Investigations of a New Reversible Strain Induced Chromic Transition in Polydiacetylene Elastomers

Abstract

In-situ visible dichroism/tensile elongation studies of segmented polyurethanes containing conjugated polydiacetylene chains within their hard segment domains have revealed a new reversible mechanochromic transition that manifests itself as a color change from blue to yellow during tensile elongation. This unusual strain induced transition, found in an elastomer whose hard segment structure is derived from hexamethylene diisocyanate and 5,7-dodecadiyne-l,12 diol, closely resembles the thermochromic transition also exhibited by this same material. The color change and the associated shift in the position of the polydiacetylene absorption band to higher energies is not simply an order-disorder transition but reflects a strain induced reorganization of the hard domain structure. It has been found that this blue to yellow transition is reversible as long as the material is not strained beyond about 300%. This represents the first reversible, mechanically induced chromic transition in a cross-polymerized diacetylene containing polymer.