Viscoelastic behaviour of model polyurethane networks in the main transition zone |
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| Authors: | A Havránek M Ilavský J Nedbal M Böhm W v Soden B Stoll |
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| Institution: | (1) Faculty of Mathematics and Physics, Charles University, Prague, C.S.S.R.;(2) Institute of Macromolecular Chemistry, Czechoslovakian Academy of Sciences, 16206 Prague 6, C.S.S.R.;(3) Present address: Department of Applied Physics, University of Ulm, D-7900 Ulm, Oberer Eselsberg, FRG |
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| Abstract: | Starlike poly (oxypropylene) molecules (M=2630 resp. 710 g/mol), each with three OH-end-groups, are crosslinked with 4,4 -diphenylmethane diisocyanate in one stoichiometric and several nonstoichiometric reactions. Dynamic mechanical (frequency 10–4 to 102 Hz) and also some dielectric (10–2 to 106 Hz) measurements were made on these networks in a wide temperature range. The time-temperature-superposition principle was used to obtain master curves. Two large relaxation processes were detected (separated by many decades of frequency in some samples). The high frequency process seems to correspond to the glass-rubber transition in linear polymers, the low frequency process is probably due to the relaxation of  dangling chains . |
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| Keywords: | Mechanical measurements model networks glass relaxation unperfect crosslinking reaction |
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