Modification of cyanate ester resin by hydroxyl‐terminated liquid butadiene‐acrylonitrile rubber and free volume properties of their composites

The toughness of cyanate ester resin (CE) matrix is improved significantly with addition of hydroxyl-terminated liquid butadiene-acrylonitrile rubber (HTBN). The impact strength increased from 4.4 KJ/m2 (pure CE) to 13.3 KJ/m2 (CE/HTBN, HTBN 10 wt %). The curing behavior of the system is studied by differential scanning calorimetric and Fourier transform infrared spectroscope. The results showed that hydroxyl groups on the HTBN chains have slight activation effect to CE curing reaction at the beginning of the cure process. The toughening mechanism is mainly caused by the flexibilizing effects of the homogeneously dispersed HTBN molecules in the CE matrix. The toughening mechanism was demonstrated from the aspect of free volume using positron annihilation lifetime spectroscopy. With addition of HTBN, the mean free-volume size of the composite is smaller than pure CE. The decrease in the mean free-volume size of the system is mainly related to the partition effects of the finely dispersed HTBN molecules to the free-volume holes of CE matrix. A dramatic increase in the interfacial area occurs in this highly miscible system. Good interfacial adhesion is also reflected from the higher I2 of the composite. Therefore, more positrons annihilation in their free state occurs in the composites containing HTBN than pure CE. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010