Omekšavanje fenilsilseskvioksana modificiranih oktilnim lancima

Octyl-modifi ed phenylsilsesquioxanes were prepared from phenyltriethoxysilane and octyltriethoxysilane by two-step acid-base catalysed sol-gel process. Resulting silsesquioxanes were characterized by scanning electron microscopy, X-ray diffraction analysis, gel permeation chromatography and Fourier-transform infrared spectroscopy, while the thermal properties were investigated by differential scanning calorimetry and thermogravimetric analysis. Morphology of polysilsesquioxanes was found to greatly depend on ratio of alkoxides, presumably because of poor miscibility of long alkyl chains which results in a less homogeneous initial mixture. Long alkyl chains also present steric hindrance to condensation of phenyltriethoxysilane eventually preventing the formation of particles. Incomplete condensation caused the decrease of softening temperature from 160°C to ~50°C and overall poorer thermal stability of polysilsesquioxanes. Decrease in initial temperature of degradation by at least 150°C is probably caused by alkyl chains exposed on the surface of the particles. Increased solvent content improves incorporation of octyl chains due to better solubility and yields polysilsesquioxanes with a more regular structure and a more homogeneous particle size distribution. On the other hand it adversely infl uences the level of condensation and the softening temperature.Fenilsilseskvioksani modifi cirani oktilnim lancima pripravljeni su od feniltrietoksisilana i oktiltrietoksisilana dvostupanjskim kiselobaznim sol-gel postupkom. Nastali silseskvioksani karakterizirani su pretražnom elektronskom mikroskopijom, rendgenskom difrakcijskom analizom, kromatografijom na propusnom gelu i spektroskopijom u infracrvenom području s Fourierovim transformacijama, dok su njihova toplinska svojstva ispitivana razlikovnom pretražnom kalorimetrijom i termogravimetrijskom analizom. Ustanovljeno je da morfologija polisilseskvioksana uvelike ovisi o omjeru polaznih alkoksida, vjerojatno zbog slabe topljivosti dugih alkilnih lanaca i time nehomogenije početne smjese. Dugački alkilni lanci također sterički ometaju kondenzaciju feniltrietoksisilana, što konačno onemogućava nastajanje čestica. Nepotpuna kondenzacija uzrokuje sniženje omekšavališta sa 160 °C na ~50 °C i općenito slabiju toplinsku postojanost nastalih polisilseskvioksana. Sniženje početne temperature razgradnje za 150 °C vjerojatno je posljedica izloženosti alkilnih lanaca na površini čestica. Povećan udio otapala poboljšava ugradnju oktilnih lanaca zbog njihove bolje topljivosti i daje polisilseskvioksane pravilnije strukture i homogenije raspodjele čestica. No dodatak otapala negativno utječe na stupanj kondenzacije i omekšavalište polisilseskvioksana