Studies of precipitating and soluble hydrophobic polyelectrolytes

Polyelectrolytes may be useful osmotic agents for various controlled release applications, since their large molecular size prevents them from permeating through a wide variety of membranes. In this presentation we will discuss equilibrium and kinetic results for two classes of hydrophobic polybases. The first class precipitates upon loss of charge. The second class contains a small fraction strong basic groups, which maintain the polybase in solution even after all weak charges have been neutralized. With respect to the design of osmotic drug delivery systems based on hydrophobic polyelectrolytes, both the precipitating and the soluble systems show advantages. The former exhibit superior buffering properties, but are extremely sluggish. The soluble systems show fast response, but inferior buffering. Clearly, a system that combines the advantages is desired. We conjecture that by making the soluble systems more hydrophobic by substitution of hydrophobic comonomers, we can improve buffering properties without sacrificing the kinetic advantages.