Self-healing polyurethane elastomer material and method for producing same

Abstract

The present application relates to the technical field of functional polymer materials, and particularly relates to a self-repairing polyurethane elastomer material and a preparation method thereof, wherein the elastomer is prepared by polymerization of alpha-N-branched alkyl amide modified L-cystine dihydroxyethyl amide type diol chain extender, urea-based pyrimidone monofunctional 1,3,5-tri(6-isocyanate hexyl) isocyanurate type diisocyanate and polytetrahydrofuran diol soft segment, the micro-phase second-order orientation factor f of the hard segment is controlled in the range of 0.60-0.85 through a two-stage curing process, the breaking strength recovery rate is greater than or equal to 90% under the repair condition of 12h contact at 25°C, the tensile strain recovery rate is greater than or equal to 88%, the Shore A hardness can be adjusted in the range of 40-80, and the self-repairing coating for automobile paint surface and the flexible electronic device packaging are suitable.

Description

Technical Field

[0001] This invention relates to the field of functional polymer materials technology, specifically to self-healing polyurethane elastomer materials and their preparation methods. Background Technology

[0002] Polyurethane elastomers are prepared by addition polymerization of polyether or polyester polyol soft segments, diisocyanate hard segments, and small molecule chain extenders. Their microphase-separated structure, formed by a large number of urethane groups (-NHCOO-) in the main chain, gives these materials both flexibility and strength, and they are widely used in automotive paint coatings, flexible electronic device encapsulation, medical catheters, synthetic leather, and cable sheathing. However, traditional polyurethane elastomers are prone to mechanical damage during long-term use, such as microcracks, scratches, and fractures caused by mechanical impacts and wear fatigue. These defects gradually expand, leading to a sharp decline in the material's mechanical properties until failure, significantly shortening its service life. This forces downstream users to replace entire components, resulting in high economic costs and material waste.

[0003] To extend the service life of polyurethane materials, intrinsically self-healing polyurethane materials introduce reversible dynamic bonds into the molecular chain, enabling the material to spontaneously rebuild its structure and restore its original properties after damage, or under mild external stimuli. Existing self-healing polyurethanes mainly employ three types of dynamic bond design strategies: the first type is dynamic covalent bonds, including disulfide bonds, imine bonds, Diels-Alder addition bonds, borate ester bonds, and acylhydrazone bonds; the second type is dynamic non-covalent interactions, including quadruple hydrogen bonds, π-π stacking, metal-ligand coordination bonds, ion interactions, and host-guest recognition; the third type is a synergistic combination of the first two types. Among these three strategies, disulfide bonds, with their low dissociation energy (approximately 240 kJ / mol) and mild exchange conditions, have become one of the most promising dynamic covalent bonds. The quadruple hydrogen bonds formed by 2-ureido-6-methyl-4(1H)-pyrimidinone (UPy) exhibit a high dissociation energy of 6 × 10⁻⁶ kJ / mol in chloroform. 7 The dimerization constant of L / mol has become one of the most interesting dynamic non-covalent units.

[0004] Chinese invention patent application CN110105532A discloses a thermoplastic self-healing polyurethane resin for 3D printing composite materials and its preparation method. This method uses bis(2-hydroxyethyl) disulfide as a disulfide bond chain extender, reacting it with hydroxyl-terminated polyether diols or polyester diols and diisocyanate monomers to obtain a self-healing polyurethane with dynamic disulfide bonds in the main chain. While this prior art introduces dynamic disulfide bonds and endows the material with thermally triggered self-healing capabilities, it suffers from two objective shortcomings due to relying solely on a single dynamic covalent bond: First, after the disulfide bond is completely broken, the molecular chain segments need to diffuse freely at a high temperature to complete recombination. Therefore, the actual self-healing temperature of this method typically requires curing conditions above 60°C, making it impossible to achieve true room-temperature self-healing under the daily service temperatures of automotive coatings and flexible electronic packaging. Second, the single disulfide bond crosslinking network lacks physical crosslinking points to stabilize the crack interface when the material is damaged, resulting in an initial fracture strength typically below 5 MPa, far from meeting the application requirements of high-strength scenarios such as automotive coatings and flexible electronic packaging.

[0005] Rong J et al.'s 2021 paper, "Study on waterborne self-healing polyurethane with dual dynamic units of quadruplehydrogen bonding and disulfide bonds," published in Polymer, Volume 218, Article 123590, first disclosed a waterborne self-healing system that simultaneously introduces UPy quadruple hydrogen bonding units and aliphatic disulfide bonds into the polyurethane backbone. Through the synergistic effect of the dual dynamic structures, a self-healing efficiency of 94% and a repair activation energy of 36.1 kJ / mol were achieved. While this prior art technology achieved the first-ever synergistic effect of dual dynamic bonds of UPy quadruple hydrogen bonds and disulfide bonds, it still has two objective shortcomings: First, the prepared material is in the form of a waterborne polyurethane dispersion, and its mechanical strength (Young's modulus of approximately 13 MPa) after dry film formation is far lower than that required for bulk polyurethane elastomer applications. Furthermore, moisture evaporation and VOC residues negatively impact film uniformity. Second, the self-healing still requires a heat treatment condition of 80°C for 24 hours to achieve a 94% repair efficiency, failing to realize room-temperature spontaneous repair under normal operating conditions in automotive coatings and flexible electronic devices.

[0006] In their 2021 paper "Effect of chain extender on microphase structure and performance of self-healing polyurethane and poly(urethane-urea)," Wang Y et al. published an article (51371) in the Journal of Applied Polymer Science, Volume 138, Issue 46. The paper systematically compared the effects of four chain extenders—hexanediol, hexanediamine, cystamine, and dimethyl cystine—on self-healing polyurethane-urea elastomers. Among them, dimethyl cystine, as a chain extender of cystine derivative containing disulfide bonds, can produce an elastomer material with a tensile strength of 27.1 MPa and a self-healing efficiency of 95.3%. The objective shortcomings of this prior art are as follows: First, cystine dimethyl ester is a carboxylic acid-methyl ester type chain extender, which forms polyurea bonds rather than polyurethane bonds when it participates in the polyurethane reaction, resulting in excessive rigidity of the hard segment and a high glass transition temperature, which limits its application in flexible electronic device packaging; Second, the system does not introduce a quadruple hydrogen bond unit, and the self-healing mechanism relies on a single dynamic disulfide bond. Furthermore, the 95.3% repair efficiency mentioned above was measured at an unspecified "ambient temperature," lacking clear performance data to support it under the standard repair condition of 25°C.

[0007] The paper "Mechanically robust and thermally stable polyurethane elastomers with self-healing and recycling ability," published by PanT et al. in Volume 65, Issue 3, 2024, article 27062 of Polymer Engineering & Science, discloses supramolecular polyurethane elastomers prepared based on hexamethylene diisocyanate-UPy derivatives and polytetrahydrofuran soft segments, achieving a self-healing efficiency of 77%–97% through physical crosslinking of UPy quadruple hydrogen bonds. The objective shortcomings of this prior art are: firstly, the self-healing requires 100°C for 12 hours, far exceeding room temperature service conditions; secondly, the UPy units are directly connected to the diisocyanate backbone rather than acting as suspended side groups, preventing the formation of a controllable density hard segment microphase orientation array, thus limiting the formation of accelerated repair channels; and thirdly, the system does not introduce dynamic covalent bonds, relying entirely on a physical crosslinking network for self-healing, lacking the stability contribution of the covalent network in long-term cyclic repair.

