Softwood Lignin-Based Methacrylate Polymers with Tunable Thermal and Viscoelastic Properties

Softwood (guaiacylic) lignin -based methacrylate polymers (LBMPs) that exhibit excellent glass transition temperatures (T-g's), desirable thermal stabilities (greater than 100 degrees C above T-g) and intermediate shear-flow resistances, in comparison to polystyrene and poly(methyl methacrylate), are reported herein. Different R-groups (p-position hydrogen, methyl, ethyl, and formyl groups) in otherwise homologous LBMPs impart distinct characteristics to the flow behavior and thermal properties of these bio-based polymers, which permit the investigation of unique structure property relationships. More specifically, the zero-shear viscosities (eta(0)'s) for the LBMPs span nearly 2 orders of magnitude as the R-group is varied, while the characteristic degradation temperatures differ more modestly (by approximate to 50 degrees C over the same series of polymers), and the Tg's exhibit minimal, yet application relevant, variations between approximate to 110 and approximate to 130 degrees C. These property differences were probed independent of tacticity, molecular weight, and dispersity effects due to the nature of the well-controlled macromolecules generated via reversible addition fragmentation chain-transfer polymerization. Furthermore, heteropolymers prepared from mixtures of the lignin-based monomers have composition-dependent T-g's and component-dependent thermal degradation temperatures, thermolysis rates, and eta(0)'s. The multicomponent materials demonstrate the enhanced tunability inherent in LBMPs. Altogether, this versatile library of softwood lignin-based monomers, and the unique structure property relationships intrinsic to the resulting polymers, provides a unique platform for building potentially low-cost, high-performance, and bio-based viscoelastic materials attractive for thermoplastic elastomer and binder applications.