Hydrophobically modified water-soluble polymers undergo a self-assembly process in aqueous solutions whereby the hydrophobic side chains cluster together into micelle-like aggregates, or microdomains, of characteristic size and hydrophobicity. The resulting network, which are called two- phase hydrogels, have physical properties which are completely different from those of the initial solution and which may be exploited to good effect in numerous applications. In this AMPP investigation, two-phase hydrogels from alkyl-substituted polyacrylamides are synthesized and the relationships between polymer structure and hydrogel properties are explored. The focus is on three structural properties of the polymer, namely, the total hydrophobe content, the backbone conformation, and the length of the hydrophobic side chains. The effects of these properties on the structure and composition of the microdomains and on the rheological properties of the bulk material are investigated. One of the most interesting features of these unique materials is the demonstrated ability of the dispersed hydrophobic phase to absorb and retain organic solutes within an aqueous gel, and to release the solutes to the surroundings at a constant rate (so-called "zero-order release"). This type of release profile is much sought after in controlled drug delivery, an emerging technology of great interest in the pharmaceutical field. A controlled release dosage form is one which delivers therapeutic levels of a drug at a steady rate over long times, eliminating the need for repeated doses of a medication and avoiding the associated problems of oscillating blood levels of the drug. The basic investigations on these novel materials will be used as the design basis for two-phase hydrogels for use in controlled drug release. This work will be conducted in collaboration with colleagues at Exxon Research and Engineering Company, who will also furnish the polymers to be used in the study.
