A polyisoprene-based polyurethane and its preparation method

Abstract

This invention relates to a polyurethane, specifically to a polyisoprene-based polyurethane and its preparation method. This invention introduces liquid dihydroxy-terminated isoprene as a soft segment into the polyurethane system. Liquid dihydroxy-terminated isoprene has a high degree of unsaturation; using it as a soft segment can improve the flexibility and low-temperature performance of polyurethane materials, resulting in a lower glass transition temperature, which leads to a wider range of applications. Simultaneously, the unsaturated double bonds on the liquid dihydroxy-terminated isoprene molecular chain can provide chemical modification sites, thereby enabling the regulation of polyurethane material properties. This invention can control the microstructure and macroscopic properties of dihydroxy-terminated isoprene-based polyurethane by adjusting the molecular weight of the soft segment, the content of the hard segment, and the ratio of chain extender to crosslinker, providing important experimental basis and theoretical guidance for the design of high-performance polyisoprene-based polyurethane elastomers.

Description

Technical Field

[0001] This invention relates to a polyurethane, and more specifically, to a polyisoprene-based polyurethane and its preparation method. Background Technology

[0002] Polyurethane, as an important class of polymer materials, has wide applications in various fields due to its excellent mechanical properties, wear resistance, and high damping performance. Based on whether the polymer backbone contains ether or ester bonds, polyurethane can be divided into two main categories: polyether-based and polyester-based. Polyurethane elastomers typically use flexible polyether or polyester polyols as soft segments and rigid diisocyanates as hard segments. The ratio of soft to hard segments and the chemical structure significantly influence the microphase structure and macroscopic properties of polyurethane.

[0003] With the rapid development of the polyurethane industry, the demand for high-performance, multifunctional polyurethane products is increasing. Controlling the chemical structure of the soft and hard segments of polyurethane is a research hotspot in the field. Many researchers use silicone rubber or polyolefin rubber as the soft segments in the synthesis of polyurethane, thereby achieving high performance and functionalization of polyurethane.

[0004] Many researchers have used polyolefins with dual-terminated hydroxyl groups as soft segments in the synthesis of polyurethanes, resulting in high-performance polyurethane materials such as hydroxyl-terminated butadiene, butadiene-acrylonitrile copolymers, butadiene-styrene copolymers, and isoprene and other olefin-based polymers. However, existing polyurethanes synthesized using polyolefins with dual-terminated hydroxyl groups as soft segments typically have high glass transition temperatures. Summary of the Invention

[0005] To address the issue that existing polyolefin-based polyurethanes typically have high glass transition temperatures, this invention provides a polyisoprene-based polyurethane with a lower glass transition temperature.

[0006] This invention introduces liquid dihydroxy-terminated isoprene as a soft segment into a polyurethane system. Liquid dihydroxy-terminated isoprene possesses high unsaturation; using it as a soft segment improves the flexibility and low-temperature performance of polyurethane materials, resulting in a lower glass transition temperature. A lower glass transition temperature leads to a wider range of applications. Simultaneously, the unsaturated double bonds on the liquid dihydroxy-terminated isoprene molecular chain can provide chemical modification sites, thereby enabling the regulation of polyurethane material properties.

[0007] One of the objectives of this invention is to provide a polyisoprene-based polyurethane.

[0008] The polyisoprene-based polyurethane includes repeating structural units shown in Formula A, Formula B, and Formula C.

[0009]

[0010] In formula A, R0 is -CH2, -CH2CH2 or -CH(CH3), preferably -CH2;

[0011] X=15~50, Y=1~3, Z=1~4; Preferably, X=18~19, Y=1~2, Z=1~2, X=21~22, Y=1~2, Z=1~2,

[0012] X is 88-92% of the sum of X, Y, and Z, for example, 88-89% or 89-90%; preferably 88-90%.

[0013] Formula B is a structural unit derived from isocyanate, and R1 is preferably selected from...

[0014] Formula C is a structural unit derived from a small molecule diol, and R2 is preferably selected from -CH2CH2CH2CH2-.

[0015] The molar ratio of the repeating structural units shown in Formulas A, B, and C is 0.25-0.52:1:0.37-0.6, preferably 0.39-0.45:1:0.43-0.48.

[0016] The polyisoprene-based polyurethane further comprises repeating structural units as shown in Formula D;

[0017]

[0018] Formula D is a structural unit derived from a small molecule triol, and R3 is preferably selected from -CH2CR3(CH3)-CH2-.

[0019] The molar ratio of the repeating structural unit shown in Formula D to the repeating structural unit shown in Formula B is 0.042-0.068:1, preferably 0.047-0.054:1.

[0020] In the polyisoprene-based polyurethane, the repeating structural unit shown in Formula A comes from double-hydroxyl-terminated polyisoprene.

[0021] A second objective of this invention is to provide a method for preparing polyisoprene-based polyurethane as described in one of the objectives of this invention.

[0022] The preparation method of the polyisoprene-based polyurethane includes: dissolving the dehydrated double-hydroxyl-terminated polyisoprene in solvent A, adding isocyanate dissolved in solvent A, and pre-reacting for 2-5 hours; adding chain extender-catalyst solution dropwise, and reacting for 1-3 hours; and solidifying the reaction solution to obtain the polyisoprene-based polyurethane.

[0023] Both the pre-reaction and the reaction were carried out under a nitrogen atmosphere and at 75-85°C.

