1, synthesis principle
Bisphenol A type epoxy resin is made up of two phenolic groups propane (bpa) and epoxy chloropropane in alkaline catalyst (usually with NaOH) under the action of polycondensation. Its reaction mechanism is divided, is uncertain, it is not the be explored. However, generally speaking, in the process of synthesis of the main reaction may be as follows:
(1) under the alkali catalysis, hydroxyl and bisphenol A epoxy groups of epoxy chloropropane, generate the client base for chloride - ring opening reaction of hydroxyl compounds.
(2) hydroxy chloride reaction with NaOH and HCl to form epoxy group - the closed-loop response.
(3) of the new generation of epoxy group and bisphenol A hydroxy reaction end hydroxyl compounds - ring opening reaction.
(4) end hydroxyl compounds react with epoxy chloropropane generated end hydroxyl compound chloride - ring opening reaction.
(5) the generated hydroxy chloride reaction with NaOH, HCl regeneration into epoxy group - the closed-loop response.
Under the condition of excessive epichlorohydrin, continuously for the open loop - open loop - closed loop response, finally can get two end group for epoxy group of bisphenol A type epoxy resin.
The above reaction is the main reaction in the process of polycondensation. In addition there could be some unwanted side effects, such as hydrolysis reflect, culture reaction of epoxy group, phenolic hydroxyl and the abnormal addition reaction of epoxy group. If can strictly control the suitable reaction conditions (such as feeding ratio, dosage of NaOH concentration and feeding, reaction temperature, feed order, water content, etc.), the side effects can be controlled to a minimum. To obtain due to the relative molecular mass, the base for linear epoxy resin epoxy group.
Adjust the dosage of bisphenol A and epichlorohydrin, can produce average relative molecular mass of different epoxy resin. According to the size of the average relative molecular mass of bisphenol A type epoxy resin can be divided into:
Liquid bisphenol A type epoxy resin (low molecular weight epoxy resin, flexible resin). Average relative molecular mass is low, the average degree of polymerization of n = 0 ~ 1.8. When n = 0 ~ l, as the liquid at room temperature, such as EP0144l - 310 (51) E -, EP0l451-310-44 (E), EP01551-310 (E - 42), etc. When n = 1 ~ 1.8 for semisolid, softening point < 55 ℃, such as E - 3 l.
Solid bisphenol A type epoxy resin. The average relative molecular mass is higher. N = 1.8 ~ 19. When n = 1.8 ~ 5 for medium molecular weight epoxy resin. Softening point is 55 ~ 95 ℃. Such as EP0l661-310 (E - 20), EP01617-310 (E - 12), etc. When n > 5 of high molecular weight epoxy resin. Softening point > 100 ℃. Such as EP0l68l - 410-06 (E), EP0l69l - 410-03 (E), etc.
Usually n = 0 ~ 19 of the epoxy resin, its molecular weight < 6000, for the oligomer. If n > 100, with the performance of the polymer. The resin specifically named phenoxy resin (phenoxyesin), to distinguish it from the general epoxy resin. Relative molecular mass of phenoxy resin is larger, usually for 3 ~ 40000, epoxy group content is very few. In fact it is a kind of thermoplastic polymer, the use of its ultimate performance there is no need to provide by curing of epoxy group. It contains a lot of para hydroxy, however, can be used as a point of chemical modification and junction. For example with isocyanate or melamine - formaldehyde resin to response.
2, synthesis methods,
(1) liquid bisphenol A type epoxy resin synthesis methods of roughly classified into two kinds: one step method and the two steps. One-step method and can be divided into a plus soda and secondary and alkaline. Two steps and can be divided into intermittent and continuous method.
One-step process is to put the bisphenol A and epichlorohydrin under the effect of NaOH polycondensation, namely open loop and closed loop in the same reaction conditions. The current domestic production of the largest E - 44 epoxy resin is synthesized using one-step process.
Two steps process is bisphenol A and epichlorohydrin under the effect of catalyst, such as quaternary ammonium salt, the first step by addition reaction, producing two chlorohydrin ether phenolic groups propane intermediates, the second step for the closed-loop response in the presence of NaOH, epoxy resin. Two footwork is: the advantages of short reaction time. Operating stability, temperature fluctuation is small, easy to control; Epichlorohydrin alkaline time is short, can avoid the numerous hydrolysis; Products of good quality and stable and high yield. Domestic E - 51 epoxy resin, E - 54 is to use two steps synthesis process.
(2) the solid state synthesis methods of bisphenol A type epoxy resin in general can be divided into two kinds: one step method and the two steps. Step method and can be divided into water to wash method, solvent extraction method and solvent method. Two steps: ontology polymerization and catalytic polymerization.
