Overview[1]
Polyethylene glycol diethylene glycol methyl ether, also known as diethylene glycol diglycidyl ether: the English name is Diglycidyl ether of diethylene glycol, the English abbreviation is DGEG, polyethylene glycol diepoxy Ethane methyl ether is a low viscosity glycerol ether. Using diethylene glycol, epichlorohydrin and sodium hydroxide under the action of a catalyst, it can be used as an epoxy resin diluent after etherification and closed-loop synthesis.
Preparation method
Diethylene glycol diglycidyl ether (DGEG) is synthesized using diethylene glycol and epichlorohydrin as raw materials and boron trifluoride ether complex as catalyst. The effects of catalyst dosage, raw material ratio, alkali metal hydroxide and ring-forming reaction temperature on product yield were discussed. At the same time, it was analyzed and characterized using Fourier transform infrared spectroscopy. When the amount of boron trifluoride etherate complex is 3 parts, the material ratio of epichlorohydrin to diethylene glycol is 8:1, and potassium hydroxide is used to perform the cyclization reaction at about 30°C, it can A product with low viscosity and high yield is obtained [2].
The reaction principle of this preparation method: Diethylene glycol first undergoes complex exchange with ether in the boron trifluoride ether complex to generate positive and negative ion pairs. The positive and negative ion pairs then undergo an etherification reaction with epichlorohydrin [(,3] to generate an etherification intermediate. The etherification intermediate removes chlorine atoms under the action of alkali metal hydroxide and undergoes a ring-closing (ring-forming) reaction. , generating diethylene glycol diglycidyl ether.
Advantages of this preparation method: The molecular structure of bisphenol A-type epoxy resin contains epoxy groups and hydroxyl groups, and there are many ether bonds in the main chain. It has excellent chemical resistance and good adhesion and adhesion. , has the advantages of small volume shrinkage during curing, high dimensional stability, excellent mechanical and electrical properties, and is widely used as adhesives, coatings, laminating and casting materials. However, due to the high viscosity of bisphenol A epoxy resin, in some cases it is necessary to add a large amount of solvent to dilute it to meet the application. Therefore, it has a certain impact on the environment and the performance of the material itself. The reaction of aliphatic dihydric alcohols with epichlorohydrin can produce diglycidyl ether with low viscosity, high activity and good process performance. Diethylene glycol diglycidyl ether with low viscosity can be synthesized by using diethylene glycol and epichlorohydrin as raw materials and boron trifluoride ether complex as catalyst.
The specific preparation method is to add the refined diethylene glycol and boron trifluoride etherate complex into a four-neck bottle equipped with a stirrer, thermometer and dropping funnel, and stir evenly. When the temperature reaches 55°C, start adding epichlorohydrin dropwise. After the dripping is completed, maintain it for another 2-4 hours to complete the reaction. Then, the reaction product is distilled under reduced pressure to remove unreacted epichlorohydrin. Add sodium/potassium hydroxide ethanol solution to the above reaction product and stir until the reaction is complete. The generated sodium chloride is filtered off, and then ethanol, water, etc. are distilled off under reduced pressure. Filter again while hot to remove residual sodium chloride to obtain the product.
Product analysis and characterization methods
(1) Product viscosity measurement: Use the NDJ-79 rotational viscometer from Tongji University Mechanical and Electrical Plant to measure the sample viscosity at 25°C.
(2) Infrared spectrum analysis: Coat the synthesized product on a potassium bromide sheet, and use a Nexus 670 Fourier transform infrared spectrometer from Nicolet Company for structural analysis.
Factors affecting synthesis and preparation
(1) Effect of catalyst dosage on reaction product yield.
The etherification reaction of aliphatic glycols and epichlorohydrin is different from that of bisphenol A. Because the benzene ring on bisphenol A can form a large electron-attracting π bond with the oxygen atom, making the phenolic hydroxyl group weakly acidic, the reaction between the two can proceed more easily; while the hydroxyl group on the glycol is not easy to lose. Hydrogen atoms, the reaction between the two is relatively difficult. In the absence of catalyst-free boron trifluoride diethyl ether complex, the etherification reaction basically does not proceed. Add a small amount of catalyst to the reaction system, and the etherification reaction will start quickly. It can be seen from Figure 1 that as the amount of catalyst increases, the yield of the reaction product increases significantly; when the amount of catalyst exceeds 3 parts, the increase in the yield of the reaction product decreases rapidly. The reason may be that when the amount of boron trifluoride ether complex in the system is small, the amount of positive and negative ion pairs generated by boron trifluoride and diethylene glycol is small, and the speed of the etherification reaction is slow. high. As the amount of catalyst increases, the number of positive and negative ion pairs also increases and gradually reaches a dynamic equilibrium. Therefore, the etherification reaction speed and reaction product first increased, and then gradually stabilized. The optimal yield of the etherification product was 80.5%.
(2) Effect of the dosage of epichlorohydrin on the yield of ring-forming reaction products
When the amount of boron trifluoride ether complex is determined, the concentration when the ion pair formed by diethylene glycol and boron trifluoride reaches equilibrium is also determined. Increasing the dosage of epichlorohydrin will increase the probability of the generated positive and negative ion pairs interacting with epichlorohydrin, and the reaction rate will also increase accordingly. Within a certain period of time, the reaction conversion rate is relatively high, as shown in Figure 2. As the ratio of epichlorohydrin to diethylene glycol increases, the reaction conversion rate gradually increases. When the amount ratio of the two substances exceeds 4:1, the growth rate of product yield tends to be flat. Therefore, when the material ratio of epichlorohydrin to diethylene glycol exceeds this ratio,��The dosage of epichlorohydrin is no longer the main factor affecting product yield. Under such conditions, the optimal yield of the cyclization reaction was 79.0%.
(3) Effect of alkali metal hydroxide on the yield of cyclization reaction products
Sodium hydroxide/potassium hydroxide is a flaky solid. If it is added directly to the etherification reaction product to perform a dehydrochlorination ring-forming reaction, the reaction between the two can only occur at the solid-liquid interface. Due to the limitation of solid-liquid interface area, the ring-forming reaction proceeds slowly. The flaky sodium/potassium hydroxide is prepared into a saturated ethanol solution and added to the reaction system in batches. The ring-forming reaction can be carried out in the liquid phase and the reaction rate is greatly improved. Compared with sodium hydroxide, potassium hydroxide has greater solubility in ethanol, and the concentration of hydroxide ions in the solution is higher, which is beneficial to the ring-forming reaction and improved conversion rate, as shown in Figure 3.
(4) Effect of ring-forming reaction temperature on viscosity of reaction product
When the reaction temperature is low, the viscosity of the generated diethylene glycol diglycidyl ether is low, and the molecular weight of the resin is relatively small. However, as the ring-forming reaction temperature increases, as shown in Figure 4, its viscosity increases rapidly. The reason may be that under higher temperature conditions, hydroxide ions are more likely to cause the generated epoxy group to undergo anionic ring-opening addition reaction [3] , resulting in a polyether with too large a molecular weight but too small epoxy value (contrary to the research objectives). Therefore, the optimal temperature for the ring-forming reaction is around 30°C.
References
[1] Wei Wuji, Zheng Yaochen, Lu Gang. Synthesis of diethylene glycol diglycidyl ether [J]. Thermosetting Resins, 2002, 17(6):12-14.
[2]Xuepin Gu,.I Ssao,O Mitsuo. Synthesis,1985,(6/7):649-657.
[3] Chen Ping, Liu Shengping, Epoxy Resin［M］. Beijing: Chemistry Press, 1999, 44-47
