The ordered polymer chain

Under suitable conditions the allowable rotational states can be restricted. A given bond or sequence of bonds will be limited to rotational angles that correspond to the lowest minima in the potential function describing the hindrance to rotation. 

Consequently, a higldy ordered chain structure is evolved with the concomitant loss of the conformational versatility that characterizes the disordered chain and the liquid state. For example, the trans state represents the bond orientation with the lowest energy in polyethylene. When successive bonds in the chain assume this orientation, a fully extended planar zigzag conformation results, as is illustrated in Fig. 1.2. From the multitudinous number of conformations available to the chain in the liquid state only one ordered structure survives that is characteristic of the crystal. An extended planar, or nearly planar, ordered conformation is characteristic of many polymers including polyamides, polyesters, cellulose derivatives, polydienes, and one of the low energy forms of the polypeptides. 

The rotational states allowed for vinyl polymers derived from monomer units of the type—CH2—CH2R—depend on the configurations of the successive 

Polymers containing bulkier side-groups require more space, so that much looser heUces are formed. Typical examples of the latter type are illustrated in Fig. 1.3b, c, and d. These structures give rise to larger repeating units. For example. 

Poly(tetrafluoroethylene) also forms an ordered chain structure. The fully ordered conformation is a slowly twisting helix that comprises 13 CF2 groups in a repeat. (25) Each chain bond is rotated 20° from the precise trans position. The reason for this distortion is that, if the structure were planar zigzag, the nonbonded fluorine atoms would be uncomfortably close to one another. The rotation about each chain bond again relieves the overcrowding. 

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The ordered polymer chains are consistently oriented perpendicularly to the radius of the spherulite. 

Mesomorphic forms characterized by conformationally ordered polymer chains packed in lattices with different kinds of lateral disorder have been described for various isotactic and syndiotactic polymers. For instance, for iPP,706 sPP,201 sPS,202 syndiotactic poly(p-methylstyrene) (sPPMS),203 and syndiotactic poly(m -methylstyrene),204 mesomorphic forms have been found. In all of these cases the X-ray fiber diffraction patterns show diffraction confined in well-defined layer lines, indicating order in the conformation of the chains, but broad reflections and diffuse haloes on the equator and on the other layer lines, indicating the presence of disorder in the arrangement of the chain axes as well as the absence of long-range lateral correlations between the chains. 

In order to study the shape of a polymer-Cu complex, viscometric measurements of a homogeneous solution of QPVP were carried out (Fig. 1). At constant QPVP concentration, an increase in the added amount of Cu ions causes a decrease in viscosity, which reveals that the polymer-ligand chain is markedly contracted due to intra-polymer chelation. An intra-polymer chelate takes a very compact form and Cu ions are crowded within the contracted polymer chain (Scheme 2). The adsorption of Cu ions on the polymer ligand is sigmoidal, as can be seen in Fig. 1. At a low... 

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. 

A factor that affects the kinetics of the polymerization, and, more critically, the utility of the monomer in copolymerizations with other monomers, e.g., methyl methacrylate, is the stability of the radical formed from addition of the growing polymer chain to the vinyl terminus. In order to gauge the stabilizing effect of the phcnylethynyl group, and the sensitivity of the stabilization to substitution at the para position of the aromatic ring, Ochiai and co-workers carried out calculations at the UHF/3-21G level to evaluate... 

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