Preparation method of multi-acrylate-based self-initiating and self-repairing photocuring resin

Abstract

The application relates to a preparation method of a multi-acrylate-based self-initiating and self-repairing photocuring resin, and relates to a preparation method of a photocuring resin. The application aims at solving the problem that the photo initiator used in the existing photocuring resin cannot enter the inside of a cured product, thereby failing to fully utilize the residual unreacted functional groups in the resin after curing, and affecting the performance of the material after repair. The preparation method comprises the following steps: I, weighing; II, preparing an IPDI solution; III, preparing an HTPB solution, dropping the HTPB solution into the IPDI solution, and reacting after dropping to obtain a reaction system A; IV, preparing an HEDS solution, dropping the HEDS solution into the reaction system A, and reacting after dropping to obtain a reaction system B; and V, preparing a PETA solution, dropping the PETA solution into the reaction system B, and reacting after dropping. The application is used for the preparation of the multi-acrylate-based self-initiating and self-repairing photocuring resin.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of a photocuring resin. BACKGROUND

[0002] The photocuring resin is mainly used as a main component of a photocuring product, and plays a key role in the performance of the product, especially in the fields of adhesives, paints, inks, etc. Once the photocuring layer for connection, protection or decoration is damaged and cracks, it will lose its functionality, so it becomes a hot research topic to endow the photocuring resin with a self-repairing function. The current research mainly focuses on the recombination of dynamic covalent bonds between or within molecules to achieve re-repairing.

[0003] The resin after curing generally has residual unreacted functional groups, and the re-polymerization of the residual functional groups is also a feasible method to achieve self-repairing or promote the self-repairing process. However, the photoinitiator cannot enter the interior of the cured product, and if the dynamic covalent bond not only can itself reversibly open and close, but also can trigger the unreacted functional groups in the resin to perform chemical crosslinking, the reactive functional groups in the resin can be fully utilized, which can not only improve the performance of the material after repair, but also reduce the energy required for repair and improve the repair speed. SUMMARY

[0004] The present application aims to solve the problem that the photoinitiator used in the existing photocuring resin cannot enter the interior of the cured product, thereby failing to fully utilize the residual unreacted functional groups in the resin after curing, which affects the performance of the material after repair, and further provides a preparation method of a multi-acrylate self-initiating and self-repairing photocuring resin.

[0005] A preparation method of a multi-acrylate self-initiating and self-repairing photocuring resin, which is carried out according to the following steps:

[0006] I. 9-15 parts by mass of isophorone diisocyanate, 0.5-1 part by mass of dibutyltin dilaurate, 8-15 parts by mass of hydroxyl-terminated liquid polybutadiene rubber, 7-13 parts by mass of bis(2-hydroxyethyl)disulfide, 0.2-0.5 parts by mass of hydroquinone, 5-10 parts by mass of pentaerythritol triacrylate, and 30-60 parts by mass of tetrahydrofuran are weighed;

[0007] II. Under a nitrogen atmosphere and stirring, 9-15 parts by mass of isophorone diisocyanate, 0.5-1 part by mass of dibutyltin dilaurate, and 10-20 parts by mass of tetrahydrofuran are mixed to obtain an IPDI solution;

[0008] III. Under a nitrogen atmosphere and stirring, 8-15 parts by mass of hydroxyl-terminated liquid polybutadiene rubber is dissolved in 10-20 parts by mass of tetrahydrofuran to obtain an HTPB solution. Under a nitrogen atmosphere and stirring, the HTPB solution is added dropwise to the IPDI solution, and then the reaction is carried out after the dropwise addition to obtain a reaction system A;

[0009] IV. Under the atmosphere of nitrogen and stirring, 7-13 parts of bis(2-hydroxyethyl) disulfide was dissolved in 5-10 parts of tetrahydrofuran to obtain a HEDS solution, and the HEDS solution was added dropwise into the reaction system A under the atmosphere of nitrogen and stirring, and then the reaction was carried out after the dropwise addition to obtain a reaction system B;

[0010] V. Under the atmosphere of nitrogen and stirring, 0.2-0.5 parts of hydroquinone and 5-10 parts of pentaerythritol triacrylate were dissolved in 5-10 parts of tetrahydrofuran to obtain a PETA solution, and the PETA solution was added dropwise into the reaction system B under the atmosphere of nitrogen and stirring, and then the reaction was carried out after the dropwise addition to obtain a multi-acrylate group self-initiating and self-repairing photocuring resin.

[0011] The beneficial effects of the present application are:

[0012] 1. By adding bis(2-hydroxyethyl) disulfide, a disulfide bond structure is introduced into the molecular main chain of the resin, so that the resin not only has self-repairing performance, but also can self-polymerize under ultraviolet light irradiation, avoiding the use of a photoinitiator and reducing the use of an additional toxic photoinitiator.

[0013] 2. The large number of acrylate structures at the end of the chain makes the cured resin have more crosslinking points, thereby improving the hardness of the coating, and the hardness of the paint film can reach 6H grade, and the minimum is 4H grade.

