Role of complex formation in the polymerization kinetics of modified epoxy-amine systems

The linearly polymerizing diglycidyl ether of bisphenol A (DGEBA) + aniline modified with the low-T-g poly(ethylene glycol) (PEG) is used as a model system to study the importance of complex formation on the cure kinetics of multicomponent epoxy-amines. This system is miscible over the entire conversion range and can be studied without interference of diffusion limitations. A mechanistic model, based on the reaction of amine functionalities with epoxy-hydroxyl complexes, is extended to include physical interactions with PEG. Water and hydroxyl end groups present in the modifier act as catalysts alongside the autocatalysis caused by hydroxyl groups formed. Ether groups of PEG, on the other hand, suppress the reaction rate by forming nonreactive complexes with hydroxyl groups. Accurate reaction rate prediction is achieved of the effect of temperatures from 75 to 130 degrees C, amine/epoxy molar ratios from 0.6 to 1.4, PEG contents from 9 to 33 wt %, and molecular weights from 400 to 20 000 g mol(-1). In addition to the heat flow from modulated temperature DSC (MTDSC), corresponding to the global epoxy conversion rate, the heat capacity signal, containing mechanistic information, can be predicted. The results confirm the importance of complex formation during the polymerization of multicomponent epoxy-amines.