Polymers with heteroatom chain structure

Polymers with Heteroatom Chain Structure (Heteropolymers)... 

Fig. 8. Schematic representation of heteroatom-containing structural elements in polymers that are disposed for characterisation by 1H/X/Y triple resonance experiments where X = 13C and Y = 19F, 31P, 29Si, 119Sn, with possible coherence transfer pathways being indicated by single and double headed arrows.36 39 Selective observation of the correlations of the building blocks in (a)-(c) requires experiments involving out-and-back coherence transfer via Vc.h/ -A.x (a), Vc.h/ cx (b), or / . (c), whereas the simultaneous observation of all correlation signals originating from a chain of an isotope labelled sample (d) is feasible by means of a HCa(Y)-CC-TOCSY sequence.39...

Polymers with triple bonds and heteroatoms in the macromolecule chain were among the first photoconducting polymers [8, 93-96]. The structural formulas for some among nearly seventy polymers investigated may be represented by... 

As the name implies, polysilane polymers consist of chains made up exclusively of sihcon atoms. (In the ht-erature these polymers are named either as polysUanes or poly(silylenes) thus (Et2Si) can be called polydiethylsilane or poly(diethylsilylene).) Unlike the heteroatomic polysiloxanes, with alternating silicon and oxygen atoms in the polymer backbone, the poly silanes are homoatomic and therefore structurally closer to aUcene polymers. However, because the atoms in the main chain are all silicon, the polysilanes show quite special properties. ... 

Triple resonance 3D-NMR experiments can be useful for studying polymeric structures without resorting to isotopic labeling, even when the nuclei involved are present in low natural abundance. This study of MD3M shows that the considerable spectral dispersion obtained in the Si NMR spectra of siloxanes, compared with the narrow H and C chemical shift ranges, permits detailed examination of the structure of PDMS by the 3D H/ C/ Si NMR correlation experiment. These techniques can also be usefiil for characterizing star-branched polymers which contain NMR active nuclei, polymers with low concentrations of heteroatoms (e.g. at the chain end or at low occurrence branch points) and many organometallic compounds. 

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. 

In contrast to many other polymers classified as biodegradable, PVA exhibits a backbone solely made up of carbon. The presence of a heteroatom like O or N in the main chain is definitely not a prerequisite for Nature to handle a polymeric structure that does not exist in nature. PVA degradation starts with random oxidations of the polymer backbone in the extracellular or periplasmic space of some microbes. Specific enzymes able to detect such sites of first attack continue in a hydrolytic way, yielding ever smaller polymer fragments that finally can be metabolised by the microbe or the microbial community. 

Polystyrene (PS) is the simplest carbon-chain polymer, which contains a phenyl ring. This polymer contains no heteroatoms and is readily soluble in most organic solvents this makes it possible to use its solutions to assess the effect of the spatial organization of macromolecules (conformation) on the micro structure of the carbon obtained, for it is known that the change in fumed carbon structure may be caused by a difference in the supramolecular structure of carbonization precursors [12]. According to Ref.[13], the mean size of aggregates for solutions of PS in ethyl acetate with a concentration of 0.25 g/100 mL is 1000 A at 1.5g/100 mL concentration, it is 4000 A, and for 5.0 g/100 mL it is 890 A, their number (N10"9/sm"3) being 0.017, 0.27 and 6.88 respectively. 

Polyheterocycles (PHCs) constitute another class of conducting polymers they can be viewed as a carbon chain with the structure of c/.v-polyacetylene stabilized by a heteroatom. 

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