The search for quantitative structure-property relationships for the control and prediction of the mechanical behaviour of polymers has occupied a central role in the development of polymer science and engineering. Mechanical performance factors such as creep resistance, fatigue life, toughness and the stability of properties with time, stress and temperature have become subjects of major activity. Within this context microhardness emerges as a property which is sensitive to structural changes.

The microindentation hardness technique has been used for many years for the characterization of such ‘classical’ materials as metals, alloys, inorganic glasses, etc. Its application to polymeric materials was developed in the 1960s. The potential of this method for structural characterization of polymers was developed and highlighted to a large extent by the studies carried out in the Instituto de Estructura de la Materia, CSIC, Madrid.

Nowadays, the microhardness technique, being an elegant, non-destructive sensitive and relatively simple method, enjoys wide application, as can be concluded from the publications on the topic that have appeared during just the last five years – they number more than 100, as is shown by a routine computer-aided literature search. In addition to some methodological contributions to the technique, the microhardness method has also been successfully used to gain a deeper understanding of the microhardness-structure correlation of polymers, copolymers, polymer blends and composites.