CN108976387B - Azo side chain liquid crystal polyurethane urea material and preparation method thereof - Google Patents
Azo side chain liquid crystal polyurethane urea material and preparation method thereof Download PDFInfo
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Abstract
The invention provides an azo side chain liquid crystal polyurethane urea material and a preparation method thereof, wherein a single-ended dihydroxy azo compound (DEH) and double-ended hydroxy polyethylene glycol (PEG) are mixed, and after N, N-Dimethylformamide (DMF) is dissolved, diisocyanate (HBH) containing carbamido is used for chain extension to obtain the azo side chain liquid crystal polyurethane urea. The azo liquid crystal group is positioned on the branched chain, the utilization rate is high, the liquid crystal phase is easier to form, and the azo liquid crystal material has the dual excellent characteristics of polyurethane microphase separation and liquid crystal polymer molecule ordered arrangement, and has the liquid crystal property and photochromic property on the basis of having the polyurethane performance. Meanwhile, the main chain of the polyurethane is a hard segment with an ordered structure, so that the mechanical property of the polyurethane is ensured, and the polyurethane urea has the thermoreversible and photoinduced reversible properties of azo liquid crystal and the properties of polyurethane materials.
Description
Technical Field
The invention belongs to the technical field of high polymer materials, and particularly relates to a cholesterol side chain liquid crystal polyurethane urea material and a preparation method thereof.
Background
The liquid-crystalline polyurethane exhibits an aggregation state in which crystalline and amorphous states coexist at room temperature. In a molten state, the liquid has liquid fluidity and physical property anisotropy of crystals, the molecular arrangement of the liquid is between that of ideal liquid and crystals, and one-dimensional or two-dimensional remote order is presented. The novel liquid crystal polyurethane material is not only developed in the fields of spinning, self-reinforced composite materials, reaction injection molding, elastomers, coatings and the like, but also increasingly widely applied in the fields of shape memory, photoelectric display materials, data storage materials and the like due to the liquid crystal property of the novel liquid crystal polyurethane material. The liquid crystal polyurethane product has excellent performances of high strength, high modulus, dimensional stability, flame retardance, good insulativity, high temperature resistance, radiation resistance, chemical corrosion resistance, low linear expansion coefficient and the like, and has wide application prospect in the fields of electronic and electric appliances, aerospace, optical fiber communication, mechanical manufacturing, chemical industry and the like.
Liquid-crystalline polyurethanes are classified into main chain type, side chain type and liquid-crystalline polyurethane elastomers. Mesogens of the side chain liquid crystal macromolecules are connected to a macromolecular main chain as side chains, the liquid crystallinity of the side chain liquid crystal macromolecules depends on the mesogens to a great extent, the main chain has small influence on the liquid crystallinity of the polyurethane, and the macromolecular main chain and the side chains of the mesogens are independent. Because the mesogens of the side chain type liquid crystal polyurethane are mostly connected with the main polymer chain through flexible chains, the limitation of the side chain type liquid crystal polyurethane on translation and rotation is controllable, and the movement is relatively free, so that the same liquid crystal level as that of corresponding micromolecular liquid crystal can be achieved. The side chain type liquid crystal polyurethane can well integrate the property of small molecular liquid crystal and the property of a polyurethane material, has good nonlinear optics, and is a novel material with great development potential.
Azo groups are a type of functional groups having optical activity, and the N ═ N double bond in the molecule can undergo the isomerization transformation of Trans → cis and cis → Trans under the action of light and heat (see the reaction formula in fig. 1). Therefore, the azo compound has cis and trans isomers, and trans is more stable than cis. The unique property of the azo compound enables the azo compound to have wide application in the fields of liquid crystal materials, optical information storage materials, photochromic materials, biological materials, nonlinear optical materials, nano materials and the like.
