Supramolecular polymer networks applications

Because of their transient and reversible cross-linking, supramolecular polymer networks are responsive [4] to external stimuli such as variation in temperature [31], pH [32], polarity of the solvent [33], redox reactions [34], and competitive ligation [35]. This tunability makes them useful for a plethora of applications. They can be used as drug delivery systems [36] and as matrixes in tissue engineering [37]. Drugs and cells can be encapsulated and protected within these materials and... 

The following sections describe the preparation and characterization of supramolecular polymer networks, particularly emphasizing their physical-chemical features with regard to the type and strength of physical chain cross-linking and the resulting macroscopic material properties. Furthermore, recent work on the formation and characterization of supramolecular hydrogels based on synthetic and natural precursors is summarized with a focus on their application and potential in biomedicine. 

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. 

In this review, the term macromer is used to describe oligomer or polymer precursors that undergo reversible association to form supramolecular polymers or networks. Macromer synthesis, although a crucial aspect of supramolecular science, is also out of the scope of this review. Several comprehensive reviews of the synthesis of H-bonding polymers are available [10, 11,42] and primarily describe the application of controlled radical polymerization techniques, including atom-transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) polymerization, and nitroxide-mediated polymerization (NMP). For synthesis of telechelic polymers, avoiding monofunctional impurities that can act as chain stoppers is crucially important [43],... 

In view of the extensive literature, this chapter does not aim to be comprehensive, but uses selected notable examples from the field to demonstrate the concepts and applications of these fascinating species. For example, there are numerous examples of linear supramolecular polymers in solution [32], solvated nanotubes [33], vesicles [34] and gel networks [35-38] that rely on donor-acceptor interactions however, this review focuses on unsolvated, cross-linked supramolecular polymers and their bulk properties. 

Miyata, T. Gels and interpenetrating polymer networks. In Supramolecular Design for Biological Applications, Yui, N., Ed. CRC Boca Raton, 2002 pp 95-136. 

Xerox Corporation has filed two patents in which supramolecular polymers are used as binders in ink compositions. One application relates to hot-melt inks, consisting of a colorant and a binder [29]. These inks are solid at temperatures below 50°C, and liquid with a viscosity around 20 cps at 160 C. The binder is a multifunctional low molecular weight compound that has been functionalized with 2 to 5 UPy-groups, resulting in polyether compounds that form supramolecular networks. Mixing these materials at elevated temperatures with other ingredients like UV-stabilizers, antioxidants, and colorants, results in inks that can be used in hot-melt ink printers. 

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 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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