MOLECULAR SHAPE

MOLECULAR SHAPE
Previously, polymer molecules have been shown as linear chains, neglecting the zigzag arrangement of the backbone atoms (Figure 14.1b). Single chain bonds are capable of rotating and bending in three dimensions. Consider the chain atoms in Figure 14.5a; a third carbon atom may lie at any point on the cone of revolution and still subtend about a 109° angle with the bond between the other two atoms.
A straight chain segment results when successive chain atoms are positioned as in Figure 14.5b. On the other hand, chain bending and twisting are possible when there is a rotation of the chain atoms into other positions, as illustrated in Figure 14.5c.5 Thus, a single chain molecule composed of many chain atoms might assume a shape similar to that represented schematically in Figure 14.6, having a multitude of bends, twists, and kinks.6 Also indicated in this figure is the end-to-end distance of the polymer chain r; this distance is much smaller than the total chain length.
Polymers consist of large numbers of molecular chains, each of which may bend, coil, and kink in the manner of Figure 14.6.This leads to extensive intertwining and entanglement of neighboring chain molecules, a situation similar to a heavily tangled fishing line. These random coils and molecular entanglements are responsible