Characterization of diol modified epoxy resins by near- and mid-infrared spectroscopy

Near- and mid-infrared spectroscopy has been used for the characterization of epoxy networks based on diglycidyl ether of bisphenol-A cured with linear aliphatic diols of different chain length in the presence of magnesium perchlorate. Absorption bands due to epoxide, hydroxyl, and ether groups were investigated. The intensity of the hydroxyl absorption and the formation of branched and unbranched ether structures in dependence on the molar ratio and the diol chain length are discussed. A mechanism for the network formation process with respect to diol chain length and concentration is proposed: networks with low density are rapidly formed if long diols are used for modification, whereas the incorporation of short diols into the network takes a longer time but yields networks with a higher density. Glass-transition temperatures of the networks obtained by dynamic thermomechanical analysis confirm the proposed mechanism.