Catenanes polycatenanes

Later, gel formation was observed by Garcia et al. during the preparation of polyamides containing the benzo-18-crown-6 unit, and was ascribed to the formation of rotaxane/polyrotaxane and catenane/ polycatenane structures [156]. However, as the ring size of the benzo-18-crown-6 was considered too small to be threaded, it was thought uidikely that gel formation would occur due to catenane formation via threading of the crown ether moieties. 

The interest in macromolecular systems containing defined topological bonds, such as polyrotaxanes 7, multicatenanes 8, polycatenanes 9, poly[2]catenanes 10, and polymeric catenanes 11, is dual. First, these macromolecules represent daunting synthetic and characterization challenges which deserve attention in their own... 

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. 

Two outstanding forerunners of high molecular-weight polycatenanes are the [5]catenane 30, also named olympiadane, and the [7]catenanes 31 reported by Stoddart and coworkers (Scheme 10) [46, 49]. The synthetic strategy leading to... 

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. 

Greets Y (1999) Polycatenanes, poly[ 2]-catenanes and polymeric catenanes. In Sauvage JP, Dietrich-Buchecker CO (eds) Molecular Catenanes, Rotaxanes, and Knots. Wiley-VCH, Weinheim... 

A wide range of other related catenanes and polycatenanes, many designed with particular functions in mind, have been reported.By way of example, a system was constructed to act as a potential model for aspects of the electron-transfer... 

Besides simple rotaxanes and catenanes, a great variety of more complex systems have been synthesized, including branched [n]rotaxanes [26a], [n]rotaxanes bearing dendritic stoppers [26b], catenanes composed by two, three, five, or seven interlocked macrocycles [26c,e], polyrotaxanes and polycatenanes [2-6, 8], catenanes with very special shapes [27], rotocatenanes [28], pretzelanes [29], and knots [4], Some of these compounds are shown in Figure 8. 

Menzer, S., White, A. J. P., Williams, D. J., Belohradsky, M., Hamers, C., Raymo, F. M., Shipway, A. N., and Stoddart, J. F. Molecular meccano. 25. Self-assembly of functionalized [2]catenanes bearing a reactive functional group on either one or both macrocyclic components - From monomeric [2]catenanes to polycatenanes Macromolecules 1998, U, 295-307. 

There are reviews including two comprehensive articles of Gibson [1] and Stoddart [2] on the polyrotaxanes and polycatenanes [3-12], in addition to a lot of review articles and books on the rotaxanes and catenanes [13-28]. Short reviews on the applications of polyrotaxanes are also reported [29-38]. 

Scheme 1 illustrates the simplest structures of rotaxane, catenane, and knot besides polyrotaxane and polycatenane. From the fact that the main chain-type polyrotaxane at the left side is the only interlocked polymer synthesized so far among the three polymers shown at the bottom of the scheme, progress in synthesis of interlocked polymers appears to be sluggish judging from the level of activity in synthetic polymer chemistry in the world. 

In addition to three typical structures of poly[2]catenanes (G-I), polyca-tenane (i.e., [n]catenane) of which the structure is comprised only of wheel components is simply interlinked like a chain (J). The polycatenane is one of the most difficult goals in the synthesis of unknown interlocked polymers, like poly[2]rotaxane as already pointed out, although it will be accomplished in the near future because so much effort has been made by synthetic chemists, and this will be continued. 

---