The liquid crystal azo compound and the polyurethane are combined into the same molecular system to form the liquid crystal polyurethane with azo groups, and the liquid crystal polyurethane has the double excellent characteristics of the polyurethane and the liquid crystal azo compound. According to the characteristics of azo liquid crystal polyurethane, it has the photoelectric sensitivity of small molecular liquid crystal, and at the same time, it is used as a polymer and has the characteristics of high molecular substance. The azo liquid crystal polyurethane has great potential application value in the fields of optical switches, laser writing, photosensitive functional materials, nonlinear optical equipment and the like, and particularly has important research significance in the direction of high-efficiency storage. The side chain type azo polyurethane urea synthesized by MDI by Occidenta et al cannot form a liquid crystal phase, while the side chain type azo polyurethane urea synthesized by HDI can form a liquid crystal phase, but the synthesis is synthesized by a two-step method, namely, a prepolymerization reaction and a chain extension reaction; the Cao Shi Juan is also a side chain type azobenzene polyurethane urea synthesized by a two-step method, namely NDPD is synthesized firstly by coupling reaction and then the side chain type azobenzene polyurethane urea is synthesized, the preparation condition method is complicated, the side chain in the synthesized side chain type azobenzene polyurethane is directly connected with the main chain, the main chain is easy to generate coupling effect with the side chain, the movement of the side chain is blocked, and the utilization rate of the liquid crystal phase is low.
Patent CN105829380A discloses a liquid crystal polyurethane elastomer which has low temperature for liquid crystal to appear and has rubber elasticity when liquid crystal appears, and a manufacturing method thereof. The isocyanate-terminated prepolymer is synthesized by the reaction of polypropylene glycol and 2, 4-toluene diisocyanate, and mesogenic diol containing azo groups is introduced at two ends of the prepolymer molecule to synthesize the liquid crystal polyurethane. The liquid crystal polyurethane elastomer synthesized by the synthesis method has low liquid crystal appearing temperature, and has rubber elasticity when liquid crystal appears because the high molecular mesh structure endows flexibility. However, it is extremely required to have a crosslinked molecular weight, and when the molecular weight is too small, the intramolecular crosslinking points are too large, and the liquid crystal is difficult to appear or the rubber elasticity is difficult to be exhibited when the liquid crystal appears, and when the molecular weight is too large, it is difficult to obtain a liquid crystal polyurethane elastomer by curing. The preparation condition and the method are complex, and the requirement on the molecular weight of the raw material is high.
Patent CN103408713A discloses a preparation method and application of supramolecular liquid crystal shape memory polyurethane. The pyridine-containing polyurethane is obtained by adding short-chain dihydric alcohol into dihydric alcohol containing pyridine groups and diisocyanate for chain extension, and then the pyridine-containing polyurethane is mixed with alkoxy benzoic acid or alkoxy phenol to obtain the supermolecule liquid crystal polyurethane. Although the production cost of the supramolecular liquid crystal polymer is reduced, the supramolecular liquid crystal polymer is still deficient in the aspect of simultaneously obtaining the comprehensive balance of heat resistance and mechanical property while improving the processability, and has a plurality of problems in the aspect of practical application.
Therefore, a photochromic liquid crystal polyurethane material with simple preparation process, good reproducibility, capability of reducing the anisotropy of a product, good thermotropic property and high mechanical property is needed at present.
Disclosure of Invention
Aiming at the problems in the prior art, the azo side chain liquid crystal polyurethane urea material is prepared in one step by adjusting the technical scheme and adopting a simple process. The liquid crystal elements are positioned on the side chains and are linked with the main chain through the flexible chain segments with certain lengths, thus being more beneficial to the polyurethane to show the smectic liquid crystal phase which is the same as that of the azo monomers on the basis of not influencing the mechanical property of the main chain, meanwhile, the main chain of the polyurethane is uniformly distributed by the hard segments and the soft segments with ordered structures, and more carbamate groups and carbamido groups in the hard segments can form compact hydrogen bonds, thereby ensuring the mechanical property of the polyurethane. The existence of the flexible chain segment of the side chain reduces the coupling effect between the main chain and the side chain, so that the side chain keeps the ordered structure of liquid crystal to move independently, the formation of a liquid crystal phase is facilitated, and the utilization rate of a liquid crystal group is high. The polyurethane urea has the thermoreversible and photoreversible performances of azo liquid crystal and the performance of polyurethane materials.