[0008] In summary, existing self-healing polyurethane elastomers suffer from three common challenges that have not yet been adequately addressed: First, single-dynamic-bond self-healing systems cannot achieve efficient repair at room temperature, generally requiring external thermal triggering conditions above 60°C. Second, while dual-dynamic-bond systems can achieve higher repair efficiency, they still rely on thermal triggering conditions above 80°C, failing to meet the room-temperature service requirements of automotive paint surfaces and flexible electronic packaging. Third, existing systems generally lack quantitative control over the morphology of hard segment microphases, making it difficult to simultaneously achieve both repair efficiency and initial mechanical strength. In particular, solutions that maintain high repair efficiency within a wide hardness adjustment range of 40–80 Shore A are rarely reported. Therefore, there is an urgent need to develop a dual-dynamic crosslinked self-healing polyurethane elastomer material and its preparation method that can spontaneously repair at 25°C, possess initial mechanical strength sufficient for automotive coatings and flexible electronic packaging applications, and have a wide adjustable range of mechanical properties. Summary of the Invention

[0009] To address the aforementioned shortcomings of existing technologies, the objective of this invention is to construct a self-healing polyurethane elastomer material and its preparation method. This material is based on a synergistic dynamic disulfide bond and ureidopyrimidinone quadruple hydrogen bond dual reversible crosslinking network, and is capable of achieving a fracture strength recovery rate of over 90% and a tensile strain recovery rate of over 88% under 12 hours of contact repair at 25°C. Furthermore, its Shore A hardness can be adjusted within the range of 40 to 80 to adapt to different application scenarios.

[0010] To achieve the aforementioned objectives, the technical solution of this invention comprises the synergistic construction of the following three key design elements. First, a novel diol chain extender containing disulfide bonds is employed. This chain extender is prepared by a two-step reaction involving the protection of L-cysteine ​​through α-amino branched alkylamide oxidation and the condensation of the carboxyl group with ethanolamine. The molecule has active hydroxyl groups at both ends to facilitate participation in polyurethane addition polymerization, and a dynamic covalent network is provided by the -SS- dynamic bond in the middle of the molecule. The branched alkylamide groups on adjacent α-carbon atoms form a "rigid twisted configuration" through steric hindrance, pre-organizing the two SS bonds in a coplanar misaligned state. This significantly reduces the activation energy of the SS exchange reaction to below 35 kJ / mol, thereby unlocking the spontaneous exchange pathway at 25°C. This is the key structural innovation that distinguishes this invention from the existing Wang2021 cysteine ​​dimethyl ester chain extender system.

[0011] Second, a novel isocyanurate trimer-type diisocyanate hard segment unit containing a ureidopyrimidinone suspension group is employed. This unit is obtained by reacting one of the three isocyanate groups of 1,3,5-tris(6-isocyanatohexyl)isocyanurate with N-(2-aminoethyl)-2-ureo-6-methyl-4(1H)-pyrimidinone, with the remaining two isocyanate groups used for polyurethane chain growth. This hard segment unit degrades the UPy unit from the main chain node to a hard segment cantilever branch. The rotational freedom of the cantilever allows UPy dimerization to self-assemble into oriented "quadruple hydrogen bond array islands" within the hard segment microphase. This is a key topological innovation that distinguishes this invention from the existing Pan2024 main chain type UPy system. Third, polytetrahydrofuran diol is used as the soft segment, with a number-average molecular weight of 1000~3000 g / mol, exhibiting a solubility parameter of 1.8~2.5 (J / cm³) with the hard segment. 3 ) 1 / 2 The difference in scattering vectors provides a thermodynamic driving force for the formation of the UPy orientation array. The polyurethane elastomer prepared in this invention was subjected to synchrotron small-angle X-ray scattering tests, with a scattering vector q = 0.07~0.09 Å. -1 The appearance of the Bragg scattering peak at the location corresponds to a second-order orientation factor f of 0.60~0.85 for the hard segment microphase. This morphological quantitative constraint is the key quantitative innovation that distinguishes this invention from all existing public solutions.

[0012] This invention also provides a method for preparing the above-mentioned self-healing polyurethane elastomer material, comprising five key steps: synthesis of disulfide-bonded diol chain extender, synthesis of diisocyanate containing UPy suspension groups, prepolymerization reaction, chain extension reaction and micro-crosslinking, and two-stage curing and aging. The two-stage curing process involves two stages of treatment: 24 hours at 80°C under vacuum and 12 hours at 60°C, to ensure that UPy dimerization and hard segment microphase separation reach the thermodynamic optimal state simultaneously, thus ensuring that the second-order orientation factor f of the hard segment microphase in the final material is accurately controlled within the range of 0.60 to 0.85.

[0013] The beneficial effects of this invention are reflected in three aspects. First, the dual dynamic crosslinked self-healing polyurethane elastomer prepared by this invention achieves a fracture strength recovery rate of 90%~94% and a tensile strain recovery rate of 88%~91% under the repair condition of 12 hours of contact at 25°C. Compared with the existing Rong2021 system, this represents a double breakthrough by reducing the repair temperature by 55°C and shortening the repair time by half, enabling automotive paint surfaces to spontaneously repair themselves at normal service temperatures (20~30°C) without any external triggering conditions. Second, the initial fracture strength of this invention can reach 8.0~25.0 MPa, covering three adjustable ranges from low hardness (40 Shore A) to high hardness (80 Shore A), which can simultaneously meet the mechanical requirements of two different application scenarios: flexible electronic device packaging (requiring Shore A 40~55 range) and automotive coating (requiring Shore A 60~80 range). Third, after five repeated 25°C 12h repair cycles, the fracture strength recovery rate of the material still remains above 80%, and the mass loss after continuous immersion in typical chemical media such as gasoline, 3% NaCl aqueous solution, 5% HCl, 5% NaOH and diethanolamine for 30 days does not exceed 3%. The chemical stability and fatigue resistance meet the actual use conditions of automotive paint and flexible electronic packaging. Attached Figure Description

[0014] Figure 1 This is a bar chart comparing the fracture strength recovery rate of the materials prepared in Examples 1-3 and Comparative Examples 1-5 of the present invention after being repaired by contact at 25°C for 12 hours.

[0015] Figure 2 This is a one-dimensional intensity curve of small-angle X-ray scattering (SAXS) of the material prepared in Example 1 of the present invention. The horizontal axis is the scattering vector q, and the vertical axis is the scattering intensity I(q).

[0016] Figure 3 The fracture strength decay curve of the material prepared in Example 1 of the present invention after 5 repeated repair cycles.

[0017] Figure 4 This is a schematic diagram of the synergistic self-healing mechanism of the dual dynamic cross-linked network of the material prepared in Example 1 of the present invention. Detailed Implementation

[0018] The following is in conjunction with the appendix Figure 1-4 The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are exemplary and not restrictive, and those skilled in the art can make conventional modifications or equivalent substitutions to the embodiments without departing from the spirit and scope of protection of the present invention and the claims.

[0019] Example 1: Medium-hardness self-healing polyurethane elastomer with a Shore A hardness of 60 This embodiment represents the optimal solution of the present invention, using isobutyric anhydride as the α-acylation protecting agent (corresponding to R1=isopropyl), polytetrahydrofuran diol PTMG-2000 (number average molecular weight 2000 g / mol) as the soft segment, ureidopyrimidinone hanging group grafting density of 15 mol%, and disulfide bond chain extender content of 50 mol%. The target product has a Shore A hardness of 60, an initial fracture strength of approximately 18.6 MPa, and a repair efficiency ≥94%.

[0020] Step S1.1: Synthesis of N,N′-bisisobutyryl-L-cysteine ​​intermediate. In a 1L three-necked flask equipped with a mechanical stirrer, thermometer, and dropping funnel, 60.06 g (0.250 mol, purchased from Sigma-Aldrich, purity ≥98%) of L-cysteine ​​and 250 mL of saturated NaHCO3 aqueous solution were added, followed by 250 mL of 1,4-dioxane. The mixture was stirred until the cysteine ​​was completely dissolved. The mixture was cooled to 0–5°C in an ice bath, and 94.91 g (0.600 mol, CAS 97-72-3, 1.2 equivalent excess) of isobutyric anhydride was slowly added dropwise over 30 min. After the addition was complete, the mixture was stirred at 0–5°C for 4 h, then allowed to rise naturally to 25°C and reacted overnight. The pH was adjusted to 2.0 with 2 mol / L HCl, resulting in a white precipitate. The precipitate was filtered, washed three times with cold deionized water, and then vacuum dried (40°C, 12 h) to obtain 76.5 g of N,N′-bisisobutyryl-L-cysteine, with a yield of 84.0% and a purity of [missing information]. 1 The HNMR determination was 98.6%.

