Title
Green synthesis and isoconversional thermal analysis of HPMC acetate: a potent matrix for drug delivery
Authors
MUHAMMAD AMIN MUHAMMAD AJAZ HUSSAIN SYEDA AQSA BATOOL BUKHARI MUHAMMAD SHER and ZAHID SHAFIQ

Received September 24, 2015
Published Volume 51 Issue 3-4 March-April
Keywords acetylation, acetic anhydride, esterification, hydroxypropylmethylcellulose, iodine, isoconversional thermal analysis

Abstract
An efficient, green and commercially viable method for acetylation of cellulose ethers has been developed using acetic anhydride activated with iodine. Iodine was dissolved in acetic anhydride followed by the addition of commercially important cellulose ether, i.e., hydroxypropylmethylcellulose (HPMC) and reaction proceeded under solvent-free conditions for 3 h at 50 °C. HPMC acetates were efficiently synthesized, purified and characterized. These HPMC acetates were found soluble in different organic solvents. Under solvent-free conditions, HPMC acetate was synthesized with a DS of 2.53. Highly functionalized HPMC acetate was characterized by FTIR and 1H NMR spectroscopic techniques. Thermal analysis and kinetics have revealed higher thermal stability imparted to HPMC after acetylation. The Flynn-Wall-Ozawa (FWO) isoconversional method was applied for kinetic studies and the energy of activation (Ea) value for HPMC acetates was found to be 71.07 kJ/mol, higher than that for unmodified HPMC. Thermodynamic parameters (∆H*, ∆G* and ∆S*) are also reported. Thermal stability was compared in terms of integral procedural decomposition temperature (IPDT) and comprehensive index of intrinsic thermal stability (ITS) using Doyle’s method. The IPDT values for HPMC and HPMC acetates were found to be 354 and 362 °C, respectively, confirming higher thermal stability of HPMC acetate as compared to HPMC.