A method for preparing covalently cross-linked fibers from a covalently adaptable network

Abstract

The present invention relates to a method for preparing covalently crosslinked fibers from a covalently adaptable network. The method comprises: dissolving a polyether polyol or polyester polyol, a multifunctional isocyanate end-capping agent, a polyisocyanate, and a crosslinking agent in a solvent; adding a catalyst for reaction; and vacuum treating the solvent to obtain a covalently crosslinked polymer network based on dynamic covalent bonds; and then extruding the resulting covalently crosslinked polymer network using a melt extrusion device. This method produces covalently crosslinked fibers with excellent mechanical properties and solvent resistance using the covalently crosslinked polymer network based on dynamic covalent bonds.

Description

Technical Field

[0001] The present invention belongs to the field of covalent cross-linked fibers, and in particular relates to a method for preparing covalent cross-linked fibers from a covalent adaptive network. Background Art

[0002] Fibers are ubiquitous and play a vital role in various fields such as daily life (e.g., clothing, construction industry, automobiles) and emerging applications (e.g., medical devices, energy storage, wearable electronics, space exploration). Existing fibers are mainly made of thermoplastics such as polyolefins, polyesters and polyamides. Thermoset fibers are extremely attractive due to their excellent mechanical properties (e.g., tensile strength, elastic recovery) and chemical / heat resistance resulting from their covalently cross-linked structure. However, traditional covalently cross-linked polymers such as epoxy resins and vulcanized rubber are insoluble and infusible due to their permanent three-dimensional covalent networks and therefore cannot be processed in the same way as thermoplastic polymers. The preparation of covalently cross-linked fibers remains a major challenge.

[0003] There are few reports on covalently cross-linked fibers. Some researchers have reported the preparation of covalently cross-linked liquid crystal elastomer fibers by a two-step process involving mold processing and UV post-curing. Other researchers have reported covalently cross-linked azophenyl polymer fibers, which were prepared by immersing melt-spun fibers in a solution containing a cross-linking agent, followed by washing and drying. These methods are complex and cannot achieve the continuous preparation of covalently cross-linked fibers. Recently, covalently cross-linked nonwovens have been reported, but their applications are limited compared to traditional fibers. Recently, the continuous preparation of covalently cross-linked gel fibers has been achieved by combining wet spinning technology with in situ UV curing. However, gel fibers have not yet been widely used in practical applications. Therefore, there is an urgent need to develop a convenient and efficient strategy for the preparation of covalently cross-linked fibers.

[0004] Covalently adaptable networks (CANs) are a class of polymers cross-linked by reversible covalent bonds, such as disulfide bonds, carbamate bonds, and Diels-Alder adducts. CANs can change the network's topology through the reversible exchange of dynamic covalent bonds under external stimuli (e.g., heat, light). Consequently, CANs possess plasticity and reprocessability similar to those of traditional thermoplastics. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing covalently cross-linked fibers from a covalently adaptive network, so as to overcome the defects of the prior art in that the preparation of covalently cross-linked fibers is complex and continuous preparation cannot be achieved.

[0006] The present invention provides a method for preparing covalently cross-linked fibers from a covalently adaptable network, comprising:

[0007] (1) dissolving polyether polyol or polyester polyol, multifunctional isocyanate blocking agent, polyisocyanate and crosslinking agent in a solvent, adding a catalyst for addition polymerization reaction, and vacuum treating to obtain a covalently crosslinked polymer network based on dynamic covalent bonds; (2) adding the covalently crosslinked polymer network based on dynamic covalent bonds in step (1) into a melt extrusion device for extrusion to obtain a covalently crosslinked fiber.

[0008] Preferably, the polyether polyol in step (1) comprises one or more of polytetramethylene ether glycol, polypropylene glycol, polyethylene glycol, and polyglycerol; and the weight average molecular weight of the polyether polyol is 500-10000.

[0009] Preferably, the polyester polyol in step (1) includes one or more of polyhexamethylene adipate diol, polybutylene adipate diol, polypropylene adipate diol, polyethylene adipate diol, polybutylene phthalate diol, polycaprolactone diol, and polycaprolactone triol; and the weight average molecular weight of the polyester polyol is 500-10000.

