The heat capacity signal from modulated temperature DSC in non-isothermal conditions as a tool to obtain morphological information during reaction-induced phase separation

Thermal properties of materials formed during reaction-induced phase separation (RIPS) of modified epoxy–amines can be obtained from the derivative of the heat capacity signal (dCp/dT) in non-isothermal conditions following a certain cure schedule. A method is proposed in which the dCp/dT signal is deconvoluted, resulting in values of Tg and ΔCp at Tg, which can be used as probes for the composition and fraction of each phase, respectively. The following modified epoxy–amine systems, showing LCST-type demixing behavior, are presented: (i) the linearly polymerizing system diglycidyl ether of bisphenol A (DGEBA)+aniline; (ii) the network-forming system DGEBA+methylenedianiline (MDA) both modified with the high-Tg thermoplastic poly(ether sulphone) (PES: Tg=223 °C) and (iii) DGEBA+MDA modified with the low-Tg copolymer poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (triblock: Tg=−70 °C). The onset of RIPS can be detected before the cloud point for systems (i) and (ii), indicating that the dCp/dT signal is sensitive to phases in the sub-micron scale. Evolutions of the composition and fraction as a function of conversion during RIPS in isothermal conditions contribute to the understanding of the relation between the cure schedule and the morphological development. For the network-forming systems (ii) and (iii), overlapping peaks in the dCp/dT signal reveal complex phase structures with interphases arising in certain cure conditions. The network structure in combination with limited interdiffusion rates results in fixation of the morphology in the former system. On the contrary, higher interdiffusion rates gives rise to a better segregation between the PES-rich and epoxy–amine-rich phases in system (i).