Surface Initiated Polymerization (SIP) on Nanoparticle Surfaces: Demonstration of First Principles and Preparation of Na
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Surface Initiated Polymerization (SIP) on Nanoparticle Surfaces: Demonstration of First Principles and Preparation of Nanocomposite Materials Rigoberto Advincula*, Qingye Zhou, Jimmy Mays Department of Chemistry, University of Alabama at Birmingham Birmingham, AL 35294-1240 ABSTRACT To investigate the grafting of polymer chains onto nanoparticles (metal, semi-conductor, inorganic, etc) and nanostructured (patterned) surfaces, we have investigated anionic surface initiated polymerization (SIP) on a variety of surfaces. Understanding the surface chemistry issues involved is critical for future applications and protocols. SIP of polystyrene from Silicate and clay nanoparticles surfaces have been made by the living anionic polymerization method with 1,1-diphenylethylene (DPE) initiation sites attached to nanoparticle surfaces using chlorosilane and amino functional groups. Model studies were initially done on flat Si-wafer surface and recently with Au surfaces. For the nanoparticles, the grafted polymers were cleaved and characterized by FTIR, NMR, AFM, TGA and SEC. Polymers grafted from nanoparticle surfaces show higher polydispersity and lower molecular weight than those formed in solution. We observed that diffusion of the monomer, stability of the initiator attachment to the surface, and aggregation of the particles controls the properties of the grafted polymers on particle surfaces. On the other hand, the use of the anionic polymerization method on surfaces allows the possibility of combining a variety of polymers (organic) with various nanoparticle and surfaces (inorganic) for the preparation of hybrid nanocomposite materials. INTRODUCTION Surface Initiated Polymerization (SIP) is a method for preparing an assembly of tethered polymer chains in mutual proximity forming so called “polymer brushes”. A huge amount of theoretical work has been devoted on tethered polymer brushes compared to the limited experimental information available on their properties and structure [1,2]. Ideally, the unique geometry at solid interfaces results in end-grafted, strictly linear chains of the same length where the grafting density is sufficiently high with respect to the equilibrium radius of gyration (Rg) of the grafted macromolecules [3]. To avoid steric crowding, polymer chains are forced to stretch away from the interface, resulting in a brush height (h), significantly larger than Rg (usually a few nm). For nanoparticles, these dimensions are coincident, therefore investigating tethered polymers in this regime are of great interest. Tethered polymers on flat surfaces have involved polymer physisorption [4] and chemisorption (covalent attachment). For covalent attachment, this has been accomplished by grafting preformed polymers to tethering sites, a “grafting to” approach or by polymerizing from surface-immobilized initiators, a “grafting from” approach. Examples of the latter include polymerization using surfaceimmobilized azo-bis isobutyronitrile (AIBN) analogues [5], atom-transfer radical polymerization (ATRP) [6], 2,2,6,6-t
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