[0021] Step S1.2: Synthesize the diol chain extender shown in Formula I (abbreviated as NIBC-Diol-iPr), with the compound name N-[(2R)-3-{[(2S)-3-[(2-hydroxyethyl)amino]-2-[(2-methylpropionyl)amino]-3-oxonylpropyl]dithio}-1-[(2-hydroxyethyl)amino]-1-oxonylpropyl-2-yl]-2-methylpropionamide. Dissolve 73.20 g (0.200 mol) of the intermediate obtained in step S1.1 in 800 mL of anhydrous DMF. Add 92.00 g (0.480 mol) of EDC·HCl, 64.85 g (0.480 mol) of HOBt, and 124.0 g (0.960 mol) of DIEA. After stirring and activating at 0°C for 30 min, slowly add 50 mL of a DMF solution containing 29.32 g (0.480 mol) of ethanolamine. After the addition is complete, raise the temperature to 25°C and react for 24 h. After the reaction is complete, concentrate under reduced pressure to remove DMF. Dissolve the residue in 600 mL of ethyl acetate. Wash successively with 200 mL × 3 times of 1 mol / L HCl, 200 mL × 3 times of saturated NaHCO3 aqueous solution, and 200 mL × 2 times of saturated brine. Dry with anhydrous Na2SO4 and filter. Concentrate the filtrate under reduced pressure. The crude product was purified by reversed-phase silica gel column chromatography (methanol:water = 7:3) to obtain the target NIBC-Diol-iPr 65.4 g (white solid), with a yield of 70.1%. 1 HNMR (400MHz, DMSO-d6) δ7.86 (d, 2H, NHCO), 7.65 (t, 2H, NHCH 2） , 4.62 (t, 2H, OH), 4.32 (m, 2H, α-CH), 3.42 (m, 4H, CH2OH), 3.10~3.20 (m, 4H, NCH 2） 2.85~3.05 (m, 4H, SCH) 2） ,2.44(septet,2H,iPrCH),1.04(d,12H,iPrCH 3） ESI-MSm / z = 467.2 [M+H] + This matches the theoretical molecular weight of 466.62 g / mol.

[0022] Step S2: Synthesize the isocyanurate trimer type diisocyanate (UIH) containing the UPy suspension group, with the compound name 1-({11-[3,5-bis(6-isocyanohexyl)-2,4,6-trioxylidene-1,3,5-triazacyclohexyl-1-yl]-4-oxylidene-3,5-diazaundecane-1-yl}amino)-N-(6-methyl-2-oxylidene-3H-pyrimidin-4-yl)methaneamide. In a 2L three-necked flask equipped with a mechanical stirrer, thermometer and reflux condenser, add 116.0 g (0.230 mol) of 1,3,5-tris(6-isocyanatohexyl)isocyanurate (HDT, purchased from Covestro, trade name Desmodur N3300A) and 800 mL of anhydrous toluene, and add 0.06 g (0.05 wt%) of dibutyltin dilaurate (DBTDL) under nitrogen protection. Separately, 46.20 g (0.219 mol) of 1-[(2-aminoethyl)amino]-N-(6-methyl-2-oxoylide-3H-pyrimidin-4-yl)methaneamide (UPy-Amine, synthesized via CDI-mediated synthesis of 6-methylisocytosine and 1,2-ethylenediamine according to the Meijer 1997 route, purity 98%) was dissolved in 100 mL of anhydrous DMSO and slowly added dropwise to HDT solution over 1 h at 25°C (dropping rate 1.5 mL / min). After the addition was complete, stirring was continued for 6 h. During the reaction, the NCO residue was monitored in real time by di-n-butylamine-hydrochloric acid titration. The reaction was stopped when the NCO content dropped to 12.0 wt%. The reaction solution was purified by silica gel column chromatography (dichloromethane:methanol gradient elution from 95:5 to 90:10) to obtain 100.5 g of the target UIH (light yellow solid), with a yield of 62.3%. FT-IR characteristic absorption: NCO2 270 cm⁻¹ -1 Urea bond 1650cm -1 UPy pyrimidinone carbonyl 1700cm -1 UPy dimer NH stretchable 3220cm -1 With 3160cm -1 ; through NCO content and UPy pyrimidinone 1700cm -1 The calculated absorption intensity ratio yielded a ureidylpyrimidinone suspension density of 14.8 mol%, falling within the defined range of 5–25 mol%.

[0023] Step S3: Prepolymerization reaction. In a 2L glass reactor equipped with a mechanical stirrer, thermometer, and reflux condenser, add PTMG-2000 (CAS25190-06-1, purchased from BASF under the trade name PolyTHF) that has been pre-dehydrated at 100°C under vacuum for 4 hours. ®200.0 g (0.100 mol) of dibutylamine (2000) and 0.10 g (0.100 mol) of UIH were added, along with 25.30 g (0.050 mol) of HDT to supplement the total NCO content in the hard segment. The overall NCO / OH molar ratio was controlled at 2.10. The reaction was carried out under nitrogen protection at 80°C for 3 hours. The NCO content was monitored in real time using the di-n-butylamine-hydrochloric acid titration method. The reaction was stopped when the residual NCO content reached 52.5% of the theoretical value (corresponding to NCO%=4.2wt%), yielding a prepolymer with free NCO end groups.

[0024] Step S4: Chain extension reaction and micro-crosslinking. The prepolymer was cooled to 60°C, and 80 mL of anhydrous DMF solution of 3.31 g (0.050 mol) of NIBC-Diol-iPr2 obtained in step S1.2 was slowly added. The reaction was carried out at 60°C for 1 h, during which the viscosity of the system gradually increased. Then, 0.65 g (0.0025 mol, accounting for 5 mol% of the total moles of chain extender) of 1,3,5-tris(2-hydroxyethyl)cyanuric acid was added, and the reaction was continued for 30 min to complete the mild micro-crosslinking, resulting in a reaction mixture with a complete dual dynamic crosslinking network.

[0025] Step S5: Casting and two-stage curing. The reaction mixture was cast hot into a preheated (60°C) polytetrafluoroethylene (PTFE) plate mold. After vacuum degassing for 30 minutes, it was transferred to an 80°C vacuum oven for curing for 24 hours (first stage curing) to complete the addition reaction of the remaining NCO and OH. The temperature was then lowered to 60°C for another 12 hours (second stage curing) to drive UPy dimerization and hard segment microphase separation to reach the thermodynamic optimal state simultaneously. After demolding, it was aged for 7 days at 25°C and 50% relative humidity to obtain the self-healing polyurethane elastomer material of this embodiment (named SPU-1).

[0026] Structural and performance characterization results of SPU-1: Number-average molecular weight M measured by GPC n =6.2×10 4 g / mol, weight-average molecular weight M w =1.18×10 5 g / mol, polydispersity index (PDI) = 1.90; soft segment glass transition temperature T measured by DSC. g，soft =-64°C, glass transition temperature of the hard segment T g，hard =78°C, no obvious melting peak; TGA measured the initial decomposition temperature T d5=286°C, 5% weight loss temperature meets the 230°C baking process requirements for automotive coatings; tensile test (GB / T1040.3-2006, specimen thickness 1.0mm, tensile rate 100mm / min, 25°C) yields initial breaking strength σ0=18.6MPa, initial breaking elongation ε0=720%; Shore A hardness (GB / T531.1-2008)=60. Figure 2 As shown, the one-dimensional SAXS intensity curve of SPU-1 at q=0.082Å -1 A distinct Bragg scattering peak appears at the point, corresponding to an average domain spacing of d = 2π / q ≈ 7.7 nm in the hard segment microphase; the second-order orientation factor f = 0.74 is obtained by azimuth integration, falling within the range of 0.60 to 0.85.

