Syntheses of cyclic poly(lactones) by zwitterionic ring opening polymerization catalyzed by N-heterocyclic carbene



Synthesis of cyclic biopolymers from renewable monomers remains a big challenge because of lack of efficient catalysts. The organocatalyst of N-heterocyclic carbene (NHC), (+)-1-methyl-3-menthoxymethyl imidazol-2-ylidene, is used to prepare cyclic polylactones including poly(ε-caprolactone) (poly(ε-CL)), poly(δ-valearolactone) (poly(δ-VL)), and poly(ε-caprolactone-co-δ-valearolactone) (poly(ε-CL-co-δ-VL)) via zwitterionic ring opening polymerization. The NHC catalyst is founded a highly efficient organic catalyst for the polymerization. The resulting cyclic polymers show a melting temperature (Tm) in a range of 20–60°C, which is dramatically lower than the Tm of cyclic poly(lactide) (Tm = 120–150°C). The resulting copolymer, cyclic poly(ε-CL-co-δ-VL) owns high molecular weight comparing with corresponding linear poly(ε-CL-co-δ-VL) produced by other catalysts. The synthesized cyclic homo and copolymers were characterized by 1H-, 13C-NMR spectroscopy, gel permeation chromatography, differential scanning calorimetry–thermogravimetric analysis and matrix-assisted laser desorption ionization-time of flight mass spectrometry. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013