Synthesis and characterization of stereoregular functionalized polysaccharides from biomass-derived Levoglucosan

Levoglucosan is a bicyclic acetal obtained from the pyrolysis of cellulosic biomass at a projected price point of $1.33 to $3.0/kg, which is competitive with many petroleum-derived monomers. Levoglucosan also offers rich hydroxyl functionality which can be synthetically modified to install a variety of pendant groups for tailored properties. With the aim of developing tailored sustainable polymers from renewable feedstock, a series of 1,6-α linked stereoregular polysaccharides with different pendant functional groups were synthesized from levoglucosan via cationic ring-opening polymerization (cROP). Biocompatible and recyclable metal triflate catalysts – scandium and bismuth triflate – were employed for green cROP of levoglucosan derivatives. Combined experimental and computational studies provided key kinetic, thermodynamic, and mechanistic insights into the cROP of these derivatives with metal triflates. Computational studies revealed 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. Post-polymerization modification of levoglucosan-based polysaccharides was readily performed via UV-initiated thiol–ene click reactions. The reported levoglucosan based polymers demonstrate excellent thermal stability and a vast T_g window of >180C is accessible with the few pendant groups highlighted in this study. This work demonstrates the potential of levoglucosan as a renewable feedstock for the development of next generation sustainable and biocompatible polymers as well as fully functionalized dextran derivatives with tailored properties.

Levoglucosan based stereoregular functionalized polysaccharides