Synthesis And Process Investigation Of TDI-TMP Mixed Prepolymer

TDI-TMP adducts is widely used in furniture wood finishing,anti-corrosion coating,waterproof coating and other surface coating,which offers films with a variety of excellent properties.The reaction process and kinetics of TDI and TMP play a crucial role in the structure,properties and content of free-TDI.In this paper,the reaction system is analyzed comprehensively by a variety of physical,chemical and instrumental methods.Moreover,the kinetics of the reaction and the changes in various reaction component concentrations are studied systematically.The study mainly includes the following aspects:Firstly,the effects of reaction temperature and reaction progress on the physical and chemical properties of the prepolymers are discussed.the reaction temperature of 50? and NCO conversion rate of 55-60 % are the optimal reaction conditions,under which the as-prepared product exhibits uniform molecular weight distribution and low free monomer content.The chemical structure of the prepolymers is analyzed by FITR,GPC,HRMS and 1H-NMR.The results show that temperature can significantly affect the reaction selectivity of 2'-and 4'-NCO in TDI.Low temperature favors the preferential reaction of 4'-NCO,while high temperature favors the reaction involving 2'-NCO.Secondly,the concentrations of reaction intermediates at the reaction temperatures of 50?,65? and 80? are tracked by LCMS,and a basic reaction model of three-step consecutive reaction between TDI and TMP is proposed.The reaction rate constants at different temperatures for each reaction step are obtained.Temperature has small influence on the production rates of reaction intermediates AB and AB2,whose activation energy is 12.76 kJ/mol and 16.58 kJ/mol,respectively.The final product of reaction AB3 is more sensitive to temperature,with the activation energy reaching 25.63 kJ/mol.The overall apparent activation energy of reaction is obtained through calculation,which is Ea = 54.97 kJ/mol.In addition,the concentrations of various reaction intermediates obtained by Matlab kinetics fitting match with the experimental results,thus verifying the accuracy of the experimentally obtained kinetic parameters.Finally,TDI-TMP prepolymer with low viscosity,low F-TDI and high tolerance is prepared by chemical modification using self-made catalyst and long chain alcohols.It is experimentally found that the optimal catalyst dosage is 0.5 wt%,whose optimal addition time is when the NCO conversion rate reaches 39.0%.The ratio of raw material m(TDI)/m(TMP)= 4.0 is appropriate,at which the TDI-TMP prepolymers synthesized has a F-TDI = 0.38,and a viscosity = 900 mPa·s.Modification with 3wt% n-dodecanol yields excellent result,where the xylene tolerance can reach above 3.5.