A method for green enzymatic polycondensation synthesis of polyamide 6,5

Abstract

The application discloses a kind of green enzymatic polycondensation synthesis polyamide 6,5 method, with dimethyl glutarate and 1,6-hexanediamine as raw material, using Novozym435 immobilized lipase as biological catalyst, by direct enzymatic polycondensation reaction preparation biobased polyamide 6,5.The method uses toluene as reaction medium, combined with vacuum by-product, molecular sieve water absorption balance control strategy, realizes the green efficient synthesis of polyamide 6,5, product has excellent thermal stability (melting point 221 DEG C, maximum decomposition temperature 434 DEG C), suitable for melt spinning and other industrial processes, compared with traditional chemical synthesis method, greatly reduce energy consumption, reduce the use of toxic chemicals, provide a new way for the green manufacturing of polyamide.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, specifically a method for green enzymatic condensation polymerization to form polyamide 6,5. Background Technology

[0002] Polyamides, as important engineering polymer materials, are widely used in textiles, engineering plastics, automobile manufacturing, and electronic devices due to their excellent mechanical strength, wear resistance, chemical stability, and processability. However, the synthesis of traditional polyamides (such as PA6 and PA66) relies on fossil-based monomers and requires chemical polycondensation under high temperature and pressure conditions. This process results in high energy consumption, a large environmental footprint, the use of toxic chemicals, and the generation of large amounts of waste, contradicting global carbon neutrality goals and the trend towards green manufacturing.

[0003] Bio-based polymers, using renewable biomass resources as raw materials, represent an important direction for replacing fossil-based polymers. Enzymatic polymerization, with its advantages of high catalytic efficiency, excellent selectivity, mild reaction conditions, and good biocompatibility, has become a preferred method for green polymer synthesis. Lipases, as the most widely used enzymes in organic synthesis, can catalyze the formation of amide bonds in non-aqueous media. Furthermore, Novozym 435 immobilized lipase exhibits good stability in non-aqueous media, making it an ideal catalyst for enzymatic polycondensation reactions. Currently, there are no reports on the use of Novozym 435 to catalyze the synthesis of polyamide 6,5 from dimethyl glutarate and 1,6-hexanediamine. Therefore, developing an efficient and sustainable enzymatic synthesis method for polyamide 6,5 has significant industrial application value. Summary of the Invention

[0004] The purpose of this invention is to overcome the defects of traditional polyamide 6,5 synthesis processes and provide a green enzymatic condensation polymerization method for synthesizing bio-based polyamide 6,5, achieving mild, efficient and sustainable synthesis of polyamide 6,5, reducing production energy consumption and environmental impact, while obtaining polyamide 6,5 products with excellent thermal stability.

[0005] To achieve the above objectives, the technical solution provided by this invention is as follows: a method for green enzymatic condensation polymerization to synthesize bio-based polyamide 6,5, using dimethyl glutarate and 1,6-hexanediamine as monomer raw materials, Novozym 435 immobilized Candida antarcticis lipase B as a biocatalyst, toluene as a reaction medium, adding ZSM-5 molecular sieve, and carrying out enzymatic condensation polymerization under reduced pressure and magnetic stirring conditions, followed by separation, purification, and drying to obtain bio-based polyamide 6,5; the molar ratio of the monomer raw materials dimethyl glutarate to 1,6-hexanediamine to toluene is 1:1:0.05.

[0006] Furthermore, the pressure of the depressurization environment is 20-40 mm Hg, and the magnetic stirring speed is 120 rpm.

[0007] Furthermore, the process parameters for the enzymatic polycondensation reaction are: reaction temperature 90℃, reaction time 72h, and Novozym435 lipase concentration of 20wt% of the total mass of the monomer raw materials.

[0008] Furthermore, the SiO2 / Al2O3 molar ratio of the ZSM-5 molecular sieve is 25-30, which is used to adsorb the water generated in the reaction and regulate the equilibrium of the polycondensation reaction.

[0009] Furthermore, the separation and purification steps are as follows: after the reaction is completed, toluene is removed by rotary evaporation, the crude product is dissolved in formic acid and then filtered to remove lipase and molecular sieve, the filtrate is concentrated and poured into excess tetrahydrofuran, precipitated at -20℃ for 24h, the precipitate is collected by centrifugation and dried under vacuum at 40℃ for 3 days to obtain pure polyamide 6,5.

[0010] The bio-based polyamide 6,5 obtained by the above method has a melting point of 221℃, a crystallization temperature of 170℃, a maximum decomposition temperature of 434℃, and a number-average molecular weight (Mn) ≥ 8600 g·mol⁻¹. -1 Weight-average molecular weight (Mw) ≥ 14100 g·mol -1 The polydispersity index (PDI) is 1.64.

