Caprolactam copolymer as well as preparation method and application thereof

Abstract

The invention relates to a caprolactam copolymer as well as a preparation method and application thereof. The caprolactam copolymer contains 0.05%-10% by mass of a structural unit derived from alpha-amino-epsilon-caprolactam and 90%-99.95% by mass of a structural unit derived from caprolactam. The caprolactam copolymer provided by the invention not only improves the processability on the premise of keeping the mechanical properties of nylon 6, but also has higher melt strength, better elasticity and certain antibacterial property.

Description

Technical Field

[0001] This application relates to the field of polymer chemistry, specifically to a caprolactam copolymer, its preparation method, and its application. Background Technology

[0002] Caprolactam is an important organic chemical raw material, mainly used in the production of nylon 6. Nylon 6 is a commonly used engineering plastic with good mechanical properties, wear resistance, and chemical stability, and is widely used in the automotive, electronics, and machinery industries. However, nylon 6 has poor flowability, low melt strength, and unsatisfactory storage modulus and loss modulus, which not only imposes high processing requirements but also limits its application in certain high-performance materials to some extent.

[0003] The properties of nylon 6 can be altered by copolymerizing caprolactam with functionalized monomers. However, on the one hand, copolymerization can change the composition and structure of nylon 6, making it difficult to improve the shortcomings of nylon 6 without affecting its inherent excellent properties. On the other hand, the production of nylon 6 is already very mature, making it difficult to change its inherent processes and equipment.

[0004] Existing literature discloses methods for copolymerizing caprolactam with functionalized monomers. For example, introducing a cinnamoyl group onto the amino group of α-amino-ε-caprolactam, followed by anionic copolymerization with caprolactam, aims to obtain reversibly photosensitive copolymers. Another method involves first preparing α-fluorobutylyl chloride-ε-caprolactam monomer, then anionic copolymerizing it with caprolactam under a catalyst to increase the polymer's glass transition temperature. Yet another method involves polymerizing caprolactam with double-bonded substituents, followed by free radical polymerization, to obtain branched polymers. However, these methods often require catalysts, employ different polymerization methods, and involve more complex operational steps.

[0005] ε-Polylysine possesses excellent biocompatibility and antibacterial properties, showing promising applications in the biopharmaceutical field. However, its high water solubility makes it unsuitable for the commercial use of nylon 6. ε-Lysine is a naturally occurring amino acid with abundant sources, but it is difficult to directly polymerize it into useful polymers using chemical methods. Commercially available ε-polylysine is primarily produced through fermentation. To fully utilize the abundant resources of ε-lysine, methods for manufacturing caprolactam using ε-lysine have been investigated in this field, as illustrated in CN101006051B, CN102037131A, and CN111217750A.

[0006] CN108586729B discloses a method for preparing branched nylon by copolymerizing lysine and caprolactam. This disclosure describes the need for a catalyst, with lysine dosage ranging from 0.01% to 0.5% of the weight of caprolactam. Within this dosage range, a gel structure will not form. When the dosage is less than 0.01%, the yield of branched nylon 6 is low; when the dosage is greater than 0.5%, the quality of branched nylon 6 is poor. On the one hand, lysine is not easily copolymerized with caprolactam; on the other hand, it is not easy to form a branched structure in the molecular chain, thus its improvement on the performance of nylon 6 is limited.

[0007] In summary, there are very few existing documents that improve upon the aforementioned shortcomings of nylon 6 while maintaining its inherent excellent properties, and even fewer that impart new properties to nylon 6.

[0008] The information disclosed in the foregoing background section is only for enhancing the understanding of the background of this application, and may include information not known to those skilled in the art. Summary of the Invention

[0009] Existing nylon 6 materials suffer from drawbacks such as poor flowability, low melt strength, and unsatisfactory storage modulus and loss modulus, which not only impose high processing requirements but also limit their application in certain high-performance materials. This application aims to solve one or all of the above-mentioned technical problems.

