Design and combined casting applications of high-elasticity polyurethane gels

Abstract

This invention discloses the design and combined casting application of a highly elastic polyurethane gel. The method first designs and synthesizes a dedicated polyol monomer, using polypropylene glycol as an initiator, and performs ring-opening polymerization with propylene oxide in the presence of a bimetallic cyanide complex catalyst. Through segmented temperature control, polyols with hydroxyl values ​​of 80-120 mg KOH / g and molecular weights of 2000-4000 are obtained. Based on this, prepolymers A and B for the soft gel component, and prepolymers C and D for the hard gel component are prepared. Finally, through a combined casting process, the inner and outer gel layer prepolymer mixtures are sequentially cast, cured in stages, and then demolded to obtain a product with a composite structure. This invention, through molecular structure innovation and process synergy, solves the technical problems of traditional gel materials that make it difficult to simultaneously achieve high elasticity and high strength, and the ease of interlayer peeling. The resulting product has comprehensive advantages such as low hardness, high resilience, low permanent deformation, and excellent pressure dispersion.

Description

Technical Field

[0001] This invention relates to the field of polymer material preparation and application, specifically to a method for preparing polyurethane elastomer materials and their combined products. Background Technology

[0002] Polyurethane gel, as an important polymer material, has shown broad application prospects in medical care, sports protection, and household products due to its excellent elasticity, controllable mechanical properties, and good biocompatibility. Particularly in the medical care field, polyurethane gel pads are used as rehabilitation aids for long-term bedridden patients or postoperative recoveries. Their core function lies in effectively dispersing concentrated pressure on bony prominences through the material's own deformation capabilities, thereby reducing the risk of pressure sores and other pressure injuries. An ideal medical gel pad must possess a series of key properties: First, the material should have a low hardness close to that of human soft tissue, generally with a Shore 00 hardness of 0-20, to ensure an excellent skin-friendly feel and initial fit; second, it must have a high resilience of over 80% and a permanent deformation rate of less than 3% to ensure rapid recovery to its original shape after long-term, repeated pressure, maintaining stable support performance and extending product lifespan; furthermore, given the hygiene requirements of the medical environment, high-efficiency antibacterial properties are also an indispensable indicator; simultaneously, peak pressure reduction rate and average pressure reduction rate are key parameters for measuring its pressure dispersion effectiveness. A well-performing gel positioning pad can achieve a peak pressure reduction rate of 40-50% and an average pressure reduction rate of 30-40%. The comprehensive achievement of these properties not only directly relates to patient comfort and safety but is also a core metric for measuring product technology level, possessing significant social and economic value. Especially against the backdrop of an aging population and upgraded health needs, the development of high-performance gel pad products is particularly urgent.

[0003] Currently, existing technologies for preparing polyurethane gel products still face numerous challenges in achieving the aforementioned comprehensive performance. From a materials system perspective, most solutions rely on commercially available polyol raw materials. These general-purpose raw materials typically have a wide molecular weight distribution and limited precision in controlling functionality uniformity, resulting in insufficient regularity of the final polyurethane gel network structure and difficulty in forming an ideal microphase separation structure. The direct consequence is that the macroscopic mechanical properties of the material are often difficult to achieve simultaneously. For example, increasing crosslinking density to improve strength often sacrifices the mobility of molecular chain segments, leading to increased material hardness, decreased elastic recovery performance, and a higher permanent deformation rate, affecting product durability. Regarding prepolymer formulation and network construction strategies, existing technologies mostly employ relatively simple single prepolymer systems or A / B component designs. This approach makes it difficult to precisely and synergistically control the microstructure and distribution of the soft segments providing elasticity and the hard segments providing strength, making it difficult to achieve a high level of balance between the key indicators of high elasticity, high strength, and low permanent deformation in the gel material. Furthermore, for products with multilayer composite structures, a prominent problem faced by existing technologies is weak interlayer bonding. Common physical bonding or simple secondary casting processes struggle to achieve strong chemical bonding and effective molecular chain interpenetration at the interface of heterogeneous materials. This leads to interlayer delamination or peeling under long-term dynamic pressure, severely impacting the product's structural integrity and lifespan. From a manufacturing perspective, existing casting technologies often lack sufficient compatibility with material properties and are not precisely controlled for key process parameters such as gel time window, vacuum degassing efficiency, and curing temperature profile. This can easily result in internal bubbles, defects, or stress concentrations within the product, leading to inconsistent product performance, low yield rates, and hindering the large-scale, stable production of high-quality products.

[0004] The shortcomings of the aforementioned existing technologies stem from the failure to develop a systematic and integrated solution encompassing molecular design and molding processes. Technological improvements are often fragmented, focusing either on minor formulation tweaks or process optimization, failing to consider materials, structure, and processes as a cohesive whole. This results in a performance ceiling for products, unable to simultaneously achieve comprehensive high-end indicators such as high elasticity, low permanent deformation, high wear resistance, strong interlayer bonding, and excellent antibacterial properties. This creates a significant market gap: on the one hand, consumers and medical institutions urgently need high-quality products; on the other hand, technological bottlenecks hinder performance improvements. This supply-demand imbalance underscores the urgency and immense potential of original innovation and the development of next-generation high-performance polyurethane gel materials and their preparation technologies.

[0005] Based on a profound understanding of the limitations of existing technologies, this invention aims to fundamentally solve these problems. Its core design concept lies in breaking down the fragmented nature of traditional technological paths and constructing an integrated technological system that is closely linked and interconnected from the molecular source to the final product. The starting point of this invention is not to improve a single component or step in isolation, but rather to lay a solid foundation for the entire technology chain through independent molecular structural innovation. Specifically, the design concept of this invention begins with the redesign and controllable synthesis of polyol monomers—the key building block of polyurethane gels. By carefully selecting initiators, employing highly active bimetallic cyanide complex catalysts, and implementing a precise "segmented temperature-controlled" polymerization process, the aim is to synthesize specialized polyol monomers with specific soft segment structures, narrow molecular weight distributions, and high regularity. These structurally regular monomers are the molecular basis for forming a perfect microphase separation structure and achieving high resilience and low entropy change properties similar to bioelastomers, providing a possibility for overcoming the challenge of synergistically achieving high strength and high elasticity.

[0006] Building upon the successful acquisition of specialized polyol monomers, this invention extends its design philosophy further to the innovative design of prepolymer combinations. Addressing the different functional requirements of the inner and outer gels, this invention designs two sets of functionally synergistic prepolymer combinations. For the inner gel system, an innovative strategy combining long-chain flexible prepolymers with high-functionality rigid prepolymers is employed. The mixture not only forms a basic urethane network but also utilizes the excess NCO groups in the rigid prepolymer to construct a unique dynamic physical-chemical double-crosslinked network, synergistically enhancing elasticity and strength through an entropy-enthalpy compensation mechanism. For the outer gel system, a combination is designed consisting of a polyester-type prepolymer providing mechanical strength and a prepolymer containing both NCO groups and acrylate double bonds. This design introduces an innovative "dual curing mechanism": on the one hand, the NCO groups at the ends of the prepolymer can chemically react with the residual active hydrogen on the inner gel surface to form a strong covalent interfacial bond; on the other hand, the acrylate double bonds can undergo free radical polymerization under appropriate conditions, resulting in graft copolymerization with the polyester prepolymer, thereby forming a strong and tough physical-chemical double crosslinking network inside and between the layers of the outer gel. This prepolymer combination design based on functional synergy is key to ensuring that each gel layer performs its specific function and achieves a strong bond.

[0007] Finally, the design concept of this invention is perfectly embodied in the combined casting molding process that is highly compatible with the aforementioned material system. This process is not a general method, but rather a customized one. It innovatively introduces a thermoplastic polyurethane film as a functional surface layer, and ensures its perfect fit with the mold through vacuum adsorption technology. This film can also react with the outer gel during subsequent curing, preventing surface delamination. The core of the process lies in "sequential casting and staged curing": first, the inner gel prepolymer combination is cast and initially cured at a lower temperature to form a certain initial strength while retaining active functional groups on the surface; then, the outer gel prepolymer combination is cast, utilizing its highly reactive NCO groups to rapidly undergo interfacial chemical reactions with the inner gel surface; finally, overall co-curing is carried out through stepped heating, promoting the formation of chemical bonds and interpenetrating molecular chains between layers. This process design cleverly utilizes the differences in reactivity and functional group characteristics of each prepolymer to ensure strong interlayer bonding, fundamentally solving the technical problem of easy delamination in multilayer composite materials. Summary of the Invention

[0008] This invention relates to the design and combined casting application of a highly elastic polyurethane gel, specifically including a self-synthesized polyol monomer, a method for preparing a prepolymer based on the monomer, the formulation design of inner and outer gels, and a combined casting molding process. The following is a detailed description of the invention.

[0009] The technical solution adopted by this invention to solve its technical problem includes the following steps:

[0010] 1. Design and preparation of polyol monomers

[0011] This invention innovates first in the molecular design of polyol monomers. Its core lies in the preparation of a specialized polyol with a specific soft segment structure, expected to significantly improve the elastic recovery performance of the final polyurethane gel, through raw material selection and controlled synthesis processes. This design concept is deeply inspired by natural bioelastomers, whose high elasticity stems from a sophisticated microphase separation structure, enabling them to maximize elastic recovery and minimize permanent deformation during deformation through an entropy-enthalpy compensation mechanism. Traditional high-elasticity reinforcement strategies often sacrifice the degrees of freedom of chain segment movement, while this invention aims to solve the key challenge of achieving a balance between high strength and high resilience from the molecular level.

