UV-Initiated Ring Opening Polymerization of l-Lactide Using a Photobase Generator

Photoinitiated ring-opening polymerization of l-lactide (L-LA) using a photobase generator (PBG) able to release 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) is reported. Polymerization using the PBG with ketoprofenate counteranion (TBDH⁺.keto^-) was studied in dichloromethane either in the presence or in the absence of 1-butanol as initiator. In both cases, full monomer conversion was reached at room temperature after 10 min of irradiation at 254 nm. In the presence of 1-butanol, linear poly(L-LA) chains (PLA) were obtained, as confirmed by ¹H NMR and MALDI-TOF analyses. The polymerization was well controlled as attested by the production of polymers with low dispersity (Đ < 1.26) and by the linear evolution of molecular weights with the quantity of initiator. Without 1-butanol, although MALDI-TOF analyses revealed cyclic PLA chains (actually formed in situ during MALDI-TOF analysis), linear PLA chains were formed as proven by ¹H NMR, viscosity measurement, and phosphitylation titration. This fast and "on demand" polymerization opens the way to biodegradable UV coatings.