Reza Jahanmardi - Department of Polymer Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran
Faramarz Afshar-Taromi - Department of Polymer Engineering, Amir Kabir University of Technology,Tehran, Iran
Saeed Pourmahdian - Department of Polymer Engineering, Amir Kabir University of Technology,Tehran, Iran

Polymerization of tetrahydrofuran (THF) is one of the widely studied cationic ring opening polymerizations [1]. The products of THF polymerization are commercially used asmediate materials for polyurethane and polyester elasomers. Since the original report of THF polymerization by Meerwein in the late 1930 s, various types of compounds have been reported as initiators [2]. However, only a few systems are suitable for preparing polymer of narrow molecular weightdistribution in high conversion with good molecular weight control. One of these systems is perchloric acid (HClO4)-acetic anhydride (Ac2O) mixture which has been used in commercial production of poly(tetrahydrofuran) (PTHF) in some cases [3]. Although, there is much information aboutmechanistic features of THF polymerization in this particular system, there is a few thermodynamic data for it. In this article, we report the results of thermodynamic study of THF polymerization initiated by HClO4- Ac2O mixture