Super-tensile polylactic acid-based polyurethane urea based on internal plasticizing effect of T-type chain extender and preparation method of super-tensile polylactic acid-based polyurethane urea

Abstract

The invention belongs to the field of polymer synthesis, and particularly relates to super-stretched polylactic acid-based polyurethane urea based on the internal plasticizing effect of a T-type chain extender and a preparation method of the super-stretched polylactic acid-based polyurethane urea. A side group structure is introduced into a main chain of polyurethane urea through a T-shaped chain extender, and the toughness and the elasticity of the polylactic acid-based polyurethane urea material are improved based on the internal plasticizing effect of a side group, and the preparation method comprises the following steps: taking polylactic acid dihydric alcohol as a soft segment, mixing the T-shaped chain extender containing a short-chain side group structure with excessive diisocyanate, and uniformly stirring to obtain the polylactic acid-based polyurethane urea material. Meanwhile, water is used as an in-situ indirect chain extender, and polylactic acid-based polyurethane urea containing a side group structure is synthesized. By adjusting the variety and proportion of the reaction raw materials, the polylactic acid-based polyurethane urea material has excellent tensile property. The polylactic acid-based polyurethane urea material provided by the invention has the characteristics of ultra-long tensile property (the elongation at break is 400-1000%), good biocompatibility, degradability and convenience in processing and forming, and has a wide application prospect.

Description

Technical Field

[0001] The invention belongs to the field of polymer synthesis, and in particular relates to an ultra-stretched polylactic acid-based polyurethane urea based on the internal plasticizing effect of a T-type chain extender and a preparation method thereof. Background Art

[0002] Polyurethane urea (PUU) is a block copolymer with repeated carbamate and urea segments in the molecular chain, and its block structure is divided into soft segments and hard segments. The soft segment is composed of oligomeric diols (polyester, polyether, etc.), and the hard segment is composed of diisocyanate and small molecule chain extenders. The properties of polyurethane urea can be adjusted by changing the structure and ratio of the hard segment and soft segment in polyurethane urea, such as polymer materials with excellent toughness and elasticity, which can greatly broaden its application field.

[0003] Thermoplastic polyurethane urea materials have the advantages of excellent performance, easy processing and various product forms, which enable them to meet the diverse needs of the market and have good application prospects in many fields. However, the raw materials for preparing polyurethane urea materials are mostly obtained from petroleum resources. With the rapid consumption of petroleum resources and the intensification of environmental pollution problems, bio-based polyurethane urea materials have become a new research hotspot.

[0004] Polylactic acid (PLA), as a bio-based polyester, has good biodegradability, biocompatibility and excellent mechanical properties. However, due to the inherent hard and brittle characteristics of PLA, polyurethane urea with PLA as the soft segment is also a brittle material. In practical applications, it exhibits problems such as insufficient toughness or elasticity, which greatly limits its many potential applications. Currently, most methods for toughening polylactic acid-based polyurethane urea are to improve the toughness and elasticity of polylactic acid-based polyurethane urea by adding other flexible materials and small molecule plasticizers for blending or chemical copolymerization, but this will also affect some properties of the material itself, reducing the degradability and practicality of the material. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides an ultra-stretchable polylactic acid-based polyurethane urea based on the internal plasticizing effect of a T-type chain extender and a preparation method thereof. By changing the structure of the chain extender, a short-chain side group structure is introduced into the main chain hard segment of the polylactic acid-based polyurethane urea, and a thermoplastic polylactic acid-based polyurethane urea with good toughness and elasticity is prepared through the internal plasticizing effect of the T-type chain extender. The polylactic acid-based polyurethane urea of ​​the present invention has better elongation at break, and the tensile stress-strain curve has no obvious yield phenomenon, showing an elastomeric behavior with excellent tensile properties.

[0006] In order to solve the above-mentioned technical problems, this application provides the following technical solutions:

[0007] The present invention provides a polylactic acid-based polyurethane urea with super stretchability, comprising a soft segment and a hard segment, wherein the soft segment is selected from a low molecular weight polylactic acid diol, and the hard segment is a polymerization unit composed of a diisocyanate, a branched small molecule diol T-type chain extender and water; the chemical structural formula of the polylactic acid-based polyurethane urea with super stretchability is as follows:

[0008]

[0009] Among them, R 1 is polylactic acid; R' is an alkyl, alicyclic or aromatic group in diisocyanate; R 2 is a small molecule diol chain extender containing a branched structure; Cx is the number of carbon atoms contained in the branch;

[0010] a is any number from 1 to 20, b is any number from 1 to 10, n is any number from 3 to 30, and x is any number from 0 to 50.

