Gradient‐IPN‐modified hydrogel beads: Their synthesis by diffusion–polycondensation and function as controlled drug delivery agents

Abstract

AbstractInterpenetrating polymer network (IPN) membranes and gradient–IPN polymers were synthesized by immersing crosslinked, 2‐hydroxyethylmethacrylate copolymer beads which were swollen in polyol in solutions of diisocyanates. Diffusion of reactants and polycondensation take place simultaneously, and the polymer beads are modified by a polyurethane–IPN layer whose thickness and compositional gradient are a function of reaction rate and diffusion rate. When the reaction is fast relative to diffusion, the reaction zone is narrow and the IPN boundary layer is sharp, whereas when diffusion dominates, the reaction zone and the IPN‐modified region becomes broader and more diffuse. A water‐soluble drug imbibed into such gradient‐IPN‐modified hydrogel beads is released over a prolonged time period due to the less permeable IPN barrier and because of a drug‐distribution gradient in the polymer, which follows the polyurethane gradient. Diffusion polycondensation can be considered a special case of interfacial polycondensation, one in which the interface area is expanded into and stabilized by a preformed polymer matrix, which serves as reaction medium.