Thermal stability of POSS/methylsilicone nanocomposites

Methylsilicone nanocomposites containing polyhedral oligomeric silsesquioxane (POSS) were prepared, including three kinds of POSS silanols (TriSilanolPhenyl-POSS, TriSilanolIsobutyl-POSS and MonoSilanolIsobutyl-POSS) reinforced methylsilicone through chemical modification method and one kind of non-hydroxyl-containing POSS (Methacryl-POSS) modified methylsilicone through physical blend. The structures of the obtained hybrid materials were characterized with Gel Permeation Chromatograph (GPC), Fourier transform infrared (FTIR) and transmission electron microscopy (TEM). The GPC and FTIR spectra suggested successful bonding of three kinds POSS silanols and methylsilicone resin. TEM analysis showed that POSS silanols can dissolve in methylsilicone resin at the molecular level. However, there was some aggregation of Methacryl-POSS in the polymer resin systems. Thermal stability of POSS/methylsilicone nanocomposites was investigated by thermogravimetric analysis (TGA), solid-state ²⁹Si NMR and X-ray photoelectron spectroscopy (XPS). All these techniques showed that POSS incorporation result in increased decomposition temperatures and thermal oxidation resistance. Chemically bonded POSS silanols reinforced methylsilicone nanocomposites are thermally more stable than the original methylsilicone, primarily by reducing the effects of silanol end groups on the thermolysis through condensation reaction of Si-OH groups and the nanoscaled dispersion of POSS cages in methylsilicone matrixes. For the physically mixed system, the enhancement of thermal stability could be mainly ascribed to the nanoreinforcement effect of Methacryl-POSS on the polymer matrix. The formation of protective inorganic SiO₂ layer and the hydrogen bonding existed between the hydroxyl group and the siloxane groups of four kinds of POSS are also important factors for the improvement of the thermal stability of methylsilicone.