Functionalized Unsaturated Polyester as Electrical Insulation Varnish

Silsesquioxanes (SQs) are mostly used to provide high-temperature electrical insulation of resins. Here, SQ is used to functionalize unsaturated polyester (UPE) varnish and investigate the effect of functionalization on the thermal and electrical properties of UPE varnishes. The solvent-free varnish incorporates a reactive diluent to decrease viscosity and a catalyst to expedite hardening, eliminating the need for solvents. Vinyl toluene (VT) and 1,4-butanediol dimethacrylate (BDDMA) serve as hardening agents, consistent with prior research. Various characterization tests, including Fourier transform infrared, thermogravimetric analyzer, assessment of thermal conductivity coefficient, and determination of electrical volume–surface resistance, are conducted to determine the physical, thermal, chemical, and electrical properties of the synthesized SQ-functionalized UPE (UPES) varnishes. Results indicate that the UPES–BDDMA varnish demonstrates the highest thermal decomposition temperature at 438.0 °C, while the UPES–VT varnish exhibits the highest electrical volume resistance of 2.85 × 10¹⁵ Ω cm. Volatile organic compound levels in UPE coatings range between 4.9% and 5.10% reflecting the growing demand for eco-friendly products. It is shown in this study that the use of BDDMA and VT reactive monomers in the synthesis of SQ-functionalized UPE resin and the properties of the resulting varnishes, especially electrical insulation and thermal stability, are improved.