Extended-chain molecule

FIGURE 2.37 Microfibrillar structure with noncrystalline extended-chain molecules. 

The general type of crystal structure in linear macromolecular substances is essentially that also shown by the simplest long chain molecules, the paraffins. The extended chain molecules, are plane zigzag structures, lying parallel to each other, and pack like flattened rods or ribbons. 

Thermotropic LCPs are melt processed by injection molding and extrusion to form highly oriented rods, strands and molded articles. It is well known [348,364,365] that extrudates have high molecular orientation which develops as a result of the effect of the flow field on the easily oriented extended chain molecules. Molded articles composed of thermotropic LCPs have properties that are better than short fiber reinforced composites, and they have been termed... 

To meet the available computer resources, the extended chain molecule has to be represented by a fairly small model molecule for the quantum chemistry calculations. It is to be demonstrated that no excessive errors are introduced by truncating the long polymer chain. In other words, the endgroup effects must be shown to be small. Again, there are two ways, remote parts of the chain molecule might influence the chemical shift in the central part. 

The sequence of amino acids determines the primary structure, but this is not the only problem in protein chemistry. When several hundred amino acids join to form an extended chain molecule, it is easy to imagine that such a molecule may be arranged in space in various ways. For example, it may retain a straight linear form, or bunch up randomly in a ball, or arrange itself in a highly ordered helix (screw shape). These arrangements are called the secondary structure. We shall see that only a few types of secondary structures are actually found in nature. 

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