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 pol ymers is generally described in term of ideal modifications, a limit ordere d form, characterized by ideal three-dimensional order, and a limit disorde red form, characterized by the presence of statistical disorder in the pack ing, 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 p roduce defects frozen in the crystals of syndiotactic polypropylene, is ana lyzed.