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Rheologica Acta

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01-12-2011 | Original Contribution

Viscoelastic properties of a silicone resin during crosslinking

Authors: Friedrich Wolff, Christoph Kugler, Helmut Münstedt

Published in: Rheologica Acta | Issue 11-12/2011

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Abstract

Viscoelastic properties of a silicone resin crosslinked at various extents were characterised by means of rheology. The influence of temperature on the viscoelastic properties of the material as-delivered and in a state pre-crosslinked approximately to the gel point has been investigated by dynamic-mechanical measurements. While the glass transition temperature is increased by the crosslinking, no changes of the free volume fraction at T _g and its thermal expansion coefficient were observed. Taking the different glass transition temperatures into account, it could be shown that the corresponding WLF-parameters are the same. The molar mass and, hence, the viscosity of the material can be increased by a heat treatment. The dependence of the zero shear-rate viscosity on the weight average molar mass indicates that the existence of entanglements of the polymer molecules is not very probable.

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Steady-state measurements at shear rates higher than 10 s^− 1 were not possible since in this case the material flows out of the gap.

For low frequencies, the phase angle δ reaches values of almost 90°. Values higher than 89.9° cannot be resolved any more resulting in incorrect measurements of G ^′. Therefore, at low frequencies the values of G ^′ are not shown in Fig. 4, but the trend is indicated by the dotted line. Investigating another batch of the same type of silicone resin, Takahashi et al. (2001a) observed a bending of the G ^′ curve at about 5 rad/s. Such a bending was not found in the present work. The reasons for that are not clear, but possibly it can be explained by a different pretreatment of the samples prior to the measurement.

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Title: Viscoelastic properties of a silicone resin during crosslinking
Authors: Friedrich Wolff
Christoph Kugler
Helmut Münstedt
Publication date: 01-12-2011
Publisher: Springer-Verlag
Published in: Rheologica Acta / Issue 11-12/2011
Print ISSN: 0035-4511
Electronic ISSN: 1435-1528
DOI: https://doi.org/10.1007/s00397-010-0513-2

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