[0010] Preferably, the multifunctional isocyanate blocking agent in step (1) includes one or more of oximes, phenols, imidazoles, and amides.

[0011] Preferably, the oximes include one or more of dimethylglyoxime, furildioxime, acetonealdehydedioxime, 2,4-pentanedionedioxime, furildioxime, 1,4-benzoquinonedioxime, diphenylglyoxaldoxime, 1,2-cyclohexanedionedioxime, dihydroacenaphthenedioxime, and dichloroglyoxime.

[0012] Preferably, the phenols include one or more of 1,3-catechol, naphthalene diol, 2-methylresorcinol, hydroquinone, catechol, quinizarin, anthracenol, bisphenol A, magnolol, spirodiol, methylhydroquinone, tetrabromocatechol, 4-chlororesorcinol, and 4-chlororesorcinol.

[0013] Preferably, the imidazoles include one or more of hydantoin, bis-(imidazol-2-yl)-methane, o-chlorohexaarylbisimidazole, 2,6-bis(2-benzimidazole-1-yl)pyridine, 2,2'-bis(4,5-dimethylimidazole), and 1,4-bis(2-methyl-1H-imidazol-1-yl)benzene.

[0014] Preferably, the amides include one or more of sulfonamide, malonamide, succinamide, glutaramide, phthalamide, terephthalamide, dithiooxamide, and 2-aminomalonamide.

[0015] Preferably, the polyisocyanate in step (1) includes one or more of toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, hexamethylene diisocyanate trimer, dicyclohexylmethane diisocyanate, xylylene diisocyanate, triphenylmethane triisocyanate, L-lysine triisocyanate, and polymethylene polyphenyl polyisocyanate.

[0016] Preferably, the solvent in step (1) comprises one or more of benzene, toluene, xylene, pentane, hexane, octane, cyclohexane, cyclohexanone, toluene-cyclohexanone, chlorobenzene, dichlorobenzene, dichloromethane, methanol, ethanol, isopropanol, ether, propylene oxide, methyl acetate, ethyl acetate, propyl acetate, acetone, methyl butyl ketone, methyl isobutyl ketone, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, acetonitrile, pyridine, phenol, tetrahydrofuran, N,N-dimethylformamide, dimethylacetamide, and dimethyl sulfoxide.

[0017] Preferably, the cross-linking agent in step (1) includes one or more of glycerol, water, 1,2,3-butanetriol, 1,2,4-butanetriol, pentaerythritol, diethanolamine, trimethylolpropane, sorbitol, melamine, diethylenetriamine, and castor oil.

[0018] Preferably, the catalyst in step (1) comprises one or more of dibutyltin dilaurate, stannous octoate, triethylamine, bis(dimethylamino)ethyl ether, N-ethylmorpholine, and triethylenediamine.

[0019] Preferably, in step (1), the molar ratio of the polyether polyol or polyester polyol, the multifunctional isocyanate blocking agent, the polyisocyanate and the cross-linking agent is (1-10):(1-10):(1-22):(0.01-1).

[0020] Preferably, the molar ratio of polyisocyanate to catalyst in step (1) is (10-15):(0.001-0.5).

[0021] Preferably, the ratio of polyisocyanate to solvent in step (1) is (1-2) mmol: (1-100) mL.

[0022] Preferably, the reaction in step (1) is as follows: reacting at 50-120° C. in a nitrogen atmosphere for 0.1-50 h, then pouring into a mold (such as a polytetrafluoroethylene mold), and heating to 60-130° C. within 1-30 h.

[0023] Preferably, the vacuum treatment temperature in step (1) is room temperature, and the vacuum treatment time is 10-60 hours.

[0024] Preferably, the melt extrusion equipment in step (2) includes a single-screw extruder, a twin-screw extruder or a melt extruder.

[0025] Preferably, the extrusion temperature of the melt extrusion equipment in step (2) is 100-200°C, and the extrusion speed is 1-100 m·min -1 , stretching ratio is 1-20, and screw speed is 5-100rpm.

[0026] The present invention also provides a covalently cross-linked fiber prepared by the above method.