[0012] The monomer is prepared through the following steps: Polypropylene glycol (PPG, molecular weight 1000-2000) is used as the initiator and undergoes ring-opening polymerization with propylene oxide in the presence of a bimetallic cyanide complex catalyst. The catalyst dosage is 0.05-0.2 wt% of the initiator. The reaction process employs segmented temperature control: the first stage is carried out at 80-90℃ and 0.1-0.2 MPa pressure for 1-2 hours; the second stage involves raising the temperature to 100-120℃ and continuing the reaction at 0.3-0.5 MPa pressure for 1-4 hours. After the reaction, post-treatment processes such as vacuum dehydration, neutralization, and filtration are performed to obtain a polyol monomer with a hydroxyl value of 80-120 mg KOH / g and a molecular weight of 2000-4000.

[0013] PPG was chosen as the initiator because it can provide sufficiently long flexible segments, which is fundamental to achieving high elasticity and low hardness. DMC catalysts exhibit high activity, enabling the preparation of polyether polyols with low unsaturation and narrow molecular weight distribution. By precisely controlling its dosage to 0.05-0.2% of the initiator weight, side reactions can be effectively suppressed, ensuring that the final synthesized polyol monomers have higher molecular weight regularity and more uniform functionality. This lays the molecular foundation for the subsequent formation of a regular polymer network structure, achieving excellent resilience and low permanent deformation.

[0014] Simultaneously, a "segmented temperature control" strategy was introduced. The first stage initiates the reaction under relatively mild conditions (80-90℃, 0.1-0.2MPa), which helps control the reaction rate and ensures uniform initiation of chain growth. The second stage, increasing the temperature and pressure (100-120℃, 0.3-0.5MPa), effectively accelerates the insertion efficiency of propylene oxide, pushing the molecular chain further to the target range and promoting the microscopic ordered arrangement of chain segments. This controlled polymerization process helps form potential physical crosslinking points in the molecular chain, which are beneficial for stress dispersion. The resulting polyol monomer has a hydroxyl value of 80-120 mg KOH / g. This range allows it to react sufficiently with isocyanates to form a adequate crosslinking network to ensure strength, while its high molecular weight preserves the excellent flexibility and mobility of the soft segments. This polyol, based on a specific structural design, serves as a dedicated soft segment raw material for synthesizing highly elastic polyurethane gels. Its molecular chain structure creates ideal conditions for achieving low-entropy penalty properties similar to biological elastin, breaking through the limitations of traditional polyurethane gels in balancing elasticity and strength.

[0015] 2. Preparation of soft gel component prepolymer

[0016] Prepolymer A was prepared based on a self-synthesized polyol monomer. First, the polyol monomer was placed in a reactor and dehydrated for 2-4 hours at 105-125℃ and a vacuum of -0.095 MPa until the moisture content was below 0.03%. After dehydration, the system was cooled to 60-75℃, and 4,4'-diphenylmethane diisocyanate (MDI-100, purity ≥99.5%) was slowly added dropwise under nitrogen protection, controlling the NCO / OH molar ratio at 1.8-2.5. During the dropwise addition, the stirring rate was maintained at 200-400 rpm, and the temperature fluctuation did not exceed ±2℃. After the addition was complete, the temperature was gradually increased to 75-90℃, and the reaction was continued for 2-4 hours, with NCO content measured every 30 minutes. The reaction was terminated when the NCO content reached 8-12%, yielding prepolymer A with a viscosity range of 3000-5000 mPa·s (25℃).

[0017] Prepolymer B was prepared by reacting 1,4-butanediol (BDO, purity ≥99.8%) as a chain extender with toluene diisocyanate (TDI-80, 2,4-isomer content 80%). TDI-80 was first added to the reactor, preheated at 40-55℃ under a nitrogen atmosphere; then, BDO was slowly added dropwise over 1 hour, controlling the NCO / OH molar ratio at 2.5-3.5. During the dropwise addition, the reaction temperature was controlled to not exceed 70℃ by circulating cold water to avoid localized overheating and side reactions. After the addition was complete, the reaction was maintained at 65-75℃ for 0.5-2 hours until the NCO content reached 15-18%. The final viscosity range of prepolymer B was 1500-2500 mPa·s (25℃), and it was stored in a sealed, dry environment.

[0018] This invention breaks through the limitations of traditional single prepolymer structures in polyurethane gels in the design of prepolymers A and B. By stepwise controlling the ratio of soft and hard segments and their reactivity, it achieves precise optimization of the internal gel network structure. First, the invention incorporates a synergistic toughness and dynamic crosslinking design. Prepolymer A uses a high molecular weight polyol to react with MDI to form a flexible long-chain soft segment matrix, while prepolymer B constructs a rigid short-chain structure with high NCO content through a high molar ratio of TDI to BDO. After mixing, the excess isocyanate groups in prepolymer B not only react with the hydroxyl groups of prepolymer A but also form biuret crosslinking points with water or urea groups in the system, forming a dynamic physical-chemical double crosslinking network. When subjected to deformation, the hard segments act as physical crosslinking points dispersed in the soft segment phase, dissipating energy through entropic elasticity, thereby simultaneously improving resilience and resistance to permanent deformation. Meanwhile, the low NCO content (8-12%) of prepolymer A ensures a sufficient operating window (gel time 5-15 minutes) when mixed with prepolymer B, while the high reactivity of prepolymer B guarantees curing efficiency. In addition, by controlling the temperature in stages (80-90℃ reaction of prepolymer A and ≤70℃ temperature control of prepolymer B), side reactions such as TDI dimerization or urea reduction at high temperatures are avoided, ensuring the regularity of the network structure.

[0019] 3. Preparation of rigid gel component prepolymers

[0020] Prepolymer C was prepared using polyethylene adipate diol with a number average molecular weight of 1000-2000 and a hydroxyl value of 56-112 mg KOH / g as the soft segment raw material. First, it was dehydrated at 105-120℃ and a vacuum of -0.095 MPa for 2-4 hours until the moisture content was below 0.03%. After dehydration, the system was cooled to 70-85℃, and 4,4'-diphenylmethane diisocyanate (MDI-100, purity ≥99.5%) was slowly added under nitrogen protection at a molar ratio of NCO to OH of 1.5-2.0. During the dropwise addition, the stirring rate was maintained at 200-400 rpm, and the temperature fluctuation did not exceed ±2℃. After the addition was complete, the temperature was gradually increased to 85-95℃, and 0.01-0.05 wt% of dibutyltin dilaurate catalyst was added. The reaction was carried out for 2-4 hours, with samples taken every 30 minutes to determine the NCO content. The reaction was terminated when the NCO content reached 10-15%, yielding prepolymer C with a viscosity of 2000-4000 mPa·s (25℃).

[0021] Prepolymer D uses hydroxyethyl methacrylate (HEMA, hydroxyl value 430±10 mg KOH / g) as the active monomer and reacts with isophorone diisocyanate (IPDI, NCO content 37.5±0.5%) at an NCO to OH molar ratio of 1.2-1.6. First, IPDI is added to the reactor and preheated at 45-55℃. Then, HEMA is slowly added dropwise over 1 hour, followed by 0.01-0.05 wt% of dibutyltin dilaurate catalyst, while controlling the temperature to not exceed 80℃. After the addition is complete, the reaction is maintained at 65-80℃ for 1-2 hours, with NCO content measured every 30 minutes until the NCO content drops to 6-9%, at which point the reaction is terminated. The resulting prepolymer D is a pale yellow transparent liquid with a viscosity range of 800-1500 mPa·s (25℃).

[0022] The core design of prepolymers C and D in this invention lies in achieving high mechanical properties, excellent wear resistance, and strong adhesion to the inner gel layer through molecular structure innovation and synergistic effects, thereby solving the common interlayer delamination problem in multilayer gel materials. Prepolymer C uses a polyadipate-based polyester diol reacted with MDI to construct the strength framework of the outer gel. The polyester-type soft segments help form a regular structure, significantly improving the tensile strength, tear strength, and other mechanical properties of the product. Prepolymer D introduces hydroxyethyl methacrylate, a reactive monomer containing both acrylate double bonds and hydroxyl groups, and reacts with isophorone diisocyanate. This design allows the ends of prepolymer D molecules to retain both NCO groups and acrylate double bonds, achieving a dual curing mechanism: the NCO groups can chemically react with the hydroxyl or amine groups remaining on the inner gel surface to form strong chemical bonds; while the acrylate double bonds undergo graft copolymerization with the ester groups and other groups of prepolymer C, thus forming a physical-chemical double crosslinking network inside and between the layers of the outer gel. This synergistic effect is expected to enable the outer gel layer to have good mechanical properties while generating a strong interfacial bond with the inner gel that far exceeds physical adsorption.

[0023] 4. Combined casting of gels

[0024] Preheat the porous aluminum alloy mold to 35-45℃. Then, cut a 60-100μm thick thermoplastic polyurethane film and lay it flat on the mold surface. The polyurethane should have a hardness of 60-70A, an antibacterial rate (Staphylococcus aureus) of over 99%, and an elongation at break of ≥400%. Activate the vacuum system connected to the mold to achieve a vacuum level of -0.085 to -0.095 MPa inside the mold. Use the negative pressure to tightly adhere the TPU film to the mold cavity surface. Maintain vacuum adhesion for 3-6 minutes to ensure complete film shaping and eliminate surface wrinkles.

