Vinyl　group　capped　urethane　acrylate　(UA)　was　prepared　with　diisocyanate　(IPDI),　hydroxyethyl　methacrylate　(HEMA)　and　dimethylolpropionic　acid　(DMPA).　The　UA　was　grafted　onto　sodium　alginate　via　free-radical　polymerization　with　KPS/Na2SO3　as　initiator　and　then　crosslinked　by　Ca2+.　Grafted　polymers　(UA-g-CaA)　were　characterized　by　FT-IR,　SEM,　TGA,　XRD　and　tension　gauge.　The　swelling　behavior　was　also　investigated.　It　is　found　that　urethane　acrylate　grafted　calcium　alginate　possesses　lower　swelling　degree　and　is　improved　in　thermal　stability　as　well　as　mechanical　performance.　The　reason　is　that　hydrophobic　urethane　acrylate　provides　alginate　with　physical　crosslinking　and　forms　partial　crystal　regions.　The　optimum　condition　for　synthesis　of　UA-g-CaA　with　lower　swelling　degree　is　that　weight　percentage　of　initiator　to　monomer　is　0.8%,　mass　ratio　of　reductant　to　oxidant　is　0.45:1,　monomer　concentration　is　0.0385mol/L　and　grafting　reaction　temperature　is　55°C.　©　2015　Elsevier　B.V.