Novel polyolefin nanocomposites: Synthesis and characterizations of metallocene-catalyzed polyolefin polyhedral oligomeric silsesquioxane copolymers

Novel organic/inorganic hybrid copolymers have been prepared using single site catalysis. Ethylene copolymers incorporating a norbornylene-substituted polyhedral oligomeric silsesquioxane (POSS) macromonomer have been prepared using a metallocene/methylaluminoxane (MAO) cocatalyst system. Isotactic polypropylene-containing POSS nanoparticles were also synthesized for the first time using a similar approach utilizing a C-2 symmetric ansa-metallocene. A wide range of POSS concentrations were obtained in these polyolefin POSS copolymers under mild conditions, up to 56 wt % for PE-POSS copolymers and 73 wt % for PP-POSS copolymers. Initial findings point to improved thermooxidative stability for these nanocomposite polyolefins containing the "molecular silica" side groups relative to their homopolymer analogues. Thermogravimetric analysis of the PE-POSS copolymers under air shows a 90 degreesC improvement, relative to a polyethylene control sample of similar molecular weight, in the onset of decomposition temperature based upon 5% mass loss. On the basis of dynamic mechanical thermal analysis, the tensile properties of the PE-POSS copolymer were maintained at low POSS loadings. A modulus plateau at temperatures above 175 degreesC is observed, indicating suppression of melt flow for polyethylene POSS copolymers.