Branched Base-Amplifying Oligomers Enhancing UV-Curing of Epoxy Resins

This paper describes the preparation and the enhancing effect on anionic UV-curing of epoxy resins of three and four-armed oligomers bearing 9-fluorenylmethyl carbarnate residues, which displayed the autocatalytic formation of primary amino residues triggered by a photogenerated amine. The branched oligomers were readily synthesized by the Michael addition of the corresponding polythiol with 9-fluorenylmethyl 2-acryloyloxyethylcarbamate, which were obtained from 9-fluorenylmethanol and commercially available 2-isocyanatoethyl acrylate. Films of poly(glycidyl methacrylate) and a glycidylated novolac resin doped with a photobase generator exhibited boosted photosensitivity leading to photoinsolubilization in the presence of the base-amplifying oligomers. The more marked effect of the branched oligomers on UV-curing of epoxy resins was demonstrated by using films of a fluid epoxy, which were converted into hard films after UV exposure and postexposure baking, whereas no hardening occurred in the absence of the oligomers.