Kinetics of the topochemical solid‐state polymerization of diacetylenes as studied by a flash photochemical experiment

The kinetics of an organic solid‐state reaction is studied by a flash‐photochemical experiment. A set‐up is described which allows the detection of a photoreaction monitoring the change in reflectivity of a polycrystalline sample reacting upon photoinitiation with a laser light pulse. The time scale of the measurement extends from 5 ns to several hundred ms. The topochemical polymerization of two different diacetylenes is investigated measuring the formation of the polymer as a function of time after the initiating light pulse of wavelength λ = 337.1 nm. The first polymer is formed after a timelag of 300 ns. The total conversion per light pulse is less than 1 percent. The time conversion curve is described by an exp √t‐law for virgin samples suggesting a kinetic model which includes a strongly scattering random walk of photo‐excited states to randomly distributed reaction centers as the rate determining factor of the photopolymerization. The average life time of the photoexcited state is 758.5 ps. The overall quantum yield of the polymerization is approximately 10 and the frequency of addition of a monomer unit to a reactive chain end is v a , ≤ 3.3 · 10 7 s −1 .