Bond angle distribution packing

Figure 59. Nearest-neighbor bond angle distribution functions for dense random packings of hard disks. The figure shows the contributions from ordered regions (dotted line), disordered regions (dashed line), and the overall distribution (solid line). The horizontal scale is in degrees. The inset shows an expanded view.

Flexible molecules, such as those in Fig. 2-7, permit rotational motions of one bond about another, so that a combinatorially huge number of configurations is accessible (Flory 1969). On length scales of tens or hundreds of such monomers, the details of the distribution of allowed bond angles average out, producing in the melt a configuration distribution equivalent to that of a random walk (see Fig. 2-8). Because of the flexibility of these molecules, even in the densely packed melt state, they remain unoriented, or isotropic, at equilibrium. 

Table 2 shows polymerization conditions for the high-pressure process and density, molecular weight, and weight distribution of the polyethene (LDPE). Bunn [54] was the first to study the structure of polyethene by x-ray. At a time when there was still considerable debate about the character of macromolecules, the demonstration that wholly synthetic and crystalline polyethene has a simple close-packed structure in which the bond angles and bond lengths are identical to those found in small molecules such... 

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