Toluene diisocyanate (TDI) can undergo a trimerization reaction under catalytic action to form a trimer containing isocyanurate ring.TDI trimer has the advantages of low volatility, low toxicity, high functionality, good thermal stability, good corrosion resistance and so on, and it is often used as a polyurethane curing agent in coatings and adhesives. In the 1970s, many foreign companies began to industrialize the production and application of these products, such as Bayer, BASF, Dow and so on. At present, high-performance TDI trimers with low free monomer still need to rely heavily on imports.

In this study, the catalyst NT CAT P100 was used to synthesize TDI trimer polyurethane curing agent, and the experimental results showed that the catalyst has the advantages of fast catalytic rate, high activity, low reaction temperature, etc. The catalyst was used to synthesize TDI trimer polyurethane curing agent at 40 ℃ by dropwise reaction. The catalytic reaction was carried out dropwise at 40 ℃, and the end point of the reaction was reached in 8 h. The TDI trimer was obtained with low free monomer content.

Raw materials and reagents

TDI(80/20): industrial product, BASF; Butyl acetate: analytical pure, Guangzhou Panyu Li-Fortified Factory; NT CAT DMP-30: industrial product, Shinden Chemical; NT CAT K-15: industrial product, Shinden Chemical; NT CAT P100: Shinden Chemical;

Synthesis process

Under nitrogen protection, 100 g of TDI (80/20) monomer and 100 g of butyl acetate were added to a dry four-necked round-bottomed flask equipped with stirring, a thermometer, and a reflux condenser tube, and the mixture was stirred for 5-10 min, heated to 40 ℃, and then 0.5 g of catalyst was added dropwise to a solution of butyl acetate (10 mL of butyl acetate). After dropping, the temperature was controlled between 40 and 80 ℃, and the reaction was kept warm for about 8 h. The -NCO value of the reaction solution was measured every 1 h. When the content of -NCO was reduced to 8.5%-9%, 1 g of benzoyl chloride was added, and the reaction was continued for 0.5 h. After stopping the heating and stirring, the material was discharged at reduced temperature, and a light-yellow transparent liquid was obtained.

On the basis of the above process, a preset amount of alcohol was added dropwise, and the reaction was kept warm for 30-60 min to modify the TDI trimer.

Influence of catalyst type, dosage and dropwise addition method

The selection of catalyst is the key to the TDI trimerization reaction. Commonly used TDI trimerization catalysts include tertiary amines, organometallic compounds, organophosphine compounds, alkali metal carboxylates and so on. DMP-30, K-15 and P100 were selected to catalyze the reaction on 50% butyl acetate TDI solution respectively, and the results are shown in Table 1 and Figure 2.

Table 1 Effect of different catalysts (0.5% addition) on TDI trimerization reaction

Catalyst type None K-15 DMP-30 P100

Reaction temperature/°C 70 80 70 70

Reaction time/h 24 26 6 5

w(-NCO)/% 24.2 12.3 10.4 6.8

Product Appearance Colorless transparent Yellow transparent Slightly yellow transparent Nearly water white transparent

From Table 1 and Figure 2, it can be seen that the trimerization reaction of TDI does not occur without catalyst; K-15 catalyzes the trimerization poorly, with higher temperature and longer reaction time, which tends to produce more polymer structure; DMP-30 and P100, both tertiary amine catalysts, catalyze the reaction better, compared to the catalytic performance of P100, which has stronger catalytic performance, and can react quickly and reduce the -NCO value in a short time. The catalytic performance of P100 was better than that of DMP-30 and P100, which were both tertiary amine catalysts. Therefore, P100 was chosen as the catalyst. Figure 3 shows the effect of P100 catalyst on the TDI trimerization reaction when the amount of P100 catalyst accounted for 2%, 0.5% and 0.8% of the total mass of TDI monomer, respectively.

Fig. 2 Comparison of catalytic efficiency of three catalysts

As seen in Fig. 3, with other conditions being the same, the reaction rate was accelerated with the increase of P100 dosage, while the content of -NCO group was reduced. When the catalyst dosage was too low, the -NCO content was still higher than 12% even if the reaction time was extended; while when the catalyst dosage was too high, a large amount of residual catalyst affected the performance of the product to some extent. The experiments showed that the dosage of P100 was more suitable at 0.5%.

Figure 3 Effect of catalyst dosage on TDI trimerization reaction

In addition, the dropwise addition of catalyst will also affect the trimerization reaction. Experiments show that if the catalyst is added at one time, the monomer immediately reacts violently, with a large amount of exothermic, and the local temperature can rise by 10 ℃, and the increase of reactant activity may lead to the increase of the relative molecular mass of the product, broaden its distribution, and generate a large number of polymers, which increases the viscosity of the product, deepens the color, and decreases the product performance. The reaction temperature can be well controlled by using butyl acetate to dilute the catalyst and then adding drop by drop.

