Polymer planar zigzag

The repeat distance along the chain axis (0.468 nm) is significantly less than that calculated for a planar zigzag stmcture. Therefore, the polymer must be in some other conformation (65—67). Based on k and Raman studies of PVDC single crystals and normal vibration analysis, the best conformation appears to be where the skeletal angle, is 120°, and the torsional of opposite sign) is 32.5°. This conformation is in... 

Fig Planar zigzag structure of polymer molecules showing (I) isotactic, (II) syndiotactic, and (III) heterotactic configurations, (Hydrogen atoms are not shown for the purpose of clarity.)... 

Linear macromolecules having a constitutional repeating unit such as -CH2-CHX- (X H) show two further stereoisomerisms, i.e., optical isomerism and tacticity. The stereoisomerism named tacticity has its origin in the different spatial arrangements of the substituents X. When we arrange the carbon atoms of the polymer main chain in a planar zigzag conformation in the paper plane. 

The shape of macromolecules within a folded lamella is not the same for all polymers. In crystalline polyethylene, for example, the chains assume a planar zigzag conformation, but in some other polymers like polypropylene and polyoxymethylene the chains prefer a helical shape, as in proteins. The helix might have three, four, or five monomer units per turn, i.e., the helices are three-, four-, or five-fold (Fig. 1.12)... 

As pointed out earlier, the fluorine atoms are too large to allow planar zigzag structure, which confers rigidity on the polymer.20 The PTFE molecule has a regular folded structure, which produces a laminar crystal.16... 

In all cases, linear polymers were obtained with chains that consisted predominantly of l-methylene-3-cyclopentyl or l-methylene-3-cyclohexyl units, respectively, and were characterised by a chain planar zigzag conformation [446, 495, 496],... 

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