Fabrication of well-defined lignin-derived elastomers by atom transfer radical polymerization and Diels-Alder reaction towards sustainable, super-tough and high temperature-resistant hot-melt adhesives

Hot-melt adhesives synthesized from sustainable resource have attracted increasing attention in fields of home decoration, handicraft production, automotive industries, etc., due to their free of volatile organic compounds (VOCs) and environmentally friendly advantages. However, it is still challenging to fabricate super-tough and heat-resistant hot-melt adhesives with utilization of the inherited properties of sustainable resource as feedstock. Herein, a combination of photoinduced metal-free atom transfer radical polymerization (ATRP) and Diels-Alder (DA) reaction was applied to prepare lignin-derived elastomers for super-tough and high temperature-resistant hot-melt adhesives. Firstly, photoinduced metal-free ATRP of lauryl methacrylate (LMA) derived from fatty acids and furfuryl methacrylate (FMA) derived from furfural, were employed to fabricate sustainable well-defined multi-arm lignin-graft copolymers bearing furfuryl groups with the aid of lignin based macro-initiator (L-Br). The photoinduced metal-free ATRP in this work could be activated and deactivated by an “ON–OFF” ultraviolet (UV) light switch, and successfully achieved the precise control over the molecular weight and composition of lignin-graft copolymers. Then, Diels-Alder (DA) reaction was applied to functionalize the lignin-graft copolymers with dynamic crosslinked network and obtain the lignin-derived elastomers. Benefiting from the multi-arm structure and the dynamic crosslinked network, these lignin-derived elastomers exhibited favorable mechanical property, thermal stability, shape memory, self-healing and recycled properties. In addition, the lignin-derived elastomers could be used as hot-melt adhesives and their lap shear strengths could reach 5.95 MPa, while being bonded with aluminum plates. Moreover, the steel plate bonded with lignin-derived elastomers could remain stable even at 100 °C. We believe that this work will offer a new approach for designing lignin-derived elastomers towards sustainable, strong, super-tough and high-temperature-resistant hot-melt adhesives.