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Gohy, J.F. ; Creutz, S. ; Garcia, M. ; Mahltig, B. ; Stamm, M. ; Jérome, R.
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 diblock copolymers has been studiedin water in the dilute regime as a function of pH and salt concentration. Dynamic light scattering (DLS)has been used to monitor the association behavior and transmission electron microscopy (TEM) to visualizethe morphology of the aggregates. At and around the isoelectric point (IEP) of the ampholytic diblocks,strong electrostatic interactions occur and lead to the formation of insoluble complexes between negativelyand 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 containinga major PDMAEMA block, spherical micelles are observed below the IEP. These micelles consist of aPMAA core surrounded by a water-soluble protonated PDMAEMA corona. At and above the IEP, thesesamples are insoluble. Spherical micelles are also formed below the IEP for samples containing a minorPDMAEMA block. These copolymers are insoluble at and around the IEP, whereas solubility is observedabove the IEP with formation of aggregates of remarkable morphologies, including hollow spheres andcomplex compartmentalized aggregates. This aggregation is most favorable at high pH, and it ca
nnot beaccounted for only by electrostatic interaction between oppositely charged blocks. Indeed, short-rangehydrophobic interaction between uncharged PDMAEMA blocks seems to play a key role in the associationprocess. This is emphasized by quaternized poly(2-(dimethylamino)ethyl methacrylate)-b-poly(methacrylicacid) ampholytic copolymers which are carrying a permanent positive charge on the aminated monomericunits and do not form these particular aggregates.

Source
Macromolecules 33

Pages
6378-6387

DOI
http://dx.doi.org/10.1021/ma992016j

Published
September 2000
 
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Publications

Departments

Nanostructured Materials