ABSTRACT
This chapter attempts to reveal something of the world within the bondline to those whose knowledge of chemistry and physics has become more practical than theoretical. Useful polymers have molecular weights which range from about ten thousand to many millions. The atoms of these large molecules are usually arranged in a linear or a crosslinked fashion. Linear amorphous and lightly crosslinked polymers tend to expand more than crystalline or highly crosslinked structures because their molecular segments are further apart and, thus, can move more easily. Thermal motion, as well as free volume, influences the behavior of polymers. At low temperatures polymers exist as solids in which the molecular segments vibrate rather gently and independently. Increased peel strengths result when a rigid resin is made more flexible. Permeation by moisture and solvents is also favored by molecular mobility because the adhesive polymer can “get out of the way” of the diffusing molecules.
