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银虫 (小有名气)

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专业: 应用有机化学

[求助] 1968年一篇文献

Equilibrations in Aprotic Systems （在非质子体系的平衡）
  Equilibrations in refluxing toluene were all carried out for limited times, since the solutions were slightly supersaturated with respect to phenyl-T8, and precipitated it steadily. In a typical procedure, phenyltrichlorosilane( 3 kg.) diluted with an equal volume of toluene was run into water (12 kg.) with stirring. After separation of the aqueous acid layer, the toluene solution of condensate was distilled to remove residual water and acid, along with 1300 g. of toluene. Next, potassium hydroxide pellets (1.41 9.) were added, and refluxing and trapping of the evolved water continued until dehydration was complete and the infrared spectrum no longer showed any silanol bands (9 hr.). The resulting mixture of sirup and precipitated phenyl-T8 was cooled and filtered to remove the T8(245 g., unwashed wt.); the filtrate (3155 g., 50.3%; phenylsilsesquioxanes) deposited no further crystals after standing for several weeks. Dry, unfractionated prepolymer [η] 0.12 dl./g. (in benzene at 250), 14,000, could be isolated by precipitation into methanol or ligroin. Similar preparations at a phenylsilsesquioxane concentration of 36%  in toluene were carried out longer (16 hr.), but the amount of T8 formed was lower (6-8%), as was also the intrinsic viscosity of the unfractionated prepolymer(0.085 dl . / g . ) .
The use of refluxing diglyme (b.p. 1600, phenyl-T8 solubility 0.52 g./100 ml.) circumvented the precipitation problem. Samples (10-20 g.) of dried but not decatalyzed prepolymers prepared in toluene were dissolved in freshly redistilled diglyme and the solutions refluxed 4 days under nitrogen. When a prepolymer specimen containing 6% suspended phenyl-T8 was used, the solutions were homogeneous after refluxing for 1 day.
  The attainment of equilibrium in these systems was demonstrated by the invariance of the product spectra, and by the constancy of the equilibrium constants calculated from runs made at different concentrations.
Fractionation of Prepo1ymers
The toluene or diglyme solutions of equilibrated phenylsilsesquioxanes were neutralized with HCI, seeded with phenyl-T8 crystals, and allowed to stand for several days while the bulk of the T8 crystallized out. The soluble silsesquioxanes were then recovered from solution, dissolved in three times their weight of acetone, and allowed to stand overnight, whereupon much of the phenyI-Tl2 and any prepolymer above [η] ca. 0.14 precipitated. These were filtered off and separated by extracting the prepolymer with tetrahydrofuran. The acetone solutions were then diluted to give polymer concentrations of about l0% and fractionated in the conventional way by adding successive increments of methanol at the boiling point, allowing the mixture to cool and stand until phase separation was complete, removing the solution, and reprecipitating the polymer from acetone into methanol. The prepolymer fractions thus recovered ranged in molecular weight (ebullioscopic in benzene)  from 14,000 down to 3,000, and had  ratios near 1.4. (Fractionation of a l% solution in acetone was attempted, but was found to require extremely long times for the phase separations.) All of the methanolic filtrates, as well as the final solution of materials soluble in 90% methanol, were retained and evaporated to recover the lower silsesquioxanes. A toluene solution of these deposited a little additional T8 and T12, which were separated from each other by extracting the T12 with a little boiling toluene. The final separation of the cage-like species (mol. wt. <1500, one u,SiOSi near 1127 cm.-l) from the lowest prepolJ-mer fraction (mol. wt. >2900, SiOSi's near 1135 and 1062 cm.-l) was accomplished by repeated precipitation from toluene solution into nine volumes of methanol. The material soluble in 1 : 9 toluene-methanol was dissolved in an equal weight of toluene and allowed to stand several days while the Tl0 crystallized out, leaving behind the noncrystalline T9-T12 cage compounds.

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