Organosiloxane chains

It is interesting to note that silicon disulfide, SiS2, is even more closely analogous to the flexible organosiloxane chain polymers than is the oxide. In the crystal structure of the sulfide as determined by X-ray analysis, the silicon atoms are linked to two pairs of sulfur... 

Polyorganosiloxanes (organosiloxane elastomers) with linear molecular chains have the following formula ... 

Cyclolinear structure of synthesized POCS-4, POCS-5 and POCS-6 polymers was proved by hydro-dynamic study of properties of their solutions [56], The expected results of these investigations should indicate the predominant influence of the equilibrium flexibility of macromolecules and other specific properties of polymeric chains in block on occurrence of the thermotropic mesophase in cyclolinear organosiloxanes. 

In particular, introduction of cyclic fragments to linear poly(organosiloxanes) [4, 5] hampers the chain transfer reaction accompanied by ring separation which, in its turn, increases stability of the mentioned polymers. 

Summary Graft copolymers with poly(organosiloxane) backbone and thermoplastic side chains have been synthesized via the "grafting fi om" method based on azo- and triazene modified poly(organosiloxane)s. Initiation of free radical polymerization is possible from the polymeric azo and triazene initiators after thermal decomposition of the labile frmctions in solution. The graft products have been characterized by NMR, GPC, and DSC. Stable, free standing films can be cast from the graft copolymers. 

Polymeric initiators based on azo or triazene modified poly(organosiloxane)s can be used to synthesize graft copolymers with silicone backbone and thermoplastic side chains. The azo functionality has some advantages such as lower thermal stability, known reaction mechanism, no homopolymer formation and cleaner graft products. However, the synthesis of the triazene polymeric initiators requires fewer synthetic steps. The graft products microseparate but form stable films. 

Equilibrium polymerization, which can be anionic or cationic, is utilized to convert cyclic organosiloxanes into polydiorganosiloxane polymer chains. In the chemical industry octamethylcyclotetrasiloxane is preferred as such, or as a mixture with other siloxanes for chain termination and/or production of copolymers for specific applications. Particularly indu.strially important is anionic polymerization with basic catalysts such as alkali hydroxides, whereby the activity falls off in the order Cs > Rb > K > Na > Li. KOH is most frequently used e.g. as a suspension in octamethylcyclotetrasiloxane at 140°C, the catalyst being active from a concentration of several ppm. According to the assumed mechanism of this catalytic process, potassium siloxanolate is initially formed, which leads to cleavage of the Si-O-Si bonds and chain formation ... 

Researchers have now learned how to modify organosiloxane polymers by using various alkyl groups in chains of various lengths and conformations to produce a very wide array of products. All are organosiloxanes, but with very... 

The catalysed reaction of the dehydrocondensation of a,co-bis(trimethylsiloxy) ethylhydridsiloxanes with hydroxyorganocyclosiloxanes in the presence of an alkaline metal catalyst has been investigated and organosiloxane copolymers with various amounts of cyclic fragments in the side chain has been obtained. Dehydrocondensation reaction order, rate constants and activation energy were measured. 

The main reason for the investigation was to create convenient methods for the synthesis of organosiloxane copolymers with monocyclosiloxane fragments in the side chain. To establish the influence of the cyclic fragment on the properties of copolymers the initial difunctional organodichlorosiloxyorganocyclosiloxanes and a new class of cyclolinear copolymers, with monocyclic fragments in the side chain were synthesised. 

Synthesis of Organosiloxane Copolymers with Monocyclic Fragments in the Side Chain... 

Synthesis of Organosiloxane Oligomers with Cyclic Fragments in the Side Chain by the Reaction of Catalytic Dehydrocondensation... 

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