Über Zusammenhänge zwischen Konstitution, Eigenschaften und Anwendungen von Siliconen
It is tried to demonstrate how it is possible to deduct the technologically important properties of the silicones from the characteristics of their molecular structure and bond relations; in addition it is shown which specific characteristics of the polymers determine their practical applications....
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| Format: | Article |
| Language: | deu |
| Published: |
Swiss Chemical Society
1962-08-01
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| Series: | CHIMIA |
| Online Access: | https://www.chimia.ch/chimia/article/view/8160 |
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| Summary: | It is tried to demonstrate how it is possible to deduct the technologically important properties of the silicones from the characteristics of their molecular structure and bond relations; in addition it is shown which specific characteristics of the polymers determine their practical applications.
The heat stability can only be represented very summarily as an expression of the similarity of the silicones to the silicates since the organosiloxane polymers differ greatly in their thermal behaviour as a function of type and extent of the organo-substitution. The limits of high-temperature application result partly from the fact that oxidation reactions leading to crosslinking may take place at the organo-groups and partly to the fact that partial depolymerization may take place under given conditions. The empirical fact that phenylmethylpolysiloxanes have a higher heat stability than methylpolysiloxanes is interpreted on this basis, and in line with electron-theoretical concepts on the influence exerted on the strength of the Si–C- or Si–O-bonds by electron donator or electron acceptor substituents.
Apart from this nearly all specific characteristics of the methylpolysiloxane polymers can be deducted from molecule properties which result, on the one hand, from their paraffin-like character – high proportion of hydrocarbon rests – and, on the other hand, their content of siloxane dipoles which are not similar to paraffins. The chain molecules which are highly mobile in themselves, by preferably taking on helical form, generally compensate the dipoles in such way that low remaining valency and intramolecular binding forces are left. This leads to water repellent properties, release effect, physiological inertness, stability of liquid and rubber-elastic phases, also at very low temperatures. On the other hand, as shown by spreading measurements, their high dipole content makes the molecules orientable to polar or semipolar interfaces, which explains their ease of spreading, interfacial activity, but also the possibility to produce water reppellent films with a minimum of film thickness.
The properties of the silicone polymers can be greatly modified by substitutions to the hydrocarbon rests. In accordance with this organo-functional siloxanes are a highly promising complement to the ‘‘classical” silicones. The still recent experience with such products has indicated effects which are technically surprising and theoretically to some extent enigmatic, as is shown by means of some examples, especially from the chemistry of plastics and surface active materials.
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| ISSN: | 0009-4293 2673-2424 |