Synthesis Of Biuret Polyisocyanate Based On HDI And Study On Mechanism

Aliphatic polyurethane coatings are popular at present when they are used as the plane's or the car's surface paint because of their perfect performance, especially the unique weather resistance. But the manufacture of HDI biuret, one of the most important and the most popular polyisocyanates, is not practical in our country.On the basis of the traditional process of adding the drop of water into hex-amethylene diisocyanate (HDI) monomer, the replacement by using crystal water and steam and reacting in gas phase were proposed to produce HDI biuret with light color and low viscosity successfully in this paper. The advantages and disadvantages of each way were stated respectively and many problems and phenomena were also explained. The free HDI monomer remained in the product was removed by the way of the continuous extraction. Cyclohexane was the best extractant to remove free HDI monomer and the apparatus was improved. The paint was of great performance as the hydroxy acrylic resin was used as the B component in the aliphatic polyurethane coatings.The catalysts of tertiary amine and organotin were used to accelerate the reaction of HDI and H₂O. The synergism was detected in the experiments. The Mechanism of the two catalysts was proposed in this system.The reactivity of the first NCO group in HDI was different from that of the second one on the basis of the kinetic study in the system of HDI and isopropanol at different conditions. This difference indicated the fact that the selection of HDI biuret was natural in the product.A series of analytical methods were established to provide scientific data in this system, such as infrared spectrum, the gel penetration chromatography (GPC), the gas chromatography (GC). It's helpful during the project.