Chain packing, characterization

Although the diffraction techniques are unique in providing detailed information on the structural organization at the molecular level in the different crystalline forms, there are other characterization techniques which are sensitive to the chain conformation and in some cases to the chain packing, which can be used advantageously (and in some case more efficiently than diffraction techniques) in the recognition and quantification of the different polymorphs in polymeric materials. 

Mesomorphic forms characterized by conformationally ordered polymer chains packed in lattices with different kinds of lateral disorder have been described for various isotactic and syndiotactic polymers. For instance, for iPP,706 sPP,201 sPS,202 syndiotactic poly(p-methylstyrene) (sPPMS),203 and syndiotactic poly(m -methylstyrene),204 mesomorphic forms have been found. In all of these cases the X-ray fiber diffraction patterns show diffraction confined in well-defined layer lines, indicating order in the conformation of the chains, but broad reflections and diffuse haloes on the equator and on the other layer lines, indicating the presence of disorder in the arrangement of the chain axes as well as the absence of long-range lateral correlations between the chains. 

The chain conformation it was treated mathematically in terms of atoms regularly spaced along helices, an approach equivalent to defining the contents of the unit cell in terms of cylindrical coordinates. Packing of the chains was characterized by defining the distances between molecules as determined from the equatorial reflections on an x-ray fiber pattern. j ... 

The chains, now characterized in terms of intramolecular features, can also be characterized with regard to how they pack themselves into ordered arrangements in crystallites. This is understood in terms of the unit cell, which is the simplest volume by means of which the entire crystallite can be generated by translations in three directions. 

The properties of dense films are often equated with the Intrinsic properties of the bulk polymer. However, this comparison must be made with caution because chain packing, and thus transport properties, may be dependent upon thermal history or solution history during film preparation and upon the attainment of equilibrium prior to characterization. Dense films can be prepared by melt extrusion, compression molding or solution casting,... 

When in the dry state, the homogeneous, single-phase hypercrossUnked polystyrenes are characterized by extremely low density of chain packing and exhibit a large free volume. This can be thought of as real porosity of a new type (today, porosity of a material is interpreted only as a result of its... 

Permeability properties are very sensitive to chain packing in the solid state. Chain packing is often characterized in terms of free volume. However, a simple, direct, unambiguous measurement of free volume in polymers is not available. The most common characterization of solid state chain packing is fractional free volume, FFV, which is defined as follows (14) ... 

In order to characterize the neighboring chain-chain correlation quantitatively, a measure of the order of the chain packing has been introduced [53]. We define the following function ... 

The mesomorphic forms of sPP [29,267], sPS [268,269] and sPPMS [270] are characterized by chains in ordered trans-planar conformations packed in small disordered aggregates, which maintain the structural features of one of the polymorphic forms of the polymers, only up to very short distances. In the case of sPS and sPPMS, the small aggregates of chains are characterized by packing modes very close to those of the a form of sPS [268,269] and form III of sPPMS [270]. 

Each of the chain-packing subcells described above is characterized by a unique set of X-ray diffraction lines in the wide-angle region between 3.5 and 4.5 A, which correspond to the different crystallographic planes of the subcell. X-ray data of the most common subcells in lipids will be given here. 

Therefore, the results of the present paper showed interrelation of elasticity modulus and amorphous chains tightness characterized by fiactal dimension of chain part between its fixation points for nanocomposites based on the semi-crystalline polypropylene. This assumes the polymeric matrix structure change in comparison with initial polymer the role of densely-packed regions for it is played by interfacial areas. An offered fractal model allows estimation of elasticity modulus limiting values. 

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