Branched polymers with different branching densities and their cross-linked analogues are synthesized by photoinduced self-condensing vinyl polymerization via benzodioxinone photochemistry. Thus, methyl methacrylate is copolymerized with two different comonomers, namely, 2-hydroxyethyl methacrylate (HEMA) and 2-(dimethylamino) ethyl methacrylate in the presence of bisbenzodioxinone (BBNZ) under UV light. Upon irradiation, BBNZ undergoes irreversible decomposition leading to the formation of benzophenone photosensitizer and bisketene. The released benzophenone is further photoexcited at the same wavelength to give the initiating radicals through hydrogen abstraction from the inimer. In the case of HEMA, additional branching sites are formed by the reaction of bisketene with the hydroxyl functionalities of HEMA.