Polycatenane network

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. 

E Polycatenanes based on cyclic polymers F and G Polycatenane networks... 

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 synthesis of polycatenanes requires, like the synthesis of catenanes, the preorientation of the macrocycle precursors into a favorable geometry before cycliza-tion (Scheme 4) [5], This pre-orientation is commonly achieved via a template, resulting from rc-donor-acceptor interactions, hydrogen-bonding, and coordination bonds [1-3, 5, 41], The use of a template in catenane synthesis is the subject of Chapters 4 and 6-8 and will not be treated further in this section. The aim of this section is to present the state of the art of the various synthetic approaches leading to the polycatenane polymers and networks. 

The principle of the second synthetic approach to polycatenanes, i.e. stepwise polycondensation, has been proposed by Shaffer and Tsay, but not experimentally demonstrated [42, 43], This approach has the advantage over multifunctional polycondensation that a linear polymer is formed before cyclization (Scheme 7). However, the second step, which consists of the cyclization of n macrocycles along the polymer chain 19, is likely, again, to give rise to an undefined network, containing some rotaxane and catenane units 21, similar to the multifunctional polycondensation approach. 

In this section the unprecedented oligocatenanes, i.e. the [5]- and [7]catenanes 30 and 31 and the scarce experimental approaches to high molecular-weight linear polycatenane 9 have been presented. No synthetic Olympic network 32 has been reported to date, although their DNA analogs are known. The next section is dedicated to a new type of macromolecular architecture, structurally related to polycatenane 9, i.e. poly[2]catenanes. 

Scheme 29. Unreported macromolecular architectures containing defined topological bonds polycatenane 9, linear poly[3]catenane 74, poly[2]catenane network 75, multicatenane network 76, rigid polymeric catenane 77, polymeric trefoil knot 78, and polyknot 79.

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. 

The ligand l,4-bis(imidazol-l-ylmethyl)benzene 53 interacts with Ag to form a pol5aner 54 of the composition [Ag2(53)3(N03)2]oo [139]. Two onedimensional chains penetrate in a polycatenane-analogous structure (Fig. 7-15). However, in contrast, the reaction of 53 with Zn yields a polymer 55 of the composition [Zn(53)2](N03)2-4.5 H2O [140]. This polymer consists of two independent two-dimensional networks lying parallel. Zinc is tetracoordinated (Fig. 7-16). 

Recently, a polyrotaxane network material has been practically used, for the first time, as a coating material for mobile phones in Japan. This is an epoch-making event in the science and technology of interlocked molecules, macromolecules, and related materials. Polymers possessing interlocked structures as key skeletons are, therefore, the most promising and intriguing materials, especially in the application fields. Polyrotaxanes and polycatenanes are characterized by the specific feamres based on the unique mobility of the noncovalently bonded components in their... 

Type III The metal is part of a polymer chain or network. This type considers homochain or heterochain polymers with covalent bonds to the metal, coordinative bonds between metal ions and a polyfunctional ligand (coordination polymers), Ti-complexes in the main chain with a metal, cofacially stacked polymer metal complexes and different types (polycatenanes, polyrotaxanes, dendrimers with metals) (Figure 3). 

Catenanes are two interlocked cycles, like two links in a chain, which cannot be separated without the breaking of a covalent bond. Rotaxanes are similar but are composed of a cycle encircling an acydic molecule like a ring around a thread. A naturally occurring rotaxane, DNA polymerase III encircles DNA dining replication. Polyrotaxanes and polycatenanes are well-defined repetitions of these interlocking stmctures and should not be confused with intertwined cross-linked polymers whose interconnectivity is random in nature. These intricate polymeric networks have posed challenges to synthetic chemists, and a few have utilized ROMP in their preparation. 

In reahty, the situation with polycatenanes is much more comphcated. The problem is that a catenane-like structure of IPN is hard to identify by any single method. The difficulty is that neither catenanes nor other topological compounds (knots, rotaxanes) differ from the mixture of their individual components [ 11,12]. If IPNs were true polycatenanes, they would exhibit no phase separation. Therefore, catenane-Hke IPNs may be formed only in the case when the network components are miscible for the whole range of composition and temperature values [13], and when the IPNs have a one-phase homogeneous structure. 

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