Strong　acid　cation-exchange　membranes　were　obtained　by　radiation-induced　grafting　of　acrylic　acid　and　sodium　styrene　sulfonate　onto　high-density　polyethylene　(HDPE).　Thermal　and　chemical　properties　of　the　cation-exchange　membranes　were　investigated.　The　effectiveness　of　-SO3Na　containing　membranes　was　conformed　in　inducing　high　resistance　to　oxidative　degradation.　The　char　residue　of　the　grafted　HDPE　is　greater　than　that　of　ungrafted　HDPE.　It　shows　that　the　branch　chains,　including　-SO3Na　and　-COOH　groups,　give　catalytic　impetus　to　the　charring.　The　crystallinity　of　the　grafted　membranes　was　decreased　when　increasing　the　grafting　yield.　It　was　assumed　that　the　decreased　crystallinity　was　due　to　collective　effects　of　the　inherent　crystallinity　dilution　by　the　amorphous　grafted　chains　and　the　crystal　distortion　of　the　HDPE　component.　(c)　2006　Wiley　Periodicals,　Inc.