Reaction-induced phase separation in polyethersulfone-modified epoxy-aminesystems studied by temperature modulated differential scanning calorimetry

In epoxy-amine systems with a thermoplastic additive, the initially homogen eous reaction mixture can change into a multiphase morphology as a result o f the increase in molecular weight or network formation of the curing matri x. Temperature modulated DSC (TMDSC) allows the real-time monitoring of thi s reaction-induced phase separation. A linear polymerizing epoxy-amine (DGE BA-aniline) and a network-forming epoxy-amine (DGEBA-methylene dianiline), both with an amorphous engineering thermoplastic additive (polyethersulfone , PES), are used to illustrate the effects of phase separation on the signa ls of the TMDSC experiment. The non-reversing heat flow gives information a bout the reaction kinetics. The heat capacity signal also contains informat ion about the reaction mechanism in combination with effects induced by the changing morphology and rheology such as phase separation and vitrificatio n. In quasi-isothermal (partial cure)TMDSC experiments, the compositional c hanges resulting from the proceeding phase separation are shown by distinct stepwise heat capacity decreases. The heat how phase signal is a sensitive indication of relaxation phenomena accompanying the effects of phase separ ation and vitrification. Non-isothermal (post-cure) TMDSC experiments provi de additional real-time information on further reaction and phase separatio n, and on the effect of temperature on phase separation, giving support to an LCST phase diagram. They also allow measurement of the thermal propertie s of the in situ formed multi-phase materials. (C) 1999 Elsevier Science B. V. All rights reserved.