A method for the living anionic ring-opening polymerization of lactam with controllable molecular weight

Abstract

The present invention relates to a method for active anionic ring-opening polymerization of lactam with controllable molecular weight, comprising: (1) batching: adding lactam and an initiator into a batching tank at a specified temperature, preheating and stirring to obtain a solution or a suspension; the initiator is one or more bases capable of generating amide nitrogen anions; (2) polymerization: transporting the solution or the suspension to a reactor under heat preservation, and then adding a molecular weight regulator to carry out polymerization reaction, so as to obtain a polyamide melt; relative to the initiator, the addition amount of the molecular weight regulator is 100-10000 mol%. The method of the present invention is simple, realizes controllable molecular weight of polyamide and maintains conversion rate, and is suitable for melt direct spinning.

Description

Technical Field

[0001] The invention relates to the fields of polymer chemistry and materials science, and in particular to a method for molecular weight-controllable lactam active anion ring-opening polymerization. Background Art

[0002] Polyamide (PA), commonly known as nylon, has a huge market demand due to its superior wear resistance, hygroscopicity and dyeability over polyester and is widely used in many fields.

[0003] There are many varieties of polyamide. Currently, my country is the world's largest producer and consumer of nylon, among which PA6 is the main production capacity. In the early 1990s, Sinopec developed the "amine oxime" caprolactam production technology with independent intellectual property rights, breaking the foreign monopoly on raw materials and promoting a major leap in the production capacity and output of domestic PA6.

[0004] PA6 chips are mainly used to produce civilian silk, and caprolactam hydrolysis and polycondensation is the most widely used PA6 chip production process in China. However, the content of hot water extractables in the polymer product is generally 8-10%, of which monomers account for 75%, cyclic dimers and oligomers account for 10-15% each. These impurities or bubbles are important factors affecting high-speed spinning. According to the provisions of FZ / T 51004-2011, the content of hot water extractables in PA6 chips should be less than 0.5wt% (superior products). Therefore, the industry currently needs to perform multi-stage extraction and re-melting of PA6 chips before spinning, which consumes a lot of energy, resources and time, greatly limiting the development speed of the industry.

[0005] Living anionic polymerization of lactams is usually carried out by a two-component initiator / activator system, which consists of lactam anions or their precursors and N-acyl lactams (NALs) or similar compounds. Anionic polymerization is a unique method that is usually carried out at temperatures below the melting point of the polymer. It has the characteristics of high reaction rate and high conversion, which has made it mostly used for the efficient preparation of PA engineering plastics for a long time.

[0006] The literature "European Polymer Journ M, 1971, 7, 1637-1648." pointed out that when using sodium caprolactam as an initiator to study caprolactam anionic polymerization, at around 200°C, the polymer will undergo disproportionation, condensation and cracking reactions, and the final number of molecules (N) depends on the balance between these reactions. Their relative rates are particularly affected by the sodium initiator concentration (Cs), and a semi-empirical formula was derived.

[0007] In the literature Journal of Applied Polymer Science, 2010, 52, 9, 1249-1262, caprolactam anionic polymerization was carried out in a twin-screw extruder and melt-blown smoothly, with a conversion rate of more than 90%, but the control of molecular weight was not deeply explored from a mechanism perspective.

[0008] Commonly used molecular weight regulators include N-acyl lactam or diisocyanate and its derivatives. The feed ratio will greatly affect the polymerization conversion rate and the properties of the polymer. In the literature "Journal of Vinyl & Additive Technology, 2010, 16 (2): 152-160.", sodium caprolactam is used as an initiator and hexamethylene diisocyanate is used as a molecular weight regulator. By adjusting the dosage and process conditions, the mechanical properties of PA6 obtained are close to those of commercial PA6 produced by hydrolysis, and the monomer conversion rate is 97%, but it can only be used as an engineering plastic.