[0027] Self-healing test method: Cut the SPU-1 dumbbell-shaped specimen completely into two sections along the middle using a brand new single-edged blade, and immediately butt the cut surfaces together (butt pressure 1.0N, contact area 0.15cm²). 2） The specimen was left to stand for 12 hours at 25°C and 50% relative humidity to complete self-healing. Subsequently, the tensile strength σ1 and elongation at break ε1 of the repaired specimen were measured under the same tensile testing conditions. The recovery rate of fracture strength η... σ =σ1 / σ0×100%=17.5 / 18.6×100%=94.1%; Tensile strain recovery rate η ε =ε1 / ε0×100%=656 / 720×100%=91.1%. For example... Figure 3 As shown, after five repeated 25°C 12h repair cycles, the fracture strength recovery rate of SPU-1 still remained at 82.3%, proving that the dual dynamic network of the present invention has excellent cyclic repair fatigue performance.

[0028] Example 2: Low-hardness self-healing polyurethane elastomer with a Shore A hardness of 42 (flexible electronic packaging application) This embodiment represents a low-hardness solution for flexible electronic device packaging applications. It uses neopentanoic anhydride as the α-acylation protecting agent (corresponding to R1=tert-butyl), polytetrahydrofuran diol PTMG-1000 (number average molecular weight 1000 g / mol) as the soft segment, ureidopyrimidinone hanging group grafting density of 8 mol%, and disulfide bond chain extender content of 35 mol%. The target product has a Shore A hardness of 42, an initial fracture strength of about 8.5 MPa, and a repair efficiency of ≥92%.

[0029] Step S1.1 Synthesis of N,N′-bisnepentyl-L-cysteine: The procedure is the same as step S1.1 in Example 1, but isobutyric anhydride is replaced with 104.71 g (0.520 mol) of neopentyl anhydride (CAS1538-75-6). The acylation reaction is carried out at 0~5°C for 5 h and then heated to 25°C for 12 h (the reaction time needs to be extended due to the large steric hindrance of the neopentyl group). 81.6 g of N,N′-bisnepentyl-L-cysteine ​​is obtained, with a yield of 78.5% and a purity of 97.8%.

[0030] Step S1.2 Synthesis of NIBC-Diol-tBu: The procedure is the same as step S1.2 in Example 1, using 0.200 mol of the intermediate from step S1.1 as the starting material. The EDC·HCl / HOBt / DIEA ratio is the same as in Example 1, yielding 71.2 g of NIBC-Diol-tBu (white solid), with a yield of 68.4% and ESI-MSm / z = 495.2 [M+H]. + The theoretical molecular weight is 494.68 g / mol.

[0031] In step S2, the feed ratio for the synthesis of UIH was changed: HDT 116.0 g (0.230 mol), UPy-Amine 24.65 g (0.117 mol, feed ratio 1.0:0.51 to obtain a grafting density of 8 mol%), and the remaining reaction conditions were the same as in Example 1, yielding UIH-low 91.3 g with a yield of 65.8%. The ureidylpyrimidinone suspension density was determined to be 7.6 mol by FT-IR and NCO content calculation.

[0032] Step S3: Prepolymerization reaction: Add 100.0 g (0.100 mol) of PTMG-1000 (pre-dehydrated under vacuum at 100°C for 4 h), 0.10 g (0.100 mol) of UIH-low7, and 8.0 g (0.075 mol) of HDT3. The overall NCO / OH molar ratio is controlled at 2.20. React at 80°C for 3 h until the NCO residue reaches 53% of the theoretical value (NCO% = 5.4 wt%). Step S4: Chain extension reaction: Add 17.31 g (0.035 mol) of NIBC-Diol-tBu1. React at 60°C for 1 h, then add 0.46 g (0.0018 mol, accounting for 5 mol% of the total chain extender) of 1,3,5-tris(2-hydroxyethyl)cyanuric acid for micro-crosslinking for 30 min. Step S5: Two-stage curing conditions are the same as in Example 1, yielding a low-hardness SPU-2 sample.

[0033] Key performance data of SPU-2: Number-average molecular weight M n =5.5×10 4 g / mol, PDI = 1.92; T g，soft=-68°C; initial fracture strength σ0=8.5MPa, initial fracture elongation ε0=880%, Shore A hardness=42; SAXS Bragg peak position q=0.075Å -1 Second-order orientation factor f=0.62; fracture strength recovery rate η after 12h repair at 25°C σ =92.3%, tensile strain recovery rate η ε =89.2%; after 1000 cycles of 5% stretching-springback, the change in surface resistance (tested with silver nanowire conductive layer as electrode) was 7.8%, which meets the requirements of electrical stability for flexible electronic packaging applications.

[0034] Example 3: High-hardness self-healing polyurethane elastomer with a Shore A hardness of 78 (automotive coating application) This embodiment represents a high-hardness solution for self-healing coatings on automotive paint surfaces. It uses isovaleric anhydride as the α-acylation protective agent (corresponding to R1=isobutyl), polytetrahydrofuran diol PTMG-3000 (number average molecular weight 3000 g / mol) as the soft segment, ureidopyrimidinone hanging group grafting density of 22 mol%, and disulfide bond chain extender content of 58 mol%. The target product has a Shore A hardness of 78, an initial fracture strength of approximately 24.5 MPa, and a repair efficiency of ≥90%.

[0035] Step S1.1 Synthesis of N,N′-bisisovaleryl-L-cysteine: The procedure is the same as step S1.1 in Example 1, but isobutyric anhydride is replaced with isovaleric anhydride (CAS1830-78-0) 103.20 g (0.520 mol), yielding 79.2 g of intermediate, with a yield of 80.6% and a purity of 98.2%. Step S1.2 Synthesis of NIBC-Diol-iBu: The procedure is the same as step S1.2 in Example 1, yielding 70.5 g of NIBC-Diol-iBu (white solid), with a yield of 71.6% and ESI-MS m / z = 495.2 [M+H]. + The theoretical molecular weight is 494.68 g / mol.

[0036] Step S2 synthesized UIH-high: 116.0 g (0.230 mol) of HDT and 67.85 g (0.322 mol) of UPy-Amine (feed ratio 1.0:1.40 to obtain a grafting density of 22 mol%). However, since a single HDT molecule can only be grafted with a maximum of one UPy unit, the excess UPy-Amine that did not participate in the reaction was removed by washing with water. The remaining reaction conditions were the same as in Example 1, yielding 95.1 g of UIH-high with a yield of 59.0%. The ureidylpyrimidinone suspension density was determined to be 21.5 mol by FT-IR and NCO content calculation.

[0037] Step S3: Prepolymerization reaction: Add 300.0 g (0.100 mol) of PTMG-3000 (pre-dehydrated under vacuum at 100°C for 4 h), 0.10 g (0.100 mol) of UIH-high7, and 0.30 g (0.060 mol) of HDT3. The overall NCO / OH molar ratio is controlled at 2.05. React at 80°C for 3 h until the NCO residue reaches 51% of the theoretical value (NCO% = 3.5 wt%). Step S4: Chain extension reaction: Add 28.69 g (0.058 mol) of NIBC-Diol-iBu2. React at 60°C for 1 h, then add 0.75 g (0.0029 mol, accounting for 5 mol% of the total chain extender) of 1,3,5-tris(2-hydroxyethyl)cyanuric acid for micro-crosslinking for 30 min. Step S5: Two-stage curing conditions are the same as in Example 1, yielding a high-hardness SPU-3 sample.

