Solvation effect in the thermal decomposition of 2,2 '-azoisobutyronitrilein the three-component system

The thermal decomposition rate constant (k(d)) of 2,2'-azoisobutyronitrile in acrylonitrile (AN; monomer A)-methyl methacrylate (MM; monomer B) comono mer mixtures in N,N-dimethylformamide (DMF) as a function of the comonomer mixture composition and its concentration in the solvent at 60 degrees C wa s studied. The dependences k(d) = f(x(A),C) [x(A) (mole fraction of A in th e comonomer mixture) = A/(A + B) = A/C, where C is the comonomer mixture co ncentration] have a different course as a function of C: from a curve k(d) = f(x(A)) approaching the straight line (C = 2 mol.dm(-3)) to a convex curv e possessing a maximum at a point x(A) = 0.7 (C = 4 mol.dm(-3)) to a curve with a flattened wide maximum within the range of x(A) = 0.2-0.8 (C = 7 mol .dm(-3)) to a curve with the shape of a lying s (C = 9 mol.dm(-3)), All the courses of the experimental dependences k(d) = f(x(A),C) can be explained with a hypothesis of initiator solvation by the comonomers AN and MM and th e solvent DMF. The existing solvated forms, their relative stability consta nts, the thermal decomposition rate constants, and the relative contents in the system were determined. (C) 2000 John Wiley & Sons, Inc.