Revisiting aromatic thiols effects on radical photopolymerization

Influence of thiols on kinetics of acrylate radical photopolymerization in the presence and absence of photoinitiators was studied. The kinetics was monitored by infrared absorption and photo-differential scanning calorimetry. It was found that aromatic thiols at concentrations, <0.5% (∼0.05 M), can accelerate radical photopolymerization. Initiation of radical photopolymerization by some aromatic thiols in the absence of conventional photoinitiators was observed. As well as expected inhibition of photopolymerization at higher concentration of aromatic thiols due to chain transfer was detected. A ground state charge-transfer complex formation between thiols and benzoin based photoinitiators was detected. ism of thiols participation in photopolymerization involving reduction of oxygen inhibition and dissociation of charge-transfer complexes is discussed.