Rubber‐modified epoxies. I. Influence of carboxyl‐terminated butadiene‐acrylonitrile random copolymers (CTBN) on the polymerization and phase separation processes

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Abstract
A bisphenol‐A diglycidylether (DGEBA) based epoxy was cured with a cycloaliphatic diamine (4,4′‐diamino‐3,3′‐dimethyldicyclohexylmethane, 3DCM), in the presence of an epoxy terminated butadiene‐acrylonitrile random copolymer (ETBN). Results showed that vitrification is slightly delayed with the rubber addition. With ETBN the auto‐catalytic mechanism by [OH]0 is predominant at the beginning of the reaction, and on the contrary dilution is the dominant factor after x = 0.15. Phase separation takes place completely, well before gelation and vitrification; the conversion at the onset of phase separation decreases with the rubber amount but does not depend significantly on the temperature. The maximum Tg of the rubber‐modified matrix does not depend on the cure temperature but decreases with the initial rubber concentration. This implies that a significant amount of rubber remains in solution in the continuous phase. This explains the delay in vitrification.