[0009] The molecular weight regulator concentration in the patent with the patent number of US3423372A and the name of "Polylactams Produced by the AnionicPolymerization of Higher Lactams Using Polymethylene Polyphenyl Isocyanate asPromoter" is very low (1 / 200 mol-1 / 50 mol). At this concentration, polymerization takes only 3 minutes, and the molecular weight is difficult to control. When the molecular weight regulator ratio is greater than the initiator, the conversion rate is poor. However, according to the active polymerization mechanism of anionic polymerization, the degree of polymerization increases with the increase of conversion rate, the increase of monomer concentration and the decrease of molecular weight regulator concentration. Then the theoretical ratio of monomer to initiator needs to be between 90 / 1 and 260 / 1 to meet the spinning requirements (molecular weight 1-3W), but the polymerization rate depends on the concentration of alkali and molecular weight regulator, which respectively determine the concentration of activated monomer and propagation chain. However, high concentration will lead to excessive polymerization rate and heat release, and excessive temperature will derive a series of side reactions such as branching, cross-linking and depolymerization, and it cannot be directly applied to the preparation of PA6 fiber raw materials.

[0010] The literature "Effects of Molecular Weight on the Dynamic Mechanical and Rheological Properties of Anionically Polymerized Polyamide 6 Containing Nanofiber. Journal of Vinyl & Additive Technology, 2010, 16 (2): 152-160." describes the melt polymerization of caprolactam in a Haake mixer at 230°C using sodium caprolactam / hexamethylene diisocyanate as the catalyst system. The effects of different concentrations of the catalyst system on the reaction rate and conversion rate were determined, and a high conversion rate formula was obtained. However, the regulation principle was not explored in depth, and there is still no accurate report on the polymerization kinetics and molecular weight regulation of PA.

[0011] Patent CN111566143A provides a method for preparing polyamide including an amide molecular weight regulator and the polyamide prepared thereby. Through this patent, it is found that adding urea molecules to the polymerization reaction can significantly change the molecular weight of the polymer, but the specific mechanism and how to make the molecular weight fall within the required range are not studied.

[0012] The 2022 master's thesis of North University of China, "Research on APA6 Polymerization System and Its T-RTM Process Composite Materials", studied the polymerization process and polymerization results of different molar ratios of sodium methoxide and toluene diisocyanate (TDI), with a temperature range of 140-180°C. The results showed that with the increase of the molar ratio of TDI, the polymerization rate of the polymerization system slowed down significantly. Among them, the viscosity of the system with the largest ratio of 1 / 3 increased the slowest, the conversion rate was less than 70%, and the crystallinity was only 12%.

[0013] Copolymerization modification is another important method to regulate polymer properties. Both the ring-opening polymerization and copolymerization of lactams have high commercial value and are widely used in various applications. Since the 1960s, many researchers have studied the anionic copolymerization of different lactams and the properties of their copolyamides. Among them, the anionic copolymerization of caprolactam (CL) and ω-laurolactam (LL) has been a frequently explored research area in recent decades. The advantages of the anionic copolymerization of CL and LL outweigh the disadvantages. The most important advantages include excellent mechanical properties (especially tensile strength), low hygroscopicity, low melting point and acceptable chemical resistance.

[0014] The literature "Technology, 2010, 16, 152." conducted a comprehensive study on the effects of various initiator and activator concentrations on CL polymerization parameters and measured the physical and mechanical properties of the final PCL. They found the optimal content of catalyst and activator to obtain the lowest residual monomer and improve mechanical properties. It can also only be used for engineering plastics and cannot be melt-spun.

[0015] Therefore, it is very important to control the molecular weight during the active anionic polymerization of lactam. In the previous study, it was found that in all the studies on PA polymerization, the discussion scope of the auxiliary agent (molecular weight regulator) was close to the ratio of the initiator, and there was no mature report on the situation where the molecular weight regulator was much more than the initiator in the field of civil spinning. Theoretically, each acylated lactam will rapidly grow a polymer chain. Under the condition of stabilizing the amide exchange, the more quantitative monomer segments, the lower the number average molecular weight. This is the most direct way to control the molecular weight and improve the conversion rate. However, in the actual literature reports, alkali metal initiators have not been able to maintain a high conversion rate at high temperature when the molecular weight regulator is several times more than the initiator. This may be caused by non-selective rapid side reactions and rapid deactivation of active species. Based on the particularity of the rapid chain growth of caprolactam ring-opening polymerization, as long as a suitable chain transfer agent is found to maintain a certain polymerization activity and a catalytic system with high main reaction selectivity, the current bottleneck can be broken. Once the technology iteration is achieved, the production cost and cycle of PA will be greatly reduced. Summary of the invention

[0016] The purpose of the invention is to solve the problems existing in the prior art and provide a method for the living anionic ring-opening polymerization of lactam with controllable molecular weight.

