A new family of Type I photoinitiators based on N-heterocyclic carbene borane is introduced.
The compounds are synthesized using a previously unknown homolytic B–N cleavage reaction.
Three original NHC-amino borane compounds were designed and synthesized, and their
UV absorption properties were assessed. All exhibit high molar extinction coefficients
and frontier orbitals on the N-atom-bearing group. Their photolysis is rapid. ESR
experiments clearly support the B–N homolytic bond cleavage to both NHC-BH2
• and a delocalized radical centered mostly on sulfur. Outstanding polymerization profiles
of a benchmark trifunctional acrylate monomer are noted in laminate, where the final
acrylate conversions reached 70% with filtered light (λ > 300 nm).
Key words
radical reactions - photochemistry - polymerization - cleavage - N-heterocyclic carbenes
- boranes
