Introduction: Polymer Morphology
Two different states or forms can be identified in which a polymer can display the mechanical or thermomechanical properties that can be associated with solids, viz., the form of a crystal or the form of a glass. It is not really the case that all polymers are able to crystallize. As a matter of fact, a high degree of molecular symmetry and microstructural regularity within the polymer chains are a prerequisite for crystallization to occur. Even in those polymers, which do crystallize in any rate, the ultimate degree of crystallinity developed is mostly less than 100%.
Studies of physical form, arrangement and structure of the molecules or the molecular aggregates of a material system relates to what is known as its morphology. Polymer morpho-logy covers the study of the arrangement of macromolecules over the crystalline, amorphous and the overlapping regions and the overall physical clustering of the molecular aggregates.
When cooled from, the molten states, different polymers exhibit different tendencies to crystallize at different rates depending on many factors including prevailing physical conditions, chemical nature of the repeat units and of the polymer as a whole, their molecular or segmental symmetry and structural regularity or irregularity, as referred to above. Bulky pendent groups or chain branches of different lengths hinder molecular packing and hence crystallization. The nature of the crystalline state of polymers is not simple and it should not be confused with the regular geometry of the crystals of low molecular weight compounds such as sodium chloride or benzoic acid. There are polymers, which are by and large amorphous, and they have very poor tendency to get transformed into ordered or oriented structures on cooling to near or even below room temperature. Natural or synthetic rubbers and glassy polymers such as polystyrene, …