Polycatenanes properties

The ring topology is the potential to form unique polymer structures. Like linear polymers, cyclic polymers not only can be branched or cross-linked, but also can form non-covalently linked structures based on their loop topology. These are referred to as topological polymers, including rotaxane, catenane, threaded rings, and rings threaded by network chains. Recently, much attention has been paid to how their particular properties not only differ from linear polymers, but also how they differ from a component of an interlocked polymer system, such as polycatenanes and polyrotaxanes. 

From the analyses of NMR and electron-spray ionization mass (ESI-MS) spectroscopy, the polymers obtained from the polymerization of cyclic disulfides were found to be a cyclic structure [202], The cyclic structure consisting of poly(DT) is assumed to be formed by a backbiting reaction of propagating species [203]. Thermal and mechanical properties of the polymers, and decomposition behaviors of the polymers demonstrate that the polymers obtained from thermal polymerization of cyclic disulfides include a polycatenane structure. From polymerization of cyclic disulfides in the presence of cyclic polyethylene oxide), a polycatenane consisting of two different cyclic polymers was obtained [199]. Thus, poly(DT) contains spatial entanglements of cyclic polymers with each other (a polycatenane structure was presumed) (Fig. 61). 

It is vital that simple and cheap synthesis of interlocked polymers is achieved in order to make progress in the chemistry of polyrotaxanes and polycatenanes. Since bulk property is essential in polymer science, difficulty in synthesis of interlocked polymers should be avoided, this being different from the case of molecular materials such as molecular devices functioning at a molecular level. Both polyrotaxanes and polycatenanes as well as both rotaxanes and catenanes are becoming easy to synthesize with the progress... 

Formation of polycatenane network has recently been suggested by Endo et al. during the thermal polymerization of cyclic disulfides such as 1,2-dithi-ane, where involvement of the cyclic polymers in the polydisulfide formed is proved by mass spectrometry [268] (Scheme 55). The elastic properties of the corresponding polydisulfide is believed to come from the polycatenane network structure. 

As illustrated by types C and D in Figure 17.1, side-chain polycatenanes are polymers that contain catenane subunits within their pendant groups, and which are expected to possess different properties compared to the main-chain polycatenanes. However, due to similar synthetic problems being encountered as for the preparation of linear poly[ ]catenanes, only poly[2]catenane-type side-chain polycatenanes have been reported to date. 

Over the past few decades, much attention has been focused on polycatenanes, which consist of mechanically interlocked structures that have novel topologies and, not unexpectedly, display somewhat different properties than do commonly used, conventional polymers. The linear polycatenanes (type A in Figure 17.1) are aesthetically perfect, and are expected to possess maximized effects of topologically bonded structures on properties. However, the synthesis of such linear polycatenanes remains one of the most difficult and as-yet unachieved synthetic goals in polymer science. Due to the relatively easy preparation of bifunctionaUzed [2]catenanes, success in the directed synthesis of polycatenanes has been mainly limited to the poly[2]catenanes, which contain essential mechanical hnkages. Nonetheless, some progress has been made recently towards creating polymeric catenanes and polycatenane networks. 

The sahent features of the polycatenanes, as discussed above, are summarized in Table 17.1. Whilst many analytical tools, including NMR spectroscopy, mass spectrometry, GPC, and FTIR, have been used to characterize the polycatenanes, studies of their properties have been hampered by poor yields, even when using readily prepared poly[2]catenane systems. Gonsequendy, the development of more efficient synthetic methods, and/or of more readily-prepared systems, is critical to the research and development of these materials. 

Based on the current rapid pace of development of the polycatenanes, many new compounds, with unique and highly interesting properties, wiU surely be discovered in the near future. 

Macromolecules incorporating repeating units connected by covalent bonds are widespread in nature [1], Synthetic procedures for the construction of their artificial counterparts are well established [2], Furthermore, the properties of these unnatural macromolecules are now rather well understood and, indeed, polymeric materials have found applications in numerous branches of science and technology [2], In recent years, synthetic chemists have learned how to introduce mechanical bonds (Fig. 1) into small molecules. Mechanically interlocked rings, as well as wheels mechanically trapped onto axles, can be constructed efficiently to afford molecular compounds, named catenanes and rotaxanes, respectively.t Metal coordination [18-32], donor/acceptor interactions [33-43], hydrogen bonds [44-64] and/or hydrophobic interactions [65-78] between appropriate components have all been employed to template the formation of these exotic molecules. Making the transition from simple catenanes and rotaxanes to their macromolecular counterparts—namely, polycatenanes and polyrotaxanes. 

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