THE CURING OF DIALLYLTEREPHTHALATE DETERMINATION OF THE KINETIC TRIPLET A, Ea,app, ƒ(α) USING THE ISOCONVERSIONAL METHOD
University of Maribor, Faculty of Chemistry and Chemical Engineering, Smetanova 17, 2000 Maribor, Slovenia
Janvit Golob, Matjaž Krajnc
University of Ljubljana, Faculty of Chemistry and Chemical Technology,Aškerčeva 5, 1000 Ljubljana, Slovenia
Allyl polymers are important materials for the production of high performance ophthalmic lenses by free-radical bulk polymerization in the casting process. Isoconversional model-free analysis was applied to the isothermal and nonisothermal curing of diallylterephthalate performed by DSC at different sets of heating rates. The results of the kinetic analysis in a form of kinetic triplet (Ea, A, ƒ(α)) present the variation of the Arrhenius parameters with the calculation method, reaction extent, process mode and heating rates applied. This variation is a sign of the complex and multi-step reaction mechanism. Such a mechanism was approximated with one step (1-α)n reaction model. With the isokinetic relationship - IKR (compensation effect) in the form of lnA=aEa,app+b it was found out that the isothermal and nonisothermal IKR lines converge to different singular points. From the correlation procedure with the experimental data isothermal narrowest point – NPI was selected as a common point. The curing process in the isothermal and nonisothermal process conditions, respectively, was successfully simulated with the obtained kinetic parameters. The possible alternative reaction paths and the partial diffusion control of the curing process are the reasons for the limiting usage of the model-free kinetic analysis method. This method was mainly used as a preliminary step for further analysis with other methods.