Amorphous chemical configuration

Noncrystalline polymers are characterized by the absence of long-range order, other than that associated with prerequisite connectivity of the polymer molecule itself. However, to merely classify a polymeric material as "amorphous" serves only to both overlook the various substructures that may exist, and fail to account for the particular differences in macroscopic properties which result from varying chemical configurations, or from, for example, specific thermal or mechanical treatments. In terms of classification, the first order structures of "noncrystalline" polymers are clearly not crystalline or liquid crystalline, and we usually have an a priori knowledge of the chemical configuration. Rather, the interest in structure in noncrystalline polymers and its interaction with bulk properties is centered on additional somewhat subtle variations in molecular... 

There are only three unique triad combinations, mm, mr and rr thus a methyl configurational sensitivity to just nearest neighbor configurations would produce only three resonance in the methyl region of the C-13 spectrum. From an earlier spectrum of the amorphous polymer, we noted at least ten methyl resonances. We must therefore consider the situation where the next-nearest as well as nearest neighbor configurations are affecting the chemical shift, that is. 

Hatley and Blair [3.69] presented mean Tg data for anhydrous carbohydrates (Table 3.1), which vary in the literature owing to measurement and interpretation differences. Small amounts of water may depress the data substantially. The physical stability of amorphous formulations below Tg is generally accepted, and a collapse can be avoided. This does not always apply to the chemical stability. If the temperature is reduced below T, the configurational entropy diminishes until it reaches zero. This T0 (also shown in Table 3.1) is called the zero mobility temperature at which the molecular motion stops. The authors define three areas of chemical reactions above Tg, chemical reactions are generally possible at T, reactions such as aggregation, which require substantial molecular motion, stop and between Tg and T0, reactions involv-... 

The chemical structure of a polymer determines whether it will be crystalline or amorphous in the solid state. Both tacticity (i.e., syndio-tactic or isotactic) and geometric isomerism (i.e., trans configuration) favor crystallinity. In general, tactic polymers with their more stereoregular chain structure are more likely to be crystalline than their atactic counterparts. For example, isotactic polypropylene is crystalline, whereas commercial-grade atactic polypropylene is amorphous. Also, cis-pol3nsoprene is amorphous, whereas the more easily packed rans-poly-isoprene is crystalline. In addition to symmetrical chain structures that allow close packing of polymer molecules into crystalline lamellae, specific interactions between chains that favor molecular orientation, favor crystallinity. For example, crystallinity in nylon is enhanced because of... 

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