Internal demoulding polyurethane composite material as well as preparation method and application thereof

Abstract

The invention discloses an internal demoulding polyurethane composite material as well as a preparation method and application thereof, and belongs to the technical field of polyurethane materials. The composite material is prepared by mixing and curing a first component (modified polyurethane containing side chain carboxyl and end group double bonds) and a second component (cyclic polyurethane). The first component is prepared through ring opening esterification of itaconic anhydride, introduced side chain carboxyl effectively reconstructs a hydrogen bond network to enhance the mechanical strength, and end group double bonds promote demolding components to efficiently migrate to a mold interface; the unique end-group-free topological structure of the second component effectively limits excessive slippage of a macromolecular chain segment, and the demolding component is permanently and stably anchored at an interface. The composite material effectively solves the problems that a traditional composite material is difficult to demould and the mechanical property is difficult to consider at the same time, realizes an excellent and lasting internal demoulding effect, greatly improves the tensile strength and toughness of the material, and is especially suitable for preparation of composite materials such as PHC cover plates of automobile trunks and the like.

Description

Technical Field

[0001] This invention belongs to the field of polyurethane material technology, specifically, it relates to an internal release polyurethane composite material, its preparation method and application. Background Technology

[0002] PHC (Paper Honeycomb Core) covers are typically sandwich structures, using honeycomb paperboard, corrugated paperboard, or plastic sheets as the core material, with upper and lower composite surface layers and decorative layers (such as fabric, non-woven fabric, PVC leather, etc.). Due to their impact resistance, corrosion resistance, sound and heat insulation, high strength, durability, and high production efficiency, PHC covers are widely used in construction, transportation, and municipal engineering, especially in interior and storage components such as automotive trunk covers, spare tire covers, and shelves. In the process of manufacturing these automotive parts using glass fiber reinforced polyurethane composites, polyurethane (PU) compounds play a crucial role as both the skeleton and the adhesive. With the increasing demand for lightweight and multifunctional materials, the performance requirements for polyurethane compounds are also becoming more stringent. Early general-purpose rigid polyurethane foam compounds used in PHC trunk covers suffered from high brittleness and mismatched coefficients of thermal expansion. To improve these properties, the industry often introduces blends of polyether polyols and polyester polyols, and adds silane coupling agents to enhance adhesion. However, in the continuous molding process of polyurethane composites, the demolding effect is another core factor determining production efficiency, product appearance, and manufacturing cost. Traditional demolding methods often rely on frequent spraying of external release agents on the mold surface. This not only severely slows down the production pace, but the residue of the external release agent can easily cause surface discoloration of the product, affecting subsequent coating or bonding processes. Adopting an internal demolding process is an effective way to solve these problems. The mechanism of action of internal release agents mainly relies on the migration of release components to the interface between the product and the mold during the polyurethane curing process, forming an isolation layer. However, existing internal demolding polyurethane systems face a difficult technical bottleneck: on the one hand, the addition of conventional internal release agents often weakens the interaction between polyurethane molecular chains, leading to an irreversible decrease in the material's mechanical strength, flexibility, and temperature resistance; on the other hand, it is difficult to simultaneously achieve both curing speed and demolding performance. In rapidly curing systems, release agents often do not have enough time to migrate sufficiently to the interface. In conventional systems, due to the continuous movement of linear polyurethane segments, the migration rate of internal release agents is difficult to control precisely, and the release durability is poor in continuous production, often only maintaining a very limited number of release cycles, significantly restricting production efficiency. To further optimize the overall performance of polyurethane, researchers have explored various modification strategies, mainly including physical blending and chemical modification. While chemical modification can adjust the polarity and hydrogen bond network of polyurethane to some extent, almost all existing industrial polyurethanes are prepared from polyisocyanates and polyols through stepwise polymerization mechanisms, forming traditional linear or branched topologies. The topology of a polymer significantly affects its physical properties and application potential. For systems requiring control of the interfacial migration behavior of small molecules (such as internal release agents), traditional linear polyurethane matrices lack sufficient spatial physical constraints, making it difficult to persistently and stably confine and anchor the effective release agent to the interfacial region.

[0003] In summary, there is an urgent need to develop a novel polyurethane compound and its preparation process that integrates rapid curing, nano-modification, and internal release. This compound not only needs to reconstruct the polymer network at the molecular level to address the mechanical property degradation caused by mold release agent migration and achieve excellent tensile strength and toughness, but also needs to overcome the structural limitations of traditional linear molecular chains to possess durable and efficient continuous release capabilities, thus fully meeting the stringent requirements of efficient, continuous, and automated production of lightweight automotive composite materials. Summary of the Invention

[0004] To address the technical problems in existing polyurethane composite materials (especially when used in automotive trunk PHC cover panels) that are difficult to demold during molding, result in low production efficiency and easy contamination of the product surface due to frequent use of external release agents, and cause irreversible reduction in mechanical strength (such as tensile strength and elongation at break) and extremely poor demolding durability, this invention provides an internal demolding polyurethane composite material, its preparation method, and its application.

