Crosslinked Polymers and Rubber Elasticity

An elastomer is defined as a cross-linked amorphous polymer above its glass transition temperature. This chapter describes the chemical and physical behavior of the polymers that form rubber bands, automotive tires, and related materials. The basic equations describing the extension of an elastomer are similar to those familiar to the student as the ideal gas equation, and this analogy is used to prepare for the derivation of the equation of state for rubber elasticity, both the gas and rubber elasticity derivations are based on the fundamental principles of statistical thermodynamics. The Flory-Rehner equation describes the swelling equilibrium behavior of elastomers. Thermoplastic elastomers have physical crosslinks, and can be made to flow at elevated temperatures. An example of rubber use is given by the composition of and temperature behavior of a modern automotive tire.