Synthesis of bisphenol A epoxy resin

1 Synthesis principle: bisphenol A epoxy resin is formed by condensation of bisphenol A and epichlorohydrin under the action of basic catalyst (usually NaOH) There are different opinions on its reaction course, and there is no final conclusion This book does not discuss it However, in general, the main reactions in the synthesis process may be as follows: (1) under the catalysis of alkali, the hydroxyl group of bisphenol A reacts with the epoxy group of epichlorohydrin to form a compound with the end group of chloride hydroxyl ring opening reaction (2) the reaction of hydroxyl chloride with NaOH, dehydrogenation of HCl and formation of epoxy closed-loop reaction (3) the new epoxy group reacts with the hydroxyl group of bisphenol A to form a hydroxyl terminated compound ring opening reaction (4) the reaction of hydroxyl terminated compounds with epichlorohydrin resulted in the ring opening reaction of hydroxyl terminated compounds (5) the generated chlorinated hydroxyl reacts with NaOH, dehydrogenation reacts with HCl to form epoxy group closed-loop reaction In the case of epichlorohydrin excess, the above open-loop open-loop closed-loop reaction is carried out continuously, and the bisphenol-A epoxy resin with epoxy as the end group is finally obtained The above reaction is the main reaction in the polycondensation process In addition, there may be some undesired side reactions, such as hydrolysis reaction of epoxy group, cultural reaction, abnormal addition reaction between phenolic hydroxyl group and epoxy group, etc If the appropriate reaction conditions (such as feeding ratio, NaOH dosage, concentration and feeding mode, reaction temperature, feeding sequence, water content, etc.) can be strictly controlled, the side reaction can be controlled to the minimum Thus, a linear epoxy resin with a predetermined molecular weight and an epoxy end group can be obtained By adjusting the ratio of bisphenol A and epichlorohydrin, epoxy resins with different average molecular weight can be prepared According to the average molecular weight, bisphenol A epoxy resin can be divided into liquid bisphenol A epoxy resin (low molecular weight epoxy resin, soft resin) The average relative molecular weight is low, and the average degree of polymerization n = 0-1.8 When n = 0-l, it is liquid at room temperature, such as ep0144l-310 (E-51), ep0l451-310 (E-44), ep01551-310 (E-42), etc When n = 1 ~ 1.8, it is semi-solid, and when softening point is 5, it is high molecular weight epoxy resin Softening point > 100 ℃ For example, ep0l68l-410 (e-06), ep0l69l-410 (e-03), etc Generally, epoxy resin with n = 0-19 and molecular weight of 100 has the properties of polymer This kind of resin is specially named phenoxysin to distinguish it from the general epoxy resin The relative molecular weight of phenoxy resin is usually 30000-40000, and the content of epoxy group is very small In fact, it is a kind of thermoplastic polymer, its final use performance does not need to be provided by curing of epoxy However, it contains a lot of secondary hydroxyl, which can be used as chemical modification point and crosslinking point For example, it can react with isocyanate or melamine formaldehyde resin 2 Synthesis methods (1) there are two kinds of synthesis methods of liquid bisphenol A epoxy resin: one step and two step The one-step method can be divided into one-step alkali addition method and two-step alkali addition method The two-step method can be divided into intermittent method and continuous method The one-step process is to polycondensate bisphenol A and epichlorohydrin under the action of NaOH, that is, the open-loop and closed-loop reactions are carried out under the same reaction conditions At present, the E-44 epoxy resin with the largest output in China is synthesized by one-step process In the two-step process, bisphenol A and epichlorohydrin are reacted with catalyst (such as quaternary ammonium salt), the first step is to generate the intermediate of bisphenol propane chlorohydrin ether through addition reaction, and the second step is to generate epoxy resin through closed-loop reaction in the presence of NaOH The advantages of the two-step method are: short reaction time, stable operation, small temperature fluctuation, easy to control; short alkali adding time, which can avoid large amount of hydrolysis of epichlorohydrin; good product quality and stability, high yield Domestic E-51 and e-54 epoxy resins were synthesized by two-step process (2) the synthesis methods of solid bisphenol A epoxy resin can be divided into two kinds: one step and two step One step method can be divided into water washing method, solvent extraction method and solvent method The two-step method can be divided into bulk polymerization and catalytic polymerization One step process (taffy process) is the polycondensation of bisphenol A and epichlorohydrin under the action of NaOH, which is used to produce solid epoxy resin with medium molecular weight This method is basically used in domestic production of E-20, E-14, E-12 and other epoxy resins In the water washing method, bisphenol A is first dissolved in 10% NaOH aqueous solution, and epichlorohydrin is added at a certain temperature to make it react rapidly and control the temperature After the reaction is completed, it is allowed to stand still After the upper alkaline water is removed, it is washed with boiling water for more than ten times to remove the residual alkali and by-product salt in the resin Then dehydrate to get the finished product The solvent extraction method