ABSTRACT
This chapter is concerned with the development of controlled release systems that function by the movement of active molecules from a reservoir to a sink through a polymeric film membrane that offers a predetermined resistance to said movement. The factors governing the behavior of membrane systems used for barrier, permselective, or controlled release applications are similar in that the physicochemical composition and structure of the polymeric membrane system govern the solution and transport properties. The medium for diffusion in a homogeneous polymeric membrane is its amorphous phase. The diffusion of a solute molecule within an amorphous polymer matrix is an activated process involving the cooperative movements of the penetrant and of the polymer-chain segments that surround it. Hydrophilic microporous membranes, especially cellulosics, have been in use for a long time. A modest number of publications have appeared disclosing exploratory investigations in which ethylene vinylacetate membranes have been evaluated as to their control of release rates.
