Ultralow-temperature-resistant polyurea foam as well as preparation method and application thereof

Abstract

The invention discloses ultralow-temperature-resistant polyurea foam as well as a preparation method and application thereof. The preparation method comprises the following steps: step 1, carrying out ring-opening reaction and condensation polymerization on amino double-terminated polydimethylsiloxane and ethylene carbonate to obtain polyurea containing a monoureido structure; and step 2, mixing the polyurea, the polymethylhydrosiloxane and the catalyst to obtain a premix, and foaming to obtain the polyurea foam. The foam is prepared by taking polyurea as a matrix and polymethylhydrosiloxane as a cross-linking agent and a foaming agent through one-step cross-linking foaming, wherein the polyurea is prepared from amino double-terminated polydimethylsiloxane and ethylene carbonate through a non-isocyanate route. The polyurea foam has an interval cross-linked structure, ureido groups are separated by flexible PDMS chain segments, and the material is endowed with chain segment motility and dynamic hydrogen bond recombination capability at extremely low temperature. The material has excellent impact resistance and elastic recovery capability, and is suitable for extreme environments such as aerospace, polar equipment and the like.

Description

Technical Field

[0001] This invention relates to the field of low-temperature material preparation technology, specifically to an ultra-low temperature resistant polyurea foam, its preparation method, and its application. Background Technology

[0002] With the rapid development of fields such as polar exploration, aerospace, cryogenic engineering, and extreme environment transportation, there is an urgent need for foam materials that can maintain excellent impact resistance and toughness in extremely low-temperature environments. Taking space debris disposal as an example, with the increasing number of spacecraft launched by humans, space debris in low Earth orbit has become a real and increasingly serious threat. Although various cleanup solutions have been proposed, there is currently no solution that is both economical and feasible for collecting this space debris. Against this backdrop, foam materials with extremely low-temperature toughness and high impact resistance offer a new approach to capturing these constantly tumbling space debris.

[0003] However, in extremely low-temperature environments, traditional polymer foam materials become brittle due to restricted chain segment movement, resulting in a sharp decline in impact resistance and toughness, which fails to meet the impact-resistant material requirements of aerospace, polar equipment, deep space exploration, and other fields. Therefore, developing a class of ultra-tough foam materials that can maintain high impact resistance in extremely low-temperature environments has become a key research focus and technological bottleneck in this field.

[0004] Several low-temperature resistant foams have been reported in the prior art. For example, CN115746239A discloses a method for preparing a low-temperature resistant and impact-resistant foam material based on nanoparticle reinforcement. The foam material is formed by the foaming reaction and curing of silica nanoparticles, a low-temperature resistant polyol mixture, and isocyanate. The method includes the following steps: preparing the low-temperature resistant polyol mixture, including: mixing a polymer polyol mixture with additives to form a low-temperature resistant polyol mixture; shearing and dispersing nano-silica nanoparticles in the low-temperature resistant polyol mixture to form a first mixture; adding isocyanate to the first mixture, rapidly stirring until uniform, pouring into a mold for foaming, and demolding after constant temperature curing to obtain the low-temperature resistant and impact-resistant foam material based on nanoparticle reinforcement. The additives include foam stabilizers, catalysts, and solid accelerators; the polymer polyol mixture includes one or more of high molecular weight polyoxypropylene polyols, medium and low molecular weight polyether polyols, polyethylene glycol, and 1,4-butanediol, but only meets the low-temperature application requirements of -18 to -40°C.

[0005] CN109438666A discloses a low-temperature resistant and impact-resistant material, its preparation method, and its application. The raw materials of the material include: 60-120 parts of polyether polyol, 1-5 parts of foaming agent, 0.1-2 parts of foam stabilizer, 0.05-1 parts of catalyst, 60-130 parts of toluene diisocyanate, 0.5-5 parts of chain extender, and 0.5-10 parts of shear-thickening gel. The catalyst is a composite formulation of ether amine catalyst and organotin catalyst, and the mass ratio of ether amine catalyst to organotin catalyst is 1:0.3-3. The preparation method includes: (1) mixing polyether polyol, foaming agent, catalyst, foam stabilizer, chain extender, and shear-thickening gel, stirring at high speed for 60-180s, adding toluene diisocyanate, stirring at a speed of 1500-2000r / min for 5-30s to obtain the material; pouring the material into a mold and foaming for 6-10min to obtain the material. This material showed no signs of cracking after being kept at temperatures between -30 and -40°C for 24 hours, making it suitable for use in extremely cold conditions, such as polar skiing and military cold-weather training. However, no publicly available reports exist on foam materials exhibiting excellent impact resistance at even lower temperatures. Summary of the Invention

