Cyclotetrasiloxane frameworks for the chemoenzymatic synthesis of oligoesters?

RSC Advances Pub Date: 2014-11-28 DOI: 10.1039/C4RA14828B

Abstract

Immobilized lipase B from Candida antarctica (Novozym? 435, N435) was utilized as part of a chemoenzymatic strategy for the synthesis of branched polyesters based on a cyclotetrasiloxane core in the absence of solvent. Nuclear magnetic resonance spectroscopy and matrix-assisted laser desorption ionization time-of-flight mass spectrometry were utilized to monitor the reactions between tetraester cyclotetrasiloxanes and aliphatic diols. The enzyme-mediated esterification reactions can achieve 65–80% consumption of starting materials in 24–48 h. Longer reaction times, 72–96 h, resulted in the formation of cross-linked gel-like networks. Gel permeation chromatography of the polymers indicated that the masses were Mw = 11?400, 13?100, and 19?400 g mol?1 for the substrate pairs of C7D4 ester/octane-1,8-diol, C10D4 ester/pentane-1,5-diol and C10D4 ester/octane-1,8-diol respectively, after 48 h. Extending the polymerization for an additional 24 h with the C10D4 ester/octane-1,8-diol pair gave Mw = 86?800 g mol?1. To the best of our knowledge this represents the first report using lipase catalysis to produce branched polymers that are built from a cyclotetrasiloxane core.

Graphical abstract: Cyclotetrasiloxane frameworks for the chemoenzymatic synthesis of oligoesters
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