[0017] To achieve the above object, the scheme adopted by the present invention is as follows:

[0018] A method for the living anionic ring-opening polymerization of lactam with controllable molecular weight comprises the following steps:

[0019] (1) Preparation: Add lactam and initiator into a preparation tank at a specified temperature, preheat and stir to obtain a solution or suspension;

[0020] The initiator is one or more bases capable of generating amide nitrogen anions;

[0021] The specified temperature is 30-130℃;

[0022] The purpose of preheating is to make the mixture molten. Most of the lactams used have a melting point less than 130°C, and the lactams in the molten state have good mutual solubility. The melting point of butyrolactam, which has the lowest melting point, is around 28°C. Therefore, the specified temperature must be greater than or equal to 28°C. At the same time, the specified temperature should not be too high, otherwise it will cause polymerization to start directly, which is not conducive to controlling the molecular weight of polyamide. Therefore, the two lactams with melting points greater than 130°C are not applicable.

[0023] (2) Polymerization: The solution or suspension is transported to a reactor under heat preservation, and a molecular weight regulator is added to carry out polymerization reaction to obtain a polyamide melt; the amount of the molecular weight regulator added is 100-10000 mol% relative to the initiator;

[0024] The timing of adding the molecular weight regulator is very important. If the molecular weight regulator is added too early, it will only produce side reactions, and polymerization will not be possible no matter how the temperature is raised. Therefore, in the present invention, the molecular weight regulator is mixed with the mixture after the mixture reaches the specified temperature.

[0025] In the process of lactam anionic ring-opening polymerization, controlling the molecular weight regulator to be much more than the initiator is the most direct and effective method to control the molecular weight and improve the conversion rate. However, the prior art cannot maintain a high conversion rate when the molecular weight regulator is several times more than the initiator. This may be because the traditional initiator has no selectivity, and the rates of other side reactions other than chain growth are also very high, such as branching, decomposition, amide exchange, etc. After the main reaction reaches equilibrium, the more molecular weight regulators there are, the stronger the side reactions are, not only the molecular weight cannot be regulated, but also the conversion rate advantage is lost; the initiator of the present invention has been screened in large quantities, has selectivity, can form a stable complex, and stably catalyzes the main reaction. The increase of the molecular weight regulator will not increase the relative rate of the side reaction, and the polymerization reaction is mild and controllable;

[0026] In the present invention, the amount of the molecular weight regulator added is 100-10000 mol% relative to the initiator. Each molecular weight regulator can produce a polymer chain. Too little dosage will result in too few starting segments, the monomer conversion will be completed within five minutes, the melt will solidify immediately, and the molecular weight will be huge. This is the practice of making engineering plastics; too much dosage will produce too many segments, and the degree of branching is high, which will ultimately lead to no polymer.

[0027] As a preferred solution:

[0028] In the method for the living anionic ring-opening polymerization of lactam with controllable molecular weight as described above, in step (1), the lactam is one or more of propiolactam, butyrolactam, valerolactam, caprolactam, enantholactam, capryllactam, nonanolactam, decanolactam, azacyclododecane-2-one and laurolactam.

[0029] In the above-mentioned method for the living anionic ring-opening polymerization of lactam with controllable molecular weight, in step (1), the initiator is one or more of a non-metallic organic base, a metal weak acid salt, an alkyl metal base, a metal hydroxide (oxide), a metal element and a metal alkoxide.

[0030] In the above method for the living anionic ring-opening polymerization of lactam with controllable molecular weight, in step (1), the amount of the initiator added is 0.01-5 mol % relative to the lactam.

