Viscoelastic behaviour of model polyurethane networks in the main transition zone

Abstract

Starlike poly (oxypropylene) molecules (M = 2630 resp. 710 g/tool), 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".

Influence of crosslinking on mechanical and dielectric properties of nitrile-butadiene-rubber

“…4 and 5 -at both temperatures (-22 ~ and -2 ~ where a direct comparison is possible. Such a difference between the maxima of the imaginary part of the shear compliance 1" and the dielectric constant d' are often found in polymers [2,5,10]. It should be noted that the maximum frequencies of the imaginary part G" of the shear modulus are usually 2 to 5 decades higher than those of/".…”

“…The construction of master curves from our mechanical measurements between 10 -4 and 100 Hz is described in [1,5,6]. The molecular weight dependence and the influence of nitrile content was studied on pure NBR samples (Figs.…”

“…Specimens I mm thick were used for dynamic mechanical (simple shear) and dielectric measurements (description of equipment see [5,6] resp. [7]).…”

“…The influence of molecular weight and of crosslinking on such measurements has often been investigated in the literature (for instance [1][2][3][4][5]). The aim of this work is to characterize selected samples of nitrile-butadienerubber (NBR) and to contribute to the study of the kinetics of vulcanization.…”

Effect of some curatives on the properties of ethylene propylene diene rubber/polyethylene blends

“…10 The samples (cylinders with diameter 7 mm cut from the vulcanized sheets) were dynamically sheared in the apparatus. The shear frequency was 1 Hz and the temperature range was room temperature to about 120°C.…”