AbstractThe properties of chlorinated and chlorosulfonated ethylene polymers and copolymers have been examined. The effect of such variables as polymer chain structure, molecular weight, degree of chlorination, and chlorination conditions was studied. A variation in physical properties of different polyolefins chlorinated to the same degree is attributed to differences in residual crystallinity in the chlorinated product. Chlorinated linear polyethylenes are more crystalline than chlorinated branched polyethylene and are semicrystalline, flexible plastics in the 15–35 wt. % range. The chlorinated branched polyethylenes of this chlorine content are soft and rubbery. Chlorination conditions can influence the degree of residual crystallinity in the chlorinated product, and hence have a pronounced effect on the properties of the products Molecular weight of the polymer and degree of chlorination influence the properties of the chlorinated product. Chlorosulfonated linear ethylene polymers and copolymers were tested as elastomers. Stress‐strain properties were better for the chlorosulfonated linear copolymers as compared to chlorosulfonated linear polyethylene or branched polyethylene. Poor residual elongation was characteristic of the chlorosulfonated linear polymers. An increase in the number of side groups in the basic polymer chain did not affect residual elongat