Water uptake effects in resins based on alkenyl‐modified cyanate ester–bismaleimide blends

The analysis of cured resin blends comprising a commercial dicyanate, bismaleimide and a range of novel alkenyl‐substituted cyanates, to determine the chemical effects of long‐term exposure to water, is reported. The cured resin blends underwent accelerated water uptake by immersion at temperatures of 50 °C and 70 °C, for a period of 14–17 months. The presence of about 10–15% (by weight) of alkenyl‐substituted cyanate in the blend leads to a marked reduction in moisture absorption in comparison with the unmodified bismaleimide/cyanate blend containing a comparable amount of bismaleimide. All samples display non‐Fickian diffusion behaviour at both immersion temperatures, although this is most marked at the higher temperature. Thermogravimetric analysis was performed on alkenyl‐modified neat resin samples before and after the immersion period. The modified samples display thermal stabilities that are indistinguishable from cured resins that have not undergone immersion. Spectroscopy (near infrared Raman and mid‐infrared attenuated total reflectance) was performed on cured resin plaques to determine the sample composition as a function of modifier content. The elemental composition of the samples was also determined before and after the immersion period, and no significant variation in elemental composition was recorded for the modified samples.