[0010] The first aspect of this application provides a caprolactam copolymer containing 0.05% to 10% by mass of structural units derived from α-amino-ε-caprolactam and 90% to 99.95% by mass of structural units derived from caprolactam.

[0011] A second aspect of this application provides a composition comprising the caprolactam copolymer and at least one polyamide different from the caprolactam copolymer.

[0012] A third aspect of this application provides a method for preparing the caprolactam copolymer, comprising:

[0013] S1 involves mixing α-amino-ε-caprolactam, caprolactam, and water, and reacting them at 150–220°C and atmospheric pressure to 0.5 MPa for 0.5–4 hours; wherein water accounts for 0.1–10% of the total mass of the reactants.

[0014] S2 reacts at 220–280℃ and 0.3–0.8 MPa for 1–5 hours;

[0015] S3 reacts at 220–290℃ and 0.1–0.2 MPa for 0.5–3 h;

[0016] S4 reacts at 220–290℃ and -0.09–0 MPa for 1–2 hours.

[0017] The fourth aspect of this application provides a caprolactam copolymer prepared by the aforementioned preparation method.

[0018] The fifth aspect of this application provides an article comprising the caprolactam copolymer, the composition, or the caprolactam copolymer prepared by the method.

[0019] The sixth aspect of this application provides the use of the caprolactam copolymer in improving the mechanical properties and / or processing properties of polyamides different from the caprolactam copolymer.

[0020] Compared with conventional nylon 6, this application achieves one or all of the following technical effects.

[0021] (1) The caprolactam copolymer of this application significantly improves the flowability of the product while maintaining the mechanical properties of nylon 6;

[0022] (2) The melt strength of the caprolactam copolymer of this application is qualitatively improved;

[0023] (3) The caprolactam copolymer of this application can be adapted to different processing processes with very different viscosity requirements by adjusting the shear conditions;

[0024] (4) The caprolactam copolymer of this application has better elasticity;

[0025] (5) The caprolactam copolymer of this application has a certain antibacterial effect;

[0026] (6) No gel structure is formed in the copolymerization method of this application;

[0027] (7) The caprolactam copolymer of this application has low manufacturing cost, simple process and is easy to industrialize.

[0028] Other features and advantages of this application will be described in detail in the Detailed Description section. Attached Figure Description

[0029] Figure 1 The carbon NMR spectrum of the copolymers in this application.

[0030] Figure 2 The storage modulus variation diagram of the copolymer in this application.

[0031] Figure 3 The loss factor variation diagram of the copolymer in this application.

[0032] Figure 4 The graph shows the variation of the composite viscosity of the copolymer in this application with shear rate.

[0033] Figure 5 Images of antibacterial tests on Nylon 6.

[0034] Figure 6 Images of the antibacterial properties of the copolymers in this application. Detailed Implementation

[0035] The present application is described in detail below with reference to specific embodiments. However, it should be noted that the scope of protection of the present application is not limited by these specific embodiments and principle explanations, but is determined by the claims.

[0036] Any implementation described in this application may be freely combined with one or more other implementations described herein. Any technical solutions or technical ideas formed therefrom shall be regarded as part of the original disclosure or record of this application, and shall not be regarded as new content not disclosed or anticipated herein, unless those skilled in the art believe that such combination is obviously unreasonable.

[0037] All features disclosed in this application can be combined arbitrarily, and such combinations should be considered as specifically disclosed and recorded in this application unless they are obviously unreasonable to those skilled in the art. The numerical points disclosed in this specification include not only the numerical points specifically disclosed in the embodiments, but also the endpoints of each numerical range in the specification. Any range of combinations of these numerical points should be considered as the range disclosed or recorded in this application.

[0038] In this application, technical and scientific terms that are given a definition shall be used as defined thereon, while those that are not given a definition shall be understood according to their common meaning in the art.

[0039] In this article, α-amino-ε-caprolactam can be simply referred to as aminocaprolactam.

[0040] The term "optional" means that something can be either present or absent. For example, "A and optional B" includes both "having A and having B" and "having A but not B".

