Disulfide bond-containing modified vinyl ester resin as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of high polymer materials, and particularly relates to disulfide bond-containing modified vinyl ester resin as well as a preparation method and application thereof. The preparation method of the disulfide bond-containing modified vinyl ester resin comprises the following steps: mixing epoxy resin, unsaturated monocarboxylic acid, a polymerization inhibitor and a catalyst, heating to 100-115 DEG C, reacting until the acid value is less than 30mg KOH / g, then adding dithiodipropionic acid, continuously reacting at 100-115 DEG C until the acid value is less than 15mg KOH / g, then cooling to 80 DEG C or below, adding an active diluent, and uniformly mixing to obtain the disulfide bond-containing modified vinyl ester resin. And uniformly mixing to obtain the product. Dynamic disulfide bonds are introduced into the vinyl ester resin, and a dynamic cross-linked network is constructed in a thermosetting network, so that the glass-transition temperature and the tensile property of a cured film can be flexibly regulated and controlled, the elongation at break and the toughness are obviously improved, and hot-pressing recovery of a vinyl ester resin cured material can also be realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and particularly relates to a disulfide bond-containing modified vinyl ester resin, a preparation method thereof, and an application thereof. Background Art

[0002] The complex marine environment easily causes stress corrosion cracking, corrosion fatigue, hydrogen embrittlement, and intergranular corrosion of materials, which in turn damages marine engineering equipment. This is one of the bottlenecks restricting the development of marine resources and the construction of the marine economy. Coating the metal surface with an organic coating is a common and effective anti-corrosion strategy.

[0003] Traditional vinyl ester resins are obtained by reacting epoxy resins with acrylic acid or methacrylic acid under certain temperature and in the presence of a catalyst. Vinyl ester resins are widely used in anti-corrosion coatings due to their low cost, simple synthesis, and good performance. However, the permanent cross-linked structure formed during the free radical curing process of traditional vinyl ester resins results in extremely low self-healing ability. Therefore, any damage to the coating will significantly reduce its corrosion resistance, leading to the rapid deterioration of the underlying metal substrate. In addition, thermosetting materials such as vinyl ester resins are difficult to degrade or recycle, which leads to the accumulation of solid waste and causes environmental problems. Therefore, there is an urgent need to develop new anti-corrosion resins with reprocessing and recycling capabilities. Summary of the Invention

[0004] The first object of the present invention is to provide a preparation method of a disulfide bond-containing modified vinyl ester resin. The second object of the present invention is to provide the disulfide bond-containing modified vinyl ester resin prepared by this preparation method. The third object of the present invention is to provide the application of the disulfide bond-containing modified vinyl ester resin.

[0005] According to the first aspect of the present invention, there is provided a preparation method of a disulfide bond-containing modified vinyl ester resin, comprising the following steps:

[0006] Mix epoxy resin, monounsaturated carboxylic acid, inhibitor, and catalyst, heat up to 100 - 115 °C and react until the acid value is less than 30 mg KOH / g, then add dithiodipropionic acid, continue to react at 100 - 115 °C until the acid value is less than 15 mg KOH / g, then cool to below 80 °C, add an active diluent, and mix evenly to obtain the product.

[0007] The present invention uses epoxy resin as the basic raw material, semi-caps it with a monounsaturated carboxylic acid, then uses dithiodipropionic acid as a chain extender to react with the remaining epoxy groups to complete chain extension, and finally adds an active diluent to adjust the viscosity, obtaining a disulfide bond-containing modified vinyl ester resin. The present invention introduces dynamic disulfide bonds into the vinyl ester resin, constructs a dynamic crosslinked network within the thermosetting network, can achieve flexible regulation of the glass transition temperature and tensile properties of the cured film, significantly improve the elongation at break and toughness, and can also achieve hot pressing recovery of the vinyl ester resin cured material.

[0008] In some embodiments, the epoxy resin is at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, and glycidyl ether epoxy resin.

