Hydroxypropyl methyl cellulose succinate (HPMCS) was synthesized from hydroxypropyl methyl cellulose (HPMC) by esterification using succinic anhydride as esterifying agent

anhydrous sodium acetate as catalyst and acetic acid as organic solvent. By varying reaction temperature and the amount of esterifying agent and catalyst

five kinds of HPMCS with the different content of carboxybutyryl groups were prepared. The content of carboxybutyryl groups in HPMCS was determined by conductometric titration. Its structure and properties were analyzed by IR

viscometer and rheometer. The result showed that the number of carboxybutyryl groups per macromolecular chain was from 6.57 to 12.42

that the gelation temperature of 1% by weight HPMCS solutions ranged from 48.7℃ to 41.95℃

whereas that of a 1wt% HPMC solution was 59.85℃ and that with an increase in carboxybutyryl content and distribution homogeneity

its gelation temperature decreased but its gel strength increased.