Polyphenylsiloxane

Polyphenylsiloxanes are produced from alkoxyphenylsilanes, triacetoxy-phenylsilane, pure phenyltrichlorosilane or undistilled phenylchlorosilanes. Depending on the functionality of the parent monomer and the preparation technique, polyphenylsiloxanes can be branched or ladder. Often, to improve the properties of polyphenylsiloxanes, they are modified with various organic substances (by mechanical mixing or chemically). 

Alkoxyphenylsilanes, which are used as raw stock in the production of polyphenylsiloxanes and polyphenylsiloxane varnishes, can be produced by the Grignard technique and etherification of phenyltrichlorosilane with alcohol. 

Fig. 66. Production diagram of polyphenylsiloxane varnishes 1 - agitator 2 - 5, 9 - 12, 16, 20, 21, 23 - batch boxes 6, 18 - coolers 7 - reactor 8 - hydrolyser 13 -faolite tower 14, 15 - collectors 17 - distillation tank 19, 25 - settling boxes 22 -apparatus for varnish preparation 24 - nutsch filter 26 - ultracentrifuge 27 - container...

After the distillation of the solvent, tank residue, which is a mixture of polyphenylsiloxanes, is cooled in apparatus 17 down to 50-60 °C and tested for varnish concentration. Then the product is sent out of the tank with vacuum through batch box 20 into apparatus 22. The apparatus is also filled from batch box 21 with a calculated amount of toluene (or xylene) to prepare a 50% solution of varnish. The mixture in apparatus 22 is agitated, heated to 60-70 °C and held at this temperature for 3 hours. 

The prepared polyphenylsiloxane varnish is filtered through nutsch filter 24 and sent into settling box 25. Sometimes the varnish is subjected to prior modification. For this purpose, apparatus 22 is filled with a necessary amount of glyptal polymer or polybutylmethacrylate. In this case the mixture is agitated for 2 hours and sent through the nutsch filter into settling box 25. The varnish is held there for 3 days and centrifuged. The finished varnish is collected in containers 27. 

Polyphenylsiloxane varnishes are light-brown to brown liquids without visible mechanical impurities. The volatile content is 45-85% (depending on the brand) the acidity number is 3-15 mg KOH/g. 

These varnishes can be used to produce heat-resistant enamels, which are prepared directly before use by mixing varnishes with aluminum power (usually 5 weight parts of powder per 100 weight parts of varnish). This enamel can be used for parts which operate at 450-500 °C (automobile radiators, calorifers, ventilation units, etc.). Polyphenylsiloxane can be used... 

The most important properties of some polyphenylsiloxanes and poly-phenylsiloxane varnishes are given in Table 25. 

Below let us use poly [4-[2-(hydroxyphenyl)propyl-2]-phenyl]phenyl siloxane as an example and illustrate the production of polyphenylsiloxanes from trialkoxyphenylsilane (in our case tributoxy-phenylsilane) synthesised by the second technique, the etherification of phenyltrichlorosilane. The production comprises the following main stages the synthesis of tributoxyphenylsilane and its partial hydrolytic condensation the re-etherification of polybutoxyphenylsiloxane with diphenylolpropane. 

Table 25. Most important properties of polyphenylsiloxane varnishes KO-85, KO-815 and polymer F-9...

Moreover, the differences in the segmental anisotropy of ladder polymers may be related to the differing extent of the defectiveness of their double-chain structure (see p. 100). This can be demonstrated by a comparison of the anisotropy of various samples of ladder polyphenylsiloxanes with an identical chemical structure of monomer units but with the values of ([n]/[r ])oo and, hence, of Oj - 2 which may differ by a factor of 2.5. In fact, if angle bonds are introduced into a cyclic chain a partially ladder structure results which greatly decreases the equilibrium chain rigidity. 

The study of birefringence in films of cyclolinear polyphenylsiloxane (CLPhS) gave the following results in a polarizing microscope with crossed Nicol prisms it was distinctly seen that the CLPhS films not subjected to external mechanical influences are on the whole optically inhomogeneous. The film consists of birefringent parts, the optical axes of which are oriented randomly over the entire sample. 

Furthermore, inorganic polyphenylsiloxane has been prepared by hydrolysis of PhSiCls and subjected to further functionahzation [183-185]. After initial formation of a prepolymer, the polymer formed in the presence of KOH catalyst [183], is subjected to chloromethylalion with chloromethylmethylether and ZnCh catalyst, and phosphination by reaction with LiPRj (Scheme 1.12) [184,185] ... 

Fig. 158. Kinetics of the destruction of polymers at 350 C. 1) Viniflex 2) phenol-formaldehyde resin 3) polymethylsiloxane 4) polyphenylsiloxane.

Even quadruple-chain ladder polyphenylsiloxane structures are feasible by a supra-molecular template-directed stepwise coupling and polymerization method [35]. 

Chen Z, Li Z, Guo H, Zhang J, Ren Z, Yan S, Xie P, Zhang R (2012) Supramolecular template-directed synthesis of soluble quadruple-chain ladder polyphenylsiloxane (Ph-QCLP) with high molecular weight. Chem Mater 24(10) 1968-1973. doi 10.1021/ cm300951x... 

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