ACS Sustainable Chemistry & Engineering (2019).
The use of naturally available building blocks for the preparation of high-performance polymers is attracting increasing interest. Betulin (or betulinol) is a naturally occurring, large, non-aromatic diol with a pentacyclic ring structure that can be extracted in high percentages from the bark of birch trees. Here, we demonstrate that betulin can be used to prepare polyesters with exceptional thermal attributes through industrially viable and scalable melt polycondensation reactions. Specifically, betulin-based thermoplastics were synthesized using succinic acid, adipic acid, 1,12-dodecanedioic acid and 1,18-octadecanedioic acid as comonomers and showed good solubility in common industrial solvents. Additionally, betulinbased polyester thermosets were formulated via the incorporation of glycerol as a crosslinker. A systematic study evaluating the effect of various co-monomers on the structure-property relationships of these betulin-derived thermoplastics (Mws ranging from 7,500 g mol-1 to about 60,000 g mol-1) and thermosets (Eʹ at room temperature ranging from 20 MPa to 780 MPa) reveals that betulin is a renewable and versatile platform chemical for the preparation of highperformance polymeric materials. Indeed, these materials displayed glass transitiontemperatures ranging from 20 °C to about 215 °C, thermal stabilities in excess of 300 °C in both N2 and air, and Young's moduli and tensile strengths exceeding 600 MP and 9 MPa, respectively. These investigations provide new insights into the rational design of approaches towards betulin-based products for high-performance polymer applications.
