Tri-functional crosslinking system based on glycerol and its applications

Abstract

The present application relates to the technical field of high polymer materials, and particularly relates to a glycerol-based trifunctional crosslinking system and application thereof. Glycerol is added into a round-bottom flask, (meth)acrylic acid isocyanylethyl ester is added dropwise under continuous stirring, and the crosslinking system is obtained after reacting for 3 hours at room temperature. A crosslinking agent tetra (3-mercaptopropionic acid) pentaerythritol ester is added into the trifunctional crosslinking system, and a urethane-based adhesive containing the crosslinking agent is prepared through curing. The urethane-based adhesive prepared by the present application has a trifunctional network structure, and thus the problems of poor water resistance and poor high-temperature resistance are solved, and the method of the present application is environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a trifunctional crosslinking system based on glycerol and its applications. Background Technology

[0002] Polyurethane adhesives have a wide range of bonding capabilities, exhibiting excellent chemical adhesion to porous materials such as foam plastics, wood, leather, and ceramics, as well as smooth-surfaced materials such as metals, glass, and plastics. They also possess excellent flexibility, low-temperature resistance, and outstanding cushioning and shock absorption functions, making them suitable for bonding substrates with different coefficients of thermal expansion.

[0003] However, polyurethane adhesives also have limitations that cannot be ignored, with poor water resistance being one of their most prominent shortcomings. Most water-based polyurethane adhesives have a linear thermoplastic structure, containing hydrophilic groups in their molecular chains, resulting in poor water resistance. Furthermore, insufficient heat resistance is another major limiting factor. Except for specially modified varieties, ordinary polyurethane adhesives generally cannot withstand temperatures above 100°C and cannot withstand prolonged heat exposure. Summary of the Invention

[0004] To overcome the technical problems mentioned in the background art, this invention provides a trifunctional crosslinking system based on glycerol, and uses it to prepare high-performance urethane-based adhesives, solving the problem of poor water and heat resistance of linear thermoplastic polyurethane structures. Fiberglass boards cured and bonded at 120°C showed no significant change in bonding performance after being immersed in water for 10 days; similarly, fiberglass boards cured and bonded under the same conditions, when reheated to 160°C and held at that temperature for 2 hours, also showed no significant change in bonding performance after cooling to room temperature.

[0005] The trifunctional crosslinking system based on glycerol in this invention is obtained by reacting glycerol with isocyanate monomers at room temperature, and the reaction formula is as follows:

[0006]

[0007] Among them, the isocyanate monomers are ethyl isocyanate methacrylate (IEM) or ethyl isocyanate acrylate (AOI).

[0008] The preparation method of the trifunctional crosslinking system based on glycerol is as follows: weigh glycerol and add it to a two-necked round-bottom flask equipped with anhydrous calcium chloride drying tail tube, place a magnetic stir bar, and then slowly add isocyanate monomers into the flask while stirring continuously. After the addition is complete, react at room temperature for 3 hours. During the experiment, the reaction solution is always a transparent colorless solution.

[0009] The molar ratio of glycerol to isocyanate is 1:3.

[0010] The reaction principle of the crosslinking system (monomer 1) prepared by isocyanate monomer ethyl isocyanate is as follows: glycerol molecules have three hydroxyl groups, while ethyl isocyanate (IEM) molecules contain one isocyanate group (-NCO). This isocyanate group will undergo an addition reaction with the hydroxyl groups to form a carbamate bond. The synthesis reaction equation is shown in Formula 1-1.

[0011]

[0012] Equation 1-1: Reaction equation for monomer 1

[0013] The reaction principle of the crosslinking system (monomer 2) prepared by isocyanate monomer ethyl isocyanate acrylate is as follows: IEM is replaced by ethyl isocyanate acrylate (AOI). AOI has olefin bonds, its structure belongs to acrylate, and it does not have α-methyl. Its reactivity is often higher than that of the methacrylate structure of IEM. The synthesized product is a trifunctional monomer with three acrylate groups and three-armed ends. The synthesis reaction equation is shown in Formula 1-2.

