聚脲是一种用途广泛的聚合物，其成分包括硬链段和软链段。硬链段通常由异氰酸酯组成，而软链段由氨基化合物组成。聚脲的性能可以通过操纵硬软比例来精确控制。这可以通过改变异氰酸酯和胺的量和类型来实现。增加聚脲中异氰酸酯的浓度会导致硬链段比例增加，从而提高硬度、强度和耐久性。相反，增加氨基化合物的含量会增加软链段的比例，从而增强聚脲的柔韧性、弯曲性和弹性。因此，调整异氰酸酯与氨基化合物的比例直接影响聚脲结构内硬链段和软链段之间的平衡。例如，提高异氰酸酯的比例，同时减少氨基化合物的用量，可以提高聚脲的硬度和强度，但代价是牺牲柔韧性和弯曲性。这种定制硬段和软段比例的能力使聚脲性能的定制成为可能，以符合特定的应用要求。

不同类型的异氰酸酯和氨基化合物具有不同的性质和反应性。通过选择这些化合物的不同组合，可以调整聚脲中硬链段和软链段的比例，以及耐热性和耐化学性等其他性能。M.F. Sonnenschein等[21]的一项研究以聚醚多元醇为原料，与对氨基苯甲酸酯进行酯交换反应，合成封端苯胺多元醇。与母体多元醇相比，所得胺表现出更高的热氧化稳定性和粘度。从反应动力学、拉伸性能、形貌和老化性能等方面对由苯胺封端基制备的聚脲/聚氨酯弹性体的物理性能进行了评价。研究发现，由于硬链段扩链剂的苯胺端基和羟基之间的反应性不均匀，增加硬链段的体积以提高弹性体硬度和拉伸强度导致相分离方面的挑战。这阻碍了硬段所需的相分离。

PU和PUR涂层的机械和热性能受脂肪族链的长度和芳香族扩链剂的性能的显著影响[22]。V. Shahi等[23]的研究以PTMO基二胺和MDI二异氰酸酯为原料，通过阶梯式生长聚合合成了聚氨酯弹性体。热力学性能研究表明，随着长链二胺的掺入量增加，PU-HB05表现出较低的导热系数和热容，更无定形的结构和更高的高温稳定性。在另一项研究中，H. Guo等[24]通过调整原聚脲组分中氨基封端聚醚类型和胺链扩展剂类型的比例，合成了各种聚脲涂层材料。通过对这些涂层性能的分析，得出的结论是，氨基封端聚醚D2000与T5000的最佳比例为12：1，胺链延伸剂E100与W6200的最佳比例为1.6：1，因为这些比例导致了聚脲涂层的最佳性能指标。

共价热固性塑料以其强大的机械性能而闻名，但是，它们缺乏再加工或回收能力，因此很脆弱。B. Qin等[25]的一项研究提出了一种提高交联超分子聚氨酯（CSPUs）韧性和可回收性的新方法。这是通过将非共价键引入聚合物主链来实现的。采用二异氰酸酯单体、四氢键二胺单体和共价二胺/三胺单体共聚制备了CSPUs。由于共价交联和非共价键的结合，所得的CSPU表现出优异的力学性能和耐溶剂性。此外，L. Zhang等[26]通过设计具有不同强度的氢键相互作用并结合永久共价键，成功合成了一种超分子聚脲弹性体。这种弹性体表现出卓越的机械强度，断裂伸长率超过 1600%，对缺口不敏感的拉伸能力高达 800%，韧性高达 12,500 J m⁻².共价交联提供了高强度，而多强度氢键在室温下提供了弹性、能量耗散和快速自愈性能。

需要考虑的一个关键方面是，通过改变异氰酸酯和氨基化合物来改性聚脲需要细致的处理。这些化合物的反应性和性能可以显著影响所得聚脲的结构和特性。因此，必须在聚脲的整个制备和改性过程中进行彻底的实验和测试。这些措施对于确保材料达到所需的性能和稳定性至关重要。仔细的关注和精度对于优化结果和保证改性聚脲的可靠性至关重要。

Polyurea materials have the potential to be optimized by incorporating various forms of reinforcing materials [37]. By introducing fiber reinforcing materials, particle filling materials, foam reinforcing materials and nano reinforcing materials, the properties of polyurea such as strength, hardness, abrasion resistance, temperature resistance and chemical resistance can be enhanced.