[0005] The present invention adopts the following technical solution: a method for preparing an internal release polyurethane composite material, comprising the following steps by weight: S1, preparing a first component, wherein the first component is a modified polyurethane containing side chain carboxyl groups and terminal double bonds: 100 parts of a macromolecular diol; 3.0-10.0 parts of a first polyisocyanate; 0.1-1.5 parts of itaconic anhydride (CAS No.: 2170-03-8); 10.0-30.0 parts of a second polyisocyanate; and a small molecule aliphatic diol. The raw materials are 2.0-8.0 parts of chain extender and 0.01-0.05 parts of organometallic catalyst. The main chain of the first component is constructed by the urethane bond formed by the polymerization of the macromolecular diol and polyisocyanate. The itaconic anhydride undergoes a single-end ring-opening esterification reaction with the terminal hydroxyl group of the polyurethane prepolymer through its internal anhydride group, so that one end of the macromolecular chain of the first component is covalently grafted with α,β-unsaturated double bonds, and the side chain free carboxyl group is carried on the carbon atom adjacent to the grafting site. S2. Preparation of the second component (the second component is a cyclic polyurethane): (1) Controlled ring-opening polymerization (ROP) of macrocyclic monomers: Using a bifunctional primary amine as initiator A, the macrocyclic monomers are initiated to undergo ring-opening polymerization in a solvent, and then a quencher is added to terminate the reaction to obtain an amino-terminated telechelic polyurethane; (2) End-group modification reaction: The amino-terminated telechelic polyurethane obtained in step (1) is redissolved in a solvent, and in the presence of triethylamine, it undergoes an amine-active ester coupling reaction with p-nitrobenzene active esterifying agent compound B to obtain an azido-terminated telechelic polyurethane; (3) Bimolecular ring-closing reaction: The azido-terminated telechelic polyurethane solution obtained in step (2) is slowly added dropwise to a solution containing the small molecule linker sym-dibenzo-1,5-cyclooctadiene-3,7-diyne (DIBOD, CAS No.: 137351-40-7), and the reaction is carried out by self-accelerated bimolecular ring-closing reaction. The ring-closure is achieved through force-promoted azido-yne click reaction (DSPAAC), a metal-free click chemistry process. The cyclooctyne structure in DIBOD exhibits significant ring strain, which can substantially reduce the activation energy of the cycloaddition reaction. When the azide groups at both ends of the polymer successively dock with the two triple bonds of DIBOD, due to the "self-acceleration effect," the intramolecular ring-closure rate is much higher than the intermolecular collision rate, thus precisely constructing a perfect ring topology; a cyclic polyurethane is obtained. S3: The first component prepared in step S1 and the second component prepared in step S2 are mixed and cured. Further, in step S3, the mass ratio of the first component to the second component is 100:(10-20); the curing conditions are curing at 70-90℃ for 12-36 hours to obtain the internally release polyurethane composite. Because the primary hydroxyl group has a much higher reactivity with isocyanate than the free carboxyl group, chain extension preferentially occurs under organotin catalysis, thus maximizing the retention of the free carboxyl groups in the side chains. The structural formula of DIBOD is as follows: .

[0006] The first component of this invention precisely introduces α,β-unsaturated double bonds into the polyurethane chain ends through single-end ring-opening esterification of itaconic anhydride. Due to the high degree of freedom of chain segment movement and low surface energy of the end groups with double bonds, during the evaporation molding process of the composite solution, these hydrophobic end groups spontaneously and efficiently migrate and accumulate towards the low-polarity air / mold interface under thermodynamic drive, thereby forming a dense, low-surface-energy physical isolation layer between the product and the mold. Simultaneously, combined with the physical crosslinking and topological steric hindrance of the second component, it permanently anchors the product at the interface, achieving excellent internal demolding performance.

[0007] Preferably, in step S1, the macromolecular diol is selected from at least one of polycaprolactone diol (CAS No.: 36890-68-3), polycarbonate diol (CAS No.: 24937-06-2), or polytetrahydrofuran diol (CAS No.: 25190-06-1), and its number-average molecular weight is between 1000-3000 g / mol; the first polyisocyanate and the second polyisocyanate have the same or different chemical structures, and are both selected from 4,4'-diphenylmethane diisocyanate (CAS No.: 101-68-8), toluene diisocyanate, etc. The cyanate ester (CAS No.: 584-84-9) or isophorone diisocyanate (CAS No.: 4098-71-9) is selected from at least one of the following: the small molecule aliphatic diol chain extender is selected from at least one of 1,4-butanediol (CAS No.: 110-63-4), 1,6-hexanediol (CAS No.: 629-11-8) or ethylene glycol (CAS No.: 107-21-1); the organometallic catalyst is dibutyltin dilaurate (CAS No.: 77-58-7) or stannous octoate (CAS No.: 301-10-0).

[0008] Preferably, the preparation of the first component in step S1 specifically includes the following consecutive operation steps: (1) Dehydration reaction: 100 parts of macromolecular diol are continuously stirred at 110-130℃ under vacuum for 1.5-3h; (2) Hydroxyl-terminated prepolymerization: Under the protection of aprotic inert gas, the system temperature is lowered to 50-70℃, 3.0-10.0 parts of the first polyisocyanate are added, and then the temperature is raised to 75-85℃ and kept at the temperature for 1.5-3h to obtain the hydroxyl-terminated polyurethane prepolymer; (3) Ring-opening single-end grafting: 0.1-1.5 parts of itaconic anhydride are added to the prepolymer system, and under the protection of aprotic inert gas, the reaction is carried out at 8℃. Stir at 5-95℃ for 2.5-4h to achieve end capping on the main chain of the prepolymer; (4) Catalytic chain extension and crosslinking: Lower the system temperature to 75-85℃, add 10.0-30.0 parts of second polyisocyanate and 2.0-8.0 parts of small molecule aliphatic diol chain extender in sequence, and add 0.01-0.05 parts of organometallic catalyst and reaction medium dropwise, and stir at constant temperature for 1.5-3h; The reaction medium used is N,N-dimethylformamide (CAS No.: 68-12-2) or N-methylpyrrolidone (CAS No.: 872-50-4), and its added mass is 10-50% of the total solid mass of the system.

