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

摘要

One-pot synthesis of sugar-functionalized oligomeric caprolactone was carried out by lipase-catalyzed esterification of epsilon-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 degrees 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 (V-max), Michaelis constant for MGP (K-mMGP), and Michaelis constant for ECL (K-mECL) at 3.848 x 10(-3) M H-1, 8.189 x 10(-2) M, and 6.050 M, 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, M-n (g mol(-1)), of functionalized oligomer was observed. Synthesized functionalized oligomer showed narrow range of molecular weight from 1,400 to 1,600 g mol(-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.