Effects of Methyl and Carbon-Carbon Double Bond in Anhydride Molecule on Dielectric Properties of Epoxy/Al2O3 Composite

Epoxy/Al
2
O
3
composites are widely used as electrical insulating materials for high voltage electrical apparatuses. Organic acid anhydrides are important curing agents of electrical insulating epoxy composites. Functional groups and molecular structures of the acid anhydrides play significant roles in determining physical properties of the epoxy/Al
2
O
3
composites. In this work, we investigate effects of the methyl and carbon-carbon double bond in organic acid anhydride molecule on the dielectric properties of epoxy/Al
2
O
3
composite. We test the resistivities and AC breakdown voltages of epoxy/Al
2
O
3
composites cured with five kinds of anhydrides, which are only different in the number and position of methyl and double bond. To explore the influence laws obtained from experimental results, we analyze the distributed energy level structures of five epoxy resin/anhydride oligomer molecules by carrying out a quantum chemical calculation, and the laws are used to predict the relative magnitude of molecular orbital energy levels of epoxy resin/phthalic anhydride oligomer molecule, which are consistent with the energy levels calculated. The double bond in acid anhydride molecule affects the LUMO and HOMO energy levels of an epoxy resin/anhydride polymer molecule, and the methyl in acid anhydride molecule affects the strengths of hydrogen bonds formed between the molecular chains and the silane coupling agents.