Roghayyeh Marefat Seyyedlar - Polymer Science Department, Iran Polymer and Petrochemical Institute, Tehran, Iran.
Mohammad Atai - Polymer Science Department, Iran Polymer and Petrochemical Institute, Tehran, Iran.
Azizollah Nodehi - Polymer Science Department, Iran Polymer and Petrochemical Institute, Tehran, Iran.
Mohammad Imani - Polymer Science Department, Iran Polymer and Petrochemical Institute, Tehran, Iran.

HPMC aqueous solutions form reversible gels with increasing temperature via hydrophobic interaction with a lower critical gelation temperature (LCST) between 75 to 90 °C. HPMC hasmany applications in drug delivery and tissue engineering [1]. Gelation temperature of HPMC, however is higher thanphysiological temperature. To reduce the temperature , salts (e.g. Na2SO4) are usually incorporated into the aqueous solution of HPMC. In this study gelation temperature of twograde of HPMC determined with rheological investigation. Molecular weights of the HPMCs were measured by gelpermeation chromatography (GPC). The influence of Na2SO4 on the cloud point and gelation temperature was also determined using UV/Vis spectroscopy and rheological measurements, respectively.