One-pot lipase-catalyzed esterification of ε-caprolactone with methyl-d-glucopyranoside and its elongation with free 6-hydroxyhexanoate monomer units.

Abstract

One-pot synthesis of sugar-functionalized oligomeric caprolactone was carried out by lipase-catalyzed esterification of ε-caprolactone (ECL) with methyl-d-glucopyranoside (MGP) followed by the elongation of functionalized oligomer chain. Functionalization was performed in a custom-fabricated glass reactor equipped with Rushton turbine impeller and controlled temperature at 60°C using tert-butanol as reaction medium. The overall reaction steps include MGP esterification of ECL monomer and its subsequent elongation by free 6-hydroxyhexanoate monomer units. A ping-pong bi-bi mechanism without ternary complex was proposed for esterification of ECL and MGP with apparent values of kinetic constant, namely maximal velocity (Vmax ), Michaelis constant for MGP (KmMGP ), and Michaelis constant for ECL (KmECL ) at 3.848×10-3 MH-1 , 8.189×10-2 M, and 6.050M, respectively. Chain propagation step of MGP-functionalized ECL oligomer exhibits the properties of living polymerization mechanism. Linear relationship between conversion (%) and number average molecular weight, Mn (gmol-1 ), of functionalized oligomer was observed. Synthesized functionalized oligomer showed narrow range of molecular weight from 1,400 to 1,600gmol-1 with more than 90% conversion achieved. Structural analysis confirmed the presence of covalent bond between the hydroxyl group in MGP with carboxyl end group of ECL oligomer.