[0041] The first aspect of this application provides a caprolactam copolymer containing 0.05% to 10% by mass of structural units derived from α-amino-ε-caprolactam and 90% to 99.95% by mass of structural units derived from caprolactam.

[0042] According to the caprolactam copolymer of the first aspect of this application, the α-amino-ε-caprolactam has the structure shown in formula (I):

[0043]

[0044] According to a first embodiment of the first aspect of this application, the caprolactam copolymer contains 0.05% to 0.5% by mass of structural units derived from α-amino-ε-caprolactam and 99.5% to 99.95% by mass of structural units derived from caprolactam; preferably, the caprolactam copolymer contains 0.05% to 0.3% by mass of structural units derived from α-amino-ε-caprolactam and 99.7% to 99.95% by mass of structural units derived from caprolactam. In this embodiment, by using a small amount of structural units derived from α-amino-ε-caprolactam, the flowability of nylon 6 can be significantly improved while maintaining the mechanical properties of nylon 6.

[0045] According to a second embodiment of the first aspect of this application, the caprolactam copolymer contains 0.5% to 1% by mass of structural units derived from α-amino-ε-caprolactam and 99% to 99.5% by mass of structural units derived from caprolactam; preferably, the caprolactam copolymer contains 0.5% to 0.75% by mass of structural units derived from α-amino-ε-caprolactam and 99.25% to 99.5% by mass of structural units derived from caprolactam. In this embodiment, the copolymer molecular chain is still mainly linear, and the melt strength of nylon 6 can be significantly improved by using a small amount of structural units derived from α-amino-ε-caprolactam.

[0046] According to a third embodiment of the first aspect of this application, the caprolactam copolymer contains 1% to 5% by mass structural units derived from α-amino-ε-caprolactam and 95% to 99% by mass structural units derived from caprolactam; preferably, the caprolactam copolymer contains 1% to 4.5% by mass structural units derived from α-amino-ε-caprolactam and 95.5% to 99% by mass structural units derived from caprolactam. In this embodiment, the copolymer molecular chain clearly contains branched chains, resulting in a qualitative improvement in the copolymer's processing performance. Furthermore, the copolymer's zero-shear viscosity is an order of magnitude higher than that of conventional nylon 6, but its apparent viscosity at a certain shear rate is only half that of conventional nylon 6. Therefore, it is suitable for various applications with significantly different viscosity requirements; and the copolymer exhibits good elasticity.

[0047] According to the fourth embodiment of the first aspect of this application, the caprolactam copolymer contains 5% to 10% by mass structural units derived from α-amino-ε-caprolactam and 90% to 95% by mass structural units derived from caprolactam. In this embodiment, the copolymer exhibits significantly improved processing performance and zero-shear viscosity, as well as better elasticity. Surprisingly, the copolymer also possesses a certain antibacterial effect, with an antibacterial rate exceeding 80%, making it particularly suitable for use in humid environments prone to bacterial growth.

[0048] According to the caprolactam copolymer of the first aspect of this application, the copolymer molecule may optionally contain a structural component derived from a molecular weight regulator in a mass fraction greater than 0 to 3%. The molecular weight regulator is a dibasic fatty acid or a diaromatic acid, preferably adipic acid.

[0049] The caprolactam copolymer according to the first aspect of this application has a relative viscosity between 1.5 and 3.0, preferably between 1.8 and 2.8. It is well known in the art that the relative viscosity can be controlled by changing the polymerization conditions.

[0050] The caprolactam copolymer according to the first aspect of this application has a weight-average molecular weight of 2,000 to 500,000, preferably 5,000 to 200,000, and more preferably 5,000 to 100,000.

[0051] According to the caprolactam copolymer of the first aspect of this application, the molar ratio of terminal amino groups to terminal carboxyl groups in the caprolactam copolymer is 1.05 to 7, which can be 1.05 to 2, 2 to 4 or 4 to 7.