[0024] The chain extender-catalyst solution comprises a chain extender, a catalyst, and solvent A;

[0025] When the polyisoprene-based polyurethane contains the repeating structural unit shown in formula D, the chain extender-catalyst solution also contains a crosslinking agent.

[0026] The dehydration process for hydroxyl-terminated polyisoprene is a standard procedure. For example, the hydroxyl-terminated polyisoprene is heated to 110°C and then vacuumed for 2 hours to remove water.

[0027] The reaction mechanism is as follows: Dihydroxyl-terminated polyisoprene polymerizes with isocyanate to form a polyurethane prepolymer. Upon addition of a chain extender, the two ends of the chain extender connect to the polyurethane prepolymer and / or isocyanate, while the polyurethane prepolymer and / or isocyanate continue to polymerize, ultimately forming a linear polyurethane linked together by the chain extender. In the presence of a crosslinking agent, the three hydroxyl ends of the crosslinking agent connect to one or more of the polyurethane prepolymer, isocyanate, and linear polyurethane, while the polyurethane prepolymer and / or isocyanate continue to polymerize, ultimately forming a crosslinked polyurethane linked together by the crosslinking agent.

[0028] The isocyanate is selected from one or more of 4,4-diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, and dicyclohexylmethane diisocyanate.

[0029] The chain extender is selected from small molecule diols, preferably 1,4-butanediol.

[0030] The crosslinking agent is selected from small molecule triols, preferably trimethylolpropane or glycerol.

[0031] Solvent A is selected from one or more of tetrahydrofuran, dioxane, dichloromethane, and dimethylformamide (DMF).

[0032] The catalyst is selected from organotin or tertiary amine catalysts; preferably, dibutyltin dilaurate (T-12) is an organotin catalyst.

[0033] A method for preparing polyisoprene-based polyurethane includes: heating hydroxyl-terminated polyisoprene to 105-115℃, evacuating for 2-3 hours to remove water, then lowering the temperature to 75-85℃, adding tetrahydrofuran to dissolve the hydroxyl-terminated polyisoprene, adding 4,4-diphenylmethane diisocyanate dissolved in tetrahydrofuran, and reacting for 2-5 hours to prepare a prepolymer. The reaction is carried out under a nitrogen atmosphere. 1,4-butanediol, a chain extender dissolved in tetrahydrofuran, and dibutyltin dilaurate, a catalyst, are added dropwise to the reaction solution. If preparing a crosslinked polyurethane, trimethylolpropane, a crosslinking agent, is added simultaneously. After reacting for another 1-3 hours, the reaction solution is poured into a tetrafluoroethylene mold, placed at room temperature for 10-14 hours, and then cured in a vacuum oven at 75-85℃. The reaction process is illustrated below:

[0034]

[0035] in represent

[0036] The structural formula of the double-hydroxyl-terminated polyisoprene is shown in formula (I);

[0037]

[0038] In formula (I),

[0039] R can be -CH2OH, -CH2CH2OH, or -CH(CH3)OH, with -CH2OH being the preferred option.

[0040] X=15~50, Y=1~3, Z=1~4; Preferably, X=18~19, Y=1~2, Z=1~2, X=21~22, Y=1~2, Z=1~2,

[0041] X is 88-92% of the sum of X, Y, and Z, preferably 88-90%.

[0042] In formula (I), X is 88-92% of the sum of X, Y and Z; that is, in the homopolymer isoprene unsaturated segments containing the three polyisoprene, the molar ratio of 1,4-polyisoprene is 88-92%.

[0043] Preferably, the structural formula of the hydroxyl-terminated polyisoprene is:

[0044] in,

[0045] X=15~50, Y=1~3, Z=1~4; for example, X=18~19, Y=1~2, Z=1~2, X=21~22, Y=1~2, Z=1~2, X=33~34, Y=1~2, Z=2~3 or

[0046] X is 88-90% of the sum of X, Y, and Z, for example, 88-89% or 89-90%.

[0047] The X, Y, and Z components in the structural formula of the double-hydroxyl-terminated polyisoprene are the same as those in the repeating structural unit shown in Formula A.

[0048] The number-average molecular weight of the hydroxyl-terminated polyisoprene liquid rubber is 1,000 to 50,000; the molecular weight distribution of the hydroxyl-terminated polyisoprene liquid rubber is less than 1.7, preferably less than 1.4.

[0049] The method for preparing the hydroxyl-terminated polyisoprene includes:

[0050] Isoprene, chain transfer agent, initiator, and solvent B are mixed and reacted under heat and pressure to obtain the double-hydroxyl-terminated polyisoprene liquid rubber; the reaction temperature is 65-130℃; the reaction pressure is 0.5-1 MPa; and the reaction time is 2-24 h.

[0051] The molar ratio of the isoprene, the chain transfer agent, the initiator, and the solvent is 100–2000:1:0.2–0.5:100–500; preferably 500–1000:1:0.3–0.5:200–400.

[0052] The structure of the chain transfer agent is shown in formula (II).

[0053]

[0054] In formula (II), R is -CH2OH, -CH2CH2OH, -CH(CH3)OH; or / and,

[0055] The initiator includes azo initiators and / or organic peroxide initiators, preferably selected from at least one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, acetophenone peroxide, and di-tert-butyl peroxide; or / and,

[0056] The solvent B is selected from at least one of dioxane, tetrahydrofuran, n-hexane, and cyclohexane.

[0057] In this invention, the hydroxyl-terminated polyisoprene is the hydroxyl-terminated polyisoprene liquid rubber described in patent application 2023112670982.