[0009] In some embodiments, the monounsaturated carboxylic acid is at least one of acrylic acid, methacrylic acid, crotonic acid, and β-phenylacrylic acid.

[0010] In some embodiments, the inhibitor is at least one of hydroquinone, p-tert-butylcatechol, and catechol.

[0011] In some embodiments, the catalyst is at least one of benzyltriethylammonium chloride, triethylamine, and triphenylphosphine.

[0012] In some embodiments, the active diluent is at least one of hydroxyethyl acrylate, isobornyl acrylate, tripropylene glycol diacrylate (TPGDA), and trimethylolpropane triacrylate.

[0013] In some embodiments, the dosage ratio of the epoxy resin, monounsaturated carboxylic acid, and dithiodipropionic acid is 1 mol:(0.2 - 1.8) mol:(0.1 - 0.9) mol.

[0014] In some embodiments, the dosage of the inhibitor is 0.005 - 0.045 wt% of the total mass of the epoxy resin, monounsaturated carboxylic acid, and dithiodipropionic acid.

[0015] In some embodiments, the dosage of the catalyst is 0.1 - 2.5 wt% of the total mass of the epoxy resin, monounsaturated carboxylic acid, and dithiodipropionic acid.

[0016] In some embodiments, the dosage of the active diluent is 10 - 50 wt% of the total mass of the epoxy resin, monounsaturated carboxylic acid, and dithiodipropionic acid.

[0017] According to the second aspect of the present invention, there is provided a disulfide bond-containing modified vinyl ester resin prepared by the above preparation method.

[0018] According to the third aspect of the present invention, there is provided the use of the above-mentioned disulfide bond-modified vinyl ester resin in the preparation of UV coatings, anticorrosive coatings, inks or engineering plastics.

[0019] The beneficial effects of the present invention include:

[0020] (1) By introducing dithiodipropionic acid containing disulfide bonds as a chain extender into the vinyl ester resin system, a dynamic disulfide bond crosslinked network is introduced into the thermosetting network, realizing the hot pressing physical recycling of the thermosetting material of the vinyl ester resin and solving the problem that the traditional thermosetting film of the vinyl ester resin cannot be recycled. Moreover, with different dosages of dithiodipropionic acid, the storage modulus, glass transition temperature, mechanical properties and crosslinking density of the cured film can be regularly regulated. The appearance of the resin is uniform and non-stratified, and the viscosity is appropriate. The cured coating has good mechanical properties, substrate adhesion, thermal stability, chemical stability and anticorrosion properties, and is suitable for the preparation of UV coatings, anticorrosive coatings, inks or engineering plastics.

[0021] (2) The disulfide bond-modified vinyl ester resin of the present invention contains terminal carbon-carbon double bonds. During the curing process of the resin, the carbon-carbon double bonds undergo free radical polymerization to obtain a crosslinked network mainly composed of C-C covalent bonds. The crosslinked network is stable, so that the resin has good chemical stability, solvent resistance and anticorrosion properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the reaction route of the disulfide bond-modified vinyl ester resin of Example 1 of the present invention.

[0023] Figure 2 is the Fourier transform infrared spectrogram of the disulfide bond-modified vinyl ester resin, epoxy resin, dithiodipropionic acid and acrylic acid of Example 1 of the present invention.

[0024] Figure 3 is the hot pressing recovery cyclic tensile diagram and physical diagram of the cured film prepared from the disulfide bond-modified vinyl ester resin of Example 3 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto. The materials involved in the following examples can be obtained from commercial channels.

[0026] Example 1

[0027] The preparation method of the disulfide bond-modified vinyl ester resin of this example includes the following steps:

[0028] In a 1000 mL three-necked round-bottom flask, 156.80 g of bisphenol A epoxy resin E-51 (molecular weight 392 g / mol), 40.35 g of acrylic acid, 0.0445 g of inhibitor hydroquinone, and 1.1119 g of catalyst benzyltriethylammonium chloride were added. The temperature was raised to 105 °C and the reaction was carried out until the acid value was less than 30 mg KOH / g. Then, 25.23 g of dithiodipropionic acid was added, and the reaction was continued at 105 °C until the acid value was less than 15 mg KOH / g. Then, it was cooled to below 80 °C, and 95.31 g of hydroxyethyl acrylate was added and mixed evenly to obtain a light yellow transparent dithiol-modified vinyl ester resin.

