The thermal decomposition rate constant of AIBN (kd) in N, N‐dimethylformamide (DMF)/acrylonitrile (AN) mixtures of various compositions at 60°C is studied. The kd value is (6.45 ± 0.3) × 10−4 min−1 for pure DMF and (7.20 ± 0.3) × 10−4 min−1 for pure acrylonitrile. The kd values of DMF/AN mixtures were found to be dependent on the mixture composition. This dependence is not a linear function of the monomer mole fraction (xM), but has a minimum at ca. 70 mol % of AN. The relationship kd = f(xM) has been interpreted on the basis of the hypothesis of initiator solvation by monomer AN and solvent DMF. © 1996 John Wiley & Sons, Inc.

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Streszczenie-Zbadano elementarn¹ reakcjê procesu polimeryzacji rodnikowej, tj. termiczny rozpad szeregu inicjatorów azowych-kwasu 4,4'-azobis(4-cyjanowalerianowego) (ACPA) oraz pochodnych 2,2'-azobisizobutyronitrylu (AIBN)-w mieszaninach akrylonitryl (AN)/N,N-dimetyloformamid (DMF), w funkcji stê¿enia monomeru (xM) w temp. 60 o C. Jednoznacznie stwierdzono I-rzêdowooeae tej reakcji w przypadku wszystkich u¿ytych inicjatorów. Zale¿nooeci kd = f(xM) wyznaczone dooewiadczalnie s¹ nieliniowe, ró¿ni¹ siê przebiegiem, co wi¹¿e siê ze zró¿nicowan¹ budow¹ chemiczn¹ azoinicjatorów, mo¿na je opisaae modelem solwatacji inicjatora (I) monomerem (M) i rozpuszczalnikiem (S). Okreoelono wystêpuj¹ce w uk³adzie postacie solwatacyjne, obliczono (stosuj¹c algorytm Marquardta) ich wzglêdne sta³e stabilnooeci, sta³e szybkooeci termicznego rozpadu i wzglêdny udzia³ w mieszaninie. W warunkach ma³ych stê¿eñ AN w roztworze DMF przewa¿aj¹ solwaty podwójne z rozpuszczalnikiem SIS (rozpuszczalnik, inicjator, rozpuszczalnik) i mieszane MIS (monomer + rozpuszczalnik), natomiast w stê¿onych roztworach, gdy xM > 0,5 zwiêksza siê udzia³ podwójnych postaci solwatacyjnych z monomerem MIM, charakteryzuj¹cych siê najwy¿sz¹ sta³¹ szybkooeci rozpadu. S³owa kluczowe: polimeryzacja rodnikowa akrylonitrylu, rozpad termiczny azoinicjatorów, rzêdowooeae reakcji rozpadu termicznego, sta³a szybkooeci rozpadu termicznego, solwatacja inicjatora. FUNCTIONAL AZO-INITIATORS-THERMAL DECOMPOSITION IN ACRYLONITRILE/N,N-DI-METHYLFORMAMIDE MIXTURES Summary-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 o C, was investigated. It was found unambiguously that the reaction order equaled 1 for all initiators tested (Fig. 2). Experimentally determined courses of k d = f(x M) 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.

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