In order to achieve the purpose, the technical scheme of the invention is as follows:
the invention provides azo side chain liquid crystal polyurethane urea, which is prepared by mixing a single-ended dihydroxy azo compound (DEH) with double-ended hydroxy polyethylene glycol (PEG), using diisocyanate with a carbamido structure as a chain extender to carry out chain extension, and purifying;
the formula is shown as formula 1:
wherein:
m＝15～90，n＝15～50。
preferably, the azo side chain liquid crystalline polyurethane urea has a number average molecular weight of 1.0 × 105～6.0×105The dispersion coefficient is 1.20-1.31, the mass content of DEH in the polyurethane urea is 30-46%, and the mass content of PEG in the polyurethane urea is 10-37%.
The invention provides a preparation method of azo side chain liquid crystal polyurethane urea, which comprises the steps of mixing a single-end dihydroxy azo compound (DEH) and double-end hydroxy polyethylene glycol (PEG), adding N, N-Dimethylformamide (DMF) for dissolving, adding a DMF solution containing diisocyanate (HBH) with a carbamido structure for chain extension reaction, cooling to normal temperature after reaction, diluting DMF to 4-7% (g/mL), and preparing a polyurethane urea film material by a solvent volatilization film-forming method.
Further, the feeding molar ratio of DEH to PEG is preferably 3: 1-5: 1.
Further, it is preferable that the PEG has a number average molecular weight of 600-2000 and a dispersion coefficient of 1.15-1.30.
Further, the chain extender HBH is preferably added dropwise in a DMF solution of HBH with the concentration of 0.5-1.0g/mL and the dropwise adding speed of 5-10 mL/min.
Further, it is preferable that the molar ratio of-NCO of the chain extender to the sum of-OH of DEH and PEG is 1.01:1 to 1.05: 1.
Further, preferably, the chain extension reaction is carried out under dry argon, the reaction temperature is 60-90 ℃, and the reaction time is 3-5 h.
Further, preferably, the preparation conditions of the membrane material are as follows: preparing a membrane material in a polytetrafluoroethylene mould by a solvent volatilization method: firstly volatilizing the solvent at 40-45 ℃ for 60-90 h, and then drying in vacuum at 30 ℃ to constant weight to obtain the polyurethane urea film material.
Preferably, the chemical structural formula of the single-end bishydroxyazo compound (DEH) is as follows:
the preparation method comprises the following steps:
dissolving 1-thioglycerol in anhydrous dimethyl sulfoxide, drying argon to remove oxygen, adding a liquid crystal monomer and a catalyst diisopropylamine, reacting for 24-36h at normal temperature, settling a mixture with 20-30 times volume of anhydrous ether after the reaction is finished, filtering, washing with the anhydrous ether, and finally drying in vacuum at 70-90 ℃ to constant weight.
The reaction equation is:
further, it is preferable that the concentration of 1-thioglycerol in anhydrous dimethylsulfoxide is 1.0 g/mL;
further, it is preferable that the molar ratio of 1-thioglycerol to the liquid crystal monomer is 1.05:1 to 1.08:1
Further, preferably, the catalyst diisopropylamine accounts for 1-3% of the total mass of the reactants.
Further, preferably, the liquid crystal monomer is 4-alkoxy-4' -undecene- [10] acyloxy azobenzene, and the specific structure is as follows:
the specific synthesis of the liquid crystal monomer is described in Houshisheng, Shuoshi paper, Shandong university 2002.
Preferably, the diisocyanate chain extender (HBH) containing a urea group structure is 1, 6-hexamethylene diisocyanate-1, 4-butanediamine-1, 6-hexamethylene diisocyanate (HBH) having the formula:
the preparation method comprises the following steps:
1) dropping dried 1, 4-butanediamine into hexamethylene diisocyanate under the protection of dry nitrogen and mechanical stirring, and reacting at normal temperature for about 3-5h to obtain suspension A;
2) after the reaction is finished, adding n-hexane into the suspension A, stirring uniformly, performing suction filtration to obtain a white solid, repeatedly washing with n-hexane until no-NCO absorption peak (2270 cm) is detected by filtrate IR-1) And (5) carrying out rotary evaporation and vacuum drying to constant weight to obtain white powdery HBH.
The equation is:
further, it is preferable that-NCO of hexamethylene diisocyanate and-NH of 1, 4-butanediamine in step 1)2The molar ratio of (a) to (b) is 6:1 to 10: 1.
Further, it is preferable that the volume of n-hexane in the step 2) is 2 times the volume of the suspension A.
The azo side chain liquid crystal polyurethane urea is applied to the fields of shape memory, photoelectric display materials, data storage materials and the like.
