Sulfur-containing hyperbranched polymeric photoinitiator end-capped with benzophenone and tertiary amine moieties prepared via simultaneous double thiol-ene click reactions used for UV curing coatings

A series of sulfur-containing hyperbranched polymeric photoinitiators end-capped with benzophenone (BP) and tertiary amine moieties (B/A-HPIs) were synthesized via the simultaneous double thiol-ene click reactions of thiolated hyperbranched polymer with both dimethylaminoethyl acrylate and 3-(4-benzoylphenoxy)propyl acrylate. The molecular structures were characterized by 1H NMR and FT-IR spectroscopy. From the UV–vis spectra, B/A-HPIs showed the stronger n-π* absorption at ∼340 nm with a higher molar extinction coefficients of 371 L mol−1 cm−1 than 148 L mol−1 cm−1 of BP, and an obvious red shift of π–π* absorption from ∼250 nm of BP to ∼280 nm. According to the photo-DSC study, the photopolymerization rate of 1,6-hexanediol diacrylate initiated by 5 wt% B/A-HPI was twice higher than that by BP. The DMTA results showed the good miscibility of B/A-HPIs with acrylate resins and high crosslinking density of cured films.

► A series of hyperbranched polymeric photoinitiators, B/A-HPIs, were synthesized via the thiol-ene click reaction.
► There are much stronger absorption and obvious red shift for B/A-HPIs in comparison with benzophenone in UV–vis spectra.
► B/A-HPIs possess much higher photoinitiating efficiency than BP in the photopolymerization of 1,6-hexanediol diacrylate, indicated by photo-DSC study.