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1 Materials Science Poland

1 2006

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Structure-property relationships in brittle polymer networks modified by flexible cross-links

Kripotou S., Pissis P., Kontou E., Fainleib A.M., Grygoryeva O., Bey I.

Materials Science Poland

2006

Vol. 24, No. 2/2

477--492

Hybrid polycyanurate/polyoxytetramethylene glycol (PCN/PTMG) networks were prepared from PCN and PTMG (molar mass 1.000 g/mol) with 10, 20, 30 and 40 wt. % PTMG. The degree of incorporation of PTMG into the PCN network was determined by gel fraction measurements. Earlier morphological and thermal transition studies indicated a non-crystalline structure, considerable nanostructural heterogeneity and a wide dispersion of glass transition temperatures of the hybrid networks. The present paper reports on a continued investigation of structure-property relationships and employ dielectric techniques to focus on molecular dynamics. Two secondary relaxations of PCN, one secondary relaxation of PTMG and a single, broad ? relaxation (dynamic glass transition) were detected in the hybrids. The ? relaxation was studied in detail over wide ranges of temperature and frequency. The results were systematically analyzed in terms of time scale, relaxation strength and shape of the response, and are discussed in terms of plasticization, presence of nanostructural heterogeneities (composition fluctuations) and hybridization. A distinctly different behaviour, observed for the hybrid with 30% PTMG, is explained in terms of a more pronounced nanoheterogeneous structure. Finally, stress-strain measurements were performed and their results are discussed in terms of structure and molecular dynamics.