Among the fiber reinforcing materials, glass fibers, carbon fibers and aramid fibers, among others, are known to significantly improve the strength, stiffness and durability of polyurea while also enhancing its temperature and chemical stability [11]. Typically, these fibers are integrated into polyurea in the form of yarn or cloth, creating a composite material. Additionally, polyurea-based hybrid composites can be synthesized [12]. Previous research studies have demonstrated that polyurea-coated fiber-reinforced composites can enhance the impact resistance of concrete slabs [13,14]. Furthermore, the combination of polyurea coatings with carbon fibers and basalt fiber-reinforced polymer reinforcement techniques has shown positive effects in enhancing the blast resistance of urban utility tunnels [15]. The use of glass-fiber reinforced polyurea materials has also been found to enhance the bullet intrusion resistance of steel plates [16]. In summary, the incorporation of various reinforcing materials into polyurea holds great potential for improving its properties and expanding its application range. In a study conducted by J. Lv et al. [17], a hierarchical interfacial phase with high interfacial shear strength and toughness was created in an aramid composite through in situ grafting and foaming of polyurea on the fiber surfaces, as well as epoxy infiltration into the pores of the aramid composite. This resulted in the construction of a “rigid-flexible” interlocking three-dimensional interfacial structure, further increasing the interfacial shear strength and toughness of aramid fiber composites. N.V. Vuong et al. [18] developed different types of composites consisting of corrugated glass fibers/vinyl ester and polyurea using a conceptual composite panel inspired by mollusk shell pearl laminates. Various interlocking corrugated laminates were simulated and compared with planar and conventional dog-bone interlocking laminates, demonstrating a significant improvement in the performance of this composite under blast and impact loading.

Particulate fillers, including silica sand, alumina, carbon black and nanoparticles, are recognized for enhancing the hardness, abrasion resistance and durability of polyurea, as well as for improving its thermal and chemical stability [27]. A study conducted by A.S. Roy et al. [27] used a detailed all-atom MD model confirmed these results. Typically, granular filler materials are mixed into polyurea in the form of powder or granules. For instance, Q. Liu et al. [28] performed quasi-static and dynamic compression tests on pure polyurea and polyurea/SiC nanocomposites with varying amounts of nanofillers at different strain rates using an electronic universal testing machine and a SHPB device. The researchers found that, in comparison to pure polyurea, the addition of nanoparticles influences on the compression properties. Under static loading, the nanocomposites with the content 1.5 wt% fillers greatly affected the compressive mechanical properties. However, under dynamic loading, the mechanical behaviors of nanocomposites with the additional amount of SiC (0.7 wt%) was observed to be more active compared to other nanocomposites. The reason may be that more cracks were formed on the inside of the specimens with the increased content of particles under a high stain rate which leads to the decrease of mechanical properties.

Nano-reinforcement materials such as nano-oxides, carbon nanotubes and nanofibers, can enhance the strength, toughness and durability of polyurea while improving its thermal and chemical stability. These nano-reinforcement materials are typically incorporated into polyurea as nanoparticles. G. Wu et al. [29] developed a novel highly elastic protective coating by reinforcing polyurea with nano-silica filler composites. The polyurea material exhibited a tensile strength of 15.7 MPa and an elongation at break of 472%. Application of the polyurea coating resulted in a 9.7 kJ/m² increase in the impact strength of the substrate, while maintaining good mechanical properties and ductility. Simulation results indicated that the polyurea coating could effectively mitigate the impact caused by the ball’s equivalent force at different velocities.

Polyurea is a high-performance polymer with outstanding protective properties, making it suitable for resisting blast impact loading and ballistic penetration. Its protection mechanism encompasses several aspects. Firstly, the complex structure formed by the hard and soft segments of polyurea provides it with high strength and toughness. Consequently, when subjected to impact loading or ballistic penetration, polyurea effectively withstands external forces using its strength and toughness. Secondly, polyurea exhibits excellent energy absorption capabilities, allowing it to absorb and disperse the energy from external impact loading and ballistic penetration, thereby safeguarding the protected objects. Moreover, polyurea possesses the ability to undergo deformation in response to external forces, thereby dispersing and mitigating their effects and ultimately protecting the objects within. Additionally, polyurea’s chemical stability ensures that its performance remains unaffected under diverse environmental conditions. This stability prevents any chemical reactions or decomposition from occurring when exposed to external impact loading and ballistic intrusion, further contributing to the protection of the object.

Polyurea is known for its high strength, stiffness, hardness, flexibility and toughness, which can be attributed to the presence of hydrogen bonding within its molecules. The hardening of polyurea is achieved through the dissociation of hydrogen bonds and the reorganization of soft and hard segments via a heat curing reaction. During this reaction, the amide and urea bonds within the polyurea molecules are broken and reorganized, resulting in the formation of new hydrogen bonds and molecular chain cross-links. This cross-linking process enhances the strength and hardness of polyurea [31,38,39]. To investigate the temperature-dependent microscale impact response of polyurea at a fixed impact velocity, Y. Sun et al. [40] observed an increased absorption of localized impact energy at approximately 115 °C, which corresponds to the transition temperature from the glassy to the rubbery state when subjected to high-speed dynamic loading. Notably, materials that exhibit a wider temperature range in the glass transition zone and lower microphase segregation demonstrate superior flexibility and energy absorption under high strain rate loading conditions [41,42].

