Simultaneously cured diglycidyl ethers of bisphenol A and polyethylene glycol: DSC, TGA, and DMA measurements

Abstract

In this study, to improve the physico‐mechanical properties of epoxy thermosets, simultaneous curing of two resins with a stoichiometric amount of an aromatic amine hardener was investigated. The two resins used included the well‐known diglycidyl ether of bisphenol A (DGEBPA) with relatively rigid molecular structure and a diglycidyl ether derived from a popular polymer, polyethylene glycol (PEG), with loose molecular structure (DGEPEG). DGEPEG was used in amounts of 10 and 25 mol% in the resin mixture. A single‐resin curing process, including only DGEBA, was also examined. Before isothermal curing, differential scanning calorimetry (DSC) was used to determine the position of the curing exotherm. To ensure the completion of the curing processes, infra‐red (IR) and DSC techniques were performed on both simultaneously‐cured thermosets and the control thermoset. The thermogravimetric analysis (TGA) of the prepared thermosets showed that the addition of DGEPEG resin in the curing process of DGEBA resin has no significant effect on reducing the thermal resistance of the thermoset. In addition, the storage moduli (E′) and the damping coefficients (tan δ) were measured by dynamic mechanical analysis (DMA). As the mole percentage of DGEPEG resin increased, the rapid drop in the E′ value and the α‐relaxation, which is a measure of the glass transition (Tg), occurred at lower temperatures.