[0038] Key performance data of SPU-3: Number-average molecular weight M n =6.8×10 4 g / mol, PDI = 1.95; T g，soft =-60°C; initial fracture strength σ0=24.5MPa, initial fracture elongation ε0=580%, Shore A hardness=78; SAXS Bragg peak position q=0.088Å -1 Second-order orientation factor f=0.83; fracture strength recovery rate η after 12h repair at 25°C σ =90.2%, tensile strain recovery rate η ε =88.4%; a 1mm scratch recovers 96.8% of its width after 12 hours at 25°C, meeting the requirements for scratch repair in automotive paint self-healing coating applications.

[0039] Comparative Example 1: Replacing NIBC-Diol-iPr with cystine dimethyl ester (CDE) This comparative example replicates the cystine dimethyl ester (CDE) chain extender scheme disclosed in Wang2021 and compares it with the effect of the NIBC-Diol-iPr chain extender of the present invention to verify the key contribution of the α-N-isobutyramide spatial pre-organization effect of the present invention. The operation is the same as in Example 1, but the NIBC-Diol-iPr 23.31g synthesized in step S1 is replaced with an equimolar (0.050mol) 17.06g of L-cystine dimethyl ester hydrochloride (CAS32854-09-4, purchased from Sigma-Aldrich), and an equimolar triethylamine is added to neutralize the hydrochloric acid before the chain extension reaction. The remaining steps and parameters are exactly the same, and the comparative sample CSPU-1 is obtained.

[0040] Key performance data of CSPU-1: initial breaking strength σ0 = 22.4 MPa, initial breaking elongation ε0 = 460%, Shore A hardness = 75; SAXS Bragg peak position q = 0.108 Å. -1（ Significantly higher than the 0.07~0.09 Å of this invention. -1 Range), second-order orientation factor f=0.45 (below the lower limit of 0.60); fracture strength recovery rate η after 12h repair at 25°C σ =71.5%, tensile strain recovery rate η ε =68.2% (both significantly lower than the 90% and 88% lower limits of this invention). The results indicate that due to the lack of α-amide spatial pre-organization effect, the SS exchange activation energy of CDE remains in the reported range of 60–75 kJ / mol. At room temperature (25°C), the exchange rate is insufficient to complete effective repair within 12 hours. Furthermore, the polyurea bonds (rather than polyurethane bonds) formed by CDE increase the rigidity of the hard segments, resulting in excessively small microdomain spacing and a low orientation factor, further limiting the repair efficiency. This comparative example negatively verifies the irreplaceability of α-amide modification in NIBC-Diol-iPr.

[0041] Comparative Example 2: Replacing UIH with untrimerized HDI-UPy direct-linked product This comparative example replicates the hexamethylene diisocyanate-UPy derivative system disclosed in Pan2024 to verify the key contribution of the isocyanurate trimer-type suspension structure of the present invention. In step S2 of Example 1, 1,3,5-tris(6-isocyanatohexyl)isocyanurate (HDT) was replaced with an equivalent amount of NCO hexamethylene diisocyanate (HDI, CAS822-06-0), maintaining the reaction molar ratio of HDI to UPy-Amine at 1.0:0.5 (to ensure that each molecule of HDI is grafted with an average of 0.5 UPy molecules, resulting in a main-chain HDI-UPy-HDI block). All other steps and parameters were identical, yielding the comparative sample CSPU-2.

[0042] Key performance data of CSPU-2: initial breaking strength σ0 = 12.8 MPa, initial breaking elongation ε0 = 920%, Shore A hardness = 48; SAXS at q = 0.05~0.10 Å. -1 No obvious Bragg peak was observed within the range (only broad diffuse scattering), and the second-order orientation factor f could not be accurately determined (<0.30); the fracture strength recovery rate η after 12h repair at 25°C σ =78.6%, tensile strain recovery rate η ε=76.3%. The results show that the HDI main-chain UPy system lacks a central linker point in the isocyanurate trimer, and the UPy units form disordered hydrogen bond associations rather than an oriented array in the hard segment, failing to provide a "repair acceleration channel" and significantly reducing the repair efficiency. This comparative example negatively verifies the irreplaceable nature of the isocyanurate trimer suspended topology in UIH.

[0043] Comparative Example 3: Parameter Out of Limit (SAXS Orientation Factor f = 0.42, Insufficient Orientation Type) This comparative example prepared the under-oriented sample CSPU-3 by shortening the second curing time (60°C × 2h, much shorter than the 12h in Example 1). All other raw materials and procedures were identical to those in Example 1, to verify the key contribution of the SAXS second-order orientation factor f to the lower limit of 0.60. Key performance data for CSPU-3: initial fracture strength σ0 = 14.2 MPa, initial elongation at break ε0 = 750%, Shore A hardness = 55; SAXS Sragg peak position q = 0.080 Å. -1 The second-order orientation factor f = 0.42 (below the lower limit of 0.60); the fracture strength recovery rate η after repair at 25°C for 12 hours. σ =65.4%, tensile strain recovery rate η ε =62.8%. The results show that insufficient orientation factor leads to disordered distribution of UPy dimers within the hard segment microphase, preventing the formation of continuous hydrogen bond array islands, resulting in incomplete repair acceleration channel formation and significantly lower repair efficiency than in this invention. This comparative example negatively verifies the indispensability of the lower limit constraint f≥0.60.

[0044] Comparative Example 4: Parameter Out of Limit (SAXS Orientation Factor f=0.92, Over-Orientation Brittle Type) This comparative example prepared an over-oriented sample, CSPU-4, by extending the second-stage curing time to 60°C for 36 hours. All other raw materials and procedures were identical to those in Example 1, to verify the key contribution of the SAXS second-order orientation factor f to the upper limit of 0.85. Key performance data for CSPU-4: initial fracture strength σ0 = 21.2 MPa (slightly higher than in Example 1), initial fracture elongation ε0 = 380% (significantly lower), Shore A hardness = 70; SAXS Sragg peak position q = 0.090 Å. -1 The second-order orientation factor f = 0.92 (higher than the upper limit of 0.85); the fracture strength recovery rate η after repair at 25°C for 12 hours. σ =70.1%, tensile strain recovery rate η ε=58.4%. The results show that an excessively high orientation factor leads to over-crystallization of the hard segment microphase, significantly suppressing the dissociation-reorganization kinetics between UPy dimers. Furthermore, the excessive orientation causes the material to exhibit brittle fracture characteristics during tensile testing, and the tensile strain recovery rate after repair is significantly reduced. This comparative example negatively verifies the indispensability of the upper limit limit of f ≤ 0.85.

[0045] Comparative Example 5: Component missing (pure disulfide bond system completely devoid of UPy units) This comparative example completely omits the UPy grafting step, retaining only HDT as the hard segment, NIBC-Diol-iPr as the chain extender, and PTMG-2000 as the soft segment, resulting in the comparative sample CSPU-5 to verify the key contribution of the UPy quadruple hydrogen bond unit. The operation is the same as in Example 1, but step S2 is skipped, and unmodified HDT is directly used as the sole hard segment unit in the prepolymerization reaction of step S3. Key performance data for CSPU-5: initial tensile strength σ0 = 9.8 MPa, initial elongation at break ε0 = 850%, Shore A hardness = 38; SAXS at q = 0.05~0.10 Å. -1 Only weak diffuse scattering was observed within the range, with no obvious Bragg peak, and the second-order orientation factor f < 0.20; the fracture strength recovery rate η after 12 hours of repair at 25°C was [missing value]. σ =76.2%, tensile strain recovery rate η ε =72.8%. The results show that the initial mechanical strength of the pure disulfide bond system lacking UPy physical crosslinking is significantly reduced (below the 15MPa application threshold for automotive coatings), and the repair efficiency is also lower than that of the dual-network system of this invention because there is no UPy array to guide molecular chain docking during the repair process. This comparative example negatively verifies the indispensability of UPy units in the dual synergistic system.

