Current Possibilities for Improving Polymer Photochromic Systems

Photochromic effects in polymers—repeatable color changes after irradiation with short-wave light—offer considerable potential for enhancing the functionality of products. The textile industry especially shows a keen interest in such materials.1,2 However, polymers containing photochromic dyes have two specific peculiarities: •• The real photochromic reaction is accompanied by unwelcome side effects. These processes continuously decrease the color change (so-called fatigue). •• Both the reversible color change itself (the rate, the depth, and the relaxation in the dark) and photochromic fatigue are influenced to a large extent by the type and the condition of the fiber and plastic, respectively. Photochromic dyes react sensitively to their immediate micro-environment, to the structure of the polymer matrix, to the presence of degradation products, to substances being added, or to outside influences.3 For industrial use, photochromic fatigue considerably constrains most potential applications. There has been a lot of activity in this field, for example, concerning the influences of oxygen or heat.4 Also, the development of photochromic dyes has seen an increased interest. Up to now, however, it has not been possible to achieve lightfastness matching that of the usual colorings of dyes or plastics. Therefore, in manufacturing photochromic polymers (no matter whether by fiber spinning, extrusion or injection molding) one has to deal with these problems. This paper provides an overview of some approaches to extend the photochromic life as long as possible—approaches that are feasible for every user.