The invention has the beneficial effects that:
1. according to the azo side chain liquid crystal polyurethane urea provided by the invention, the hard segment and the flexible spacer with ordered structures in the main chain are uniformly distributed, and the mechanical property is good; the azo liquid crystal group is positioned on the side chain, the side chain is connected with the main chain through a flexible chain segment with a certain length, the toughness of the polyurethane is enhanced, the coupling effect between the main chain and the side chain is reduced, the side chain keeps the ordered structure of the liquid crystal to move independently, the utilization rate is high, the liquid crystal phase is easier to form, the azo liquid crystal material has the dual excellent characteristics of polyurethane microphase separation and liquid crystal polymer molecule ordered arrangement, and the azo liquid crystal material has liquid crystallinity and photochromic property on the basis of having the performance of the polyurethane.
2. The azo liquid crystal polyurethane urea synthesized by the method combines the optical activity of an azo liquid crystal monomer and the excellent mechanical property and processability of a high polymer material, and has important application value in the fields of photochromism, holographic image storage, optical switches, optical calculation, liquid crystal materials, optical information storage materials, nonlinear optical materials and the like.
3. The synthesis method of the liquid crystal polyurethane urea is a one-step method, namely, the organic polyisocyanate, the polymeric polyol and the modified mesogen are dissolved in the solvent at one time, the product is prepared by directly extending the chain, the process is simple, the raw material source is rich, the cost is lower, and the content of the liquid crystal group in the polyurethane urea can be simply regulated and controlled by controlling the feed ratio.
4. The chain extender used in the invention is multi-block aliphatic diisocyanate containing carbamido, the carbamido enhances the microphase separation of the material, and more carbamate groups and carbamido groups in the hard segment can form compact hydrogen bonds, thereby improving the mechanical property of the material.
Drawings
FIG. 1 shows a photograph of a sample II at 145 ℃ under polarized light (. times.250);
FIG. 2 is a photograph of sample II at 165 ℃ in polarized light (. times.250).
Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
The present invention will be further described with reference to the following specific examples.
The following examples were carried out using the following method for preparing a bishydroxyazo side chain compound (DEH):
dissolving 1-thioglycerol in anhydrous dimethyl sulfoxide (1.0g/mL), drying argon for deoxidization, adding a liquid crystal monomer (the molar ratio of 1-thioglycerol to the liquid crystal monomer is 1.06:1) and a catalyst diisopropylamine (1.5 percent of the total mass of reactants), reacting for 30 hours at normal temperature, after the reaction is finished, settling the mixture by using anhydrous ether with the volume being 20 times that of the mixture, filtering, washing by using the anhydrous ether, and finally drying in vacuum at 75 ℃ to constant weight.
Of DEH1H NMR structural characterization results:
1H NMR(400MHz,CDCl3,):7.07-7.09(m,8H,H-Ph),4.04(m,3H,CH-OH,PhO-CH 2),3.46(t,2H,CH 2-OH),2.82(t,2H,CH2CH 2-S),2.56(m,4H,CH 2COO-,S-CH 2CH),1.20-1.56(m,17H,S-CH2-(CH 2)8-,CH3CH 2CH 2-,CH-OH),1.19(br,1H,CH2-OH),0.96(t,3H,-CH 3).
the preparation of the urea group-containing diisocyanate chain extender (HBH) used in the following examples was:
the preparation method of HBH comprises the following steps: under the protection of dry nitrogen and mechanical stirring, taking HDI into a three-neck flask, preparing dried 1, 4-butanediamine according to the molar ratio of 6:1, slowly dropwise adding into the three-neck flask within half an hour, and reacting for 4 hours at normal temperature. After the reaction is finished, adding n-hexane with the volume twice that of the reaction product, stirring, transferring to a beaker, stirring by using a glass rod until the solid product is completely separated into fine powder, carrying out suction filtration on the suspension to obtain a white solid, repeatedly washing by using the n-hexane, repeating the steps for three times until no-NCO absorption peak (2270 cm) exists in the filtrate in the IR detection process-1). Then the white solid is dried in vacuum at 40 ℃ to constant weight, and white powdery HBH is obtained.
