Résumé
A study has been made on the possibility of combining anionic monomers with hydrophilic vinyl alcohol monomer and to explore their potential for colonic drug delivery. Vinyl acetate [VAC] and acrylic acid [AA] monomers were polymerized and the effect of monomer ratio on copolymer composition was studied. It was observed that by increasing the VAC fraction in ratios higher than that of AA in the monomeric mixture, the process of polymerization was hindered. A big difference in reactivity ratio affects the polymerization process and copolymer composition. Poly[vinyl acetate-co-acrylic acid] polymer was hydrolysed in methanolic potassium hydroxide [KOH] solution. Salt form was converted into acid form by adding hydrochloric acid [HCI]. In hydrolysed copolymers it was observed that by increasing the AA, the systems were indeed pH-sensitive but no effect of free hydroxyl [OH] groups was observed, because OH groups were linked in the lactone rings with the dominent carboxylic COOH groups. Monomer ratio affects the swelling and drug release properties of the hydrogels. Swelling shifts to lower pH values by increasing the acrylic acid traction in the copolymer. Two samples of V AL/AA of different monomer ratio were loaded with betamethasone. The drug release from these samples is dependent on the acrylic acid fraction in the copolymer and on the pH of the medium. Thus it has been shown that it is possible to prepare pH-sensitive systems for well accepted monomers without using crosslinking agents