Covalent surface grafting of branched polyethylenes on silica nanoparticles by surface-initiated ethylene Living polymerization with immobilized Pd-diimine catalysts

We report in this article a new versatile surface-initiated ethylene living coordination polymerization technique for grafting from surface functionalization of silica nanoparticles with narrow-distributed branched polyethylene brushes of controllable length. The key to the success of this technique is the use of acetonitrile Pd-diimine complex, [(ArN=C(Me)-(Me)C=NAr)Pd(CH3)(N=CMe)]+SbF6 (Ar = 2,6-(iPr)(2) C6H3) (1), which possesses unique immobilization and polymerization chemistry. In this technique, complex 1 was immobilized covalently onto acryloyl-functionalized silica particle surface by reacting with the surface-tethered acryloyl groups, giving rise to Pd-diimine chelate complexes covalently tethered on silica surface through an ester linkage. The tethered Pd-diimine chelate complexes catalyzed successfully surface-initiated ethylene living polymerization at 5 degrees C and ethylene pressure of 400 psi, leading to narrow-distributed branched polyethylene chains covalently tethered on silica surface through the ester linkage. The branched polyethylene brushes, after cleaved off from the silica particles, were found to possess narrow molecular weight distribution (polydispersity index of about 1.18) and have a linear increase of their number-average molecular weight and relative mass content with the polymerization time. The covalent grafting of polymer brushes was confirmed by using characterization techniques including nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). To the best of our knowledge, this represents the first report on the use of surface-initiated ethylene living coordination polymerization technique for surface functionalization of inorganic particles with polyethylene brushes.