Functional azo-initiators – thermal decomposition in acrylonitrile/N,N-dimethylformamide mixtures
Polimery 2007, No 7/8, 562
The elementary reaction in radical polymerization process i.e. thermal decomposition of series of azo-initiators - 4,4'-azobis(4-cyanopentanoic) acid (ACPA) and 2,2'-azobisisobutyronitrile (AIBN) derivatives (Scheme A) - in the mixtures of acrylonitrile (AN)/N,N-dimethylformamide (DMF), in relation to monomer concentration (xM) at temp. 60°C, was investigated. It was found unambiguously that the reaction order equaled 1 for all initiators tested (Fig. 2). Experimentally determined courses of kd=f(xM) dependence are nonlinear (Fig. 3), their plots differ what can be connected with diverse chemical structures of azo-initiators, and they can be described by a model of initiator solvation by monomer (M) and solvent (S). The solvated forms occurring in the system were determined. Their relative stability constants and thermal decomposition rate constants were calculated (applying Marquardt's algorithm) as well as relative parts in the mixture (Table 3). At low AN concentrations in DMF solutions the double solvates with solvent SIS and mixed MIS (monomer + solvent) predominate whereas in the concentrated solutions, when xM > 0.5, the contribution of double solvated forms with monomer MIM, characterized with the highest decomposition rate constant, increases.
Key words: radical polymerization of acrylonitrile, thermal decomposition of azo-initiators, order of thermal decomposition reaction, thermal decomposition rate constant, initiator solvation
E. Wiśniewska, B. Pabin-Szafko
Functional azo-initiators - thermal decomposition in acrylonitrile/N,N-dimethylformamide mixtures