[0014] 3. The acrylate structures in the system that are not completely reacted will be reactivated by the disulfide bond after heating, thereby initiating repolymerization and improving the healing efficiency of the resin.

[0015] 4. The hydroxyl-terminated liquid polybutadiene rubber is inexpensive and easy to obtain, and through end group modification, it can be photocured, thereby expanding the application range of the liquid polybutadiene rubber.

[0016] 5. The self-repairing performance of the multi-acrylate group self-initiating and self-repairing photocuring resin is realized through a weak dynamic covalent bond (disulfide bond), and the self-healing can be realized at 85℃. Compared with other strong dynamic covalent bonds such as D-A bonds (the healing temperature is generally above 110℃), the healing temperature is relatively low.

[0017] 6. The multi-acrylate group self-initiating and self-repairing photocuring resin has excellent mechanical properties, and the tensile strength reaches 3MPa, and the healing efficiency reaches 89.8%.

[0018] 7. The light transmittance of the multi-acrylate group self-initiating and self-repairing photocuring resin reaches 80%. Good light transmittance is not only conducive to the deep curing of the resin, but also compared with colored resins, the application range of the resin with good transparency is more extensive.

[0019] The accompanying drawings

[0020] Figure 1 Synthetic route of the multi-acrylate-based self-initiated, self-repairing photo-cured resin of Example 1;

[0021] Figure 2 Infrared spectrum of PUA-S resin, A) HEDS and IPDI, B) HTPB and PUA-S resin;

[0022] Figure 3 NMR spectrum of PUA-S resin;

[0023] Figure 4 Raman spectrum of PUA-S resin;

[0024] Figure 5 GPC spectrum of PUA-S resin, A) GPC curve, B) molecular weight distribution;

[0025] Figure 6 Polymerization principle diagram of PUA-S resin;

[0026] Figure 7 Thermal stability of PUA-S resin, A) thermogravimetric curve, B) thermogravimetric rate curve;

[0027] Figure 8 Transmittance curve of PUA-S resin;

[0028] Figure 9 Transmittance photograph of PUA-S1 resin;

[0029] Figure 10 DSC curve of PUA-S resin;

[0030] Figure 11 Self-healing photograph of PUA-S1 resin and photograph of lifting heavy object after healing;

[0031] Figure 12 Repairing process schematic diagram of PUA-S resin;

[0032] Figure 13 Initiation free radical polymerization process schematic diagram of PUA-S resin;

[0033] Figure 14 Stress-strain curves of PUA-S resin before and after healing, A) PUA-S0 resin, B) PUA-S1 resin, C) PUA-S2 resin, D) PUA-S3 resin;

[0034] Figure 15 Healing efficiency of PUA-S resin;

[0035] Figure 16The scratch change of PUA-S resin under optical microscope;

[0036] Figure 17 The glossiness test of paint film after PUA-S resin coating;

[0037] Figure 18 The pencil hardness test of paint film after PUA-S resin coating;

[0038] Figure 19 The adhesion test of paint film after PUA-S resin coating;

[0039] Figure 20 The solvent resistance test (toluene wiping 200 times) of paint film after PUA-S1 resin coating. DETAILED DESCRIPTION

[0040] Embodiment 1: A preparation method of a multi-acrylate-based self-initiating and self-repairing photocuring resin, which is carried out according to the following steps:

[0041] I. 9-15 parts by mass of isophorone diisocyanate, 0.5-1 part by mass of dibutyltin dilaurate, 8-15 parts by mass of hydroxyl-terminated liquid polybutadiene rubber, 7-13 parts by mass of bis(2-hydroxyethyl) disulfide, 0.2-0.5 parts by mass of hydroquinone, 5-10 parts by mass of pentaerythritol triacrylate, and 30-60 parts by mass of tetrahydrofuran are weighed;

[0042] II. Under a nitrogen atmosphere and stirring, 9-15 parts by mass of isophorone diisocyanate, 0.5-1 part by mass of dibutyltin dilaurate, and 10-20 parts by mass of tetrahydrofuran are mixed to obtain an IPDI solution;

[0043] III. Under a nitrogen atmosphere and stirring, 8-15 parts by mass of hydroxyl-terminated liquid polybutadiene rubber is dissolved in 10-20 parts by mass of tetrahydrofuran to obtain an HTPB solution. Under a nitrogen atmosphere and stirring, the HTPB solution is added dropwise to the IPDI solution, and then the reaction is carried out after the dropwise addition to obtain a reaction system A;

[0044] IV. Under a nitrogen atmosphere and stirring, 7-13 parts by mass of bis(2-hydroxyethyl) disulfide is dissolved in 5-10 parts by mass of tetrahydrofuran to obtain an HEDS solution. Under a nitrogen atmosphere and stirring, the HEDS solution is added dropwise to the reaction system A, and then the reaction is carried out after the dropwise addition to obtain a reaction system B;

[0045] V. Under nitrogen atmosphere and stirring, 0.2-0.5 parts of hydroquinone and 5-10 parts of pentaerythritol triacrylate were dissolved in 5-10 parts of tetrahydrofuran to obtain a PETA solution. Under nitrogen atmosphere and stirring, the PETA solution was added dropwise to the reaction system B, and the reaction was carried out after the dropwise addition to obtain a multi-acrylate group self-initiating and self-repairing photocuring resin.

