Synthesis of Ladder Silsesquioxanes by in situ Polycondensation of Cyclic Tetravinylsiloxanetetraol.
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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. Subsequently, it was quenched to 118 K and heated again at 10 K/min. Thermogravimetric measurements were performed by use of a Hi-Res TGA 2950 Thermogravimetric Analyzer (TA Instruments) in nitrogen atm...