Table of Contents
ISRN Pharmaceutics
Volume 2013, Article ID 958712, 7 pages
http://dx.doi.org/10.1155/2013/958712
Research Article

Photoinitiated Polymerization of 2-Hydroxyethyl Methacrylate by Riboflavin/Triethanolamine in Aqueous Solution: A Kinetic Study

1Institute of Pharmaceutical Sciences, Baqai Medical University, 51 Deh Tor, Toll Plaza, Super Highway, Gadap Road, Karachi 74600, Pakistan
2Department of Dental Material Sciences, Baqai Dental College, Baqai Medical University, 51 Deh Tor, Toll Plaza, Super Highway, Gadap Road, Karachi 74600, Pakistan

Received 17 June 2013; Accepted 30 July 2013

Academic Editors: F.-R. Chang, D. Kuzmich, and R. Veerasamy

Copyright © 2013 Iqbal Ahmad et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The polymerization of 1–3 M 2-hydroxyethyl methacrylate (HEMA) initiated by riboflavin/triethanolamine system has been studied in the pH range 6.0–9.0. An approximate measure of the kinetics of the reaction during the initial stages (~5% HEMA conversion) has been made to avoid the effect of any variations in the volume of the medium. The concentration of HEMA in polymerized solutions has been determined by a UV spectrophotometric method at 208 nm with a precision of ±3%. The initial rate of polymerization of HEMA follows apparent first-order kinetics and the rates increase with pH. This may be due to the presence of a labile proton on the hydroxyl group of HEMA. The second-order rate constants for the interaction of triethanolamine and HEMA lie in the range of 2.36 to  M−1 s−1 at pH 6.0–9.0 suggesting an increased activity with pH. An increase in the viscosity of HEMA solutions from 1 M to 3 M leads to a decrease in the rate of polymerization probably as a result of the decrease in the reactivity of the flavin triplet state. The effect of pH and viscosity of the medium on the rate of reaction has been evaluated.