The detection of mechanical stress in polymeric materials through optical variations has attracted considerable interest over the past ten years. In this tutorial review, the current state of knowledge concerning the preparation of polymers with mechanochromic features is summarized. Two types of procedures are illustrated and thoroughly discussed along with their respective structure-property relationships: the first resides in the physical dispersion of the dye in the form of supramolecular aggregates in a preformed polymer matrix; the second involves the covalent insertion of chromophoric units into the macromolecule backbone or side chains. Herein we review the simplicity of the preparative routes available, and their influence over the properties of the resulting dye-polymer systems, by focussing on the most illustrative examples described in the literature. Special reference is made to stimuli-responsiveness as a mechanical means towards innovative smart and intelligent materials.

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Mechanochromic polymer blends, i.e. polymer blends characterised by optical responsiveness to mechanical stimuli, have evoked major interest and experienced significant progress in recent years. Various examples are reported of chromogenic materials composed of a functional dye covalently linked to the polymer chains or physically dispersed in the continuous macromolecular matrix, the latter appears to be a more sustainable route for the industrial scale-up of these materials. This feature article examines the properties and performances of various mechanochromic materials prepared by using different thermoplastic polymers with non-covalently incorporated aggregachromic dyes. More specifically, the general mechanism underlying the optical phenomenon is introduced and the different approaches used to obtain chromogenic materials are presented and discussed considering both dye features and polymer characteristics. The combination of the properties of the blend components can often result in drastic differences in the material chromogenic responsiveness. The article concludes commenting and discussing the application of these kind of polymer devices as a new type of advanced materials and the perspective thereof. © 2011 The Royal Society of Chemistr