Views: 5 Author: Site Editor Publish Time: 2023-05-26 Origin: Site
Polyols were prepared by using linoleic acid and resorcinol diglycidyl ether as raw materials and N,N-dimethylbenzenemethanamine as catalyst at a certain temperature and a series of material ratios. The effects of reaction temperature and molar ratio of resorcinol diglycidyl ether to linoleic acid on the synthesis of the products were investigated. The products were characterized by infrared spectroscopy, and the disappearance of epoxy groups and the production of hydroxyl groups proved the successful synthesis of polyols.
Urethane has a wide range of applications in coatings and paints because of its good performance. It has gradually become an important industry for our economic development. As one of the main raw materials for the preparation of polyurethane, the demand of polyol is gradually increasing with the increase of polyurethane demand. Polyol mainly provides soft segments for the synthesis of polyurethane and has a great influence on the performance of polyurethane, such as viscosity, adhesion and mechanical strength. However, most of the polyols currently used in industry are non-renewable and difficult to be degraded, which is not friendly to either the economy or the environment. Therefore, it is important to synthesize an environmentally friendly and renewable polyol.
1.1 Main drugs
Resorcinol diglycidyl ether: industrial grade; Linoleic acid: industrial grade; N,N-dimethylbenzylamine, KOH, NaOH are industrial grade; Acetone, hydrochloric acid.
The synthesis of linoleic acid polyester polyol is mainly based on the high activity of the epoxy group at both ends of the epoxy, which is able to react with the hydroxyl group of linoleic acid in a ring-opening reaction to generate hydroxyl groups, thus producing linoleic acid polyester polyol.
Add a certain amount of resorcinol diglycidyl ether and linoleic acid into a four-necked flask, install stirring device, condenser tube and thermometer, turn on the stirring device under the environment of nitrogen to make full contact with the raw materials, stir for about 5 min, heat to 120 ℃, and add a certain amount of catalyst dropwise at the same time, stop the reaction when the acid value in the system is basically unchanged, and measure the epoxy value at the same time to produce polyether polyol.
1.3 Testing and characterization
(1) Infrared spectroscopy: The infrared spectrometer of Thermo Fisher Nicolet 5700 was used for testing.
(2) Determination of acid value: Weigh the sample accurately, dissolve the sample in 50 mL of anhydrous ethanol, add 2-3 drops of phenolphthalein as indicator, titrate with 0.05 mol/L KOH solution, and stop the titration when the solution turns pink and does not fade within 10 s. At the same time, a blank experiment was performed as described above. The formula is as follows: Acid value = (V-V0)C×56.1/m where V: volume of KOH consumed by the sample, mL; V0: volume of KOH consumed by the blank experiment, mL; C: concentration of KOH solution, mol/L; m: mass of the sample, g.
(3) Determination of epoxy value: weigh 1-2 g of the sample in a conical flask, add 8 mL of hydrochloric acid-acetone (1:4, v/v) solution and add a stopper. The sample was dissolved completely, and phenolphthalein was used as the indicator, and the solution was titrated with the calibrated NaOH-ethanol solution until it turned pink and did not fade within 30 s. The formula is as follows: E=(V1-V2)×C ÷ 10m where E: epoxide value, equivalent/100g; V1: average volume of NaOH ethanol solution consumed by titrating two blank samples, mL; V2: volume of NaOH ethanol solution consumed by titrating a known mass of the reaction mixture, mL; m: mass of the reaction mixture, g; C: concentration of NaOH ethanol solution, mol/L. mol/L.
