Abstract
In the field of electrical equipments such as motor, unsaturated polyester resins and vinyl ester resins are widely used for adhesive and insulator. These resins are generally cured by radical polymerization and have several advantages such as low cost and good insulation and adhesion. Recently, downsizing of electrical equipments have resulted in them generating more heat, and thus resins need to have better thrmostability. In the case of thermosetting resins cured by radical polymerization, thermal decomposition occurre from terminal vinyl groups derived from disproportionation reaction. It is known that the living radical polymerization inhibits the disproportionation reaction. Thus, we attempt to use living radical polymerization to improve thermalstability of resins. A mixture of styrene and vinyl ester, which has a weight ratio of 50:50, was used as a varnish. The thermal decomposition temperature of resins cured by various radical initiators was measured by using thermal gravimetric analysis. The thermal decomposition temperature of resin cured by the borane compound, a living radical initiator, was higher than that cured by non-living radical initiators such as peroxide. Furthermore, the glass-transition temperature of the resin cured by the borane compound was higher than that cured by peroxide. From these results it was revealed that living radical initiator is a very effective reagent to improve thermostability of thermoset resins.
