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Synthesis Of Ladder Silsesquioxanes By In Situ Polycondensation Of Cyclic Tetravinylsiloxanetetraol

623 words - 3 pages

Liquid state NMR (1H, 13C and 29Si NMR) spectra for the precursors and condensed soluble materials were recorded in CDCl3 as a solvent on a Bruker DRX-500 MHz spectrometer, with TMS as the reference. Solid-state 29Si NMR spectra were recorded on a AV-400 Bruker spectrometer at 59.627 MHz. The use of the high power decoupling (hpdec) method of direct polarization enabled a quantitative integration. The peak positions were referenced to the signal of Q8M8 (trimethylsilyl ester of cubic octameric silicate) standard.
Phase transitions of polymers were studied by differential scanning calorimetry (DSC) technique (DuPont 2000 thermal analysis system). Thermograms were taken for samples (sealed in aluminium pans) quenched rapidly from the melt (room temperature) and then heated at the rate of 10 K/min from 118 K to 323 K. The sample was kept at 323 K for 3 min to destroy any thermal history. ...view middle of the document...

Size exclusion chromatography (SEC) was performed using Agilent 1100 series chromatograph composed of degasser, pump, and autosampler. Two PL Gel 5 μm MIXED-C columns (7.8 x 300 mm) were used in a series (temp. 27 °C). RI (OPTILAB T-rex, Wyatt) and MALLS (DAWN HEOS, II, Wyatt, λ= 682 nm) were used as detectors. Dichloromethane was used as a mobile phase at the flow rate of 0.8 mL/min. Samples (concentration of polymers: 7 mg/mL) and filtered through 0.2 μm pore size SRP membrane filters. Injection volumes of the sample solutions were 100 μL. Molecular masses were derived from a calibration curve based on polystyrene standards. Astra 4.90.07 software was used to treat the data.
WAXS (wide angle-X-ray scattering) was used for the determination of sample structure. The experiments were performed on Philips X’Pert Pro MD diffractometer. Radiation used was Cu Kα1 line monochromatized by Ge(111) monochromator. Standard Bragg-Brentano geometry with θ–2θ setup was applied (0.008° step size and 5–90° 2θ range).

2.3 Synthetic porcedures:
2.3.1.Potassium tetravinyltetracyclosiloxanolate
Potassium tetravinyltetracyclosiloxanolate was prepared according to the previously described procedure [24]. Triethoxyvinylsilane (0.235 mol) and a mixture of anhydrous ethanol (30 ml) and water (0.4 ml) were simultaneously added drop-wise to a mixture of hexanes (220 ml) and KOH (0.276 mol) charged into a round-bottom flask equipped with a magnetic stirrer and a thermometer. The rate of addition was adjusted not to exceed 24oC. Once the addition was completed, the reaction mixture was stirred for another 1.5 h at room temperature, then it was cooled to 0-4°C in a water/ice bath for 5 hours. A fine white precipitate precipitated from the solution. It was filtered under reduced pressure, washed with large volumes of n-pentane and dried under high vacuum (1 Torr) at room temperature to constant weight. A white crystalline powder was obtained in a yield of 2.37 g (76%). It was stable for months at low temperatures.

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