Poly(ethylene glycol) (PEG) star polymer hydrogels mere prepared by gamma-irradiation of aqueous solutions of star PEG polymers. The swelling behavior of these gels in deionized water at 37 degrees C indicated that the gels prepared from PEG star polymers with a small number of long arms swelled to a greater extent than those prepared from PEG star polymers with a large number of short arms. PEG star polymers and branched PEG polymers were modified to incorporate acrylate groups on the ends of the polymer arms. These acrylated star or branched polymers were copolymerized with poly(ethylene glycol) diacrylate in the presence of UV light. The ensuing materials swelled to a greater extent than hydrogels prepared without acrylated star or branched PEG polymers. Number-average molecular weights were calculated using several rubber elasticity-based theories.