Structure and Property Relationship in Organic Polymers

For a very large proportion of polymeric materials in commercial use, mechanical properties are of paramount importance, because they are used as structural materials, fibers, or coatings and these properties determine their usefulness. Properties that also determine their utilization are compressive, tensile, and flexural strength, and impact resistance. Hardness, tear, and abrasion resistance are also of concern. In addition, polymers may be shaped by extrusion in molten state into molds or by deposition from solutions on various surfaces. This makes the flow behaviors in the molten state or in solution, the melting temperatures, the amount of crystallization, as well as solubility parameters important. 

The physical properties of polymer molecules are influenced not only by their composition, but also by their size and by the nature of their primary and secondary bond forces. They are also affected by the amount of symmetry, by the uniformity in their molecular structures, and by the arrangements of the macromolecules into amorphous or crystalline domains. This, in turn affects melting or softening temperatures, solubilities, melt and solution viscosities, and other physical properties [1]. 

Due to the large sizes of polymeric molecules, the secondary bond forces assume much greater roles in influencing physical properties than they do in small organic molecules. These secondary bond forces are van der Waal forces and hydrogen bonding. The van der Waal forces can be subdivided into three types dipole-dipole interactions, induced dipoles, and time varying dipoles. 

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