[0031] Theoretically, the ratio of lactam to initiator needs to be between 90 / 1 and 260 / 1 (i.e., the amount of initiator added is 0.38-1.11wt% of the lactam) to meet the spinning requirements (molecular weight 1-3W); this theoretical ratio does not take other additives into consideration, and after the molecular weight regulator participates in the reaction, the ratio of lactam to initiator needs to be adjusted; the present invention controls "the amount of initiator added is 0.01-5mol% relative to lactam", this is because: too little initiator cannot initiate polymerization, too much initiator will inevitably lead to too high a polymerization rate, uncontrolled molecular weight, usually cross-linking, very high modulus, and difficult processing.

[0032] In the above method for the living anionic ring-opening polymerization of lactam with controllable molecular weight, in step (1), the amount of the initiator added is 0.1-2.5 mol % relative to the lactam.

[0033] In the above-mentioned method for the living anionic ring-opening polymerization of lactam with controllable molecular weight, in step (1), the specified temperature is 80-110°C.

[0034] In the above-mentioned method for the living anionic ring-opening polymerization of lactam with controllable molecular weight, in step (1), the preheating and stirring time is 3-25 minutes.

[0035] In the above-mentioned method for the living anionic ring-opening polymerization of lactam with controllable molecular weight, in step (2), the molecular weight regulator is one or more of acyl halide, anhydride, isocyanate, N-acyl lactam, carbon dioxide, urea and guanidine.

[0036] In the above-mentioned method for the living anionic ring-opening polymerization of lactam with controllable molecular weight, in step (2), the amount of the molecular weight regulator added is 200-1000 mol % relative to the initiator.

[0037] In the above-mentioned method for the living anionic ring-opening polymerization of lactam with controllable molecular weight, in step (2), the temperature of the heating jacket of the reactor is 170-250° C., and the pressure inside the reactor is 0-2 MPa.

[0038] In the above-mentioned method for the living anionic ring-opening polymerization of lactam with controllable molecular weight, in step (2), the temperature of the heating jacket of the reactor is 180-240° C. and the pressure is 0-0.5 MPa.

[0039] The above-mentioned method for the active anionic ring-opening polymerization of lactam with controllable molecular weight also includes step (3): devolatilization: the reactor is quickly heated to a specified temperature and then vacuum devolatilization is performed, the devolatilization temperature is 200-230°C, the devolatilization pressure is 100-600Pa, and the devolatilization time is 5-10min.

[0040] In the method for controlling the molecular weight of lactam living anionic ring-opening polymerization as described above, the number average molecular weight of the polyamide is 1981-46130Da, the caprolactam content is ≤2.99wt%, and the caprolactam cyclic dimer content is ≤0.18wt%.

[0041] Beneficial effects:

[0042] (1) The present invention is based on the anionic polymerization process of caprolactam and the catalytic mechanism and characteristics, and can still achieve a high conversion rate even when the molecular weight regulator is several times more than the initiator;

[0043] (2) The present invention can effectively control the molecular weight of the obtained polyamide and the content of hot water extractables in the melt, and has the characteristics of high efficiency, high production stability, low energy consumption, and green environmental protection. The obtained melt can be directly melt-spun, which is easy to achieve large-scale production and can be applied to the fields of clothing fibers, industrial silk, etc. DETAILED DESCRIPTION

[0044] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0045] The following are the test methods involved in the embodiments:

[0046] Number average molecular weight: gel chromatography (GPC), hexafluoroisopropanol system;

[0047] Lactam content and caprolactam cyclic dimer content of polyamide: After the polyamide pellets are extracted by a Soxhlet extractor, the lactam content and caprolactam cyclic dimer content in the extract are detected by HPLC, and the lactam content and caprolactam cyclic dimer content of the polyamide are calculated.