[0009] Preferably, in step S2(1), 40-60 parts (preferably 49.8 parts) of macrocyclic monomer are dissolved in 300-350 parts (preferably 339.8 parts) of N,N-dimethylformamide (CAS No.: 68-12-2) solvent, and then 0.1-1 parts (preferably 0.81 parts) of initiator A are added; the mixture is reacted at 85-95℃ (preferably 90℃) for 1-2 h (preferably 1.5 h), and then the reaction is quenched by adding trifluoroacetic acid (CAS No.: 76-05-1); the reaction solution is precipitated twice in methanol, and the amino-terminated telechelic polyurethane is collected by filtration through a 0.22 μm filter membrane. In step S2 (2), the purified and collected terminal amino teleclaw polyurethane is redissolved in 450-500 parts (preferably 472 parts) of N,N-dimethylformamide (CAS No.: 68-12-2) by mass, followed by the addition of 100-200 parts (preferably 145.2 parts) of triethylamine and 100-130 parts (preferably 118 parts) of compound B; the reaction is carried out at room temperature for 2-4 hours (preferably 3 hours); the reaction product is precipitated twice in methanol and the terminal azido-based teleclaw polyurethane is collected; wherein the molar ratio of compound B, terminal amino of teleclaw polymer and triethylamine is set to 12.5:1:12.5.

[0010] Preferably, in step S2 (3), 30-50 parts (preferably 40 parts) of terminal azido-based teleclaw polyurethane are dissolved in 18625 parts of chloroform solvent to prepare a polymer solution, and 10-30 parts (preferably 20 parts) of sym-dibenzo-1,5-cyclooctadiene-3,7-diyne are dissolved in 55875 parts of chloroform solvent to prepare a linker solution. The polymer solution is continuously and uniformly added to the linker solution by a syringe pump over 12 hours, and then the ring-closing reaction is continued at room temperature for 6-18 hours (preferably 12 hours). The crude product is precipitated twice in methanol to obtain purified cyclic polyurethane (second component). The mass ratio of terminal azido-based teleclaw polyurethane to sym-dibenzo-1,5-cyclooctadiene-3,7-diyne is (1-2):1, and the yield concentration of the obtained cyclic polyurethane system is approximately 0.8 g / L.

[0011] Preferably, the preparation method of initiator A in step S2 includes: dissolving 4.5-8.5 parts (preferably 6.5 parts) of hydroquinone (CAS No.: 123-31-9) in 113.3 parts of N,N-dimethylformamide (CAS No.: 68-12-2) by weight, adding 30-35 parts (preferably 32.6 parts) of potassium carbonate, stirring at room temperature for 20-40 min (preferably 30 min), and then adding 35-40 parts (preferably 37.9 parts) of N-(3-bromopropyl)phthalimide (CAS No.: 5460-29-7); reacting at 75-85℃ (preferably 80℃) for 24-48 h (preferably 36 h); collecting the filtrate by filtration through a 0.22 μm filter membrane and rotary evaporating (vacuum set at 10-20 mbar; water bath temperature set at 60-80℃). The mixture was purified by rotating the flask at 100-200 rpm between ℃ and ℃. The residue was dissolved in chloroform and washed successively with 2M sodium carbonate aqueous solution and deionized water until pH=7. The residue was purified by silica gel column chromatography to obtain compound one. 1-3 parts (preferably 1.4 parts) of compound one were dissolved in 20-25 parts (preferably 22.9 parts) of anhydrous ethanol, and 0.2-0.6 parts (preferably 0.41 parts) of hydrazine hydrate (CAS No.: 7803-57-8) were added. The mixture was reacted at 75-85℃ (preferably 80℃) for 1-3 h (preferably 2 h). After removing the solvent, the residue was dispersed in water, and the pH was adjusted to 4 with 1M hydrochloric acid aqueous solution and filtered through a 0.22 μm filter membrane. The filtrate was collected and the pH was adjusted to 12 with 1M sodium hydroxide aqueous solution. The precipitate was collected by filtration through a 0.22 μm filter membrane to obtain initiator A.