[0029] The reaction route of the dithiol-modified vinyl ester resin in this example is as Figure 1 shown.

[0030] The Fourier transform infrared spectra of the dithiol-modified vinyl ester resin, epoxy resin, dithiodipropionic acid, and acrylic acid in this example are as Figure 2 shown. In the figure, the raw materials are epoxy resin (denoted as E51), dithiodipropionic acid (denoted as DPDTA), acrylic acid (denoted as AA), and the product is the dithiol-modified vinyl ester resin (denoted as VER).

[0031] It can be seen from Figure 2 that at 3010, 1607, and 803 cm -1 , they respectively correspond to the C-H stretching vibration of the alkyl group, the C═C stretching vibration on the benzene ring, and the bending vibration absorption peak of the para-substituent on the benzene ring. It is worth noting that a characteristic peak of the epoxy functional group also appears at 915 cm -1 . For the spectra of DPDTA and AA, the broad peak appearing at 2700 - 3500 cm -1 corresponds to the O-H stretching vibration of -COOH, and the peak at 1697 cm -1 corresponds to the C═O stretching vibration of the carboxylic acid group, proving the existence of the carboxylic acid group in the above two raw materials. As the ring-opening reaction between the epoxy resin and the organic acid proceeds, in the VER spectrum, the epoxy functional group at 915 cm -1 gradually disappears, and instead, a new O-H stretching vibration peak appears at 3417 cm -1 . The peak at 1697 cm -1 corresponds to the C═O stretching vibration of the ester group, and this peak coincides with the C═O stretching peak of DPDTA and AA, which proves that DPDTA and AA have been successfully grafted onto the E51 resin, the ring-opening reaction of the carboxylic acid and the epoxy has been successfully carried out, and the dithiol-modified vinyl ester resin has been successfully prepared.

[0032] Example 2

[0033] The preparation method of the disulfide bond-containing modified vinyl ester resin in this example includes the following steps:

[0034] Put 156.80 g of bisphenol A epoxy resin E-51 (molecular weight 392 g / mol), 23.06 g of acrylic acid, 0.0460 g of inhibitor hydroquinone, and 1.1516 g of catalyst benzyltriethylammonium chloride into a 1000 mL three-necked round-bottom flask, heat up to 105 °C and react until the acid value is less than 30 mg KOH / g. Then add 50.46 g of dithiodipropionic acid and continue to react at 105 °C until the acid value is less than 15 mg KOH / g. Then cool to below 80 °C, add 98.71 g of hydroxyethyl acrylate, mix evenly to obtain a light yellow transparent disulfide bond-containing modified vinyl ester resin.

[0035] The Fourier transform infrared spectroscopy detection was carried out on the disulfide bond-containing modified vinyl ester resin, epoxy resin, dithiodipropionic acid, and acrylic acid prepared in this example. The characteristic peaks of the obtained detection results are basically the same as those of Example 1. For the sake of saving space, they will not be elaborated here.

[0036] Example 3

[0037] The preparation method of the disulfide bond-containing modified vinyl ester resin in this example includes the following steps:

[0038] Put 156.80 g of bisphenol A epoxy resin E-51 (molecular weight 392 g / mol), 11.53 g of acrylic acid, 0.0471 g of inhibitor hydroquinone, and 1.1780 g of catalyst benzyltriethylammonium chloride into a 1000 mL three-necked round-bottom flask, heat up to 105 °C and react until the acid value is less than 30 mg KOH / g. Then add 67.29 g of dithiodipropionic acid and continue to react at 105 °C until the acid value is less than 15 mg KOH / g. Then cool to below 80 °C, add 100.98 g of hydroxyethyl acrylate, mix evenly to obtain a light yellow transparent disulfide bond-containing modified vinyl ester resin.