[0011] The present invention also provides applications of the above-mentioned polymer, namely polyamide 6,5, which can be used in melt spinning, textiles, engineering plastics, automotive manufacturing or electronic equipment.

[0012] By adopting the above technical solution, the present invention has achieved significant beneficial effects: 1. Green synthesis and environmentally friendly: Novozym435 lipase is used as a biocatalyst, the reaction conditions are mild (90°C, reduced pressure), and no high temperature and high pressure are required; toluene is used as a non-aqueous medium, and the reaction balance is controlled by reduced pressure and molecular sieve, which reduces the use of toxic chemicals and the generation of waste, reduces the environmental footprint of the production process, and reduces the dependence on fossil resources. 2. High efficiency and controllable parameters: The optimal process parameters were determined through optimization, resulting in a product yield of 72% and a uniform molecular weight distribution (PDI=1.64). The influence of each process parameter is clear, facilitating industrial scale-up and process control. 3. Excellent product performance: The synthesized bio-based polyamide 6,5 has a melting point of 221℃ and a maximum decomposition temperature of 434℃. It has strong stability within the melt spinning temperature range and is suitable for industrial fields such as melt spinning, textiles, and engineering plastics. Moreover, its melting point is lower than that of traditional polyamides, which enhances its spinnability. 4. Low equipment requirements and low energy consumption: The reaction is carried out in conventional round-bottom flasks, rotary evaporators, vacuum drying ovens and other equipment, without the need for special high-pressure reaction equipment, which greatly reduces equipment investment and production energy consumption, and has good prospects for industrial application. Attached Figure Description

[0013] Figure 1 This is a synthetic route diagram for the present invention.

[0014] Figure 2 The image shows the FTIR spectrum of the bio-based polyamide 6,5 synthesized by the enzymatic method of this invention.

[0015] Figure 3 This invention relates to the enzymatic synthesis of bio-based polyamide 6,5. 1 H NMR spectrum.

[0016] Figure 4 The cooling curve is obtained by heating-cooling-heating cycle for the bio-based polyamide synthesized by the enzymatic method of this invention.

[0017] Figure 5 The image shows the secondary heating curves obtained by heating-cooling-heating cycles for the bio-based polyamide synthesized by the enzymatic method of this invention.

[0018] Figure 6 The thermal stability of the synthesized polyamide 6,5 was characterized by TGA. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0020] Example 1: Raw Materials and Reagents All raw materials and reagents used in this invention were provided by Macklin (Shanghai, China), specifically including: • Novozym435 immobilized lipase: Candida antarcticis lipase B (CALB) immobilized on acrylic resin, with an enzyme activity ≥5000 U·g -1 ; • 1,6-Hexanediamine (1,6-HDA): 98% purity; • Dimethyl glutarate (DMG): 98% purity; • Toluene (C7H8): 99.8% purity, used as a reaction medium; Formic acid (C2H2O): Used to dissolve crude products; Tetrahydrofuran (THF): Used for polymer precipitation; • ZSM-5 molecular sieve: SiO2 / Al2O3 molar ratio ≈ 25-30, used to adsorb water generated in the reaction; • Hexafluoroisopropanol (HFIP), trifluoroacetic acid-d (TFA-d), potassium bromide (FTIR grade): used for product characterization.

[0021] The method for synthesizing bio-based polyamide 6,5 includes the following steps, and the synthetic route is as follows: Figure 1 As shown: 1. Raw material weighing: Weigh 0.05 mol dimethyl glutarate, 0.05 mol 1,6-hexanediamine, 20 wt% (based on total monomer mass) of pre-dried Novozym 435 lipase, and an appropriate amount of ZSM-5 molecular sieve (SiO2 / Al2O3≈25-30), add them to a 50 mL round-bottom flask, and then add 5 mL of toluene; 2. Reaction setup: Place the flask in a vacuum device, adjust the pressure to 20-40 mm Hg, turn on the magnetic stirrer at 120 rpm, heat to 90℃, and react for 72 h; 3. Separation and purification: After the reaction is complete, toluene is removed by rotary evaporation, formic acid is added to dissolve the crude product, and lipase and molecular sieve are removed by filtration; the filtrate is concentrated to 3 mL by rotary evaporation, poured into excess THF, precipitated at -20℃ for 24 h, and the precipitate is collected by centrifugation; 4. Drying: The precipitate was placed in a vacuum drying oven at 40°C and dried for 3 days to obtain white solid polyamide 6,5 with a yield of 72%.