[0058] The structure of the hydroxyl-terminated polyisoprene liquid rubber is shown in formula (I).

[0059]

[0060] In formula (I), R is -CH2OH, -CH2CH2OH or -CH(CH3)OH; X = 1 to 700, Y = 1 to 100, Z = 1 to 100.

[0061] The structural formula of the hydroxyl-terminated polyisoprene liquid rubber shows that: the molecular chain of the hydroxyl-terminated polyisoprene liquid rubber has a terephthalic acid group at its center, with homopolymer isoprene unsaturated segments on both sides of the terephthalic acid group, trithioester groups on the outer sides of the homopolymer isoprene unsaturated segments, and hydroxyl groups at both ends of the molecular chain (i.e., the ends of the trithioester groups). The homopolymer isoprene unsaturated segments include three types of polyisoprene, namely 3,4-polyisoprene, 1,2-polyisoprene, and 1,4-polyisoprene, from the middle to the outer side of the chain.

[0062] The number-average molecular weight of the hydroxyl-terminated polyisoprene liquid rubber is 1,000 to 50,000; the molecular weight distribution of the hydroxyl-terminated polyisoprene liquid rubber is less than 1.7.

[0063] The preparation method of the double-hydroxyl-terminated polyisoprene liquid rubber includes:

[0064] Isoprene, a chain transfer agent, an initiator, and a solvent are mixed and reacted under heat and pressure to obtain the hydroxyl-terminated polyisoprene liquid rubber; wherein the chain transfer agent is a trithioester chain transfer agent with hydroxyl-terminated ends. Specifically, the following technical solution can be adopted:

[0065] A hydroxyl-terminated polyisoprene liquid rubber was obtained by reversible addition-fragmentation chain transfer polymerization of isoprene using a trithioester compound with dihydroxyl groups as a chain transfer agent. In the preparation method of the hydroxyl-terminated polyisoprene liquid rubber of this invention, the polymerization process is carried out in a stainless steel high-temperature and high-pressure reactor equipped with a magnetic stirrer. Isoprene, chain transfer agent, initiator, and solvent are added to the reactor. After freezing and venting, the reactor is pressurized and sealed under nitrogen, and the reaction is carried out under stirring. After the polymerization reaction is completed, the reaction liquid is dropwise into methanol solvent. The mixture is centrifuged, and the resulting solid product is dried in a high-temperature vacuum oven to obtain the hydroxyl-terminated polyisoprene liquid rubber.

[0066] The structure of the trithioester chain transfer agent with dual hydroxyl terminals is shown in formula (II).

[0067]

[0068] In formula (II), R is -CH2OH, -CH2CH2OH, or -CH(CH3)OH. That is, the trithioester chain transfer agent with dihydroxyl terminals is...

[0069]

[0070] Any one of them.

[0071] When the trithioester chain transfer agent with dihydroxyl terminals is At that time, the prepared double-hydroxyl-terminated polyisoprene liquid rubber was

[0072]

[0073] When the trithioester chain transfer agent with dihydroxyl terminals is At that time, the prepared double-hydroxyl-terminated polyisoprene liquid rubber was

[0074]

[0075] When the trithioester chain transfer agent with dihydroxyl terminals is At that time, the prepared double-hydroxyl-terminated polyisoprene liquid rubber was

[0076]

[0077] Technicians can select appropriate trithioester chain transfer agents with dihydroxyl terminals according to actual needs.

[0078] The initiator includes azo initiators and / or organic peroxide initiators. Preferably, the azo initiator includes azobisisobutyronitrile and / or azobisisoheptanenitrile; the organic peroxide initiator includes at least one selected from benzoyl peroxide, acetophenone peroxide, and di-tert-butyl peroxide. Those skilled in the art can select a suitable initiator according to actual needs. In another preferred embodiment of the invention, the solvent includes at least one selected from dioxane, tetrahydrofuran, n-hexane, and cyclohexane. Those skilled in the art can select a suitable solvent according to actual needs.

[0079] The molar ratio of the isoprene, the chain transfer agent, the initiator, and the solvent is 100–2000:1:0.2–0.5:100–500; preferably 500–1000:1:0.3–0.5:200–400. Those skilled in the art can select a suitable molar ratio according to actual needs.

[0080] The reaction time is 2–24 hours; the reaction temperature is 65–130℃; and the reaction pressure is 0.5–1 MPa. Technicians can select the appropriate reaction time, temperature, and pressure according to actual needs.

[0081] In the above method for preparing hydroxyl-terminated polyisoprene liquid rubber, different molecular weights of hydroxyl-terminated polyisoprene liquid rubber can be obtained by changing the reaction time or the feeding ratio of isoprene, initiator, and chain transfer agent.

[0082] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0083] This invention uses hydroxyl-terminated polyisoprene as the soft segment and a two-step method to successfully synthesize polyisoprene-based polyurethane.

[0084] This invention introduces liquid dihydroxy-terminated isoprene as a soft segment into a polyurethane system. Liquid dihydroxy-terminated isoprene possesses high unsaturation; using it as a soft segment improves the flexibility and low-temperature performance of polyurethane materials, resulting in a lower glass transition temperature. A lower glass transition temperature leads to a wider range of applications. Simultaneously, the unsaturated double bonds on the liquid dihydroxy-terminated isoprene molecular chain can provide chemical modification sites, thereby enabling the regulation of polyurethane material properties.

