The effect of impurities in reactive diluents prepared from lignin model compounds on the properties of vinyl ester resins

Vinyl ester resins (VERs) often contain high concentrations of a petroleum-based reactive diluent, such as styrene. Reactive diluents that can be derived from lignin, including phenyl methacrylate (PM), 2-methoxyphenyl methacrylate (MG), and 4-propyl-2-methoxyphenyl methacrylate (M4PG), were synthesized and investigated as potential styrene replacements. A commercial VER was blended with each lignin-derived reactive diluent, and styrene, in 7:3 and 1:1 weight ratios and cured to ≥ 94%, based on near-IR spectral analysis. The substituents on the aromatic ring of the lignin-derived reactive diluent are shown to have small effects on viscosity, thermogravimetric, and thermomechanical properties of the cured resins, where, in general, the smaller the reactive diluent, the greater the glass-transition temperature (T_g) and the lower the viscosity. Increasing purity of the reactive diluents through chromatographic separations substantially increases the T_g and degradation temperatures of the resins. The results suggest that PM, MG, and M4PG are effective bio-based reactive diluent replacements for styrene.