Aromatic heterochain polymers

No such investigations have been performed for aromatic heterochain polymers (AHP). Thus there are many unclear and doubtful aspects in understanding the degradation mechanism. Studies performed at G. Petrov Research Institute for Plastics (Moscow) and Research and Production Company Polyplastic (Moscow) over the last 15 years concerning APH ageing and stabilisation, have been analysed. Specific features of high-temperature oxidation (300-400 °C) in melt and solid-phase oxidation (150-200 °C) of APH have been investigated. 

From our point of view, a specific feature of thermo-oxidation of aromatic and aliphatic-aromatic heterochain polymers is displayed in TPA amide formed during PPA thermooxidation. Unfortunately, this feature is insufficiently discussed in the literature yet. Three hypotheses were put forward in discussion of PDI formation at PAI thermo-oxidation ... 

The mechanochemical polycondensation reaction has been studied using heterochain polymer systems—polyethylene terephthalate poly-(e-caprolactam), cellulose, etc.—characterized by end groups that can be activated to increase their own number by mechanochemical destruction of corresponding polymers. The mechanochemical destruction was done in the presence of some suitable condensing agents, such as aliphatic and aromatic diamines and fatty acid dichlorides. 

Another heterochain polymer which has received a lot of attention recently is polyaniline. This material is produced by chemical or electrochemical oxidation of aniline, and it seems likely that it is very similar to, if not always identical with, aniline black , an ill-defined material of some antiquity. The propensity of hetero-substituted aromatics to undergo coupling via intermediate radical cations is well established and, since a monosubstituted benzene is effectively a trifunctional monomer in this context, it seems likely that this product is a network or highly branched material, which would account for its unattractive handling properties. 

The milling of poly(ethylene terephthalate) generally causes fracture of the heterobonds of the glycol chain units [20,21]. Simionescu and co-workers [21], in a complete study on poly(ethylene terephthalate), confirmed that homolytic bond cleavage occurs mainly at the weakest links, which were thought to be the heteroatomic bonds. Electron spin resonance has been widely employed for the study of rupture in heterochain polymers. If a chain has an aliphatic ether structure, for example, poly(ethylene oxide), rupture takes place mainly at the —C—C— bond [22]. The breakdown of aromatic polyesters and ethers occurs at the relatively weak —C—C— bonds around the aromatic nuclei [23]. In general, the bond most susceptible to rupture is beta-to-chain functionality as in polyesters and nylons. 

Karyakin, N.V., Thermodynamics of Aromatic Heterochain and Heterocyclochain Polymers, Nizhny Novgorod NNUniv. Press, 1998 (in Russian). 

Among the abundance of tested classes of substances, PCA is the only additive reliably protecting PSF from oxidation in concentrations below 0.3 wt.%. As expected, by analogy with polycarbonate and other heterochain polymers processed at temperatures about 300°C, classical primary antioxidants (hindered phenols and aromatic amines) are at most neutral (amines catastrophically color PSF), which proved existence of the effective inhibition temperature limit (120 - 125°C) [11, p. 218]. It is stipulated by activity of phenoxyl radicals in reactions with hydroperoxides. Commonly, all so-called non-chain inhibitors intensify... 

These are described in literature as the new type of principal amorphous heterochain fluorine polymers containing the stable perfluorinated cycloalkane and aromatic fragments in the main chain of macromolecules [92]. The authors reported studies on the characterisation of various random polyfluorocyclobutene (PFCB) copolymers of new type of monomers F2C=CF-0-Ar-0-FC=CF2 (Ar, see Figure 8.16). These monomers were prepared from their corresponding phenolic precursors and have been described previously in paper [93]. 

A great variety of possibilities are available when a metal is part of a linear or crosslinked macromolecule (Section 1.2.1, Fig. 7-1). One possibility is the covalent incorporation of a metal into a homochain (metal-metal connections) or a heterochain (metal-heteroatom connections). Coordinative bonds between a metal ion and another coordinating donor group can lead to linear chains or to supramolecular organizations when coordination polymers are formed. n-Bonds between rt-rich aromatic compounds and metal ions can result in polymeric metallocenes. Covalent and coordinative bonds are realized in cofacially stacked metal complexes. In addition, dendrimers containing the interaction of metals and another group in different bonds are treated in this chapter. 

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