[0085] This invention can regulate the microstructure and macroscopic properties of dihydroxy-terminated isoprene polyurethane by adjusting the molecular weight of the soft segment, the content of the hard segment, and the ratio of chain extender to crosslinker, providing important experimental basis and theoretical guidance for the design of high-performance polyisoprene polyurethane elastomers.

[0086] The polyisoprene-based polyurethane provided by this invention has a low glass transition temperature and excellent low-temperature resistance, maintaining good stability in low-temperature environments. Furthermore, it exhibits superior dynamic mechanical properties, with a low loss factor and energy dissipation, effectively reducing wear. Attached Figure Description

[0087] Figure 1 DSC curves of linear polyisoprene-based polyurethane elastomers with different soft segment molecular weights prepared in Examples 1-3;

[0088] Figure 2 Stress-strain curves of linear polyisoprene-based polyurethane elastomers with different soft segment molecular weights prepared in Examples 1-3;

[0089] Figure 3 DMA curves of linear polyisoprene-based polyurethane elastomers with different soft segment molecular weights prepared in Examples 1-3;

[0090] Figure 4 DSC curves of cross-linked polyisoprene-based polyurethane elastomers with different hard segment contents prepared in Examples 4-6;

[0091] Figure 5Stress-strain curves of cross-linked polyisoprene-based polyurethane elastomers with different hard segment contents prepared in Examples 4-6;

[0092] Figure 6 DMA curves of linear polyisoprene-based polyurethane elastomers with different soft segment molecular weights prepared in Examples 4-6;

[0093] Figure 7 DSC curves of cross-linked polyisoprene-based polyurethane elastomers prepared in Examples 4, 7, and 8 with different ratios of chain extender and cross-linker.

[0094] Figure 8 Stress-strain curves of cross-linked polyisoprene-based polyurethane elastomers prepared in Examples 4, 7, and 8 with different ratios of chain extender and cross-linker.

[0095] Figure 9 DMA curves of linear polyisoprene-based polyurethane elastomers with different soft segment molecular weights prepared in Examples 4, 7, and 8;

[0096] Figure 10 The hydroxyl-terminated polyisoprene (HTPI) prepared in Example 1 1 H NMR spectrum;

[0097] Figure 1 , 4 In Figure 7, the horizontal axis represents temperature (°C), and the vertical axis represents heat flow rate dH / dt (mW).

[0098] Figure 2 , 5 In Figure 8, the horizontal axis represents strain (%) and the vertical axis represents stress (MPa).

[0099] Figure 3 , 6 In Figure 9, the horizontal axis represents temperature (°C), the left vertical axis represents the energy storage modulus E', and the right vertical axis represents the loss factor tanδ.

[0100] In this context, HTPI-1800-LPU represents the linear polyisoprene-based polyurethane elastomer with a soft segment molecular weight of 1800 prepared in Example 1; HTPI-3000-LPU represents the linear polyisoprene-based polyurethane elastomer with a soft segment molecular weight of 3000 prepared in Example 2; and HTPI-3900-LPU represents the linear polyisoprene-based polyurethane elastomer with a soft segment molecular weight of 3900 prepared in Example 3.

[0101] HS represents hard segment, SS represents soft segment, CPU represents cross-linked polyisoprene polyurethane elastomer, B represents chain extender, and T represents cross-linking agent; the subscripts of HS, SS, B and T represent relative molar numbers. Detailed Implementation

[0102] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0103] In the following examples, all reagents used were commercially available products.

[0104] Among them, di-tert-butyl peroxide (DTBP) is from Bailingwei.

[0105] Example 1

[0106] (1) Add 0.1 mol of tripotassium phosphate monohydrate, 0.1 mol of 2-mercaptoethanol, and acetone to a 1000 mL round-bottom flask. After stirring for 10 min, add 0.3 mol of carbon disulfide. The solution turns bright yellow. Then add 0.05 mol of 1,4-bis(bromomethyl)benzene dissolved in acetone to the round-bottom flask and react for 2 h. After the reaction is complete, filter the solution. Concentrate the filtrate under reduced pressure and recrystallize to obtain 1,4-phenylenebis(methylene)bis(2-hydroxyethyl)bis(trithiocarbamate) (PMHD).

[0107] (2) Take 5 mmol of 1,4-phenylenebis(methylene)bis(2-hydroxyethyl)bis(trithiocarbamate) (PMHD) (prepared in step (1), 50 mL of dioxane (dioxane), 125 mmol of isoprene, and 1.5 mmol of initiator di-tert-butyl peroxide (DTBP) into a polymerization tube. The polymerization tube was degassed by a three-cycle freezing-vacuuming-thawing process and then sealed and pressurized to 0.5 MPa under nitrogen protection. The polymerization tube was stirred (500 rpm) and reacted at 125 °C for 6 hours. After the reaction, the precipitation-centrifugation-dissolution process was repeated three times in methanol. Finally, the obtained product was vacuum dried to obtain the pure product, hydroxyl-terminated polyisoprene (HTPI). 1 H NMR (such as H NMR) Figure 10 The structural formula of the double-hydroxyl-terminated polyisoprene liquid rubber can be confirmed as follows:

[0108]

[0109] In the formula, X = 18–19, Y = 1–2, and Z = 1–2; X is 88–89% of the sum of X, Y, and Z. The number-average molecular weight is approximately 1800, and the molecular weight distribution is 1.37.

