UV-stabilisation of polystyrene-based nanocomposites provided by polyhedral oligomeric silsesquioxanes (POSS)

The photo-ageing behaviour of Polyhedral Oligomeric SilSequioxane (POSS)-polystyrene (PS) nanocomposites has been investigated for the first time. POSS having different inorganic framework and pendant organic groups have been used in the PS nanocomposite preparation and the formulated films were subjected to accelerated weathering. Compared to pristine PS, the POSS-containing PS developed a lower level of carbonyl and hydroxyl groups as a function of the exposure time, indicating a significantly improved resistance of the nanocomposites to photo-degradation. The results suggest that all of the investigated POSS molecules play a protective role and may extend the in-use lifetime of the polymeric matrix. The protection efficiency seems to depend on the structure of the POSS used, i.e. the type of their inorganic framework and organic pendant groups. The efficacy of the protection provided by POSS is more pronounced for the open-cage POSS-triols than for the closed-cage POSS, suggesting an active role of the POSS-triol free OH group in the PS stabilisation process. The pendant organic groups significantly influence the nanocomposite's local morphology by controlling the formation of POSS re-aggregates and/or the POSS dispersion into the matrix, and its response to photo-oxidation.