[0052] According to the first aspect of this application, the caprolactam copolymer can be prepared under the reaction conditions for producing nylon 6 by aqueous ring-opening polymerization of caprolactam.

[0053] According to the caprolactam copolymer of the first aspect of this application, the molar ratio of terminal amino groups to terminal carboxyl groups in the caprolactam copolymer is 1.05-2, 2-4, or 4-7 by controlling the reaction conditions of the condensation stage.

[0054] According to the caprolactam copolymer of the first aspect of this application, the caprolactam copolymer is entirely soluble in trifluoroethanol.

[0055] A second aspect of this application provides a composition comprising the caprolactam copolymer and at least one polyamide different from the caprolactam copolymer.

[0056] According to the composition of the second aspect of this application, the polyamide is preferably nylon 6 or nylon 66.

[0057] The composition according to the second aspect of this application comprises 70% to less than 100%, preferably 80% to less than 100%, more preferably 90% to less than 100% by mass of the caprolactam copolymer and at least one polyamide different from the caprolactam copolymer, with a mass fraction greater than 0% to 30%, preferably greater than 0% to 20%, more preferably greater than 0% to 10% by mass.

[0058] The composition according to the second aspect of this application further comprises, by mass fraction greater than 0% to 30%, preferably greater than 0% to 20%, and more preferably greater than 0% to 10%, an additive selected from reinforcing agents, fillers, toughening agents, plasticizers, flame retardants, colorants, fluorescent whitening agents, light stabilizers, antioxidants, heat stabilizers, lubricants, mold release agents, and combinations thereof.

[0059] According to the composition of the second aspect of this application, the caprolactam copolymer contains 5% to 10% by mass of structural units derived from α-amino-ε-caprolactam and 90% to 95% by mass of structural units derived from caprolactam.

[0060] A third aspect of this application provides a method for preparing the caprolactam copolymer, comprising:

[0061] S1 involves mixing α-amino-ε-caprolactam, caprolactam, and water, and reacting them at 150–220°C and atmospheric pressure to 0.5 MPa for 0.5–4 hours; water accounts for 0.1–10% of the total mass of the reactants.

[0062] S2 reacts at 220–280℃ and 0.3–0.8 MPa for 1–5 hours;

[0063] S3 reacts at 220–290℃ and 0.1–0.2 MPa for 0.5–3 h;

[0064] S4 reacts at 220–290℃ and -0.09–0 MPa for 1–2 hours.

[0065] According to the preparation method of the third aspect of this application, in S1, the temperature is preferably 180-220°C, the pressure is preferably 0.03-0.3 MPa, the reaction time is preferably 0.5-3 h, and the water preferably accounts for 1-5% of the total mass of the reactants.

[0066] According to the preparation method of the third aspect of this application, in S2, the temperature is preferably 240-260°C, the pressure is preferably 0.35-0.75 MPa, and the reaction time is preferably 2-4 h.

[0067] According to the preparation method of the third aspect of this application, in S3, the temperature is preferably 240-265°C, the pressure is preferably 0.1-0.2 MPa, and the reaction time is preferably 1-2 h.

[0068] According to the preparation method of the third aspect of this application, in S4, the temperature is preferably 245 to 270°C, the pressure is preferably -0.09 to -0.05 MPa, and the reaction time is preferably 1 to 2 hours.

[0069] According to the preparation method of the third aspect of this application, the obtained copolymer is completely soluble in trifluoroethanol, indicating that there is no gel in the copolymer.

[0070] According to the caprolactam copolymer of the first aspect of this application, by controlling S3 and S4 or controlling the reaction conditions of S4, the molar ratio of terminal amino groups to terminal carboxyl groups in the caprolactam copolymer is 1.05-2, 2-4 or 4-7.