[0012] Preferably, the preparation method of the p-nitrobenzene active esterifying agent (compound B) in step S2 includes: dissolving 10-30 parts (preferably 20 parts) of 2,6-diisopropylaniline (CAS No.: 24544-04-5) in 150-200 parts (preferably 177.6 parts) of acetonitrile by weight, adding 0.2-0.8 parts (preferably 0.53 parts) of potassium iodide, and slowly adding 40-70 parts (preferably 58.5 parts) of tert-butyl hydroperoxide (CAS No.: 75-91-2) dropwise over 60 min; stirring at room temperature for 30 min, then heating to 60-80℃ (preferably 70℃) and reacting for 4-6 h (preferably 5 h); adding saturated... The sodium thiosulfate solution was quenched, extracted with dichloromethane, and purified by column chromatography (silica gel column, eluent: petroleum ether / ethyl acetate (v / v) 15:1) to obtain compound two; 1-3 parts (preferably 2.07 parts) of compound two were dissolved in 30-50 parts (preferably 39.5 parts) of acetone, 1-4 parts (preferably 2.35 parts) of ammonium chloride were added, and the mixture was bubbled under nitrogen for 30 min, followed by the addition of 1-3 parts (preferably 1.43 parts) of zinc powder (200 mesh). The reaction was carried out at room temperature under a nitrogen atmosphere for 4-6 h (preferably 5 h); the mixture was rapidly filtered through a 0.22 μm filter membrane and the filtrate was concentrated (to remove all solvent), and extracted with dichloromethane to obtain the intermediate hydroxylamine derivative; the... The intermediate hydroxylamine derivative was dissolved in 15-20 parts (preferably 17.8 parts) of diethyl ether, and 25-35 parts (preferably 27.5 parts) (15% by mass) of dilute sulfuric acid aqueous solution were added; after stirring overnight at room temperature, the pH was adjusted to 8 with 2M sodium hydroxide solution, and the mixture was extracted and concentrated with diethyl ether and stirred in n-pentane for 2-4 hours (preferably 3 hours) to obtain compound III as a white solid; 1-2 parts (preferably 1.6 parts) of compound III were dissolved in a mixture of 60-80 parts (preferably 75.6 parts) of glacial acetic acid and 6-10 parts (preferably 8 parts) of water, and then 1-2 parts (preferably 1.35 parts) of sodium azide (CAS No.: 26628-22-) were added. 8) With 1-1.5 parts (preferably 1.31 parts) of sodium nitrite; react at 0℃ for 20-40 min (preferably 30 min), extract the organic phase with ethyl acetate, dry with anhydrous sodium sulfate, and purify by column chromatography (silica gel column, eluent (mobile phase): a mixture of petroleum ether (PE) and ethyl acetate (EA) in a volume ratio of 20:1) to obtain compound four; dissolve 1-2 parts (preferably 1.75 parts) of compound four in 50-55 parts (preferably 53.2 parts) of dichloromethane, add 1.5-2.5 parts (preferably 1.96 parts) of p-nitrobenzene chloroformate (CAS No.: 7693-46-1) and 1-1.5 parts (preferably 1.75 parts) of sodium nitrite.31 portions of triethylamine (CAS No.: 121-44-8); after stirring at room temperature for 20 min, the solvent was removed by rotary evaporation (water bath temperature 35℃, pressure 100 mbar, speed 150 rpm) and purified by column chromatography (purified by silica gel column chromatography, the eluent was a mixture of petroleum ether and ethyl acetate at a volume ratio of 15:1) to obtain compound B; the macrocyclic monomer in step S2 is a stress-relieved macrocyclic monomer with functional groups or sequence-defined structural units on the main chain (refer to existing literature, W. Chen, C. Guo, H. Ding, X. Yang, K. Zhang, Controlled ring-opening polymerization of macrocyclic monomers based on ring-opening / ring-closing cascade reaction, J. Am. Chem. Soc. 145 (2023)25022-25030.).

[0013] The structure of the macrocyclic monomer is as follows: The differences between M1 and M2 are as follows: .

[0014] An internal release polyurethane compound, wherein the internal release polyurethane compound is obtained by the preparation method described above.

[0015] An application of an internal release polyurethane compound: the internal release polyurethane compound prepared by the above-described preparation method is added to automotive parts for application.

[0016] Compared to existing technologies, this invention has at least the following advantages: It pioneers a synergistic internal release mechanism combining "chemical grafting and topological constraints," resulting in a qualitative leap in release durability. Existing internal release agents are prone to leaching and failure during continuous production or are carried away with the product, leading to poor release durability. The first component of this invention, through single-end ring-opening esterification of itaconic anhydride, precisely introduces α,β-unsaturated double bonds at the polyurethane chain ends. This structure, during curing, promotes the spontaneous and efficient migration of the effective release component to the product-mold interface, forming a dense isolation layer. Simultaneously, the innovatively introduced second component (cyclic polyurethane) possesses a unique end-group-free topological structure, which not only resists volatilization and migration but also restricts excessive slippage of polymer chain segments through strong physical crosslinking and steric hindrance effects, firmly anchoring the release component that migrates to the interface. Experimental data show that the preferred solution of this invention has a low demolding force of 16.8-18.5 N and a high number of consecutive defect-free demolding cycles of 48-52. In contrast, the demolding force of the system lacking cyclic polyurethane (Comparative Example 3) surges to 62.4 N, and it fails after only 8 consecutive demolding cycles. This invention completely breaks through the technical bottleneck of difficult continuous demolding of traditional polyurethane composites. It precisely reconstructs the intermolecular hydrogen bond network, achieving a reverse improvement in mechanical strength and toughness. In traditional processes, adding internal release agents often comes at the cost of weakening intermolecular forces and sacrificing the mechanical properties of the material. This invention, through itaconic anhydride modification, introduces highly polar free carboxyl groups at the grafting sites. These side-chain carboxyl groups reconstruct a dense and ordered intermolecular hydrogen bond network with the urethane groups on the polyurethane backbone (the hydrogen bond index HBI is significantly increased to 0.82-0.85), effectively driving the aggregation of hard segment microregions and significantly improving the microphase separation of the system. Performance tests show that, without the addition of additional fiber reinforcement, the tensile strength of the composite material of this invention reaches 28.4-29.1 MPa, and the elongation at break reaches 685-702%, far superior to the unmodified system, perfectly meeting the stringent requirements of high strength, impact resistance, and fatigue resistance for structural components such as PHC trunk covers in automobiles. It significantly simplifies the production process and has great potential for industrial mass production and cost reduction. The internal release polyurethane composite material provided by this invention endows the composite material with extremely excellent self-release capability, completely eliminating the cumbersome processes of frequent spraying, waiting for drying, and cleaning of external mold release agents in traditional production. This not only significantly shortens the molding cycle and improves the operating efficiency of automated production lines, but also fundamentally eliminates quality problems such as surface discoloration, poor subsequent coating, or poor adhesion caused by mold scaling and external mold release agent residue. The composite material has good component compatibility and a wide molding process window, making it particularly suitable for the continuous, efficient, and green production of lightweight automotive composite parts (such as PHC sandwich panels). Attached Figure Description

[0017] Figure 1 This is the infrared spectrum of the first component prepared in Example 1.

