Study On The Kinetics And Mechanism Of Thiol/Ene UV-Curable System

The kinetics of Thiol/Ene reaction system under ultraviolet was explored with FTIR. The generic character of the inhibition mechanism of hydroxybenzene in the Thiol/Ene system was proposed, and the influence of substituent on the inhibition behavior of hydroxybenzene was researched. The content and conclusion were as follow:The reaction order was first-order under the 254nm ultraviolet with benzophenone as photosensitizer, even when the ratio of Mercapto Ethanol and Isocyanuric Acid Triallyl Ester was changed. It affirmed the method of deciding reaction order with FTIR was available.In this paper, the kinetics and mechanism　of Thiol/Ene reaction under different wavelength ultraviolet was studied. The reaction order and mechanism were different with both benzoin ethyl ether and benzophenone when Thiol/Ene system under different wavelength ultraviolet. It was demonstrated the reaction followed first-order if it initiated by ultraviolet which wavelength was 254nm, and it followed zero-order if the wavelength was 365nm. And the reaction mechanism was brought forward. The reaction without photosensitizer followed second-order when the wavelenth is 254nm, And there was no reaction under 365nm ultraviolet without photosensitizer.The reaction was researched when inhibitor had different substituent and different concentration.The generic character of the inhibition mechanism of hydroxybenzene in the Thiol/Ene system was proposed from the k-C relations. That the k-C relations of these hydroxybenzenes followed linearity was proved in experiments, namely －dA/dt ＝ aC + k0. This phenomena demonstrated the inhibitor in the Thiol/Ene reaction was not consumed.The experiments showed the substituent of the hydroxybenzene affected its capacity of inhibition.Hydroquinone,p-aminophenol and p-methoxyphenol inhibited the reaction in air, and logA0 and Hammett constant σ followed linearity. The log｜K｜and σ followed linearity with air insulated.