Packing of macromolecules

Within the class of polymer crystals having, ideally, long-range positional order for all the atoms, different crystalline forms (polymorphs) may arise as a result of having different almost isoenergetic macromolecular conformations (of the main chain, in most known cases) or as a result of different, almost isoenergetic modes of packing of macromolecules with identical conformations [1-3]. 

The oriented elongation of the polymer increases the packing of macromolecules and decreases the molecular mobility in the polymer. This was observed by the EPR spectra of the nitroxyl radical in these films. Therefore, one can expect an increase in radical pair recombination in the cage with an increase in y. However, experiment showed an opposite pattern the more the y, the higher the e value. These results found explanation within the scope of the... 

PACKING OF MACROMOLECULES IN POLYMER CRYSTALS 3.1 General Principles... 

Just as the amino acids, sugars, and nucleotides are the building blocks for formation of proteins, polysaccharides, and nucleic acids, these three kinds of macromolecule are the units from which larger subcellular structures are assembled. Fibers, microtubules, virus "coats," and small symmetric groups of subunits in oligomeric proteins all result from the packing of macromolecules in well-defined ways, something that is often called quaternary structure. 

Fig. n. Molecular models of layer packings of macromolecules in SA mesophase with dt (a) and d2 (b) spacings for polymer B.3.5 (Table 4)... 

An ordered packing of macromolecules may also cause an optical anisotropy and birefringence, which are characteristic, for instance, of polymer spherulites. Because of the radial anisotropy of a spheruHte and the convergence of beams in the spherical structure, the interference picture represents the so-caUed Maltese cross, the center of which is located in the center of spherulite. No calculations are performed using such a picture but the photoelasticity method is very efficient in revealing qualitatively the presence of any spherulites, or a mesomorphic or ordered sate of polymeric chains. 

As indicated earlier, polymers have a semicrystalline structure that is compatible with a two-phase model of polymer conductivity. A model proposed by Epstein and co-workers [8] describes the polymer sample as a set of metallic islands embedded in the insulating matrix. Conductivity is controlled by hopping of charge carriers between metallic islands. Such a structure may be a result of nonuniform doping as well as of two-phase crystalline-amorphous morphology. Interchain transport is favorable for high-density crystalline packing of macromolecules because... 

Let us emphasize the main facts for alkyl-substituted stiff macromolecules. The conformation of the main chain is affected by side groups and depends critically on the chain length. For relatively short side chains hexagonal packing of macromolecules is possible, whereas for longer chains the boardlike shape of the molecules leads to formation of a highly ordered layered structure. In the crystal state the coplanar arrangement of the fully extended aromatic backbone for polyesters is possible. In the liquid crystalline state both a well-ordered layered structure and a nematic structure are observed. Because of the boardlike shape of the molecules, the nematic phase is biaxial. 

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