Catenated cyclic polymers

To be comprehensive, it should also be mentioned that besides the unique example of the polymeric catenane 72, there exist numerous examples of DNA catenanes [34, 50, 51, 69-73] and a few examples of protein catenanes [74]. However, these aspects are beyond the scope of this section and are treated in Chapter 12. 

With the exception of DNA catenanes and protein catenanes, and despite various synthetic attempts, only one polymeric catenane structure, i.e. the catenated block copolymer 72, is known [31]. Evidently, the fact that the two constitutive cyclic polymers have two different chemical structures greatly facilitates the syn- 

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Catenation of two cyclic polymers (CPs) is a topological change forbidden by the excluded volume constraint in real polymers. 

Venn diagram indicating the four categories of false cyclic polymers (CPs) (a) valid, (b) self-knotted, (c) catenated, and (d) self-knotted and catenated. The superscripts V, S, C, and SC are respectively used for each of these categories. The superscript A is used to denote the superset of all false CPs. In other words, A = VuSuCu SC, where V, S, C, and SC are disjoint sets. 

The average distance between beads of the four different classes of false cyclic polymers (CPs) for N = 150. As expected, the catenated, but otherwise unknotted, false CPs are the largest, and the self-knotted false CPs are the smallest. This plot is representative of the trend observed over all values of N andf. ... 

Scheme 12 Some cyclic polymer structures (a) ring (b) knotted ring (c), (d) tadpoles (e) figure of eight (f) dumbbell bicycle (g) catenated ring and (h) tricycle.

Aromatic cyclic chains are more stable than aliphatic catenated carbon chains at elevated temperatures. Thus linear phenolic and melamine polymers are more stable at elevated temperatures than polyethylene, and the corresponding cross-linked polymers are even more stable. In spite of the presence of an oxygen or a sulfur atom in the backbones of polyphenylene oxide (PPO), polyphenylene sulfide (PPS), and polyphenylene sulfone, these polymers are... 

In recent years, dehydrocoupling reactions catalysed by early transition metal complexes have become an increasingly important method for generating catenated species of the p-block elements. In addition to producing cyclic oligomers, this approach is used to prepare linear oligomers and polymers such as polysilanes and polystannanes of the type H(MR2) H (M = Si, Sn) (see Section 10.1.4). ... 

To quote Robert West. ".Although the myth that silicon i.s nut capable of e.viensive catenation still persists, very large cyclic polysilanes have been synthesized as well as polysilane polymers with molecular weights in the hundreds of thousands." Pure Appl. Cliem. 19K2. 1041-11150. 

Polysilanes are compounds which contain silicon-silicon bonds. Although the disilane Et3SiSiEt3 was reported as early as 18691, and the cyclic perphenyl compounds (Ph2Si) (n = 4-6) were prepared over 70 years ago by Kipping and Sands2, the belief that silicon had limited capability for catenation persisted until quite recently. The isolation within recent years of cyclic dialkylpolysilanes containing up to 40 silicon atoms in a ring, and of linear polymers with more than 40,000 silicon atoms in the chain, have however effectively dispelled this myth. 

Figure 21.18 Elution volume dependence of the molar mass and of the radius of gyration for a linear PS comb L-2-100 (E) and of its cyclic homolog C-2-100 (C). (Reproduced with permission from M. Schappacher and A. Deffieux, Imaging of catenated, figure-of-eight, and trefoil knot polymer rings, Angewandte Chemie International Edition, 2009, 32, 5930-5933. Wiley-VCH Verlag GmbH Co. KGaA.)...

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