[0018] Figure 2 This is the infrared spectrum of the second component prepared in Example 1. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to specific embodiments. However, these embodiments are only for illustrating the present invention and do not constitute any limitation on the scope of protection of the present invention. For those skilled in the art, simple deductions or substitutions made without departing from the concept of the present invention should be considered as falling within the scope of protection defined by the claims of the present invention. In the present invention, unless otherwise specified, intermediate values ​​are used for undefined parameter ranges by default.

[0020] Example 1.

[0021] Step S1: Preparation of the first component (modified polyurethane containing side chain carboxyl groups and terminal double bonds) (1) Dehydration reaction: 100g of polycaprolactone diol was placed in a four-necked flask equipped with a mechanical stirrer, thermometer and nitrogen inlet, and stirred for 3h under vacuum conditions of 110℃ and -0.098MPa. (2) Terminal hydroxyl prepolymerization: The temperature was lowered to 60℃, nitrogen gas was introduced for protection, 5.0g of MDI (4,4'-diphenylmethane diisocyanate) was added, the temperature was raised to 80℃ and kept for 2h to obtain terminal hydroxyl polyurethane prepolymer. (3) Ring-opening single-end grafting: 0.8g of itaconic anhydride was added, and the mixture was stirred at 90℃ for 3h under nitrogen protection. (4) Catalytic chain extension and crosslinking: Cool to 80℃, add 20.0g MDI, 5.0g 1,4-butanediol and 0.03g DBTDL (dibutyltin dilaurate) sequentially, add 45g DMF (N,N-dimethylformamide), stir at constant temperature for 2h to obtain the first component, and its infrared spectrum analysis results are as follows. Figure 1As shown. Step S2: Preparation of the second component (cyclic polyurethane) (1) Preparation of initiator A: Dissolve 6.5g hydroquinone in 113.3g DMF, add 32.6g potassium carbonate, stir at room temperature for 30min, then add 37.9g ​​N-(3-bromopropyl)phthalimide, and react at 80℃ for 36h. Filter, rotary evaporate, dissolve the residue in chloroform, wash with 2M sodium carbonate aqueous solution and deionized water to pH=7, and purify by silica gel column chromatography to obtain compound one. Dissolve 1.4g compound one in 22.9g anhydrous ethanol, add 0.41g hydrazine hydrate, and react at 80℃ for 2h. Remove the solvent, disperse the residue in water, adjust the pH to 4 with 1M hydrochloric acid, filter, adjust the pH of the filtrate to 12 with 1M sodium hydroxide, filter and collect the precipitate to obtain initiator A. (2) Preparation of amino-terminated teleclaw polyurethane: 49.8 g of macrocyclic monomer (stress-relieved macrocyclic monomer with functional groups on the main chain, M1 structure used in Example 1) was dissolved in 339.8 g of DMF, 0.81 g of initiator A was added, and the reaction was carried out at 90 °C for 1.5 h. Trifluoroacetic acid was added to quench the reaction, and the product was precipitated twice in methanol. The product was then filtered and collected to obtain amino-terminated teleclaw polyurethane (NH2-P-NH2). (3) End group modification: The above amino-terminated teleclaw polyurethane was dissolved in 472 g of DMF, 145.2 g of TEA (triethylamine) and 118 g of compound B (compound B was prepared according to the method described in the specification) were added, and the reaction was carried out at room temperature for 3 h. The product was precipitated twice in methanol to obtain azide-terminated teleclaw polyurethane (N3-P-N3). The molar ratio of compound B, amino-terminated and TEA was 12.5:1:12.5. (4) Bimolecular ring closure: 40g of terminal azido-based teleclaw polyurethane was dissolved in 18625g of chloroform, and 20g of DIBOD was dissolved in 55875g of chloroform (the mass ratio of terminal azido-based teleclaw polyurethane to DIBOD was 2:1). The polymer solution was added dropwise to the DIBOD solution at a uniform rate over 12h using a syringe pump, and the reaction was continued at room temperature for another 12h to obtain a liquid viscous cyclic polyurethane (second component, infrared spectrum as shown). Figure 2 (As shown), the yield concentration is approximately 0.8 g / L. Step S3: Mixing and curing. The first component obtained in step S1 and the second component obtained in step S2 are mixed at a mass ratio of 100:15. 1% of benzoyl peroxide by mass of the first component is added. After stirring evenly, the mixture is poured into a mold and heated and dried at 80°C for 24 hours. After demolding, an internally release polyurethane composite material is obtained.

[0022] Compared with Example 1, Example 2 only changed the amount of itaconic anhydride in step S1 to 0.3g, while the other parameters were the same as in Example 1. Parameters not listed are the same as in Example 1.

[0023] Compared with Example 1, Example 3 only changed the amount of itaconic anhydride in step S1 to 1.2g, while the other parameters were the same as in Example 1. Parameters not listed are the same as in Example 1.

