Synthesis of potassium-incorporated caged-ladder-like polyhedral oligomeric silsesquioxane hybrid macromolecules for unique thermal intumescent properties and thermal decomposition studies

This work synthesizes a series of potassium-contained phenyl oligomeric silsesquioxanes (KPOSS) through the hydrolytic condensation reaction of phenyltriethoxysilane intervened by KOH. FTIR, NMR, MALDI-TOF MS, and XPS confirmed that KPOSS possesses a distinct cyclic structure, composed of two series of oligomers with odd and even numbers of silicon atoms. Detailed analyses of various configurations at specific degrees of polymerization (fixed silicon atom numbers) were conducted. The directly obtained KPOSS powder exhibited submicron bead-chain morphology; it was also observed to have excellent film-forming properties, uniformly precipitating from the solvent and covering the substrate surface. Thermal analysis of KPOSS indicated an initial decomposition temperature and residual mass of 403.6 °C and 73.94 % respectively in N₂, demonstrating good thermal stability in inert gas environments. Py-GCMS was employed for precise analysis of the thermal pyrolysis gas products of KPOSS, revealing a simple composition comprising benzene and three types of phenylsilane gases. Through detailed analysis of the gaseous and condensed-phase products, a unique thermal pyrolysis pathway for KPOSS, attributed to the introduction of potassium ions, was inferred. Additionally, innovative direct flame treatment of KPOSS at high temperatures revealed significant thermal intumescent effects with the presence of only C, O, Si, and K elements, and the thermal intumescent mechanism was elucidated in conjunction with its thermal decomposition mechanism. This comprehensive and detailed study of the thermal decomposition of KPOSS provides a basic theoretical foundation for its subsequent application in processing high-performance polymer composites.