Characterization of colon-specific azo polymers: A study of the swelling propertoes and the permeability of isolated polymer films

Abstract

In order to prepare azo polymers for colonic targeting, copolymers of 2-hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA), and terpolymers of HEMA, MMA, and methacrylic acid (MA) were synthesized in the presence of different azo compounds. In the present study, the azo polymers were characterized by swelling and permeability studies, performed on isolated films. It was shown that MMA is the swelling capacity and rate determining compound in the azo polymers investigated. Permeability experiments revealed that the diffusion of caffeine as well as the transmission of water vapour is proportional to the concentration of HEMA in the polymers. Hydrophilic plasticizers increase water vapour transmission and diffusion of caffeine through the films. By incorporation of MA into the azo polymers, pH dependency was introduced. The swelling behaviour and diffusion of caffeine are nearly constant over the pH range from 1 to 6. A sharp increase above pH 6, corresponding with the ionization of the carboxylic acid groups appears, with a maximum around pH 8.