Polymers backbone = primary structure

The polymer molecular chains form the backbone of the thermoplastics polymer structure. The nature and orientation of the monomer units in the chain determine the primary structure of the polymer. This primary structure of the chain can be differentiated into three groups ... 

The use of the N -LC as an asymmetric solvent enabled us to synthesize polymers having a hierarchical structure with a helical conformation of the molecular backbone primary structure. We can expect that this approach can be used to freely control the helical stracture of various products to further progress in the field of polymer synthesis. 

In the last three chapters we have examined the mechanical properties of bulk polymers. Although the structure of individual molecules has not been our primary concern, we have sought to understand the influence of molecular properties on the mechanical behavior of polymeric materials. We have seen, for example, how the viscosity of a liquid polymer depends on the substituents along the chain backbone, how the elasticity depends on crosslinking, and how the crystallinity depends on the stereoregularity of the polymer. In the preceding chapters we took the existence of these polymers for granted and focused attention on their bulk behavior. In the next three chapters these priorities are reversed Our main concern is some of the reactions which produce polymers and the structures of the products formed. 

The structure of the DNA polymer is similar to that of RNA, except there are no hydroxyl groups on the 2 carbon atoms of the ribose rings. The alternating deoxyribose rings and phosphates act as the backbone, while the bases attached to the deoxyribose units carry the genetic information. The sequence of nucleotides is called the primary structure of the DNA strand. 

Long flexible pol3nners have a large number of Internal degrees of freedom. The typical primary structure of such molecules Is a linear chain of atoms (often carbon) connected by chemical bonds ("backbone"). Usually, every other backbone atom carries a side group. By rotation about the bonds In the backbone the molecule changes Its shape, and since there are many of these bonds In a polymer. a wide spectrum of conformations Is available. The rotation is hindered by the side groups, so that some of these conformations may be rather unfavourable. In some macromolecules (for instance proteins) sequences of preferred bond orientations show up as helical or folded sections In the molecules (secondary structure). 

The physical and mechanical properties of materials are the primary concern for their use in applications. However, these properties reflect the motion of the constituent molecules, which makes study of the latter essential to the fundamental understanding necessary for developing new technologies. The structural dynamics is quantified by a time constant, t, which is a measure of the time scale for reorientation of a small molecule or the correlated conformational transitions of a few backbone bonds in a polymer. For both liquids and polymer melts the structural relaxation time (and viscosity, /, which is roughly proportional to t) varies with temperature, with Arrhenius behavior... 

The primary structural feature that determines crystallinity is the concentration of short chain branches along the polymer backbone. These short chain branches disrupt the local ordering of the chains and, thus, reduce the degree of crystallinity in the material. The melting point (T, eit) of the polymer is directly related to the amount of short chain branches in the material. Regardless of the supercritical fluid used, exceptionally low solubilities are found at temperatures below Tmeit- At temperatures above the strong... 

The term "secondary structure" refers to local folding of the backbone of a linear polymer to form a regular, repeating structure. For a polypeptide, the secondary structure is determined by the amino acid sequence (i.e., the primary structure) and the solvent environment in which it is located. 

Of the various primary conjugated polymer backbones, such as poly (p-phenylenevinylene)s, poly(thiophene)s, poly(phenyleneethynylene), etc., [42] poly(fluorene) and related structures have been widely used in biological... 

Scheme 1 Primary structures of three polymers with C-C backbone.

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