Nanoparticle-Supported Molecular Polymerization Catalysts

Homogeneous molecular catalysts are immobilzed in a well-defined fashion on individual silica nanoparticles with a narrow particle size distribution by covalent attachment. This synthetic methodology is demonstrated with modified salicylaldiminato-substituted titanium(IV) complexes incorporating a trimethoxysilane- terminated linker: dichloro-bis(κ 2 -N,O-6-(3-(trimethoxysilyl)propoxyphenylimino)-2-tert-butyl-phenolato)tita- nium(IV) (3) and dichlorobis(κ 2 -N,O-6-(4-(trimethoxysilyl)propoxy-2,3,5,6-tetrafluorophenylimino)-2-tert- butylphenolato)titanium(IV) (4). 3 and 4 were bound covalently to silica nanoparticles via direct condensation of the alkoxysilane with residual silanol groups on the lipophilically modified particle surface. The resulting nonaggregated individual silica nanoparticles (ca. 50 nm diameter) with catalyst bound to the outer surface have been characterized by CP-MAS NMR, FT-IR spectroscopy and by electron microscopy (TEM, ESI). These supported catalysts exhibit single site characteristics for the polymerization of ethylene, affording ultra high molecular weight polyethylene. Polymer particles with a uniform spherical morphology and a particle size in the submicron regime are formed. TEM analyses of cross-sections of single particles formed at different polymerization times revealed a complete fragmentation of the nanoparticle support to fragments of ca. 10 nm size homogeneously distributed in the polymer matrix.