[0006] This invention addresses the problems of insufficient mechanical properties and brittleness in ultra-low temperature environments (below -50℃) by providing a polyurea foam that still exhibits excellent impact resistance in ultra-low temperature environments. Through an intermittent cross-linking structure design, the urea groups are separated by flexible polydimethylsiloxane (PDMS) segments, enabling the foam to maintain high energy absorption and dissipation capabilities even at ultra-low temperatures, thus providing a new technical solution to overcome the limitations of foam application scenarios.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing ultra-low temperature resistant polyurea foam, comprising the following steps: Step 1: The amino-double-terminated polydimethylsiloxane and ethylene carbonate are subjected to ring-opening and condensation reactions to obtain polyurea containing a monourea group structure; Step 2: The polyurea, polymethylhydrosiloxane and catalyst are mixed to obtain a premix, which is then foamed to obtain the polyurea foam.

[0008] In this invention, a lightweight polyurea foam is obtained by simultaneously forming a cross-linked network and releasing hydrogen through the hydrosilylation reaction of monourea groups isolated by flexible PDMS segments with the active hydrogen in polymethylhydrosiloxane. Furthermore, the spaced cross-linked structure design of this polyurea foam allows the PDMS segments to maintain their mobility and dynamic hydrogen bond recombination ability even in extreme low-temperature environments. This results in excellent impact resistance and energy absorption capacity even at extremely low temperatures (down to -196°C), making it suitable for use as an impact-resistant, cushioning, or energy-absorbing material in aerospace, polar equipment, deep space exploration, cryogenic engineering, or extreme environment protective equipment.

[0009] Furthermore, in the process of synthesizing polyurea foam, this invention is based on a non-isocyanate route, which does not use toxic isocyanates or solvents, and no harmful substances are generated. The preparation process is simple, green, environmentally friendly, and sustainable.

[0010] The molar ratio of ethylene carbonate to amino-double-terminated polydimethylsiloxane is 1-1.5:1.

[0011] Preferably, the molar ratio of ethylene carbonate and amino-double-terminated polydimethylsiloxane is 1:1. This ratio allows for the precise preparation of polyurea with a single urea group structure, ensuring that all urea groups are isolated by PDMS segments.

[0012] The amino-terminated polydimethylsiloxane has a number-average molecular weight of 300-2500 g / mol. A higher molecular weight indicates a higher siloxy group content in its structure, resulting in polyurea foam with superior low-temperature resistance. However, due to the high flexibility of the polymer chains, the cell morphology is difficult to maintain at room temperature.

[0013] Preferably, the amino-double-terminated PDMS has a number-average molecular weight of 500-2000 g / mol. -1 ; The ring-opening reaction is carried out at 60-100℃ for 5-10 hours; the melt polycondensation reaction is carried out at 170-200℃, with the reaction endpoint being when the reactants begin to adhere to the stir bar.

[0014] The viscosity of the polymethylhydrosiloxane is 10-100 mPa·s at 20°C, and the mass fraction of active hydrogen is 0.1-2%.

[0015] In step 2, the molar ratio of urea groups in the polyurea to active hydrogen in the polymethylhydrosiloxane is 1:1-5. More preferably, the molar ratio is 1:2-4. The molar amount of urea groups is theoretically calculated based on the raw material ratio in step 1.

[0016] The catalyst is chloroplatinic acid or casterplatinum catalyst, and its mass is 0.01-0.1% of the total mass of the reaction raw materials.

[0017] The foaming temperature is 65-120℃, more preferably 80-100℃, and the foaming time is 30-90min.

[0018] This invention constructs a three-dimensional cross-linked network and porous foam structure through the hydrosilylation reaction of urea groups in polyurea with active hydrogen in polymethylhydrosiloxane. By adjusting the molar ratio of urea groups to active hydrogen, the formation rate of the three-dimensional cross-linked network is controlled, thereby making the matrix viscosity both conducive to capturing released gas and allowing for sufficient expansion, ultimately resulting in a uniform cell morphology.

[0019] The present invention also provides a low-temperature resistant polyurea foam prepared by the aforementioned preparation method.