[0048] Example 1

[0049] A method for the living anionic ring-opening polymerization of lactam with controllable molecular weight, comprising the following steps:

[0050] (1) Preparation of raw materials:

[0051] Initiator:

[0052] Dry lactam: caprolactam;

[0053] Molecular weight regulator: terephthaloyl chloride;

[0054] (2) Preparation: Add lactam and initiator into a preparation tank at 75° C., preheat and stir for 25 min to obtain a solution; wherein the amount of initiator added is 2 mol % relative to lactam;

[0055] (3) Polymerization: The solution was conveyed to a reactor with a heating jacket temperature of 170° C., and a molecular weight regulator was immediately added. The polymerization was completed by stirring for 40 min under a pressure of 0 MPa. The amount of the molecular weight regulator added was 200 mol % relative to the initiator.

[0056] (4) Devolatilization: Devolatilization of the melt after polymerization in step (3); wherein the devolatilization temperature is 200° C., the devolatilization pressure is 100 Pa, and the devolatilization time is 5 min.

[0057] The number average molecular weight of the polyamide finally obtained was 40838 Da, the caprolactam content was 0.49 wt %, and the caprolactam cyclic dimer content was 0.008 wt %.

[0058] Comparative Example 1

[0059] A lactam anionic ring-opening polymerization method is basically the same as Example 1, except that: in step (2), the temperature of the batching tank is 140°C.

[0060] The final monomer was difficult to convert into a polymer, with a caprolactam content of 72.2 wt% and a caprolactam cyclic dimer content of 17.6 wt%.

[0061] By comparing Example 1 with Comparative Example 1, it can be seen that excessively high temperature in the batching tank will lead to premature initiation of polymerization, which will then remain in the induction period, during which active species are gradually consumed, which is not conducive to the high polymerization of lactam.

[0062] Comparative Example 2

[0063] A lactam anionic ring-opening polymerization method is basically the same as Example 1, except that the initiator prepared in step (1) is 6-aminocaproic acid.

[0064] The solution was unable to complete polymerization and had a hot water extractable content of 98.5%.

[0065] Comparing Comparative Example 2 with Example 1, it can be seen that the initiator used in Comparative Example 2 is not of the type described in the present invention, which will result in failure to complete the polymerization. This is because 6-aminocaproic acid is an initiator used for hydrolysis polymerization and cannot be used for anionic polymerization.

[0066] Comparative Example 3

[0067] A lactam anionic ring-opening polymerization method is basically the same as Example 1, except that the molecular weight regulator is added in step (2) and is added into the batching tank together with the lactam and the initiator.

[0068] The solution was unable to complete polymerization and had a hot water extractable content of 99.1%.

[0069] Comparative Example 4

[0070] A lactam anionic ring-opening polymerization method is basically the same as Comparative Example 3, except that: in step (3), the heating jacket temperature is 200°C.

[0071] The solution was unable to complete polymerization and had a hot water extractable content of 91.8%.

[0072] By comparing Example 1, Comparative Example 3 and Comparative Example 4, it can be seen that the comparative example did not complete polymerization. This is because adding the molecular weight regulator too early will only produce side reactions. Subsequently, no matter how the temperature is raised, polymerization cannot be achieved, and only small molecules react.

[0073] Example 2

[0074] A method for the living anionic ring-opening polymerization of lactam with controllable molecular weight, comprising the following steps:

[0075] (1) Preparation of raw materials:

[0076] Initiator: magnesium powder;

[0077] Dry lactam: caprolactam;

[0078] Molecular weight regulator: N,N'-dicyclohexylurea;

[0079] (2) Preparation: Add lactam and initiator into a preparation tank at 90° C., preheat and stir for 10 min to obtain a uniform suspension; wherein the amount of initiator added is 0.8 mol% relative to lactam;

[0080] (3) Polymerization: The suspension was conveyed to a reactor with a heating jacket temperature of 200° C., and a molecular weight regulator was immediately added. The polymerization was completed under a pressure of 0.5 MPa with stirring for 15 min. The amount of the molecular weight regulator added was 5000 mol % relative to the initiator.

[0081] (4) Devolatilization: Devolatilize the solution after polymerization in step (3); wherein the devolatilization temperature is 200° C., the devolatilization pressure is 350 Pa, and the devolatilization time is 7 min.

