(91d) Reactive Diluents Prepared from Lignin Model Compounds:the Effect of Structure and Impurites on the Properties of Vinyl Ester Resins

Vinyl ester (VE) resins are utilized to produce polymer matrix composites for use in a wide range of applications due to possessing relatively high moduli, strengths, and glass transition temperatures (T_gs) while maintaining low weight and cost. VE resins often contain high concentrations of a petroleum-based reactive diluent (RD), such as styrene. In addition to lowering the resin viscosity, styrene is able to improve the overall polymer performance by increasing monomeric reactivity and extent of cure; however, styrene has been designated as a HAP, potential carcinogen, and a VOC. Renewable RDs with similar performance to petroleum-based RDs are desired to mitigate the aforementioned hazards as well as to facilitate the transition from petrochemical feedstocks to bio-based feedstocks.

Lignin is an abundant renewable resource with a high aromatic content that has the potential for the development of VE resins, including RDs. RDs 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 RD, and styrene, in 7:3 and 1:1 weight ratios and cured to â?¥ 94 %, based on near-IR spectral analysis. The substituents on the aromatic ring of the lignin-derived RD are shown to have small effects on viscosity, thermogravimetric, and thermomechanical properties of the cured resins, where, in general, the smaller the RD, the higher the T_g and the lower the viscosity. Increasing purity of the RDs through chromatographic separations substantially increases the T_g and degradation temperatures of the resins. The thermogravimetric and thermomechanical properties of all lignin-derived RDs are directly comparable to that of styrene. These results suggest that PM, MG, and M4PG are effective bio-based RD replacements for styrene.