Synthetic Technology And Polymerization Process Of TDI Trimer Curing Agents

Toluene diisocyanate(TDI)trimer has been widely used as the curing agents in the 2k polyurethane materials due to their fast drying and other excellent properties.The important performance indexes of TDI trimer curing agents include free TDI content,xylene tolerance,viscosity,NCO value,colour number,solid content and storage stability.The free TDI content is still difficult to reduce below 0.5 wt%,which is the result of unsystematic and not thorough research on the synthetic technology and polymerization process of TDI trimer.Thus in this paper,the synthetic technology of TDI trimer is studied systematically and its polymerization process is thoroughly analyzed.First,the optimum catalyst was screened by comparing the catalytic activity and selectivity of the various catalysts.The results show that the oligomerized Mannich base(OMB)catalyst synthesized by two-step method has the best selectivity with high enough catalytic activity.Of all the catalysts under the same conditions,its free TDI content at NCO trimerization conversion of 60% can be reduced down to 2.1 wt%.Second,based on this catalyst,the synthetic technology of TDI trimer curing agents was optimized.The results show that the reaction selectivity increases with the decreasing of the reaction temperature and catalyst concentration,but the reaction rate decreases at the same time.The free TDI content at NCO trimerization conversion of 60% can be reduced to 1.4 wt%,when the reaction temperature is 30℃ and 0.1 wt% OMB catalyst is added in 3-4 batches.With 5% dodecanol added before the trimerization,the free TDI content at NCO trimerization conversion of 60% can be reduced to 0.9 wt%,and improving xylene tolerance of the products to 2.4,decreasing the viscosity to 150 cp.With the addition of solvent in batches through the stepwise method of initial TDI concentration of 80%,the free TDI content at NCO trimerization conversion of 60% can be reduced to 0.6 wt% and the total reaction time is reduced to 14 h.Thus,the free TDI of the final product at NCO trimerization conversion of 63% was below 0.5 wt%,and its xylene tolerance was 2.8,NCO value was 7.6%,the viscosity was less than 100 cp.Thirdly,the functional group structure and oligomers’ compositon were characterized by FTIR,13C-NMR,GPC and MALDI-TOF-MS.By tracking the oligomerization process of TDI,it was found that all oligomer constituents are increasing first and then decreasing with the passing of reaction time and the increasing of reaction conversion.Each of them have a maximum content,and reaching it in the order of the size of molecular weight.At the same time,it was found that the viscosity will increase exponentially at certain reaction conversion,and the higher the solid content,the earlier the exponential growth.In addition,the kinetic equations of TDI trimerization were deduced and based on them,the evolution curves of oligomers were simulated by Matlab.