The soft phase exhibits superelasticity, while the hard phase demonstrates elastoplastic behavior. Through a combination of experimental and simulation analysis, M.H. Jandaghian et al. [43] discovered that the performance of the formulation in response to low-intensity impacts (such as seismic waves) is primarily influenced by the soft phase. On the other hand, the interaction between the two phases determines the formulation’s overall resistance against projectile penetration into the structure, with the hard phase playing a key role in response to high-intensity indirect impacts (such as blast shockwaves). The ductility of the material increases proportionally with the length of the soft section, while the tensile strength decreases as the length of the soft section increases. The frequency required to initiate the dynamic transition process from the “rubber” to “glass” state is directly proportional to the length of the soft section [44]. Remarkably, all analyzed formulations exhibit an elastic response even under typical high-frequency blast loading conditions.

Both the length of the soft segments and the type of hydrogen bonding significantly influence the impact response [45]. The impact-induced changes in the chain segments are primarily caused by bending and torsional bonding and the molecular potential energy is predominantly stored in the soft mid-segments. Upon impact, the ordered arrangement of the hard segments is disrupted, resulting in a reduction in the number of hydrogen bonds. The dissociation of hydrogen bonds leads to a substantial increment in the potential [41,46]. Additionally, the soft phase stores a greater amount of strain energy compared to the hard phase under impact. Conversely, the hard phase dissipates plastic energy through hydrogen bond dissociation and structural disruption, which is more prominent at stronger shocks [47]. Polyureas can undergo hardening through the dissociation of hydrogen bonding and rearrangement of the soft and hard segments via a light-curing reaction. In this reaction, the amide and urea bonds within the polyurea molecule are fragmented and restructured to create new hydrogen bonds and molecular chain cross-links. As a result, the polyurea molecules become interconnected, enhancing the strength and hardness of the material. This reaction necessitates a specific light intensity and duration, typically achieved through ultraviolet or visible light irradiation.

The viscous dissipation and strain rate effects within polyurea materials primarily depend on the structure and movement mode of the polyurea molecules themselves. The polyurea molecule consists of two distinct structural units: the hard segment and the soft segment. The hard segment is formed through the reaction of diisocyanate and diol, resulting in a polyurethane structural unit with high strength and stiffness. In contrast, the soft segment is formed through the reaction of long-chain diol and dibasic acid, giving rise to a polyester structural unit with high flexibility and toughness. This combination of hard and soft segments imparts polyurea with both strength and flexibility, enabling it to undergo deformation when subjected to external stresses and thereby consuming energy [48]. The dissipation of shock wave energy occurs through three mechanisms: (1) thermal dissipation, (2) viscous dissipation and (3) plastic dissipation. Heat is dissipated due to viscosity and internal friction within the material. Viscous dissipation refers to the incomplete relaxation of molecular chains in a short period of time, resulting in the retention of potential energy. Plastic dissipation primarily occurs in the hard phase of the material. The mesoscale inhomogeneous two-phase structure must undergo deformation coordination during loading, leading to a significant lateral displacement of the soft phase. This displacement increases the deformation energy and frictional heat of the molecular chains [47]. Yao et al. [46] discovered that polyurea with a lower content of hard segments exhibits higher energy dissipation when the shock is released under the same impact pressure. The main mode of energy dissipation is through heat dissipation, which arises from an increase in kinetic energy. Unlike in a tensile simulation, under impact loading the increase in molecular potential energy is primarily partitioned into the increments of bonding energy, angular energy and dihedral angular energy, with the majority of these increments stored in the soft segments. During high-velocity impacts, the increment in hydrogen bonding potential accounts for only around 1% of the internal energy increment.

The motion mode of polyurea molecules plays a significant role in their viscous dissipation and strain rate effects. The presence of hydrogen bonding between polyurea molecules causes the bonds to break and rearrange under external stress, resulting in various modes of motion such as rotation, slippage and twisting. These modes of motion generate friction and sticking between the polyurea molecules, leading to viscous dissipation and strain rate effects. Notably, the strain rate effect becomes more pronounced at higher strain rates [20,49,50,51]. An increase in strain rate leads to higher rheological stress, compressive strength, strain rate sensitivity and strain energy, which can enhance the protection of structures against blast and shock loading [28,52,53]. Wu et al. [54] conducted an investigation on the enhancement properties of coated polyurea on localized damage of 6063-T5 aluminum alloy tubing using static and dynamic mechanical property tests, explosion tests and numerical simulation calculations. Their findings reveal that the AP103 polyurea exhibits a strain-rate sensitive effect during tensile testing, with a noticeable elastic phase followed by a slight strain-hardening phase. In dynamic compression experiments, the polyurea exhibits a significant nonlinear stress-strain relationship. At low strain rates, polyurea displays superelastic properties, whereas at high strain rates, it exhibits clear yield slip, strain-hardening properties and strain rate effects.

