Effect of methoxy substituent position on thermal properties and solvent resistance of lignin-inspired poly(dimethoxyphenyl methacrylate)s

The macromolecular properties, including the glass transition temperature (T_g) and solvent resistance, of lignin-inspired poly(dimethoxyphenyl methacrylate)s were controlled by varying the position of the dimethoxy substituents in the constituent monomers. For the four dimethoxyphenyl methacrylate isomers investigated, with substituents at different locations on the phenyl ring (i.e., 3, 5-; 2, 3-; 2, 4-; and 2, 6-), the T_g's of the resulting polymers spanned a wide range from less than 100 °C to greater than 200 °C. Rotational freedom and segmental interactions were responsible for the varying T_g's. The polymers were thermally stable in air up to ~300 °C, providing a suitable thermal processing window. The poly(dimethoxyphenol methacrylate) homopolymers also exhibited remarkably different solvent resistances to organic solvents, including tetrahydrofuran and chloroform. Furthermore, by copolymerizing various dimethoxyphenyl methacrylate isomers, the T_g and solvent resistance of the resulting macromolecules could be tuned independently to gain enhanced control over materials design. The ability to manipulate properties through isomer composition in this lignin-inspired system may facilitate usage in applications such as components in coatings, thermoplastics, thermoplastic elastomers, and other materials.