Interpenetrating polymer networks based on modified cyanate ester resin

Abstract

Cyanate esters with inherently low relative permittivity and loss are well known as good resin materials used in the electronics industry. However, very high temperatures (> 300°C) are usually required for crosslinking by cyclo-trimerisation of cyanate ester groups in uncatalysed systems. It has been reported that phenolic hydroxy groups could have a catalytic effect on cyclo-trimerisation of cyanate esters. In this study, 2,2′-diallylbisphenol A (DBA), with two phenolic hydroxy groups, has been used as a catalyst for the crosslinking of a cyanate ester (b10). The double bonds on DBA can readily copolymerise with added bismaleimide to form interpenetrating polymer networks (IPN). High performance IPNs based on different ratios of cyanate ester (b10) and DBA with added bismaleimide have been synthesised. In these self-catalytic IPN resin systems, cyanate ester and DBA/bismaleimide are believed to crosslink via different reactions to form two interpenetrating polymer networks in the cured resin structure. Such a unique combination thus enables cyanate esters to be cured at a lower temperature while largely maintaining their superior dielectric properties. The catalytic effect of hydroxy phenolic groups and the reactivity of new CE–DBA/bismaleimide IPN resin systems were investigated by differential scanning calorimetry. The glass transition temperature and mechanical properties were evaluated by dynamic mechanical analysis and flexural and impact testing. The dielectric properties of the cured resins are also discussed. The IPN resin systems obtained have potential applications in the aerospace and microelectronics industries.