[0020] This invention also provides the application of the aforementioned cryogenically resistant polyurea foam in cryogenic environments, where cryogenic environments refer to ambient temperatures below -50°C. Further preferred applications include environments such as -80°C, -100°C, and liquid nitrogen (approximately -196°C). This foam exhibits excellent impact resistance and elastic recovery in cryogenic environments.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) In this invention, amino-terminated PDMS is reacted and polymerized with ethylene carbonate to achieve the isolation of the monourea structure by flexible PDMS segments, which can maintain excellent molecular mobility even at extremely low temperatures. At the same time, the dynamic hydrogen bonds between urea groups can continue to recombine at low temperatures, providing an effective energy dissipation mechanism for the material. This structural design also endows the material with excellent elastic recovery properties and fatigue resistance.

[0022] (2) The present invention uses a non-isocyanate route to prepare polyurea, which avoids the use of highly toxic phosgene derivatives, making the synthesis process safer and more environmentally friendly.

[0023] (3) This invention utilizes polymethylhydrosiloxane as both a crosslinking agent and a foaming agent, achieving simultaneous crosslinking and foaming in a "one-step" process, which is simple and efficient. This method effectively solves the problem of poor compatibility between PDMS and polar components, and the prepared foam has uniform cells and a stable structure. Attached Figure Description

[0024] Figure 1 This is the NMR spectrum of the Si-PU prepared in Example 1.

[0025] Figure 2 These are physical images of the polyurea foams prepared in Examples 1-4 and their scanning electron microscope (SEM) images.

[0026] Figure 3This is a diagram showing the change in the polyurea foam prepared in Example 3 after being squeezed forcefully and quickly returning to its original shape.

[0027] Figure 4 This is the compressive stress-strain curve of the polyurea foam prepared in Example 3 at -100℃.

[0028] Figure 5 This is the energy absorption curve of the polyurea foam prepared in Example 3 at -100°C.

[0029] Figure 6 This is the energy absorption efficiency curve of the polyurea foam prepared in Example 3 at -100℃.

[0030] Figure 7 This is the cyclic compression curve of the polyurea foam prepared in Example 3 at -100°C and 30% strain.

[0031] Figure 8 This is a comparison diagram of the impact resistance of the polyurea foam prepared in Example 3 and commercial polyurethane foam (PUF) in liquid nitrogen at -196°C.

[0032] Figure 9 This is a photograph of the polyurea foam prepared in Example 5.

[0033] Figure 10 These are actual photos of the polyurea foam prepared in Example 6 and after it has been left to stand for one day. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention, without departing from the spirit and scope of the invention, should be covered within the protection scope of this invention.

[0035] All raw materials used in the following specific embodiments were purchased commercially. The amino-terminated polydimethylsiloxane was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with a number-average molecular weight of 1000 g / mol. The polymethylhydrosiloxane was also purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with a viscosity of 10-40 mPa·s at 20°C and an active hydrogen mass fraction of 1.7%.

[0036] The following equipment and methods were used for performance testing and evaluation: 1. Scanning electron microscope The foam samples were imaged using a Hitachi Regulus 8230 scanning electron microscope (SEM). The average cell diameter was calculated by averaging the diameter measurements of at least 100 cells.

[0037] 2. Apparent density Apparent foam density (ρ) a The value of ρ for foam is calculated using the formula given below. a The value was calculated by weighing a cubic sample with dimensions of approximately 10 × 10 × 10 mm (V) in m.

[0038] 3. Mechanical property testing at extremely low temperatures Because the TAQ800 dynamic mechanical analyzer can operate in extremely low-temperature environments, it was used to test the compressibility of foam materials at cryogenic temperatures. In strain gradient mode, mechanical compressive force was measured using a compression fixture with a preload force of 0.01 N and a strain rate of 2% / min until the foam material deformed to 80% of its initial thickness. Under cryogenic conditions, cyclic compressive force was measured using creep mode. The force when the foam material was compressed to 30% of its initial thickness and the shape recovery after unloading were also measured.

[0039] Energy absorption (W) is defined as the energy absorbed per unit volume of material, and is calculated using the following formula: in, Indicates strain, This indicates the corresponding stress.

[0040] Energy absorption efficiency (E) is defined as the ratio of absorbed energy to stress, and is calculated using the following formula: in, Indicate strain is The stress.

[0041] The energy loss coefficient (ΔU / U) and elastic recovery rate are calculated as follows: This represents the energy absorbed during the loading process. This represents the energy released during the unloading process. This indicates the dissipation of energy.