[0025] Add prepolymer A and prepolymer B to a two-component mixing tank at a weight ratio of 1:1.2-1.5 and mechanically stir at 200-400 rpm for 3-5 minutes. Then transfer the mixture to a vacuum degassing tank, activate the vacuum system, and achieve a vacuum level of -0.095 to -0.1 MPa within 30 seconds. Maintain this condition for degassing for 2-4 minutes. Pour the degassed mixture into a mold at a flow rate of 0.5-1.0 L / min. After casting, allow it to initially cure at 40-60℃ for 15-25 minutes.

[0026] Prepolymer C and prepolymer D are added to a two-component mixing tank at a weight ratio of 1:0.8-1.2. Then, 0.5-1.0 wt% of an organic bismuth catalyst (18-22% bismuth content) and 0.5-2.0 wt% of a nano-silver antibacterial agent are added. The mixture is stirred at 200-400 rpm for 4-6 minutes. The mixture is then transferred to a vacuum degassing tank, and the vacuum system is activated to achieve a vacuum level of -0.095 to -0.1 MPa within 30 seconds. This vacuum level is maintained for 2-4 minutes for degassing. The mixture is then poured onto the surface of the initially cured inner gel at a flow rate of 0.5-1.0 L / min. After pouring, the mold is transferred to a curing chamber, and the temperature is gradually increased to 65-75℃ over 0.5 hours, and cured for 2-3 hours. Finally, the product with a "TPU film-inner gel-outer gel" composite structure is obtained by demolding.

[0027] The composite casting molding process involved in this invention is innovative in that it systematically solves the common technical problems of weak interlayer bonding and easy peeling in multilayer gel composite materials through unique process design and material synergy. First, a thermoplastic polyurethane film is used as the functional surface layer of the composite structure, and vacuum adsorption technology is used to perfectly adhere it to the mold surface. This not only provides the product with a wear-resistant and easy-to-clean surface, but its soft texture also maintains good mechanical compatibility with the gel matrix. More importantly, during the subsequent heating and curing process, the molecular chains of this film can react with the isocyanate groups in the outer gel layer to form strong chemical bonds, thereby achieving integrated fusion of the surface layer and the main structure and avoiding the problem of surface delamination. The core innovation of this casting process lies in the staged casting and curing strategy designed for the inner and outer gel systems. After the inner gel prepolymers A and B are mixed and cast, preliminary curing is first performed. The purpose of this step is to allow the inner gel network to form a certain initial strength, while ensuring that its surface still retains sufficient active functional groups. Subsequently, when the mixture of outer gel prepolymers C and D is cast onto the surface of the inner gel, the highly reactive -NCO groups in prepolymer D rapidly react chemically with these active groups on the inner gel surface, forming a robust interface with covalent bonds. Furthermore, the organic bismuth catalyst added to the outer gel formulation further enhances the efficiency and depth of this interfacial reaction.

[0028] During the overall curing stage with stepped heating, the inner and outer gels undergo a complete cross-linking reaction as a whole. This process not only ensures the internal curing of each gel layer but also allows the interfacial region between the two layers to form a robust interpenetrating network structure through the interpenetration of chemical bonds and molecular chains. This strong interface, constructed by both chemical bonding and physical interpenetration, ensures that stress can be effectively transferred and dispersed between layers, thereby fundamentally preventing interlayer delamination during use and significantly improving the structural integrity and service life of the gel pad product. This casting molding process provides an innovative solution for the reliable fabrication of high-performance multilayer flexible composite materials.

[0029] This invention provides a systematic design and combined casting application scheme for highly elastic polyurethane gels. Its core lies in constructing a complete and integrated technical system that closely links molecular structure design to molding processes. This invention does not improve a single component or step in isolation, but rather starts from the source by independently designing and synthesizing a special polyol monomer with specific soft segment structures and functionalities, laying the molecular foundation for the subsequent preparation of prepolymers. Based on this monomer, an innovative combination of inner gels (prepolymers A and B) and outer gels (prepolymers C and D) is designed. The inner gel focuses on achieving high resilience and low permanent deformation, while the outer gel focuses on high mechanical strength, wear resistance, and strong adhesion to the inner gel. Finally, based on the reaction characteristics of these prepolymers, a customized combined casting molding process is developed, including vacuum adsorption shaping, sequential casting, and staged curing. This process cleverly utilizes the differences in reactivity and functional group characteristics of each prepolymer to ensure the formation of a strong chemical bond and physical interpenetrating network between layers. This ultimately results in a high-performance gel pad product with a "TPU film-soft inner gel-hard outer gel" composite structure, excellent performance, and strong interlayer bonding. The entire technical solution is interconnected, demonstrating a high degree of systematicity and synergy. The core innovations of this invention are as follows:

[0030] (1) Molecular design and controllable synthesis process of special polyol monomers

[0031] The primary innovation of this invention lies in its molecular-level design and independent synthesis of a specialized polyol monomer for highly elastic polyurethane gels. Unlike traditional methods that directly purchase commercially available polyols, this invention selects polypropylene glycol (PPG) as the initiator, innovatively employs a highly active bimetallic cyanide complex (DMC) catalyst, and implements a precise "segmented temperature-controlled" polymerization process. This design ensures stable reaction initiation and uniform chain growth under mild conditions in the first stage, while the second stage, under higher temperature and pressure, effectively promotes chain segment growth and microscopic ordered arrangement, ultimately yielding a polyol product with hydroxyl values ​​(80-120 mgKOH / g) and molecular weights (2000-4000) controlled within specific ranges. This monomer exhibits high molecular chain regularity and a narrow molecular weight distribution, laying the foundation for the formation of a well-defined microphase separation structure in the final gel network. This is a molecular-level key to achieving high resilience, low permanent deformation, and high energy recovery similar to bioelastomers, overcoming the limitation of traditional materials that struggle to simultaneously achieve high strength and high elasticity.

[0032] (2) Prepolymer combination design and dual curing mechanism based on functional synergy

[0033] This invention breaks through the traditional approach of using a single prepolymer in the prepolymer preparation stage, innovatively designing two sets of functionally synergistic prepolymer combinations for the inner and outer gels respectively. For the inner gel, a system composed of a long-chain flexible prepolymer A (synthesized from a self-made polyol and MDI) and a high-functionality rigid prepolymer B (synthesized from BDO and TDI) is designed. After mixing, the excess NCO groups in prepolymer B can not only react with A, but also construct a unique dynamic physical-chemical double crosslinking network, synergistically improving elasticity and strength. For the outer gel, a system composed of a polyester-type prepolymer C that provides mechanical strength and a prepolymer D containing NCO groups and acrylate double bonds is designed. This design introduces an innovative "dual curing mechanism": the NCO groups of prepolymer D can form chemical bonds with the active hydrogen on the surface of the inner gel, while its acrylate double bonds can undergo free radical polymerization, resulting in graft copolymerization with prepolymer C. This synergistic effect of chemical bonding and cross-linking forms a robust physical-chemical dual cross-linking network inside and between the layers of the outer gel, which is a key innovation for solving the problem of interlayer delamination.

[0034] (3) Interlayer composite and sequential curing casting process based on material properties

[0035] The third major innovation of this invention lies in its use of a combined casting process that is highly compatible with the reaction characteristics of the specific prepolymer system, rather than employing a general casting method. This process innovatively introduces a thermoplastic polyurethane film as the surface layer and utilizes vacuum adsorption technology to ensure perfect adhesion to the mold. This not only provides a functional surface but also allows the molecular chains to react with the inner gel to form bonds, preventing surface delamination. More importantly, the process employs a sequential casting and curing strategy of "preliminary curing - interfacial reaction - final co-curing." First, the inner gel prepolymer (A+B) is preliminarily cured at a lower temperature, retaining sufficient active functional groups on its surface. Then, the outer gel prepolymer (C+D) is cast, where the highly active NCO groups of prepolymer D rapidly react with the inner gel surface to form covalent bonds. Finally, in the overall curing stage with stepped heating, the inner and outer gel layers interpenetrate through chemical bonds and molecular chains to form a robust interpenetrating network structure. This process design fully understands and utilizes the reactivity and functional group characteristics of each prepolymer, ensuring that stress is effectively transferred and dispersed between layers, fundamentally preventing interlayer delamination, and achieving product structural integrity and long service life.

[0036] (4) Integrated technical approach and performance breakthrough

[0037] The profound innovation of this invention lies in its integrated technical approach. From the synthesis of specialized monomers to the targeted design of inner and outer gel prepolymers, and then to the casting process closely related to material properties, the entire technical solution is an organic whole, with strong correlation and synergy between each step. This systematic design concept ensures that the final product perfectly combines the high elasticity of the inner gel with the high strength, wear resistance, and excellent interlayer bonding of the outer gel, while meeting comprehensive performance indicators such as high peak pressure reduction rate and high antibacterial rate. It solves the key technical problem of easy delamination of multilayer gel materials under long-term dynamic load, providing a reliable solution for the application of high-performance gel pads in medical, sports protection, and other fields. Detailed Implementation

[0038] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0039] Example 1

[0040] (1) Preparation of special polyol monomers

[0041] Following the four sets of stepwise process parameters shown in Table 1, specialized polyol monomers were prepared in a pressure-resistant reactor equipped with a stirrer, thermometer, vacuum system, and feed inlet. The resulting four different specifications of specialized polyol monomers were labeled as monomers 1-1#, 1-2#, 1-3#, and 1-4#. In the reaction, polypropylene glycol (PPG2000) with a molecular weight of 2000 was used as the initiator and added to the reactor, followed by heating and vacuum dehydration. Then, under nitrogen protection, the appropriate amounts of bimetallic cyanide complex (DMC) catalyst were added according to the process parameters shown in Table 1, and a metered amount of propylene oxide (PO) was introduced to carry out the ring-opening polymerization reaction. The reaction strictly followed a segmented temperature control strategy: the reaction was first carried out at a lower temperature and pressure for a period of time, and then the temperature and pressure were increased to continue the reaction. After the reaction, the product underwent vacuum dehydration, neutralization, filtration, and other post-treatments to obtain four polyol monomers with hydroxyl values ​​and molecular weights within the target range.

