Amorphous mobility, regions

Oxidation of polymer is accompanied by the change of their structure - physical properties - crystallinity, molecular mobility, strength and so on. Orientation of crystalline regions is disturbed in stressed samples the number of crystals with definite space orientation of crystal lattice axes decreases, the form of the curve of crystal distribution axes in respect to orientation axis changes. Change for the worse of crystals orientation is explained by stress relief, occurring in polymer at the expense of oxidative destruction of macromolecules in amorphous intercrystalline region [301]. 

This rule of thumb does not apply to all polymers. For certain polymers, such as poly (propylene), the relationship is complicated because the value of Tg itself is raised when some of the crystalline phase is present. This is because the morphology of poly(propylene) is such that the amorphous regions are relatively small and frequently interrupted by crystallites. In such a structure there are significant constraints on the freedom of rotation in an individual molecule which becomes effectively tied down in places by the crystalhtes. The reduction in total chain mobility as crystallisation develops has the effect of raising the of the amorphous regions. By contrast, in polymers that do not show this shift in T, the degree of freedom in the amorphous sections remains unaffected by the presence of crystallites, because they are more widely spaced. In these polymers the crystallites behave more like inert fillers in an otherwise unaffected matrix. 

In the case of crystaUizable polychloroprene, the cross-link density has been found to be lower in the crystalline region as compared to the amorphous portion of the mbber due to the lower radical mobility in the former. The cross-links are found to be intramolecular in the crystalline zone [387]. 

In polymer electrolytes (even prevailingly crystalline), most of ions are transported via the mobile amorphous regions. The ion conduction should therefore be related to viscoelastic properties of the polymeric host and described by models analogous to that for ion transport in liquids. These include either the free volume model or the configurational entropy model . The former is based on the assumption that thermal fluctuations of the polymer skeleton open occasionally free volumes into which the ionic (or other) species can migrate. For classical liquid electrolytes, the free volume per molecule, vf, is defined as ... 

Many polymers solidify into a semi-crystalline morphology. Their crystallization process, driven by thermodynamic forces, is hindered due to entanglements of the macromolecules, and the crystallization kinetics is restricted by the polymer s molecular diffusion. Therefore, crystalline lamellae and amorphous regions coexist in semi-crystalline polymers. The formation of crystals during the crystallization process results in a decrease of molecular mobility, since the crystalline regions act as crosslinks which connect the molecules into a sample spanning network. 

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