Photocatalyzed ring-opening polymerization of ε-caprolactone

Photocatalyzed polymerization by semiconductors has recently contributed to the methods of polymer synthesis. In this work, we developed a new type of photocatalyzed polymerization with ring-opening polymerization of lactone. A complex catalyst was designed consisting of nitrogen-doped TiO2 (N–TiO2), iodonium salt (Ph2I+PF6−) and H2O. Poly(ε-caprolactone) (PCL) with a narrow molecular weight distribution was synthesized under visible light irradiation. By using electron spin resonance (ESR), in situ 1H-nuclear magnetic resonance (1H-NMR) and MALDI-TOF mass spectrometry, the mechanism studies clearly presented the reactions of the three components in the ternary catalyst. This polymerization was ruled by the route in which ε-caprolactone (ε-CL) was activated by H+. H+ was photogenerated from the oxidation reaction of H2O. Meanwhile, H+ was stabilized by the photogenerated PF6−, forming Brønsted acid H+PF6−. The relationship between the monomer conversions and PCL molecular weights was studied.