[0039] The Fourier transform infrared spectroscopy detection was carried out on the disulfide bond-containing modified vinyl ester resin, epoxy resin, dithiodipropionic acid, and acrylic acid prepared in this example. The characteristic peaks of the obtained detection results are basically the same as those of Example 1. For the sake of saving space, they will not be elaborated here.

[0040] Then, to test the performance of the disulfide bond-containing modified vinyl ester resin of the present invention, the disulfide bond-containing modified vinyl ester resins prepared in Examples 1-3 were coated, and then the performance of the obtained cured film was tested.

[0041] 1. Preparation of the cured film

[0042] The disulfide bond-modified vinyl ester resin prepared in Example 1 was mixed uniformly with tert-butyl perbenzoate as a curing agent accounting for about 2.0 wt% of the total mass of the disulfide bond-modified vinyl ester resin. After degassing the mixture under vacuum, it was poured into a polytetrafluoroethylene mold and then placed in a high-temperature oven for curing at 120 °C, 160 °C, and 180 °C for 2 hours respectively to obtain a cured film.

[0043] Cured films were prepared from the disulfide bond-modified vinyl ester resins obtained in Examples 2-3 in the same manner.

[0044] 2. Performance Testing

[0045] (1) Tensile Property Testing of Plastics

[0046] A Shimadzu AGS-X 1kN universal testing machine was used to conduct the tensile test. The dumbbell-shaped sample specifications referred to GB / T 1040.2-2006, and the crosshead speed was 1 mm / min. The area under the tensile stress-strain curve was calculated by integration to obtain the toughness value.

[0047] For accuracy, each sample was measured three times and the average value was taken.

[0048] (2) Dynamic Thermomechanical Property Testing

[0049] A Netzsch DMA 242E dynamic thermomechanical analyzer was used. The tensile mode was selected, and the oscillation frequency was set to 1 Hz. The sample was first cooled to -80 °C with liquid nitrogen and held at -50 °C for 3 minutes during the test, and then heated to 180 °C at a rate of 5 °C / min. The sample specifications were 32 mm × 5 mm × 3 mm (length × width × thickness). The glass transition temperature (T g ) of the cured film was taken as the temperature corresponding to the peak on the tanδ vs. temperature curve.

[0050] For accuracy, each sample was measured three times and the average value was taken.

[0051] (3) Thermogravimetric Testing

[0052] A Netzsch STA 449C thermal analyzer was used to conduct the thermogravimetric analysis test. The temperature range required for the thermogravimetric test of the sample was set to 35-650 °C, the heating rate was 10 °C / min, and a nitrogen environment was maintained during the test with a nitrogen flow rate of 60 mL / min.

[0053] For accuracy, each sample was measured three times and the average value was taken.

[0054] (4) Hot Press Recycling Testing

[0055] The cured film samples were crushed into powders using a BaiXin LG-01 crusher, screened using a 200-mesh sieve, and the powder samples were poured into a stainless-steel mold (1 mm thick). They were hot-pressed using a KeJin HP-100 hot press at 160 °C and 15 MPa for 1 hour. The hot-pressed samples were cut into a size of 40 mm × 10 mm × 1 mm (length × width × thickness) using a cutting machine, and then a Shimadzu AGS-X1 kN universal testing machine was used for tensile testing.

[0056] For accuracy, each sample was measured three times and the average value was taken.

[0057] (5) Solvent resistance test

[0058] The introduction of reversible dynamic bonds usually reduces the chemical stability of materials. Therefore, it is necessary to conduct a solvent resistance test on the cured film samples of dithiol-modified vinyl ester resin. The cured film samples were cut into strips and immersed in deionized water, 3.5 wt% NaCl solution, ethanol, 1 mol / L HCl, ethyl acetate, and toluene at room temperature respectively. After soaking for 7 days, the samples were taken out and the state of the samples was observed for any phenomena such as blistering and peeling.