[0011] Preferably, the R 1 The polylactic acid is one or more selected from the group consisting of left-handed polylactic acid (PLLA), right-handed polylactic acid (PDLA) and racemic polylactic acid (PDLLA); the molecular weight of the polylactic acid diol is 600-3000 g / mol.

[0012] Preferably, the R 2 The structural formula is selected from one or more of the following structural formulas:

[0013]

[0014] Preferably, the structural formula of R' in the diisocyanate is selected from one or more of the following structural formulas:

[0015]

[0016] Furthermore, the structural formula of the diisocyanate R' is selected from one or more of the following structural formulas:

[0017] Aliphatic diisocyanates:

[0018]

[0019] Cycloaliphatic diisocyanates:

[0020]

[0021] Aromatic diisocyanates:

[0022]

[0023] Specifically, the diisocyanate R' is selected from aliphatic diisocyanates.

[0024] Furthermore, the tensile elongation at break of the polylactic acid-based polyurethane urea material is 400-1000%, and the tensile strength is 3-20 MPa.

[0025] The polylactic acid-based polyurethane material synthesized by using the several T-type chain extenders containing branched structures of the present invention has a higher elongation at break than other polylactic acid-based polyurethane materials. The reason is that the side group structure is introduced into the main chain of the polylactic acid-based polyurethane by the T-type chain extender. The introduction of the side group structure destroys the regularity between the molecular chains, weakens the intermolecular forces, and at the same time, the hanging side chains play an internal plasticizing effect, thereby making the polylactic acid-based polyurethane urea material softer and more tough. Therefore, by introducing such a T-type chain extender into the polylactic acid-based polyurethane material and adjusting the proportion of each component, its tensile properties can be adjusted, thereby further improving the toughness and elasticity of the material.

[0026] The polylactic acid-based polyurethane urea material provided by the present invention is composed of oligomer polylactic acid diol, diisocyanate and small molecule diol chain extender, has good solubility, is soluble in many organic solvents, has low processing and molding temperature, can be hot-pressed at 120°C, and has good processing application; during the synthesis, the ratio between the soft and hard segment components is adjusted to adjust the strength of the intermolecular force, thereby controlling the tensile properties of the material.

[0027] The present invention also provides a method for preparing the above-mentioned polylactic acid-based polyurethane urea with super stretchability, comprising the following steps:

[0028] (1) mixing polylactic acid diol, diisocyanate and a small molecule diol chain extender in an organic solvent A, and performing a prepolymerization reaction at 20-100° C. for 1-10 hours under the action of a catalyst to obtain a prepolymer; the polymer is selected from one or both of polyester and polyether diol, and the catalyst is selected from stannous octoate, dibutyltin dilaurate, pyridine or N,N-dimethylpyridine;

[0029] (2) polymerizing the prepolymer with water at 20-100° C. for 12-72 hours to obtain a mixed product;

[0030] (3) The mixed product is precipitated in an organic solvent B, separated, and dried to obtain the polyurethane urea.

[0031] Preferably, in step (1), the molar ratio of the polylactic acid diol, the small molecule diol chain extender and the diisocyanate is 1-20:1-10:3-30.

[0032] Preferably, in step (1), the amount of the catalyst added is 0.01-0.1% of the total mass of the polylactic acid diol, the diisocyanate and the small molecule diol chain extender.

[0033] Preferably, the organic solvent A is selected from one or more of dichloromethane, chloroform, 1,2-dichloroethane, acetone, dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc);

[0034] Preferably, the organic solvent B is selected from n-hexane, n-heptane, isohexane, isoheptane, cyclohexane or diethyl ether.

