AbstractComposite polyolefin membranes with graded chlorination gradient were obtained by photochlorination of polyethylene, polypropylene, and polystyrene films using ultraviolet and visible light. The maximum chlorine contents of these membranes were 12, 8.5, and 6.5, respectively. As for polyethylene, the surface photochlorination reduced gas permeation of carbon dioxide and oxygen down to 1/30 and 1/21 of the original polyethylene; it also improved the wettability without changing substantially other favorable physical properties such as tensile strength, elongation, and water vapor permeation. The water contact angle of chlorinated polyethylene was comparable to that of poly(vinyl chloride). The infrared spectra suggest the presence of the chlorine of the CHClCHCl type rather than of the CCl2 type in the photochlorination of polyethylene. In an effort to obtain useful membranes with a photocrosslinking functional group as a side chain, surface‐photochlorinated polyethylene was allowed to react with sodium N,N‐dimethyldithiocarbamate or sodium N‐methyl‐N‐carboxymethyldithiocarbamate in dimethylformamide at 50°C for 48 hr according to the procedure by which poly(vinyl chloride) was previously reacted. The polymer thus obtained has 4.1 mole‐ SCSNMe2and 3.4 mole‐
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