Copolymerization with Simultaneous Globule Formation

The presence of a hydrophobic-hydrophihc interface can dramatically change the reaction conditions. The hydrophobic core will selectively absorb hydrophobic species from the solution (Fig. 12), and this will result in a redistribution of monomer concentrations between the core and bulk solution. Because the probability of attachment for each comonomer is determined by its concentration in a relatively small reaction volume near an active chain end, the active center inside the hydrophobic core will mainly attach more hydrophobic species on the other hand, when the active center is located on the globule surface, it will mainly attach polar (soluble) monomers. In this way, the two-layer globule will grow, retaining its core-shell structure with a predominantly hydrophobic core and a hydrophihc outer envelope (see Fig. 12). 

The type of monomer attached to the growth center during the simulation under kinetic control (at large tr values, see Eq. 3) is determined by the conformation and primary structure of the growing chain as a whole, not only by the local concentration of reactive monomers near the active end of the macroradical. As a result of such cooperativity, the formation of sequences with specific LRCs of the L6vy-flight type was observed [76-78]. 

Experimentally, the described synthetic strategy was first reahzed by Lozinsky et aL [80,81], who studied the redox-initiated free-radical copolymerization of thermosensitive N-vinylcaprolactam with hydrophihc N-vinyl-imidazole at different temperatures. These and other experimental studies [82 - 84] showed the universahty of this approach of obtaining copolymers capable of forming nanostructures with a core-shell morphology. 

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Fig. 14 Typical core-shell microsegregated structure that is obtained via conformation-dependent copolymerization with simultaneous globule formation in a selective solvent [76]. Hydrophobic chain segments are shown in dark gray and hydrophilic segments are shown in light gray...

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