Association Behavior of Charged Amphiphilic Copolymers and Ostwald Ripening

The driving force for the molecular assembly of amphiphilic block copolymers in aqueous media is attributed to their differences in water-solubility between hydrophobic andhydrophilic blocks. To illustrate this, let us consider a temperature-responsive diblock copolymer of the type [1] MPEGn-b-NIPAAMm, where the length of the NIPAAM block is constant and n is altered. In this case, temperature-induced association is promoted when the MPEG-block is short( crew-cut micelles), whereas long MPEG chains ( hairy micelles) reduce the tendency of the copolymer to form aggregates at elevated temperatures [2]. Another way to improve the stability of particles is to attach a charged block to the copolymer to increase the stability of the speciesthrough repulsive electrostatic forces. In this work, we have synthesized a series of thermoresponsive poly(N-isopropylacrylamide)-blockpoly((3-acrylamidopropyl)trimethylammonium chloride) diblock copolymers by utilizing atom transfer radical polymerization (ATRP). [2] The products obtained from thissynthesis have the following composition: (PNIPAAMn-b- PAMPTMA(+)20). To explore the temperature-inducedassociation features of this cationic diblock copolymer, three samples have been carefully designed and synthesized withthe repeated units of NIPAAM blocks of n = 24, 48, and 65.