Poly- -catenanes

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. 

Anthracene groups are sufficiently large to prevent the dethreading of a-CD and /3-CD from an axle, and photoirradiation produces dimers. Consequently, poly(polyrotaxane)s and poly(catenane)s can be obtained by the photoirradiation of polyrotaxanes, with anthracene groups as stoppers. Recently, the present authors reported the preparation of poly(a-CD polyrotaxanes) by the photoirradiation of polyrotaxanes with 9-anthracene [87]. 

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

In the major isomer, the bipyridinium unit is located inside the cavity of the macrocyclic poly ether and the /7Y//7,v-bis(pyridinium)ethylene unit is positioned alongside, as confirmed by the electrochemical analysis. The cyclic voltammo-gram of the catenane shows four monoelectronic processes that, by a comparison with the data obtained for the free cyclophane, can be attributed as follows the first and third processes to the first and second reductions of the bipyridinium unit, and the second and fourth ones to the first and second reductions of the trans-bis (pyridinium)ethylene unit. The comparison with the tetracationic cyclophane also evidences that all these reductions are shifted toward more negative potential values (Fig. 13.33b). 

A different approach to the synthesis of oligo[2]calenanes was chosen by Mullen et al. in 1995 [57]. The bromo-substituted in/out catenane 111 was coupled with appropriate comonomers under Suzuki conditions [58]. The degree of polymerization was between one and five for the resulting oligomers 112 (Figure 45). In 1997 the same group reported the first synthesis of poly[2]catenanes of the... 

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... 

Scheme 3. Pictorial representation of polyrotaxane 7, multicatenane 8, polycate-nane 9, poly[2]catenane 10, and polymeric catenane 11.

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. 

Poly[2]catenanes Linked by Alternating Topological and Covalent Bonds... 

Table 1. Molecular-weight averages, monomer lengths (/) and estimated upper value of the Kuhn segment lengths (/k) of the poly[2]catenanes 48, 49, and 59, and the poly[2]catenands 51, 56.

Scheme 16. Synthesis of poly[2]catenanes 48 and 49, (i) 4-(dimethylamino)pyridine-p-tol-uenesulfonic acid 1 1 complex plus A -diisopropylcarbodiimide.

The high rigidity of the catenane segments has been demonstrated by a temperature-dependent NMR spectroscopic study of the catenane monomers 44 and 46 [37, 52], Almost no temperature dependence was observed for the line shape of the spectra of the catenane monomers 44 and 46 whereas the temperature had a dramatic influence on the spectra of the unmethylated catenanes 41b,d and 42b,d [30, 37, 52, 56]. Therefore, the poly[2]catenanes 48 and 49 represent one extreme case where there is very little relative mobility of the macrocycles of the catenane segments. 

Unlike the poly[2]catenanes 48 and 49, the poly[2]catenand 51b, containing catenane segments prepared from large macrocycles (45 atoms) represents the other extreme in view of the high mobility of the macrocycles of die catenane units (Scheme 17) [53, 58], From a synthetic viewpoint, the large mobility of the dihydroxy[2]catenand 50b has a dramatic influence on the resulting polycondensation products (Scheme 18). 

---