[0082] The number average molecular weight of the polyamide finally obtained was 3794 Da, the caprolactam content was 0.38 wt %, and the caprolactam cyclic dimer content was 0.01 wt %.

[0083] Example 3

[0084] A method for the living anionic ring-opening polymerization of lactam with controllable molecular weight, comprising the following steps:

[0085] (1) Preparation of raw materials:

[0086] Initiator: magnesium ethoxide;

[0087] Dry lactam: caprolactam;

[0088] Molecular weight regulator: N-acetyl caprolactam;

[0089] (2) Preparation: Add lactam and initiator into a preparation tank at 80° C., preheat and stir for 15 min to obtain a solution; wherein the amount of initiator added is 0.8 wt % relative to lactam;

[0090] (3) Polymerization: The solution was conveyed to a reactor with a heating jacket temperature of 190° C., and a molecular weight regulator was immediately added. The polymerization was completed by stirring for 25 min at a pressure of 0 MPa. The amount of the molecular weight regulator added was 400 mol % relative to the initiator.

[0091] The number average molecular weight of the polyamide finally obtained was 22996 Da, the caprolactam content was 0.98 wt %, and the caprolactam cyclic dimer content was 0.02 wt %.

[0092] Example 4

[0093] A method for the living anionic ring-opening polymerization of lactam with controllable molecular weight, comprising the following steps:

[0094] (1) Preparation of raw materials:

[0095] Initiator: trimethylamine;

[0096] Dry lactam: butyrolactam;

[0097] Molecular weight regulator: N,N'-diphenylguanidine bromate;

[0098] (2) Preparation: lactam and initiator are added into a preparation tank at 30° C., preheated and stirred for 8 min to obtain a solution; wherein the amount of initiator added is 0.5 mol % relative to lactam;

[0099] (3) Polymerization: The solution was conveyed to a reactor with a heating jacket temperature of 210° C., and a molecular weight regulator was immediately added. The polymerization was completed by stirring for 10 min at a pressure of 1 MPa. The amount of the molecular weight regulator added was 10,000 mol % relative to the initiator.

[0100] The number average molecular weight of the polyamide finally obtained was 1981 Da, the caprolactam content was 1.79 wt %, and the caprolactam cyclic dimer content was 0.09 wt %.

[0101] Example 5

[0102] A method for the living anionic ring-opening polymerization of lactam with controllable molecular weight, comprising the following steps:

[0103] (1) Preparation of raw materials:

[0104] Initiator: lithium aluminum hydride;

[0105] Dry lactam: a mixture of caprolactam and enantholactam in a molar ratio of 1:1;

[0106] Molecular weight regulator: N-benzoyl caprolactam;

[0107] (2) Preparation: Add lactam and initiator into a preparation tank at 40° C., preheat and stir for 20 min to obtain a solution; wherein the amount of initiator added is 0.01 mol% relative to lactam;

[0108] (3) Polymerization: The solution was conveyed to a reactor with a heating jacket temperature of 190° C., and a molecular weight regulator was immediately added. The polymerization was completed under a pressure of 0.5 MPa with stirring for 20 min. The amount of the molecular weight regulator added was 100 mol % relative to the initiator.

[0109] (4) Devolatilization: Devolatilize the solution after polymerization in step (3); wherein the devolatilization temperature is 230° C., the devolatilization pressure is 600 Pa, and the devolatilization time is 10 min.

[0110] The number average molecular weight of the polyamide finally obtained was 46130 Da, the caprolactam content was 0.36 wt %, the enantholactam content was 1.95 wt %, and the caprolactam cyclic dimer content was 0.10 wt %.

[0111] Example 6

[0112] A method for the living anionic ring-opening polymerization of lactam with controllable molecular weight, comprising the following steps:

[0113] (1) Preparation of raw materials:

[0114] Initiator: caprolactam magnesium bromide;

[0115] Dry lactam: a mixture of caprolactam and laurolactam in a molar ratio of 9:1;

[0116] Molecular weight regulator: p-phenylene diisocyanate;

[0117] (2) Preparation: Add lactam and initiator into a preparation tank at 80° C., preheat and stir for 15 min to obtain a solution; wherein the amount of initiator added is 1.5 mol% relative to the lactam;

[0118] (3) Polymerization: The solution was conveyed to a reactor with a heating jacket temperature of 190° C., and a molecular weight regulator was immediately added. The polymerization was completed under the condition of a pressure of 0 MPa with stirring for 25 min. The amount of the molecular weight regulator added was 300 mol % relative to the initiator.

