Synthesis and characterization of poly(L-Lactide-CO-Glycidol)

Abstract

In order to add hydrophilic segment to poly (L-lactide) (PLLA), a commercially available biodegradable polyester, copolymers of L-lactide (LLA) and glycidol (G) were synthesized. In the first part, an attempt was made to synthesize random copolymers. Both LLA and G monomers were added simultaneously in the ring-opening polymerization with various initiators: Mg(OEt)₂, Al(OiPr)₃, SnPh₄, or Sn(Oct)₂. It was found that this method could not produce copolymers with molecul¬ar weight high enough to be purified. In the second part, block copolymers of LLA and G were prepared in 2 steps. First, branched polyglycidol (PG) was synthesized using BF₃OEt₂ as an initiator. The molecular weight of PG obtained from MALDI¬TOF MS analysis was 800-1,500 Da, with polydispersity index of 1.0-1.3. Second, the hydroxyl group of PG together with Sn(Oct)₂ was used to initiate the ring-opening polymerization of LLA. Proton and COSY NMR analysis were used to characterize the copolymer structures. The molecular weight of the copolymers depended on LLA:PG feed ratio, but did not depend on mole percent of SnOct₂ (10 and 20 %). Moreover, linear LLA-b-G copolymer was synthesized in 2 steps. In the first step, O-protected glycidol (GBn) was polymerized using SnC1₄ as an initiator. In the second step, the hydroxyl end group of PGBn was used to initiate the ring-opening of LLA in the presence of Sn(Oct)₂. This work therefore presents two polymerization schemes for the preparation of LLA and glycidol copolymers. The structure of the copolymers depends on the structure of the first homopolymer block.