Photoacoustic photocalorimetry of a solid state reaction

Abstract

We have developed a new photocalorimetric technique for the study of photoinduced chain reactions. This technique is based on photoacoustic detection and is applied to the solid‐state photopolymerization of diacetylenes. At early stages of the polymerization process, the thermal energy evolved is as much as four times greater than the total light energy deposited in the sample. This result is shown to require that an average of approximately eight polymerized diacetylene units is produced per absorbed photon. This experiment is the first definitive demonstration of the exothermic, chain‐reaction nature of the photopolymerization process in these materials. A kinetic model for photoinduced reactions in highly absorbing materials is presented and shown to be in good agreement with experimental results.