Study On The Kinetics Of Thiol-Epoxy Reaction

The concept of "Click Chemistry" was raised by Sharpless and his colleagues in 2001[1]. "Click Chemistry" is a collection of carbon-heteroatom bond-forming reactions which posses fast reaction rate and high selectivity under mild conditions. As one kind of "Click Chemistry", thiol-epoxy reaction has drawn intensive attentions recently due to its outstanding advantages, especially in the field of macromolecular materials. In this work, the bulk kinetics of reactions between small thiol compound and small epoxy compound or epoxy resins were investigated in details. Thermoplastic epoxy resins were prepared in the co-rotating twin screw extruder as well.In the research of thiol-epoxy reaction between small thiol compound and small epoxy compound, glycol dimercaptoacetate, glycidyl phenyl ether and 1,8-bis(dimethylamino) naphthalene were utilized as thiol model compound, epoxy model compound and base catalyst respectively. The epoxy concentration-reaction time curves under different temperatures were obtained firstly. Then the kinetic model of the base-catalyzed mechanism of thiol-epoxy reaction was built and kinetic data of elementary reactions were fitted via MATLAB software. The real rate-controlling step of thiol-epoxy reaction was revealed through the comparison of rate constants. It is the deprotonation of thiol by base catalyst to form thiolate anion. Thiol-epoxy reaction could be simplified to second order reaction in certain reaction systems and under certain temperatures according to the comparison and analysis. Under this special conditions will the kinetics curves of thiol-epoxy reaction satisifies the features of second order reaction. Then epoxy concentration-reaction time curves under different concentrations of base catalyst and reactants ratios were obtained and compared with the fitting curves given by the kinetic model. The results of comparison illustrated that the fitting curves and the experiment points fitted well in this range of catalyst concentration and reactants ratio.In the research of thiol-epoxy reaction between small thiol compound and epoxy resins, kinetic experiments under different recipe and conditions were carried out in the Brabender(?) torque rheometer firstly. Samples were taken and analyzed to get epoxy concentration-reaction time curves. Besides kinetics curves, operation curves including torque and temperature-reaction time curves were obtained by data collected through the reaction. Torque curve can reflect the viscosity of reaction system in real time. The influences of factors including rotation speed, base catalyst concentration, reactants ratio, temperature and chain length of epoxy resin were analyzed. The results demonstrated that:120 rpm was the appropriate rotation speed; 1wt% was the proper catalyst concentration; 0.8:1 was the suitable thiol/epoxy ratio. The viscosity of reaction system decreased with the increases of temperature but started to surge and stabilized at shorter time. Reaction rate slowed down with the increase of chain lengths. The thermoplastic epoxy resins were prepared in the co-rotating twin screw extruder referring to the results acquired in the Brabender torque rheometer. A series of tests were carried out to characterize the performances of thermoplastic epoxy resins including molecular weight and its distribution, thermal proprieties and mechanical performances. The thiol-epoxy reaction could be utilized to increase the molecule weight and improve the thermal property of epoxy resin. The flexible ester chains could also be introduced into the chains of epoxy resin which could improve the impact strength of it. The impact strengths of the samples prepared at 230℃ are more than 5 kJ·m-2. These values are already close to that of some cured products of epoxy resins.