Triblock and pentablock copolymerizations of ε-caprolactone with L-lactide catalyzed by N-heterocyclic carbene

Dihydroxyl capped biodegradable poly(epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone) (PCLPEG-PCL) triblock copolymer and poly(L-lactide)-poly(epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone)-poly(L-lactide) (PLLA-PCL-PEG-PCL-PLLA) pentablock copolymer have been synthesized by using benzo-12-crown-4-imidazole carbene (B-12-C-4imY) as a catalyst, and PEG and PCL-PEG-PCL copolymer as macroinitiators, respectively. We focused on the influence of the varied reaction time, temperature and monomer/catalyst molar ratio on the copolymerizations. Chemical structures and physical properties of the block copolymers were studied through the characterization of H-1, C-13 NMR, GPC and DSC. The NMR spectral data of the copolymers displayed the chemical structures without random placement. Therefore, the pure triblock and pentablock copolymers have been synthesized successfully.