Hydrophobic polyelectrolytes as osmotic agents for a mechanochemical insulin pump

This thesis deals with the synthesis and characterization of a series of hydrophobic polyelectrolytes containing the monomer N,N-diethylaminoethyl methacrylate (DEA). These polymers are potential osmotic agents for a novel mechanochemical insulin pump.

The hydrochloride form of the homopolymer of DEA (p(DEA$\cdot$HCl)) is water soluble, but it becomes hydrophobic and insoluble when neutralized with sodium hydroxide. During titration, at a certain degree of neutralization, a precipitate phase appears. Beyond this point, the system behaves as an excellent buffer with a "buffering" pH around 7.6 when the ionic strength (set by NaCl) is 0.1 M. The "buffering pH" can be increased or decreased by incorporating hydrophilic or hydrophobic unionizable comonomers respectively.

The colloid osmotic pressures produced by p(DEA$\cdot$HCl) and copolymers of DEA$\cdot$HCl and methyl methacrylate were studied as a function of polyelectrolyte concentration and composition, degree of neutralization, and ionic strength of the reference solution. The "Cell Model" for polyelectrolyte solution is successful in predicting the colloid osmotic pressure produced by p(DEA$\cdot$HCl), but the model is successful only at low concentrations for the copolymers.

The kinetics of colloid osmotic pressure development are shown to be too slow for the precipitating system to be used in the proposed mechanochemical insulin pump.

Precipitation of the polyelectrolytes was inhibited by the incorporation of a small fraction of permanent charge which was accomplished by partial quaternization of the DEA groups. The resulting polyelectrolytes show fast kinetics of colloid osmotic pressure development, but poorer buffering quality.