Thermal cis-trans isomerization of azo dyes in poly(methyl methacrylate) matrix: A kinetic study

✍ Scribed by Pier Luigi Beltrame; Ernestina Dubini Paglia; Antonella Castelli; Gian Franco Tantardini; Alberto Seves; Bruno Marcandalli

• Publisher: John Wiley and Sons
• Year: 1993
• Tongue: English
• Weight: 291 KB
• Volume: 49
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/app.1993.070491220

✦ Synopsis

Azo dyes when irradiated by visible light undergo transcis isomerization, after which the cis form reverts progressively to the thermodynamically more stable trans isomer following a photochemical or thermal path.'-5 For a given dye, the cis-trans isomerization proceeds in different ways depending on the nature of the medium in which the reaction occurs. Thus, in solution as well as in molten or rubber polymers, the process follows a simple first-order kinetics; conversely, in polymeric matrices below the glass-transition temperature ( T,) , the kinetics of the reaction is characterized by the occurrence of a multiplicity of simultaneous first-order processes. A decrease of the free volume extent in the amorphous regions of glassy polymeric matrices results in a lowering of the rate coefficients of the isomerization. On the other hand, no significant kinetic modifications appear to occur when the crystallinity of the sample is varied.