[0042] Table 1. Synthesis process parameters and product indicators of polyol monomers

[0043] Monomer 1-1# 0.05 80℃ / 0.1MPa / 2h 100℃ / 0.3MPa / 4h 120±3 2000±100 Monomer 1-2# 0.10 80℃ / 0.15MPa / 1.5h 110℃ / 0.5MPa / 2.5h 100±3 3000±100 Monomer 1-3# 0.15 90℃ / 0.2MPa / 1h 120℃ / 0.5MPa / 1h 85±3 3600±100 Monomer 1-4# 0.20 90℃ / 0.2MPa / 1h 120℃ / 0.5MPa / 1h 80±3 4000±100

[0044] (2) Preparation of prepolymer

[0045] Based on the polyol monomers synthesized above, prepolymers A, B, C, and D were further synthesized and prepared, with prepolymer A prepared using four different monomers.

[0046] In the preparation of prepolymer A, 1 kg of the synthesized polyol monomer was first placed in a reactor and dehydrated for 3 hours at 125℃ and a vacuum of -0.095 MPa, with the moisture content measured to be less than 0.02%. After dehydration, the system was cooled to 60℃, and 4,4'-diphenylmethane diisocyanate (MDI-100) was slowly added dropwise under nitrogen protection and a stirring rate of 300 rpm, controlling the NCO / OH molar ratio at 2.5. Temperature fluctuations during the addition process were controlled within ±2℃. After the addition was complete, the temperature was gradually increased to 90℃, and the reaction was continued for 3 hours, with samples taken every 30 minutes to determine the NCO content. The reaction was terminated when the NCO content reached 8.5%, and the mixture was cooled to room temperature to obtain prepolymer A with a viscosity of 4500 mPa·s (25℃). Polyol monomers 1-4# were synthesized sequentially to obtain four prepolymers A, which were labeled as prepolymer A-1-1, prepolymer A-1-2, prepolymer A-1-3, and prepolymer A-1-4, respectively.

[0047] In the preparation of prepolymer B, 5 kg of toluene diisocyanate (TDI-80) was added to the reactor, preheated at 40°C, and maintained under a nitrogen atmosphere. 1,4-Butanediol (BDO) was slowly added dropwise over 1 hour, controlling the NCO / OH molar ratio at 2.5. During the addition, the reaction temperature was strictly controlled to not exceed 65°C using a cooling water circulation system. After the addition was complete, the reaction was maintained at 65°C for 2 hours, during which the NCO content was monitored. The reaction was terminated when the NCO content reached 17.5%, yielding prepolymer B with a viscosity of 2500 mPa·s (25°C), which was then sealed and stored.

[0048] In the preparation of prepolymer C, 10 kg of polyethylene adipate diol with a number average molecular weight of 2000 and a hydroxyl value of 56 mg KOH / g was dehydrated at 120℃ and a vacuum of -0.095 MPa for 3 hours until the moisture content was <0.03%. The temperature was then lowered to 70℃, and MDI-100 was slowly added under nitrogen protection, controlling the NCO / OH molar ratio at 2.0. After the addition was complete, the temperature was raised to 95℃, and 5 g of dibutyltin dilaurate catalyst (0.05 wt% of the total system weight) was added. The reaction was continued for 3 hours until the NCO content reached 10.5%, yielding prepolymer C with a viscosity of 3800 mPa·s (25℃).

[0049] In the preparation of prepolymer D, 4 kg of isophorone diisocyanate (IPDI) was added to a reactor and preheated at 45°C. Hydroxyethyl methacrylate (HEMA) was slowly added dropwise over 1 hour, controlling the NCO / OH molar ratio at 1.2. Simultaneously, 2 g of dibutyltin dilaurate catalyst (0.05 wt% of the total system weight) was added, and the temperature was controlled to not exceed 70°C. After the addition was complete, the reaction was maintained at 65°C for 2 hours, and the reaction was terminated when the NCO content decreased to 8.8%, yielding prepolymer D with a viscosity of 1500 mPa·s (25°C).

[0050] (3) Combined casting

[0051] Preheat a 10×10cm aluminum alloy mold with micropores to 40℃. Cut an 80μm thick thermoplastic polyurethane (TPU) film with a hardness of 65A (99.5% antibacterial rate against Staphylococcus aureus) and lay it flat on the mold cavity surface. Activate the vacuum system connected to the mold to achieve a vacuum level of -0.09MPa inside the mold. Use this negative pressure to firmly adhere the TPU film to the mold surface, maintaining vacuum for 5 minutes to ensure complete film setting and no wrinkles.

[0052] After the film has set, the casting of the inner gel layer begins. Prepolymer A and prepolymer B are added to a two-component mixing tank at a weight ratio of 1:1.35 and mechanically stirred at 300 rpm for 4 minutes. The mixture is then transferred to a vacuum degassing tank, where a vacuum of -0.098 MPa is established within 30 seconds, and this condition is maintained for degassing for 3 minutes. The degassed mixture is then injected at a flow rate of 0.8 L / min into a mold already coated with a TPU film. The mold is then transferred to an oven at 40-60°C for initial curing for 20 minutes, forming a partially cured inner gel layer with a thickness of 24 mm.

[0053] Next, the outer gel layer was cast. Prepolymer C and prepolymer D were added to another two-component mixing tank at a weight ratio of 1:1.0. 0.8 wt% of an organic bismuth catalyst (bismuth content 18-22%) and 1.0 wt% of nano-silver antibacterial agent were added to the mixture. The mixture was stirred at 300 rpm for 5 minutes. The mixture was then transferred to a vacuum degassing tank, and the vacuum level inside the tank was brought to -0.098 MPa within 30 seconds. This condition was maintained for degassing for 3 minutes. The degassed outer gel mixture was then uniformly poured onto the surface of the initially cured inner gel layer at a flow rate of 0.8 L / min, resulting in a gel layer thickness of 12 mm.

[0054] After casting, the entire mold is transferred to a temperature-controlled curing chamber. The temperature is gradually increased to 70°C over 0.5 hours and maintained at 70°C for 2.5 hours for curing. After curing, the mold is allowed to cool naturally to room temperature and then demolded to obtain the polyurethane gel pad product.

[0055] The above casting was performed using prepolymers A-1-1, A-1-2, A-1-3, and A-1-4 respectively, resulting in four types of gel pads, labeled as gel pads 1-1, 1-2, 1-2, and 1-4.

[0056] (4) Performance testing and results

[0057] The key properties of the four prepared gel pads were tested, and the results are listed in Table 2.

[0058] Table 2 Comparison of the performance of gel pads prepared using different polyol monomers

[0059] Hardness (Shore 00) ASTM D2240 17 13 10 8 Rebound rate (%) ASTM D2632 81 84 87 88 Permanent deformation rate (%) ASTM D395 Method B 3.0 2.7 2.3 2.4 Peak pressure reduction rate (%) A pressure distribution testing system was used to simulate bony prominence compression. 42 45 47 46 Average pressure reduction rate (%) A pressure distribution testing system was used to simulate bony prominence compression. 31 34 38 36

[0060] Test results show that the polyol monomers prepared using the method of this invention under different synthesis parameters can all be successfully used to prepare highly elastic polyurethane gel pads with a three-layer composite structure. All samples exhibit good overall performance, with the sample based on monomer 3 showing particularly excellent performance in terms of resilience, low permanent deformation, and pressure dispersion properties, demonstrating the feasibility and effectiveness of the technical solution of this invention.

[0061] Example 2

[0062] (1) Preparation of special polyol monomers

[0063] In a pressure-resistant reactor equipped with a stirrer, thermometer, vacuum system, and feed inlet, polypropylene glycol (PPG2000) with a molecular weight of 2000 was added as an initiator, heated to 110°C, and dehydrated under vacuum for 2 hours. Subsequently, under nitrogen protection, a bimetallic cyanide complex (DMC) catalyst (0.10 wt% of the initiator) was added, followed by the introduction of a measured amount of propylene oxide (PO) to initiate a ring-opening polymerization reaction. The reaction process employed segmented temperature control: the first stage was carried out at 85°C and 0.20 MPa for 1.8 hours; the second stage was continued at 110°C and 0.4 MPa for 2.5 hours. After the reaction, the product underwent vacuum dehydration, neutralization, filtration, and other post-treatments to obtain a polyol monomer with a hydroxyl value of 95±3 mgKOH / g and a molecular weight of 3300±100, labeled as monomer 2#.

[0064] (2) Preparation of prepolymer

[0065] Based on the polyol monomer 2# synthesized above, prepolymers A, B, C, and D were further synthesized and prepared.

[0066] In the preparation of prepolymer A, 5 kg of monomer #2 was placed in a reactor and dehydrated for 2 hours at 105℃ and -0.095 MPa vacuum, with a moisture content of less than 0.025%. After dehydration, the system was cooled to 75℃, and 4,4'-diphenylmethane diisocyanate (MDI-100) was slowly added dropwise under nitrogen protection and a stirring rate of 200 rpm, controlling the NCO / OH molar ratio at 1.8. Temperature fluctuations during the addition were controlled within ±2℃. After the addition was complete, the temperature was gradually increased to 75℃, and the reaction was continued for 4 hours, with NCO content measured every 30 minutes. The reaction was terminated when the NCO content reached 11.5%, and the mixture was cooled to room temperature to obtain prepolymer A with a viscosity of 3200 mPa·s (25℃).