[0046] The 9-15 parts of isophorone diisocyanate in Step One of the specific embodiment can be replaced by other types of diisocyanate, such as 7-12 parts of toluene diisocyanate or 7-11 parts of hexamethylene diisocyanate, as long as the number of moles of isocyanate groups in the reaction system is equal.

[0047] The beneficial effects of the present embodiment are:

[0048] 1. By adding bis(2-hydroxyethyl) disulfide, a disulfide bond structure is introduced into the main chain of the resin, which not only makes the resin have self-repairing performance, but also enables the resin to polymerize by itself under ultraviolet light irradiation, avoiding the use of photoinitiators and reducing the use of additional toxic photoinitiators.

[0049] 2. The large number of acrylate structures at the end of the chain makes the cured resin have more crosslinking points, thereby improving the hardness of the coating, and the hardness of the paint film can reach 6H grade, with a minimum of 4H grade.

[0050] 3. The unreacted acrylate structures in the system will be reactivated by the disulfide bond after heating, initiating repolymerization and thereby improving the healing efficiency of the resin.

[0051] 4. The hydroxyl-terminated liquid polybutadiene rubber is inexpensive and easy to obtain. By modifying the end groups, it can be photocured, expanding the application range of liquid polybutadiene rubber.

[0052] 5. The self-repairing performance of the multi-acrylate group self-initiating and self-repairing photocuring resin is realized through weak dynamic covalent bonds (disulfide bonds), which can achieve self-healing at 85°C. Compared with other strong dynamic covalent bonds such as D-A bonds (healing temperature generally above 110°C), the healing temperature is relatively low.

[0053] 6. The multi-acrylate group self-initiating and self-repairing photocuring resin has excellent mechanical properties, with a tensile strength of 3 MPa and a healing efficiency of 89.8%.

[0054] 7. The light transmittance of the multi-acrylate group self-initiating and self-repairing photocuring resin reaches 80%. Good light transmittance not only facilitates deep curing of the resin, but also makes the resin with good transparency more widely applicable compared to colored resins.

[0055] Specific embodiment two: the difference between this embodiment and specific embodiment one is that in step three, the HTPB solution is added to the IPDI solution at a dropping speed of 1 s / drop to 7 s / drop. The rest is the same as specific embodiment one.

[0056] Specific embodiment three: the difference between this embodiment and one of specific embodiment one or two is that in step three, the reaction is carried out at a temperature of 50°C to 90°C for 2 h to 4 h after the dropping. The rest is the same as specific embodiment one or two.

[0057] Specific embodiment four: the difference between this embodiment and one of specific embodiment one to three is that in step four, the HEDS solution is added to the reaction system A at a dropping speed of 2 s / drop to 7 s / drop. The rest is the same as specific embodiment one to three.

[0058] Specific embodiment five: the difference between this embodiment and one of specific embodiment one to four is that in step four, the reaction is carried out at a temperature of 50°C to 90°C for 2 h to 4 h after the dropping. The rest is the same as specific embodiment one to four.

[0059] Specific embodiment six: the difference between this embodiment and one of specific embodiment one to five is that in step five, the PETA solution is added to the reaction system B at a dropping speed of 2 s / drop to 7 s / drop. The rest is the same as specific embodiment one to five.

[0060] Specific embodiment seven: the difference between this embodiment and one of specific embodiment one to six is that in step five, the reaction is carried out at a temperature of 50°C to 90°C for 4 h to 6 h after the dropping. The rest is the same as specific embodiment one to six.

[0061] Specific embodiment eight: the difference between this embodiment and one of specific embodiment one to seven is that in step one, 15 parts of isophorone diisocyanate, 0.5 parts of dibutyltin dilaurate, 10 parts of hydroxyl-terminated liquid polybutadiene rubber, 9 parts of bis(2-hydroxyethyl) disulfide, 0.5 parts of hydroquinone, 9 parts of pentaerythritol triacrylate and 60 parts of tetrahydrofuran are taken by mass fraction. The rest is the same as specific embodiment one to seven.

[0062] Specific embodiment nine: the difference between this embodiment and one of specific embodiment one to eight is that in step one, 15 parts of isophorone diisocyanate, 0.5 parts of dibutyltin dilaurate, 10 parts of hydroxyl-terminated liquid polybutadiene rubber, 12 parts of bis(2-hydroxyethyl) disulfide, 0.5 parts of hydroquinone, 9 parts of pentaerythritol triacrylate and 60 parts of tetrahydrofuran are taken by mass fraction. The rest is the same as specific embodiment one to eight.

[0063] Specific implementation ten: the difference between this implementation and one to nine is that: in step one, 15 parts of isophorone diisocyanate, 0.5 parts of dibutyl tin dilaurate, 10 parts of hydroxyl-terminated liquid polybutadiene rubber, 13 parts of bis(2-hydroxyethyl) disulfide, 0.5 parts of hydroquinone, 9 parts of pentaerythritol triacrylate and 60 parts of tetrahydrofuran are weighed by mass fraction. The others are the same as one to nine.