[0110] (3) Heat 2 mmol of HTPI prepared in step (2) to 110℃, evacuate for 2 h to remove water, then lower the temperature to 70℃, add 30 mL of tetrahydrofuran to dissolve the HTPI, add 3.82 mmol of 4,4-diphenylmethane diisocyanate (MDI) dissolved in tetrahydrofuran and react for 2 h. The reaction is carried out under a nitrogen atmosphere. After the prepolymer preparation is completed, continue to add 1.64 mmol of chain extender 1,4-butanediol (BDO) dissolved in tetrahydrofuran and 126 μL of catalyst dibutyltin dilaurate (DY-12) dropwise to the reaction solution, and continue to react for 1 h. After the reaction is completed, pour the reaction solution into a tetrafluoroethylene mold, place it at room temperature for 12 h, and then cure it in a vacuum oven at 80℃ for 24 h. A linear polyisoprene-based polyurethane elastomer (HTPI-1800-LPU) with a soft segment molecular weight of 1800 is obtained, and the mass ratio of hard segment (HS) to soft segment (SS) is 25:75. The mass ratio of hard segment (HS) to soft segment (SS) is calculated as the ratio of the sum of the masses of isocyanate, crosslinking agent, and chain extender to the sum of the total masses of isocyanate, crosslinking agent, chain extender, and polyisoprene.

[0111] Example 2

[0112] (1) 5 mmol of 1,4-phenylenebis(methylene)bis(2-hydroxyethyl)bis(trithiocarbamate) (PMHD) (prepared in Example 1), 50 mL of dioxane (50 mL), 275 mmol of isoprene, and 1.5 mmol of initiator di-tert-butyl peroxide (DTBP) were added to a polymerization tube. The tube was degassed using a three-cycle freeze-vacuum-thaw process, and then sealed and pressurized to 0.5 MPa under nitrogen protection. The polymerization tube was stirred (500 rpm) and reacted at 125 °C for 6 hours. After the reaction, the product was subjected to a three-cycle precipitation-centrifugation-dissolution process in methanol. Finally, the product was vacuum dried to obtain the pure product, hydroxyl-terminated polyisoprene (HTPI). 1 H NMR confirmed the structural formula of the dihydroxyl-terminated polyisoprene liquid rubber as follows:

[0113]

[0114] In the formula, X = 33–34, Y = 1–2, and Z = 2–3; X is 89–90% of the sum of X, Y, and Z. The number-average molecular weight is approximately 3000, and its molecular weight distribution is 1.33.

[0115] (2) Heat 1.5 mmol of HTPI prepared in step (1) to 110°C, evacuate for 2 h to remove water, then lower the temperature to 70°C, add 30 mL of tetrahydrofuran to dissolve the HTPI, add 3.05 mmol of 4,4-diphenylmethane diisocyanate (MDI) dissolved in tetrahydrofuran and react for 2 h. The reaction is carried out under a nitrogen atmosphere. After the prepolymer preparation is completed, continue to add 1.40 mmol of chain extender 1,4-butanediol (BDO) dissolved in tetrahydrofuran and 149 μL of catalyst dibutyltin dilaurate (DY-12) dropwise to the reaction solution, and continue to react for 1 h. After the reaction is completed, pour the reaction solution into a tetrafluoroethylene mold, place it at room temperature for 12 h, and then cure it in a vacuum oven at 80°C for 24 h. A linear polyisoprene-based polyurethane elastomer (HTPI-3000-LPU) with a soft segment molecular weight of 1800 was obtained, and the mass ratio of hard segment (HS) to soft segment (SS) was 25:75.

[0116] Example 3

[0117] (1) 5 mmol of 1,4-phenylenebis(methylene)bis(2-hydroxyethyl)bis(trithiocarbamate) (PMHD) (prepared in Example 1), 50 mL of dioxane, 500 mmol of isoprene, and 1.5 mmol of initiator di-tert-butyl peroxide (DTBP) were added to a polymerization tube. The tube was degassed using a three-cycle freeze-vacuum-thaw process, and then sealed and pressurized to 0.5 MPa under nitrogen protection. The polymerization tube was stirred (500 rpm) and reacted at 125 °C for 6 hours. After the reaction, the product was subjected to a three-cycle precipitation-centrifugation-dissolution process in methanol. Finally, the product was vacuum dried to obtain the pure product, hydroxyl-terminated polyisoprene (HTPI). 1 H NMR confirmed the structural formula of the dihydroxyl-terminated polyisoprene liquid rubber as follows:

[0118]

[0119] In the formula, X = 46–47, Y = 2–3, and Z = 3–4; X is 89–90% of the sum of X, Y, and Z. The number-average molecular weight was determined to be approximately 3900, and its molecular weight distribution was 1.36.

[0120] (2) Heat 1 mmol of HTPI prepared in step (1) to 110°C, evacuate for 2 h to remove water, then lower the temperature to 70°C, add 30 mL of tetrahydrofuran to dissolve the HTPI, add 2.55 mmol of 4,4-diphenylmethane diisocyanate (MDI) dissolved in tetrahydrofuran and react for 2 h. The reaction is carried out under a nitrogen atmosphere. After the prepolymer preparation is completed, continue to add 1.43 mmol of chain extender 1,4-butanediol (BDO) dissolved in tetrahydrofuran and 129 μL of catalyst dibutyltin dilaurate (DY-12) dropwise to the reaction solution, and continue to react for 1 h. After the reaction is completed, pour the reaction solution into a tetrafluoroethylene mold, place it at room temperature for 12 h, and then cure it in a vacuum oven at 80°C for 24 h. A linear polyisoprene-based polyurethane elastomer (HTPI-3900-LPU) with a soft segment molecular weight of 3900 was obtained, and the mass ratio of hard segment (HS) to soft segment (SS) was 25:75.

