Castor‐oil‐modified epoxy resins as model systems of rubber‐modified thermosets. 2: Influence of cure conditions on morphologies generated

Phase separation during polymerization was studied in a model system consisting of a diepoxide based on the diglycidyl ether of bisphenol A (DGEBA), ethylenediamine (EDA) and variable amounts of castor oil (CO). Different events taking place during cure, i.e. phase separation, gelation and vitrification, are described in temperature versus time transformation diagrams (TTT), and conversion versus temperature phase diagrams. Thevconcentration (P) and average size (D̄) of dispersed‐phase particles followed opposite trends, i.e. one increased while the other decreased, when varying the castor oil concentration and the cure temperature. This is explained by assuming that the competition between nucleation and growth is determined by the viscosity at the cloud point, ηcp. Low values of ηcp favour growth over nucleation while the opposite is observed for conditions leading to high values of ηcp. The greater the conversion range between the cloud point and gelation, the broader the particle‐size distribution.