[0042] Indicates the maximum compressive strain. This represents the residual strain after unloading.

[0043] Example 1 Step S1: Amino-terminated PDMS and ethylene carbonate are mixed uniformly at a molar ratio of 1:1, and then subjected to a ring-opening reaction at 60°C for 10 hours. Under a nitrogen atmosphere, the temperature is raised to 170°C and a vacuum is applied to continue the polycondensation reaction until the reactants begin to adhere to the stir bar, yielding polyurea (Si-PU). The number average molecular weight of the amino-terminated PDMS is 1000 g / mol. -1 The NMR spectrum of Si-PU is shown below. Figure 1 GPC data show that the number-average molecular weight (M) of Si-PU is... n The value is 1.3 × 10 4 g mol -1 The polydispersity index is 2.7.

[0044] Step S2: Weigh the synthesized polyurea and mix it with polymethylhydrosiloxane at a molar ratio of 2 (the content of urea groups is theoretically calculated according to the feed ratio in Step 1) of active hydrogen to urea groups (this mixture is denoted as Si-PU2). Then, add 0.01 wt% of caster platinum catalyst to the mixture and stir it mechanically to form a uniform, transparent, foamable premix. The viscosity of polymethylhydrosiloxane is 10-40 mPa·s, and the mass fraction of active hydrogen is 1.7%.

[0045] Step S3: The above-mentioned foamable premix is ​​foamed and crosslinked in an oven at 100°C for 60 minutes. During this process, polymethylhydrosiloxane acts as a crosslinking agent; its active hydrogen reacts with urea groups to form Si-N covalent bonds, constructing a three-dimensional network. Simultaneously, the hydrogen gas released from the reaction acts as a foaming agent, forming a cell structure in situ, ultimately yielding an apparent density of 198 kg·m³. -3 The polyurea foam material is designated as Si-PUF2.

[0046] See the physical image and SEM image of Si-PUF2. Figure 2 The average cell diameter is approximately 0.24 ± 0.18 mm, and it has both open-cell and closed-cell structures.

[0047] Example 2 The preparation process is the same as in Example 1, except that the molar ratio of active hydrogen to urea groups is adjusted to 2.5 (this ratio system is denoted as Si-PU2.5). The resulting foam is denoted as Si-PUF2.5, and its apparent density is 210 kg·m³. -3 .

[0048] Physical images and SEM images of Si-PUF2.5 are shown below. Figure 2The average pore diameter is 0.32 ± 0.12 mm, and it has both open-cell and closed-cell structures.

[0049] Example 3 The preparation process is the same as in Example 1, except that the molar ratio of active hydrogen to urea groups is adjusted to 3 (this ratio system is denoted as Si-PU3). The resulting foam is denoted as Si-PUF3, and its apparent density is 193 kg·m³. -3 .

[0050] See the physical image and SEM image of Si-PUF3. Figure 2 The average pore diameter is 0.34 ± 0.14 mm, and it has both open-cell and closed-cell structures. Figure 3 This is a graph showing how Si-PUF3 rapidly recovers its original shape after being squeezed at room temperature, demonstrating its excellent elastic recovery ability.

[0051] The compressive stress-strain curve of Si-PUF3 foam at -100℃ is shown below. Figure 4 The curves show three typical regions of foam material compression: the initial linear elastic region, the plateau region, and the densification region. The energy absorption curve at -100℃ is shown below. Figure 5 As stress increases, energy absorption initially increases slowly and then rapidly, eventually reaching as high as 171 kJ·m. -3 The energy absorption efficiency curve at -100℃ is shown below. Figure 6 It exhibits the highest energy absorption efficiency of 24% over a relatively wide stress range (0.3-0.8 MPa). The cyclic compression curves at -100℃ and 30% strain are shown below. Figure 7 The curves of the four cycles basically overlapped, the energy dissipation coefficient was as high as about 74%, and the elastic recovery rate exceeded 92%.

[0052] More significantly, such as Figure 8 As shown, in liquid nitrogen at -196°C, the foam can withstand the impact energy of 0.49J generated by a 50g weight falling from a height of 1m while maintaining its structural integrity, demonstrating excellent low-temperature impact resistance.

[0053] Example 4 The preparation process is the same as in Example 1, except that the molar ratio of active hydrogen to urea groups is adjusted to 3.5 (this ratio system is denoted as Si-PU3.5). The resulting foam is denoted as Si-PUF3.5, and its apparent density is 206 kg·m³. -3 .