2 Results and Discussion
2.1 Effect of reaction temperature on the synthesis of polyester polyol
When the amount of catalyst, the molar mass of the substance is certain. The temperature of the reaction has a great influence on the color, viscosity and acid value of the product of synthesis of linoleic acid and resorcinol diglycidyl ether. From Fig. 1 and Fig. 2, it can be seen that the time for the reaction to reach a constant at different temperatures is not very different. However, when the reaction temperature was too high (140 °C), the reaction almost reached a constant within half an hour, and the polyol obtained became dark brown in color, as shown in Fig. 1, and it was difficult to control the reaction process; When the reaction temperature was 100 ℃ and 110 ℃, the reaction time was 2.5, and the acid values were 37.65 mg KOH/g and 30.77 mg KOH/g when the reaction reached equilibrium, which indicated that the reaction between linoleic acid and resorcinol diglycidyl ether was slow at this temperature. In conclusion, 120 ℃ was chosen as the optimum reaction temperature. The effect of temperature on the reaction is shown in Figure 2.
2.2 Effect of molar ratio of substances on the reaction
When the reaction temperature was controlled at 120 ℃ and the amount of catalyst was 0.5%, the effects of different molar ratios of resorcinol diglycidyl ether and linoleic acid were investigated at 1:2, 1:1.95, 1:1.9, 1:1.85 and 1:1.8, respectively.
From Fig. 3, the reaction time to equilibrium increases and then remains constant as the molar ratio increases; and the acid value increases, then decreases and finally increases as the molar ratio increases; The measured epoxy values were 0.074 mol/100 g, 0.033 mol/100 g, and 0.055 mol/100 g as the molar ratios changed, and the epoxy values were not measured because the 1:1.95 and 1:2 acid values did not drop to 5 mg KOH/g. As the molar ratio changes, the measured epoxy values are 0.074 mol/100 g, 0.033 mol/100 g, 0.055 mol/100 g, the epoxy values of 1:1.95 and 1:2 acids were not measured because they did not drop to 5 mg KOH/g. The reason for the incomplete reaction according to the theoretical molar ratio is that linoleic acid has a large molecular structure during the reaction, and the viscosity of the system will increase during the ring-opening reaction, and some of the carboxyl groups will be wrapped, so that the chance of collision between the epoxy group and the carboxyl group will be reduced and the reaction time will be prolonged. The difference in acid values is not significant at molar ratios of 1:1.8, 1:1.85 and 1:1.9, but the epoxy value is relatively low at a molar ratio of 1:1.85; It was concluded that the reaction proceeded more thoroughly when the molar ratio was 1:1.85. In order to investigate more precise molar ratios, further investigations were carried out in the molar ratios of 1:1.85-1:1.9 and 1:1.9-1:1.95, respectively.
As can be seen from Table 1, the reaction equilibrium time was relatively long at 3 h for the molar ratio of 1:1.94 and 2.5 h for all other molar ratios. The reaction at the molar ratio of 1:1:1.93 showed the smallest acid and epoxide values compared to other molar ratios, indicating that the reaction proceeded very thoroughly. Therefore, the optimum molar ratio for the reaction of resorcinol diglycidyl ether with linoleic acid was 1:1.93.
2.3 Structural characterization of linoleic acid polyester polyol
In Figure 4, a is polyether polyol and b is resorcinol diglycidyl ether. 908 cm-1 is the characteristic absorption peak of the epoxy group, and the comparison between the two figures shows that the characteristic peak of the epoxy group disappears in product a, indicating that the epoxy group reacts with the carboxyl group. The absorption peaks of the ester group appeared at 1738 cm-1, 1265 cm-1, 1050 cm-1 and a broad -OH characteristic peak at 3459 cm-1, indicating the formation of -OH. Therefore, it was concluded that the epoxy group opened the ring and successfully reacted with the carboxyl group to produce the polyol.
This paper focuses on the reaction of resorcinol diglycidyl ether and linoleic acid to synthesize a linoleic acid polyol. The effect of temperature and molar ratio on the reaction was mainly investigated. The following conclusions were drawn:
(1) When the reaction temperature was 120 ℃, the amount of catalyst was 0.5%, the reaction time was 2.5 h, and the molar ratio of 1:1.93 between resorcinol diglycidyl ether and linoleic acid was the best condition for the reaction.
(2) The stability of the product was good, and the color was light yellow. The hydroxyl value was 108.26 mg KOH/g and the epoxy value was 0.016 mol/100g.