[0014]

[0015] Equation 1-2: Reaction equation for monomer 2

[0016] The trifunctional crosslinking system of the present invention is used to prepare urethane-based adhesives; the preparation method is to add a crosslinking agent to the trifunctional crosslinking system and cure it to obtain urethane-based adhesives.

[0017] The crosslinking agent is pentaerythritol tetrakis(3-mercaptopropionic acid); the curing temperature is 100℃-120℃, and the curing time is 2 h-6 h.

[0018] The thiol-alkene crosslinking reaction was achieved through a thermally initiated free radical mechanism. Pentaerythritol tetrakis(3-mercaptopropionic acid) ester was selected as the tetrafunctional thiol compound and thermosetting with a synthesized urethane monomer containing terminal alkene bonds. Under heating conditions, the thiol group was activated to generate free radicals, initiating an addition reaction with the alkene bond, gradually forming a three-dimensional network structure. The reaction equations are shown in Equations 1-3.

[0019]

[0020] Beneficial effects:

[0021] This invention synthesizes two crosslinkable monomers based on glycerol (triol) and two isocyanate-containing olefin monomers (IEM, AOI), and uses mercapto-olefin click reaction as a thermosetting crosslinking method to prepare a high-performance urethane-based adhesive.

[0022] The polyurethane-based adhesive prepared in this invention, due to its trifunctional network structure, effectively solves the problem of poor water resistance. Fiberglass boards bonded by thermal polymerization of monomer 1 at 120°C for 4 hours, after being immersed in water for 10 days, still exhibit a maximum tensile strength of 2600-2700 N, showing little change from the initial tensile strength before immersion. Furthermore, since this polymerization reaction is carried out at 100-120°C in a bulk polymerization process without the use of other solvents, it is relatively environmentally friendly and possesses good high-temperature resistance. Fiberglass boards bonded by thermal polymerization at 120°C for 4 hours were reheated to 160°C, held at that temperature for 2 hours, and then cooled to room temperature; their mechanical properties showed no significant changes. Attached Figure Description

[0023] Figure 1 The image shows the hydrogen NMR spectrum of monomer 1.

[0024] Figure 2 The image shows the hydrogen NMR spectrum of monomer 2.

[0025] Figure 3 The image shows the hydrogen NMR spectrum of monomer 3.

[0026] Figure 4 The image shows the infrared spectrum of monomer 1 (glycerol-IEM).

[0027] Figure 5 The image shows the infrared spectrum of monomer 2 (glycerol-AOI).

[0028] Figure 6 The graphs show the tensile strength test results of monomer 1 after 2, 4, and 6 hours of thermal polymerization at 100℃.

[0029] Figure 7 The graphs show the tensile strength test results of monomer 2 after 2, 4, and 6 hours of thermal polymerization at 100℃.

[0030] Figure 8 The graph shows the tensile strength test results of monomer 1 after 2 and 4 hours of thermal polymerization at 120℃.

[0031] Figure 9 The graph shows the tensile strength test results of monomer 2 after 2 and 4 hours of thermal polymerization at 120℃.

[0032] Figure 10 The tensile strength test results are shown for monomer 1 after thermal polymerization at 120℃ for 4 hours, immersion in water, and heating to 160℃.

[0033] Figure 11 The left and right images are images of monomer 1 and monomer 2 after curing, respectively, in Experiment Example 2.

[0034] Figure 12 The two images above and below show the cured monomers 1 and 2 of Experiment Example 3, respectively. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0036] The main raw materials used in the experiment were: glycerol (Shanghai Lingfeng); ethyl isocyanate methacrylate (Shanghai Aladdin); ethyl isocyanate acrylate (Shanghai Aladdin); and pentaerythritol tetrakis(3-mercaptopropionic acid) ester (Shanghai Mairui).

