Ring-heteroatom backbone structure

A comparison of polymers with different polymer backbones is shown in Fig. 5.13 for the non-ionic polymers poly(ethylene oxide) (PEO), poly(acrylamide) (PAAm), and methyl cellulose (ME) in aqueous solution. The heteroatom in the backbone of PEO leads to an expanded coil structure compared to PAAm with the heteroatom in the side chain. Cellulose derivatives have in addition to the heteroatom the ring structure of the anhydroglucose unit in the polymer backbone. The methyl cellulose in this example has a less expanded coil than the synthetic PAAm and PEO. Again, it is hard to distinguish between the influence of the solvation of the polar backbone and the pure steric hindrance of the different backbone structures. 

Cyclic structures form on polymer backbones through 1,3-dipolar additions to caibon-to-caibon or carbon-to-nitrogen double bonds. Because many 1,3-dipoles are heteroatoms, such additions can lead to formations of five-membered heterocyclic rings. An example is addition of nitrilimine to an unsaturated polyesters ... 

Another path in which the science of cycloparaphenylenes is expanding is via the inclusion of heteroatoms into the CPP backbone. Itami reported the synthesis of [18]CPP with two 2,2 -bipyridyl units replacing four of the phenyl rings in the CPP structure (Fig. 42) [46]. This [14,4]CPPy was synthesized using established methodology developed by the Itami group and shows a pH dependent fluorescence that can be reversibly red shifted by addition of acid. These preliminary results may open a door towards the controllable fluorescence of nitrogen-doped CPPs. 

After polyacetylene, PPy is one of the simplest ECPs. The i-conjugated backbone of a neutral PPy resembles that of cis-polyacetylene, except PPy has an additional nitrogen heteroatom every four carbon atoms, linking between the 1st and 4th carbon atoms (Fig. 5b) [56]. The nitrogen heteroatom and the ring structure of the repeating unit stabilise the polymer s molecular structure. PPy is very attractive for... 

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