Abstract: Critical concentration cp^* of lyotropic liquid crystalline hydroxypropyl methyl cellulose(HPMC) in twelve solvents was determined using both Abbe refractometer and polarized microscopy.cp^* is related not only to the acidity of solvents,but also to the solubility parameter δof solvents,There was a general tendency that the more the δof solvents closed to that of HPMC,the lower the cp^* was,although the experimental points were somewhat disperse.When the sort of solvents was limited to a simple series such as acetic acid,chloroacetic acid,dichloroacetic acid and trichloroacetic acid,a good linear relation was found between cp^* and δ.Alower chain rigidity of HPMC was also evaluated by the persistence length value of Kuhn chain theoretically deduced from critical concentration.

Key words: Hydroxypropyl methyl cellulose, Lyotropic liquid crystalline, Critical concentration, Solubility parameter, Chain rigidity