[0022] The product obtained in Example 1 was characterized and tested: 1. Fourier Transform Infrared Spectroscopy (FTIR): The dried polyamide 6,5 product was characterized using a Thermo Nicolet iS5 Fourier Transform Infrared Spectrometer. The spectral acquisition was set to 32 scans with a resolution of 4 cm⁻¹. -1 . Figure 2 The image shows the FTIR spectrum of the bio-based polyamide 6,5 synthesized enzymatically in this embodiment. Analysis reveals the characteristic absorption band of the amide group, confirming the successful enzymatic synthesis of polyamide 6,5.

[0023] Among them, 3309.41cm -1 The peak at 1636.61 cm⁻¹ represents the characteristic peak of NH stretching vibration. -1 The peak at 1539.42 cm⁻¹ represents the characteristic peak of the C=O stretching vibration of the amide bond. -1 The peak at 1277 cm⁻¹ is a characteristic peak of NH bond bending vibration. -1 The peak at 2924.28 cm⁻¹ represents the characteristic peak of CN bond stretching vibration, and both are typical characteristic absorptions of amide groups. Furthermore, the spectrum shows a peak at 2924.28 cm⁻¹. -1A CH2 asymmetric stretching vibration peak appears at 2854.32 cm⁻¹. -1 A CH2 symmetric stretching vibration peak appears at this point, corresponding to the stretching vibration of saturated CH bonds.

[0024] The presence of characteristic peaks of amide groups indicates that dimethyl glutarate and 1,6-hexanediamine successfully underwent a condensation reaction to form amide bonds, generating polyamide 6,5, which confirms the success of the lipase-catalyzed polyamide synthesis reaction.

[0025] 2. Nuclear Magnetic Resonance Spectroscopy (NMR): The chemical structure of the enzymatically synthesized polyamide 6,5 was characterized using a Bruker AVANCE III 500MHz NMR spectrometer. The sample was dissolved in deuterated trifluoroacetic acid (TFA-d), and samples were collected at room temperature. 1 ¹H NMR spectra, with resonance frequencies at 500 MHz, and chemical shifts reported in parts per million (ppm). The synthesized polyamide 6,5... 1 HNMR spectrum as follows Figure 3 As shown, the test solvent was deuterated trifluoroacetic acid (TFA-d). The characteristic proton signals are assigned as follows ( 1 H NMR, 500 MHz, TFA-d, δ): 7.98 (s, 1H), 3.26 (s, 4H), 2.53 (t, 4H), 1.92 (m, 2H), 1.47 (m, 4H), 1.22 (m, 4H).

[0026] The signal at 7.98 ppm is attributed to the amide proton (–NH–CO–); the resonance signals at 2.53 ppm (–CH2–CONH–) and 1.92 ppm (–CH2–CH2–CONH–) correspond to the methylene proton in the glutaric acid unit; the signals at 3.26 ppm (–CONH–CH2–CH2–), 1.47 ppm (–CONH–CH2–CH2–), and 1.22 ppm (–CONH–CH2–CH2–CH2–) originate from the methylene proton in the 1,6-hexamethylenediamine unit.

[0027] Based on the FTIR test results, 1 1H NMR data further confirmed the successful synthesis of polyamide 6,5.

[0028] 3. Elemental Analysis (EA): The elemental contents of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) in the polyamide 6,5 samples were determined using an Elementar Vario Micro cube elemental analyzer. The measured values ​​were compared with the theoretical values, and the elemental deviation rate was calculated using the following formula: Elemental Deviation Rate = Theoretical Value - Measured Value - Theoretical Value × 100%. The elemental analysis results of the enzymatically synthesized polyamide 6,5 are shown in Table 1. The polyamide 6,5 macromolecule is composed of four elements: C, H, O, and N. The theoretical mass percentage of each element was calculated based on the molecular formula of the polyamide 6,5 structural unit. The deviation rate was calculated by comparing the measured values ​​with the theoretical values.

[0029] Table 1. Elemental analysis data of synthesized polyamide 6,5

[0030] The results showed that the measured elemental values ​​of the synthesized product deviated little from the theoretical values, with all deviation rates below 2%. The highly consistent results confirmed that the elemental composition of the synthesized product was completely matched with the expected composition of the polyamide 6,5 structural unit.