Of HBH1H NMR structural characterization results:
1H NMR(400MHz,CDCl3,):6.01(s,4H,NH),3.41(t,4H,CH 2-NCO),3.04(q,8H,CH 2-NH),1.20-1.61(m,20H,NHCH2CH 2CH 2CH2NH,CH 2CH 2CH 2CH 2CH2NCO)。
example 1
Under the protection of dry nitrogen, 8.13g (15mmol) of single-end dihydroxy azo compound (DEH) and 3.0g (5mmol) of polyethylene glycol (PEG, M)n600), adding N, N-Dimethylformamide (DMF) to dissolve (0.6g/mL), heating the reaction system to 80 ℃, dropwise adding a DMF solution (1.0g/mL) of HBH chain extender (20.4mmol), keeping the temperature for continuous reaction for 3.5 hours after the dropwise adding is finished, cooling to the normal temperature after the reaction, and diluting the DMF to 5.5% (g/mL). And (3) volatilizing the solvent in a polytetrafluoroethylene mould to form a film to obtain a polyurethane film material, volatilizing the solvent at 40 ℃ under normal pressure for 70 hours, and then drying in vacuum at 30 ℃ to obtain a polyurethane urea film material I.
Example 2
Under the protection of dry nitrogen, 10.84g (20mmol) of single-end dihydroxy azo compound (DEH) and 3.0g (5mmol) of polyethylene glycol (PEG, M)n600), adding N, N-Dimethylformamide (DMF) to dissolve (0.6g/mL), heating the reaction system to 80 ℃, dropwise adding a DMF solution (1.0g/mL) of HBH chain extender (25.5mmol), keeping the temperature for continuous reaction for 3.5h after the dropwise adding is finished, cooling to the normal temperature after the reaction, and diluting the DMF to 6.0% (g/mL). And (3) volatilizing the solvent in a polytetrafluoroethylene mould to form a film to obtain a polyurethane film material, volatilizing the solvent at 40 ℃ under normal pressure for 70 hours, and then drying in vacuum at 30 ℃ to obtain a polyurethane urea film material II.
Example 3
13.55g (25mmol) of the single-end dihydroxy azo compound (DEH) and 5.0g (5mmol) of polyethylene glycol (PEG, M) under the protection of dry nitrogenn1000), adding N, N-Dimethylformamide (DMF) to dissolve (0.6g/mL), heating the reaction system to 85 ℃, dropwise adding a DMF solution (1.0g/mL) of HBH chain extender (30.6mmol), keeping the temperature for continuous reaction for 3 hours after the dropwise adding is finished, cooling to the normal temperature after the reaction, and diluting the DMF to 5.5% (g/mL). And volatilizing the solvent in a polytetrafluoroethylene mold to form a film so as to obtain a polyurethane film material, volatilizing the solvent at the temperature of 40 ℃ under normal pressure for 70h, and then drying in vacuum at the temperature of 30 ℃ to obtain a polyurethane urea film material III.
Example 4
Under the protection of dry nitrogen, 10.84g (20mmol) of single-end double hydroxyl coupleNitrogen compound (DEH) and 5.0g (5mmol) of polyethylene glycol (PEG, M)n1000), adding N, N-Dimethylformamide (DMF) to dissolve (0.6g/mL), heating the reaction system to 75 ℃, dropwise adding a DMF solution (1.0g/mL) of HBH chain extender (25.5mmol), keeping the temperature for continuous reaction for 4 hours after the dropwise adding is finished, cooling to the normal temperature after the reaction, and diluting the DMF to 5.5% (g/mL). And volatilizing the solvent in a polytetrafluoroethylene mold to form a film so as to obtain a polyurethane film material, volatilizing the solvent at the temperature of 40 ℃ under normal pressure for 70 hours, and then drying in vacuum at the temperature of 30 ℃ to obtain a polyurethane urea film material IV.
Example 5
Under the protection of dry nitrogen, 10.84g (20mmol) of single-end dihydroxy azo compound (DEH) and 10.0g (5mmol) of polyethylene glycol (PEG, M)n2000), adding N, N-Dimethylformamide (DMF) to dissolve (0.6g/mL), heating the reaction system to 80 ℃, dropwise adding a DMF solution (1.0g/mL) of HBH chain extender (25.5mmol), keeping the temperature for continuous reaction for 3.5h after the dropwise adding is finished, cooling to the normal temperature after the reaction, and diluting the DMF to 5.5% (g/mL). And (3) volatilizing the solvent in a polytetrafluoroethylene mould to form a film to obtain a polyurethane film material, volatilizing the solvent at 40 ℃ under normal pressure for 70 hours, and then drying in vacuum at 30 ℃ to obtain the polyurethane urea film material V.
