Copolymerzation of L,L-lactide with ε-caprolactone by using novel zinc L-proline organometallic catalyst

Abstract

Copolyesters based on L,L-lactide (LA) and ε-caprolactone (CL) with different LA: ε-CL ratios were synthesized by ring opening polymerization using zinc (L-proline) as a catalyst. Ring opening polymerization results in random P(L, L-lactide-ε-caprolactone) copolymers of molecular weights between 9,800 to 30,000 and block copolymer up to 51,800 Da. 1H NMR spectroscopy analysis was used for calculation of monomer incorporation in the copolymer. FT-IR spectra were used to differentiate between random and block copolymer using carbonyl region splitting. 13C quantitative NMR spectroscopy analysis coupled with information from TGA and DSC allowed determination of the polymer structure. Copolymers (CP-1, CP-2 and CP-3) prepared by ROP are random copolymer (h>1), while CP-4 prepared by ROP (sequential addition of έ-caprolactone and L, L-lactide) has a multi block character (h<1). The LA number-average sequence length (L LA) decreased from 14 to 5 for LA-CL 80:20 to 50:50 copolymers prepared by ROP. The copolymer (CP-4) prepared by sequential addition showed the number-average sequence length (LLA) to be 83.0.