[0035] Specifically, the preparation method comprises the following steps:

[0036] (1) By mole, a part of polylactic acid diol, b part of T-type chain extender and n parts of diisocyanate are mixed and dissolved in an organic solvent A, and a prepolymerization reaction is carried out at a temperature of 20-100° C. under the action of a catalyst for a reaction time of 1-10 hours;

[0037] Wherein, the molar ratio of each component is a:b:n=1-20:1-10:3-30;

[0038] (2) adding water as an indirect chain extender to the prepolymer obtained in step (1), in a molar ratio of 2 (nab) parts of water, at a temperature of 20-80° C., and continuing the reaction for 12-72 hours;

[0039] (3) The product obtained in step (2) is precipitated in an organic solvent B, and the precipitate is dried to obtain a product, polylactic acid-based polyurethane urea.

[0040] The present invention also provides a polylactic acid-based polyurethane urea film, which is prepared from the polylactic acid-based polyurethane urea with super stretchability.

[0041] When the polyurethane urea is used and tested, it can be formed into a film by solution, that is, the dried product is dissolved in a certain amount of organic solvent, poured into a mold for molding, and after most of the solvent evaporates and dries, it is placed in a vacuum oven to completely remove the residual solvent in the film, and finally a polyurethane urea film is obtained; it can also be formed into a film by hot pressing, that is, directly hot pressing the film with a hot press.

[0042] The organic solvent is selected from one or more of acetone, dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dichloromethane, chloroform and 1,2-dichloroethane.

[0043] Since polylactic acid is crystalline, it is hard and brittle in itself. Its toughness can be increased by adding other flexible materials, so it is relatively easy to make a super-tough material. However, it is difficult to make a super-stretchable material without yielding behavior. The present invention uses pure polylactic acid as the soft segment, without adding other flexible materials, and through a T-type chain extender, it can make a super-stretchable material without yielding behavior.

[0044] The technical solution of the present invention has the following advantages over the prior art:

[0045] In the present invention, without blending the soft segment or modifying the polylactic acid, a simple "one-pot two-step method" is used to carry out a step-by-step polymerization reaction, and a side group structure is introduced into the polylactic acid-based polyurethane urea. The steric hindrance effect of the short chain side group in the T-type chain extender is used to destroy the regularity of the polymer chain, especially the hard segment, and weaken the interaction force between the chains to achieve the effect of internal plasticization, thereby improving the toughness and elasticity of the polylactic acid-based polyurethane urea. By adjusting the content of different components, the polylactic acid-based polyurethane urea material with super stretching can be obtained in the example of the present invention, and its elongation at break can reach up to 1000%. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 is the infrared spectrum of the polylactic acid-based polyurethane urea prepared in Example 1 of the present invention;

[0047] Figure 2 are stress-strain diagrams of tensile tests of several polylactic acid-based polyurethane ureas prepared in Example 1 of the present invention;

[0048] Figure 3 is a differential scanning calorimetry analysis diagram of the polylactic acid-based polyurethane urea prepared in Example 1 of the present invention;

[0049] Figure 4 is a stress-strain diagram of a cyclic tensile test of polylactic acid-based polyurethane urea prepared in Example 2 of the present invention;

[0050] Figure 5 is a photograph of a hot-pressed film obtained at 120° C. of the ultra-stretched polylactic acid-based polyurethane urea prepared in Example 4 of the present invention;

[0051] Figure 6 It is a stress-strain diagram of the tensile test of the ultra-stretched polylactic acid-based polyurethane urea prepared in Example 4 of the present invention. DETAILED DESCRIPTION

[0052] The present invention is further described below in conjunction with the drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0053] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods, and the materials, reagents, etc. used are all available from commercial sources unless otherwise specified.

[0054] Example 1

[0055] This embodiment provides a method for preparing a polylactic acid-based polyurethane urea with super stretchability, and the chemical structure of the polylactic acid-based polyurethane urea is as follows:

[0056]

[0057] The specific preparation steps are as follows:

[0058] (1) Weigh 20.00 g (10 mmol) of PLA (Mn = 2000 g / mol), 1.03 g (5 mmol) of C5 T-type chain extender and 5.04 g (30 mmol) of hexamethylene diisocyanate (HDI) and dissolve them in DMAc solvent. After the reactants are completely mixed, add 20 μL of dibutyltin dilaurate (catalyst), raise the temperature to 70°C, and heat and stir the reaction for 4 hours to carry out a prepolymerization reaction.

