Synthesis And Properties Of Toluene Diisocyanate Trimer Curing Agent

Toluene diisocyanate (TDI) tirmer is widely used as polyurethane curing agent in coating industry due to its excellent properties of high thermal stability, corrosion resistance, fast curing and high hardness. But TDI trimer has the defects of high free monomer content and poor compatibility with hydroxyl resin at present. The synthesis of TDI trimer and characterization of the products composition were studied in this research. The research mainly focuses on the following aspects:1. The traditional synthetic technology of TDI trimer was discussed. DMP-30was used as the catalyst. When the dosage of DMP-30was0.5%(mass percent) of TDI and added dropwise after mixed with butyl acetate, DMP-30does favor of the trimerization reaction for reacting quickly and stably. The optimal temperature was in range of70℃to80℃. It’s beneficial to reduce free monomer content when TDI monomer was charged at first and butyl acetate was added by batch. Good storage stability was obtained when the inhibitor was added for1:1of the catalyst by mass. Its compatibility for resin could be improved when butanol was used as modifier and the molar ratio of NCO/OH was15:1to10:1. In spite of that, this traditional method is far away from our goal.2. Synthesis of high-performance TDI trimer by new catalyst was studied. A new kind of trimerizational catalyst with high activity and high efficiency was made by Mannich reaction using bisphenol A, formaldehyde and dimethylamine to form a Mannich base. The results about effect of different types and amounts of alcohol on TDI trimer show that dodecanol could greatly improve the xylene tolerance of the TDI trimer. The optimal addition amount of dodecanol was when the molar ratio of NCO/OH in range of14:1to12:1. A combination of back titration, GC, mass spectrometry (MS) and gel permeation chromatography (GPC) were adopted to explore the effect of catalyst, reaction temperature, time and modifier on the structures of TDI trimer. After optimizing by improving the process and analysising with instruments, the high-performance TDI trimer was obtained with low monomer content of0.94%, NCO content of7.21%and the value of xylene tolerance of6.4.3. The catalysis mechanism for TDI trimerization reaction of Mannich-base catalyst, which contains tertiary amine group and hydroxyl group, was discussed. Optimization and control for TDI trimerization reaction has been discussed by GC and GPC.