[0064] The beneficial effects of the present application are verified by the following examples:

[0065] Example one:

[0066] A preparation method of a multi-acrylate-based self-initiating and self-repairing photocuring resin, which is carried out by the following steps:

[0067] I. 15 parts of isophorone diisocyanate, 0.5 parts of dibutyl tin dilaurate, 10 parts of hydroxyl-terminated liquid polybutadiene rubber, 9 parts of bis(2-hydroxyethyl) disulfide, 0.5 parts of hydroquinone, 9 parts of pentaerythritol triacrylate and 60 parts of tetrahydrofuran are weighed by mass fraction;

[0068] II. Under the conditions of nitrogen atmosphere and stirring, the weighed 15 parts of isophorone diisocyanate, 0.5 parts of dibutyl tin dilaurate and 20 parts of tetrahydrofuran are mixed to obtain an IPDI solution;

[0069] III. Under the conditions of nitrogen atmosphere and stirring, the weighed 10 parts of hydroxyl-terminated liquid polybutadiene rubber is dissolved in 20 parts of tetrahydrofuran to obtain an HTPB solution. Under the conditions of nitrogen atmosphere and stirring, the HTPB solution is added to the IPDI solution at a drop adding speed of 4s / drop. After drop adding, the reaction is carried out at a temperature of 80℃ for 2h to obtain a reaction system A;

[0070] IV. Under the conditions of nitrogen atmosphere and stirring, the weighed 9 parts of bis(2-hydroxyethyl) disulfide is dissolved in 10 parts of tetrahydrofuran to obtain an HEDS solution. Under the conditions of nitrogen atmosphere and stirring, the HEDS solution is added to the reaction system A at a drop adding speed of 4s / drop. After drop adding, the reaction is carried out at a temperature of 80℃ for 2h to obtain a reaction system B;

[0071] V. Under the conditions of nitrogen atmosphere and stirring, the weighed 0.5 parts of hydroquinone and 9 parts of pentaerythritol triacrylate are dissolved in 10 parts of tetrahydrofuran to obtain a PETA solution. Under the conditions of nitrogen atmosphere and stirring, the PETA solution is added to the reaction system B at a drop adding speed of 4s / drop. After drop adding, the reaction is carried out at a temperature of 80℃ for 5h to obtain a multi-acrylate-based self-initiating and self-repairing photocuring resin, which is named as PUA-S1 resin.

[0072] Wherein the raw material isophorone diisocyanate is abbreviated as IPDI, tetrahydrofuran is abbreviated as THF, dibutyltin dilaurate is abbreviated as DBTDL, hydroxyl-terminated liquid polybutadiene rubber is abbreviated as HTPB, bis(2-hydroxyethyl) disulfide is abbreviated as HEDS, hydroquinone is abbreviated as HQ, and pentaerythritol triacrylate is abbreviated as PETA.

[0073] Figure 1 The synthesis route of the multi-acrylate-based self-initiating and self-repairing photocuring resin of Example One; the preparation of the multi-acrylate-based self-initiating and self-repairing photocuring resin is carried out in a 100 mL three-necked flask equipped with mechanical stirring and a constant-pressure dropping funnel, under the conditions of N2 atmosphere and oil bath heating.

[0074] Example Two: The difference between this example and Example One is that in Step One, 12 parts of bis(2-hydroxyethyl) disulfide are weighed; in Step Four, under the conditions of nitrogen atmosphere and stirring, 12 parts of bis(2-hydroxyethyl) disulfide weighed are dissolved in 10 parts of tetrahydrofuran to obtain an HEDS solution; and in Step Five, the multi-acrylate-based self-initiating and self-repairing photocuring resin obtained is named as PUA-S2 resin. The others are the same as in Example One.

[0075] Example Three: The difference between this example and Example One is that in Step One, 13 parts of bis(2-hydroxyethyl) disulfide are weighed; in Step Four, under the conditions of nitrogen atmosphere and stirring, 13 parts of bis(2-hydroxyethyl) disulfide weighed are dissolved in 10 parts of tetrahydrofuran to obtain an HEDS solution; and in Step Five, the multi-acrylate-based self-initiating and self-repairing photocuring resin obtained is named as PUA-S3 resin. The others are the same as in Example One.

[0076] Comparative Experiment: The difference between this comparative experiment and Example One is that bis(2-hydroxyethyl) disulfide is replaced by 1,6-hexanediol; and the photocuring resin obtained in Step Five is named as PUA-S0 resin. The others are the same as in Example One.

[0077] Wherein the PUA-S1 resin, the PUA-S2 resin, the PUA-S3 resin and the PUA-S0 resin are collectively referred to as PUA-S resin.

[0078] The PUA-S resins prepared in Examples One to Three and the comparative experiment are subjected to performance testing, wherein infrared, nuclear magnetic, Raman, and gel permeation chromatography (GPC) are used to test the resins in liquid state (uncured state), and the rest of the experiments are used to test the resins in solid state (cured state).