[0037] Example 1

[0038] Weigh 0.460 g (0.005 mol) of glycerol and add it to a two-necked round-bottom flask equipped with anhydrous calcium chloride drying tail tube. Place a magnetic stir bar in the flask and then slowly add 2.123 mL (0.015 mol) of isocyanate methacrylate into the round-bottom flask while stirring continuously. After the addition is complete, react at room temperature for 3 hours. During the experiment, the reaction solution remains a transparent and colorless solution. The reaction yields monomer 1.

[0039] The 1H NMR spectrum of monomer 1 shows a singlet signal at δ1.93 ppm, representing the α-methyl group (-CH3) on the methacrylate. Multiplet signals are observed at δ3.51-3.57 ppm, generated by the methylene hydrogen (-CH2-) on the glycerol backbone. A similar multiplet signal appears at δ4.08-4.19 ppm, originating from the methylene hydrogen (-CH-) on the glycerol backbone. Another multiplet signal is observed at δ4.26-4.33 ppm, originating from the hydrogen (-O-CH2-) on the ethylene group attached to the ester group. Singlet signals are present at δ5.58 ppm and δ6.12 ppm, representing the two hydrogens (=CH2) on the methacrylate double bond. A broad peak around δ5.18 ppm indicates the hydrogen on the -NH- group in the carbamate bond. These main peaks conform to the carbamate structure, and the product is monomer 1.

[0040] Analysis of the infrared spectra of monomer 1, the starting material glycerol, and IEM reveals that the starting material glycerol has an infrared spectrum at approximately 3400 cm⁻¹. -1 The broad and strong OH absorption peak at 3340 cm⁻¹ was significantly weakened, while the absorption peak at approximately 3340 cm⁻¹ was also significantly weakened. -1 A new, relatively sharp absorption peak appeared at approximately 2280 cm⁻¹, which is attributed to the stretching vibration of the NH group in the newly formed carbamate bond. The original IEM image shows an absorption peak at approximately 2280 cm⁻¹. -1 The weakening of the characteristic absorption peak of -NCO at 1530 cm⁻¹ indicates a reaction between the isocyanate and hydroxyl groups. -1A new intermediate-intensity absorption peak appeared, which is attributed to the combined absorption of the NH bending vibration and CN stretching vibration in the urethane bond. Based on the changes in the above characteristic peaks, it can be clearly concluded that glycerol and IEM synthesized a trifunctional crosslinked monomer containing urethane bonds and terminal olefin bonds via an isocyanate-hydroxyl reaction.

[0041] Example 2

[0042] Weigh 0.460 g (0.005 mol) of glycerol and add it to a two-necked round-bottom flask equipped with anhydrous calcium chloride drying tail tube. Place a magnetic stir bar in the flask and then slowly add 2.02 mL (0.015 mol) of ethyl isocyanate acrylate into the round-bottom flask while stirring. After the addition is complete, continue the reaction at room temperature for 3 hours. During the experiment, the reaction solution is always a clear and colorless liquid. After the reaction is completed, monomer 2 is obtained.

[0043] The 1H NMR spectrum of monomer 2 shows that the multiplet signals at δ4.10-4.20 ppm represent the methylene and methine hydrogens (-CH2- and -CH-) on the glycerol backbone, the multiplet signals at δ4.24-4.32 ppm represent the hydrogens (-O-H2-) on the ethylene group adjacent to the ester group, the multiplet signals at δ5.87 ppm, δ6.15 ppm and δ6.45 ppm represent the three hydrogens (=CH2 and =CH-) on the acrylate double bond, and the broad peak near δ5.30 ppm represents the hydrogen on the -NH- in the carbamate bond. Compared with monomer 1, there is no methyl signal near δ1.9 ppm here, and the double bond region shows the three sets of splitting peaks characteristic of acrylate. The main peak is consistent with the expected carbamate structure, and the product is monomer 2.

