Crystal

Macromolecules are giant polymer molecules made up of long chains of repeating molecular units and bonded

covalently to one another. Macromolecules occur widely in nature as carbohydrates, proteins, and nucleic acids. Polymers, plastics, and rubber also are macromolecules.

Macromolecules may be likened to a plate of spaghetti, in which the individual strands of the macro-molecules are entangled. Notably, there is a lack of order in this system, and a lack of crystallinity. However, a marked degree of order does exist in certain regions of these entanglements where segments of neighboring chains may be aligned, or where chain folding may promote the alignment of a chain with itself. Regions of high order in macromolecules, called crystallites, are very important to the physical and chemical properties of macromolecules. The increased forces of attraction between chains in these regions give the polymer strength, impact resistance, and resistance to chemical attack. Polymers can be subjected to some form of heat treatment followed by controlled cooling and, sometimes, stretching, in order to promote greater alignment of chains, a higher degree of crystallinity, and a consequent improvement in properties.