[0031] 4. Differential Scanning Calorimetry (DSC): A Netzsch 3500 differential scanning calorimeter was used for testing. Approximately 10 mg of sample was weighed and sealed in an aluminum dish, and the sample was analyzed under a nitrogen atmosphere (flow rate 40 mL / min). -1 Under these conditions, a hot-cold-hot cycle test was conducted from 25°C to 300°C, with both heating and cooling rates set at 10°C·min. -1 The cooling curves and secondary heating curves obtained through the heating-cooling-heating cycle are as follows: Figure 4 , Figure 5 As shown. Based on the test curve, the melting point (Tm), crystallization temperature (Tc), and enthalpy of fusion of the polymer were determined.

[0032] The results showed that polyamide 6,5 had a melting point of 221℃ and a crystallization temperature of 170℃. The melting initiation temperature Tm-on was 196℃, the melting peak temperature Tm was 223℃, the melting termination temperature Tm-end was 223℃, and the enthalpy of melting ΔHm = 62.06 J·g. -1 The crystallization initiation temperature Tc-on is 160℃, the crystallization peak temperature Tc is 181℃, the crystallization termination temperature Tc-end is 181℃, and the crystallization enthalpy ΔHc = 61.09 J·g -1 .

[0033] Polyamide 6,5 exhibits only one endothermic peak and one exothermic peak during heating and cooling, indicating its uniform thermal behavior and that the crystallization and melting processes are single-step processes, consistent with the random chain scission degradation thermodynamic mechanism of polycondensation products. Furthermore, its melting point is lower than that of traditional polyamides, giving it superior processability and spinnability.

[0034] 5. Thermogravimetric Analysis (TGA): The thermal stability of the synthesized polyamide 6,5 was tested using a Hitachi STA200 analyzer under a nitrogen atmosphere. The heating rate was 10℃ / min, and the test temperature range was 30℃ to 600℃. The thermal stability of the synthesized polyamide 6,5 was characterized by TGA, and the test curves are shown below. Figure 6 As shown in the figure, the TGA curves show that the product exhibits a single, smooth mass loss step in the range of 30-600℃, corresponding to a single-stage thermal decomposition process. The maximum decomposition temperature (Tmax) was measured to be 434℃, indicating that the enzymatically synthesized polyamide 6,5 has excellent heat resistance.

[0035] In current industrial production, the typical temperature range for polyamide melt spinning is approximately 270 to 290°C. Within this temperature range, polyamide 6,5 maintains extremely high stability, proving that it is fully suitable for industrial processing such as melt spinning.

[0036] 6. Gel permeation chromatography (GPC): The number-average molecular weight (Mn), weight-average molecular weight (Mw), and polydispersity index (PDI) of the synthesized polyamide 6,5 were determined using an Agilent PL-GPC50 system. Distilled and purified hexafluoroisopropanol (HFIP) was used as the mobile phase, with a flow rate of 1 mL / min and a column temperature of 40 °C. The product's number-average molecular weight (Mn) reached 8600 g·mol⁻¹. -1 Weight-average molecular weight (Mw) ≥ 14100 g·mol -1 The polydispersity index (PDI) is 1.64.

[0037] The following is a partial list of the research and development process of this invention, used to illustrate the creative effort put into this invention.

[0038] Influence of process parameters on polymerization: Lipase-catalyzed polyamide synthesis is a reversible condensation equilibrium process, and hydrolysis side reactions directly determine the molecular weight and yield of the product. To improve the polymerization efficiency of polyamide 6,5, this study continuously removed the byproduct methanol under vacuum conditions and added water generated by molecular sieve adsorption, shifting the reaction equilibrium towards condensation polymerization. Simultaneously, toluene was chosen as the reaction medium to limit the system's moisture concentration, inhibit hydrolysis, and provide a suitable microenvironment for enzyme catalysis.

[0039] Based on this, this study systematically investigated the effects of reaction temperature, reaction time, and enzyme concentration on the molecular weight and yield of the polymer products. The GPC data of polyamide 6,5 prepared under different conditions are shown in Table 2.

[0040] Table 2. GPC data for the synthesis of polyamide 6,5 under different process conditions.

[0041] 1. Effect of reaction temperature Within the studied temperature range of 80-110℃, the lipase maintained relatively high catalytic activity during heating. Increasing the temperature effectively accelerated the catalytic reaction, improved substrate conversion, and significantly promoted the molecular chain growth of polyamide 6,5, thereby obtaining a higher molecular weight.

[0042] Under the conditions of 72 h reaction time and 20 wt% enzyme concentration, the product Mn at 80 °C was 6900 g·mol⁻¹. -1 Yield 63%; Mn increases to 8600 g·mol⁻¹ at 90℃. -1 The yield increased to 72%. When the reaction temperature reached 100℃ and above, the polyamide chain growth approached the critical level, and further increases in temperature only caused slight changes in Mn and yield; at the same time, lipase activity decreased above 100℃, and the PDI of the product increased. Considering both catalytic efficiency and product performance, 90℃ was determined to be the optimal reaction temperature.

