Poly(dichlorobutane sulfide) I and poly(dichlorobutane disulfide) II have been prepared in 97% yield by addition copolymerization of butadiene with sulfur dichloride and sulfur monochloride, respectively. The polymers were characterized by elemental analysis, infrared spectrum, inherent viscosity, and thermogravimetric analysis. The reactions of several dienes with sulfur dichloride (but not with sulfur monochloride) have been reported in the literature. All were reported to give mainly the intramolecular addition products. However, it has very recently been found that diolefins with double bonds rigidly separated from each other, or with double bonds so situated that intramolecular reaction is thermodynamically unfavorable, preferentially undergo polymerization with sulfur monochloride or sulfur dichloride. In the case of butadiene, polymerization is thermodynamically more feasible than intramolecular addition due to the dipole repulsion and eclipsing chain which would be present in the intramolecular reaction products.