Polymers, heteroatom/heterocyclic

Ladder polymers have their backbone made from an interrupted series of condensed rings. In such polymers, very frequently the rings contain heteroatoms, and the polymer can be considered as part of the class of polymers with heterocycles in the main chain. One of the first synthesized polymers from this class was obtained from the oxidation and heating of polyacrylonitrile [1, 2]. Multifunctional condensations also can lead to ladder polymers. For example, a poly(phenoxazine) is formed from the reaction of a substituted quinone and a diaminodihydroxybenzene as shown below ... 

The seniority of different types of subunits is heterocyclic rings > heteroatoms or acyclic subunits containing heteroatoms > carbocyclic rings > acyclic subunits containing only carbon. The presence of various types of atoms, groups of atoms, or rings that are not part of the main polymer chain but are substituents on the CRU do not affect this order of seniority. 

Polymers with Conjugated Bonds, Heteroatoms and Heterocycles in the Backbone Chain... 

Now the research in the photoconductive properties of the polyconjugated materials is growing fast. Heterocycle or heteroatom-containing polymers are involved in this process due to their excellent mechanical and electric properties. The sensitized photoeffect in polyconjugated materials was first observed in 1964 [19,20] and the high significance of the increase in the photosensitivity of these compounds became apparent... 

The coordination polymerisation of heterocyclic and heterounsaturated monomers consists in the nucleophilic attack of the metal initiating substituent (or the growing polymer chain) on the carbon atom of the coordinated monomer. Scheme 2.6 shows initiation and propagation steps in the coordination polymerisation of epoxides, as the most representative heterocyclic monomers with an endocyclic heteroatom, with catalysts containing an Mt-X active bond [68,114,115] ... 

Although any coordination polymerisation involves a monomer coordination in each step, literature data that might concern complex formation between the monomer heteroatom and the metal atom at the active site are rather scant. This is due to the lability of such complexes of monomers with active sites if they were stable enough, they would not undergo any further rearrangement, which might lead to polymer chain growth. Thus, models have been studied that have consisted of a metal complex, of no effectiveness as a catalyst, and a monomer, or of a catalyst and a non-polymerisable heterocycle. 

Saturated six-membered heterocyclic rings can be found in various fields of chemistry, e.g., natural products, drugs and polymers. Representative molecules are cyclohexane derivatives in which ring methylenes are either substituted by alkyl or other functional groups or replaced by one or more heteroatoms (mainly nitrogen, oxygen, and sulfur). 

In addition to the demonstrated biological usefulness of the selected number of fused heterocycles listed in Table 2, increasing numbers of (5,5)-fused heterocycles containing a variety of heteroatoms are continuously evaluated and patented for potential use in various sectors of industry, including agricultural chemicals, dyes, pharmaceuticals and polymers. 

By ring-opening polymerization, polymers can formed from cycloalkenes, but mostly from simple and more complicated heterocycles containing heteroatoms such as O, N, S, P and Si. Ring-opening polymerizations are mostly initiated by the ionic mechanism. 

The discussion is limited to the reactions of heteroaromatic molecules, nonaromatic heterocycles are discussed elsewhere in this book in accordance with the appropriate heteroatom-containing functionality. The most important electron-transfer phenomena involving heteroaromatics are to be found on the one hand in biochemistry, where some heterocycles have a key role in metabolism, and on the other in material science, the applications of conductive polymers derived from... 

Generation of a diene from a polymer-bound benzocyclobutane [320] The polymer-bound benzocyclobutene (358) can be converted into a very reactive diene upon thermal 47r-conrotatory ring opening. The resulting diene (359) can react with a series of dienophiles containing heteroatoms to afford a series of heterocycles (Scheme 75). Lewis acid-catalyzed reductive alkylation concluded the synthesis to give 363. 

In the polymerization of heterocyclic monomers, the polymer backbone possesses heteroatoms able to participate in chain transfer. The result of this reaction is the formation of inactive branched onium ions (termination). In other instances scrambling is observed leading to changes in the microstructure of the chain and interconversion of active centers. Intramolecular chain transfer to polymer is accompanied by pie formation of macrocycles. Low-molecular-weight cyclic oligomers may escape detection, particularly when the polymer is separated by precipitation. Cyclic oligomers are better soluble and may remain in solution which leads to an erroneous... 

Hundreds of carbon- and heteroatom-centered nucleophilic agents have been involved in Sn reactions, which proved to be both a convenient and powerful synthetic tool for applicatimi in heterocyclic and medicinal chemistry, polymer chemistry, and other branches of chemistiy. It should be noted, however, that C-nucleophiles are still prevailing in the Sn reactimis over heteroatom-centered ones because of the following reasons (1) the C-C bond formation is one of the main of tasks of organic synthesis (2) as a rule, the C-adducts are more stable in comparison with the o -adducts derived from additimi of heteroatom-centered nucleophiles to the same aromatic substrates. 

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 ... 

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