Porwal MK, Reddi Y, Saxon DJ, Cramer CJ, Ellison CJ, Reineke TM.
Stereoregular Functionalized Polysaccharides via Cationic Ring-Opening Polymerization of Biomass-derived Levoglucosan.
Chem Sci 2022;
13:4512-4522. [PMID:
35656133 PMCID:
PMC9019921 DOI:
10.1039/d2sc00146b]
[Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2022] [Accepted: 03/08/2022] [Indexed: 11/24/2022] Open
Abstract
We report the facile synthesis and characterization of 1,6-α linked functional stereoregular polysaccharides from biomass-derived levoglucosan via cationic ring-opening polymerization (cROP). Levoglucosan is a bicyclic acetal with rich hydroxyl functionality, which can be synthetically modified to install a variety of pendant groups for tailored properties. We have employed biocompatible and recyclable metal triflate catalysts – scandium and bismuth triflate – for green cROP of levoglucosan derivatives, even at very low catalyst loadings of 0.5 mol%. Combined experimental and computational studies provided key kinetic, thermodynamic, and mechanistic insights into the cROP of these derivatives with metal triflates. Computational studies reveal that ring-opening of levoglucosan derivatives is preferred at the 1,6 anhydro linkage and cROP proceeds in a regio- and stereo-specific manner to form 1,6-α glycosidic linkages. DFT calculations also show that biocompatible metal triflates efficiently coordinate with levoglucosan derivatives as compared to the highly toxic PF5 used previously. Post-polymerization modification of levoglucosan-based polysaccharides is readily performed via UV-initiated thiol–ene click reactions. The reported levoglucosan based polymers exhibit good thermal stability (Td > 250 °C) and a wide glass transition temperature (Tg) window (<−150 °C to 32 °C) that is accessible with thioglycerol and lauryl mercaptan pendant groups. This work demonstrates the utility of levoglucosan as a renewably-derived scaffold, enabling facile access to tailored polysaccharides that could be important in many applications ranging from sustainable materials to biologically active polymers.
We demonstrate the facile synthesis and characterization of stereoregular polysaccharides from the biomass-derived platform molecule levoglucosan via metal-triflate mediated cationic-ring opening polymerization.![]()
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