pH Reversible Self-Assembly of Nonionic Alternating Copolymer Vesicles

We will present here recent developments on alternating copolymers of alkylmaleimides and vinyl gluconamide that spontaneously form ultra-small (10-20 nm) and medium (50-300 nm) size vesicles (Macromolecules 2009, 42, 2702-2707). The size and shape of these vesicles have been characterized by cryogenic-transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), and small angle neutron scattering (SANS). These alternating copolymer vesicles exhibit alkyl chain length dependent release characteristics and bilayer thickness (1.7, 2.0, and 2.6 nm for alkyl chains of 10, 12, and 14 carbons, respectively).

Recent unpublished results on the unique pH reversible self-assembly of these polymers in solution will also be presented here. Carrying no charged, acid, or base groups, these alternating polymers are insensitive to ionic strength, yet respond strongly to small changes in acidity/basicity near pH ~6, by reversibly precipitating and reassembling. DLS measurements show no change in size distribution of the vesicles before and after the acid or base additions to effect pH change. We attribute this unique behavior to hydrogen bonding interactions as observed by FTIR.