Poly- -Polycatenanes

Polycatenanes, 17 60 Poly(y-caprolactone)dimethylacry, in shape-memory polymers, 22 357 Poly(y-caprolactone)/OMLS nanocomposite, 20 311 Poly(y-caprolactone) switching segment, in shape-memory polymers, 22 362-363 Polychlorinated biphenyls (PCBs),... 

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... 

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.

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). 

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... 

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. 

Fig. 8 Thermodynamic self-assembly of a polycatenane. Formation of a linear poly[2]catenane containing covalent, topological, and...

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. 

Scheme 17.24 Synthesis of poly(l,2-dithiane)s 85 and 86 with polycatenane entanglement structures.

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. 

Figure 3.33 More complicated catenanes include (a) [n]-polycatenanes and (b) poly-(2)-catenanes. (c) molecular necklaces, (d) Covalent modifications can be made to produce pretzelanes and (e) chirality can be imparted by using macrocycles in which directionality can be defined by the covalent order of atoms in the ring.

The detailed general structures of the representative poly-catenanes are shown in Figure 2. Polycatenanes can also be... 

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