[0079] Wherein the curing process of the PUA-S1 resin, the PUA-S2 resin and the PUA-S3 resin prepared in Examples One to Three is as follows: under the condition that the distance between the high-pressure mercury lamp and the resin is 15 cm, the resin is irradiated for 3 min.

[0080] The curing process of PUA-S0 resin prepared by comparative experiment: TPO was added to PUA-S0 resin, and the mass percentage of TPO in PUA-S0 resin was 3%. Then, it was irradiated for 3 minutes under the condition of high pressure mercury lamp and the distance between the lamp source and the resin was 15 cm.

[0081] (1) Structural characterization of polyacrylate-based self-initiating and self-healing photocurable resins:

[0082] Figure 2 Infrared spectra, A) HEDS and IPDI, B) HTPB and PUA-S resins; infrared analysis was performed on the raw materials HEDS and IPDI, such as... Figure 2 As shown in A). Where 2950cm -1 The broad peak at 646 cm⁻¹ is related to the stretching vibration of -CH₂. -1 The absorption peak is related to the stretching vibration of SS, and IPDI is at 2243 cm⁻¹. -1 The absorption peak is related to the -NCO group. The infrared spectra of HTPB and a series of PUA-S resins are shown in Figure 2B). HTPB shows an absorption peak at 3341 cm⁻¹. -1 The broad absorption peak at 3330 cm⁻¹ is related to -OH. After the reaction, PUA-S resin showed some new absorption peaks. -1 A distinct absorption peak appeared at 1529 cm⁻¹, which is related to the stretching vibration of -NH₃. -1 The absorption peak is related to the bending vibration of -NH-. (1706 cm⁻¹) -1 The peak at 1633 cm corresponds to -C = O. -1 and 779cm -1 The absorption peak at 2243 cm⁻¹ is attributed to -C=CH₂. The PUA-S resin at this peak is at -C=CH₂. -1 The absorption peak at 646 cm⁻¹ completely disappeared, indicating that the -NCO groups had reacted completely. Furthermore, the absorption peaks of PUA-S1, PUA-S2, and PUA-S3 resins at 646 cm⁻¹... -1 The broad absorption peak observed is related to SS. These results demonstrate that disulfide bonds have been introduced into the molecular chain of the self-healing resin, and PUA-S resin has been synthesized.

[0083] Figure 3PUA-S1, PUA-S2, PUA-S3 resins have similar chemical structure. Several characteristic peaks at 5.7-6.4 ppm (1, 1', 2) are attributed to the protons on the acrylate groups, several characteristic peaks around 0.8-1.1 ppm (3, 4, 5, 6) and 1.7 ppm (7, 8) correspond to the protons on the IPDI. The characteristic peaks at 4.9 ppm (10) and 5.4 ppm (9) correspond to the protons on the -CH=CH- in the main chain, respectively. The peak at 2.9 ppm (11) corresponds to the protons on the -CH2- connected to the urethane bond, and the peak at 3.7 ppm (12) corresponds to the protons on the -CH2-S, PUA-S0 resin has almost no characteristic peak at this position. The above results prove that the PUA-S resins have been successfully synthesized.

[0084] Figure 4 The Raman spectrum of PUA-S resins; PUA-S1 resin, PUA-S2 resin, PUA-S3 resin can be observed at 510 cm -1 The stretching vibration peak of -S-S- is obviously observed, and the characteristic peaks at 640 cm -1 The vibration peak of -C-S- appears, while the control PUA-S0 resin without -S-S- does not have characteristic peaks at these two positions, which indicates that the disulfide bond has been successfully introduced into the molecular chain of PUA-S1 resin, PUA-S2 resin, PUA-S3 resin.

[0085] Figure 5 The GPC spectrum of PUA-S resins, A) is the GPC curve, B) is the molecular weight distribution; the molecular weight of the polymer plays an important role in the performance of the polymer. The molecular weight and molecular weight distribution (M w / M n ) of PUA-S resins were analyzed by GPC. It is found that the molecular weight of PUA-S resins is between 5300 and 7200, with no large fluctuations, and the GPC curve of PUA-S resins is shown in Figure 5 A). The molecular weight distribution of PUA-S0 resin, PUA-S1 resin, PUA-S2 resin and PUA-S3 resin is 7.7, 3.9, 3.7 and 3.34, respectively. The control PUA-S0 resin without disulfide bond has the widest molecular weight distribution, and the molecular weight distribution of PUA-S1 resin, PUA-S2 resin and PUA-S3 resin containing disulfide bond is more than 3, and the molecular weight distribution slightly decreases with the increase of disulfide bond content, as shown in Figure 5B) shown. This may be related to the formation of long chains between small molecule diols (HEDS or 1,6-hexanediol). After the reaction of HTPB with IPDI, the -NCO at the end of its own molecular chain is easily embedded, leading to difficulty in reacting with small molecule diols. Therefore, after the addition of small molecule diols, small molecule diols themselves are easy to react with IPDI to form chain segments of different lengths, so the molecular weight distribution of the polymer is relatively wide. With the increase of the number of small molecule diols, the chain segments formed by them become longer, the molecular weight gradually increases, and it is close to or even equal to PUA-S resin, so the molecular weight distribution has a downward trend with the increase of HEDS content.

