Morphology exerts an important influence on the properties of thermoplastics. Properties can be tailored by altering the crystallinity during processing. Slow cooling rate leads to more crystalline product. Each morphology has desirable properties.
Some polymers are partly crystalline and partly amorphous to achieve a blend of properties.
The nature of the thermal transitions a polymer undergoes reveals the crystallinity of the polymer. As an amorphous material is heated, it undergoes a transition from a solid glass to a fluid. A crystalline polymer exhibits a sharp melting point when it is heated. A polymer with both morphologies can have both a glass transition temperature and a melting point. Molecular structure also affects macroscopic properties.