[0044] The infrared spectral characteristics of monomer 2 are basically consistent with those of monomer 1, reflecting a similar chemical reaction nature. The following key changes were also observed in this spectrum: the starting material glycerol showed a change at approximately 3400 cm⁻¹. -1 The broad OH peak at approximately 3340 cm⁻¹ is significantly reduced. -1 A new NH absorption peak is generated at 2280 cm⁻¹; the raw material AOI has a new NH absorption peak at 2280 cm⁻¹. -1 The -NCO characteristic peak at 1720 cm⁻¹ is somewhat weakened; -1 The strong C=O peak at 1635 cm⁻¹ was preserved. - 1 and approximately 810cm -1 The characteristic peaks of the olefin bond at the alkene bond were also preserved, which is sufficient to show that glycerol and AOI did indeed react and produce the expected product.

[0045] Analysis of both infrared spectroscopy and proton nuclear magnetic resonance spectroscopy shows that both target monomers have been successfully synthesized and their structures have been clarified, providing a material basis for subsequent operations and performance studies.

[0046] Comparative Example 1

[0047] Weigh 0.761 g (0.01 mol) of 1,2-propanediol and add it to a two-necked round-bottom flask equipped with anhydrous calcium chloride drying tail tube. Place a magnetic stir bar in the flask and then slowly add 2.83 mL (0.02 mol) of isocyanate methacrylate to the round-bottom flask while stirring. After the addition is complete, continue the reaction at room temperature for 3 hours. During the experiment, the reaction solution is always a clear, transparent, and colorless liquid. After the reaction is completed, monomer 3 is obtained.

[0048] The reaction principle of monomer 3 is as follows: the 1,2-propanediol molecule has two hydroxyl groups, while the isocyanate ethyl methacrylate (IEM) molecule contains one isocyanate group (-NCO). This isocyanate group will undergo an addition reaction with the hydroxyl group to form a carbamate bond. The synthesis reaction equations are shown in Equations 1-4.

[0049]

[0050] Equation 1-4: Reaction equation for monomer 3

[0051] The 1H NMR spectrum of monomer 3 shows multiple peaks at 1.07-1.15 ppm, representing the methyl group (-CH3) on the 1,2-propanediol. A single peak at 1.87 ppm represents the α-methyl group (-CH3) on the methacrylate. The peak at 3.41-4.44 ppm is generated by the methylene group (-CH2-) attached to the nitrogen atom. The multiple peaks at 3.97-4.15 ppm originate from the methine hydrogen (-CH-) on the 1,2-propanediol backbone. The multiple peaks at 4.94-5.19 ppm originate from the hydrogen (-O-CH2-) on the ethylene group attached to the ester group. Single peaks at 5.53 ppm and 6.05 ppm represent the two hydrogens (=CH2) on the double bond of the methacrylate. These main peaks conform to the urethane structure, and the product is monomer 3.

[0052] Experimental Example 1

[0053] Fiberglass sheets were used as the carrier material. 6 μL each of monomer 1 and monomer 2 were taken, and 2 μL of pentaerythritol tetrakis(3-mercaptopropionic acid) was added and thoroughly mixed. This mixture was then applied to the carrier surface, covering an area of ​​approximately 10 mm × 10 mm. The sample was clamped and placed in an oven for curing. After curing, the fiberglass sheets showed a strong bond and did not detach when gently pulled, indicating that the adhesive has good bonding strength.

[0054] The fiberglass board specimen coated with monomer prepolymer was mounted into the clamping device of the universal testing machine. The loading rate was set to 5 mm / min, the bonding area was 10 mm × 10 mm, the thickness and width of the fiberglass board were entered, and the test was started. The stress-strain curve of the specimen under tensile load over time was recorded. The shear strength was calculated using the formula τ = Fmax / A, where Fmax is the maximum tensile force and A is the bonding area.

