ChemS Graduate Seminar: Surface Initiated Polyhomologation of Polyethylene Brushes on Silica Nano Particles Surface

Oct 16 2016 12:00 PM - Oct 16 2016 01:00 PM

​Surface Initiated Polyhomologation of Polyethylene Brushes on Silica Nano Particles Surface

ABSTRACT: Surface initiated polymerization (SIP) yields polymer brushes covalently bonded to the substrates, specifically nano substrate such as silica nanoparticles (Si-NPs), graphene oxide sheet, gold nanoparticles and carbon nanotubes (CNs), since the properties of such nanomaterials are unique and essential in a wide range of applications. Among inorganic–organic hybrids, silica-polymer hybrid materials are the most commonly reported [1]. This may be due to the easy synthesis of silica particles, beside their wide usage in paints, drug delivery, chromatography, etc.

In this work, the Stober route [2] was followed to synthesize practically monodispersed spherical silica particles. The hydroxyl groups on the surface of silica particles can be easily reacted with dicloro(divinyl)silane or vinyl triethoxysilicate (VTES) to introduce vinyl groups, which by further reaction with organoboranes afford cycloborane initiator groups on the silica’s surface. This opens up the possibility of using the borane-initiated polyhomologation of ylides, discovered by Shea [3] and advanced by our Group [4], [5] for the surface modification of silica nanoparticles (Si-NPs) with well-defined polyethylene for the first time. Polyhomologation or C1 polymerization is considered as the best method of preparing linear, well-defined polyethylene (PE)-based polymeric materials with controllable molecular weight (Mn) and low polydispersity index (PDI). The mechanical and thermal properties of polyethylene mixed with PE-grafted silica will be significantly enhanced and thus can be find conventional and high-tech applications.

The physicochemical properties of these hybrid materials were studied and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), Solid state NMR and Thermogravimetric analysis (TGA).

Initial results show successful modification on the surface of monodispersed spherical nano silica that will lead to obtain a good inorganic substrate to initiate polyethylene (PE).

This method is general and can be applied on other nanoparticles and thus opens horizon for advanced applications such as nanolithography.

[1] Radhakrishnan, B.; Ranjan, R.; J. Brittain, W. Surface initiated polymerizations from silica nanoparticles. Royal Society of Chemistry 2006, 2, 386-396.
[2] Stöber, W.; Fink, A.; Bohn, E. Controlled Growth of Monodisperse Silica Spheres in the Micron Size Range. Journal of Colloid and Interface Science 1968, 26 (1), 62–69.
[3] Luo, J.; Shea, K. J. Polyhomologation. A Living C1 Polymerization. Accounts of Chemical Research 2010, 43 (11), 1420–1433.
[4] Zhang, H.; Zhang, Z.; Gnanou, Y.; Hadjichristidis, N. Well-Defined Polyethylene-Based Random, Block, and Bilayered Molecular Cobrushes. Macromolecules 2015, 48 (11), 3556–3562.
[5] Zhang, Z.; Zhang, H.; Gnanou, Y.; Hadjichristidis, N. Polyhomologation Based on in Situ Generated Boron-Thexyl-Silaboracyclic Initiating Sites: A Novel Strategy towards the Synthesis of Polyethylene-Based Complex Architectures. Chem. Commun. 2015, 51 (49), 9936–9938.​