Karim Poorjamal - Laboratory of Polymer, Faculty of Chemistry, University of Tabriz, Tabriz, Iran.
Marziyeh Fathi - Laboratory of Polymer, Faculty of Chemistry, University of Tabriz, Tabriz, Iran.
Ali Akbar Entezami - Laboratory of Polymer, Faculty of Chemistry, University of Tabriz, Tabriz, Iran.

Physically crosslinked hydrogels are formed spontaneously under appropriate conditions. They do not require introduction of external crosslinking agents, which are usually nondegradableand may prevent degradability of the entire hydrogel. Moreover, the crosslinking agents are often toxicagents[1].The freez-thawing method is one of the best way forPhysically crosslinking. The hydrogels so produced were porous, spongy, rubbery and elastic and displayed goodmechanical strength [2]. In this work, we synthesised starch-g- P(NIPAAm-co-IA) nanohydrogel via free radicalcopolymerization and were characterized by FT-IR andthermal gravimetric analysis (TGA). We investigated the effect of freez-thawing on swelling behavior of synthesisednanohydrogels. The water sorption capacity decreased with an more increase in the number of freeze–thawing cycles