(573f) Biomass Lignin-Based Stimulus Responsive Polymers

Lignin is the second most abundant plant-based biopolymer after cellulose, and it is a sustainable raw material. In addition to its abundance and inexpensive supply, lignin is favorable for its numerous attractive properties, such as biodegradability, antioxidant activity, high carbon content, high thermal stability, and stiffness. These important features of lignin can be synergistically combined with the advanced functionalities of well-defined other polymers via covalent bond linkages. In this talk, we will discuss a new photoredox catalyzed reaction for polymeric lignin modification and a lignin-based heat-responsive shape memory polymer. In photoredox catalyzed lignin modification, the alkene-containing lignin was reacted with various thiol-compounds. The Ru(bpy)₃Cl₂ showed the best efficiency under blue visible LED light. In particular, thiol terminal poly(ethylene glycol) also displayed 94%. The photoredox catalyzed thiol-ene reaction was very efficient, and therefore, it readily occurred even under natural sunlight with high yield close to 100%. The newly developed photoredox catalyzed lignin modification was used to synthesize heat-responsive shape memory polymer. The multi-alkene containing lignin was used as a crosslinker to produce crosslinked polycaprolactone (PCL). The lignin served as hard segment as well as crosslinker between PCLs. The prepared flat rectangular shape lignin-crosslinked PCL sample demonstrates rapid thermal responsive shape memory behavior at 10 ^oC and 80 ^oC showing interconversion between a permanent and temporary shape. The melting temperature of the lignin-crosslinked PCL is tunable by varying the percent weight of lignin. The 11, 21, and 30 wt % lignin demonstrated melting points (T_m) of 42 ^oC, 35 ^oC, and 26 ^oC, respectively. The role of lignin as a crosslinker presented in this work suggests that lignin can serve as an efficient biomass-based functional additive to polymers.