[0071] Surprisingly, this application, through aqueous ring-opening copolymerization of α-amino-ε-caprolactam and caprolactam, discovered that more copolymer units can be introduced into the middle of the polymer molecular chain, making it easier to form branched structures and improving the crystallization and rheological behavior of the copolymer. Through the combined action of amino groups and branched chains, not only can the flowability of nylon 6 be significantly improved while maintaining its mechanical properties, but it also endows the copolymer with new properties that existing technologies have failed to achieve, such as high melt strength, high elasticity, and antibacterial properties. In contrast, using lysine as a comonomer does not significantly improve the properties of nylon 6 and cannot endow it with new properties. Furthermore, the comonomers used in this application are relatively inexpensive, do not require catalysts, and the copolymerization process can be carried out on existing nylon 6 production equipment, thus facilitating industrial production.

[0072] The fourth aspect of this application provides a caprolactam copolymer prepared by the method of the third aspect.

[0073] The fifth aspect of this application provides an article comprising the caprolactam copolymer, the composition, or the caprolactam copolymer prepared by the method.

[0074] The articles of manufacture according to aspect five of this application are selected from textiles, daily necessities, building materials, packaging materials and panels.

[0075] The sixth aspect of this application provides an application of the caprolactam copolymer in improving the properties of polyamides.

[0076] According to the application of the sixth aspect of this application, the properties are one or more of mechanical properties, processing properties, and antibacterial properties.

[0077] The following are the test methods used in the examples and comparative examples.

[0078] Relative viscosity test: A ZVISCO-IV2000 fully automatic viscometer was used. The sample was dissolved in 96wt% concentrated sulfuric acid, with a solute-to-solvent ratio of 1(m):100(v). A glass viscometer with a diameter of 1.013mm was selected, and the water bath temperature was 25℃. The solvent and solution were tested three times respectively, with the time difference between the three tests not exceeding 0.01s. The average value was taken to calculate the relative viscosity.

[0079] 13 C10 NMR analysis: Measured using a Beuker AVANCE NEO 500MHz NMR spectrometer. The reactants were dissolved in formic acid, followed by the addition of deuterated DMSO, and then scanned on the NMR spectrometer. Delay time (DI) 5 s, number of scans (NS) 2000.

[0080] Dynamic viscoelasticity: Dynamic viscoelasticity was measured using a HAAKE MARS 40 / 60 rotor. The rotor model was P25L. In oscillation mode, angular frequency scanning was selected, with a scanning range of 0.1–500 rad / s, to obtain the curves of storage modulus (G′), loss modulus (G″), and loss factor (δ) as a function of angular frequency (ω).

[0081] Melt index: Measured using a melt indexer (M40) from GOETTFRT GmbH, Germany. A load of 2.16 kg was selected, and the chamber temperature was set to 230℃ for testing. The unit is g / 10 min.

[0082] Rheological properties: measured using a HAAKE MARS 40 / 60 oscilloscope. The rotor model was P25L. Angular frequency scanning was performed in oscillation mode, with a scanning range of 0.1–500 rad / s, to obtain the curve of complex viscosity (η) as a function of angular frequency (ω).

[0083] Yield strength: determined using an MTS / SANS CMT2000 electronic universal tensile testing machine. Test standard: ASTM D638-14; test head speed: 10 mm / min.

[0084] Antibacterial test: The antibacterial properties of the samples were tested in accordance with the national standard QB / T 2591-2003.

[0085] Terminal group content testing: The terminal group content was determined using a Metrohm 916T-touch potentiometric titrator. According to GB / T38138-2019, the terminal amino and carboxyl groups were tested in a trifluoroethanol system using potentiometric titration. Approximately 0.8 g of sample was dissolved in an 88% trifluoroethanol-water solution under magnetic stirring at 60°C. First, an amino group concentration titration was performed. After complete dissolution and cooling to room temperature, the sample solution was potentiometrically titrated with a 0.02 mol / L hydrochloric acid-ethanol standard solution. The potential change was observed, and a blank test was performed after titration. Then, a carboxyl group concentration titration was performed. The solution from the amino group titration was titrated with a 0.02 mol / L potassium hydroxide-ethanol standard solution. Excess hydrochloric acid was neutralized first, and then titration was performed to the endpoint.

