Noncrystallizable polymer

For homogeneous blends, % < 0 and consequently the presence of another noncrystallizable polymer depresses the melting point of a polymer. 

Most polymers are partially crystalline. The degree of crystallinity of polymers may, however, range very widely from 0 percent for noncrystallizable polymers, through intermediate crystallinities, up to nearly 100 percent for polytetrafluo-roethylene and linear polyethylene. A direct evidence of the crystallinity in polymers is obtained from x-ray diffraction studies. The x-ray patterns of many crystalline polymers show both sharp features characteristic of ordered regions (called crystallites) and diffuse features characteristic of a molecularly disordered phase... 

Isolated chains of a noncrystallizable polymer tend to adopt the random coil form. The same applies to both blocks of an amorphous biblock polymer. If the space requirements of both blocks are of the same magnitude, then all A blocks will be arranged in one layer, and all B blocks in another. Because of compatibility, the A layer faces another A layer and the B layer correspondingly faces another B layer. Thus, the block polymer forms lamellae of alternating A and B layers (Figure 5-31). 

The preparation of crystallizable polypropylene, as practiced in the earlier days of polypropylene, involved the preparation of catalyst, polymerization, purification, solvent recovery, and, finally, compounding. Typically, yields were 500 1000 lb of polymer per pound of catalyst [6]. Each manufacturer practiced one s own version of these process steps in an effort to produce a uniform product with regard to molecular weight and molecular weight distribution, ash content, color and color stability, and atactic, noncrystallizable polymer content. As discussed earlier, some systems used solvents that kept the atactic polymer in solution. 

Most cases of radiation-induced polymerizations of crystalline monomers lead to atactic, noncrystallizable polymers. This occurs because of the density difference between the polymer and monomer crystal, which does not allow the monomer enough mobility to orientate sufficiently during the propagation step to produce a stereoregular polymer. 

In a noncrystallizable polymer such as atactic polystyrene, is dose to 8wt%. In semicrystalline PE it is 5 wt%, presumably due to segregation of the CB to the noncrystalline phase or the phase boundaries in PE. This segregation is further enhanced in PE/PS blends when the composition allows for continuity of the PE phase and double percolation of the phases and conductive regions [27, 37]. This has been observed at a 45/55 ratio by weight of PE/PS in a melt-blended composition with more than 0.4 wt% (0.2 vol%) carbon black [27]. The effect seems to depend upon the relative interfacial tensions of the polymers and the CB in a manner consistent with the independent observations of Miyasaka et al. [38]. 

This polymer should ideally be formed by a head-to-tail succession of monomer units having randomly equal and opposite configurations. Although the term atactic polypropylene has been used in the literature in a very broad soise to indicate all noncrystallizable polymers, in fact no noncrystallizable polymer of propylaie, whose structure has been studied so far, is strictly atactic (12, 37). Even in polymers in which the isotactic and syndiotactic diad content approaches S)%, the succession is not Bernoullian, since sequences of homo-diads are generaUy preferred over sequences of heta-o-diads hence these polymers also contain short isotactic stereoblocks near short syndiotactic stereoblocks. ... 

At least in some cases, noncrystallizable polymers of opylene are such, not because trf a complete lack of stereospecificity of propagation, but because of frequent changes in the type of steric control during propagation. 

The most active polymerization initiators for the polymerization of substituted oxiranes, particularly propylene oxide, produce a significant amount of product that is stereospecific and crystallizable. Most uses for polymers of propylene oxide, however, are in elastomeric systems (see chapter 2, table 4). For elastomers, the amorphous, noncrystallizable polymers are pre-... 

The variation of the mechanical properties near the glass transition is discussed in Chapter 12, and techniques developed to this end such as dynamic mechanical analysis (DMA) are usually employed. Figure 11.3 illustrates the shape taken by the curve that reflects the variation of the volume of a polymer sample as a function of the temperature this technique is sometimes used but in spite of the simplicity of its principle, it is delicate to handle. The calorimetric technique is preferred, especially differential scanning calorimetry (DSC). The typical shape taken by a thermogram for a noncrystallizable polymer is shown in Figure 11.6. 

P.H. Geil In the case of wholly amorphous polymers, and this applies to crystallizable or noncrystallizable polymers, there is no order on the 50 A or larger size scale. There may be local order on that size scale in samples which people might call amorphous, but those are not truly amorphous, and one has to worry, practically, in terms of the degree of amorphousness. If there s... 

The question concerning order in the amorphous state of polymers and oligomers is still a matter of controversy. Through the identification of transition phenomena like the Tn transition and the transitions- within the liquid state, this controversy took on a new dimension. This is evident because the occurrence of a phase transition generally suggests the question about structural changes at the transition and the nature of the connected order parameter(s). The Tn and T transitions seem to be of a different nature. Whereas the former is mainly observed in noncrystallizable polymers, the latter manifests itself mainly in oligomers and polymers which are able to crystallize. But the T transition has also been detected recently in a noncrystallizable side chain liquid crystalline polymer (cf. II1.2).lO... 

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