Nanodroplets of polyisoprene fluid contained within poly(acrylic acid-co-acrylamide) shells

The preparation and characterization of macromolecular nanostructures possessing an amphiphilic core-shell morphology with a hydrophobic, fluidlike core domain with a low glass-transition temperature are described. The nanostructures were prepared by the self-assembly of polyisoprene-b-poly(acrylic acid) diblock copolymers into polymer micelles, followed by crosslinking of the hydrophilic shell layer via condensation between the acrylic acid functionalities and 2,2'-(ethylenedioxy)bis(ethylamine), in the presence of 1-(3'-dimethylaminopropyl)-3-ethylearbodiimide methiodide. The properties of the resulting shell-crosslinked knedel-like (SCK) nanoparticles were dependent on the microstructure and properties of the polyisoprene core domain. SCKs containing polyisoprene with a mixture of 3,4- and 1,2-microstructures underwent little shape distortion upon adsorption from aqueous solutions onto mica or graphite. In contrast, when SCKs were composed of polyisoprene of predominantly cis-1,4-repeat units, the glass-transition temperature was -65 degreesC, and the nanospheres deformed to a large extent upon adsorption onto a hydrophilic substrate (mica). Adsorption onto graphite gave a less pronounced deformation, as determined by a combination of transmission electron microscopy and atomic force microscopy. Subsequent crosslinking of the core domain (in addition to the initial shell crosslinking) dramatically reduced the fluid nature and, therefore, reduced the SCK shape change. (C) 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1659-1668, 2003.