UV Cross-Linkable Lignin Thermoplastic Graft Copolymers

This work highlighted a new method to prepare UV curable lignin thermoplastic copolymers, which are expected to show applications as functional materials (e.g., carbon fiber precursors) with improved thermal stability, solvent resistance and surface hardness. UV cross-linkable lignin graft copolymers were synthesized via activator regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP) and characterized. By incorporating a photosensitive compound, acryloyl benzophenone (ABP), as a comonomer during the polymerization, lignin-g-poly(styrene-co-ABP) copolymers with 6–9% (mol %) of ABP moieties were obtained. The lignin graft copolymers showed similar glass transition temperature (∼100 °C) as polystyrene. The carbon yields during pyrolysis decreased as the degrees of polymerization of the graft copolymers increased. Under UV irradiation, up to ∼30 wt % of the lignin-g-poly(styrene-co-ABP) copolymers cross-linked to form polymer networks, whereas less than ∼5 wt % of the lignin-g-polystyrene copolymers formed gelled structures.