[0059] (2) Set the temperature of the oil bath to 50°C. When the temperature of the oil bath drops to 50°C and stabilizes, weigh 600 μL (30 mmol) of water and add it to the flask. Since the reaction activity of HDI and water is relatively high, it is necessary to observe the viscosity of the reaction more within two hours after adding water. When a large number of bubbles are generated, DMAc needs to be added during the reaction to reduce the viscosity of the reaction and prevent the reaction from gelling. After adding water for 30 to 40 hours, stop the reaction.

[0060] (3) After the reaction solution is cooled to room temperature, ether is used for precipitation. After precipitation, white floccules are obtained. Most of the high-boiling point solvent DMAc is replaced and removed by replacing ether and ultrasonically oscillating with an ultrasonic cleaner. This is repeated 3 to 4 times, and then placed in a vacuum oven at 80°C for one night. After drying, the product polylactic acid-based polyurethane urea (PUU) is obtained. This product is named PUUC5-6.

[0061] At the same time, according to the above preparation steps, the number of carbon atoms contained in the side group of the T-type chain extender was changed to prepare PUUCx-6 with different side group lengths (x is the number of carbon atoms contained in the T-type chain extender, and 6 is the molar amount of diisocyanate).

[0062] Figure 1 is the infrared spectrum of PUUC5-6 provided in Example 1; Figure 1 Visible in the middle, 3340cm -1 The N-H stretching vibration absorption peak is at 2940cm -1 The methylene peak is at 1743cm -1The carbamate carbonyl group is at 1627 cm -1 The carbonyl stretching vibration peak in the urea group is at 1558 cm -1 The peak at 2260-2280 cm-1 is the characteristic vibration peak of amide II. -1 The characteristic peak at disappeared, and the synthesized sample had the structural characteristic peaks of typical polyurethane urea.

[0063] Figure 2 The stress-strain curves of PUUC5-6, PUUC9-6 and PUUC15-6 provided in Example 1 are shown in the figure. As can be seen from the figure, with the introduction of the T-type chain extender, the PUU containing the side group structure all exhibits an elastic behavior without yielding phenomenon, and its tensile strength is 13-20 MPa and the elongation at break is 390-670%, indicating that the polymer has good toughness.

[0064] Figure 3 The differential scanning calorimetry analysis provided in Example 1 shows that the glass transition temperature (T g ) gradually decreases with the increase of the carbon chain length of the short-chain side group, among which the T g At 26°C, the T of PUUC9-6 g At 24°C, the T of PUUC15-6 g It is 22℃.

[0065] Example 2

[0066] This embodiment provides a method for preparing a polylactic acid-based polyurethane urea with ultra-stretchability, and its structural formula is as follows:

[0067]

[0068] The specific steps of preparation are as follows:

[0069] Weigh 20.00 g (10 mmol) of PLA (Mn = 2000 g / mol), 1.73 g (5 mmol) of C15 chain extender and 4.20 g (25 mmol) of HDI. After the reactants are completely mixed, add 20 μL of dibutyltin dilaurate (catalyst), heat to 70°C, heat and stir for 4 hours to carry out prepolymerization.

[0070] After the reaction was completed, the temperature was lowered to 50 °C and 400 μL (20 mmol) H 2 O continued to react for 30 to 36 hours. After the reaction was completed, the reaction solution was slowly poured into ether to obtain a white block precipitate. The precipitate was cut into pieces, replaced with ether and ultrasonicated for 45 minutes, and then dried in a vacuum oven at 70°C for 12 hours to obtain the product PUUC15-n.

[0071] In this embodiment, T-type chain extender C15 was selected, the molar ratio of PLA to T-type chain extender was fixed at 2:1, and the molar number of HDI n (n=3, 5 and 6) was changed to prepare PUUC15-n with different HDI contents. When the content of diisocyanate is reduced, the hard segment content in the polyurethane urea material is reduced, thereby making the material more elastic and tough.

[0072] Figure 4 This is the cyclic tensile test of PUUC15-5 provided in Example 2. The test method is to conduct 10 continuous loading-unloading cyclic tensile tests with a maximum strain of 50%. After each cycle is completed, a 5-minute pause is made before the next cyclic test is started. As can be seen from the figure, the cyclic tensile curves of PUUC15-5 are highly consistent, indicating that the polymer has good resilience.

