Expanding the chemical functionality of levoglucosenone-based monomers for degradable thiol-ene thermosets with high bio-derived content

Abstract

Levoglucosenol, the reduced form of levoglucosenone (LGO), was utilized in this work to synthesize seven novel monomers bearing both pendant alkene functional groups and the inherent internal double bond of the bicyclic LGO structure. Monomers possessing ester, carbonate and carbamate linkers were prepared with a specific focus on developing compounds with a high fraction of bio-derived carbon, which was achieved using fatty acids (oleic and linoleic acid) and plant-based acids (citronellic and 10-undecenoic acid). The monomers were cured via ultraviolet (UV)-initiated radical thiol-ene “click” chemistry with commercially available multifunctional thiols generating optically transparent cross-linked thermosets in typically less than 60 seconds, and which possessed tuneable thermal and mechanical properties. Thermogravimetric analysis revealed that most polymers were stable up to 300 °C, with glass transition temperatures ranging from 0.3 to 37.4 °C and tensile strength values varying from 0.5 to 54.0 MPa, depending on the nature of the structure of the LGO-based monomer. The hydrolytic degradation of these thermosets via ester hydrolysis was demonstrated in an alkaline medium, the rate of which could be controlled by the length of the monomer side chain and nature of the linker unit.