The purpose of this chapter is to provide the background principles from polymer physics and chemistry which are essential to understanding the role which chemorheology plays in guiding the design and production of novel thermoplastic polymers as well as the complex changes which occur during processing. The focus is on high-molar-mass synthetic polymers and their modification through chemical reaction and blending, as well as degradation reactions. While some consideration is given to the chemistry of multifunctional systems, Chapter 2 focuses on the physical changes and time—temperature-transformation properties of network polymers and thermosets that are formed by reactions during processing.

The attention paid to the polymer solid state is minimized in favour of the melt and in this chapter the static properties of the polymer are considered, i.e. properties in the absence of an external stress as is required for a consideration of the rheological properties. This is addressed in detail in Chapter 3. The treatment of the melt as the basic system for processing introduces a simplification both in the physics and in the chemistry of the system. In the treatment of melts, the polymer chain experiences a mean field of other nearby chains. This is not the situation in dilute or semi-dilute solutions, where density fluctuations in expanded chains must be addressed. In a similar way the chemical reactions which occur on processing in the melt may be treated through a set of homogeneous reactions, unlike the highly heterogeneous and diffusion-controlled chemical reactions in the solid state.