Packing of chains

Modes of Packing of Chains Having Identical Conformations. .. 192... 

A polymorphic behavior involving packing of chains having completely different conformations has been found also for isotactic polymers. For instance, isotactic polystyrene, under suitable experimental conditions, can produce crystalline gels in which the chains assume a nearly fully extended conformation [11,12], very close to a truns-planar, rather than the classical conformation of three-fold helix [13]. The two possible conformations proposed for the two crystalline forms of i-PS are shown in Fig. 2. 

Although in the frequency region of the conventionally measured infrared and Raman spectra (400-4000 cm ) only intramolecular modes appear, some particular bands can be sensitive to intermolecular interactions typical of the different modes of packing of chains with identical conformations. 

The vector field entirely and uniquely determines the stream lines and their properties. As we focus our attention on the mesoscopic properties of stream lines, assuming that they can resemble a polymer-like amorphous packing of chain backbones, we have to consider in greater detail their intrinsic properties. As shown in the next section, Santos and Suter [98] elaborated a model for generating packing structures of Porod-Kratky chains. 

Kitian, H. G. and Pieper, T. Packing of Chain Segments, A Method for Describing X-Ray Patterns of Crystalline, Liquid Crystalline and Non-Crystalline Polymers. Vol. 108, pp, 49-90. 

Figure 2.22 Models of packing of chains in form I of sPP according to space groups (a) Ibca59 and (b) P2 /a.146 Arrows indicate crystallographic twofold axes, present in (a) and lost in (b). In (b) chains are rotated by nearly 5° around chain axes, according to direction indicated by the arrows.

Figure 2.24 Models of packing of chains in a-form of sPS according to space groups (a) / 3cl52 and (b) P3150. In (a) dotted lines indicate crystallographic glide planes coincident with local glide planes of chains. In (b) triplets of chains are rotated around threefold axes and crystallographic glide planes are lost.

Figure 2.26 Model of packing of chains in form III of iP4MP according to space group /4x, 33. tS3 jwo eqUivaient unit cells characterized by chains having opposite azimuthal orientations indicating possible packing in different microdomains of crystal are shown.

Figure 2.38 Schematic model of packing of chains of sPP in form I showing disorder in stacking of be layers of chains along a axis. Squares indicate chains of sPP in twofold helical conformation and numbers indicate relative heights of methyl carbons in c/4 units. Dashed lines indicate positions of defects which correspond to shift of be layers of chains of b/4 along b axis.

Fig. 157. Packing of chain molecules in polyethylene and some of the polyesters. The chains, seen end-on, appear to be compact groups of atoms at P and Q.

Schwarz31) has modified the equation of state for the Gaussian polymer network by introducing a coefficient taking into account the influence of the packing of chains and their sizes on the mean square end-to-end distance of deformed chains. 

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