Green polymerisation of a renewable lignin-derived vinyl ketone monomer to form UV-degradable polymers

Abstract

We report the synthesis of a novel aromatic vinyl ketone monomer (BioPVK) from an abundant product of lignin depolymerisation, syringaldehyde. We demonstrate that BioPVK can be homopolymerised and copolymerised with styrene (St) in green solvents (ethyl lactate or water) to produce UV-degradable polymers. The homopolymers produced showed good thermal properties with high stability (up to 370 °C) and a high glass transition temperature (91 °C), similar to that of polystyrene. After irradiation with UV-light for only 30 minutes, substantial loss of molar mass was observed by size exclusion chromatography, demonstrating the degradability of these polymers under mild reaction conditions. Furthermore, MALDI-TOF analysis revealed that UV-degradation produced small molecule aromatic compounds. Copolymerisation of BioPVK with styrene was performed both as a solution polymerisation in ethyl lactate and as a conventional emulsion polymerisation in water. As expected, the solution-derived copolymers degraded under UV-light irradiation. The aqueous emulsion copolymerisation of BioPVK and St produced high molar mass UV-degradable copolymers (M_w of 172 kDa) as colloidally stable latexes in 2 h. These high molar mass copolymers degraded readily in dilute solutions when irradiated with UV-light, but were less susceptible to degradation when cast as solid films. This work provides insights into the development of lignin-derived, UV-degradable polymers and copolymers, offering industrially relevant and environmentally conscious degradable alternatives to current commodity plastics.