Synthesis of multifunctional lignin graft alternating copolymers of cyclic anhydrides and epoxides catalyzed by metal-free Lewis pairs

In this study, a series of enzymatic hydrolytic lignin (EHL) graft copolymers (EHL- g -P(CA- alt -EPO)s) were successfully synthesized via lignin-initiated ring-opening copolymerization (ROCOP) of cyclic anhydrides (CA) and epoxides (EPO) catalyzed by a metal-free Lewis pair consisting of organic base and triethylborane (TEB). The optimized lignin-initiated ROCOP exhibited widespread monomer adaptability and permitted the synthesis of lignin-based copolymers with tailorable structures and performances via altering anhydrides and epoxides. The chemical structures and thermal properties of EHL- g -P(CA- alt -EPO)s were thoroughly investigated by 1 H, 13 C, HSQC, and 31 P nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FT-IR), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Furthermore, the EHL- g -P(PA- alt -CHO) exhibited good absorption in the ultraviolet (UV) region with the maximum absorption wavelength of 289 nm and prevented photochromic paint from discoloration via effectively blocking UV light. Benefitting from the conjugated structural moieties in EHL- g -P(PA- alt -CHO), good photothermal effect of E-P1C1 with a photothermal conversion efficiency of 44.93% was achieved under near-infrared (NIR) irradiation, indicating the potential application of EHL- g -P(PA- alt -CHO) in organic UV protective agents and photothermal functional materials .