The present invention includes photocurable, liquid polymers incorporating coumarin ester endgroups into their molecular structure, which polymers are crosslinked upon irradiation with ultraviolet light by photochemically allowed [2+2] cycloaddition reactions among the chain ends, and which crosslinked polymers are useful in the preparation of medical devices, tissue engineering scaffolds, drug delivery systems and, in particular, in vivo preparation of implants in an open surgical procedure or laproscopically.