[0121] Example 4

[0122] (1) 5 mmol of 1,4-phenylenebis(methylene)bis(2-hydroxyethyl)bis(trithiocarbamate) (PMHD) (prepared in Example 1), 50 mL of dioxane (50 mL), 175 mmol of isoprene, and 1.5 mmol of initiator di-tert-butyl peroxide (DTBP) were added to a polymerization tube. The tube was degassed using a three-cycle freeze-vacuum-thaw process, and then sealed and pressurized to 0.5 MPa under nitrogen protection. The polymerization tube was stirred (500 rpm) and reacted at 125 °C for 6 hours. After the reaction, the product was subjected to a three-cycle precipitation-centrifugation-dissolution process in methanol. Finally, the product was vacuum dried to obtain the pure product, hydroxyl-terminated polyisoprene (HTPI). 1 H NMR confirmed the structural formula of the dihydroxyl-terminated polyisoprene liquid rubber as follows:

[0123]

[0124] In the formula, X = 21–22, Y = 1–2, and Z = 1–2; X is 88–89% of the sum of X, Y, and Z. The number-average molecular weight is approximately 2100, and its molecular weight distribution is 1.31.

[0125] (2) Heat 2 mmol of HTPI prepared in step (1) to 110℃, evacuate for 2 h to remove water, then lower the temperature to 70℃, add 30 mL of tetrahydrofuran to dissolve the HTPI, add 4.45 mmol of 4,4-diphenylmethane diisocyanate (MDI) dissolved in tetrahydrofuran and react for 2 h. The reaction is carried out under a nitrogen atmosphere. After the prepolymer preparation is completed, continue to add 1.92 mmol of BDO dissolved in tetrahydrofuran, 150 μL of DY-12 and 0.21 mmol of crosslinking agent trimethylolpropane (TMP) dropwise to the reaction solution, and continue to react for 1 h. After the reaction is completed, pour the reaction solution into a tetrafluoroethylene mold, place it at room temperature for 12 h, and then cure it in a vacuum oven at 80℃ for 24 h. A crosslinked polyisoprene-based polyurethane elastomer (HS) with a soft segment molecular weight of 2100 is obtained. 25 -SS 75 -CPU); its hard segment (HS) to soft segment (SS) mass ratio is 25:75, and the chain extender to crosslinker ratio is 9:1.

[0126] Example 5

[0127] 1.5 mmol of HTPI prepared in step (1) of Example 4 was heated to 110°C and vacuum-dried for 2 hours to remove water. The temperature was then lowered to 70°C, and 30 mL of tetrahydrofuran was added to dissolve the HTPI. 2.63 mmol of 4,4-diphenylmethane diisocyanate (MDI) dissolved in tetrahydrofuran was added and reacted for 2 hours under a nitrogen atmosphere. After the prepolymer preparation was completed, 0.86 mmol of BDO dissolved in tetrahydrofuran, 107 μL of DY-12, and 0.10 mmol of crosslinking agent trimethylolpropane (TMP) were added dropwise to the reaction solution, and the reaction was continued for 1 hour. After the reaction was completed, the reaction solution was poured into a tetrafluoroethylene mold, placed at room temperature for 12 hours, and then cured in a vacuum oven at 80°C for 24 hours. A crosslinked polyisoprene-based polyurethane elastomer (HS) with a soft segment molecular weight of 2100 was obtained. 20 -SS 80 -CPU); its hard segment (HS) to soft segment (SS) mass ratio is 20:80, and the chain extender to crosslinker ratio is 9:1.

[0128] Example 6

[0129] 1.5 mmol of HTPI prepared in step (1) of Example 4 was heated to 110°C and vacuum-dried for 2 hours to remove water. The temperature was then lowered to 70°C, and 30 mL of tetrahydrofuran was added to dissolve the HTPI. 1.98 mmol of 4,4-diphenylmethane diisocyanate (MDI) dissolved in tetrahydrofuran was added and reacted for 2 hours under a nitrogen atmosphere. After the prepolymer preparation was completed, 0.33 mmol of BDO dissolved in tetrahydrofuran, 101 μL of DY-12, and 0.04 mmol of crosslinking agent trimethylolpropane (TMP) were added dropwise to the reaction solution, and the reaction was continued for 1 hour. After the reaction was completed, the reaction solution was poured into a tetrafluoroethylene mold, placed at room temperature for 12 hours, and then cured in a vacuum oven at 80°C for 24 hours. A crosslinked polyisoprene-based polyurethane elastomer (HS) with a soft segment molecular weight of approximately 2100 was obtained. 15 -SS 85 -CPU); its hard segment (HS) to soft segment (SS) mass ratio is 15:85, and the chain extender to crosslinker ratio is 9:1.