[0024] Example 4 differs from Example 1 only in that the macromolecular diol in step S1 is replaced with 100g of polycarbonate diol, the first polyisocyanate is replaced with 6.0g of IPDI, the second polyisocyanate is replaced with 18.0g of IPDI, and the small molecule chain extender is replaced with 4.0g of 1,6-hexanediol. All other parameters are the same as in Example 1. Parameters not listed are the same as in Example 1.

[0025] Compared with Example 1, Example 5 only changed the amount of macrocyclic monomer in step S2 to 55.0 g, the amount of initiator A to 0.90 g, and the amount of terminal azido-based telechelic polyurethane to 45 g. All other parameters were the same as in Example 1. Parameters not listed were the same as in Example 1.

[0026] Compared with Example 1, Comparative Example 1 (without itaconic anhydride) did not include itaconic anhydride in step S1, and the other parameters were the same as in Example 1.

[0027] Comparative Example 2 (Itaconic anhydride dosage exceeding limits): Compared with Example 1, the dosage of itaconic anhydride in step S1 was adjusted to 2.0g, and the other parameters were the same as in Example 1.

[0028] Comparative Example 3 (lacking the second component of cyclic polyurethane) differs from Example 1 in that the second component is not added in step S3, and only the first component is used for curing. The remaining parameters are the same as in Example 1.

[0029] Comparative Example 4 (DIBOD dosage exceeds limits) Compared with Example 1, the dosage of DIBOD in step S2 (3) was adjusted to 10g (the mass ratio of terminal azido-based teleclaw polyurethane to DIBOD was 4:1), and the other parameters were the same as in Example 1.

[0030] Comparative Example 5 (Molecular weight of macromolecular diol exceeds the limit): Compared with Example 1, the macromolecular diol in step S1 was replaced with 100g of polycaprolactone diol with a number average molecular weight of 800g / mol, and the other parameters were the same as in Example 1.

[0031] Comparative Example 6 (without bimolecular ring closure) Compared with Example 1, step S2 omitted the (3) bimolecular ring closure step, and directly used terminal azido-based teleclaw polyurethane as the second component. The remaining parameters were the same as those in Example 1.

[0032] Test Methods and Results: Demolding Performance Test Instrument: Universal Testing Machine (Instron 5567); Mold: Standard automotive parts simulation mold (aluminum alloy, surface Ra0.8μm). Method: The composite material was injected into the mold and cured at 80℃ for 24 hours. Demolding was then performed at 50mm / min under conditions of 25℃ and 50%RH. The peak tensile force was the demolding force (N). Five tests were performed per group, and the average value was taken. Tests were conducted according to the company's internal control standards. Results are shown in Table 1. Tensile Strength and Elongation at Break Test Instrument: Universal Testing Machine (Instron 5567). Method: Dumbbell-shaped specimens (gauge length 25mm, thickness 2mm) were prepared according to GB / T 528-2009. Tensile speed was 500mm / min, 25℃, 50%RH. Five tests were performed, and the average value was taken. Results are shown in Table 1. Continuous production demolding test simulating the production line: After each injection and curing, demolding was performed, and the number of consecutive demoldings without sticking or surface defects was recorded until obvious sticking or surface defects appeared. Results are shown in Table 1. Microphase separation degree (FTIR hydrogen bonding index) instrument: Fourier transform infrared spectrometer (Nicolet iS50, ATR mode). Method: Scanning range 4000-400 cm⁻¹ -1 4cm resolution -1 For the carbonyl region (1660-1770 cm⁻¹) -1 Gaussian deconvolution was performed, and the hydrogen bond index HBI was calculated as (hydrogen bond carbonyl area) / (free carbonyl area). The results are shown in Table 1.

[0033] Table 1 Performance test results of the examples and comparative examples

[0034]

[0035] Results Analysis: Example 1, as the preferred embodiment, has parameters within the reasonable range of the claims, exhibiting the lowest demolding force (18.5 N), tensile strength of 28.4 MPa, elongation at break of 685%, 48 consecutive demolding cycles, and a hydrogen bond index of 0.82, demonstrating the best overall performance. When itaconic anhydride is applied, the side-chain carboxyl groups and double bonds synergistically promote the formation of hard-segment hydrogen bonds, enhancing the degree of microphase separation. Simultaneously, the terminal double bonds participate in the reaction during curing, forming an interfacial isolation layer, achieving an internal demolding effect. Example 2, by reducing the amount of itaconic anhydride, decreases the carboxyl content, lowers the hydrogen bond index to 0.71, weakens microphase separation, increases the demolding force to 22.3 N, reduces the number of consecutive demolding cycles to 39, and slightly decreases the strength and elongation. This indicates that the amount of itaconic anhydride needs to reach a certain threshold to effectively construct the synergistic effect of the side-chain polar groups and terminal double bonds. Example 3: Increasing the amount of itaconic anhydride resulted in the highest hydrogen bond index (0.85), the lowest demolding force (16.8 N), and 52 consecutive demolding cycles, further improving mechanical properties. This demonstrates that appropriately increasing the amount within the scope of the claims can strengthen the hydrogen bond network and interfacial migration ability. Example 4: Changing the type of polyol and isocyanate, polycarbonate diol provided higher polarity, and IPDI improved flexibility, while maintaining excellent demolding and mechanical properties, verifying the universality of the raw material selection in the claims. Example 5: Fine-tuning the amount of the second component slightly increased the content of cyclic polyurethane, and the topological structure further restricted chain segment movement, resulting in slightly better demolding and mechanical properties. This indicates that the cyclic structure has a significant auxiliary effect on internal demolding. Comparative Example 1: Lacking itaconic anhydride, it was impossible to introduce side chain carboxyl groups and terminal double bonds. The hydrogen bond index was only 0.48, resulting in poor microphase separation, a demolding force as high as 45.6 N, and only 12 consecutive demolding cycles. The strength and elongation decreased significantly, indicating that this monomer is the core component for constructing the internal demolding function, and its absence prevents the formation of the interfacial isolation layer. In Comparative Example 2, the amount of itaconic anhydride exceeded the upper limit. Excessive carboxyl groups led to excessive aggregation of hard segments, forming disordered aggregates, a decrease in the hydrogen bonding index, and a release force of 35.2 N, which was inferior to the example, verifying the criticality of the dosage range. Comparative Example 3 lacked the cyclic polyurethane second component, resulting in the disappearance of topological constraints, increased chain segment movement freedom, and a release force of 62.4 N, exhibiting the worst mechanical properties. This demonstrates the necessity of the cyclic structure for limiting chain slippage and improving internal demolding durability. In Comparative Example 4, the amount of DIBOD was insufficient, resulting in low ring-closing efficiency, decreased cyclic polyurethane yield, and weakened auxiliary effect. The release force was 28.7 N, with performance between the example and the comparative examples. In Comparative Example 5, the molecular weight of the macromolecular diol was too low, the soft segment was too short, crystallinity increased, flexibility was poor, and both demolding and mechanical properties decreased. In Comparative Example 6, no ring closure was performed, and the second component remained a linear telechelic polymer, lacking the advantages of cyclic topology. The release force was 39.8 N, which was inferior to the example.

