Oleanolic Acid-Derived High-Glass-Transition-Temperature Methacrylic Polymers

Four new monomers based on the naturally occurring pentacyclic triterpenoid oleanolic acid (OA) were synthesized by introducing a methacrylate group at either the hydroxyl or carboxylic acid positions. After establishing their (in)solubility in a range of solvents, three monomers could notably be polymerized in the green solvent N-butyl-2-pyrrolidone (NBP), in which soluble polymers were obtained. Dithiobenzoate-mediated radical polymerization of all four monomers led to polymethacrylates with theoretical number-average molecular weights (Mn) of up to 45 kg/mol and single-detection size-exclusion chromatography Mn values of up to 24 kg/mol. The purified polymers show thermal stabilities in the range of 300–350 °C and high glass-transition temperatures, up to 220 °C.