[0054] Physical images and SEM images of Si-PUF3.5 are shown below. Figure 2 The average pore diameter is 0.36 ± 0.12 mm, and it has both open-cell and closed-cell structures.

[0055] Comparative Example 1 The preparation process is the same as in Example 1, except that the number-average molecular weight of the amino-terminated PDMS is adjusted to 248 g / mol, and the molar ratio of active hydrogen to urea groups is adjusted to 3 (this ratio system is denoted as C0.2-Si-PU3). The resulting foam is denoted as C0.2-Si-PUF3.

[0056] See the physical image of C0.2-Si-PUF3. Figure 9 Because siloxanes have a short molecular weight, they generate a large amount of gas, making it impossible to form a uniform cell morphology.

[0057] Comparative Example 2 The preparation process is the same as in Example 1, except that the number-average molecular weight of the amino-double-terminated PDMS is adjusted to 3000 gmol. -1 The molar ratio of active hydrogen to urea groups is adjusted to 3 (this ratio system is denoted as C3-Si-PU3), and the resulting foam is denoted as C3-Si-PUF3.

[0058] See the physical image of C3-Si-PUF3. Figure 9 Because of the long molecular weight of siloxane, the molecular chain of this foam is relatively flexible, and the foam cells collapse after being left at room temperature for a period of time.

[0059] This invention synthesizes polyurea via a non-isocyanate route and utilizes polymethylhydrosiloxane to achieve "spaced crosslinking" and "in-situ foaming," successfully solving the technical challenges of poor compatibility between PDMS and polar components, as well as low-temperature embrittlement caused by high crosslinking density. Example 3 (Si-PUF3) exhibits the best overall performance. Its unique molecular structure allows the material to maintain chain segment mobility and dynamic hydrogen bonding even at extreme low temperatures of -196°C, thus demonstrating excellent impact resistance and elastic recovery in extreme low-temperature environments. It is expected to meet the stringent requirements for cryogenic protective materials in aerospace, polar exploration, and other fields.

Claims

1. A method for preparing ultra-low temperature resistant polyurea foam, characterized in that, Including the following steps: Step 1: The amino-double-terminated polydimethylsiloxane and ethylene carbonate are subjected to ring-opening and condensation reactions to obtain polyurea containing a monourea group structure; Step 2: The polyurea, polymethylhydrosiloxane and catalyst are mixed to obtain a premix, which is then foamed to obtain the polyurea foam.

2. The method for preparing ultra-low temperature resistant polyurea foam according to claim 1, characterized in that, The molar ratio of ethylene carbonate to amino-double-terminated polydimethylsiloxane is 1-1.5:

1.

3. The method for preparing ultra-low temperature resistant polyurea foam according to claim 1, characterized in that, The number-average molecular weight of the amino-double-terminated polydimethylsiloxane is 300-2500 g / mol.

4. The method for preparing ultra-low temperature resistant polyurea foam according to claim 1, characterized in that, The ring-opening reaction is carried out at 60-100℃ for 5-10 hours; the melt polycondensation reaction is carried out at 170-200℃, with the reaction endpoint being when the reactants begin to adhere to the stir bar.

5. The method for preparing ultra-low temperature resistant polyurea foam according to claim 1, characterized in that, The viscosity of the polymethylhydrosiloxane is 10-100 mPa·s at 20°C, and the mass fraction of active hydrogen is 0.1-2%.

6. The method for preparing ultra-low temperature resistant polyurea foam according to claim 1, characterized in that, In step 2, the molar ratio of urea groups in the polyurea to active hydrogen in the polymethylhydrosiloxane is 1:1-5.

7. The method for preparing ultra-low temperature resistant polyurea foam according to claim 1, characterized in that, The catalyst is chloroplatinic acid or casterplatinum catalyst, and its mass is 0.01-0.1% of the total mass of the reaction raw materials.

8. The method for preparing ultra-low temperature resistant polyurea foam according to claim 1, characterized in that, The foaming temperature is 65-120℃, and the foaming time is 30-90 minutes.

9. The ultra-low temperature resistant polyurea foam prepared by the preparation method according to any one of claims 1-8.

10. The application of the ultra-low temperature resistant polyurea foam according to claim 9 in an ultra-low temperature environment, characterized in that, The ultra-low temperature environment refers to an ambient temperature below -50℃.

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