Synthesis and aqueous solution properties of sterically stabilized pH-responsive polyampholyte microgels

Emulsion copolymerization of poly(methacrylic acid) and poly(2-(diethylamino)ethyl methacrylate) (PMAA/PDEA) yielded pH-responsive polyampholyte microgels of 200–300 nm in diameter. These microgels showed enhanced hydrophilic behavior in aqueous medium at low and high pH, but formed large aggregates of ∼2500 nm at intermediate pH. To achieve colloidal stability at intermediate pH, a second batch of microgels of identical monomer composition were synthesized, where monomethoxy-capped poly(ethylene glycol)methacrylate (PEGMA) was grafted onto the surface of these particles. Dynamic light-scattering measurements showed that the hydrodynamic radius, RhRh, of sterically stabilized microgels was approximately 100 nm at intermediate pH and increased to 120 and 200 nm at pH 2 and 10, respectively. Between pH 4 and 6, these microgels possessed mobility close to zero and a negative second virial coefficient, A2A2, due to overall charge neutralization near the isoelectric pH. From the RhRh, mobility, and A2A2, cross-linked MAA–DEA microgels with and without PEGMA retained their polyampholytic properties in solution. By varying the composition of MAA and DEA in the microgel, it is possible to vary the isoelectric point of the colloidal particles. These new microgels are being explored for use in the delivery of DNA and proteins.

Graphical abstractThe cloudy region near the IEP indicates that PMAA-co-PDEA polyampholyte microgels became more compact due to charge neutralization. The solution is transparent below and above the cloudy region due to presence of positive DEA groups and negatively charged carboxylic groups.Figure optionsDownload full-size imageDownload as PowerPoint slide