ABSTRACT
Amphiphilic copolymers of various chain architectures and composition were shown in Chapter 2 to form a variety of self-assembled aggregate structures in dilute aqueous solution. Spherical and wormlike micelles as well as polymer vesicles were the most frequently observed self-assembled structures, but other more or less exotic morphologies such as toroids, disks, multicompartment, and bicontinuous micelles have been documented as well. Most of the research in the last decade was focused on the control of the chemistry of the constituent moieties whereby manipulation of the properties of the self-assembled structures can be achieved. Many examples demonstrating systematic variations of, for instance, morphology through synthetic manipulations of a series of self-associating copolymers can be found in the scientic literature. Surprisingly, however, considerably less attention has been given to another approach to inuence the self-assembly, in general, and properties of the self-assembled structures. This approach is the co-assembly. It is a straightforward and feasible approach providing an experimentally simple way to modify self-assembled structures and allowing expanding the utility of the latter. The method consists of blending of a given amphiphilic copolymer with other substances, not necessarily of polymeric nature or even not necessarily of amphiphilic character (Figure 3.1), thus providing access to composite, hybrid self-assembled structures. To diversify the approach, mixing of two or more homopolymers that do not self-associate, taken separately or adding of a substance (surfactant, homopolymer, block copolymer, protein, etc.), to preformed self-assembled structures has been considered. Different types of forces like hydrophobic interactions, electrostatic interactions, hydrogen bonding, donor-acceptor interactions, metal-ligand coordination bonds, etc., have been found to facilitate the formation of mixed structures or to contribute to the introduction of new functionality and properties. Whatever the type of interactions, in all cases, the systems rearrange accordingly, thus optimizing their self-organization to approach a thermodynamic equilibrium state. The introduction of additional entities incorporated even in small amounts in the mixed self-assembled structures is an excellent approach to tune the aggregate morphology, to signicantly alter the aggregate characteristics, and to produce new functionality and properties. In this chapter, many examples of formation of such hybrid structures are given. Properties originating from their mixed nature will be shown to expand the range of possible applications and utility. In particular, hybrid structures resulting from co-assembly of an amphiphilic copolymer and a surfactant as well as copolymer-lipid, copolymer-homopolymer, and copolymer-copolymer interactions will be considered (Figure 3.1). Recent examples from the scientic
literature of construction of mixed structures from inherently nonassociating species, formation of nanoreactors by incorporation of proteins as well as hybrid structures formed upon interactions of polymers with oligo-and polynucleotides such as DNA, will be shown. Particular focus will be placed upon the control of the overall shape of the mixed structures, their external and internal morphology, the introduction of desired functions, and alteration of the properties. Adding salts to solutions of polyelectrolytes, self-assembled structures involving polymer-drug conjugates, and lipoplexes are not considered in this chapter.