[0119] (4) Devolatilization: Devolatilize the solution after polymerization in step (3); wherein the devolatilization temperature is 215° C., the devolatilization pressure is 300 Pa, and the devolatilization time is 5 min.

[0120] The number average molecular weight of the polyamide finally obtained was 12155 Da, the caprolactam content was 0.28 wt %, the content of laurolactam monomer was 0.99 wt %, and the content of caprolactam cyclic dimer was 0.03 wt %.

[0121] Example 7

[0122] A method for the living anionic ring-opening polymerization of lactam with controllable molecular weight, comprising the following steps:

[0123] (1) Preparation of raw materials:

[0124] Initiator: rubidium carbonate;

[0125] Dry lactam: caprolactam;

[0126] Molecular weight regulator: carbon dioxide;

[0127] (2) Preparation: Add lactam and initiator into a preparation tank at 130° C., preheat and stir for 3 min to obtain a uniform suspension; wherein the amount of initiator added is 5 mol% relative to lactam;

[0128] (3) Polymerization: The suspension was conveyed to a reactor with a heating jacket temperature of 250° C., and a molecular weight regulator was immediately introduced. The polymerization was completed by stirring for 10 min at a pressure of 2 MPa. The amount of the molecular weight regulator added was 200 mol % relative to the initiator.

[0129] The number average molecular weight of the polyamide finally obtained was 42379 Da, the caprolactam content was 2.99 wt %, and the caprolactam cyclic dimer content was 0.18 wt %.

[0130] Example 8

[0131] A method for the living anionic ring-opening polymerization of lactam with controllable molecular weight, comprising the following steps:

[0132] (1) Preparation of raw materials:

[0133] Initiator: calcium hydride;

[0134] Dry lactam: a mixture of caprolactam and capryllactam in a molar ratio of 10:3;

[0135] Molecular weight regulator: a mixture of N-acetylcaprolactam and N,N'-dicyclohexylurea in a molar ratio of 2:1;

[0136] (2) Preparation: Add lactam and initiator into a preparation tank at 80° C., preheat and stir for 15 min to obtain a uniform suspension; wherein the amount of initiator added is 0.06 mol% relative to lactam;

[0137] (3) Polymerization: The suspension was conveyed to a reactor with a heating jacket temperature of 190° C., and a molecular weight regulator was immediately added. The polymerization was completed by stirring for 15 min under a pressure of 0 MPa. The amount of the molecular weight regulator added was 200 mol % relative to the initiator.

[0138] (4) Devolatilization: Devolatilize the solution after polymerization in step (3); wherein the devolatilization temperature is 210° C., the devolatilization pressure is 200 Pa, and the devolatilization time is 5 min.

[0139] The number average molecular weight of the polyamide finally obtained was 36748 Da, the caprolactam content was 0.46 wt %, the capryllactam monomer content was 1.19 wt %, and the caprolactam cyclic dimer content was 0.03 wt %.

[0140] Example 9

[0141] A method for the living anionic ring-opening polymerization of lactam with controllable molecular weight, comprising the following steps:

[0142] (1) Preparation of raw materials:

[0143] Initiator: lithium hydroxide;

[0144] Dry lactam: caprolactam;

[0145] Molecular weight regulator: phthalic anhydride;

[0146] (2) Preparation: Add lactam and initiator into a preparation tank at 80° C., preheat and stir for 15 min to obtain a uniform suspension; wherein the amount of initiator added is 0.3 mol% relative to lactam;

[0147] (3) Polymerization: The suspension was conveyed to a reactor with a heating jacket temperature of 190° C., and a molecular weight regulator was immediately added. The polymerization was completed by stirring for 15 min under a pressure of 0.5 MPa. The amount of the molecular weight regulator added was 300 mol % relative to the initiator.

