Highly efficient sulfur-containing polymeric photoinitiators bearing side-chain benzophenone and coinitiator amine for photopolymerization

Novel polymeric sulfur-containing photoinitiators bearing side-chain benzophenone and coinitiator amine, copolymers of 4-[(4-methacrylamido)thiophenyl]benzophenone (MAATPBP) and of 4-chloro-4′-[(4-methacrylamido)thiophenyl]benzophenone (CMAATPBP) with N,N-dimethylaminoethyl methacrylate (DMAEMA), as well as their hompolymers of poly(MAATPBP), poly(CMAATPBP) and poly(DMAEMA) were prepared and structurally characterized. The most commercially used photoinitiator BP and their corresponding low molecular weight combinations (MAATPBP/DMAEMA and CMAATPBP/DMAEMA) were selected as the reference to evaluate their photoefficiency. Polymeric photoinitiators display similar UV–vis maximal absorption spectra to the low molecular counterparts, which are greatly red-shifted in comparison with BP. Photopolymerization of difunctional 1,6-hexanediol diacrylate (HDDA) and trifunctional trimethylolpropane triacrylate (TMPTA) were studied by photo-DSC to investigate the photoefficiency of the copolymers, homopolymers and the combination of their homopolymers. The results show surprising high efficiency of the two copolymeric photoinitiators and their homopolymeric combinations. Poly(MAATPBP) and poly(CMAATPBP) can also efficiently initiate the photopolymerization without the coinitiator because of the photolysis at C–S bond. Their activity data obtained are discussed and related to the structural requirements of the above systems.