[0086] (2) Polymerization mechanism of multi-acrylate self-initiating and self-repairing light-cured resin:

[0087] Figure 6 The polymerization principle diagram of PUA-S resin; the bond energy of disulfide bond is relatively low, about 250 KJ / mol. Under the irradiation of ultraviolet light, -S-S- can be broken to generate sulfur free radicals, thereby initiating free radical polymerization. In the preparation of PUA-S resin, by adding bis(2-hydroxyethyl) disulfide, the disulfide bond structure is inlaid on the main chain of the resin. Under the irradiation of ultraviolet light, PUA-S resin generates sulfur free radicals, which act as initiators. The end of PUA-S resin has acrylate structure, which can occur polymerization under the action of free radicals, thereby forming crosslinking points and curing.

[0088] (3) Thermal stability test:

[0089] Figure 7For thermal stability of PUA-S resin, A) thermal weight loss curve, B) thermal weight loss rate curve; from TG curve, it can be known that the thermal degradation curve trend of PUA-S1 resin, PUA-S2 resin and PUA-S3 resin cured sample is basically the same, but the thermal stability of PUA-S1 resin is slightly higher than that of PUA-S2 resin and PUA-S3 resin, which is related to the content of disulfide bond. The bond (251 KJ / mol) of disulfide bond is smaller than that of -C-C- (347 KJ / mol), and the more the content, the worse the thermal stability. From the DTG curve, it can be found that the thermal decomposition of PUA-S1 resin, PUA-S2 resin and PUA-S3 resin mainly presents three thermal degradation stages. The first thermal degradation stage is between 210-290℃, which is mainly the disulfide bond breaking stage, and the more the content of disulfide bond, the higher the peak value; the second thermal degradation stage is between 290-390℃, which is mainly caused by the breaking of urethane bond; the third thermal degradation stage is between 390-493℃, which is mainly caused by the breaking of polybutadiene main chain and acrylate structure. The percentage content of acrylate in PUA-S1 resin is higher, so the peak value of PUA-S1 resin at this place will be higher than that of PUA-S0 resin, PUA-S2 resin and PUA-S3 resin.

[0090] The thermal degradation data of PUA-S resin is arranged as shown in Table 1. When the degradation mass is 5%, the temperature of PUA-S0 resin is 94.9℃, and the temperature of PUA-S1 resin, PUA-S2 resin and PUA-S3 resin is all above 150℃, which is mainly due to the volatilization of unreacted small molecular substances, solvents and the like in the system. When the thermal degradation mass is 10%, the thermal degradation temperature of PUA-S resin is all around 250℃, which indicates that it has good thermal stability.

[0091] Table 1 Thermal degradation data table of PUA-S resin

[0092]

[0093] T da : Temperature when the thermal degradation mass is a%; T dmaxb : b-stage thermal degradation rate peak value.

[0094] (4) Light transmittance test:

[0095] Figure 8 Light transmittance curve of PUA-S resin; Figure 9The transmittance of PUA-S1 resin is about 80%, which is better than that of PUA-S resin. The cured sample is colorless and transparent, so it has a high transmittance. The color logo of "Northeast Forestry University" can be clearly seen through the 1 mm thick cured sample.

[0096] (5) DSC test:

[0097] Figure 10 The DSC curve of PUA-S resin; from the figure, the T g of PUA-S resin is below 70℃. This is because the molecular main chain structure contains cyclic compounds, which not only reduces the flexibility of the molecular main chain, but also reduces the proportion of single bonds that can rotate within the chain. In addition, the presence of -NH-COO- bonds also makes the rotation of the molecular chain severely hindered, so the T g of PUA-S resin is significantly higher than that of HTPB liquid rubber. PUA-S resin has only one obvious endothermic peak, indicating that there is no obvious phase separation in the system.

[0098] (6) Mechanical property test:

[0099] The cured sample of PUA-S resin was cut with a blade, then one half of the sample was placed on a glass slide and fixed with tape, then it was placed at an angle of 70° in an oven, and the remaining half of the resin was aligned with the fixed resin along the cut, relying on its own gravity to make full contact between the two, and finally heated at 85℃ for 8h. It was found that the two cut resins healed together. The healed resin has certain mechanical properties and can lift a 100g weight; Figure 11 The PUA-S1 resin self-healing physical picture and the physical picture of lifting the weight after healing.

[0100] Figure 12 The repair process of PUA-S resin is shown in the figure. After UV irradiation, the resin cures and forms a crosslinked structure. Due to the restriction of molecular chain movement, there are unreacted acrylate structures in the system. After heating, the molecular chain segment movement ability is enhanced, and mutual diffusion occurs. Since the damaged part of the object contains disulfide bonds, the disulfide bonds will break and recombine under heat stimulation, causing molecular chain exchange, thereby achieving self-repair. In addition, the disulfide bond will produce sulfur free radicals after heating and breaking, which will activate the acrylate structure and cause polymerization again, forming new molecular chains and promoting the self-healing process. The initiation polymerization process is shown in Figure 13 .