[0148] (4) Devolatilization: Some formulas require devolatilization treatment, the devolatilization temperature is 200℃, the devolatilization pressure is 100Pa, and the devolatilization time is 5min.

[0149] The number average molecular weight of the polyamide finally obtained was 28937 Da, the caprolactam content was 0.38 wt %, and the caprolactam cyclic dimer content was 0.11 wt %.

[0150] Example 10

[0151] A method for the living anionic ring-opening polymerization of lactam with controllable molecular weight, comprising the following steps:

[0152] (1) Preparation of raw materials:

[0153] Initiator: a mixture of magnesium ethoxide and lithium aluminum hydride in a molar ratio of 2:1;

[0154] Dry lactam: caprolactam;

[0155] Molecular weight regulator: N-acetyl caprolactam;

[0156] (2) Preparation: Add lactam and initiator into a preparation tank at 80° C., preheat and stir for 15 min to obtain a uniform suspension; wherein the amount of initiator added is 0.02 mol% relative to lactam;

[0157] (3) Polymerization: The suspension was conveyed to a reactor with a heating jacket temperature of 190° C., and a molecular weight regulator was immediately added. The polymerization was completed by stirring for 15 min at a pressure of 0 MPa. The amount of the molecular weight regulator added was 1000 mol % relative to the initiator.

[0158] The number average molecular weight of the polyamide finally obtained was 17712 Da, the caprolactam content was 0.79 wt %, and the caprolactam cyclic dimer content was 0.01 wt %.

Claims

1. A method for the living anionic ring-opening polymerization of lactam with controllable molecular weight, characterized in that: The following steps are involved: (1) Preparation: Add lactam and initiator into a preparation tank at a specified temperature, preheat and stir to obtain a solution or suspension; The lactam is one or more of propiolactam, butyrolactam, valerolactam, caprolactam, enantholactam, capryllactam, nonanolactam, decanolactam, azacyclododecane-2-one and laurolactam; the initiator is one or more of non-metallic organic base, metal weak acid salt, alkyl metal base, metal hydroxide (oxide), metal element and metal alkoxide; The specified temperature is 30-130℃; (2) Polymerization: The solution or suspension is transported to a reactor under heat preservation, and a molecular weight regulator is added to carry out polymerization reaction to obtain a polyamide melt; the amount of the molecular weight regulator added is 200-10000 mol% relative to the initiator; The molecular weight regulator is one or more of acyl halides, anhydrides, isocyanates, N-acyl lactams, carbon dioxide and guanidines; The number average molecular weight of the polyamide is 1981-46130 Da, the caprolactam content is ≤2.99 wt %, and the caprolactam cyclic dimer content is ≤0.18 wt %.

2. A method for the living anionic ring-opening polymerization of lactam with controllable molecular weight according to claim 1, characterized in that: In step (1), the amount of initiator added is 0.01-5 mol% relative to the lactam; and the specified temperature is 80-110°C.

3. A method for the living anionic ring-opening polymerization of lactam with controlled molecular weight according to claim 2, characterized in that: In step (1), the amount of the initiator added is 0.1-2.5 mol% relative to the lactam.

4. A method for the living anionic ring-opening polymerization of lactam with controlled molecular weight according to claim 1, characterized in that: In step (1), the preheating and stirring time is 3-25 min.

5. A method for controlling the molecular weight of lactam living anionic ring-opening polymerization according to claim 1, characterized in that: In step (2), the temperature of the heating jacket of the reactor is 170-250° C., and the pressure inside the reactor is 0-2 MPa.

6. A method for controlling the molecular weight of lactam living anionic ring-opening polymerization according to claim 5, characterized in that: In step (2), the temperature of the heating jacket of the reactor is 180-240° C. and the pressure is 0-0.5 MPa.

7. A method for controlling the molecular weight of lactam living anionic ring-opening polymerization according to claim 1, characterized in that: The method further comprises step (3): devolatilization: the devolatilization temperature is 200-230° C., the devolatilization pressure is 100-600 Pa, and the devolatilization time is 5-10 min.