[0067] In the preparation of prepolymer B, 5 kg of toluene diisocyanate (TDI-80) was added to the reactor, preheated at 55°C, and maintained under a nitrogen atmosphere. 1,4-Butanediol (BDO) was slowly added dropwise over 1 hour, controlling the NCO / OH molar ratio at 3.5. During the dropwise addition, the reaction temperature was controlled to not exceed 70°C by circulating cold water. After the addition was complete, the reaction was maintained at 75°C for 0.5 hours, during which the NCO content was monitored. The reaction was terminated when the NCO content reached 15.5%, yielding prepolymer B with a viscosity of 1800 mPa·s (25°C), which was then sealed and stored.

[0068] In the preparation of prepolymer C, 10 kg of polyethylene adipate diol with a number average molecular weight of 1000 and a hydroxyl value of 112 mgKOH / g was dehydrated at 105℃ and a vacuum of -0.095 MPa for 2 hours until the moisture content was <0.03%. The temperature was then lowered to 85℃, and MDI-100 was slowly added under nitrogen protection, controlling the NCO / OH molar ratio at 1.5. After the addition was complete, the temperature was raised to 85℃, and 3 g of dibutyltin dilaurate catalyst (0.03 wt% of the total system weight) was added. The reaction was carried out for 4 hours until the NCO content reached 14.5%, yielding prepolymer C with a viscosity of 2200 mPa·s (25℃).

[0069] In the preparation of prepolymer D, 4 kg of isophorone diisocyanate (IPDI) was added to a reactor and preheated at 55°C. Hydroxyethyl methacrylate (HEMA) was slowly added dropwise over 1 hour, controlling the NCO / OH molar ratio at 1.6. Simultaneously, 3 g of dibutyltin dilaurate catalyst (0.075 wt% of the total system weight) was added, and the temperature was controlled to not exceed 80°C. After the addition was complete, the reaction was maintained at 80°C for 1 hour, and the reaction was terminated when the NCO content decreased to 6.5%, yielding prepolymer D with a viscosity of 900 mPa·s (25°C).

[0070] (3) Combined casting

[0071] This embodiment employs a combination of four sets of stepped parameters for casting to investigate the impact of casting process parameters on product performance. The four sets of casting process parameters are shown in Table 3. First, a 10×10cm aluminum alloy mold with micropores is preheated to the appropriate temperature. An 80μm thick thermoplastic polyurethane (TPU) film with a hardness of 65A (Staphylococcus aureus antibacterial rate ≥99%) is cut and laid flat on the mold cavity surface. The vacuum system is activated to achieve the appropriate vacuum level inside the mold, using negative pressure to adsorb and shape the TPU film, maintaining this adsorption for the appropriate time.

[0072] Next, the inner gel layer is cast. Prepolymer A and prepolymer B are mixed at a weight ratio of 1:1.35 and mechanically stirred at 300 rpm for the appropriate time. The mixture is then transferred to a vacuum degassing tank, where the vacuum level is reached within 30 seconds, followed by degassing for the appropriate time. The degassed mixture is then injected into the mold at a flow rate of 0.8 L / min and pre-cured at the appropriate temperature for the appropriate time, forming a pre-cured inner gel layer with a thickness of 23 mm.

[0073] Then, the outer gel layer was cast. Prepolymer C and prepolymer D were mixed at a weight ratio of 1:1.0, and 0.8 wt% of an organic bismuth catalyst (bismuth content 18-22%) and 1.0 wt% of nano-silver antibacterial agent were added to the mixture, which was stirred for the appropriate time. The mixture was then transferred to a vacuum degassing tank, and the vacuum level inside the tank was raised to the appropriate value within 30 seconds, followed by degassing for the appropriate time. The mixture was poured onto the surface of the initially cured inner gel at a flow rate of 0.8 L / min, resulting in a gel layer thickness of 11 mm. Finally, the mold was transferred to a curing chamber, and the temperature was gradually increased to the appropriate level over 0.5 hours, and then maintained at that temperature for the appropriate time. After demolding, four types of gel pads were obtained, labeled gel pads 2-1# to 2-4#.

[0074] Table 3 Casting process step parameters

[0075] Mold preheating / pouring temperature (°C) 35 38 42 45 TPU film vacuum adsorption Vacuum degree (MPa): -0.085 Time (min): 3 Vacuum degree (MPa): -0.088 Time (min): 4 Vacuum degree (MPa): -0.092 Time (min): 5 Vacuum degree (MPa): -0.095 Time (min): 6 Intragel mixture Stirring time (min): 3 Degassing vacuum degree (MPa): -0.095 Degassing time (min): 2 Initial curing temperature (°C): 40 Time (min): 15 Stirring time (min): 3.5 Degassing vacuum (MPa): -0.097 Degassing time (min): 2.5 Initial curing temperature (°C): 45 Time (min): 18 Stirring time (min): 4 Degassing vacuum degree (MPa): -0.098 Degassing time (min): 3 Initial curing temperature (°C): 50 Time (min): 20 Stirring time (min): 5 Degassing vacuum (MPa): -0.1 Degassing time (min): 4 Initial curing temperature (°C): 60 Time (min): 25 External gel mixture Stirring time (min): 4. Degassing conditions are the same as for internal gelation. Stirring time (min): 4.5. Degassing conditions are the same as for internal gel. Stirring time (min): 5. Degassing conditions are the same as for internal gel. Stirring time (min): 6. Degassing conditions are the same as for internal gel. Final curing Temperature (°C): 65 Time (h): 2 Temperature (°C): 68 Time (h): 2.5 Temperature (°C): 72 Time (h): 2.5 Temperature (°C): 75 Time (h): 3

[0076] (4) Performance testing and results

[0077] The key properties of the four prepared gel pads were tested, and the results are listed in Table 4.

[0078] Table 4. Performance comparison of gel pads prepared using different casting methods

[0079] Hardness (Shore 00) ASTM D2240 12 11 10 9 Rebound rate (%) ASTM D2632 82 84 86 85 Permanent deformation rate (%) ASTM D395 Method B 3.2 2.8 2.5 2.6 Peak pressure reduction rate (%) Pressure distribution testing system 43 46 48 47 Average pressure reduction rate (%) Pressure distribution testing system 32 35 37 36

[0080] Test results show that the method of this invention can successfully prepare highly elastic polyurethane gel pads with a three-layer composite structure under different casting process parameters. All samples exhibit good overall performance, with the product using the third group of processes showing the most balanced and excellent performance across all aspects. This demonstrates the significant impact of casting process parameters on the final product performance, as well as the rationality and controllability of the process parameter range of this invention.

[0081] Example 3

[0082] (1) Preparation of special polyol monomers

[0083] In a pressure-resistant reactor equipped with a stirrer, thermometer, vacuum system, and feed inlet, polypropylene glycol (PPG2000) with a molecular weight of 2000 was added as an initiator, heated to 115°C, and dehydrated under vacuum for 2.5 hours. Subsequently, under nitrogen protection, a bimetallic cyanide complex (DMC) catalyst (0.12 wt% of the initiator) was added, followed by the introduction of a measured amount of propylene oxide (PO) to initiate a ring-opening polymerization reaction. The reaction process employed segmented temperature control: the first stage was carried out at 87°C and 0.18 MPa for 1.5 hours; the second stage was continued at 115°C and 0.45 MPa for 2 hours. After the reaction, the product underwent vacuum dehydration, neutralization, filtration, and other post-treatments to obtain a polyol monomer with a hydroxyl value of 98±3 mg KOH / g and a molecular weight of 3200±100, labeled as monomer 3#.

[0084] (2) Preparation of prepolymer

[0085] Based on the polyol monomer 3# synthesized above, prepolymers A, B, C, and D were further synthesized and prepared.

[0086] Based on the polyol monomer 3# synthesized above, this embodiment uses appropriate process parameters to prepare four prepolymers.

[0087] In the preparation of prepolymer A, 5 kg of monomer #3 was placed in a reactor and dehydrated for 3 hours at 115℃ and a vacuum of -0.095 MPa, with the moisture content measured to be less than 0.028%. After dehydration, the system was cooled to 68℃, and 4,4'-diphenylmethane diisocyanate (MDI-100) was slowly added dropwise under nitrogen protection and a stirring rate of 300 rpm, controlling the NCO / OH molar ratio at 2.2. Temperature fluctuations during the addition process were controlled within ±2℃. After the addition was complete, the temperature was gradually increased to 82℃, and the reaction was continued for 3 hours, with samples taken every 30 minutes to determine the NCO content. The reaction was terminated when the NCO content reached 10.2%, and the mixture was cooled to room temperature to obtain prepolymer A with a viscosity of 3800 mPa·s (25℃).

[0088] In the preparation of prepolymer B, 5 kg of toluene diisocyanate (TDI-80) was added to the reactor, preheated at 48°C, and maintained under a nitrogen atmosphere. 1,4-Butanediol (BDO) was slowly added dropwise over 1 hour, controlling the NCO / OH molar ratio at 3.0. During the dropwise addition, the reaction temperature was controlled to not exceed 68°C by circulating cold water. After the addition was complete, the reaction was maintained at 70°C for 1.2 hours, during which the NCO content was monitored. The reaction was terminated when the NCO content reached 16.8%, yielding prepolymer B with a viscosity of 2000 mPa·s (25°C), which was then sealed and stored.