[0101] Figure 14The stress-strain curves of PUA-S resins before and after healing, A) is PUA-S0 resin, B) is PUA-S1 resin, C) is PUA-S2 resin, D) is PUA-S3 resin; the control group PUA-S0 resin without disulfide bond occurs ductile fracture, although it has higher tensile strength (11.7 MPa) and elongation at break (176%), but no self-repairing performance. After adding disulfide bond, PUA-S1 resin, PUA-S2 resin and PUA-S3 resin occur brittle fracture, their elongation at break are all < 5%, and their tensile strength only decreases slightly, which are 3.14 MPa, 3.1 MPa and 2.98 MPa respectively. This is because although the increase of disulfide bond content can accelerate the photocuring reaction rate and form more crosslinking points, but the bond energy of -S-S- is smaller than that of -C-C-. According to the theory of molecular fracture, the macroscopic fracture of polymer corresponds to the microcosmic chemical bond fracture, when subjected to external force, the activation energy barrier of chemical bond fracture is reduced, and the -S-S- with smaller bond energy is preferentially broken, so after adding disulfide bond, the tensile strength of PUA-S1 resin, PUA-S2 resin and PUA-S3 resin decreases slightly. Under the condition of heating at 85℃ for 8h, the tensile strength of PUA-S1 resin, PUA-S2 resin and PUA-S3 resin after healing is 2.1 MPa, 2.47 MPa and 2.68 MPa respectively, which indicates that with the increase of disulfide bond content, the healing effect is better.

[0102] Figure 15 The healing efficiency of PUA-S resin; its calculation formula is shown as formula (1).

[0103]

[0104] With the increase of disulfide bond content, the healing efficiency gradually increases. When the disulfide bond content is 5%, the healing efficiency of PUA-S1 resin is 66.9%, when the content is 8%, the healing efficiency of PUA-S2 resin is 78.8%, and when the disulfide bond content is 10%, the healing efficiency of PUA-S3 resin is 89.8%.

[0105] The calculation formula of disulfide bond is shown as formula (2).

[0106]

[0107] In the formula, the molecular weight of disulfide bond is 64, the molecular weight of HEDS is 154.25, and the purity of HEDS is 90%.

[0108] (7) Optical microscope test:

[0109] Figure 16The scratch changes of PUA-S resin under optical microscope were observed. The changes of cross scratch were observed by optical microscope to study the self-repairing performance. One scratch was deeper (white arrow direction) to determine the scratch position, and the other scratch (white frame) was used to observe the healing. After heating at 85℃ for 8h, when the disulfide bond content was 0% (PUA-S0), both of the two scratches had almost no change, and when the disulfide bond was added, both of the two scratches were obviously reduced. When the disulfide bond content was 5% (PUA-S1), the scratch in the white frame was almost completely healed, and the deep scratch also had healing signs; when the disulfide bond content was 8% (PUA-S2), the scratch in the white frame almost disappeared, and the deep scratch was also obviously healed; when the disulfide bond content was 10% (PUA-S3), both of the two scratches almost disappeared. This indicates that the healing ability is enhanced with the increase of disulfide bond content, and when the disulfide bond content is 8%, the healing ability is better, and the effective healing can be achieved for the deep damage and the superficial damage on the surface.

[0110] (8) Wood coatings:

[0111] The surface of Fraxinus mandshurica veneer (24cm x 17cm x 3.8mm) was polished clean along the wood grain with sandpaper (1500 mesh), and then the PUA-S resin was directly brushed on the Fraxinus mandshurica veneer for film performance test.

[0112] The hardness of the film was determined according to the standard GB / T6739-2006, and the lead pencils used for testing included B-6H, and the hardness increased in turn, in which 6H was the highest.

[0113] The adhesion of the film was tested according to the standard GB / T9286-1998 "Paint and varnish - Cross-hatch test of paint films", and the adhesion grade decreased from 0 to 5 in turn.

[0114] The gloss was tested by WGG-60 digital gloss meter according to the standard ISO 2813, and each group of samples was tested three times, and the average value was taken.

[0115] The roughness of the film was measured by Surtronic Duo surface roughness meter, and each group of samples was tested three times, and the average value was taken.

[0116] The solvent wiping resistance test was carried out according to the standard GB / T 23989-2009, and the hand wiping method (A method) was used, and the solvents were ethanol, acetone and toluene.

[0117] Table 2 Performance of the film

[0118]

[0119] Figure 17This is a photograph of the actual product after PUA-S resin coating gloss test; the gloss of the wood board after resin coating was measured by the instrument to be between 23-45°. This is because the cured sample is colorless and transparent, with high light transmittance and low light intensity reflection.

