Polymerization of Poly(Itaconic Acid) on Surfaces by Atom Transfer Radical Polymerization in Aqueous Solution
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Polymerization of Poly(Itaconic Acid) on Surfaces by Atom Transfer Radical Polymerization in Aqueous Solution Amit Y. Sankhe, Scott M. Husson, and S. Michael Kilbey II Department of Chemical Engineering, Clemson University, Clemson, SC 29634-0909, U.S.A. ABSTRACT Poly(itaconic acid) (PIA) was grown from surface-tethered initiator sites via atom transfer radical polymerization (ATRP). The surface-tethered PIA layers were grown from hydroxylterminated SAMs capped with initiator molecules of 4-(chloromethyl)-benzoylchloride. This polymerization initiator molecule and a copper-based organometallic catalyst allowed tethered PIA chains to be grown via ATRP at room temperature in aqueous solutions. Ellipsometric studies and external-reflection, Fourier-transform infrared spectroscopy (ER-FTIR) confirm the presence and growth of the surface-tethered PIA layer. We describe here how changing the temperature of polymerization alters the layer growth and kinetics of the process, and demonstrate, via ER-FTIR spectroscopy, that these surface-tethered layers do bind cationic dyes through ion-exchange mechanisms. INTRODUCTION Surface-initiated, radical polymerization is a robust technique for creating grafted polymer layers on a surface. A reactive species attached to the surface initiates the polymerization reaction by generating a radical that can open double bonds of monomers [1]. The discovery of surface-initiated, transition metal-catalyzed living radical polymerization developed independently by Matyjaszewski and coworkers [2] and Sawamato and coworkers [3] has lead to polymerization reactions that produce surface-tethered polymers of controlled molecular weights and narrow molecular weight distributions. ATRP is an example of living free-radical polymerization. It is a catalytic process wherein a transition metal complex reversibly activates the dormant polymer chains via a halogen atom transfer reaction [1]. Since its discovery, ATRP has been used to polymerize a wide variety of monomers, including acrylates, styrenes, and acrylonitriles [4]. In the present study, we report on the surface-tethered ATRP of poly(itaconic acid) (PIA). PIA is a diacid polymer with two carboxylic acid groups per monomer. Because of its ionic character and solubility in aqueous solutions [5], PIA can extract organic ions or metal ions from solution by ion-exchange. As a result, polymers of itaconic acid may be used to create separation agents. The process used to create the surface-tethered PIA layer on model gold surfaces involves multiple self-assembly steps, which are depicted in Figure 1. First, a selfassembled monolayer (SAM) is made by alkane thiol chemisorption, followed by attachment of the initiator onto the SAM. The polymerization is then initiated from these surface-tethered initiator sites on the SAM.
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Figure 1. Schematic diagram showing the steps involved in growing the PIA layer from the initiator-capped SAM. EXPERIMENTAL Surface-initiated polymerization of it
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