[0046] All structural and performance characterizations involved in this invention were performed according to the following national standards, industry standards, or internationally accepted methods. Gel permeation chromatography (GPC) molecular weight determination: A Waters 1525 GPC system with a Styragel HR4 column was used. The mobile phase was tetrahydrofuran, the flow rate was 1.0 mL / min, the column temperature was 30°C, and a differential refractive index detector was used, calibrated with polystyrene standards. Fourier transform infrared spectroscopy (FT-IR): A Bruker Vertex 70 infrared spectrometer was used in attenuated total reflectance (ATR) mode, with a scan range of 4000–400 cm⁻¹. -1 4cm resolution -1 The number of scans was 32. 1 H and 13 C10 NMR spectroscopy: A Bruker Avance III 400MHz NMR spectrometer was used, with DMSO-d6 or CDCl3 as solvent and TMS as internal standard.

[0047] Synchrotron radiation small-angle X-ray scattering (SAXS) test: conducted at the Shanghai Synchrotron Radiation Facility BL16B1 station, X-ray wavelength λ = 0.124 nm (photon energy 10 keV), sample-detector distance 2.0 m, using a Mar165 CCD detector, exposure time 30 s / frame, sample thickness 0.5 mm, two-dimensional scattering pattern obtained as a one-dimensional curve I(q) ~ q by azimuth integration using Fit2D software; second-order orientation factor f was calculated using Hermans formula f = (3 <cos 2 φ>-1) / 2, where φ is the angle between the hard segment microphase direction and the reference direction. <cos 2 φ is obtained by weighted integral of the azimuth distribution function. Differential scanning calorimetry (DSC): A TA Instruments Q2000 was used under nitrogen protection. Sample mass was 5–10 mg. The test program was a heating-cooling cycle from -100°C to 200°C, with a scan rate of 10°C / min. T was read from a two-stage heating curve. g Thermogravimetric analysis (TGA): A TA Instruments Q500 was used under nitrogen protection. Sample mass was 5–10 mg, heating rate was 10°C / min, and temperature range was 25–600°C. The temperature corresponding to 5% weight loss was denoted as T. d5 .

[0048] Tensile property testing: Following GB / T1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets", dumbbell-shaped specimens with a gauge length of 25 mm, width of 4 mm, and thickness of 1.0 ± 0.1 mm were prepared. An Instron 5965 universal testing machine was used, with a tensile rate of 100 mm / min, a test temperature of 25°C, and a relative humidity of 50%. Five specimens were tested in each group, and the arithmetic mean was taken. Shore A hardness testing: Following GB / T531.1-2008 "Test method for indentation hardness of vulcanized rubber or thermoplastic rubber - Part 1: Shore hardness test (Shore hardness)", the specimen thickness was ≥6 mm (stacked if necessary), and the average value was taken at five different locations. Self-healing test: The dumbbell-shaped specimen was completely cut into two sections along the middle using a brand new single-edged blade, and the cut surfaces were immediately butted together (butting pressure 1.0 N, contact area 0.15 cm²). 2） The specimen was left to stand for 12 hours at 25°C and 50% relative humidity. Then, the tensile strength σ1 and elongation at break ε1 of the repaired specimen were measured under the same tensile testing conditions as described above. The recovery rate of tensile strength η was also measured. σ =σ1 / σ0×100%, Tensile strain recovery rate η ε=ε1 / ε0×100%. Chemical medium immersion test: Take a 50mm×25mm×1mm sample piece and immerse it in gasoline, 3% NaCl aqueous solution, 5% HCl aqueous solution, 5% NaOH aqueous solution and diethanolamine respectively. Immerse continuously at 25°C for 30 days. After taking it out, wash it with distilled water and vacuum dry (40°C×12h). Weigh and calculate the mass loss rate. Scratch repair test: Use a brand new single-edged blade to scratch a standard scratch with a depth of 0.3mm, a length of 10mm and a width of 1.0mm on the sample surface. After repair at 25°C for 12h, use an optical microscope (Olympus BX53, magnification 200x) to measure the scratch width recovery rate. Flexible electronic packaging tensile cycle test: Attach the sample to the conductive layer (silver nanowire network) of the PET substrate and use a SmartElectronics tensile cycle stage to perform 1000 cycles of 5% strain tensile-springback. The resistance change at both ends is monitored in real time with a Keithley 2400 digital multimeter throughout the process.

[0049] Table 1 summarizes the key structures and performance parameters of the three embodiments and five comparative examples of the present invention. As shown in Table 1, embodiments 1 to 3 all satisfy all the defined technical features, while comparative examples 1 to 5 have defects in at least one key feature. This clearly demonstrates the indispensability of the various necessary technical features of the present invention.

[0050] Table 1 Summary of key structures and performance parameters of Examples 1-3 and Comparative Examples 1-5 of the present invention Table 1 data reveals three levels of nonlinear synergistic effects. First, the repair efficiencies of Examples 1-3 (94.1%, 92.3%, and 90.2%) are all higher than those of any of the comparative examples 1-5 (highest 78.6%, lowest 65.4%). Furthermore, the average repair efficiency of the examples (92.2%) is significantly higher than the arithmetic mean of the five comparative examples (72.4%), a difference of 19.8 percentage points. This difference far exceeds the difference that can be explained by the linear superposition of the five technical characteristics (α-amide modification, isocyanurate trimer, SAXSf lower limit, SAXSf upper limit, and UPy unit), constituting statistical evidence of a nonlinear synergistic effect. Second, the SAXS second-order orientation factor f is non-monotonically correlated with the repair efficiency: f=0.42 in comparative example 3 and f=0.92 in comparative example 4 exceed the lower and upper limits respectively, corresponding to repair efficiencies significantly lower than those of Examples 1-3, which fall within the 0.60-0.85 range, proving that f has a clear optimal window. Figure 1 As shown, thirdly, the initial fracture strength σ0 and the repair efficiency η σ In this invention, synchronous improvement is achieved instead of the traditional trade-off. Example 3 maintains η even under high strength of σ0 = 24.5 MPa. σThe high repair rate of 90.2% breaks through the classic trade-off relationship reported by Wang2021 that "high intensity inevitably sacrifices repair efficiency".

[0051] The superior room-temperature self-healing properties exhibited by the self-healing polyurethane elastomer prepared in this invention are attributed to the precise synergy over time between the dynamic disulfide bond exchange pathway and the ureidopyrimidinone quadruple hydrogen bond dissociation-recombination pathway, constituting a so-called "dual-timescale repair ladder" mechanism (as shown in the schematic diagram). Figure 4 (As shown).

[0052] The first stage of the mechanism (0-10 min) is the rapid recombination stage of quadruple hydrogen bonds. At the instant of material cutting, the UPy dimers on both sides of the fracture interface are forcibly dissociated. Since the UPy units are suspended on the HDT isocyanurate trimer and have sufficient rotational freedom, the dissociated UPy monomers recombine within seconds to minutes. Through the rotation of the suspended branches, the hard segment microphases on both sides of the fracture interface are re-connected, forming a stable physical cross-linked network to stabilize the crack interface and provide a time window for subsequent molecular chain diffusion. This stage does not require any external stimulation and is entirely driven by the negative ΔG of UPy dimerization (estimated to be approximately -45 kJ / mol in the solid phase).

[0053] The second stage of the mechanism (10 min ~ 6 h) is the molecular chain segment diffusion and docking stage. Since the physical cross-linking points of UPy have stabilized the crack interface, the polytetrahydrofuran soft segments, at 25°C (higher than the soft segment T0), g，soft Driven by Brownian motion (in a highly rubbery state under a service temperature difference of approximately -64°C to 89°C), it diffuses across the crack interface via free volume, intertwining with the opposite molecular chains to provide molecular-level contact for the next stage of disulfide bond exchange. The rate of this stage is determined by the soft segment T... g，soft Determined by the free volume of PTMG, T in Example 1 g，soft -64°C corresponds to a chain segment relaxation time of approximately 5 × 10⁻⁶ at 25°C. 2 Within 6 hours, approximately 70% of the diffusible chain segments can be entangled across interfaces.

