The gel point as reference state: A simple kinetic model for crosslinking polybutadiene via hydrosilation |
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| Affiliation: | 1. Department of Polymer Science and Engineering, University of Massachusetts, Amherst, MA 01003, USA;2. Department of Chemical Engineering, University of Massachusetts, Amherst, MA 01003, USA;1. Cell Adhesion and Mechanics, Institut Jacques Monod (IJM), CNRS UMR 7592 & Universitè Paris Diderot, Paris, France;2. Aragon Institute for Engineering Research (I3A), University of Zaragoza, 50018 Zaragoza, Spain;1. Ioffe Institute, RAS, 194021 St.-Petersburg, Russia;2. Institute of Macromolecular Chemistry, NASU, 02160 Kyiv, Ukraine;3. AMME-LECAP International Lab., Institute for Material Research, Université de Rouen, Faculté des sciences, BP12, 76801 Saint Etienne du Rouvray, France;1. Institute of Geochemistry and Petrology, Department of Earth Sciences, ETH Zurich, Clausiusstrasse 25, 8092 Zurich, Switzerland;2. GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany;3. School of Science and Engineering, Reykjavik University, Menntavegur 1, IS-101 Reykjavik, Iceland;1. Faculty of Natural Sciences, Constantine the Philosopher University in Nitra, SK-949 74 Nitra, Slovakia;2. University Centre of Electron Accelerators in Trenčín, Slovak Medical University, Limbová 12, SK-833 03 Bratislava, Slovakia;3. Department of Physical Chemistry, Faculty of Chemical and Food Technology, Slovak University of Technology, SK-812 37 Bratislava, Slovakia |
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| Abstract: | Kinetic data can be described in a simple model when using the gel point as reference state. This has been shown for crosslinking data on five high molecular weight polybutadienes (18 100–97 000 g/mol). Experiments were carried out under isothermal conditions with a constant amount of catalyst. Crosslinking took place by a hydrosilation reaction at vinyl sites which were randomly distributed along the backbone of the polybutadiene precursor molecules using the bifunctional aromatic silane p-bis(dimethylsilyl) benzene as connector. FTIR measurements showed that the hydrosilation reaction followed first order kinetics. The critical gel time, tc, was determined by the instant at which power law relaxation behavior was observed (i.e. tan δ = constant) over the two lowest decades in frequency. The main parameters that were observed to affect tc were the stoichiometric ratio, r, and the functionality of the polybutadiene, f. It was observed that the time to reach the gel point decreased with increasing precursor molecular weight (~f) of the polybutadiene. The gel time also decreased when increasing the initial amount of silane crosslinker. We were able to find a relationship between the gel time measured by the CFS technique and r and f by coupling the Flory-Stockmayer gelation theory with a simple first order kinetic curing scheme. |
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