SYNTHESIS OF NOVEL HYDROPHILIC POLY(ESTER-CARBONATES) CONTAINING PENDENT CARBOXYLIC ACID GROUPS

Abstract

A functional cyclic carbonate, 5-methyl-5-benzyloxycarbonyl-1,3-dioxan-2-one (MBC), was utilized in the synthesis of novel poly(ester-carbonates) containing pendent carboxylic acid groups. Copolymers with ε-caprolactone (CL) and L-lactide (LLA) were synthesized by ring-opening polymerization (ROP) using either an Al-alkoxide (solution) or Sn(Oct)₂-alcohol (bulk) initiating system. Analysis of the copolymers revealed a random distribution of the comonomer units along the polymer chain. The copolymers exhibited amorphous character at low MBC incorporations despite the crystalline nature of homo-poly(ε-caprolactone) (PCL) and homo-poly(L-lactide) (PLLA). Removal of the benzyl protecting group by hydrogenolysis yielded carboxylic acidfunctional copolymers. It was observed that the benzyl ester group of MBC became susceptible to transesterification reactions at ROP temperatures ≥ 135°C, and the corresponding copolymers were insoluble in both organic and aqueous solvents. It is proposed that carboxylic acid functionality will allow an improvement in the biodegradability and physical properties of PCL and PLLA and possibly improve their utility for biomedical applications such as time-released drug delivery. Moreover, polymerization of comonomers at high temperature may present a pathway toward the synthesis of new biodegradable hydrogels.

Keywords:

• Ring opening polymerization
• Polycarbonate
• Biodegradable polymer
• Hydrogenolysis
• Stannous octoate
• Polyester

ACKNOWLEDGMENTS

The research upon which this material is based was supported by the Office of Naval Research through Award No. N00014-00-1-0884. The authors also thank Dr. William Jarrett for his technical assistance in the ¹H-¹³C-HETCOR experiments.