Synthesis process of prepolymer

The synthesis process of prepolymer can be divided into laboratory method and industrial production method. The latter has manual batch method and mass production method. They will be introduced separately below.

(1)   Laboratory method

      Laboratory method is used for new product formulation research and rawmaterial verification. The method is to add a metered oligomer polyol into a three-necked reaction flask equipped with a stirrer, a thermometer, a vacuum system and an electric heating mantle. The temperature is raised to 100-120°C and dehydrated under high vacuum for 1 to 2 hours until the water content is low. At 0.05%, then cool to 40-60°C. Remove the vacuum and add to the polyisocyanate. The reaction heat causes the system to rise naturally. After the natural heating stops, slowly heat up the temperature and react at 80°C±5°C for 2 to 3 hours. Take samples and analyze the NCO content. After defoaming, the prepolymer is obtained. The process is characterized by simple reaction device and convenient operation.

(2) Industrial Production

①Manual batch method

The operating procedure of the manual batch method for prepolymer production is similar to the laboratory method, except that the glass flask is changed to a stainless steel kettle of different sizes, and electric heating is often used. The commonly used agitator is anchor type or frame type, and the rotating speed is 70-100r/min. The operation process is the same as the laboratory method. In order to ensure the quality of the prepolymer, it is better not to carry out the dehydration of the oligomer polyol and the production of the prepolymer in the same tank, and it is not advisable to carry out the polyester or polyether prepolymer in the same tank. At the same time, the synthesis reaction of the prepolymer should be carried out under the protection of dry nitrogen. In addition, the order of addition is also very important. It is advisable to add isocyanate first and then oligomer polyol. It is better to add oligomer polyol in stages. In this way, the reaction process is stable, the reaction temperature is easy to control, the synthesized prepolymer has low viscosity, low free monomer content, and relatively regular structure.

② Large-scale production method

Large-scale production of prepolymer adopts larger reaction equipment and more complete production equipment. The liquid isocyanate is first pumped into the reactor, and the oligomer polyol is sent to the tubular heat exchanger via the circulating pump under stirring to be heated, and then fed into the reactor via the metering pump for reaction. The temperature of the reactor is controlled by an instrument. After the reaction is completed, the prepolymer is vacuum degassed, and then the prepolymer is sent to the cooling storage tank for cooling and packaging. The entire operation process is controlled by a computer program, which not only reduces the labor intensity of the workers, but also ensures the product quality.