The molecular interactions that influence the plasticizer dependent dissolution of acrylic polymer films

Poly(methacrylic acid-methyl methacrylate, 1:2) (Eudragit S) is a commonly used pH-responsive polymer that can facilitate delivery to the ileo-colonic region of the gastrointestinal tract. Different plasticizers have been used to reduce the brittleness of Eudragit S films for the coating of solid dosage forms. To better correlate the dissolution rates of Eudragit S films, we have examined their dielectric response to understand the specific polymer-plasticizer interactions. Solvent cast Eudragit S films were prepared with one of four citrate plasticizers ranging from low to moderate aqueous solubility. Film dissolution was determined using a two-compartment permeation cell. Dielectric properties were measured by thermally stimulated depolarisation currents (TSDC). Secondary relaxations were deconvoluted and identified. The glass transition temperature (T(g)) was measured using TSDC, differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Dissolution of the films was influenced by the solubility and structure of the plasticizers. While no correlation was found among the T(g)'s obtained by TSDC, DSC, and DMA with dissolution time, the low temperature TSDC spectra showed a relationship of the total secondary relaxation area and relaxation of the carboxylic acid functional group with dissolution time. Dielectric secondary relaxations may be a good probe to predict plasticizer influence on dissolution of Eudragit S polymer films.