In conclusion, the viscous dissipation and strain rate effects in polyurea are predominantly influenced by the molecular structure and motion modes. These effects contribute to polyurea’s remarkable energy absorption and stability capabilities under high stress-strain rates, making it highly promising for a wide range of applications requiring high strength and high speed.

当基材和聚脲之间存在界面反射和透射时，就会发生阻抗失配，从而导致能量损失和信号衰减等潜在问题。这种不匹配主要是由物理参数的变化引起的，例如介电常数、声波速度和基材和聚脲之间的密度。界面附着力不足是阻抗失配的常见原因，这是由化学成分、表面形态和基材表面粗糙度等因素引起的。这些因素会削弱材料之间的结合，并引起界面剥落、裂纹扩展和材料分离等问题[55,56,57]。阻抗不匹配的另一个原因是基材和聚脲之间的热膨胀系数存在差异。当温度发生变化时，基材和聚脲可能会发生不同程度的热膨胀，从而导致应力和应变差异。这种不匹配会导致界面剪切应力、应力集中以及随后的材料损坏和降解。基材和聚脲之间机械性能的差异也会导致阻抗不匹配。例如，基材可能具有更高的刚度和强度，而聚脲则表现出更大的韧性和能量吸收。这种不匹配会导致界面应力集中和失效，从而影响材料的整体性能[58,59,60,61]。基材和聚脲之间的化学相容性不足也会导致阻抗失配。这种化学不匹配可能会导致界面反应、溶解或腐蚀等问题，最终影响材料的性能和耐久性。基材和聚脲之间的表面能差异也会导致阻抗不匹配。这些差异会使涂层、粘接或润湿等工艺更具挑战性，从而影响材料的界面性能和耐久性。

从宏观角度来看，聚脲与基材之间的阻抗不匹配是影响聚脲抗爆和抗冲击的主要因素。为了减轻这种不匹配导致的材料性能下降，可以提高聚脲和基材之间的界面强度[56]。此外，当由于材料和施工方法的差异而无法改变界面特性时，可以采用阻抗失配的定量设计来达到所需的保护目标[62]。故意制造阻抗失配的目的是在材料特性和能量吸收之间取得平衡。T. Rahimzadeh等[62]在多层防护装甲的设计中，利用有限元分析，确定装甲的外层应比其相邻层具有更高的声阻抗。这允许在两层之间的界面处进行多次反射，从而有效地调整波。然而，必须确保阻抗不匹配不会过多，因为这会导致应力波在连续层之间的低效传输。

研究发现，低厚度聚脲涂料会增加高阻抗聚脲/钢界面处的波反射频率，从而显著提高聚脲的压力水平和瞬时比能量密度[63]。但是，增加钢板的抗弹性对抗爆性有相反的作用。在G.Wu等[64]进行的现场爆炸试验中，观察到当冲击侧喷涂一层薄薄的聚脲层时，聚脲层内部的卸荷波无法及时赶上加载波。因此，承载更多能量的压缩波穿过聚脲层，直接撞击钢板，造成更严重的损伤。聚脲层与钢板之间的粘结强度在抗冲击性方面也起着至关重要的作用。聚合物与基材的过早脱粘会阻止涂层最大限度地发挥其能量吸收效果[65]。L. Zhang等[66]研究了ASTM 1045钢板用不同力学性能的聚脲增强的抗爆性能，观察到涂覆在板正面的高延展性聚脲的早期整体倒塌严重限制了聚脲的保护效果。因此，在负载下对板的损坏并没有显着减少。正面的高延展性聚脲涂层优化了目标内部的阻抗关系，通过负载波的卸载作用降低了反射载荷并减轻了损伤。然而，由于聚脲和钢板的脱粘，有效性降低。在靶板的背面涂上高延展性的聚脲，可以在适当的时间范围内消散冲击能量，同时反射和卸载应力波。这大大提高了靶板的抗爆性。

研究纳米尺度的界面阻抗。Y. Chen等[67]进行了MD模拟，分析了单晶铜在圆柱形收敛冲击下的激发波预熔化和色散过程。他们的研究结果表明，由于反射波和空载波之间的相互作用，在自由表面附近形成了拉伸区，因此自由表面附近的预熔区在卸载后发生了剥落。通过在纳米尺度的冲击表面上存在聚合物层，可以有效地减轻冲击损伤。然而，冲击波的混响削弱了背面的聚合物层。在另一项研究中，M.A.N. Dewapriya等[68]对多层纳米结构的弹道冲击试验进行了MD模拟。结果表明，施加在冲击表面的超薄聚脲层有效地将冲击载荷重新分配到下面的金属层，从而改善了能量吸收。