Polymer chemists use the term crystalline to describe the areas in a polymer where the chains are packed in a regular way.
Many polymers have a mixture of crystalline (ordered) areas and amorphous (unordered) regions.
Amorphous regions have more freedom of movement as the chains are further apart.
Any one polymer chain may be part of an amorphous region and a crystalline region.
Spaghetti is a good representation of the different areas; when looking at the underside of a clear glass bowl containing spaghetti some regions of the spaghetti are grouped together in a regular layout, while other regions are totally mixed up.
Polymers with regular chain structures (e.g. isotactic polypropene) and without bulky side groups or extensive chain branching are the most likely to form crystalline regions.
The percentage of crystallinity in a polymer is important in determining its properties; the more crystalline a polymer is, the stronger and less flexible it becomes.
