In situ monitoring of reaction-induced phase separation with Modulated Temperature DSC: comparison between high-T_g and low-T_g modifiers

摘要

A linearly polymerizing and network forming epoxy-amine system will be modified withrna high-T_g thermoplastic poly(ether sulphone) (PES: T_g=223℃) and with a low-T_g copolymerrnpoly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (triblock: T_g=-rn70℃). Both PES and the triblock show Lower Critical Solution Temperature (LCST)-typerndemixing behavior with epoxy resins. Reaction-induced phase separation (RIPS) in thesernmodified systems is studied using Modulated Temperature DSC (MTDSC) as an in situ tool. Thernthermoplastic-rich phase of the high-Tg modifier will vitrify at some point, while that of the low-rnT_g modifier stays mobile during curing at the useful curing temperatures, affecting the diffusionrnrates of the epoxy-amine species in(to) this phase differently. By using the heat capacity signalrnduring quasi-isothermal cure, phase separation can be measured indirectly as a step-wise decreaserndue to vitrification of the thermoplastic-rich phase or directly as a peak when the heat of phasernseparation occurs on the time-scale of the modulation. The latter effect has been detected for thernfirst time with MTDSC in the case of RIPS. Temperature-conversion-transformation diagramsrnunambiguously show the LCST-type demixing behavior of these systems, while informationrnabout the in situ developed morphology can be obtained from the heat capacity evolutions in nonisothermalrnpost cures.rnThermal properties of materials formed during reaction-induced phase separation (RIPS)rnof modified epoxy-amines can be obtained from the derivative of the heat capacity signalrn(dC_p/dT) in non-isothermal conditions following a certain cure schedule. A method is proposed inrnwhich the dC_p/dT signal is deconvoluted, resulting in values of T_g and △C_p at T_g, which can bernused as probes for the composition and fraction of each phase, respectively. The Couchmanrnrelation links the Tg of phase i (T_(g,i)) to the composition by assuming that the phase is a blend ofrnthe epoxy-amine species at conversion x and the modifier. The fraction of this phase can berndetermined from the △DC_p at T_g when additivity is assumed. Evolutions of the composition andrnfraction as a function of conversion during RIPS in isothermal conditions thus contribute to thernunderstanding of the relation between the cure schedule and the morphological development.