[0086] Unless otherwise stated herein, all reagents used in the following examples and comparative examples are commercially available products of analytical purity.

[0087] Example

[0088] This embodiment illustrates the preparation method of the caprolactam copolymer of this application.

[0089] 2000g of caprolactam, a certain amount of amino-caprolactam, and 62g of water were weighed into a 5L high-pressure reactor. The reaction system was purged with nitrogen at room temperature, heated to 105℃, and stirred at 70 rpm. The reaction was maintained at 200℃ and 0.2MPa for 2 hours; then heated to 255℃ and maintained at 0.65MPa for 3 hours; the pressure was reduced to 0.1MPa and the reaction was continued at 250℃ for 1 hour; finally, the pressure was reduced to -0.08MPa and the reaction was continued at 250℃ for 1 hour to obtain the caprolactam copolymer. The amounts of amino-caprolactam and the properties of the caprolactam copolymer are shown in Tables 1 and 2, respectively. Figure 1 , 2 3, 4, 6.

[0090] Table 1

[0091]

[0092] As shown in Table 1, the melt index of the copolymer remained essentially unchanged when the amount of aminocaprolactam ranged from 0.05% to 1%, but it was significantly higher than that of conventional nylon 6, indicating a significant improvement in the flowability and processability of the copolymer. When the mass fraction of aminocaprolactam was greater than 1%, the increase in the melt index of the polymer was even greater, indicating significantly better flowability and processability. In the relative viscosity test, all copolymers were completely soluble, and the solution was clear without precipitation. Similarly, all copolymers were also completely soluble in trifluoroethanol, and the solution was clear without precipitation, indicating that there was no gel structure in the copolymer. As shown in Table 1, with the increase of aminocaprolactam content, the ratio of terminal amino groups to terminal carboxyl groups in the copolymer increased significantly, and the melt index of the copolymer also increased significantly.

[0093] Table 2

[0094]

[0095] As shown in Table 2, the mechanical properties of the copolymer in this application are basically the same as or better than those of conventional nylon 6. With the increase of aminocaprolactam content, the yield strength of the copolymer increases and the yield elongation decreases.

[0096] Figure 1 The NMR 13C spectrum of the copolymer of this application is shown below. Figure 1 It can be seen that aminocaprolactam and caprolactam copolymerized, and the copolymer has a branched structure.

[0097] Figure 2 This is a graph showing the change in storage modulus of the copolymer in this application. From... Figure 2 It can be seen that when the amount of aminocaprolactam is less than 0.75%, the storage modulus of the copolymer increases with the increase of the amount of aminocaprolactam, but the trend is basically consistent with that of nylon 6, both showing a linear relationship with the angular frequency, indicating that the copolymer molecular chain is mainly linear. When the amount of aminocaprolactam is greater than 1%, the storage modulus of the copolymer increases significantly, the copolymer elasticity is better, and the storage modulus plateaus when the angular frequency is less than 1 rad / s, indicating that there are more branches in the copolymer molecular chain. When the amount of aminocaprolactam is greater than 2% of the total mass of the comonomer, the storage modulus of the copolymer is even greater, the copolymer elasticity is better, and the plateau range is larger.

[0098] Figure 3 This is a graph showing the variation of the loss factor of the copolymer in this application. From... Figure 3 It can be seen that the polymer elasticity increases with the increase of aminocaprolactam dosage.

[0099] Figure 4 This is a graph showing the composite viscosity of the copolymers in this application as a function of shear rate. From... Figure 4It can be seen that at low shear rates, the apparent viscosity of the copolymers is greater than that of nylon 6, and the melt strength increases. As the shear rate increases, the copolymers all exhibit shear thinning behavior and tend to have a lower apparent viscosity than nylon 6. This indicates that at high shear rates, the copolymers have better flowability and are easier to process.

[0100] Figure 5 and Figure 6 These are images showing the antibacterial test results for nylon 6 and the antibacterial test results for the copolymer of this application, respectively. From... Figure 5 and Figure 6 It is known that the copolymer of this application has certain antibacterial properties. The antibacterial rate of the copolymer with 5% aminocaprolactam content was 81%.

