyl to thiophene to furan. The results have been attributed to the decreased resonance energy of the aromatic rings.