A positron annihilation study on the microstructure of cyanate ester resin toughened by carboxyl‐terminated butadiene‐acrylonitrile rubber system

Abstract

AbstractThe toughness of cyanate ester (CE) resin matrix improves significantly with the addition of carboxyl‐terminated butadiene‐acrylonitrile rubber (CTBN). The curing behavior of the system was studied by differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. The results show that carboxyl groups on the CTBN chain have a slight activation effect on the CE curing reaction at the beginning of the curing process. Phase separation was found to be the main toughening mechanism for CE/CTBN composites. The existence of macro‐size pores induced by the decomposition of a small amount of the low weight molecular part of CTBN might be another toughening mechanism. It is confirmed that positron annihilation lifetime spectroscopy (PALS) is still valid in such a system where macropores filled with gas molecules exist. When a high weight percentage of CTBN (>8%) was added to CE, free‐positron annihilation was found to be the dominant annihilation process in the macropores. For CTBN weight percentage higher than 8%, the contribution of ortho‐positronium (o‐Ps) annihilation in the macropores to τ3 and I3 was found to be insignificant. It is effective to use PALS as a probe of free‐volume properties in such systems by determining the changes in the τ3 and I3 of the composite. The compatibility and interfacial adhesion of the composites can be estimated from the changes in the free‐volume properties of the composites. Copyright © 2008 John Wiley & Sons, Ltd.