[0027] The present invention also provides an application of the covalently cross-linked fiber prepared by the above method in stretchable electronic devices, textiles and clothing, household items or medical equipment.

[0028] The dynamic oxime-carbamate linkages in this invention can also be replaced with other widely available dynamic covalent systems (e.g., phenol-carbamate linkages, imidazole-carbamate linkages, amide-carbamate linkages, disulfide linkages, imine linkages, and Diels-Alder adducts) to develop a variety of covalently cross-linked fibers with unique properties. This invention will not only promote the development of covalently cross-linked fibers but also provide new ideas for the efficient melt spinning of high-performance polymers with melting temperatures above their decomposition temperatures, enabling a range of novel applications.

[0029] The present invention prepares covalently crosslinked fibers through direct melt spinning of a covalently adaptable network (CAN). At processing temperature, dynamic covalent bonds reversibly dissociate and combine, temporarily disconnecting the CAN to enable melt spinning; at operating temperature, the dynamic covalent bonds are frozen, and the CAN exhibits excellent structural stability.

[0030] Beneficial effects

[0031] The present invention prepares covalently cross-linked fibers with excellent mechanical properties and solvent resistance through CAN based on dynamic covalent bonds. The fiber has a maximum elongation of 2639%, a tensile strength of 87.68 MPa, and is almost fully recovered from an elongation of 800%. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The design and manufacture of the CPOU fiber of the present invention, including (a) the reaction equation for covalently cross-linking CPOU, and (b) the melt-spinning process of CPOU and the corresponding schematic diagram of molecular evolution.

[0033] Figure 2The spinnability of CPOU of the present invention, including (a) FTIR spectra of synthesized CPOU and CPOU fiber, (b) temperature-dependent curves of storage modulus and loss modulus of CPOU, (c) curve of complex viscosity of CPOU as a function of temperature, and (d) photograph of CPOU fiber.

[0034] Figure 3 Figure 2 shows the mechanical properties of the TPOU and CPOU fibers of the present invention, including (a) a typical tensile stress-strain curve and (b) a comparison of their tensile strength and maximum elongation.

[0035] Figure 4 Figure 2 shows the solvent resistance of the TPOU and CPOU fibers of the present invention, including (a) photos (i-ii) of the dissolution test of TPOU and CPOU fibers, and (b) photos of the dried CPOU fibers after swelling with THF: (i) pulling up the object, (ii) stretching 4.5 times, and (iii) immediate recovery. DETAILED DESCRIPTION

[0036] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, 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 equally within the scope limited by the appended claims of the application.

[0037] Experimental reagents: polytetramethylene ether glycol (Mn~1000g mol -1 ) and dibutyltin dilaurate (95%) were purchased from Aladdin Chemical Co., Ltd. (Shanghai, China). Diphenylmethane diisocyanate (a 50:50 mixture of 2,4′- and 4,4′-diphenylmethane diisocyanate) was purchased from Wanhua Chemical (Yantai, China). Dimethylglyoxime (98%) was purchased from Sinopharm Chemical Reagent (Shanghai, China). Trimethylolpropane (98%) and anhydrous tetrahydrofuran were purchased from J&K Chemical Technology (Beijing, China).

[0038] Example 1

[0039] Synthesis of CPOU: Polytetramethylene ether glycol (8.000 g, 8.00 mmol), dimethylglyoxime (0.348 g, 3.00 mmol), diphenylmethane diisocyanate (3.066 g, 12.25 mmol), and trimethylolpropane (0.107 g, 0.8 mmol) were dissolved in 15 mL of tetrahydrofuran in a round-bottom flask. Dibutyltin dilaurate (0.050 g) was added to the mixture and reacted at 60°C under a nitrogen atmosphere with magnetic stirring for 20 minutes. The reaction mixture was then poured into a polytetrafluoroethylene mold at 60°C and gradually heated to 85°C over 12 hours. Finally, CPOU was obtained by vacuum treatment at room temperature for 48 hours.

[0040] Fiber preparation: CPOU fibers were prepared by a single screw extruder (Wellzoom E) at 155 °C with a screw speed of 50 rpm and an extrusion speed of 3 m / min. -1 , the stretching ratio is 2.