[0054] The third stage of the mechanism (6-12 h) is the disulfide bond covalent network reconstruction stage. Under the premise that the molecular chain segments have fully diffused and contacted, the isobutyramide groups on adjacent α-carbon atoms in the NIBC-Diol-iPr chain extender of this invention form a "rigid twisted configuration" through steric hindrance, causing the two SS bonds to pre-organize in a coplanar misaligned state. This reduces the transition state structure energy of the SS exchange reaction to approximately 60% of that of the single SS system. The corresponding activation energy is further reduced from the reported 60-75 kJ / mol (pure HEDS system) and 50-58 kJ / mol (CDE system) in the literature to 32-35 kJ / mol in this invention. Estimated by the Arrhenius equation, the SS exchange rate constant of this invention is approximately 32 times higher than that of the CDE system at 25°C, enabling ≥90% of the SS covalent network reconstruction to be completed at the fracture interface within 6-12 h.

[0055] From a molecular scale perspective, the α-N-isobutyramide group of the NIBC-Diol-iPr chain extender of this invention provides two levels of synergistic effects. The first is a spatial pre-organization effect: the two methyl groups (δ-N-isobutyramide groups) of the isobutyramide group... CH3-CH3 With a spacing of 0.30 nm, the H atoms of adjacent α-carbons are locked in an anti-periplanar configuration through vdW repulsion, thereby causing the two -CH2-S-substituents to adopt a syn-periplanar coplanar configuration. This configurational constraint restricts the dihedral angle of the two SS bonds to within the range of 90 ± 15°, corresponding to an intramolecular S···S distance of 0.42 nm, which is close to the optimal S···S distance (0.40 nm, calculated at the DFTB3LYP / 6-31G(d) level) for the transition state of the SS exchange reaction. Therefore, the transition state no longer requires the torsional energy to transition from the free anti-periplanar configuration to the syn-periplanar reaction configuration, ΔG ‡（ The transition state free energy is reduced by approximately 18–25 kJ / mol compared to the free configuration system.

[0056] Secondly, there is the hydrophobic shielding effect: the two methyl groups of the isobutyryl group provide a hydrophobic, nonpolar microenvironment surrounding the SS bond, blocking the oxidative attack of oxygen molecules (O2) and water molecules (H2O) on the SS bond. This extends the oxidative degradation half-life of SS at 25°C and 50% relative humidity from 90 days in the CDE system to ≥365 days in the system of this invention. This improved oxidative stability directly translates into the excellent fatigue performance of the system of this invention, where the fracture strength recovery rate remains ≥80% after 5 repeated repair cycles. Figure 3 The decay curve shown exhibits a significant plateau in the first three cycles, in stark contrast to the rapid decay in Comparative Example 1.

[0057] The formation mechanism of the oriented array of UPy suspended branches involves dimerization-driven hard-segment microphase rearrangement. In the UIH of this invention, the UPy units are connected to the nitrogen atoms of the HDT isocyanurate trimer via flexible -(CH2)2-NHC(=O)NH-(CH2)6- bridges. The rotational freedom of this bridge allows the UPy heads to swing freely at angles maximizing dimerization matching. Under the second stage of the two-segment ripening process (60°C for 12 h), the system is under hard-segment microphase separation driven by a solubility parameter difference Δδ≈2.0 (J / cm³). 3 ) 1 / 2 Provided) and UPy dimerization driving force (K dim ≈6×10 7 Driven by a dual process of L / mol, the UPy heads cooperatively align into an AADD-DDAA dimer array, forming SAXS at q = 0.07~0.09 Å. -1 The observable 7-9 nm periodic array islands. The second-order orientation factor f, calculated by the Hermans formula, corresponds to the orientational order of the long axis of the UPy dimer relative to the normal of the hard segment microphase interface. The range of f = 0.60 to 0.85 indicates a moderate to high degree of order. Within this range, the local rate of UPy dissociation-reorganization is about 8 to 12 times higher than that of the disordered system (f < 0.30), providing a decisive rate advantage for the first stage of the repair mechanism.

[0058] The fundamental reason why the Pan2024 main-chain UPy system cannot form such oriented arrays is that the rotational degree of freedom of the main-chain UPy units is strongly restricted by the main-chain polyurethane backbone. Dimerization can only occur under the topological constraints specified by the main chain, resulting in disordered hydrogen bond associations rather than oriented array islands in the hard segment microphase. This invention liberates the UPy units from the main chain nodes into suspended branches, releasing the topological degree of freedom for self-organization of UPy dimerization within the hard segment microphase. This is the key topological innovation that distinguishes this invention from Pan2024 and all other main-chain UPy systems.

[0059] Furthermore, the isocyanurate trimer, as the central node of the UPy dangling branch, provides three important functions. Firstly, the high symmetry of the isocyanurate three-membered ring (C... 3v Symmetry allows the three -(CH2)6-NCO branches to be equidistantly distributed at 120° intervals. The suspending UPy on one branch, along with the other two NCOs participating in polyurethane chain growth, forms an "umbrella-like" spatial arrangement, providing ample space for the free swinging of the UPy head. Secondly, the isocyanurate three-membered ring itself possesses a high glass transition temperature (estimated T). g>100°C) provides a rigid framework for the hard segment microphase, improving the overall dimensional stability of the material. Thirdly, the carbonyl group of the isocyanurate ring forms an additional secondary hydrogen bond array with the NH of the adjacent carbamate, forming a "double hydrogen bond framework" with the UPy quadruple hydrogen bond array in the hard segment microphase, further enhancing the orientation factor f and the mechanical stability of the hard segment microphase.

[0060] Quantitative analysis of the SS exchange pathway in this invention from a kinetic perspective further confirms the crucial contribution of the α-amide spatial pre-organization effect. According to Eyring's transition state theory, the SS exchange reaction rate constant k satisfies k = (k... B T / h)·exp(-ΔG ‡ / RT), where k B Where is Boltzmann constant, h is Planck constant, R is gas constant, T is absolute temperature, and ΔG is... ‡ The transition state free energy is given. The stress relaxation time τ in Example 1 of this invention, within the temperature range of 30–70°C, was determined using a variable-temperature rheological method. The Arrhenius activation energy E was obtained by plotting ln(τ) against 1 / T. a =33.2 kJ / mol, compared to Comparative Example 1 (using CDE instead of NIBC-Diol-iPr) under the same testing conditions, E was measured. a =64.5kJ / mol, the difference in activation energy between the two is ΔE a =31.3 kJ / mol. At 25°C (298 K), the ratio of the SS exchange rate constant between Example 1 and Comparative Example 1 was estimated to be k. 实施例1 / k 对比例1 =exp(31300 / (8.314×298))≈2.9×10 5 Specifically, the room-temperature SS exchange rate of the system of this invention is about five orders of magnitude higher than that of the CDE system. This order of magnitude leap directly explains why the present invention can achieve ≥90% mechanical property recovery at 25°C for 12 hours, while the CDE system can only achieve about 70% recovery under the same conditions. The above quantitative evidence further supports the irreplaceable nature of the α-amide spatial pre-organized design of this invention from a kinetic perspective, forming a complete chain of evidence supporting Formula I.

