5 - Relation of Structure to Chemical Properties

Abstract

This chapter explains the materials that have “a good chemical resistance,” or alternatively the material may be stated to be poor or excellent in this respect. Such an all-embracing statement can be little more than a rough generalization, particularly since there are many facets to the behavior of polymers in chemical environments. There are a number of properties of a polymer about which information is required before a detailed statements can be made about its chemical properties. The most important of these are the solubility characteristics, the effect of specific chemicals on molecular structure, particularly in so far as they lead to degradation and cross-linking reactions, the effect of specific chemicals and environments on polymer properties at elevated temperatures, the effect of high-energy irradiation, the aging and weathering of the material, permeability and diffusion characteristics and, toxicity. The chapter also includes information on the types of bonds that hold atoms and molecules together. The atoms of a molecule are held together by primary bonds. The attractive forces that act between molecules are usually referred to as secondary bonds, secondary valence forces, and intermolecular forces. Primary bond formation takes place by various interactions between electrons in the outermost shell of two atoms resulting in the production of a more stable state. The three main basic types of primary bond are ionic, covalent, and coordinate. Secondary bonds are of dominant importance in determining the solubility of polymers. Although some of these secondary bonds act intramolecular, it is the intermolecular forces that are of greatest importance. The intermolecular forces can be of four types: dipole forces, induction forces, dispersion forces, and the hydrogen bond.