[0036] In summary, this invention introduces side-chain carboxyl groups and end-group double bonds through itaconic anhydride modification, combined with the topological constraints of cyclic polyurethane, achieving a synergistic effect of internal demolding and excellent mechanical properties within the scope defined by the claims. The absence of key components or out-of-bounds parameters lead to weakened microphase separation, failure of the interfacial isolation layer, or uncontrolled chain segment movement, thereby significantly deteriorating demolding performance and mechanical properties, fully demonstrating the superiority and necessity of the technical solution of this invention.

[0037] The above description, in conjunction with specific embodiments, provides a further detailed explanation of the present invention. However, it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection defined by the claims. Furthermore, for any issues that may arise with the claims, the embodiments described in the specification shall prevail.

Claims

1. A method for preparing an internally release polyurethane composite material, characterized in that: The method comprises the following steps by mass: S1, preparing the first component: 100 parts of macromolecular diol; 3.0-10.0 parts of the first polyisocyanate; and 0.1-1.5 parts of itaconic anhydride; The second component is prepared by using 10.0-30.0 parts of a second polyisocyanate, 2.0-8.0 parts of a small molecule aliphatic diol chain extender, and 0.01-0.05 parts of an organometallic catalyst as raw materials, and undergoing single-end ring-opening esterification with an anhydride group; S2, preparing the second component: using a bifunctional primary amine as initiator A, the macrocyclic monomer undergoes a ring-opening polymerization reaction in a solvent to obtain an amino-terminated telechelic polyurethane, which undergoes an amine-active ester coupling reaction with p-nitrobenzene active esterifying agent compound B in the presence of triethylamine to obtain an azide-terminated telechelic polyurethane, which is added dropwise to a solution containing the small molecule linker sym-dibenzo-1,5-cyclooctadiene-3,7-diyne to obtain a liquid cyclic polyurethane; S3, mixing and curing the first component prepared in step S1 with the second component prepared in step S2.

2. The method for preparing the internal release polyurethane composite material according to claim 1, characterized in that; In step S1, the macromolecular diol is selected from at least one of polycaprolactone diol, polycarbonate diol, or polytetrahydrofuran diol, and its number-average molecular weight is between 1000-3000 g / mol; the first polyisocyanate and the second polyisocyanate have the same or different chemical structures, and are both selected from at least one of 4,4'-diphenylmethane diisocyanate, toluene diisocyanate, or isophorone diisocyanate; the small molecule aliphatic diol chain extender is selected from at least one of 1,4-butanediol, 1,6-hexanediol, or ethylene glycol; and the organometallic catalyst is dibutyltin dilaurate or stannous octoate.

3. The method for preparing the internal release polyurethane composite material according to claim 1, characterized in that: The preparation of the first component in step S1 specifically includes the following sequential steps: 100 parts of macromolecular diol are continuously stirred at 110-130℃ under vacuum for 1.5-3 hours; under the protection of an inert gas, the system temperature is lowered to 50-70℃, 3.0-10.0 parts of the first polyisocyanate are added, and then the temperature is raised to 75-85℃ and kept at that temperature for 1.5-3 hours to obtain a hydroxyl-terminated polyurethane prepolymer; 0.1-1.5 parts of itaconic anhydride are added to the prepolymer system, and the reaction is carried out under the protection of an inert gas. Under constant temperature and stirring at 85-95℃ for 2.5-4h, end-capping is achieved on the main chain of the prepolymer; the system temperature is then lowered to 75-85℃, and 10.0-30.0 parts of the second polyisocyanate and 2.0-8.0 parts of the small molecule aliphatic diol chain extender are added sequentially, along with 0.01-0.05 parts of organometallic catalyst and reaction medium, and the mixture is stirred at constant temperature for 1.5-3h; the reaction medium used is N,N-dimethylformamide or N-methylpyrrolidone, and its added mass is 10-50% of the total solid mass of the system.