[0089] In the preparation of prepolymer C, 10 kg of polyethylene adipate diol with a number average molecular weight of 1500 and a hydroxyl value of 75 mg KOH / g was dehydrated at 112℃ and a vacuum of -0.095 MPa for 3 hours until the moisture content was <0.03%. The temperature was then lowered to 78℃, and MDI-100 was slowly added under nitrogen protection, controlling the NCO / OH molar ratio at 1.8. After the addition was complete, the temperature was raised to 90℃, and 4 g of dibutyltin dilaurate catalyst (0.04 wt% of the total system weight) was added. The reaction was continued for 3 hours until the NCO content reached 12.8%, yielding prepolymer C with a viscosity of 3000 mPa·s (25℃).

[0090] In the preparation of prepolymer D, 4 kg of isophorone diisocyanate (IPDI) was added to a reactor and preheated at 50°C. Hydroxyethyl methacrylate (HEMA) was slowly added dropwise over 1 hour, controlling the NCO / OH molar ratio at 1.4. Simultaneously, 2.5 g of dibutyltin dilaurate catalyst (0.06 wt% of the total system weight) was added, and the temperature was controlled to not exceed 75°C. After the addition was complete, the reaction was maintained at 72°C for 1.5 hours, and the reaction was terminated when the NCO content decreased to 7.8%, yielding prepolymer D with a viscosity of 1200 mPa·s (25°C).

[0091] (3) Combined casting

[0092] Preheat a 10×10cm aluminum alloy mold with micropores to 40℃. Cut an 80μm thick thermoplastic polyurethane (TPU) film (with an antibacterial rate of ≥99% against Staphylococcus aureus) and lay it flat on the mold cavity surface. Activate the vacuum system connected to the mold to achieve a vacuum level of -0.09MPa inside the mold. Use the negative pressure to tightly adhere the TPU film to the mold surface, maintaining vacuum adhesion for 5 minutes to ensure the film is completely set and wrinkle-free.

[0093] Prepolymer A and prepolymer B were added to a two-component mixing tank at a weight ratio of 1:1.35 and mechanically stirred at 300 rpm for 4 minutes. The mixture was then transferred to a vacuum degassing tank, where a vacuum of -0.098 MPa was established within 30 seconds, and this condition was maintained for degassing for 3 minutes. The degassed mixture was then injected at a flow rate of 0.8 L / min into a mold pre-coated with a TPU film. The mold was then placed at 50°C for initial curing for 20 minutes, forming a 24 mm thick initial cured inner gel layer.

[0094] Prepolymer C and prepolymer D were added to another two-component mixing tank at a weight ratio of 1:1.0. 0.8 wt% of an organic bismuth catalyst (bismuth content 18-22%) and 1.0 wt% of nano-silver antibacterial agent were added to the mixture. After stirring at 300 rpm for 5 minutes, the mixture was transferred to a vacuum degassing tank. The vacuum level inside the tank was brought to -0.098 MPa within 30 seconds, and degassing was performed for 3 minutes. The degassed outer gel mixture was then uniformly poured onto the surface of the initially cured inner gel layer at a flow rate of 0.8 L / min, controlling the outer gel layer thickness to 13 mm.

[0095] After casting, the entire mold was transferred to a programmable temperature curing chamber. The temperature was gradually increased to 70°C over 0.5 hours and then maintained at 70°C for 2.5 hours for curing. After curing, the mold was allowed to cool naturally to room temperature and then demolded to obtain a gel pad product with a "TPU film-inner gel-outer gel" composite structure, labeled as Sample 3.

[0096] Comparative Examples 1-3

[0097] For comparison, three commercially available polyurethane gel prepolymers were purchased.

[0098] Comparative Example 1 uses a soft two-component prepolymer. Component A has a viscosity of 2800±300 mPa·s (25℃) and an NCO content of 10.5±0.5%. Component B has a viscosity of 1200±200 mPa·s (25℃) and a hydroxyl value of 95±5 mg KOH / g.

[0099] Comparative Example 2 uses a medium-hardness two-component prepolymer. Component A has a viscosity of 3600±300 mPa·s (25℃) and an NCO content of 11.0±0.5%. Component B has a viscosity of 1300±200 mPa·s (25℃) and a hydroxyl value of 85±5 mg KOH / g.

[0100] Comparative Example 3 uses a relatively rigid two-component prepolymer. Component A has a viscosity of 4000±300 mPa·s (25℃) and an NCO content of 12.0±0.5%. Component B has a viscosity of 1600±200 mPa·s (25℃) and a hydroxyl value of 80±5 mg KOH / g.

[0101] Following the supplier's recommended formulation and process parameters, and using the same mold and TPU film as in Example 3, three types of polyurethane gel prepolymers were cast to obtain gel pad samples of Comparative Examples 1, 2, and 3, respectively.

[0102] The performance of the gel pad samples from Example 3 and Comparative Examples 1-3 was tested, and the results are listed in Table 5.

[0103] Table 5. Performance comparison of gel pads in Example 3 and Comparative Examples 1-3

[0104] Hardness (Shore 00) ASTM D2240 9 15 20 28 Rebound rate (%) ASTM D2632 88 78 72 66 Permanent deformation rate (%) ASTM D395 Method B 2.3 4.7 4.2 3.5 Peak pressure reduction rate (%) Pressure distribution testing system 51 41 36 33 Average pressure reduction rate (%) Pressure distribution testing system 39 31 26 22 Antibacterial properties (film surface) (%) GB / T 31402 99.6 99.5 99.6 99.5 Antibacterial properties (bottom seal) (%) GB / T 31402 99.3 65.1 63.2 66.5

[0105] As shown in Table 5, the sample of Example 3, prepared using the method of this invention, significantly outperformed the three commercially available comparative products in all key performance indicators. Although the hardness of Comparative Examples 1-3 showed a gradient from soft to relatively hard, their resilience, resistance to permanent deformation, and pressure dispersion efficiency all decreased with increasing hardness. In contrast, the sample of Example 3 successfully achieved an excellent balance between low hardness and high resilience (86%), low permanent deformation, and efficient pressure dispersion, fully demonstrating the comprehensive advantages of high elasticity brought about by the invention through independent material design and combined casting process. Furthermore, the antibacterial properties of the product of this invention are also superior and more uniform. This proves the effectiveness and advancement of the technology of this invention in solving the problem of the difficulty in achieving the desired performance of traditional polyurethane gels.

[0106] Example 4

[0107] (1) Preparation of special polyol monomers

[0108] In a pressure-resistant reactor equipped with a stirrer, thermometer, vacuum system, and feed inlet, polypropylene glycol (PPG1500) with a molecular weight of 1500 was added as an initiator, heated to 118°C, and dehydrated under vacuum for 2.2 hours. Subsequently, under nitrogen protection, a bimetallic cyanide complex (DMC) catalyst (0.08 wt% of the initiator) was added, followed by the introduction of a measured amount of propylene oxide (PO) to initiate a ring-opening polymerization reaction. The reaction was carried out using segmented temperature control: the first stage was conducted at 82°C and 0.16 MPa for 1.2 hours; the second stage was conducted at 108°C and 0.38 MPa for 1.8 hours. After the reaction, the product was subjected to vacuum dehydration, neutralization, filtration, and other post-treatments to obtain a polyol monomer with a hydroxyl value of 92±3 mg KOH / g and a molecular weight of 2800±100, labeled as monomer 4#.

[0109] (2) Preparation of prepolymer

[0110] Based on the polyol monomer 4# synthesized above, prepolymers A, B, C, and D were further synthesized and prepared.

[0111] In the preparation of prepolymer A, 5 kg of monomer #4 was placed in a reactor and dehydrated for 2.5 hours at 112℃ and a vacuum of -0.095 MPa, with a moisture content of less than 0.026%. After dehydration, the system was cooled to 65℃, and 4,4'-diphenylmethane diisocyanate (MDI-100) was slowly added dropwise under nitrogen protection and a stirring rate of 280 rpm, controlling the NCO / OH molar ratio at 2.0. Temperature fluctuations during the addition were controlled within ±2℃. After the addition was complete, the temperature was gradually increased to 78℃, and the reaction was continued for 2.5 hours, with NCO content measured every 30 minutes. The reaction was terminated when the NCO content reached 9.8%, and the mixture was cooled to room temperature to obtain prepolymer A with a viscosity of 3500 mPa·s (25℃).

[0112] In the preparation of prepolymer B, 5 kg of toluene diisocyanate (TDI-80) was added to the reactor, preheated at 46°C, and maintained under a nitrogen atmosphere. 1,4-Butanediol (BDO) was slowly added dropwise over 1 hour, controlling the NCO / OH molar ratio at 2.8. During the addition, the reaction temperature was controlled to not exceed 66°C by circulating cold water. After the addition was complete, the reaction was maintained at 68°C for 1.0 hour, during which the NCO content was monitored. The reaction was terminated when the NCO content reached 16.2%, yielding prepolymer B with a viscosity of 1900 mPa·s (25°C), which was then sealed and stored.

[0113] In the preparation of prepolymer C, 10 kg of polyethylene adipate diol with a number average molecular weight of 1800 and a hydroxyl value of 68 mg KOH / g was dehydrated at 108℃ and a vacuum of -0.095 MPa for 2.5 hours until the moisture content was <0.03%. The temperature was then lowered to 76℃, and MDI-100 was slowly added under nitrogen protection, controlling the NCO / OH molar ratio at 1.7. After the addition was complete, the temperature was raised to 88℃, and 3.5 g of dibutyltin dilaurate catalyst (0.035 wt% of the total system weight) was added. The reaction was carried out for 2.5 hours until the NCO content reached 11.8%, yielding prepolymer C with a viscosity of 2800 mPa·s (25℃).

