Well defined block copolymers of ε‐caprolactone and L‐lactide using Y₅(μ‐O)(OⁱPr)₁₃ as an initiator

Abstract

SUMMARYDiblock copolymers composed of poly(e-caprolactone) and poly(L4actide) were synthesized via sequential living ring-opening polymerization of &-caprolactone and L-lactide in dichloromethane initiated by Y 5(p-0)(OiPr),, (yttrium isopropoxide). A series of diblock copolymers was synthesized with e-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. I3C 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(L4actide) blocks. Crystallization of L-lactide sequences did not occur when the block length consisted of less than 40 L-lactic acid residues.

Rare earth metal initiated ring-opening polymerization of lactones

“…Other Ln isopropoxides (M = Er, Sm, Dy, La) were also found to be effective ROP initiators for lactones even at -64 8C. All isopropoxide groups were established to be active as initiators in the CL polymerization and end group analysis of low molecular weight PCL (M -n a 10 000) by means of 1 H NMR spectroscopy suggests a coordination insertion mechanism with acyl-oxygen bond cleavage 78,79) . Structural rearrangement processes involving partial or complete disassembly of the O-bridged initiator upon the coordination of monomer and/or polymer giving the actual active catalyst species is proposed.…”

“…Structural rearrangement processes involving partial or complete disassembly of the O-bridged initiator upon the coordination of monomer and/or polymer giving the actual active catalyst species is proposed. A series of diblock copolymers of PCL and PLA with PCL blocks of constant length (DP = 70) and PLA blocks of varying length (DP = 5 -80) with polydispersities of 1.18 -1.27 were also prepared by sequential polymerization without transesterification and racemization 79) . Borgen et al extended these studies and used yttrium alkoxide (yttrium 2-methoxyethoxide) for ROP of bbutyrolactone (BL) 80) .…”

Anionic coordinated polymerization ofɛ-caprolactone with aluminium, zirconium and some rare earths alkoxides as initiators in the presence of alcohols

“…These compounds are known to form pentanuclear complexes with oxo ligands of general formula Ln 5 (l-O)(OiPr) 13 and the monomeric species are generally unstable, unless using bulky ligands. For example, tris(2,6-di-tert-butylphenoxy)yttrium is disassociated in solution 42) , but Y(OiPr) 3 is thermally unstable and gives Y 5 O(OiPr) 13 in boiling 2-propanol 18) . Most alkoxide solvates with 2-propanol are unstable and give the pentanuclear aggregate.…”

“…As an example, polymerization carried out with yttrium isopropoxide at room temperature is very fast, and a living character has been observed with low polydispersities. The synthesis of poly(lactide-b-lactone) has also been reported 13) , that highlights the living character of the polymerization.…”

“…For instance, Al(OiPr) 3 in toluene solution appears as trimeric and tetrameric species in equilibrium with one another 14) and the trimer reacts faster than the tetramer 15) . In the same way, rare earth alkoxides exist as clusters of general formula Ln 5 (l-O)(OiPr) 13 (Ln = Y, Nd) [16][17][18] . Bulky ligands have been proposed to avoid aggregated structures.…”