Thermal degradation of differently substituted Polyhedral Oligomeric Silsesquioxane (POSS) nanoparticles

The use of Polyhedral Oligomeric Silsesquioxane (POSS) nanoparticles is an efficient method for obtaining hybrid nanocomposite materials. A typical POSS nanoparticle consists of a rigid inorganic core of eight silicon atoms linked by oxygen atoms (Si8O12 nanostructured skeleton) surrounded by eight organic groups attached to each corner to promote the solubility in conventional solvents and compatibility with a host polymer matrix. The size of this molecules lies in a range of 1-3 nm. A POSS molecule with an isobutyl periphery has a diameter of approximately 1.5 nm. Then POSS are isodimensional spherical particles which can form truly dispersed nanocomposites and for this reason have been used as fillers in a number of polymeric matrices with the aim to improve physical, mechanical and thermal polymer properties [1-2]. The most common molecular formula of POSS is (RSiO1.5)8 or (R)7(SiO1.5)8R’1; when the substituents are aliphatic groups, the POSS derivatives show good compatibility and miscibility in polymer matrix but poor thermal properties (evaporation and sublimation loss weight); on the contrary POSS full phenyl substituted shows excellent thermal properties but low compatibility. The aim of this work was to prepare hetero monosubstituted POSS derivatives of formula (R)7(SiO1.5)8R’1, where R- and R’ are a cyclopentyl and a substituted phenyl group, respectively (Fig.1), and to study their thermal and thermooxidative behaviour as a function of the substituents on the aromatic ring. In order to verify if and how much the nature of organic R- groups affects the thermal behaviour of our compounds, degradation TG and DTA experiments, in both flowing nitrogen and static air atmosphere, were carried out.