[0130] Example 7

[0131] 1.5 mmol of HTPI prepared in step (1) of Example 4 was heated to 110°C and vacuum-dried for 2 hours to remove water. The temperature was then lowered to 70°C, and 30 mL of tetrahydrofuran was added to dissolve the HTPI. 3.38 mmol of 4,4-diphenylmethane diisocyanate (MDI) dissolved in tetrahydrofuran was added and reacted for 2 hours under a nitrogen atmosphere. After the prepolymer was prepared, 1.37 mmol of BDO dissolved in tetrahydrofuran, 114 μL of DY-12, and 0.23 mmol of crosslinking agent trimethylolpropane (TMP) were added dropwise to the reaction solution, and the reaction was continued for 1 hour. After the reaction was completed, the reaction solution was poured into a tetrafluoroethylene mold, placed at room temperature for 12 hours, and then cured in a vacuum oven at 80°C for 24 hours. A cross-linked polyisoprene-based polyurethane elastomer (B6-T1-CPU) with a soft segment molecular weight of 2100 was obtained; the mass ratio of hard segment (HS) to soft segment (SS) was 25:75, and the ratio of chain extender to cross-linker was 6:1.

[0132] Example 8

[0133] 1.5 mmol of HTPI prepared in step (1) of Example 4 was heated to 110°C and vacuum-dried for 2 hours to remove water. The temperature was then lowered to 70°C, and 30 mL of tetrahydrofuran was added to dissolve the HTPI. 3.38 mmol of 4,4-diphenylmethane diisocyanate (MDI) dissolved in tetrahydrofuran was added and reacted for 2 hours under a nitrogen atmosphere. After the prepolymer was prepared, 1.15 mmol of BDO dissolved in tetrahydrofuran, 114 μL of DY-12, and 0.38 mmol of crosslinking agent trimethylolpropane (TMP) were added dropwise to the reaction solution, and the reaction was continued for 1 hour. After the reaction was completed, the reaction solution was poured into a tetrafluoroethylene mold, placed at room temperature for 12 hours, and then cured in a vacuum oven at 80°C for 24 hours. A cross-linked polyisoprene-based polyurethane elastomer (B3-T1-CPU) with a soft segment molecular weight of 2100 was obtained; the mass ratio of hard segment (HS) to soft segment (SS) was 25:75, and the ratio of chain extender to cross-linker was 3:1.

[0134] Performance testing

[0135] The thermal and mechanical properties of the polyisoprene-based polyurethane elastomers prepared in Examples 1-8 were tested. The DSC test results are as follows: Figure 1 , Figure 4 , Figure 7 As shown, the DMA test results are as follows: Figure 3 , Figure 6 , Figure 9 As shown, the stress-strain curve is as follows: Figure 2 , Figure 5 , Figure 8 .

[0136] Depend on Figure 1 , Figure 4 , Figure 7 It can be concluded that the glass transition temperatures of the polyisoprene-based polyurethanes prepared in Examples 1-8 are all below -50°C. This indicates that the polyisoprene-based polyurethanes synthesized in this invention using hydroxyl-terminated polyisoprene as the soft segment have a low glass transition temperature, excellent low-temperature resistance, and can maintain good stability in low-temperature environments.

[0137] Depend on Figure 2 , Figure 5 , Figure 8 It can be concluded that the polyisoprene-based polyurethanes prepared in Examples 1-8 have an elongation at break of up to 450° and a tensile strength of up to 11.63 MPa. This indicates that the polyisoprene-based polyurethanes synthesized in this invention using hydroxyl-terminated polyisoprene as the soft segment possess excellent mechanical properties.

[0138] Depend on Figure 3 , Figure 6 , Figure 9It can be concluded that the polyisoprene-based polyurethanes prepared in Examples 1-8 have a storage modulus of up to 2911 MPa and a loss factor close to 1. This indicates that the polyisoprene-based polyurethanes synthesized in this invention using dihydroxyl-terminated polyisoprene as the soft segment have low energy dissipation and can effectively reduce wear.

[0139] Compare Figures 1-3 It can be observed that when the content of hard segments in linear polyurethane remains constant, the continuity of the hard segment phase of polyurethane decreases with the increase of the molecular weight of the soft segments. This is manifested in a decrease in the glass transition temperature of polyurethane, a decline in mechanical properties, lower tensile strength and elongation at break, and a lower storage modulus. However, its loss factor is close to 1, meaning that the storage modulus is close to the loss modulus, indicating that polyurethane has low energy dissipation and can effectively reduce wear.

[0140] Compare Figures 4-6 It can be observed that when the molecular weight of the soft segments of cross-linked polyurethane remains unchanged, changing the content of the hard segments in the cross-linked polyurethane material does not affect the chemical structure of the polyurethane. As the content of the hard segments increases, the degree of microphase separation is higher, the polyurethane material is stronger, and it has higher tensile strength and elongation at break. The glass transition temperature of the polyurethane material increases slightly, the storage modulus decreases slightly, and the change in the thermal properties of the polyurethane material is not significant.

[0141] Compare Figures 7-9 It can be observed that when a crosslinking agent is added to form a crosslinked (three-dimensional) polyurethane, the change in the ratio of chain extender to crosslinking agent mainly affects the crosslinking density and toughness of the polyurethane. As the amount of crosslinking agent increases, the number of crosslinking points in the polyurethane network increases, the crosslinking density increases, the degree of freedom of chain segment movement is restricted, the polyurethane material tends to be rigid, and the toughness of the polyurethane material is weakened. This is manifested in the lower storage modulus and loss factor, the glass transition temperature of the polyurethane material increases slightly, and the elongation at break decreases.

Claims

1. A polyisoprene-based polyurethane, characterized in that, The polyisoprene-based polyurethane includes repeating structural units shown in Formula A, Formula B, and Formula C. Formula A Formula B Formula C In formula A, R0 is -CH2, -CH2CH2, or -CH(CH3); X=15~50, Y=1~3, Z=1~4; X is 88-92% of the sum of X, Y, and Z; Formula B is a structural unit derived from isocyanate; Formula C is a structural unit derived from a small molecule diol; The repeating structural unit shown in Formula A is derived from dihydroxyl-terminated polyisoprene, which has a number-average molecular weight of 1800-3900 g / mol. The molar ratio of the repeating structural units shown in Formulas A, B, and C is 0.25-0.52:1:0.37-0.

