3.3 Conjugated Polymers

The use of poly(3-alkyl thiophene)s as thermochromic pigments for the introduction of thermochromism into host polymers has been reported [33, 34]. Poly(3-alkyl thiophene)s belong to the group of conjugated polymers exhibiting thermochromism due to temperature-dependent conformational changes of the conjugated ?-electron system. To vary the switching temperature of the polythiophene pigments, modifications of their chemical structure are necessary. A set of poly(3-alkyl thiophene)s that visually and reversibly change colour at a prescribed temperature in the region of -35 to +125 C were developed. However, no list of chemical structures and corresponding switching temperatures of the investigated polythiophene pigments was published. The pigments obtained were reported to be thermally stable to above 200 C. By dispersing 0.1 1.0 wt% of them into commercially available paints, plastics and rubbers visible thermochromic effects were observed in the doped host polymer matrices.