Nanostructured brush block copolymers

Figure 5.14 Isocyanate-based brush block copolymers assembled to large lamellar nanostructures, with reflection peaks into the near infrared. (From Ref. [50].)...

The molecular organization of biopolymers is often much more complex than that of polymers synthesized in a chemical laboratory. Work is underway to systematically close this gap. Recent progress in controlled radical polymerization has made it possible to synthesize increasingly complex ionic macromolecules with controlled dimensions and topology. As a result, well-defined ionic block copolymers [10], colloidal [4] and molecular [8] PE brushes, and star-like PEs [9] have become available. In addition to emerging applications, such nanostructures constitute excellent model systems. 

A number of theoretical studies have been devoted to analysis of the self-assembly of amphiphilic ionic/hydrophobic diblock copolymers [13-24]. Most of these studies considered copolymers with strongly dissociating (also referred to as quenched ) PE blocks [13-18, 20] and extensively exploited the analogy between the conformation of PE blocks in a corona and that in a spherical PE brush [25-33] or PE stars (see [10] for a review). The micellization and the responsive behavior of nanostructures formed by copolymers with pH-sensitive PE blocks have also been systematically studied in recent years [19, 21-23]. 

Scanning electron microscopy (SEM) is one of the very useful microscopic methods for the morphological and structural analysis of materials. Larena et al. classified nanopolymers into three groups (1) self-assembled nanostructures (lamellar, lamellar-within-spherical, lamellar-within-cylinder, lamellar-within-lamellar, cylinder within-lamellar, spherical-within-lamellar, and colloidal particles with block copolymers), (2) non-self-assembled nanostructures (dendrimers, hyperbranched polymers, polymer brushes, nanofibers, nanotubes, nanoparticles, nanospheres, nanocapsules, porous materials, and nano-objects), and (3) number of nanoscale dimensions [uD 1 nD (thin films), 2 nD (nanofibers, nanotubes, nanostructures on polymeric surfaces), and 3 nD (nanospheres, nanocapsules, dendrimers, hyperbranched polymers, self-assembled structures, porous materials, nano-objects)] [153]. Most of the polymer blends are immiscible, thermodynamically incompatible, and exhibit multiphase structures depending on the composition and viscosity ratio. They have two types of phase morphology sea-island structure (one phase are dispersed in the matrix in the form of isolated droplets, rods, or platelets) and co-continuous structure (usually formed in dual blends). 

Linear amphiphilic block copolymers have been assembled in a selective solvent with a great diversity of kinetically frozen micelles. When a perfect control of nanostructure size and shape was required, brush copolymers were found to be the preferred templates to prepare cylindrical nanoparticles. Wooley et al. 

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