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

Novel organic/inorganic hybrid copolymers have been prepared using single s ite catalysis. Ethylene copolymers incorporating a norbornylene-substituted polyhedral oligomeric silsesquioxane (POSS) macromonomer have been prepare d using a metallocene/methylaluminoxane (MAO) cocatalyst system. Isotactic polypropylene-containing POSS nanoparticles were also synthesized for the f irst time using a similar approach utilizing a C-2 symmetric ansa-metalloce ne. A wide range of POSS concentrations were obtained in these polyolefin P OSS copolymers under mild conditions, up to 56 wt % for PE-POSS copolymers and 73 wt % for PP-POSS copolymers. Initial findings point to improved ther mooxidative stability for these nanocomposite polyolefins containing the "m olecular silica" side groups relative to their homopolymer analogues. Therm ogravimetric analysis of the PE-POSS copolymers under air shows a 90 degree sC improvement, relative to a polyethylene control sample of similar molecu lar weight, in the onset of decomposition temperature based upon 5% mass lo ss. On the basis of dynamic mechanical thermal analysis, the tensile proper ties of the PE-POSS copolymer were maintained at low POSS loadings. A modul us plateau at temperatures above 175 degreesC is observed, indicating suppr ession of melt flow for polyethylene POSS copolymers.