Vinyl polymers, disordered conformations

The problem is further complicated for vinyl polymers with their problems of stereoisomerism. The first descriptions of the conformational state of isotactic polypropylene in solution go back 25 years (178, 179, 192, 193). Corradini, Allegra, and Ganis proposed a model, still essentially valid today, according to which macromolecules possess a local helical structure analogous to that observed in the crystalline state. The helix segments are rather short, only a few monomer units, after which an inversion of the helix sense occurs, with simultaneous alteration of its direction (Figure 15). As a whole this disordered con-... 

In the Raman spectra of conformationally disordered polyethylene, the D-LAM mode found at a frequency (near 200 cm ) that is proportional to the concentration of gauche bonds [74]. This D-LAM mode is also observed in other molten vinyl polymers including polypropylene, polybutene and polystyrene. The presence of this Raman line in these polymers suggests a common structural basis although the chains themselves have different side chains [75]. In the vinyl polymers the band may appear as a doublet. For polypropylene, for example, there is a line near 200 cm and 400 cm and it is suggested that these two components are associated with the conformationally ordered (gt)4 polypropylene. 

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