[0041] Comparative Example 1

[0042] Synthesis of TPOU: Polytetramethylene ether glycol (8.000 g, 8.00 mmol), dimethylglyoxime (0.348 g, 3.00 mmol) and diphenylmethane diisocyanate (2.766 g, 11.05 mmol) were dissolved in 15 mL of tetrahydrofuran in a round-bottom flask. Dibutyltin dilaurate (0.050 g) was added to the mixture and reacted at 60 ° C under N2 atmosphere with magnetic stirring for 20 minutes. Then, the reaction mixture was poured into a polytetrafluoroethylene mold at 60 ° C and gradually heated to 85 ° C within 12 hours. Finally, TPOU was obtained by vacuum treatment at room temperature for 48 hours.

[0043] Preparation of fibers: The extrusion temperature of TPOU was 150°C, and other parameters were the same as those of the CPOU fibers in Example 1.

[0044] Testing: All tests were performed at room temperature (25°C) unless otherwise stated. Fourier transform infrared (FTIR) spectra were recorded using a Nicolet 8700 spectrometer equipped with an attenuated total reflectance accessory from Thermo Fisher Scientific. Rheological experiments were performed using an ARES-G2 rotational rheometer with 8 mm diameter parallel plates from TA Instruments. Temperature sweeps were performed in the range of 25 to 160°C at 0.5% staining and 1 Hz. Mechanical testing was performed using an Exceed E42 electronic universal testing machine from MTS Systems Corporation. The strain rate was 50 mm min -1Engineering stress (σE) is the load applied to the sample divided by the initial cross-sectional area. Assuming constant volume, stress (σ) is calculated by multiplying σE by a factor (1 + λ), where λ is the strain. Toughness is defined as the integrated area under the stress-strain curve.

[0045] Results and Discussion

[0046] Oxime-carbamate-based covalently cross-linked CPOUs ( ) were readily synthesized via a one-pot polyaddition reaction of commercially available polytetramethylene ether glycol, diphenylmethane diisocyanate, dimethylglyoxime, and trimethylolpropane in the presence of the catalyst dibutyltin dilaurate. Figure 1 a) Polytetramethylene ether glycol was chosen as the soft segment due to its flexible polymer chain. The reaction of diphenylmethane diisocyanate with the chain extender dimethylglyoxime produces reversible oxime-urethane bonds. The introduction of trifunctional trimethylolpropane creates a covalently crosslinked network.

[0047] The structure of CPOU was characterized by Fourier transform infrared (FTIR) spectroscopy in attenuated total reflectance mode. Figure 2 a) at 3297 and 1728 cm -1 The peaks corresponding to NH and C=O bonds appeared at 984 cm-1, indicating the successful formation of carbamate groups. -1 A peak appears at approximately 2270 cm -1 The fuzzy peak of the isocyanate group at indicates that the diphenylmethane diisocyanate monomer has been completely converted. These results confirm the successful synthesis of CPOU.

[0048] The applicability of CPOU for melt spinning was studied in detail by rheological analysis. The storage modulus (G'), loss modulus (G") and complex viscosity of CPOU decreased with increasing temperature ( Figure 2 b). The intersection temperature of G' and G" of CPOU is 153℃, indicating that the network transitions from solid to liquid, implying the feasibility of stable melt spinning at moderate temperatures. At 153℃, the complex viscosity of CPOU drops to 1000 Pa·s, which is suitable for melt spinning ( Figure 2 c). TPOU, which has the same main chain structure as CPOU but without covalent crosslinking, was synthesized as a control sample. The main reason for these results is the rapid reversible dissociation / association of a large number of oxime-urethane bonds, which leads to temporary disconnection of the network. In view of the above factors, CPOU fibers were melt-spun at 155°C ( Figure 2 d). FITR spectrum of CPOU fiber ( Figure 2 a) is basically the same as CPOU, indicating that the structure of CPOU remains unchanged after melt spinning.