[0043] 2 Effect of reaction time Under reaction conditions of 90℃ and 20wt% enzyme concentration, the Mn and yield of polyamide 6,5 both increased with increasing reaction time. After 24 h of reaction, the polymer Mn was only 4300 g·mol⁻¹. -1 The corresponding yield was 39%; the product performance showed a significant improvement between 24h and 72h, with Mn increasing from 4300 g·mol⁻¹. -1 Rise to 8600 g·mol -1 The productivity increased by 33 percentage points.

[0044] When the reaction time was extended to 96 hours, neither Mn nor yield improved significantly, and the reaction entered a plateau phase. Simultaneously, due to increased system viscosity and a higher proportion of reverse reaction, the PDI of the product increased. Considering both reaction efficiency and production cycle, 72 hours (3 days) was determined to be the optimal reaction time.

[0045] 3. Effect of enzyme concentration Under the conditions of reaction temperature of 90℃ and reaction time of 72h, the Mn and yield of polyamide 6,5 were relatively low at low lipase concentrations, and the overall Mn and yield of the product increased with increasing enzyme concentration.

[0046] When the enzyme concentration reached 20 wt%, the reaction activity was significantly enhanced, and the product Mn reached 8600 g·mol⁻¹. -1 The yield was 72%; when the concentration was further increased to 25 wt%, the enzymatic synthesis efficiency approached the peak value, with Mn reaching 8900 g·mol⁻¹. -1 The yield was 75%, but the improvement from 20wt% to 25wt% was limited, indicating that the product synthesis was already at a high efficiency level. However, excessively high enzyme concentrations led to increased system viscosity and PDI. Considering both catalytic efficiency and economic cost, 20wt% was determined to be the optimal enzyme concentration.

[0047] In summary, in the polycondensation reaction of dimethyl glutarate and 1,6-hexanediamine catalyzed by Novozym 435, temperature, reaction time and enzyme concentration all have a significant impact on the Mn and yield of polyamide 6,5. The optimal synthesis conditions determined by optimization are: reaction time 72 h, reaction temperature 90 °C and enzyme concentration 20 wt%.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for green enzymatic condensation polymerization to synthesize bio-based polyamide 6,5, characterized in that, Using dimethyl glutarate and 1,6-hexanediamine as monomer raw materials, Novozym 435 as a biocatalyst, and toluene as the reaction medium, ZSM-5 molecular sieve was added, and an enzymatic condensation reaction was carried out under reduced pressure and magnetic stirring conditions. After separation, purification, and drying, bio-based polyamide 6,5 was obtained. The molar ratio of the monomer raw materials dimethyl glutarate to 1,6-hexanediamine to toluene was 1:1:0.

05.

2. The method according to claim 1, characterized in that, The pressure of the depressurization environment is 20-40 mm Hg, and the magnetic stirring speed is 120 rpm.

3. The method according to claim 1, characterized in that, The process parameters for the enzymatic polycondensation reaction are: reaction temperature 90℃, reaction time 72h, and Novozym 435 lipase concentration of 20wt% of the total mass of the monomer raw materials.

4. The method according to claim 1, characterized in that, The SiO2 / Al2O3 molar ratio of the ZSM-5 molecular sieve is 25-30, which is used to adsorb water generated in the reaction and regulate the equilibrium of the polycondensation reaction.

5. The method according to claim 1, characterized in that, The separation and purification steps are as follows: after the reaction is completed, toluene is removed by rotary evaporation, the crude product is dissolved in formic acid and then filtered to remove lipase and molecular sieve, the filtrate is concentrated and poured into excess tetrahydrofuran, precipitated at -20℃ for 24h, the precipitate is collected by centrifugation and dried under vacuum at 40℃ for 3 days to obtain pure polyamide 6,5.

6. The bio-based polyamide 6,5 prepared by any one of the methods described in claims 1-5, characterized in that, The polyamide 6,5 has a melting point of 221℃, a crystallization temperature of 170℃, a maximum decomposition temperature of 434℃, and a number-average molecular weight (Mn) ≥ 8600 g·mol⁻¹. -1 Weight-average molecular weight (Mw) ≥ 14100 g·mol -1 The polydispersity index (PDI) is 1.

64.

7. The bio-based polyamide 6,5 according to claim 6, characterized in that, This polyamide 6,5 can be used in melt spinning, textiles, engineering plastics, automotive manufacturing, or electronic equipment.

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