Aggregates formed by amphoteric diblock copolymers in water

The associating-behavior of a series of monodisperse poly(2-(dimethylamino) ethyl methacrylate)-b-poly(methacrylic acid) (PDMAEMA-b-PMAA) ampholytic di block copolymers has been studied in water in the dilute regime as a functi on of pH and salt concentration. Dynamic light scattering (DLS) has been us ed to monitor the association behavior and transmission electron microscopy (TEM) to visualize the morphology of the aggregates. At and around the iso electric point (IEP) of the ampholytic diblocks, strong electrostatic inter actions occur and lead to the formation of insoluble complexes between nega tively and positively charged blocks. These electrostatic interactions can be screened by the addition of salt, which leads to the partial dissolution of the material, according to Debye screening. For samples containing a ma jor PDMAEMA block, spherical micelles are observed below the IEP. These mic elles consist of a PMAA core surrounded by a water-soluble protonated PDMAE MA corona. At and above the IEP, these samples are insoluble. Spherical mic elles are also formed below the IEP for samples containing a minor PDMAEMA. block. These copolymers are insoluble at and around the IEP, whereas solub ility is observed above the IEP with formation of aggregates of remarkable morphologies, including hollow spheres and complex compartmentalized aggreg ates. This aggregation is most favorable at high pH, and it cannot be accou nted for; only by electrostatic interaction between oppositely charged bloc ks. Indeed, short-range hydrophobic interaction between uncharged PDMAEMA b locks seems to play a key role in the association process. This is emphasiz ed by quaternized poly(2-(dimethylamino)ethyl methacrylate)-b-poly(methacry lic acid) ampholytic copolymers which are carrying a permanent positive cha rge on the aminated monomeric units and do ndt form these particular aggreg ates.