Repeat distance triclinic

As determined from X-ray diffraction measurements, the unit cell of crystalline PET is triclinic with a repeat distance of 1.075 nm along the major axis [5, 6], This corresponds to >98 % of the theoretical extended length of the monomer repeat unit [6], There is very little molecular extensibility remaining in a PET crystal, resulting not only in a high modulus but also a relatively short extension range over which the crystal can be extended and still recover elastically. The density of the crystalline structure is 1.45 g/ml, or about 9% higher than the amorphous structure [3],... 

The chemical structure was deduced to involve mainly (1 —> 4)-linked 2-deoxy-2-(sulfoamino)-a-D-glucose 6-sulfate and (1 —> 4)-linked 2-sulfated a-L-idopyranosyluronic acid residues. The X-ray patterns from sodium salts of hog-mucosal heparin index with a triclinic unit-cell, having a = 1.30 nm, b = 1.02 nm, c = 1.65 nm, a = 104°, /3 = 96°, and y = 116°, containing one chain. The macromo-lecular heparin from rat skin, at 84% relative humidity (r.h.), gives a pattern consistent with a highly oriented version of the hog-mucosal heparin. On lowering the r.h. to 76%, the repeat distance along the fiber axis increases to 1.73 nm, with meridional reflections on the even layer-lines. 

The solid state structure of a homologous series of mesogenic aromatic-aliphatic azomethine ether polymers (AZMEP-n), with n (=1-16) methylene spacers in the main chain, has been studied by X-ray fiber diffraction techniques. Unit cell parameters determined from the fiber patterns of heat-treated single filaments have been used to classify the polymers into distinct groups having different chain conformations and crystal systems. The even members of the. series, where n = 2 4, have C-centered monoclinic unit cells while the unit cells for polymers with n = 6 8 are I-centered monoclinic. When n is even and 10 the unit cells are (primitive) triclinic. The fiber repeat, in the triclinic cells correspond to one chemical moiety while in the monoclinic cells the fiber repeat corresponds to two chemical residues. In addition, the fiber repeat distances are consistent with the methylene spacers adopting an all-trans conformation for all even AZMEP-n polymers. 

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