Reaction scheme for the synthesis of photolymerizable 4KG5DA, 4KG5DM, and 4KG5UDM. Poly (ethylene glycol)-co-poly-(glycolic acid) (4KG5) was synthesized by ring-opening polymerization of glycolide/poly(ethylene glycol) using stannous octoate as a catalyst. The molar ratio of glycolide to PEG is 5:1, which means 2.5 of glycolide per chain end. However, since 2 glycolic acid moieties are generated from one glycolide, 5 glycolic acid units are extended per chain end. 4KG5 copolymer, which has α- and ω-terminated hydroxyl groups, was subsequently end-capped with acrylate, methacrylate, and 2-isocyanatoethyl methacrylate.