Supramolecular polymer networks noncovalent interactions

Having discussed self-assembly strategies toward noncovalently functionalized side chain supramolecular polymers as well as studies toward the orthogonahty of using multiple noncovalent interactions in the same system, this section presents some of the potential applications of these systems as reported in the literature. The apphcations based on these systems can be broadly classified into two areas 1) self-assembled functional materials and 2) functionalized reversible network formation. 

Supramolecular noncovalent interactions [13], such as metal coordination, hydrogen bonding, hydrophobic forces, van der Waals forces, pi-pi interactions, and electrostatic interactions, are very appealing for the self-assembly of molecules, and they could be used to create nanostractured materials. Metal coordination, for instance in metal organic frameworks (MOFs) [14] or coordination polymers [15], has been applied to construct nanoporous supramolecular networks. 

Keywords Supramolecular polymer gels Stimuli-responsive materials Noncovalent interactions Supramolecular network dynamics Self-assembly... 

More recently, the importance of introducing supramolecular interactions between macromolecular chains has become evident, and many new options have been introduced. The final step in this development would be to develop polymers based on reversible, noncovalent interactions. Rather than linking the monomers in the desired arrangement via a series of polymerization reactions, the monomers could be designed in such a way that they self-assemble autonomously into the desired stracture. As with covalent polymers, a variety of structures of these so-called supramolecular polymers are possible, with block-copolymers or graft copolymers - as well as polymer networks - being created in this way. 

Self-assembled structures are supramolecular assemblies of covalent backbones structured through intra- and interchain noncovalent interactions. These secondary structures arise from steric constraints and a network of weak interactions (i.e., hydrogen or Van der Waals bonding, dipole-dipole or amphiphilic interactions). Helical morphologies are stiU rarely represented in these artificial species but the control of the heHx sense, and a better knowledge of the chiral amplification mechanism, is highly desirable due to their potential use in many applications. For example, helically chiral polymers can be used as chiral stationary phases for HPLC or for catalysis. 

In main-chain supramolecular polymers, noncovalent interactions are used to form the polymer chain, which consists of bi- or multifunctional molecules (monomers) that bind to each other noncovalently to form polymers (linear when bi-functional monomers are used, branched polymers or networks for multifunctional monomers). Besides monomers, end-group-functionalized polymers can also be used as supramolecular macromonomers. Such polymers can then create block copolymers [8]. 

In the first part of this chapter, we aim to introduce and discuss complementary functional groups that have beeu developed to allow for reversible network formation in bulk materials. The second part of the chapter deals mainly with polymer matrices in the gel state. In both parts of the chapter, we highlight how material properties at the meso-and macroscopic scales are governed by noncovalent forces on the molecular level, and how supramolecular interactions can offer opportunities in the development of stimuli-responsive materials. Lead examples and applications are highlighted throughout. 

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