[0114] In the preparation of prepolymer D, 4 kg of isophorone diisocyanate (IPDI) was added to a reactor and preheated at 48°C. Hydroxyethyl methacrylate (HEMA) was slowly added dropwise over 1 hour, controlling the NCO / OH molar ratio at 1.3. Simultaneously, 2.2 g of dibutyltin dilaurate catalyst (0.055 wt% of the total system weight) was added, and the temperature was controlled to not exceed 76°C. After the addition was complete, the reaction was maintained at 68°C for 1.2 hours, and the reaction was terminated when the NCO content decreased to 7.2%, yielding prepolymer D with a viscosity of 1100 mPa·s (25°C).

[0115] (3) Combined casting

[0116] Preheat a 10×10cm aluminum alloy mold with micropores to 38℃. Cut a 75μm thick thermoplastic polyurethane (TPU) film with a hardness of 63A (≥99% antibacterial rate against Staphylococcus aureus) and lay it flat on the mold cavity surface. Activate the vacuum system connected to the mold to achieve a vacuum level of -0.088MPa inside the mold. Use the negative pressure to tightly adhere the TPU film to the mold surface, maintaining vacuum adhesion for 4.5 minutes to ensure the film is completely set and wrinkle-free.

[0117] Prepolymer A and prepolymer B were added to a two-component mixing tank at a weight ratio of 1:1.28 and mechanically stirred at 280 rpm for 3.5 minutes. The mixture was then transferred to a vacuum degassing tank, where a vacuum of -0.096 MPa was established within 30 seconds, and this condition was maintained for degassing for 2.5 minutes. The degassed mixture was then injected at a flow rate of 0.7 L / min into a mold pre-coated with a TPU film. The mold was then placed at 48°C for initial curing for 18 minutes, forming a 26 mm thick initial cured inner gel layer.

[0118] Prepolymer C and prepolymer D were added to another two-component mixing tank at a weight ratio of 1:0.9. 0.7 wt% of an organic bismuth catalyst (bismuth content 18-22%) and 0.8 wt% of nano-silver antibacterial agent were added to the mixture. After stirring at 280 rpm for 4.5 minutes, the mixture was transferred to a vacuum degassing tank. The vacuum level inside the tank was brought to -0.096 MPa within 30 seconds, and degassing was performed for 2.5 minutes. The degassed outer gel mixture was then uniformly poured onto the surface of the initially cured inner gel layer at a flow rate of 0.7 L / min, controlling the outer gel layer thickness to 12 mm.

[0119] After casting, the entire mold was transferred to a temperature-controlled curing chamber. The temperature was gradually increased to 68°C over 0.5 hours and then maintained at 68°C for 2.2 hours for curing. After curing, the mold was allowed to cool naturally to room temperature and demolded to obtain a gel pad product with a "TPU film-inner gel-outer gel" composite structure, labeled as Sample 4.

[0120] Comparative Examples 4-6

[0121] In comparison, four groups of commercially available polyurethane gel prepolymers were purchased, whose apparent parameters (viscosity, NCO content, etc.) were similar to those of prepolymers A, B, C, and D used in Example 4.

[0122] Comparative Example 4 used commercially available prepolymers including:

[0123] Prepolymers A and B are the prepolymers prepared in Example 4.

[0124] Prepolymer G (rigid type, similar to prepolymer C): viscosity 2700±300 mPa•s (25℃), NCO content 12.0±0.5%;

[0125] Prepolymer H (active type, similar to prepolymer D): viscosity 1150±200 mPa•s (25℃), NCO content 7.5±0.5%.

[0126] The commercially available prepolymers used in Comparative Example 5 include:

[0127] Prepolymer E (soft type, similar to prepolymer A): viscosity 3400±300 mPa•s (25℃), NCO content 10.0±0.5%;

[0128] Prepolymer F (chain-extended, similar to prepolymer B): viscosity 1850±200 mPa•s (25℃), NCO content 16.5±0.5%;

[0129] Prepolymers C and D are the prepolymers prepared in Example 4.

[0130] Comparative Example 6 uses only commercially available prepolymers:

[0131] Prepolymers E, F, G, H (parameters as above).

[0132] Following the formulation and process parameters recommended by each prepolymer supplier, the gel pads were cast using the same molds and thermoplastic polyurethane film (75 μm thick, 63A hardness) as in Example 4. The casting process for Comparative Example 4 was as follows: first, a mixture of prepolymers E and F was injected to form the inner gel layer and pre-cured; then, a mixture of prepolymers C and D was cast to form the outer gel layer. For Comparative Example 5, a mixture of prepolymers A and B was injected first, followed by a mixture of prepolymers G and H. For Comparative Example 6, a mixture of prepolymers E and F was injected first, followed by a mixture of prepolymers G and H. All comparative examples were cured under the same curing conditions as in Example 4, and gel pad samples of Comparative Examples 4, 5, and 6 were obtained after demolding.

[0133] The performance of the gel pad samples of Example 4 and Comparative Examples 4-6 was tested, and the results are listed in Table 6.

[0134] Table 6. Performance comparison of gel pads in Example 4 and Comparative Examples 4-6

[0135] Hardness (Shore 00) ASTM D2240 9 12 18 20 Rebound rate (%) ASTM D2632 89 83 76 74 Permanent deformation rate (%) ASTM D395 Method B 2.2 4.1 5.5 5.9 Peak pressure reduction rate (%) Pressure distribution testing system 52 43 38 36 Average pressure reduction rate (%) Pressure distribution testing system 40 33 27 26 Interlaminar tear strength (N / cm) ASTM D903 53 35 32 23

[0136] Test results show that the performance of the gel pads in Comparative Examples 4-6 is significantly lower than that in Example 4. Comparative Example 4 is close to Example 4 in terms of hardness, resilience, permanent deformation rate, and pressure dispersion efficiency, but its interlayer tear strength is significantly lower, reflecting the inadequacy of commercially available prepolymers G and H in interfacial bonding. Comparative Example 5 shows a further decline in performance, with increased hardness, decreased resilience, increased permanent deformation rate, and further deterioration of interlayer bonding. Comparative Example 6 exhibits the worst performance and a significant decrease in pressure dispersion efficiency. In contrast, Example 4, through the special prepolymer combination and sequential casting process of this invention, achieves an excellent balance of low hardness, high resilience, and low permanent deformation, and its interlayer bonding strength far exceeds that of the comparative examples, fully demonstrating the unique advantages of this invention in material co-design, interlayer chemical bonding, and overall performance integration.

[0137] Example 5

[0138] (1) Preparation of special polyol monomers

[0139] In a pressure-resistant reactor equipped with a stirrer, thermometer, vacuum system, and feed inlet, polypropylene glycol (PPG1800) with a molecular weight of 1800 was added as an initiator, heated to 117°C, and dehydrated under vacuum for 2.8 hours. Subsequently, under nitrogen protection, a bimetallic cyanide complex (DMC) catalyst (0.14 wt% of the initiator) was added, followed by the introduction of a measured amount of propylene oxide (PO) to initiate a ring-opening polymerization reaction. The reaction was carried out using segmented temperature control: the first stage was conducted at 88°C and 0.19 MPa for 1.8 hours; the second stage was conducted at 118°C and 0.48 MPa for 2.2 hours. After the reaction, the product was subjected to vacuum dehydration, neutralization, filtration, and other post-treatments to obtain a polyol monomer with a hydroxyl value of 105±3 mg KOH / g and a molecular weight of 3500±100, labeled as monomer 5#.

[0140] (2) Preparation of prepolymer

[0141] Based on the polyol monomer 5# synthesized above, prepolymers A, B, C, and D were further synthesized and prepared.

[0142] In the preparation of prepolymer A, 5 kg of monomer #5 was placed in a reactor and dehydrated for 3.5 hours at 118℃ and a vacuum of -0.095 MPa, with a moisture content of less than 0.022%. After dehydration, the system was cooled to 72℃, and 4,4'-diphenylmethane diisocyanate (MDI-100) was slowly added dropwise under nitrogen protection and a stirring rate of 350 rpm, controlling the NCO / OH molar ratio at 2.4. Temperature fluctuations during the addition process were controlled within ±2℃. After the addition was complete, the temperature was gradually increased to 88℃, and the reaction was continued for 2.2 hours, with NCO content measured every 30 minutes. The reaction was terminated when the NCO content reached 8.2%, and the mixture was cooled to room temperature to obtain prepolymer A with a viscosity of 4200 mPa·s (25℃).

[0143] In the preparation of prepolymer B, 5 kg of toluene diisocyanate (TDI-80) was added to the reactor, preheated at 52°C, and maintained under a nitrogen atmosphere. 1,4-Butanediol (BDO) was slowly added dropwise over 1 hour, controlling the NCO / OH molar ratio at 3.2. During the dropwise addition, the reaction temperature was controlled to not exceed 68°C by circulating cold water. After the addition was complete, the reaction was maintained at 72°C for 0.8 hours, during which the NCO content was monitored. The reaction was terminated when the NCO content reached 15.2%, yielding prepolymer B with a viscosity of 2200 mPa·s (25°C), which was then sealed and stored.

[0144] In the preparation of prepolymer C, 10 kg of polyethylene adipate diol with a number average molecular weight of 1800 and a hydroxyl value of 65 mg KOH / g was dehydrated at 118℃ and a vacuum of -0.095 MPa for 3.5 hours until the moisture content was <0.03%. The temperature was then lowered to 82℃, and MDI-100 was slowly added under nitrogen protection, controlling the NCO / OH molar ratio at 1.9. After the addition was complete, the temperature was raised to 92℃, and 4.5 g of dibutyltin dilaurate catalyst (0.045 wt% of the total system weight) was added. The reaction was carried out for 2.2 hours until the NCO content reached 10.8%, yielding prepolymer C with a viscosity of 3500 mPa·s (25℃).

