One-Step Synthesis of Thermoplastic Phenylsilsesquioxane Polymer and Its Copolymers with Diphenylsiloxanes

The preparation of reversibly softening polymers and copolymers of phenylsilsesquioxane in a one-step synthesis has been studied. The synthetic methods are based on hydrolytic polycondensation of PhSiCl₃ or copolycondensation of PhSiCl₃ with Ph₂SiCl₂ using moistened or hydrated salts: (1) moistened Na₂CO₃, K₂CO₃, (2) Na₂B₄O₇·10H₂O, (3) Na₃PO₄·12H₂O. Syntheses (1) and (2) gave products as reversibly softening and soluble materials, whereas synthesis (3) produced partially cross-linked resins from which a soluble material might be extracted. Polycondensation using borax gave polymers and copolymers with incorporated boron atoms. The polysilsesquioxanes were characterized by size exclusion chromatography (SEC), ¹H and ²⁹Si NMR, IR spectroscopy, and elemental analysis. Thermal properties were studied by DSC and thermogravimetry.