Tight chain, regular

Crystallinity. Polymer chains which possess a regular structure, not only chemically but also sterically, are able to crystallize under suitable conditions, either from the melt, or from solution. This means that the chain molecules change from a coiled and disordered state to a tightly folded, aligned, and ordered state (Figure 2). 

Crystallization is a consequence of molecular symmetry. A macromolecule with a precise, regular sequence of side groups arrayed along the chain will be more prone to pack tightly with neighboring molecules than will a polymer that has an irregular disposition of side groups. 

Fig. 1 An ideal self-assembled monolayer of alkanethiolates supported on a gold surface. The terminal groups are amenable to synthesis, providing a means to immobilize and present ligands from the surface the alkyl chain spacer promotes tight, regular packing, and the gold-sulfur interface stabilizes surface atoms and alkane chains during packing...

There is uncertainty about the regularity and tightness of the folds in solution-grown single crystals. Three models of chain conformations in a single crystal are illustrated in Fig. 11-4. 

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