Crosslinking vs. filler effect of carboxylate-substituted zirconium oxo clusters on the thermal stability of polystyrene

Inorganic-organic hybrid materials were prepared by step-wise free radical polymerization of styrene in the presence of zirconium oxo clusters of the general compositions Zr6O4(OH)4(carboxylate)12 (carboxylate = 5-norbornene-2-carboxylate or isobutyrate/methacrylate) and Zr12O8(OH)8(carboxylate)24 (carboxylate = acetate/propionate, vinylacetate, or acetate/methacrylate). Clusters with non-polymerizable ligands resulted in cluster/polystyrene blends which were soluble in toluene, whereas clusters with polymerizable ligands gave cluster-crosslinked, swellable polymers for which solvent uptake correlated with the functionality of the corresponding cluster. The onset temperatures of thermal decomposition and the glass transition temperatures of all cluster-containing polymers were higher than that of neat polystyrene, independent of whether the clusters were crosslinking or blended into the polymer.