Bio-based poly(ester-alt-thioether)s synthesized by organo-catalyzed ring-opening copolymerizations of eugenol-based epoxides and N-acetyl homocysteine thiolactone

Abstract

The anionic alternating ring-opening copolymerizations of three bio-based aromatic monomers, eugenol glycidyl ether (EGE), dihydroeugenol glycidyl ether (DEGE) and vanillin glycidyl ether (VGE), were carried out with renewable N-acetyl homocysteine thiolactone (NHTL) using benzyl alcohol and 2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine (BEMP) as the initiating system. This polymerization is a rare example of synthesis of linear polyesters using eugenol-based monomers. Alternating poly(ester-alt-thioether)s are obtained with number-average molar masses (M_n) ranging from 1.1 to 10.8 kg mol⁻¹ and dispersities as low as 1.20. The copolymer structures were carefully characterized by ¹H, ¹³C, COSY, HSQC, and ¹H–¹⁵N NMR. It was found that the alternating copolymers were obtained selectively at different monomer feed ratios. In addition, the use of EGE and VGE monomers allows the preparation of multi-functional poly(ester-alt-thioether)s respectively bearing allyl or aldehyde groups in each repeating unit. The copolymers display only clear glass transition temperatures higher than the ambient temperature. This alternating copolymerization method offers a new chemical pathway for the valorization of bio-based aromatic compounds and expands the scope of renewable polyesters.