Example 6 the following analytical methods were used in all examples unless otherwise indicated.
1. Photochromic performance test: the samples were tested for photochromic performance using a T6 ultraviolet spectrophotometer. And (2) taking N, N-dimethylformamide as a blank solvent, placing 10-5mol/L of sample solution in a sealed quartz sample cell, placing under a 365nm ultraviolet lamp, respectively measuring UV absorption curves with the irradiation time of 0, 10, 20, 30, 40 and 50min, and recording the change condition of absorbance along with the irradiation time. The samples were shielded from natural light with a black cloth during the treatment.
The composition and the light-induced variability of the azo side chain liquid crystal polyurethane urea material of examples 1-5 are shown in table 1.
TABLE 1 Properties of the polyurethaneureas
The content of PEG is the mass content in the polyurethaneurea;
the content of DEH is the mass content in the polyurethaneurea.
Under the action of ultraviolet light, the polyurethane urea film generates cis-trans isomeric variation of azo groups, and the cis-trans isomeric conversion basically reaches balance when the ultraviolet light irradiation time is 50 min. Referring to the ultraviolet absorption spectrum of the sample, the sample has two absorption bands in the range of 280-600 nm: the first absorption band is due to the pi-pi of azobenzene trans configuration*Caused by electron energy level transition; the second absorption band is due to the n-pi configuration of azobenzene cis*Electron energy level transition.
As can be seen from Table 1, the ultraviolet absorption spectra of the samples varied greatly with time, showing significant photochromic behavior. Drawing a series of spectrograms, observing the absorbance change at the maximum absorption wavelength, and finding that the change of the sample II is most obvious, the change of the sample III is second time, and the change of the sample I is second time, and the change of the sample IV and the sample V is minimum, which shows that the higher the content of mesomorphic elements in the polyurethane-urea film is, the better the photochromic performance is.
2. Testing by a polarizing microscope: the slide with the sample was placed on a POM hot stage using XPN-203E transmission polarization microscope ((POM), heated from room temperature to a clearing point and then lowered to room temperature and photographed in time.
Birefringence was observed in the sample at room temperature, observed under POM with hot stage. As the temperature increases, the sample becomes gradually soft and liquid crystal phase transition begins to occur when the melting point temperature is reached around 145 ℃. With the melting phenomenon, the sample starts to flow while a partially crystalline state exists. At this time, the liquid crystals in the small spherulite form are aggregated with each other to form a liquid crystal in the schlieren form, and a significant birefringence phenomenon is exhibited, and a POM photograph thereof is shown in FIG. 1.
The flow speed is accelerated along with the temperature rise, the crystalline state part is less and less, the bright area is increased, and the bright area has nematic phase filiform texture, as shown in figure 2, a sample in the temperature interval has the characteristics of crystal anisotropy and liquid fluidity, the visual field is blackened when the phase transition temperature is about 200 ℃, the sample is converted into isotropic liquid, and the liquid crystal phase appears again after the temperature is reduced, so that the synthesized sample shows the characteristic of typical thermotropic nematic liquid crystal.
The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.
