Preparation and properties of PMR-II polyimide/chopped quartz fibre composites

High-temperature polyimide composites with low and stable dielectric proper ties were produced by thermally curing prepolyimide moulding compounds whic h were prepared by the wet impregnation of chopped short quartz fibres with a PMR-II polyimide matrix resin solution, followed by the evaporation of t he solvent with vigorous stirring. The mechanical properties, thermo-oxidat ive stability as well as the dielectric and electric properties of the comp osites were studied. The experimental results showed that the composites ex hibit outstanding mechanical properties and excellent thermal and thermo-ox idative stability at temperatures as high as 371 degrees C. It was revealed that both the dielectric constant (similar to 3.0) and loss tangent (simil ar to 10(-3)) of the composites were not obviously changed with a frequency in the broadband wavelength (1 kHz-20 GHz).