[0055] Figure 5 This is a comparison chart of tensile strength tests for monomer 1 (glycerol-IEM) cured at 100℃ for 2, 4, and 6 hours. The sample cured for 2 hours showed a maximum tensile strength of 2339 N and a shear force of 2339 N / 100 mm. 2 =23.4 MPa; the maximum tensile strength of the sample after 4 hours of thermal polymerization was 2483 N, and the shear force was 2483 N / 100 mm. 2 = 24.8 MPa; the maximum tensile strength of the sample after 6 hours of thermal polymerization is 2588 N, and the shear force is 2588 N / 100 mm. 2 = 25.8 MPa. As the curing time increased from 2 hours to 6 hours, the shear strength of monomer 1 showed a continuous upward trend, but the increase gradually decreased: the strength increased by 1.4 MPa from 2 to 4 hours, which is about 6.0%, while it only increased by 0.14 MPa from 4 to 6 hours, which is about 4.0%. This shows that at 100 °C, the crosslinking reaction of monomer 1 is basically completed after 4 hours. Continuing the curing time further will result in smaller additional benefits from improved performance.

[0056] Figure 6 This display shows the tensile strength of monomer 2 (glycerol-AOI) under different curing conditions, with the temperature set at 100℃ and curing times of 2 hours, 4 hours, and 6 hours. The specimen that underwent thermal polymerization for 2 hours exhibited a maximum tensile strength of 1190 N, from which the calculated shear force was 1190 N / 100 mm². 2 =11.9 MPa; the maximum tensile strength of the specimen after 4 hours of thermal polymerization was 1671 N, and its shear force was 1671 N / 100 mm. 2= 16.7 MPa; while the maximum compressive stress of the specimen after 6 hours of thermal polymerization is 1429 N, and the shear force is also calculated using this formula to be 1429 N / 100 mm. 2 = 14.3 MPa.

[0057] It is noteworthy that the shear strength of monomer 2, after reaching its peak (16.7 MPa) after 4 hours of curing, actually decreased to 14.3 MPa after 6 hours of curing. This phenomenon may be related to the high reactivity of the system: the acrylate structure of AOI lacks α-methyl groups, and its double bond reactivity is higher than that of the methacrylate structure of IEM. At 100 ℃, the crosslinking reaction rate of monomer 2 is relatively fast, forming a network with a high crosslinking density after 4 hours. However, if heated to 6 hours, the adhesive mechanical properties decrease slightly. This phenomenon indicates that for highly reactive systems, there is an optimal curing time range, and a longer heat curing time is not necessarily better. The experimental data shows that after 4 hours of curing at 100 ℃, the adhesive strength of monomer 1 still slightly increased, but monomer 2 showed varying degrees of performance decline after 4 hours of curing.

[0058] Figure 7 This is a comparison chart of tensile strength tests performed on monomer 1 (glycerol-IEM) after curing at 120℃ for 2 hours and 4 hours respectively. The sample that underwent thermal polymerization for 2 hours had a maximum tensile strength of 2637 N, which translates to a shear force of 2637 N / 100 mm. 2 = 26.4 MPa; while the maximum tensile strength of the sample after 4 hours of thermal polymerization is 2749 N, and the corresponding shear force is 2749 N / 100 mm² = 27.5 MPa.

[0059] Figure 8 This is a comparison of the tensile strength of monomer 2 (glycerol-AOI) at 120℃ for 2 hours and 4 hours of curing time. The sample that has been thermally polymerized for 2 hours has a maximum stress of 2054 N and a shear stress of 2054 N / 100 mm. 2 =20.5 MPa; the maximum stress that the sample withstood after 4 hours of thermal polymerization was 2503 N, and its shear stress was 2503 N / 100 mm. 2 =25.0 MPa.

[0060] Experiment Example 2

[0061] Using a glass plate as a carrier material, 6 μL each of monomer 1 and monomer 2 were respectively aspirated. Figure 11The left and right images show the cured monomers 1 and 2, respectively. Then, 2 μL of pentaerythritol tetrakis(3-mercaptopropionic acid) was added and mixed evenly. This mixture was then coated onto the carrier surface, covering an area of ​​approximately 25 mm × 25 mm. The sample was clamped and placed in an oven for curing at 120℃ for 2 hours. After curing, a simple test was performed. It was found that the glass plate was completely bonded, and the bonded portion was transparent. A 100 g weight was applied, and the plate held firmly. Applying greater force caused the glass plate to break from the non-bonded portion.

