Stranded Polymers

Preparations of many double stranded polymers were reported. For instance, polypynolones were formed from 2,3,5,6-tetraaminobenzene and various dianhydrides or tetracaiboxylic acid Two examples follow  

Some ladder polyquinoxalines were found to be stable in air at 460 C, and in nitrogen up to 683 °C. 

Not all attempts at formations of ladder polymers yielded completely cyclized fused ring structures. For instance, an attempt to form a polymer from tetraaminonaphthalene with naphthalene tetracaiboxylic acid dianhydride failed to yield complete cyclizations.  

An interesting polymer containing macrocyclic rings was formed from pyromellitic tetranitrile by condensation with dianilino ether  

The description of all the double stranded polymers that were synthesized and reported in the literature is beyond the scope of this book. This section is concluded by a mention of a silicon-containing material prepared by an alkali-catalyzed polymerization of phenyltrichlorosilane  

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In arrays of closely packed nucleosomes composed of all four core histones, strands of H2A-H2B dimers could be incorporated in the grooves between the two H3-H4 strands, producing a four-stranded polymer. Alternatively, they could bind to the H3-H4 double-stranded fiber to give an octamer of the histones per nucleosome. This latter model is supported by the photochemical cross-linking of histones to DNA which have shown that within the nucleosome core the four core histones are not equivalently positioned with respect to... 

Note 1 For a single-strand polymer molecule with skeletal bonds all joined by the same value of valence angle, the contour length is equal to the end-to-end distance of the chain extended to the all-trans conformation. For chains of complex structures, only approximate values of the contour length may be accessible. 

Note 2 The sum of the lengths of all skeletal bonds of a single-strand polymer molecule is occasionally termed contour length . This use of the term in this sense is discouraged. 

Structure-based and source-based nomenclature rules have been extended to regular double-strand (ladder and spiro) organic polymers [7]. A double-strand polymer is defined as a polymer the molecules of which are formed by an uninterrupted sequence of rings with adjacent rings having one atom in common (spiro polymer) or two or more atoms in common (ladder polymer). 

The structure-based nomenclature rests upon the selection of a preferred CRU [1, 12] of which the polymer is a multiple the name of the polymer is the name of this repeating unit prefixed by poly . The unit itself is named wherever possible according to the established principles of organic nomenclature [3]. For double-strand polymers, this unit usually is a tetravalent group denoting attachment to four atoms. Since some of these attachments may be double bonds, the unit may be hexavalent or octavalent. Table 6 lists some examples. 

As with single-strand polymers, substituents that are part of the CRU are denoted by their names prefixed to the name of the subunit to which they are bound (see Table 7). 

In 1976, the lUPAC Commission on Macromolecular Nomenclature published rules on the nomenclature of regular single-strand organic polymers. These were later revised [1]. A regular single-strand polymer is one which can be described by constitutional repeating units with only two terminals composed of one atom each. 

Note Partial ladder (imperfect ladder, block ladder) polymers [5], in which the sequence of rings is interrupted and a divalent constitutional repeating unit can be identified, are not double-strand polymers. They are named as single-strand polymers. 

On the other hand, occasional irregular deviations from ideality can be ignored in constructing graphical representations for double-strand polymers and in assigning corresponding names. 

In using this nomenclature, the steps to be followed in sequence are the same as those for regular single-strand polymers ... 

At times, it is also useful to identify the starting monomers especially for such complex polymers as double-strand polymers, the synthesis of which is often a multi-step reaction involving condensation, cyclization and crosslinking. 

The proeedure for structure-based naming of irregular single-strand polymers is as follows ... 

Application of this system should not discourage the use of structure-based nomenclature whenever the copolymer structure is fully known and is amenable to treatment by the rules for single-strand polymers [1, 2]. It is intended that the present nomenclature system supersede the previous recommendations published in 1952 [3]. 

A classification of linear single-strand polymers (lUPAC Recommendations 1988), PureAppl. Chem. 61, 243-254 (1989). 

Kuhn element Number of repeat units needed so that the most probable distance between the first and the growing end is back at the first unit again, ladder polymer Double-stranded polymer for added stability. 

A single-strand polymer is composed of single-strand macromolecules, the structure of which comprises constitutional units connected in such a way that adjacent constitutional units are joined to each other through two atoms, one on each constitutional unit. 

As for a single-strand polymer, a single preferred CRU must be selected in order to obtain a unique name. The CRU is usually a tetravalent group denoting attachment to four atoms and is named according to the usual rules of organic nomenclature. The name of the polymer is in the form poly(CRU). 

A regular linear polymer that can be described by a preferred CRU in which only one terminal constituent subunit is connected through a single atom to the other identical CRU is a quasi-single-strand polymer. Such polymers are named similarly to single-strand coordination polymers. 

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