WELL-DEFINED BLOCK-COPOLYMERS OF EPSILON-CAPROLACTONE AND L-LACTIDE USING Y-5(MU-O)((OPR)-PR-I)(13) AS AN INITIATOR

Diblock copolymers composed of poly(epsilon-caprolactone) and poly(L-lactide) were synthesized via sequential living ring-opening polymerization of epsilon-caprolactone and L-lactide in dichloromethane initiated by Y-5(mu-O)((OPr)-Pr-i)(13) (yttrium isopropoxide). A series of diblock copolymers was synthesized with epsilon-caprolactone blocks of constant length (DP = 70) and lactide blocks of varying length (DP = 5-80), with polydispersities of 1,18-1,27. Molecular weights were close to theoretical values. C-13 NMR spectroscopy shows the absence of transesterification reactions and racemization. The thermal properties of the block copolymers were studied using differential scanning calorimetry. The block copolymers show a certain degree of phase mixing depending on the length of the poly(L-lactide) blocks. Crystallization of L-lactide sequences did not occur when the block length consisted of less than 40 L-lactic acid residues.