Study on the properties of MFE vinyl ester resin and its application in the field of anticorrosion; Zhou Runpei of East China University of Science and Technology; Xiaodong Hou Liu Zhanzhen 1. Vinyl ester refers to unsaturated polyester with vinyl groups at both ends of the molecule and epoxy resin as the middle skeleton. They are obtained by ring-opening esterification of unsaturated organic monocarboxylic acids (most commonly acrylic acid and methacrylic acid) with epoxy resin, so they can also be called unsaturated acid epoxy ester (1). Vinyl ester is a foreign word, and its meaning is not exact. The more accurate name should be epoxy vinyl ester. In the literature of the former Soviet Union, these compounds were called epoxy acrylate, epoxy methacrylate and so on. In the early literature of our country, these compounds were called epoxy methacrylate, epoxy acrylate and so on. , or collectively unsaturated acid epoxy ester. The research and development of vinyl ester resin began in the 1960s. 1964 Shell Chemical Company of the United States first developed a bisphenol A epoxy vinyl ester resin with the trade name Epicryl, and then Dow Chemical Company of the United States successively developed many similar products with the trade name Derakane. Japan has also developed a series of vinyl ester resins (2) with the trade name of Ripoxy. The research and development of this kind of resin in China began in the early 1970s. This work was first reported by East China University of Science and Technology (formerly East China Institute of Chemical Technology), Sichuan Chenguang Institute of Chemistry, Shanghai Resin Factory and Tianjin Institute of Synthetic Materials, and applied research was carried out. The application fields of vinyl ester resin are various, among which the most extensive and important is in the field of anticorrosion. East China University of Science and Technology is one of the earliest research units of corrosion-resistant vinyl ester resin in China, and it is also the first unit to apply vinyl ester resin to anti-corrosion engineering. As early as 1975, the epoxy methacrylate resin (ME-type vinyl ester resin) developed by Shanghai Institute of Chemical Technology (now East China University of Science and Technology) has been successfully applied to the aldehyde bath (containing 30%H2SO4 and formaldehyde) anticorrosion project of the newly-built vinylon plant in Shanghai Petrochemical Complex (3). At 1980 and 198 1, the first vinyl ester resin with the trade name MFE-2 was put into production in our cooperative factories and self-operated enterprises. After more than 20 years of development and application research, Huachang Polymer Co., Ltd. of East China University of Science and Technology has become the main research and production base of epoxy vinyl ester resin in China, with a series of MFE vinyl ester resin brands and rich engineering application and construction experience. Epoxy vinyl ester resin has a history of nearly forty years since it came out, during which countless brand goods, patents and documents have appeared. As far as I know, the vinyl ester resins researched and produced at home and abroad can be roughly divided into the following categories: me-type vinyl ester with methacrylic acid (M) and bisphenol A epoxy resin (E) as the main raw materials; AE vinyl ester with acrylic acid (a) and bisphenol a epoxy resin as main raw materials; MF type with methacrylic acid and phenolic polyepoxy resin (F) as main raw materials; AF type with acrylic acid and phenolic epoxy resin as main raw materials; MFE type with methacrylic acid, fumaric acid (F) and bisphenol A epoxy resin as main raw materials and MEX type with methacrylic acid and brominated bisphenol A epoxy resin as main raw materials (table 1). In addition, many vinyl ester resins are modified by modifiers such as isocyanate and rubber. Even vinyl ester resins with the same composition of raw materials have different physical and chemical properties due to different raw material ratios, different production processes and different curing conditions. Table 1 classification of corrosion-resistant epoxy vinyl ester resin (according to chemical composition) vinyl ester type main raw material characteristics unsaturated acid epoxy resin ME methacrylic acid (M) E epoxy universal AE acrylic acid (A) E epoxy toughness MF methacrylic acid (M) F epoxy high temperature resistant MFE methacrylic acid (m), fumaric acid (F) E epoxy universal AF acrylic acid (A) F epoxy toughness, High temperature resistant AFE acrylic acid (A), fumaric acid (F) E epoxy toughness meX methacrylic acid (M) EX epoxy flame retardant From the development history of vinyl ester, ME vinyl ester is a commercial resin developed successfully earlier. Some manufacturers call this kind of resin standard vinyl ester resin, but there is no typical formula. In fact, there are many kinds of ME vinyl ester resins, and the author also focused on the synthesis and properties of these vinyl ester resins in the early stage (4). What formula is the standard of ME resin? At present, there is no recognized typical formula. In the unsaturated polyester resin family, the recognized standard resin is polytrimethylene terephthalate, and its typical molecular formula is phthalic anhydride: maleic anhydride: propylene glycol = 1: 1: 2. 