Structure regularity

Figure IV-10 illustrates how F may vary with film pressure in a very complicated way although the v-a plots are relatively unstructured. The results correlated more with variations in film elasticity than with its viscosity and were explained qualitatively in terms of successive film structures with varying degrees of hydrogen bonding to the water substrate and varying degrees of structural regularity. Note the sensitivity of k to frequency a detailed study of the dispersion of k should give information about the characteristic relaxation times of various film structures.

If a polymer molecule has a sufficiently regular structure it may be capable of some degree of crystallisation. The factors affecting regularity will be discussed in the next chapter but it may be said that crystallisation is limited to certain linear or slightly branched polymers with a high structural regularity. Well-known examples of crystalline polymers are polyethylene, acetal resins and polytetrafluoroethylene. 

Figure 4.1. Effect of structure regularity, molecular stiffness and intermolecular attraction on polymer...

Several approaches have been used, all aiming at disruption of the structural regularity of aromatic polyester chains ... 

Aromatic polyamides, 5 Aromatic polyester chains, disruption of structural regularity of, 50-52 Aromatic polyesters... 

In 1992/1994, Grubbs et al. [29] and MacDiarmid et al. [30] described an improved precursor route to high molecular weight, structurally regular PPP 1, by transition metal-catalyzed polymerization, of the cyclohexa-1,3-diene derivative 14 to a stereoregular precursor polymer 16. The final step of the reaction sequence is the thermal, acid-catalyzed elimination of acetic acid, to convert 16 into PPP 1. They obtained unsupported PPP films of a definite structure, which were, however, badly contaminated with large amounts of polyphosphoric acid. 

In Sect. 4.2 we expand on pseudogap tuning concepts and illustrate these ideas and applications to the isotypic Mg2Cu6Ga5, Mg2Znn, and Na2Au6ln5. Because all the ACs we have obtained have very similar structural motifs, their structural regularities will be discussed together later in Sect. 5. 

STRUCTURAL REGULARITY-WAVEGUIDE PROPERTY RELATIONSHIPS OF LANGMUIR-BLODGETT FILMS... 

The crystal structure can be considered as a structure regularly stacked with bimolecular layers along the a-axis. Within the bimolecular layer, two molecules related by inversion symmetry face each other in the tail-to-tail fashion with their molecular axes inclined by about 26° to the bilayer surface. This inclination enables the head-to-tail arrangement of azobenzene chromophores as expected from the spectroscopic study. 

In stereoregular polymers, each monomer segment is in regular configuration, it gives a structural regularity to the polymer molecule as a whole. 

The structural regularity in such polymers gives rise to optical (D-L isomerism) and tacticity of polymers and geometrical cross-trans isomerism. 

Disilane and germasilane monomers have also been successfully coupled, and using trisilane monomers with different substituents on central and terminal silicons, the interesting, more structurally regular, sequence-ordered co-polymers have been prepared, as shown in Scheme 17 and in analogy to the report by West on the Wurtz-type preparation of sequence-ordered co-polymers.17... 

DSC and X-ray indicated a lack of crystallinity and structural regularity. 29Si NMR showed a major, broad peak at 8 —57 ppm in solution and 8 —60 ppm in the solid state (cf. 8 —24.8 ppm for poly(dihexylsilylene)),286 with minor... 

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