4. The method for preparing the internal release polyurethane composite material according to claim 1, characterized in that: In step S2, by mass, 40-60 parts of macrocyclic monomer are dissolved in 300-350 parts of N,N-dimethylformamide solvent, followed by the addition of 0.1-1 parts of initiator A; the mixture is reacted at 85-95℃ for 1-2 hours, and then the reaction is quenched by adding trifluoroacetic acid; the reaction solution is precipitated twice in methanol, and the mixture is collected by filtration through a 0.22 μm filter membrane to obtain amino-terminated teleclaw polyurethane; in step S2, by mass, the purified and collected amino-terminated teleclaw polyurethane is redissolved in 450-500 parts of N,N-dimethylformamide, followed by the addition of 100-200 parts of triethylamine and 100-130 parts of compound B; the mixture is reacted at room temperature for 2-4 hours, and the resulting azide-terminated teleclaw polyurethane is collected.

5. The method for preparing the internal release polyurethane composite material according to claim 1, characterized in that: In step S2, by mass, 30-50 parts of terminal azido-based telechelic polyurethane are dissolved in 18625 parts of chloroform solvent to prepare a polymer solution, and 10-30 parts of sym-dibenzo-1,5-cyclooctadiene-3,7-diyne are dissolved in 55875 parts of chloroform solvent to prepare a linker solution. The polymer solution is continuously and uniformly added to the linker solution by a syringe pump over 12 hours, and then the ring-closing reaction is continued at room temperature for 6-18 hours to obtain the purified cyclic polyurethane.

6. The method for preparing the internal release polyurethane composite material according to claim 1, characterized in that: The preparation method of initiator A in step S2 includes: dissolving 4.5-8.5 parts by weight of hydroquinone in 113.3 parts by weight of N,N-dimethylformamide, adding 30-35 parts by weight of potassium carbonate, stirring at room temperature for 20-40 min, and then adding 35-40 parts by weight of N-(3-bromopropyl)phthalimide; reacting at 75-85°C for 24-48 h; filtering through a 0.22 μm filter membrane, collecting the filtrate and removing impurities by rotary evaporation, dissolving the residue in chloroform, and then reacting successively with 2M carbonate... The compound was washed with sodium aqueous solution and deionized water until pH=7, and purified by silica gel column chromatography to obtain compound one. 1-3 parts of compound one were dissolved in 20-25 parts of anhydrous ethanol, and 0.2-0.6 parts of hydrazine hydrate were added. The mixture was reacted at 75-85℃ for 1-3 h. After removing the solvent, the residue was dispersed in water, the pH was adjusted to 4 with 1M hydrochloric acid aqueous solution, and filtered through a 0.22 μm filter membrane. The filtrate was collected, the pH was adjusted to 12 with 1M sodium hydroxide aqueous solution, and the precipitate was collected by filtration through a 0.22 μm filter membrane.

7. The method for preparing the internal release polyurethane composite material according to claim 1, characterized in that: The preparation method of the p-nitrobenzene active esterifying agent in step S2 includes: dissolving 10-30 parts by weight of 2,6-diisopropylaniline in 150-200 parts by weight of acetonitrile, adding 0.2-0.8 parts by weight of potassium iodide, and slowly adding 40-70 parts by weight of tert-butyl hydroperoxide over 60 min; stirring at room temperature for 30 min, then heating to 60-80℃ and reacting for 4-6 h; quenching with saturated sodium thiosulfate aqueous solution, extracting with dichloromethane and purging by column chromatography to obtain compound two; dissolving 1-3 parts by weight of compound two in 30-50 parts by weight of acetone, adding 1-4 parts by weight of ammonium chloride, bubbling with nitrogen for 30 min, then adding 1-3 parts by weight of zinc powder, and reacting at room temperature under a nitrogen atmosphere for 4-6 h; rapidly filtering with a 0.22 μm filter membrane and concentrating the filtrate, extracting with dichloromethane to obtain the intermediate hydroxylamine derivative; dissolving the intermediate hydroxylamine derivative in 15-20 parts by weight of diethyl ether, adding 25- 35 parts of dilute sulfuric acid aqueous solution; after stirring overnight at room temperature, the pH was adjusted to 8 with 2M sodium hydroxide solution, extracted and concentrated with diethyl ether, and stirred in n-pentane for 2-4 hours to obtain compound three as a white solid; 1-2 parts of compound three were dissolved in a mixture of 60-80 parts glacial acetic acid and 6-10 parts water, followed by the addition of 1-2 parts sodium azide and 1-1.5 parts sodium nitrite; the reaction was carried out at 0℃ for 20-40 minutes, the organic phase was extracted with ethyl acetate, dried over anhydrous sodium sulfate, and purified by column chromatography to obtain compound four; 1-2 parts of compound four were dissolved in 50-55 parts dichloromethane, and 1.5-2.5 parts p-nitrobenzene chloroformate and 1-1.5 parts triethylamine were added; after stirring at room temperature for 20 minutes, the solvent was removed by rotary evaporation and purified by column chromatography to obtain compound B; the macrocyclic monomer in step S2 is a stress-relieved macrocyclic monomer with functional groups or sequence-defined structural units on the main chain.

8. An internally release polyurethane composite material, characterized in that: The internal release polyurethane composite is obtained by the preparation method described in any one of claims 1-7.

9. An application of an internally release polyurethane compound, characterized in that: The internal release polyurethane compound prepared by the method of any one of claims 1-7 is added to automotive parts for application.

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