Morphology and structure of organosilicon polymer‐modified epoxy resins

Abstract

AbstractAn epoxy‐terminated organosilicon polymer (denoted as ETOP) was used as modifier to blend with bisphenol A type epoxy resins. For uncured epoxy resins/ETOP blends, the miscibility is mainly the contribution of entropy. The phase boundary was investigated. The turbidity points were determined on the basis of optical microscopic observation. While the aromatic amine curing agents were added to the systems, curing at higher temperature, an obvious phase separation between cured bisphenol A type epoxy resins (DGEBA) and ETOP was observed. The structure of the resulting cured products was investigated by differential scanning calorimetry (DSC), dynamic mechanical property analysis (DMA) and scanning electron microscopy (SEM). It is the very elastomeric phase (0,1–5 μm) that enhances the toughness of epoxy resins. Another significant phenomenon is that the crosslinked epoxy‐rich phase (matrix) possesses a higher glass transition temperature (Tg) than pure epoxy resins cured with an aromatic amine, particularly at a higher content of ETOP. This may be considered as participation of epoxide groups on ETOP molecules in the crosslinking reaction of matrix and enhancing the crosslinking density of the matrix (i.e., increasing the Tgs). The results provide ones a larger choice to improve the toughness of the epoxy resin without loss of substantial modulus and thermal resistance.