15 (molar ratio). Standard resin is not equal to the best resin, and the best resin in that year is not equal to the best forever, which has been confirmed by the development history of unsaturated polyester resin. In a word, science is developing and technology is progressing. In the future, more new varieties will join the ranks of vinyl ester resins, and the old varieties will continue to improve their quality. Molecular structure and properties 1. Molecular Structure of Epoxy Vinyl Ester (1) The chemical structures of ME-type and AE-type epoxy vinyl esters are as follows: (2) The chemical structures of MFE-type and AFE-type epoxy vinyl esters are as follows: It can be seen that the molecular structures of ME-type and MFE-type vinyl esters are very similar, but the molecular weight of MFE-type vinyl esters is almost 6544 higher than that of ME-type due to the presence of chain extender fumaric acid. The infrared spectrum of MFE vinyl ester resin produced by Huachang Company is similar to that of DERAKANE-4 1 KLOC-0/resin produced by Dow Chemical Company, which also proves this point (see figure1). Some authors accuse MFE vinyl esters of not being true vinyl esters. We don't know what the molecular structure of a real vinyl ester should be. Infrared spectrum can't tell whether it is vinyl ester or not. Is it really only by "spontaneous foaming before gel" invented by some people to distinguish between true and false vinyl esters? 2. Molecular Structure and Chemical Corrosion Resistance Polymer physics tells us that the molecular structure of polymer compounds, whether linear or network, is multi-layered, and the primary structure is the chemical structure of molecules; The secondary structure is the morphological structure of molecules; Cubic (or higher) structure is the aggregation structure of molecules. This paper does not intend to elaborate on this, but only points out that the chemical composition of molecules can not replace the chemical structure of molecules, nor is it the same as the molecular structure, so the properties of polymer compounds can not be determined solely by chemical composition. For example, polypropylene with the same chemical composition has poor mechanical properties and cannot be used as a material. Only polypropylene obtained by directional polymerization is a useful engineering material. Due to the characteristics of chemical structure: the density of ester groups is low, and they are all adjacent to cross-linkable double bonds. After epoxy vinyl ester is cross-linked with hydrophobic styrene to form a network structure, it has high hydrolysis stability. The factors affecting the hydrolysis stability of epoxy vinyl ester resin are: the density of ester group, the space protection of adjacent groups of ester group, and the content of crosslinking agent styrene (5). (1) ester group density epoxy vinyl ester, like unsaturated polyester, contains hydrolyzable groups (-c = o-o-) in its molecular structure, so the relative content of ester groups (expressed by ester group density mol/ 100g) will directly affect its hydrolysis stability. The simplest epoxy vinyl ester is obtained by the reaction of methacrylic acid with bisphenol A epoxy resin in the molar ratio of 2: 1. The schematic formula of its molecular chemical structure is: m-e-m, in which: M stands for methacrylic acid E stands for E-type epoxy resin. If e is E-5 1 and the average molecular weight is 392, the average molecular weight of the epoxy vinyl ester with the above molecular structure is 564. Since the molecule contains two ester groups on average, its average ester group equivalent is 282, that is, every 282g of epoxy vinyl ester contains 1 mole of ester groups, or its average ester group density is 0.355mol/ 100g. At present, the most common epoxy vinyl ester in the domestic market is fumaric acid modified epoxy methacrylate, and its molecular structure is as follows: m-e-f-e-m, where F stands for fumaric acid, and the meanings of M and E are the same as above. If the epoxy resin participating in the reaction is also E-5 1, the average molecular weight of MFE epoxy vinyl ester is 1072. Because the molecular structure contains four ester groups, the average ester group equivalent of epoxy vinyl ester is 268, and the average ester group density is 0.373mol/ 100g, which is higher than the simplest ME-type epoxy vinyl ester mentioned above. By analogy, it can be calculated that the average ester group density of bisphenol A unsaturated polyester synthesized by D-33 and fumaric acid with the molar ratio of 1: 1 is 0.472mol/ 100g, and the phthalic anhydride synthesized by propylene glycol, maleic anhydride and phthalic anhydride with the molar ratio of 2:1: It can be seen from the above calculation results that the ester group density of MFE epoxy vinyl ester resin is about o-phenyl 19 1 3 of polyester, but the experimental facts show that (6) the hydrolytic stability of MFE epoxy vinyl ester resin is far better than o-phenyl 19 1 resin by more than three times, which is ② Alkaline hydrolysis: both the adjacent groups R and R' of ester groups affect the hydrolysis rate of ester groups, especially R. It is reported that (7) the alkaline hydrolysis rate constant K0 of ethyl acetate in water at 20℃ is 4.8L/mol? Min, and the alkaline hydrolysis rate constant of ethyl propionate with one methylene in the same linear difference in water at 20℃ is k 1=2.3l/mol? Min, the hydrolysis rate constant of the latter is about 1/2 of the former. This result extends to the comparison of hydrolytic