One-step method (foreign says Taffy) process is the bisphenol A with epichlorohydrin under the effect of NaOH polycondensation reaction, used in the manufacture of medium relative molecular mass of solid epoxy resin. Domestic production of E - 20, E - 14, E - 12 such as epoxy resin basically adopt this method. The washing method is to bisphenol A soluble in 10% NaOH aqueous solution, under A certain temperature one-time quickly joined epichlorohydrin reaction, temperature control. Reaction after the incubation, remove the upper alkaline boiling water after washing a dozen times, remove residual alkali and by-product salt in the resin. Then get finished product dehydration. Solvent extraction with water washing method are basically the same, just in the post-treatment process after the remove of the upper alkaline, adding organic solvent extraction resin. Can obviously improve the washing effect (wash 3 ~ 4 times). Then through washing, filtering, take off a solvent that is final product. This product less impurity, resin transparency is good, the domestic factories use it more. Solvent method is to bisphenol A, epichlorohydrin, and organic solvents dissolve into the reaction kettle stirring, heating. Then in 50 ~ 75 ℃ and NaOH aqueous solution, the reaction (also can join the first open loop etherification catalysts, then adding NaOH solution of removing HCl closed-loop response). Arrived after the reaction end point and add a large number of organic solvent to extract, then through washing, filtering, take off the solvent for a quick finished products. This reaction temperature control, finished product resin good transparency, less impurity, high yield. The key is the choice of solvent.
Two steps (foreign advancment method) process is the low relative molecular mass of liquid E type epoxy resin and bisphenol A heating dissolves, in addition reaction under high temperature or catalyst, chain extender, finally form A solid epoxy resin with high relative molecular mass, such as E - 10, E - 06, E - 03 etc were synthesized using this method. Two steps process there are two ways in China. The polymerization of ontology is the liquid bisphenol A type epoxy resin and bisphenol A in reaction kettle heating dissolves, again in 200 ℃ high temperature reaction 2 h to get the product. This method was conducted in high temperature reaction, so the side reaction, products of branched chain structure. Not only epoxy value is low, and poor solubility, and even the reaction will condensate pot. Catalytic polymerization is liquid bisphenol A type epoxy resin and bisphenol A in reaction kettle heating to 80 ~ 120 ℃ dissolve, then add the catalyst reaction, make its exothermic nature. After heat cold to the 150 ~ 170 ℃ 1.5 h reaction, filtered for a quick finished products.
One-step synthesis, the reaction was conducted in emulsion in water. In the preparation of high molecular weight resin, post-processing difficult. Relative molecular mass distribution of resin with wider, organic chlorine content is high. Not easy to get the epoxy value high, high softening point and products, to meet the requirements for powder coating. And two step synthesis, reaction is homogeneous, chain extension reaction is stable, and relatively narrow molecular weight distribution of resin, organic chlorine content is low, the epoxy value and the softening point can pass ratio and reaction temperature to control and adjust. Has some advantages such as simple process, easy operation, less equipment, short hours and no three wastes, reaction at a time, the advantages of easy to control and adjust the product quality, thus increasing attention.
3, structure and performance characteristics
In each application field of epoxy resin, the use of the final performance is provided by the epoxy resin cured. Epoxy resin curing taxi performance depends on the molecular structure of the condensate. While the molecular structure of the cured and its formation depends on the structure of the structure and properties of epoxy resin, curing agent and the performance, structure and properties of the additives, and the epoxy resin curing process. Here, the first is the structure of bisphenol A type epoxy resin on the properties of epoxy resin and its curing effect introduce some.
(1) bisphenol A type epoxy resin of macromolecular structure has the following features:
1) at both ends of the macromolecular reaction the epoxy group of great ability.
2) the molecular main chain, there are many ether bond, is a kind of linear polyether structure.
3) the value of n larger resin molecular chain on a regular basis, are far apart to appear many para hydroxy, may be regarded as a kind of long chain polyols.
4) on the main chain and a large number of benzene, methyl and isopropyl.
(2) the structure unit of bisphenol A type epoxy resin to resin the following functions: epoxy and hydroxyl resin reactivity, the resin curing has A strong cohesion and sticky relay. Ether and hydroxyl is polar groups, help to improve the invasive and adhesion force. Ether and C - C key make macromolecules have flexibility. Benzene ring gives polymer with heat resistance and rigidity. Isopropyl also fu and macromolecular certain rigidity. - C - O - key in the key can be high, thus improve the alkali resistance. So, bisphenol A type epoxy resin molecular structure determines its performance has the following characteristics:
1) is a thermoplastic resin, but with a thermosetting, with a variety of curing agent, catalysts and additives to form a variety of excellent performance of condensates, almost can satisfy various application requirements.
2) the technology of resin is good. Basically do not produce small molecule volatiles when curing, but low pressure molding. Soluble in a variety of solvents.
3) condensate has a high strength and adhesive strength.
4) curing have higher corrosion resistance and electrical property.
5) curing has a certain toughness and heat resistance.
6) the main drawback is that: the heat resistance and toughness is not high, wet and heat resistance and weather resistance.