is basically the same as the water washing method, except that the organic solvent extraction resin is added after the upper alkaline water is removed in the post-treatment process It can obviously improve the washing effect Then the finished product is obtained by washing, filtering and desolvent The product of this method has few impurities and good resin transparency, which is widely used in domestic factories In the solvent method, bisphenol A, epichlorohydrin and organic solvent are first put into the reactor to be stirred and heated for dissolution Then add NaOH water solution dropwise at 50-75 ℃ to make the reaction (or add catalyst for ring opening etherification, and then add NaOH solution for closed-loop reaction of dehydrogenation) At the end of the reaction, a large number of organic solvents are added for extraction, and then washed, filtered and desolvated to obtain the finished product The reaction temperature is easy to control, the resin transparency is good, the impurities are few, and the yield is high The key is the choice of solvent The two-step process is to heat and dissolve the low molecular weight liquid E-type epoxy resin and bisphenol A, then carry out the addition reaction under the action of high temperature or catalyst, expand the chain continuously, and finally form the high molecular weight solid epoxy resin, such as E-10, e-06, e-03 and so on There are two methods of two-step process in China In bulk polymerization, the liquid bisphenol-A epoxy resin and bisphenol-A are first heated and dissolved in a reactor, and then reacted at 200 ℃ for 2h to obtain the product The reaction is carried out at high temperature, so there are many side reactions and branched chain structure in the product Not only the epoxy value is low, but also the solubility is very poor, and even the reaction will condense In the catalytic polymerization method, the liquid bisphenol A epoxy resin and bisphenol A are heated to 80-120 ℃ in the reactor to dissolve them, and then the catalyst is added to make them react, so as to let them heat naturally After heat release and cooling to 150-170 ℃ for 1.5h, the finished product can be obtained through filtration In one-step synthesis, the reaction is carried out in emulsion in water In the preparation of high molecular weight resin, post-treatment is difficult The resin has a wide molecular weight distribution and a high content of organic chlorine It is not easy to obtain products with high epoxy value and softening point to meet the requirements of powder coating In the two-step synthesis, the reaction is homogeneous and the chain growth reaction is relatively stable, so the relative molecular weight distribution of the resin is narrow and the content of organic chlorine is low The epoxy value and softening point can be controlled and adjusted by the ratio and reaction temperature It has the advantages of simple process, convenient operation, less equipment, short working hours, no three wastes, one-time reaction, easy control and adjustment of product quality, so it has been paid more and more attention 3 Structure and performance characteristics in various application fields of epoxy resin, its final performance is provided by epoxy resin curing products The performance of epoxy curing compound depends on its molecular structure The molecular structure and formation of the cured product depend on the structure and performance of the epoxy resin, the structure and performance of the curing agent, the structure and performance of the additive, and the curing process of the epoxy resin In this paper, the influence of the structure of bisphenol a type epoxy resin on the properties of epoxy resin and its cured products is introduced (1) the macromolecular structure of bisphenol A epoxy resin has the following characteristics: 1) the two ends of the macromolecular are epoxy groups with strong reaction ability 2) there are many ether bonds on the main chain, which is a linear polyether structure 3) there are many secondary hydroxyl groups in the resin chain with large n value, which can be regarded as a long chain polyol 4) there are a large number of benzene rings, methylene and isopropyl groups in the main chain (2) the structure units of bisphenol A epoxy resin give the following functions to the resin: epoxy group and hydroxyl group give the resin reactivity, which makes the cured resin have strong cohesive force and adhesive force Ether bond and hydroxyl are polar groups, which help to improve the wettability and adhesion Ether bond and C-C bond make macromolecules flexible The benzene ring gives the polymer heat resistance and rigidity The isopropyl group also gives the macromolecule certain rigidity -The bond energy of c-o-bond is high, so the alkali resistance is improved Therefore, the molecular structure of bisphenol-A epoxy resin determines its performance with the following characteristics: 1) it is a thermoplastic resin, but it has thermosetting property It can form a variety of curing products with excellent performance with a variety of curing agents, catalysts and additives, which can almost meet the requirements of various uses 2) the resin has good processability It can be formed under low pressure It is soluble in many solvents 3) the solidified product has high strength and bonding strength 4) the solidified product has high corrosion resistance and electrical performance 5) the solidified product has certain toughness and heat resistance 6) the main disadvantages are: low heat resistance and toughness, poor heat and humidity resistance and weather resistance