The physical properties of bisphenol‐A‐based epoxy resins during and after curing

A series of epoxy resins derived from diglycidyl ethers of bisphenol A with differing initial linear molecular chain lengths have been studied during and after curing with the diamines MDA (4,4′‐methylene dianiline) and DDS (4,4′‐diamino diphenyl sulfone). The properties that were measured during curing were the volume, the fictive temperature Tf, the gel fraction, the viscosity, and the equilibrium compliance. Graphs of Tf as a function the time of curing tc obtained at four curing temperatures between 40 and 100°C have been reduced to a common curve. After curing, creep compliance curves J(t) were determined which characterize the viscoelastic response from the glassy compliance level to a rubbery equilibrium compliance level. The change in properties that occurs during the time‐dependent spontaneous densification below the glass temperature Tg was monitored with repeated measurements of J(t). Time‐scale shift factors as a function of volume contraction obtained during this physical aging below Tg were reduced to a common curve.