Crystalline polymers, amorphous phase

In some crystalline polymers chemical shift differences between crystalline and amorphous phases have been observed and interpreted and for several crystalline forms the signals to be attributed to nuclei in different conformational environments have been identified [111, 112]. 

The chains that make up a polymer can adopt several distinct physical phases the principal ones are rubbery amorphous, glassy amorphous, and crystalline. Polymers do not crystallize in the classic sense portions of adjacent chains organize to form small crystalline phases surrounded by an amorphous matrix. Thus, in many polymers the crystalline and amorphous phases co-exist in a semicrystalline state. 

Many polymer-salt complexes based on PEO can be obtained as crystalline or amorphous phases depending on the composition, temperature and method of preparation. The crystalline polymer-salt complexes invariably exhibit inferior conductivity to the amorphous complexes above their glass transition temperatures, where segments of the polymer are in rapid motion. This indicates the importance of polymer segmental motion in ion transport. The high conductivity of the amorphous phase is vividly seen in the temperature-dependent conductivity of poly(ethylene oxide) complexes of metal salts. Fig. 5.3, for which a metastable amorphous phase can be prepared and compared with the corresponding crystalline material (Stainer, Hardy, Whitmore and Shriver, 1984). For systems where the amorphous and crystalline polymer-salt coexist, NMR also indicates that ion transport occurs predominantly in the amorphous phase. An early observation by Armand and later confirmed by others was that the... 

First introduced to polymer chemistry by Schaefer and collaborators, CP-MAS spectroscopy has already yielded interesting results in both stractural and dynamic studies. The comparison of spectra in solution and in bulk permits identification of frozen conformations, distinction between spectra of crystalline and amorphous phases and measurement of the rate of several eonformational transitions. For example, the C spectrum of the poly(phenylene oxide), 74, in solution consists of five signals while the CP-MAS spectrum displays six. In the solid state the resonance of the aromatic CH appears split into two components. The phenomenon is attributed to the forbidden rotation of the benzene ring around the O. .. O axis, which makes the two carbon atoms indicated with an asterisk no longer equivalent. 

Amorphous phase The part of a polymeric material that has no particular ordered arrangement in contrast to the crystalline phase, which is ordered. Semicrystalline polymers consist of different ratios of crystalline and amorphous phases. 

The separation of the crystalline and amorphous phases into their respective spectra has been carried out for a number of polymers including polyethylene terephthalateS6), polystyrene 57), poly(vinyl chloride)58), polyethylene 59,60) nylon61), polypropylene 62), and poly(vinylidene flouride)63). 

Specific interactions between PCL and PVC are clearly indicated. In the solid state (Figure 5.9a) the spectrum of neat PCL indicates the presence of crystalline (1724 cm 1) and amorphous (1737 cm"1) bands. At mole ratios up to 2 1 of PVC to PCL, the spectra indicate that in the solid state the blends consist of crystalline and amorphous phases. As the PVC concentration increases, a parallel increase of the intensity of the amorphous band is observed. Moreover, the frequency shifts observed for both the crystalline and amorphous bands as a function of the composition of the blend suggests that specific interactions between the two polymers occur. No shift is observed in the carbonyl stretching vibration of PPL/PVC blends, in the molten state or in the solid state over the entire range of compositions and the two polymers are incompatible [28]. 

The discussion of the influence of the interphase need not be limited to just linear polyethylenes. Interphases of several nm have been reported in polyesters and poly-hydroxy alkanoates. One major difference between the interphase of a flexible polymer like polyethylene and semi-flexible polymers like PET, PEN and PBT is the absence of regular chain folding in the latter materials. The interphase in these semi-flexible polymers is often defined as the rigid amorphous phase (or rigid amorphous fraction, RAF) existing between the crystalline and amorphous phases. The presence of the interphase is more easily discerned in these semi-flexible polymers containing phenylene groups, such as polyesters. 

One of the benefits of direct TEM observation is its possible accounting of the thickness of the crystalline and amorphous layers separately. The distributions of thickness for amorphous and crystalline layers are plotted in Figure 8.40 Both crystalline and amorphous thickness distribution curves have their individual maxima, whose positions are independent of prior polymer concentration. The peak top is always located at 9 nm for crystalline layer and 1.5 nm for the amorphous one. Their SAXS profiles are compared in Figure 9.40 The long periods lie in the constant position at around 0.75°, which corresponds to 11.5 nm thickness, independent of prior polymer concentration. As the lamellar thickness obtained by SAXS is the sum of thicknesses of the crystalline and amorphous phases, the average thickness of lamellae measured by TEM coincides with that by SAXS. Therefore, the morphologies seem to be independent of polymer concentration. 

From decomposition of these FID profiles into crystalline and amorphous phases, the integral width and component ratios for relaxation in crystalline and amorphous phases were plotted, as shown in Figure 11.40 The crystallinity lies around 86%, independent of prior polymer concentration, which agrees well with... 

The density method is very convenient, because the only measurement required is that of the density of a polymer sample. It suffers from some uncertainties in the assignments of crystalline and amorphous density values. An average crystallinity is estimated as if the polymer consisted of a mixture of perfectly crystalline and completely amorphous regions. The weight fraction of material in the crystalline state Wc is estimated assuming that the volumes of the crystalline and amorphous phases are additive ... 

Practical problems associated with infrared dichroism measurements include the requirement of a band absorbance lower than 0.7 in the general case, in order to use the Beer-Lambert law in addition infrared bands should be sufficently well assigned and free of overlap with other bands. The specificity of infrared absorption bands to particular chemical functional groups makes infrared dichroism especially attractive for a detailed study of submolecular orientations of materials such as polymers. For instance, information on the orientation of both crystalline and amorphous phases in semicrystalline polymers may be obtained if absorption bands specific of each phase can be found. Polarized infrared spectroscopy can also yield detailed information on the orientational behavior of each component of a pol3mier blend or of the different chemical sequences of a copoljnner. Infrar dichroism studies do not require any chain labelling but owing to the mass dependence of the vibrational frequency, pronounced shifts result upon isotopic substitution. It is therefore possible to study binary mixtures of deuterated and normal polymers as well as isotopically-labelled block copolymers and thus obtain information simultaneously on the two t3q>es of units. 

One of the most important subjects of applied polymer science is the understanding of the deformation mechanisms and the fracture properties of semi-crystalline polymers. At the same time, it is one of the most diffictdt to study, and the amount of research in this area is high (see e.g. One of the complications experienced with semi-crystalline polymers stems from the fact that they are composed of crystalline and amorphous phases, arranged in a diversity of microstructures. These are generally... 

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