Thermochimica Acta, Vol.333, No.2, 147-153, 1999
Polymorphism and polymorphic transformation of photographic coupler
The polymorphism and the solid-state transformation between two polymorphic forms of a photographic coupler were studied using differential scanning calorimetry. The two polymorphic forms, namely polymorph I(T-m=168 degrees C) and polymorph II (T-m=181 degrees C), were confirmed on melting. The polymorphic transformation of a metastable form into the stable form (I-->II) occurred upon a temperature annealing and was found to be monotropical. The isothermal transition appeared to follow a distinct rate relationship. The effects of heating rate on polymorphism and polymorphic transformation were also investigated. It is shown that the polymorphism depended upon the history of heat treatment. The kinetics parameters including rate coefficient, activation energy, and half-time for the transformation indicate that the polymorphic transformation I-->II followed a first-order reaction.