Rubber-modified epoxy resins cured with piperidine

Glass transition temperatures (Tᵍ) of epoxy resins, diglycidyl ether of bisphenol-A cured with piperidine, have been measured by differential scanning calorimetry and dynamic mechanical thermal analysis in order to follow the curing process. Optimum cure conditions have been established as 3% PP at 120°C. Tᵍs of the neat epoxy system and those modified with 5 and 16% of a carboxyl-terminated reactive rubber copolymer of butadiene and acrylonitrile (CTBN) have been determined as a function of the cure time. Addition of 5% of CTBN does not modify the process, but the higher CTBN content accelerates the initial stage. Tᵍs after long cure times (Tᵍx) are lower for the modified systems than for the neat, showing that CTBN is not fully segregated. The amounts of CTBN dissolved in the epoxy crosslinked network have been estimated. The authors thank Dr A. J. Kinloch for advice in this investigation. We are grateful to CIBAGEIGY for kindly providing the samples. Financial support by the Comisión de lnvestigación Científica y Técnica is acknowledged (89/0435).