Copolymerization of vinyl chloride with trans-1,2-dichloroethylene was camed out at various temperatures, and the properties of the copolymers obtainkd by the emulsion copolymerization at low temperature were examined. In the case of bulk mpolymerization a t temperatures higher than room temperature, the rate of polymerization, the equilibrium conversion, and [q] were lowered with increasing content of tmm-l,2dichloroethylene in the initial monomer mixture, but the T, and softening point of the copolymers containing about 15% of 1,2-dichloroethylene unit were about 10°C. higher than these of conventional PVC resin, in spite of their inability to form films. The monomer reactivity ratios at 50°C. were 5.39 (VC) and 0.072 (trans-DCE). Emulsion copolymerization was carried out at -3OOC. with the use of a redox initiator system (hydrogen peroxide-ferrous sulfate-ascorbic acid), in order to increase both the [3] and the rate of polymerization. The copolymers prepared at low temperature had higher T, and better solubility than the VC homopolymer polymerized a t the same condition or conventional PVC resin. The results of the infrared absorption spectra, the solubilities, and the calculation of sequence length of VC monomer unit in the polymer chain indicated that the stereoregularity and the crystallinity of the low temperature copolymers were lower than those of the low temperature T'C homopolymers. It was concluded that higher T, and good solubility of the low temperature copolymer were bmught about by the prevention of the free rotation of the polymer chain by the random distribution of 1,2dichloroethylene units in the polymer chain.