[0059] 3. Test results

[0060] (1) Test results of comprehensive mechanical properties

[0061] The test results of the comprehensive mechanical properties of the cured films made from the dithiol-modified vinyl ester resin of Examples 1-3 are shown in Table 1.

[0062] Table 1 Test results of the comprehensive mechanical properties of the cured film

[0063]

[0064] It should be noted that since the synthesis process of the dithiol-modified vinyl ester resin of the present invention is essentially a ring-opening reaction process of epoxy groups and carboxylic acids, in Examples 1-3, the epoxy groups were provided by bisphenol A epoxy resin E-51, and the carboxylic acid groups were provided by acrylic acid and dithiodipropionic acid. To ensure that the molar ratio of the reaction between epoxy groups and carboxylic acids is 1:1, therefore, with the increase in the amount of dithiodipropionic acid used, the amount of acrylic acid added should be correspondingly reduced while the amount of epoxy resin remains unchanged.

[0065] As can be seen from Table 1, after the resin of the present invention was modified with dithiodipropionic acid, the storage modulus, glass transition temperature, and tensile strength of the cured film all showed a slight decrease at room temperature, while the elongation at break and toughness showed a significant increase. The cured film of the resin in Example 3 showed the best toughness, reaching 485.6 J / m 3, approximately 4 times that of the cured film of the resin in Example 1 (125.5 J / m 3 ). The above reason is attributed to the fact that compared with the rigid structure of the benzene ring, the disulfide bond and C-C bond in the chemical structure of dithiodipropionic acid belong to soft segments. The addition of soft segments is beneficial to the increase of material toughness. By regulating the hard and soft segments in the chemical structure of the disulfide bond-modified vinyl ester resin, the mechanical properties of the cured film can be controllably adjusted. In addition, the increase of the soft segment and toughness of the material can better promote the movement of molecular chains and the dynamic exchange reaction of disulfide bonds at high temperatures, which is beneficial to the subsequent dynamic network reconstruction of the cured film.

[0066] It can also be seen from Table 1 that with the addition of dithiodipropionic acid, the glass transition temperature of the cured film can be controllably adjusted between 37.7 °C and 62.7 °C. This is because with the introduction of dithiodipropionic acid, the molecular weight of the vinyl ester resin increases and the molecular chain becomes longer; when the carbon-carbon double bond undergoes free radical polymerization, the crosslinking density of the crosslinked network decreases, and the movement space of the molecular chain is larger, thus realizing the decrease of the glass transition temperature of the material.

[0067] (2) Test results of thermal stability performance

[0068] The test results of the thermal stability performance of the cured films prepared from the disulfide bond-modified vinyl ester resins of Examples 1-3 are shown in Table 2.

[0069] Table 2 Test results of the thermal stability performance of the cured film

[0070]

[0071]

[0072] It can be seen from Table 2 that with the addition of dithiodipropionic acid, the thermal stability performance of the cured film shows a slight negative impact, but the T 10％ values of all cured film samples are higher than 300 °C, and the char residue rate after 800 °C remains almost unchanged, proving that the cured film of the disulfide bond-modified vinyl ester resin of the present invention has excellent thermal stability performance.

[0073] (3) Test results of hot pressing recovery

[0074] The cyclic tensile diagram and physical diagram of the hot pressing recovery of the cured film prepared from the disulfide bond-modified vinyl ester resin of Example 3 are as Figure 3 shown. In the figure, the digital picture on the left is the picture of the powder after the cured film sample is crushed, the digital picture on the right is the picture of the powder restored after hot pressing, and the curve represents the tensile stress-strain curves of the initial and 3 times of hot pressing cycles of the cured film sample.