[0120] Figure 18 The image shows the actual product after pencil hardness testing of the PUA-S resin coating film. The PUA-S coating films exhibit high pencil hardness, almost all reaching a 6H rating, with PUA-S3 resin having the lowest pencil hardness at 4H. This is a result of the combined effect of the -NH-COO- hard segment structure and the cross-linking structure. The presence of -NH-COO- makes it difficult for the molecular chains of PUA-S resin to rotate, and the cross-linking points also restrict the movement of the molecular chains, thus resulting in the high hardness of the PUA-S coating film. However, as the percentage of PETA in the resin decreases, the cross-linking density decreases, leading to a slight decrease in the pencil hardness of PUA-S3 resin.

[0121] Figure 19 The image shows the actual product after the adhesion test of the PUA-S resin coating film; the results show that the adhesion grade of the PUA-S resin coating film is Grade 1. This is because -NH-COO- has strong polarity and high surface energy, thus resulting in good adhesion.

[0122] Figure 20 The photos show the solvent resistance of the PUA-S1 resin coating film after wiping (after 200 wipings with toluene). The solvent resistance of the PUA-S coating film was tested with ethanol, acetone and toluene respectively. Ethanol and acetone can achieve more than 500 wipings without change. When wiping with toluene, obvious swelling occurs after 200 wipings. Further wiping will damage and peel off the coating film.

Claims

1. A method for preparing a polyacrylate-based self-initiating, self-healing photocurable resin, characterized in that... It is done in the following steps:

1. Weigh out 9 to 15 parts by weight of isophorone diisocyanate, 0.5 to 1 part of dibutyltin dilaurate, 8 to 15 parts of hydroxyl-terminated liquid polybutadiene rubber, 7 to 13 parts of bis(2-hydroxyethyl) disulfide, 0.2 to 0.5 parts of hydroquinone, 5 to 10 parts of pentaerythritol triacrylate and 30 to 60 parts of tetrahydrofuran; 2. Under a nitrogen atmosphere and with stirring, 9 to 15 parts of isophorone diisocyanate, 0.5 to 1 part of dibutyltin dilaurate and 10 to 20 parts of tetrahydrofuran are mixed to obtain an IPDI solution.

3. Under a nitrogen atmosphere and with stirring, 8 to 15 parts of hydroxyl-terminated liquid polybutadiene rubber were dissolved in 10 to 20 parts of tetrahydrofuran to obtain an HTPB solution. The HTPB solution was added dropwise to an IPDI solution under a nitrogen atmosphere and with stirring at a dropping rate of 1 to 7 drops. After the addition, the reaction was carried out at a temperature of 50°C to 90°C for 2 to 4 hours to obtain reaction system A. IV. Under a nitrogen atmosphere and with stirring, 7 to 13 parts of bis(2-hydroxyethyl) disulfide were dissolved in 5 to 10 parts of tetrahydrofuran to obtain an HEDS solution. The HEDS solution was added dropwise to reaction system A at a dropping rate of 2 to 7 seconds per drop under a nitrogen atmosphere and with stirring. After the addition, the reaction was carried out at a temperature of 80 to 90 degrees Celsius for 2 to 4 hours to obtain reaction system B.

5. Under a nitrogen atmosphere and with stirring, dissolve 0.2 to 0.5 parts of hydroquinone and 5 to 10 parts of pentaerythritol triacrylate in 5 to 10 parts of tetrahydrofuran to obtain a PETA solution. Add the PETA solution dropwise to reaction system B at a dropping rate of 2 to 7 seconds per drop under a nitrogen atmosphere and with stirring. After the addition, react at a temperature of 80 to 90 degrees Celsius for 4 to 6 hours to obtain a polyacrylate-based self-initiating and self-healing photocurable resin.

2. The method for preparing a polyacrylate-based self-initiating, self-healing photocurable resin according to claim 1, characterized in that... In step one, weigh out 15 parts isophorone diisocyanate, 0.5 parts dibutyltin dilaurate, 10 parts hydroxyl-terminated liquid polybutadiene rubber, 9 parts bis(2-hydroxyethyl) disulfide, 0.5 parts hydroquinone, 9 parts pentaerythritol triacrylate and 60 parts tetrahydrofuran according to the following mass proportions.

3. The method for preparing a polyacrylate-based self-initiating, self-healing photocurable resin according to claim 1, characterized in that... In step one, weigh out 15 parts isophorone diisocyanate, 0.5 parts dibutyltin dilaurate, 10 parts hydroxyl-terminated liquid polybutadiene rubber, 12 parts bis(2-hydroxyethyl) disulfide, 0.5 parts hydroquinone, 9 parts pentaerythritol triacrylate and 60 parts tetrahydrofuran according to the following mass proportions.

4. The method for preparing a polyacrylate-based self-initiating, self-healing photocurable resin according to claim 1, characterized in that... In step one, weigh out 15 parts isophorone diisocyanate, 0.5 parts dibutyltin dilaurate, 10 parts hydroxyl-terminated liquid polybutadiene rubber, 13 parts bis(2-hydroxyethyl) disulfide, 0.5 parts hydroquinone, 9 parts pentaerythritol triacrylate and 60 parts tetrahydrofuran according to the following mass proportions.

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