Changes in molecular dynamics during the bulk polymerization of an epoxide/diamine mixture containing inert diluents as studied using dielectric relaxation spectroscopy

The evolution of the dielectric a relaxation and ionic conductivity with ti me t(r) during polymerization at 60 degreesC of mixtures of the diepoxide D GEBA, the diamine PALM, and the diluent Decalin (DEC) or di-n-butyl phthala te (DBP) has been studied using real-time dielectric relaxation spectroscop y (DRS). Data are presented as permittivity epsilon(omega ,t(r)) and impeda nce Z(omega ,t(r)). For c(dil) less than or equal to 20% (w/w), the main ef fect of diluent was to displace the a process to higher frequencies and, th erefore, to increase the time required for glass formation over that for th e unplasticized system. At higher values of c(dil), the behavior of epsilon (omega ,t(r)) for DGEBA/PACM/DBP systems was more complex as the properties became stationary at long times, showing that an elastomer rather than a g lass was formed. The results are discussed in relation to the "floor temper ature" T-F for reaction introduced previously. The same data are presented as Z(omega ,t(r)), which emphasizes changes in the ac ionic conductivity wi th time. As for the a data, qualitative differences are observed for the be havior of Z(omega ,t(r)) at low and high values of cdf. It is demonstrated that changes in molecular mobility with time for all systems can be judged by the behavior of epsilon(omega ,t(r)) but not by that of Z(omega ,t(r)) f or these systems. The Fuoss-Kirkwood and KWW relaxation functions are used to express the half-width Delta log t of the plot of epsilon " vs log t(r) at fixed measuring frequencies for a reactive system. The changes in Delta log t with f and composition for the systems that became glasses are explai ned in terms of changes with time of (i) the width of the relaxation functi on and (ii) [Delta log < tau (alpha)>/Delta log t(r)], where < tau (alpha)> is the average relaxation time. The behavior of < tau (alpha)(t(r))> with time during reaction is considered in terms of the Angell fragility index m of the process. It is shown that (i) m increases during reaction for a giv en mixture and (ii) m, at fixed frequency, decreases as coil is increased.