Crystal structures and order-disorder phenomena in polymers

The crystal structure of various polymers, presenting symmetry breaking, is discussed. Owing to the presence of disorder, the crystal structure of polymers is generally described in term of ideal modifications, a limit ordered form, characterized by ideal three-dimensional order, and a limit disordered form, characterized by the presence of statistical disorder in the packing, while preserving the order in the parallelism of the chains. The real crystalline forms are generally intermediate between the limit ordered and limit disordered models. The occurrence of conformational disorder, which produce defects frozen in the crystals of syndiotactic polypropylene, is analyzed.