Claims

1. A caprolactam copolymer, characterized in that, The caprolactam copolymer contains 0.05% to 10% by mass structural units derived from α-amino-ε-caprolactam and 90% to 99.95% by mass structural units derived from caprolactam.

2. The caprolactam copolymer according to claim 1, characterized in that, The caprolactam copolymer contains 0.05% to 0.5% by mass structural units derived from α-amino-ε-caprolactam and 99.5% to 99.95% by mass structural units derived from caprolactam; or The caprolactam copolymer contains 0.5% to 1% by mass structural units derived from α-amino-ε-caprolactam and 99% to 99.5% by mass structural units derived from caprolactam; or the caprolactam copolymer contains 1% to 5% by mass structural units derived from α-amino-ε-caprolactam and 95% to 99% by mass structural units derived from caprolactam; or the caprolactam copolymer contains 5% to 10% by mass structural units derived from α-amino-ε-caprolactam and 90% to 95% by mass structural units derived from caprolactam.

3. The caprolactam copolymer according to claim 1, characterized in that, The caprolactam copolymer molecule contains a structural component of greater than 0 to 3% by mass derived from a molecular weight regulator; the molecular weight regulator is a dibasic fatty acid or a diaromatic acid, preferably adipic acid.

4. The caprolactam copolymer according to claim 1, characterized in that, The relative viscosity of the caprolactam copolymer is between 1.5 and 3.0, preferably between 1.8 and 2.

8.

5. The caprolactam copolymer according to claim 1, characterized in that, In the caprolactam copolymer, the molar ratio of terminal amino groups to terminal carboxyl groups is 1.05 to 7.

6. A composition, characterized in that, It comprises the caprolactam copolymer of claim 1 and at least one polyamide different from the caprolactam copolymer.

7. The composition according to claim 6, characterized in that, The polyamide is nylon 6 or nylon 66.

8. The composition according to claim 6, characterized in that, The copolymer comprises 70% to less than 100% by mass, preferably 80% to less than 100% by mass, more preferably 90% to less than 100% by mass, and at least one polyamide different from the copolymer by mass, comprising greater than 0% to 30% by mass, preferably greater than 0% to 20% by mass, more preferably greater than 0% to 10% by mass.

9. The composition according to claim 6, characterized in that, It contains additives selected from reinforcing agents, fillers, toughening agents, plasticizers, flame retardants, colorants, fluorescent whitening agents, light stabilizers, antioxidants, heat stabilizers, lubricants, mold release agents, and combinations thereof, with a mass fraction of greater than 0% to 30%, preferably greater than 0% to 20%, and more preferably greater than 0% to 10%.

10. The composition according to claim 6, characterized in that, The caprolactam copolymer contains 5% to 10% by mass structural units derived from α-amino-ε-caprolactam and 90% to 95% by mass structural units derived from caprolactam.

11. A method for preparing the caprolactam copolymer according to claim 1, comprising: S1 involves mixing α-amino-ε-caprolactam, caprolactam, and water, and reacting them at 150–220°C and atmospheric pressure to 0.5 MPa for 0.5–4 hours; water accounts for 0.1–10% of the total mass of the reactants. S2 reacts at 220–280℃ and 0.3–0.8 MPa for 1–5 hours; S3 reacts at 220–290℃ and 0.1–0.2 MPa for 0.5–3 h; S4 reacts at 220–290℃ and -0.09–0 MPa for 1–2 hours.

12. A caprolactam copolymer, characterized in that, Prepared by the method described in claim 11.

13. An article characterized in that, The copolymer comprises the caprolactam copolymer of claim 1, the composition of claim 6, or the caprolactam copolymer prepared by the method of claim 12.

14. The article of manufacture according to claim 13, characterized in that, Selected from textiles, daily necessities, building materials, packaging materials, and panels.

15. The use of the caprolactam copolymer of claim 1 in improving the properties of polyamides.

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