Main-chain heterocyclic polymers

As illustrated in Figures 4(b) and 4(c), the thermotropic main-chain LC polymers can be obtained from polymers that contain only rigid-rod units or a combination of rigid-rod and flexible units. The main stmctural elements of such linear polymers are composed of benzene or naphthalene rings, or different heterocyclic fragments collmearly linked to one another by such groups as... 

Main-chain manipulation offers an opportunity to dramatically change the electronic and physical properties of the PAEs. Popular approaches are the introduction of meta linkages into the polymers, the introduction of aromatic hydrocarbons other than benzene, the introduction of heterocycles, and the substitution of a fraction of the connecting alkyne groups by double bonds. The last strategy leads to polymers that are hybrids between PPEs and PPVs. 

Besides in the liquid phase, some polyreactions are also performed in the solid state, for example, the polymerization of acrylamide or trioxane (see Example 3-24). The so-called post condensation, for example, in the case of polyesters (see Example 4-3), also proceeds in the solid phase. Finally, ring closure reactions on polymers with reactive heterocyclic rings in the main chain (e.g., poly-imides, see Example 4-20) are also performed in the solid state. 

Polymers with Heterocyclic Rings in the Main Chain... 

The tetrahydrofuran heterocycle has been incorporated into the main chain of a polymer by a ring expansion reaction of an epoxidized poly(diene) (172) (79BRP1550017). The reaction apparently takes place with equal efficiency (Scheme 85) with either nucleophilic or electrophilic initiation. 

Conjugated polymers incorporated with different heterocyclic moieties were reported. Examples of these conjugated main chains are poly(phenylene vinylene) (10)60 and polybenzoxazole/polybenzthiazole (ll)64 (Scheme 7). In... 

Besides these monodentate ligands, many multidentate ones have been prepared and used in different fields of chemistry and only a few should be mentioned here. Rigid bidentate benzimidazole-based N-heterocyclic carbenes were successfully used to synthesize main-chain conjugated organometallic polymers 23, an interesting class of materials with desirable electronic and mechanical properties (Fig. 9) [110]. 

If we consider, as examples of the second group, polymers containing aromatic carbon- and/or heterocyclic links in the main chain of the macromolecules, we will notice the following general features of their pyrolysis, thermal properties and chemical structure ... 

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