Main-chain poly 2 catenanes

Scheme 14.3 Synthetic approaches to (a) a main-chain poly([2]catenane), (b) a main-chain poly (bis [2] catena ne), and (c) a pendant poly([2] catenane) (reproduced with permission from Reference 26).

Scheme 14.4 Synthesis of a main chain poly[2] catenane based on an aryl coupling reaction.27...

The synthetic routes used to prepare main-chain poly(2]catenanes are summarized in Scheme 17.3. Most often, they are prepared via the polymerization of difunctional [2]catenane monomers, such that the preparation of difimc-tional [2]catenane monomers represents the key step. In route 1, cychzation of a preorganized precursor affords the difunctional [2]catenane monomer, while in route 2 the difunctional (2]catenane monomer is synthesized directly via a template-directed cychzation reaction of two hemicyclic precursors. In route 3, stepwise threading and cyclization reactions are employed to prepare difunctional [2]catenane monomers. In route 4, urdike routes 1 to 3, covalent bonds are used as templating units during the second cyclization reactions to prepare difunctional [2]catenane monomers. Route 5 illustrates the preparation of difunctional bis[2]catenane monomers whereby, when difunctional [2]catenane or bis[2]catenane monomers are in hand, the main-chain poly[2]catenanes can be prepared via polymerization of the difunctional catenane monomers. 

Scheme 17.3 Synthetic routes for linear main-chain poly[2]catenanes. Functional group A reacts with group B to produce Z linkages, while functional group X reacts with the spacer with two Y functional groups to produce V linkages.

Figure 31 Polycatenanes (a) summary of types (i) linear, (ii) main-chain, and (iii) pendant (b) Sauvage s main-chain poly([2]catenane) and (c) Stoddart s pendant poly([2]catenane).

Hamers, C., Raymo, F. M., Stoddart, J. F., Molecular meccano, 42 - Main-chain and pendant poly([2]catenane)s incorporating complementary -electron-rich and -deficient components. Eur. J. Org. Chem. 1998, 2109-2117. 

Alternatively, ring closure metathesis reaction is applied to the formation of cyclic polymers, although the main chain does not consist of hydrocarbon. Such a method was reported in the preparation of cyclic poly(THF) as shown in Fig. 33 [112]. Such ring-close metathesis was also applied for a preparation of catenane [113]. 

Figure 2 Pass Ale types ofpolymers based upon catenane architecures A Linear mechanically-linked polymers B mechanically cross-linked polymers C stars with a flexible, potentially switchable, catenane core D combs with catenarw linkages E main chain catenanes with switchable surface properties F highly mechani-cally-crosslinked networks G poly- or [n]catenanes. Only examples of types A and F have thus far been prepared...

The first linear polymers containing [2]catenanes in their backbones (mechanically linked main chain polymers, architecture A) were based on the Sauvage transition metal-coordinated catenanes. Polycondensation reactions were carried out between a diacid and a catenane diol to give a poly[2]catenane with Mn (600000) and Mw (4200000) based on polystyrene standards (Figure 4). 

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 11 Stoddart s main-chain-type poly[2]catenane.

In 2000, Swager et al. also carried out the oxidative polymerization of [2]catenane having thiophene nnit to yield conductive poly[2]catenane consisting of polythiophene main chain. 

Poly[2]catenane occupies an important position of the topologically linked polycatenanes that incorporate the [2]cate-nane linkages in the main chain. Its preparation usually requires the polymerization of two reactive-sites-containing [2]catenane or ditopic [2]catenane. For this purpose, various... 

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