[0062] Experimental Example 3

[0063] Using galvanized iron sheets as carrier materials, 6 μL each of monomer 1 and monomer 2 were respectively absorbed. Figure 12 The two images above and below show the cured monomers 1 and 2, respectively. Then, add 2 μL of pentaerythritol tetrakis(3-mercaptopropionic acid) and mix evenly. Then, apply it to the surface of the carrier, covering an area of ​​approximately 10 mm × 10 mm. Clamp the sample and place it in an oven to perform the curing operation. When the temperature reaches 120°C, the curing process is complete. At this point, the adhesion between the galvanized iron sheets is very strong, and no detachment occurs when manually pulled.

[0064] Experiment Example 4

[0065] Using galvanized iron sheet as the substrate, the bonding area is 10mm × 10mm (i.e., 100mm). 2 After undergoing thermal polymerization at 120℃ for 2 hours and 4 hours respectively, the maximum tensile strength and shear strength are shown in the table below.

[0066] Table 1. Maximum tensile and shear strength of each monomer at different curing times at 120℃

[0067] Glycerol-IEM 2 h 1508 15.1 Glycerol-IEM 4 h 1589 15.9 Glycerol-AOI 2 h 1216 12.2 Glycerol-AOI 4 h 1378 13.8 1,2-Propylene Glycol - IEM 2 h 984 9.8 1,2-Propylene Glycol - IEM 4 h 1045 10.4

[0068] Experimental Example 5

[0069] Using fiberglass board as the carrier material, monomer 1 (glycerol-IEM) was thermocured at 120℃ for 4 hours. After cooling, it was immersed in tap water for 10 days, then removed and air-dried. Tensile strength testing was performed, and the maximum tensile strength of the sample was 2644 N, which translates to 2644 N / 100 mm². 2 = 26.4 MPa.

[0070] Experimental Example 6

[0071] Using fiberglass board as the carrier material, monomer 1 (glycerol-IEM) was thermocured at 120℃ for 4 hours, cooled to room temperature, then reheated to 160℃ and held for 2 hours, before being cooled to room temperature again to test its mechanical properties. The maximum tensile strength of the sample was 2766 N, which translates to 2766 N / 100 mm². 2 = 27.7 MPa.

Claims

1. A trifunctional crosslinking system based on glycerol, characterized in that, The crosslinking system is obtained by reacting glycerol with isocyanate monomers at room temperature, and its structural formula is: Where R is either -H or -CH3.

2. The trifunctional crosslinking system based on glycerol as described in claim 1, characterized in that, The isocyanate monomer is ethyl isocyanate IEM or ethyl isocyanate AOI.

3. The trifunctional crosslinking system based on glycerol as described in claim 1, characterized in that, The preparation method of the crosslinking system is as follows: glycerol is added to a two-necked round-bottom flask containing anhydrous calcium chloride drying tail tube, a magnetic stir bar is placed in the flask, and isocyanate monomers are added dropwise under continuous stirring. After the addition is complete, the mixture is reacted at room temperature for 3 hours to obtain a trifunctional crosslinking system based on glycerol.

4. The trifunctional crosslinking system based on glycerol as described in claim 3, characterized in that, The molar ratio of glycerol to isocyanate is 1:

3.

5. An application of the trifunctional crosslinking system based on glycerol as described in claim 1, characterized in that, The trifunctional crosslinking system is used to prepare urethane-based adhesives.

6. The application of the trifunctional crosslinking system based on glycerol as described in claim 5, characterized in that, The method for preparing the urethane-based adhesive is to add a crosslinking agent to a trifunctional crosslinking system and then cure it to obtain the urethane-based adhesive.

7. The application of the trifunctional crosslinking system based on glycerol as described in claim 6, characterized in that, The crosslinking agent is pentaerythritol tetrakis(3-mercaptopropionic acid) ester.

8. The application of the trifunctional crosslinking system based on glycerol as described in claim 6, characterized in that, The curing temperature is 100℃-120℃, and the curing time is 2 h-6 h.

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