[0145] In the preparation of prepolymer D, 4 kg of isophorone diisocyanate (IPDI) was added to a reactor and preheated at 52 °C. Hydroxyethyl methacrylate (HEMA) was slowly added dropwise over 1 hour, controlling the NCO / OH molar ratio at 1.5. Simultaneously, 2.8 g of dibutyltin dilaurate catalyst (0.07 wt% of the total system weight) was added, and the temperature was controlled to not exceed 78 °C. After the addition was complete, the reaction was maintained at 74 °C for 1.2 hours, and the reaction was terminated when the NCO content decreased to 6.8%, yielding prepolymer D with a viscosity of 1300 mPa·s (25 °C).

[0146] (3) Combined casting

[0147] Preheat a 40×40cm aluminum alloy mold with micropores to 42℃. Cut an 85μm thick thermoplastic polyurethane (TPU) film with a hardness of 68A (≥99.5% antibacterial rate against Staphylococcus aureus) and lay it flat on the mold cavity surface. Activate the vacuum system connected to the mold to achieve a vacuum level of -0.092MPa inside the mold. Use this negative pressure to firmly adhere the TPU film to the mold surface, maintaining vacuum adhesion for 5.5 minutes to ensure the film is completely set and wrinkle-free.

[0148] Prepolymer A and prepolymer B were added to a two-component mixing tank at a weight ratio of 1:1.42 and mechanically stirred at 350 rpm for 4.5 minutes. The mixture was then transferred to a vacuum degassing tank, where a vacuum of -0.099 MPa was established within 30 seconds, and this condition was maintained for degassing for 3.5 minutes. The degassed mixture was then injected at a flow rate of 0.9 L / min into a mold pre-coated with a TPU film. The mold was then placed at 55°C for initial curing for 22 minutes, forming a 27 mm thick initial cured inner gel layer.

[0149] Prepolymer C and prepolymer D were added to another two-component mixing tank at a weight ratio of 1:1.1. 0.9 wt% of an organic bismuth catalyst (bismuth content 18-22%) and 1.2 wt% of nano-silver antibacterial agent were added to the mixture. After stirring at 350 rpm for 5.5 minutes, the mixture was transferred to a vacuum degassing tank. The vacuum level inside the tank was brought to -0.099 MPa within 30 seconds, and degassing was performed for 3.5 minutes. The degassed outer gel mixture was then uniformly poured onto the surface of the initially cured inner gel layer at a flow rate of 0.9 L / min, controlling the outer gel layer thickness to 13 mm.

[0150] After casting, the entire mold was transferred to a temperature-controlled curing chamber. The temperature was gradually increased to 72°C over 0.5 hours and then maintained at 72°C for 2.8 hours for curing. After curing, the mold was allowed to cool naturally to room temperature and then demolded to obtain a gel pad product with a "TPU film-inner gel-outer gel" composite structure, labeled as Sample 5.

[0151] (4) Performance testing and results

[0152] The performance of the prepared gel pad sample from Example 5 was tested, and the results are listed in Table 7.

[0153] Table 7 Properties of the gel pad obtained in Example 5

[0154] Hardness (Shore 00) ASTM D2240 8 Rebound rate (%) ASTM D2632 91 Permanent deformation rate (%) ASTM D395 Method B 2.0 Peak pressure reduction rate (%) Pressure distribution testing system 55 Average pressure reduction rate (%) Pressure distribution testing system 43 Interlaminar tear strength (N / cm) ASTM D903 55 Antibacterial properties (film surface) (%) GB / T 31402 99.6 Antibacterial properties (bottom seal) (%) GB / T 31402 99.4 Attached image description: Figure 1 The images show actual photos of the gel pads 1-3 prepared in Example 1.

Claims

1. A design and combined casting application of a high-elasticity polyurethane gel, characterized by, Includes the following steps: (1) Design and preparation of polyol monomers: Polypropylene glycol was used as the initiator and propylene oxide was subjected to ring-opening polymerization in the presence of a bimetallic cyanide complex catalyst. Polyol monomers with hydroxyl value of 80-120 mgKOH / g and molecular weight of 2000-4000 were obtained by segmented temperature control and post-treatment. (2) Preparation of soft gel component prepolymer: using the polyol monomer obtained in step (1) as raw material, react with 4,4'-diphenylmethane diisocyanate to prepare prepolymer A; using 1,4-butanediol as chain extender, react with toluene diisocyanate to prepare prepolymer B; (3) Preparation of prepolymer of rigid gel component: Prepolymer C was prepared by reacting polyethylene adipate diol as soft segment raw material with 4,4'-diphenylmethane diisocyanate; Prepolymer D was prepared by reacting hydroxyethyl methacrylate as active monomer with isophorone diisocyanate. (4) Combined casting of gel: The thermoplastic polyurethane film is laid on the surface of the mold. After vacuum adsorption and shaping, a mixture of prepolymer A and prepolymer B is first injected to form an inner gel layer and pre-cured. Then, a mixture of prepolymer C and prepolymer D is cast to form an outer gel layer. After step-by-step heating and curing, the product with a "TPU film-inner gel-outer gel" composite structure is obtained.

2. The method of claim 1, wherein, The molecular weight of the polypropylene glycol mentioned in step (1) is 1000-2000, and the amount of the bimetallic cyanide complex catalyst is 0.05-0.2wt% of the initiator; the segmented temperature control is as follows: the first stage is reacted at 80-90℃ and 0.1-0.2MPa for 1-2 hours, and the second stage is reacted at 100-120℃ and 0.3-0.5MPa for 1-4 hours.

3. The method of claim 1, wherein, The preparation conditions of prepolymer A in step (2) include: after dehydrating the polyol monomer to a moisture content of <0.03%, it is reacted with 4,4'-diphenylmethane diisocyanate at 60-75℃ at an NCO / OH molar ratio of 1.8-2.5, and the final product has an NCO content of 8-12% and a viscosity range of 3000-5000 mPa·s (25℃); the preparation conditions of prepolymer B include: 1,4-butanediol and toluene diisocyanate are reacted at 40-70℃ at an NCO / OH molar ratio of 2.5-3.5, and the final product has an NCO content of 15-18% and a viscosity range of 1500-2500 mPa·s (25℃).

4. The method of claim 1, wherein, The preparation conditions for prepolymer C in step (3) include: the molecular weight of polyethylene adipate diol is 1000-2000, the hydroxyl value is 56-112 mgKOH / g, after dehydration, it reacts with 4,4'-diphenylmethane diisocyanate at 70-95℃ at an NCO / OH molar ratio of 1.5-2.0, and 0.01-0.05 wt% dibutyltin dilaurate catalyst is added. The final product has an NCO content of 10-15%. The viscosity range is 2000-4000 mPa·s (25℃); the preparation conditions of prepolymer D include: hydroxyethyl methacrylate and isophorone diisocyanate react at 45-80℃ with an NCO / OH molar ratio of 1.2-1.6, and 0.01-0.05 wt% dibutyltin dilaurate catalyst is added. The final product has an NCO content of 6-9% and a viscosity range of 800-1500 mPa·s (25℃).

5. The method of claim 1, wherein, The thermoplastic polyurethane film in step (4) has a thickness of 60-100 μm, a hardness of 60-70 A, an antibacterial rate of Staphylococcus aureus ≥99%, and an elongation at break ≥400%; the vacuum adsorption conditions are a mold temperature of 35-45℃, a vacuum degree of -0.085 to -0.095 MPa, and an adsorption time of 3-6 minutes.

6. The method of claim 1, wherein, The casting process of the inner gel in step (4) includes: mixing prepolymer A and prepolymer B at a weight ratio of 1:1.2-1.5, mechanically stirring for 3-5 minutes, then vacuum degassing for 2-4 minutes, and then casting and pre-curing at 40-60℃ for 15-25 minutes; the casting process of the outer gel includes: mixing prepolymer C and prepolymer D at a weight ratio of 1:0.8-1.2, adding 0.5-1.0wt% organic bismuth catalyst and 0.5-2.0wt% nano silver antibacterial agent, stirring for 4-6 minutes, then vacuum degassing, casting onto the surface of the inner gel, and finally curing at 65-75℃ for 2-3 hours.

7. The method of claim 6, wherein, The organic bismuth catalyst has a bismuth content of 18-22%, a vacuum degree of -0.095 to -0.1 MPa for vacuum degassing, and a degassing time of 2-4 minutes.

8. The method according to claim 1, characterized in that, All prepolymer reaction processes in steps (2) and (3) are carried out under nitrogen protection, with the stirring rate controlled at 200-400 rpm and the temperature fluctuation not exceeding ±2℃.

9. The method according to claim 1, characterized in that, In step (4), the pouring flow rate of the inner gel and the outer gel is 0.5-1.0 L / min, and the mold preheating temperature is the same as the pouring temperature, which is 35-45℃.

10. A prepolymer composition for preparing highly elastic polyurethane gel, characterized in that, The composition comprises: The soft gel system consists of prepolymer A, which is synthesized with the participation of polyol monomers obtained by the method described in claim 2 and has an NCO content of 8-12%, and prepolymer B, which has an NCO content of 15-18%. The rigid gel system consists of prepolymer C with an NCO content of 10-15% and prepolymer D with an NCO content of 6-9% and acrylate double bonds at the molecular ends. The weight mixing ratio of prepolymer A to prepolymer B is 1:1.2-1.5, and the weight mixing ratio of prepolymer C to prepolymer D is 1:0.8-1.2.

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