Surface-initiated polymerization with poly(n-hexylisocyanate) to covalently functionalize silica nanoparticles

New methods are needed for covalent functionalization of nanoparticles-surface with organic polymer coronas to generate polymeric nanocomposite in a controlled manner. Here we report the use of a surface-initiated polymerization approach, mediated by titanium(IV) catalysis, to grow poly(n-hexylisocyanate) chains from silica surface. Two pathways were used to generate the interfacing in these nano-hybrids. In the first one, the nanoparticles were “seeded” with SiCl₄, followed by reaction with 1,6-hexanediol to form hydroxyl groups attached directly to the surface via O-Si-O bonding. In the second pathway, the nanoparticles were initially exposed to a 9:1 mixture of trimethyl silyl chloride and chlorodimethyl octenyl silane which was then followed by hydroboration of the double bonds, to afford hydroxyl groups with a spatially controlled density and surface-attachment via O-Si-C bonding. These functionalized surfaces were then activated with the titanium tetrachloride catalyst. In our approach, surface tethered catalyst provided the sites for n-hexyl isocyanate monomer insertion to “build up” the surface-grown polymer layers from the “bottom-up”. A final end-capping, to seal off the chain ends, was done via acetyl chloride. Compounds were characterized by Fourier transform infrared spectroscopy (FTIR), ¹H nuclear magnetic resonance spectroscopy (NMR), gas chromatography-mass spectrometry (GC-MS), gel permeation chromatography (GPC), and thermogravimetric analyses. [Figure not available: see fulltext.]