Neat molecular glasses

Secondary relaxation processes of neat molecular glasses 255... 

T. Blochowicz, Broadband Dielectric Spectroscopy in Neat and Binary Molecular Glass Formers, ISBN 3-8325-0320-X, Logos Verlag, Berlin, 2003. 

Figure lA. Glass transition temperature (Tg) and molecular weight between crosslinks (Me) as a function of epoxy/amine ratio for C-stage cured neat resin. 

The dynamic mechanical thermal analysis also indicated molecular mixing of the two components. The Tg of the thermoplastic was lower than the composite, as determined from the inflection point of the E curve seen in Figures 13 1. The PEOX glass transition temperature appeared at 62°C, while that for PVP showed up at ll5°C. The discrepancy in the Tg of PVP had already been addressed. The Tg extrapolated from the DMTA thermogram was reported since no artifacts were to be introduced. The samples exemplified for all DMTA thermograms were processed in a normalized fashion. Any thermal or hygroscopic Influences were eliminated. Some water may be trapped in the neat thermoplastics but this was minimized since they are hot pressed at 150°C and stored under calcium... 

Usually an indication of molecular mixing can be theoretically calculated based on composite Tg s. When the glass transition temperature of the SIPN was between that of the neat components, molecular interactions were assumed. A definite increase in Tg resulted in these materials. No calculated Tg can be compared since the thermoset did not show a Tg. It was interesting to note that the beta transition of the triazine network was unaffected, but the Tg for the composite was much higher relative to the thermoplastic alone. System II showed a 20 C increase in Tg, while I showed a large increase, changing from 62 C to 125°C. 

Using selective labeling, 2H NMR revealed for the mixed glass chlorobenzene (CB)/decalin (DEC) that both components participate very similarly in the /i-process of this binary glass. This is evident from Fig. 34, where 2H NMR spectra of CB-d5/DEC and CB/DEC-d18 are compared for various temperatures.56 For both components, we see a tp dependence of the line shape, which resembles that found for neat type B systems, implying that the molecular dynamics involved in the [i-process are similar. Specifically, comparison with findings for TOL, suggests that the majority of CB and DEC molecules show reorientation with a typical amplitude of 4-5°. This is confirmed by 2H NMR stimulated-echo experiments (see Fig. 21). 

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