Structure of polymeric solids

This chapter opens with a description of the packing of polymer molecules in crystals. X-ray diffi-action gives an extremely precise description of this, since the polymer lattice diffracts X-rays as does any other three-dimensional lattice. The shape and mutual arrangement of the minute crystals are then described. The crystals are separated one from another amorphous regions whose dimensions are comparable with those of the crystals. The information on these matters stems from electron and light microscopy, techniques which are less precise than X-ray diffiractiotL Crystalline synthetic polymers are invariably partly ciystalUne and partly amorphous the term crystalline polymer always implies partially crystalline. 

Polymers, unlike metals, find wide application as completely amorphous solids. The two amorphous forms of greatest interest are the glasses and the elastomers or rubbers. Polymers found their earliest technical application as elastomers over 100 years ago, and it is in this form that they make a unique contribution to society. In examining the structure of the amorphous state we shall confine attention to the really significant point, which is the conformation of the molecule. It will be shown that the conformation resembles that of the molecule in dilute solution sketched at the end of the previous chapter. By means of a simple model a mathematical description of the conformation will be obtained which has fundamental and practical consequences for the mechanical properties of elastomers, the stress-strain curve in particular. 

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