[0061] Finally, it is important to highlight the nonlinear synergistic effect among the three key design elements in this invention. If the three elements are separated into independent components (e.g., Comparative Example 1 contains only NIBC-Diol-iPr but lacks a specific R1, Comparative Example 2 contains only UIH but replaces the isocyanurate trimer with HDI main-chain UPy, and Comparative Example 5 completely lacks the UPy unit), their linearly superimposed predicted repair efficiency at 25°C for 12h is approximately 75±5% (based on the average of the five comparative examples), while the actual measured repair efficiency of the embodiments of this invention is 92±2%, which is about 17 percentage points higher than the linear prediction. This significant synergistic gain is the key inventive contribution that distinguishes this invention from any existing single or binary system. Its molecular origin lies in the fact that the α-amide spatial pre-organization effect switches the SS exchange pathway from "diffusion control" to "reaction control", the UPy suspended orientation array effect switches the physical crosslinking from "disordered association" to "ordered acceleration channel", and the umbrella-shaped topology of the isocyanurate trimer provides spatial compatibility for both the SS reaction pathway and the UPy orientation pathway. The "reaction-acceleration-compatibility" triadic synergistic structure formed by the three in the hard segment microphase is something that no binary combination system can achieve.

[0062] In summary, this invention, through the synergistic design of α-N-branched alkylamide-modified cystine derivative diol chain extender, ureidopyrimidinone-suspended isocyanurate trimer-type diisocyanate hard segment units, and polytetrahydrofuran soft segments, combined with precise morphological control of the SAXS second-order orientation factor f in the range of 0.60~0.85, successfully constructed a dual-dynamic crosslinked self-healing polyurethane elastomer material capable of achieving a fracture strength recovery rate ≥90%, a tensile strain recovery rate ≥88%, and an adjustable Shore A hardness in the range of 40~80 under a 12-hour contact repair condition at 25°C. The above embodiments are merely preferred embodiments of this invention and are not intended to limit the invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A self-healing polyurethane elastomer material, prepared by polymerization of polyether diol soft segments, diol chain extenders containing disulfide bonds, and isocyanurate trimer-type diisocyanate hard segment units containing ureidopyrimidinone suspension groups, characterized in that: The disulfide-containing diol chain extender has the structure shown in Formula I, HOCH2CH2-NH-C(=O)-CH(NH-C(=O)-R1)-CH2-SS-CH2-CH(NH-C(=O)-R1)-C(=O)-NH-CH2CH2OH (I), where R1 in Formula I is selected from C3~C6 branched alkyl groups; the isocyanurate trimer type diisocyanate hard segment unit containing ureidopyrimidinone suspension group is composed of 1,3,5-tris( The polyurethane elastomer is obtained by reacting one of the three isocyanate groups of 6-isocyanato(hexyl)isocyanurate with N-(2-aminoethyl)-2-ureo-6-methyl-4(1H)-pyrimidinone, with the remaining two isocyanate groups participating in polyurethane chain growth; the polyether diol soft segment is polytetrahydrofuran diol with a number average molecular weight of 1000~3000 g / mol; the polyurethane elastomer material is subjected to synchrotron small-angle X-ray scattering testing at a scattering vector q=0.07~0.09 Å. -1 A Bragg scattering peak appears at the location, corresponding to a second-order orientation factor f of 0.60~0.85 for the hard segment microphase; under the repair condition of 12h contact at 25°C, the material has a fracture strength recovery rate ≥90%, a tensile strain recovery rate ≥88%, and a Shore A hardness of 40~80.

2. The self-healing polyurethane elastomer material according to claim 1, characterized in that, In Formula I, R1 is selected from isopropyl, isobutyl, or tert-butyl; the number-average molecular weight of the polytetrahydrofuran diol is 1000, 2000, or 3000 g / mol.

3. The self-healing polyurethane elastomer material according to claim 1, characterized in that, The grafting density of the ureidopyrimidinone suspension group is 5 to 25 mol relative to the total moles of the isocyanurate trimer.

4. The self-healing polyurethane elastomer material according to claim 1, characterized in that, The initial tensile strength of the polyurethane elastomer material is 8.0~25.0 MPa, and the initial tensile elongation is 500%~900%. After five repeated 25°C contact 12h repair cycles, the tensile strength recovery rate still remains ≥80%.

5. The self-healing polyurethane elastomer material according to claim 1, characterized in that, The material experiences a mass loss of ≤3% after continuous immersion in gasoline, 3% NaCl aqueous solution, 5% HCl, 5% NaOH, and diethanolamine for 30 days.

6. The self-healing polyurethane elastomer material according to claim 1, characterized in that, The mass ratio of the soft segment to the hard segment of the polytetrahydrofuran diol is 50:50 to 75:

25. When the mass percentage of the soft segment is 70% to 75%, the Shore A hardness of the material is in the range of 40 to 50, the initial tensile strength is 8.0 to 10.0 MPa, and the initial elongation at break is 800% to 900%. When the mass percentage of the soft segment is 60% to 65%, the Shore A hardness of the material is in the range of 55 to 65, the initial tensile strength is 16.0 to 20.0 MPa, and the initial elongation at break is 680% to 760%. When the mass percentage of the soft segment is 50% to 55%, the Shore A hardness of the material is in the range of 70 to 80, the initial tensile strength is 22.0 to 26.0 MPa, and the initial elongation at break is 540% to 620%.

7. The method for preparing the self-healing polyurethane elastomer material according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Synthesis of the diol chain extender containing disulfide bonds as shown in Formula I: L-cysteine ​​and R1-substituted acetic anhydride were reacted in a saturated NaHCO3 aqueous solution and a mixed solvent of 1,4-dioxane at 0-5°C for 4 h to obtain N,N′-bis(R1-acyl)-L-cysteine ​​intermediate. This intermediate was then reacted with ethanolamine in anhydrous DMF at 0-25°C for 24 h under EDC·HCl / HOBt / DIEA mediation to obtain the target chain extender. S2. Synthesis of isocyanurate trimer type diisocyanate containing ureidopyrimidinone suspension group: 1,3,5-tris(6-isocyanatohexyl)isocyanurate and N-(2-aminoethyl)-2-ureido-6-methyl-4(1H)-pyrimidinone were reacted in a molar ratio of 1.0:0.95 in dibutyltin dilaurate. S3, Prepolymerization: Polytetrahydrofuran diol and diisocyanate obtained in step S2 are reacted at 80°C under dry nitrogen protection at an NCO / OH molar ratio of 2.0~2.2 to obtain a prepolymer with an NCO residual content of 50%~55% of the theoretical value; S4, Chain extension reaction: The diol chain extender obtained in step S1 is added to the prepolymer and reacted at 60°C for 1 hour, and then 0~5 mol% of 1,3,5-tris(2-hydroxyethyl)cyanuric acid is added for micro-crosslinking for 30 minutes; S5, Post-curing and demolding: The reactants are poured into a mold and cured in two stages: 80°C for 24 hours under vacuum and 60°C for 12 hours, and then aged at 25°C and 50% relative humidity for 7 days to obtain a self-healing polyurethane elastomer material.

8. The preparation method according to claim 7, characterized in that, In step S1, the R1-substituted acetic anhydride is isobutyric anhydride, isovaleric anhydride, or neopentanoic anhydride; the amounts of EDC·HCl and HOBt are 2.4 times the molar amount of N,N′-bis(R1-acyl)-L-cysteine ​​intermediate, the amount of DIEA is 4.8 times, and the amount of ethanolamine is 2.4 times.

9. The preparation method according to claim 7, characterized in that, The endpoint of step S2 was determined by the NCO residue reaching 12.0 wt% as monitored in real time by di-n-butylamine-hydrochloric acid titration. The target product was purified by silica gel column chromatography with a gradient of dichloromethane / methanol from 95:5 to 90:

10. The grafting density of the ureidopyrimidinone suspension group was controlled within the range of 5-25 mol% by the reactant feed ratio.

10. The preparation method according to claim 7, characterized in that, In step S5, the first stage of the two-stage ripening process is carried out at 80°C under vacuum for 24 hours to complete the remaining addition reaction of diisocyanate-hydroxyl group. The second stage is carried out at 60°C for 12 hours to drive the dimerization of ureidopyrimidinone and the separation of hard segment microphase to reach the thermodynamic optimal state simultaneously, so that the second-order orientation factor f of the hard segment microphase of the final material is controlled in the range of 0.60~0.85.

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