Conclusion

P100 was used as the catalyst for the synthesis of TDI trimer, and the experiments showed that the catalytic activity of this catalyst was high, the catalytic rate was fast, and the catalytic effect was better than that of DMP-30 and K-15.

Toluene diisocyanate (TDI) can undergo trimerization under catalytic action to form trimers containing isocyanurate rings. TDI trimer has the advantages of low volatility, low toxicity, high functionality, good thermal stability, good corrosion resistance, etc. It is often used as a polyurethane curing agent in coatings and adhesives. In the 1970s, many foreign companies began to industrially produce and apply such products, such as Bayer, BASF, Dow, etc. At present, high-performance, low-free monomer TDI trimers still need to rely heavily on imports.

In this study, the catalyst NT CAT P100 was used to synthesize TDI trimer polyurethane curing agent. The experimental results show that the catalyst has the advantages of fast catalytic rate, high activity and low reaction temperature. At 40 ℃, the reaction was catalyzed by dropwise addition, and the end of the reaction could be reached within 8 h, resulting in a low free monomer content TDI trimer.

Raw materials and reagents

Toluene diisocyanate monomer TDI (80/20): industrial product, BASF; butyl acetate: analytically pure, Guangzhou Panyu Liqiang Factory; NT CAT DMP-30: industrial product, Xindian Chemical; NT CAT K-15 : Industrial products, Xindian chemistry; NT CAT P100: Xindian chemistry;

Synthesis

Under nitrogen protection, add 100 g of TDI (80/20) monomer and 100 g of butyl acetate to a dry four-necked round bottom flask equipped with a stirrer, thermometer and reflux condenser. Stir for 5 to 10 min, heat to 40°C, and add 0.5 g of catalyst in butyl acetate solution (butyl acetate 10 mL). After the dropwise addition, the temperature is controlled between 40 and 80 ℃, and the reaction temperature is kept for about 8 h. The -NCO value of the reaction solution is measured every 1 h. When the -NCO content decreases to 8.5% to 9%, add 1 g Benzoyl chloride, continue the reaction for 0.5 h, stop heating and stirring, lower the temperature and discharge, to obtain a light yellow transparent liquid.

On the basis of the above process, a predetermined amount of alcohol is added dropwise, and the reaction is incubated for 30 to 60 minutes to modify the TDI trimer.

Influence of catalyst type, dosage and dropping method

The choice of catalyst is the key to TDI trimerization. Commonly used TDI trimerization catalysts include tertiary amines, organic metal compounds, organic phosphine compounds, alkali metal carboxylates, and the like. DMP-30, K-15 and P100 were used to catalyze the reaction of 50% butyl acetate in TDI solution. The results are shown in Table 1 and Figure 2.

Table 1 Effect of different catalysts (0.5% addition) on TDI trimerization

Type of catalyst None K-15 DMP-30 P100

Reaction temperature/℃ 70 80 70 70

Response time/h 24 26 6 5

w(—NCO)/% 24.2 12.3 10.4 6.8

Product appearance colorless and transparent yellow transparent yellowish transparent near water white transparent

It can be seen from Table 1 and Figure 2 that without the addition of catalyst, the trimerization reaction of TDI does not occur; the effect of K-15 catalytic trimerization is poor, the temperature is higher, the reaction time is longer, and more polymers are easily produced Structure; DMP-30 and P100, both tertiary amine catalysts, have better catalytic effect. In contrast, P100 has stronger catalytic performance, and can react quickly in a short time to reduce -NCO value, and the experiment also shows that at 40 ℃ It still has very high catalytic activity. Therefore, P100 was selected as the catalyst. Figure 3 shows the effect of P100 catalyst dosage on TDI trimerization when they account for 2%, 0.5% and 0.8% of the total mass of TDI monomer, respectively.

Figure 2 Comparison of the catalytic efficiency of the three catalysts

It can be seen from Figure 3 that under other conditions being the same, with the increase in the amount of P100, the reaction rate is accelerated, and the content of -NCO groups is reduced. When the amount of catalyst is too small, even if the reaction time is prolonged, the -NCO content is still higher than 12%; when the amount of catalyst is too high, a large amount of residual catalyst affects the performance of the product to a certain extent. Experiments show that 0.5% of P100 is more suitable.

Figure 3 The effect of catalyst dosage on TDI trimerization

In addition, the dropping method of the catalyst will also affect the trimerization reaction. Experiments have shown that if the catalyst is added at once, the monomer reacts violently immediately, a large amount of heat is released, and the local temperature can rise by 10 ℃. The increase in the activity of the reactant may cause the relative molecular mass of the product to increase and the distribution to broaden, resulting in a large amount of polymer To increase the viscosity of the product, deepen the color, and reduce the performance of the product. The method of diluting the catalyst with butyl acetate drop by drop can control the reaction temperature well.

in conclusion

P100 was used as catalyst to synthesize TDI trimer. Experiments show that the catalyst has high catalytic activity and fast catalytic rate, and its catalytic effect is better than DMP-30 and K-15.