Claims (8)
1. An azo side chain liquid crystal polyurethane urea is characterized in that a single-ended dihydroxy azo compound is mixed with double-ended hydroxy polyethylene glycol, diisocyanate containing a carbamido structure is used as a chain extender for chain extension, and the azo side chain liquid crystal polyurethane urea is obtained after purification;
the formula is shown as formula 1:
wherein:
R1:
R2:
R3:
m＝15～90，n＝15～50；
the preparation method of the azo side chain liquid crystal polyurethane urea comprises the following steps: mixing a single-end dihydroxyazo compound and double-end hydroxyl polyethylene glycol, adding N, N-dimethylformamide to dissolve, adding an N, N-dimethylformamide solution containing diisocyanate with a carbamido structure to perform chain extension reaction, cooling to normal temperature after reaction, diluting N, N-dimethylformamide to 4-7% g/mL, and preparing a polyurethane urea membrane material by a solvent volatilization film forming method;
the structural formula of the single-ended dihydroxy azo compound is as follows:
the specific preparation method of the single-ended dihydroxyazo compound comprises the following steps:
dissolving 1-thioglycerol in anhydrous dimethyl sulfoxide, drying argon to remove oxygen, adding a liquid crystal monomer and a catalyst diisopropylamine, reacting for 24-36h at normal temperature, after the reaction is finished, settling the mixture with 20-30 times volume of anhydrous ether, filtering, washing with the anhydrous ether, and finally drying in vacuum at 70-90 ℃ to constant weight;
the reaction equation is:
2. the azo side chain liquid crystalline polyurethane urea of claim 1, wherein the number average molecular weight is 1.0 × 105～6.0×105The dispersion coefficient is 1.20-1.31, the mass content of the single-end dihydroxy azo compound in the polyurethane urea is 30-46%, and the mass content of the double-end hydroxy polyethylene glycol in the polyurethane urea is 10-37%.
3. The azo side chain liquid crystalline polyurethaneurea according to claim 1, wherein the concentration of 1-thioglycerol in anhydrous dimethylsulfoxide is 1.0 g/mL; the molar ratio of the 1-thioglycerol to the liquid crystal monomer is 1.05: 1-1.08: 1; the catalyst diisopropylamine accounts for 1-3% of the total mass of the reactants; the liquid crystal monomer is 4-alkoxy-4' -undecene- [10] acyloxy azobenzene, and the specific structure is as follows:
4. the azo side chain liquid crystalline polyurethane urea according to claim 1, wherein the diisocyanate chain extender having an urea group structure is 1, 6-hexamethylene diisocyanate-1, 4-butanediamine-1, 6-hexamethylene diisocyanate,
the structural formula is as follows:
the preparation method comprises the following steps:
1) dropping dried 1, 4-butanediamine into hexamethylene diisocyanate under the protection of dry nitrogen and mechanical stirring, and reacting at normal temperature for 3-5h to obtain suspension A;
2) after the reaction is finished, adding normal hexane into the suspension A, uniformly stirring, carrying out suction filtration to obtain a white solid, repeatedly washing with the normal hexane until no-NCO absorption peak is detected in filtrate IR, and carrying out rotary evaporation and vacuum drying to constant weight to obtain white powdery 1, 6-hexamethylene diisocyanate-1, 4-butanediamine-1, 6-hexamethylene diisocyanate;
the equation is:
5. the azo side chain liquid crystalline polyurethane urea according to claim 4, wherein-NCO of hexamethylene diisocyanate and-NH of 1, 4-butanediamine in step 1)2The molar ratio of (a) to (b) is 6: 1-10: 1; the volume of the n-hexane in the step 2) is 2 times of the volume of the suspension A.
6. The azo side chain liquid crystal polyurethane urea of claim 1, wherein the molar ratio of the single-end dihydroxy azo compound to the double-end hydroxy polyethylene glycol is 3: 1-5: 1; the number average molecular weight of the double-end hydroxyl polyethylene glycol is 600-2000, and the dispersion coefficient is 1.15-1.30; the addition mode of diisocyanate with a chain extender containing a carbamido structure is as follows: dropwise adding a DMF solution of diisocyanate containing a carbamido structure, wherein the concentration is 0.5-1.0g/mL, and the dropwise adding speed is 5-10 mL/min; the molar ratio of-NCO of the chain extender to the sum of-OH of the single-end dihydroxy azo compound and the double-end hydroxy polyethylene glycol is 1.01: 1-1.05: 1; the chain extension reaction is carried out under dry argon, the reaction temperature is 60-90 ℃, and the reaction time is 3-5 h.
7. The azo side chain liquid crystalline polyurethaneurea according to claim 1, wherein the film material is prepared under the conditions: preparing a membrane material in a polytetrafluoroethylene mould by a solvent volatilization method: firstly volatilizing the solvent at 40-45 ℃ for 60-90 h, and then drying in vacuum at 30 ℃ to constant weight to obtain the polyurethane urea film material.
8. Use of the azo side chain liquid crystalline polyurethaneurea according to any of claims 1 to 7 in the fields of shape memory, photoelectric display materials, and data storage materials.
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