Vinyl methyl oxazolidinone and dimethyl itaconate as styrene substitutes for conventional high‐temperature unsaturated polyester resins

Abstract Styrene substitution is a major area of interest in the unsaturated polyester resins (UPR) industry and research. For most styrene‐free UPRs the unsaturated polyester (UP) formulation was tailored for less toxic reactive diluent monomers (RDM). The main challenge is finding a RDM that can directly substitute styrene in industrial UPR formulations without deterioration of resin and thermoset properties. Therefore, this study concerns vinyl methyl oxazolidinone (VMOX®) as a reactive diluent monomer for industrial high‐temperature UPRs. VMOX® and styrene were compared with dimethyl itaconate (DMI), methyl methacrylate, 2‐hydroxyethyl methacrylate, isobornyl methacrylate, triethylene glycol dimethacrylate and 1,4‐butanediol dimethacrylate. Further, the properties of produced resins and thermosets were investigated. The most striking result was comparable glass transition temperature, crosslink density, and residual monomer content of VMOX®‐ and styrene‐based thermosets. Subsequently, DMI was applied as a reactive co‐diluent for VMOX®‐based resins and thermosets. Significant improvement of VMOX® conversion during resin curing was observed. In conclusion, VMOX® is an excellent candidate for direct styrene substitution in industrial high‐temperature UPRs. Furthermore, the application of DMI as a reactive co‐diluent improves the reactivity of VMOX®‐based resins. The application of VMOX® and reactive co‐diluent monomer certainly creates new possibilities for direct styrene substitution in conventional UPR formulations.