stability between epoxy methacrylate (ME type) and epoxy acrylate (AE type). Undoubtedly, the hydrolytic stability of the former is better than that of the latter. However, it must be pointed out that the hydrolytic stability of ME-type and AE-type epoxy vinyl esters before curing is poor. All colleagues in the glass fiber reinforced plastic industry have an understanding that only after the resin (epoxy vinyl ester resin is no exception) is fully crosslinked and cured, therefore, the author thinks that the crosslinkable double bonds adjacent to ester groups in the molecular structure of epoxy vinyl ester are cured with the participation of styrene to form a three-dimensional crosslinked network, and its spatial protection for the formation of ester groups is the most important reason for the high hydrolytic stability of epoxy vinyl ester resin (6). As shown in figure 2: groups protected by macromolecules in the space network after curing. (3) The content of crosslinking agent styrene is the same as that of unsaturated polyester. Styrene is still the most commonly used crosslinking agent and diluent for epoxy vinyl ester, and its content usually accounts for about 40% of the total amount of epoxy vinyl ester resin. Since styrene and its polymers are inert to hydrolysis, the most direct function of its existence and content is to reduce the density of ester groups in epoxy vinyl ester resin. In addition, it participates in the curing and crosslinking of epoxy vinyl ester resin in the form of polystyrene segments, forming a three-dimensional network, which plays an important role in the heat resistance, mechanical properties and hydrolysis stability of resin castings. In a word, the hydrolytic stability of epoxy vinyl ester resin curing network can not be judged only by the chemical composition of epoxy vinyl ester which constitutes the network, but also the influence of the molecular structure of curing network containing styrene segments on water resistance must be considered. Let's review the history. It has been more than 30 years since the commercial resin was successfully developed, that is, the ME-type epoxy vinyl ester resin synthesized by methacrylic acid and E-type epoxy resin in the molar ratio of 2: 1. Over the past 30 years, the varieties of commercial resins have been increasing, and various modified resins have appeared one after another. MFE epoxy vinyl ester resin modified by fumaric acid and AE epoxy vinyl ester resin 3200# synthesized by acrylic acid instead of methacrylic acid have been commercialized in China as early as the early 1980s (8). AE-type epoxy vinyl ester resin lacks the space protection function of α -methyl group on adjacent ester groups in chemical structure, but as long as the amount of styrene is appropriate and the network structure is reasonable, it can also have high hydrolysis stability, even exceeding some me-type epoxy vinyl ester resins, which has been confirmed by many years of application practice. The MFE-5 vinyl ester resin with high toughness and low shrinkage recently introduced by Huachang Polymer Company belongs to AE vinyl ester resin, but it has excellent hydrolytic stability. The test results show that the appearance and transparency of MFE-5 vinyl ester resin casting body remain unchanged after soaking in 100% NaOH at 80~ 100℃ for 2 months, with only a slight weight loss (9). It shows that the resin has excellent alkali resistance. 3. Molecular structure and physical and mechanical properties After curing and crosslinking, vinyl ester forms a three-dimensional network structure. The factors affecting the toughness of the network structure are the crosslinking density and the flexibility of molecular segments between crosslinking points. The crosslinking density is directly related to the density of double bonds of resin molecules. Take the double bond density of ME-type vinyl ester resin as an example. If the epoxy resin participating in the molecular composition is still E-5 1, since each molecule contains two double bonds, that is, 2 moles of double bonds per 564gME vinyl ester, its average double bond density is 0.355 mol/ 100 g ... and each molecule of MFE vinyl ester resin contains three double bonds, that is, per kloc on average. It can be calculated that the average double bond density of the molecule is 0.280mol/ 100g, which is 27% lower than that of ME vinyl ester. It can be seen that the three-dimensional network structure formed by the curing of MFE vinyl ester molecules is not as high as some people say, but lower than that of me vinyl ester. Another important factor affecting the toughness of vinyl ester resin curing network is the flexibility of molecular segments between network cross-linking points. As we all know, acrylic acid and its esters are called soft monomers in chemical industry, while methacrylic acid and its esters are called hard monomers. This is because the main chain of acrylate can rotate freely after polymerization, while the internal rotation of the molecular main chain is blocked due to the steric hindrance of α -methyl after polymerization. It can be seen that the cast body of AE-type vinyl ester resin is generally more tough than ME-type vinyl ester resin, but it is not absolutely so. After all, the curing network of vinyl ester resin is only the chemical structure of vinyl ester molecules, and it cannot completely determine the physical properties of vinyl ester resin castings.