Heteroatom chains

Biodegradable polymers and plastics are readily divided into three broad classifications (/) natural, (2) synthetic, and (J) modified natural. These classes may be further subdivided for ease of discussion, as follows (/) natural polymers (2) synthetic polymers may have carbon chain backbones or heteroatom chain backbones and (J) modified natural may be blends and grafts or involve chemical modifications, oxidation, esterification, etc. 

Heteroatom Chain Backbone Polymers. This class of polymers includes polyesters, which have been widely studied from the initial period of research on biodegradable polymers, polyamides, polyethers, polyacetals, and other condensation polymers. Their linkages are quite frequendy found in nature and these polymers are more likely to biodegrade than hydrocarbon-based polymers. 

The smallest [n]paracycloph ane so far isolated is the [6]paracyclo-phane, first prepared by Jones et al. in 1974. Bickelhaupt prepared and succeeded in spectroscopic characterization of [5]paracyclophane, which is stable at low temperature in solution, but not isolable. As the first example of [n paracyclophanes bridged by heteroatom chains, Ando et al. reported preparation and the crystal structure of heptasila[7]paracyclophane (47) (42) (Scheme 12). 

The largest main-chain (backbone) segment of the constitutional repeating unit that can be named as a single unit under organic nomenclature rules [4, 5], This may be a ring or ring system, a heteroatom or a heteroatom chain or an acyclic carbon chain. 

The basic order of seniority of subunits is heterocyclic rings and ring systems > heteroatom chains > carbocyclic rings and ring systems > acyclic carbon chains... 

Chap. 14 Aliphatic Polymers with Heteroatom Chains... 

The largest group of inorganic heteroatomic chain compounds with considerable industrial potential is the phosphazenes,18,23 which are based on a phosphorus-nitrogen skeleton. The electronegativity difference here (xp = 2.19, xn = 3.04) is less than in the siloxane link, but some multiple bonding is involved between N and P, which strengthens the framework. The... 

In these syntheses, the linear heteroatomic chain must contain the six atoms of the future thiazine skeleton. The chain may be cyclized between N and C-4 (type 4a), between N and C-2 (type 4b), between S and C-2 (type 4c), between S and C-6 (type 4d), or finally between C-4 and C-5 (type 4e). 

When the methoxyarene rings are tethered by carbon-heteroatom chains, as in 104, such oxidations proceed in intramolecular fashion and afford the benzo-annulated seven-membered heterocycles 105 (Scheme 33) (96CC1481, 98JOC7698, 01T345). Selected coupling reactions of the types shown in Schemes 32 and 33 have also been demonstrated with the polystyrene analogs of BTIB and DAIB (01T345). 

Bridged ferrocenes, or ferrocenophanes, have been known for many years. These compounds, in which the two Cp rings are linked by carbon and/or heteroatom chains, are... 

Polymers with Heteroatom Chain Structure (Heteropolymers)... 

Inorganic polymers or macromolecules contain no carbon but nonmetals, semimetals and/or metals in the main chain or network. Examples are polysiloxanes, polysilanes, polyphosphacenes and several polymers with metal-heteroatom chains (organometallic polymers). 

This is not true for heteroatomic chains - CH2C HX 0 such as where C is a true asymmetric center, and these polymers are optically active. In this case, an absolute configuration can be assigned, using preferably the Cahn-Ingold-Prelog system, referring either to the R-(rectus) or to the S-(sinister) form. 

For more complex chains containing rings or heteroatomic chains, e.g., polydienes, polyethers, polysaccharides, and proteins, an estimate of o is obtained from... 

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