Methods for studying radical polymerization. Part. II. The volumetric and spectrophotometric determination of the rate constant of thermal decomposition of azo initiators

The relative degree (a) of thermal decomposition of initiators was defined as a measure of the process rate. This definition (eqn. 2) was introduced into the differential equation (1) of decomposition kinetics, which is of order x greater than or equal to 1 with respect to initiator, to simplify eqn. (7) that describes the decomposition rate and the rate constant. By eqn. (7), if the initiator decomposition rate is unrelated to initiator's initial concentration, the reaction is first-order. The rate of decomposition can be followed in terms of any physical parameter that varies with the instantaneous value of a. Equation (7) incorporating the definition (2) was adjusted to the physical parameters characteristic of the volumetric method (measurement of nitrogen volume evolving on thermal decomposition of azo initiators, eqns. 12-14 & 18) and of the spectrophotometric method (measurement of absorbance, eqns. 20-22). Authors' studies were used to discuss the merits and demerits of these methods as applied to measure the thermal decomposition of AIBN and its derivatives in N,N-dimethylformamide (DMF) as solvent (Figs. 2-10). The volumetric results were affected neither by inhibitor nature nor by concentration; for systems containing both a monomer and an inhibitor, in addition to an initiator and solvent, the spectrophotometric method (UV-VIS) proved to be useless.