6.

2. The polyisoprene-based polyurethane as described in claim 1, characterized in that, The molar ratio of the repeating structural units shown in Formulas A, B, and C is 0.39-0.45:1:0.43-0.

48.

3. The polyisoprene-based polyurethane as described in claim 1, characterized in that, X is 88-90% of the sum of X, Y, and Z.

4. The polyisoprene-based polyurethane as described in claim 1, characterized in that, X=18~19, Y=1~2, Z=1~2; or, X=21~22, Y=1~2, Z=1~2; or, X=33~34, Y=1~2, Z=2~3; Or X=46~47, Y=2~3, Z=3~4.

5. The polyisoprene-based polyurethane as described in claim 1, characterized in that, In formula B, R1 is selected from , , or ; or / and, In formula C, R2 is -CH2CH2CH2CH2-.

6. The polyisoprene-based polyurethane as described in claim 1, characterized in that, The repeating structural unit shown in equation D; Formula D Formula D is a structural unit derived from a small molecule triol.

7. The polyisoprene-based polyurethane as described in claim 6, characterized in that, In formula D, R3 is -CH2CR3(CH3)-CH2-.

8. The polyisoprene-based polyurethane as described in claim 6, characterized in that, The molar ratio of the repeating structural units shown in Formula D to Formula B is 0.042-0.068:

1.

9. The polyisoprene-based polyurethane as described in claim 6, characterized in that, The molar ratio of the repeating structural units shown in Formula D to Formula B is 0.047-0.054:

1.

10. A method for preparing polyisoprene-based polyurethane as described in any one of claims 1-9, characterized in that, The preparation method includes: dissolving the dehydrated hydroxyl-terminated polyisoprene in solvent A, adding isocyanate dissolved in solvent A, and pre-reacting for 2-5 hours; adding a chain extender-catalyst solution dropwise, and reacting for 1-3 hours; and solidifying the reaction solution to obtain the polyisoprene-based polyurethane. Both the pre-reaction and the reaction were carried out under a nitrogen atmosphere and at 75-85°C. The chain extender-catalyst solution comprises a chain extender, a catalyst, and solvent A; When the polyisoprene-based polyurethane contains the repeating structural unit shown in formula D, the chain extender-catalyst solution also contains a crosslinking agent.

11. The preparation method according to claim 10, characterized in that, The isocyanate is selected from one or more of 4,4-diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, and dicyclohexylmethane diisocyanate; or / and, The chain extender is selected from small molecule diols; or / and, The crosslinking agent is selected from small molecule triols; Solvent A is selected from one or more of tetrahydrofuran, dioxane, dichloromethane, and dimethylformamide; The catalyst is selected from organotin or tertiary amine catalysts.

12. The preparation method according to claim 10, characterized in that, The chain extender is 1,4-butanediol; or / and, The crosslinking agent is trimethylolpropane or glycerol; or / and, The catalyst is dibutyltin dilaurate.

13. The preparation method according to claim 10, characterized in that, The structural formula of the double-hydroxyl-terminated polyisoprene is shown in formula (I); Equation (I) In formula (I), R is -CH2OH, -CH2CH2OH, -CH(CH3)OH; X=15~50, Y=1~3, Z=1~4; X is 88-92% of the sum of X, Y, and Z.

14. The preparation method according to claim 13, characterized in that, R is -CH2OH; X=18~19, Y=1~2, Z=1~2, X=21~22, Y=1~2, Z=1~2, X=33~34, Y=1~2, Z=2~3 or X=46~47, Y=2~3, Z=3~4; X is 88-90% of the sum of X, Y, and Z.

15. The preparation method according to claim 13, characterized in that, The molecular weight distribution of the double-hydroxyl-terminated polyisoprene is less than 1.

7.

16. The preparation method according to claim 13, characterized in that, The molecular weight distribution of the double-hydroxyl-terminated polyisoprene is less than 1.

4.

17. The preparation method according to claim 13, characterized in that, The method for preparing the hydroxyl-terminated polyisoprene includes: Isoprene, chain transfer agent, initiator, and solvent B are mixed and reacted under heat and pressure to obtain the double-hydroxyl-terminated polyisoprene liquid rubber; the reaction temperature is 65~130℃; the reaction pressure is 0.5~1MPa; and the reaction time is 2~24h. The molar ratio of the isoprene, the chain transfer agent, the initiator, and the solvent is 100~2000:1:0.2~0.5:100~500.

18. The preparation method according to claim 17, characterized in that, The structure of the chain transfer agent is shown in formula (II). Formula (II) In formula (II), R is -CH2OH, -CH2CH2OH, -CH(CH3)OH; or / and, The initiator includes azo initiators and / or organic peroxide initiators; or / and, The solvent B is selected from at least one of dioxane, tetrahydrofuran, n-hexane, and cyclohexane.

19. The preparation method according to claim 17, characterized in that, The molar ratio of the isoprene, the chain transfer agent, the initiator, and the solvent is 500~1000:1:0.3~0.5:200~400; or / and, The initiator is selected from at least one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, acetophenone peroxide, and di-tert-butyl peroxide.

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