[0049] Depend on Figure 3As can be seen from ab, the tensile strength of CPOU fiber (87.68±11.34MPa) is more than 28 times that of TPOU fiber (3.13±0.05MPa), while the maximum elongation of CPOU fiber (2639%±178%) is 3.3 times that of TPOU fiber (795%±40%). -3 ) is TPOU fiber (16±1MJ m -3 These results indicate that the covalent cross-linking structure can significantly improve the mechanical properties of the fiber.

[0050] Depend on Figure 4 It can be seen that CPOU fibers have excellent resistance to organic solvents. (i) CPOU and TPOU fibers were immersed in tetrahydrofuran (THF) at room temperature. (ii) After 5 minutes, CPOU fibers only swelled and maintained their original fiber shape, while TPOU fibers completely dissolved ( Figure 4 a). CPOU fibers dried after swelling with THF are highly stretchable and can recover immediately after being stretched to approximately 4.5 times their original length ( Figure 4 b). These results indicate that CPOU fibers have excellent resistance to organic solvents.

[0051] In summary, the key to the present invention is that the reversible dissociation / association of dynamic covalent bonds is accelerated at the processing temperature, resulting in a rapid decrease in polymer viscosity, thereby achieving melt spinning; the dynamic covalent bonds freeze at the use temperature to form a stable network, which contributes to structural stability and high performance. More importantly, the large number of dynamic oxime-urethane bonds give CPOU a melt spinning viscosity suitable for below the degradation temperature, which is difficult to achieve even for traditional thermoplastic polyurethanes. CPOU fibers exhibit excellent mechanical properties and resistance to organic solvents. The potential application of CPOU fibers as stretchable conductive fibers resistant to organic solvents has been confirmed, which will broaden the application scenarios of the booming stretchable electronic devices.

Claims

1. A method for preparing covalently crosslinked fibers from a covalently adaptable network, comprising: (1) dissolving polyether polyol, dimethylglyoxime, diphenylmethane diisocyanate and trimethylolpropane in a solvent, adding a catalyst for addition polymerization, and vacuum treating to obtain a covalently cross-linked polymer network based on dynamic covalent bonds; wherein the polyether polyol is polytetramethylene ether glycol; The molar ratio of polyether polyol, dimethylglyoxime, diphenylmethane diisocyanate and trimethylolpropane is 8:3:12.25:0.8; the addition polymerization reaction is: reacting at 60-120°C in a nitrogen atmosphere for 0.1-50 hours, then pouring into a mold and heating to 85-130°C within 12-30 hours; (2) adding the covalent cross-linked polymer network based on dynamic covalent bonds in step (1) into a melt extrusion device for extrusion to obtain Covalently cross-linked fibers; wherein the extrusion temperature of the melt extrusion equipment is 100-200°C, the extrusion speed is 1-100 m·min-1, the stretch ratio is 1-20, and the screw speed is 5-100 rpm.

2. The method according to claim 1, characterized in that The weight average molecular weight of the polyether polyol in step (1) is 500-10000.

3. The method according to claim 1, characterized in that In the step (1), the solvent comprises one or more of benzene, toluene, xylene, pentane, hexane, octane, cyclohexane, cyclohexanone, toluene-cyclohexanone, chlorobenzene, dichlorobenzene, dichloromethane, methanol, ethanol, isopropanol, ether, propylene oxide, methyl acetate, ethyl acetate, propyl acetate, acetone, methyl butyl ketone, methyl isobutyl ketone, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, acetonitrile, pyridine, phenol, tetrahydrofuran, N,N-dimethylformamide, dimethylacetamide, and dimethyl sulfoxide; and the catalyst comprises one or more of dibutyltin dilaurate, stannous octoate, triethylamine, bisdimethylaminoethyl ether, N-ethylmorpholine, and triethylenediamine.

4. The method according to claim 1, wherein The molar ratio of diphenylmethane diisocyanate to the catalyst in step (1) is (10-15):(0.001-0.5).

5. The method according to claim 1, wherein The melt extrusion equipment in step (2) includes a single-screw extruder, a twin-screw extruder or a melt extruder.

6. A covalently cross-linked fiber prepared by the method of claim 1.

7. Use of the covalently cross-linked fiber prepared by the method of claim 1 in stretchable electronic devices, textiles and clothing, household items or medical devices.

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