DEVELOPMENT OF CELLULOSE DERIVATIVES AS NOVEL ENTERIC COATING AGENTS SOLUBLE AT PH-3.5-4.5 AND HIGHER

Hydroxypropyl methylcellulose (HPMC) was selected as a base polymer to develop novel enteric coating agents for acid protection which can di ssolve at pH around 4, and was modified with trimellitic acid or malei c acid at various degrees of substitution, These carboxylic acids have higher dissociation constants and higher solubility in water than the carboxylic acids of existing enteric coating polymers. The synthesize d polymers were micronized and dispersed in aqueous medium to determin e their pK(a) values by potentiometric titration, The pH of dissolutio n and the water vapor permeability of the cast films prepared from org anic solutions were also evaluated, Hydroxypropyl methylcellulose trim ellitate (HPMCT) showed good acid resistance, and the pH at which it d issolves can be controlled in the range of pH 3.5 to 4.5 by varying th e content of trimellityl groups and the methoxyl substitution of the b ase polymer.