[0075] From Figure 3It can be seen that after 3 cycles of pulverization and hot pressing, no obvious cracks were observed on the surface of the reprocessed sample of Example 3, and the transparency was good. Due to material aging and incomplete reconstruction of the crosslinked network during hot pressing, the tensile strength and recovery rate of the material decreased with the increase in the number of recycling times. The recovery rate was calculated based on the ratio of the tensile strength of the sample before and after hot pressing. The recovery rates for 3 cycles were 92.1%, 79.6%, and 72.8% respectively, indicating that the cured film of the vinyl ester resin modified with disulfide bonds of the present invention has good recyclability. By introducing disulfide bonds into the vinyl ester resin system, the present invention constructs a dynamic disulfide crosslinked network and realizes the hot pressing physical recycling of traditional thermosetting vinyl ester resin materials.

[0076] (4) Test results of solvent resistance

[0077] The test results of the solvent resistance of the cured films prepared from the vinyl ester resins modified with disulfide bonds in Examples 1 - 3 are shown in Table 3.

[0078] Table 3 Test results of the solvent resistance of the cured film

[0079]

[0080] Note: "No change" in Table 3 means that the state of the cured film has no change, and there are no phenomena such as blistering and peeling.

[0081] As can be seen from Table 3, after being immersed in water, saline solution, organic solvents, and acidic aqueous solution for 7 days, the cured films prepared from the vinyl ester resins modified with disulfide bonds of the present invention have no change in state, showing good chemical stability and anti-corrosion performance. This is attributed to the aromatic ring structure and double bond crosslinking curing of the resin. The carbon-carbon double bonds of the resin undergo free radical polymerization to form a free radical polymerization network, and the free radical polymerization network endows the cured film with a thermosetting crosslinked structure. The good chemical stability and anti-corrosion performance enable the vinyl ester resin modified with disulfide bonds of the present invention to be applied in the field of anti-corrosion coatings.

[0082] The above are only some embodiments of the present invention. For those of ordinary skill in the art, without departing from the inventive concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A method for preparing a disulfide bond-modified vinyl ester resin, characterized in that: The steps include: Mix epoxy resin, monounsaturated carboxylic acid, polymerization inhibitor and catalyst, heat to 100-115°C to react until the acid value is less than 30 mg KOH / g, then add dithiodipropionic acid, continue to react at 100-115°C until the acid value is less than 15 mg KOH / g, then cool to below 80°C, add active diluent, mix well, and obtain the product.

2. The preparation method according to claim 1, characterized in that: The epoxy resin is at least one of bisphenol A epoxy resin, bisphenol F epoxy resin and glycidyl ether epoxy resin.

3. The preparation method according to claim 1 or 2, characterized in that: The monobasic unsaturated carboxylic acid is at least one of acrylic acid, methacrylic acid, crotonic acid, and β-phenylacrylic acid.

4. The preparation method according to claim 1 or 2, characterized in that: The polymerization inhibitor is at least one of hydroquinone, p-tert-butylcatechol and catechol.

5. The preparation method according to claim 1 or 2, characterized in that: The catalyst is at least one of benzyltriethylammonium chloride, triethylamine and triphenylphosphine.

6. The preparation method according to claim 1 or 2, characterized in that: The active diluent is at least one of hydroxyethyl acrylate, isobornyl acrylate, tripropylene glycol diacrylate and trimethylolpropane triacrylate.

7. The preparation method according to claim 1 or 2, characterized in that: The usage ratio of the epoxy resin, the monounsaturated carboxylic acid and the dithiodipropionic acid is 1 mol: (0.2-1.8) mol: (0.1-0.9) mol.

8. The preparation method according to claim 1 or 2, characterized in that: The amount of the polymerization inhibitor is 0.005-0.045wt% of the total mass of the epoxy resin, the monounsaturated carboxylic acid and the dithiodipropionic acid; The amount of the catalyst used is 0.1 to 2.5 wt% of the total mass of the epoxy resin, the monounsaturated carboxylic acid and the dithiodipropionic acid; The amount of the active diluent is 10-50wt% of the total mass of the epoxy resin, the monounsaturated carboxylic acid and the dithiodipropionic acid.

9. The disulfide bond-modified vinyl ester resin obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the disulfide bond-modified vinyl ester resin according to claim 9 in the preparation of UV coatings, anticorrosive coatings, inks or engineering plastics.

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