[0073] Example 3

[0074] This embodiment provides a method for preparing a super-stretchable thermoplastic polyurethane urea, the structural formula of which is as follows:

[0075]

[0076] The specific steps of preparation are as follows:

[0077] 10.00 g (5 mmol) of PLA (Mn = 2000 g / mol), 3.45 g (10 mmol) of C15 chain extender and 4.20 g (25 mmol) of HDI were weighed. After the reactants were completely mixed, 20 μL of dibutyltin dilaurate (catalyst) was added, the temperature was raised to 70°C, and the mixture was heated and stirred for 4 hours to carry out a prepolymerization reaction.

[0078] After the reaction was completed, the temperature was lowered to 50 °C and 400 μL (20 mmol) H 2 OContinue the reaction for 30 to 36 hours. After the reaction is completed, slowly pour the reaction solution into ether to obtain a white block precipitate. Cut the precipitate into pieces, replace ether with ultrasound for 45 minutes, and then dry it in a vacuum oven at 70°C for 12 hours to obtain the product PUU.

[0079] In this example, polylactic acid-based polyurethane ureas with different T-type chain extender contents were prepared by fixing the molar amount of HDI and changing the ratio of soft segment PLA and T-type chain extender.

[0080] Example 4

[0081] This example provides a method for hot pressing film-forming of polylactic acid-based polyurethane urea based on the above-mentioned ultra-stretch thermoplastic, and the specific production steps are as follows:

[0082] Figure 5This is the hot pressing flow chart of this embodiment, taking sample PUUC5-6 as an example. Weigh 2.5g of sample and put it directly into the mold. The hot pressing conditions are 120℃, 20MPa, and keep for 15min for hot pressing. Figure 5 As shown, through hot pressing, a transparent and uniform film can be obtained.

[0083] Figure 6 This is a tensile diagram of the hot-pressed film of PUUC5-6 provided in Example 4. It can be seen that the film also has good tensile properties under the conditions of hot-pressed film formation, indicating that the polylactic acid-based polyurethane urea can be well thermoformed at 120°C.

[0084] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. An ultra-stretched polylactic acid-based polyurethane urea based on the internal plasticizing effect of a T-type chain extender, characterized in that: It comprises a soft segment and a hard segment, wherein the soft segment is selected from a low molecular weight polylactic acid diol, and the hard segment is a polymerization unit composed of a diisocyanate, a branched small molecule diol T-type chain extender and water; the chemical structure of the ultra-stretched polylactic acid-based polyurethane urea based on the internal plasticizing effect of the T-type chain extender is as follows: Wherein, R1 is polylactic acid; R' is an alkyl, alicyclic or aromatic group in diisocyanate; R2 is a small molecule diol T-type chain extender containing a branched structure; Cx is the number of carbon atoms contained in the branched chain; a is any number from 1 to 20, b is any number from 1 to 10, n is any number from 3 to 30, and x is any number from 0 to 50.

2. The ultra-stretched polylactic acid-based polyurethane urea based on the internal plasticizing effect of a T-type chain extender according to claim 1, characterized in that: The R1 is polylactic acid, which is one or more selected from the group consisting of left-handed polylactic acid, right-handed polylactic acid and racemic polylactic acid; the molecular weight of the polylactic acid diol is 600-3000 g / mol.

3. The ultra-stretched polylactic acid-based polyurethane urea based on the internal plasticizing effect of a T-type chain extender according to claim 1, characterized in that: The R2 is a T-shaped chain extender, and its structural formula is selected from one or more of the following structural formulas:

4. The ultra-stretched polylactic acid-based polyurethane urea based on the internal plasticizing effect of a T-type chain extender according to claim 1, characterized in that: The structural formula of R' in the diisocyanate is selected from one or more of the following structural formulas:

5. A method for preparing the ultra-stretched polylactic acid-based polyurethane urea based on the internal plasticizing effect of a T-type chain extender according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) mixing polylactic acid diol, diisocyanate and T-type chain extender in an organic solvent A, and performing a prepolymerization reaction at 20-100° C. for 1-10 hours under the action of a catalyst to obtain a prepolymer; the catalyst is selected from stannous octoate, dibutyltin dilaurate, pyridine or N,N-dimethylpyridine; (2) polymerizing the prepolymer with water at 20-100° C. for 12-72 hours to obtain a mixed product; (3) The mixed product is precipitated in an organic solvent B, separated, and dried to obtain a product, polylactic acid-based polyurethane urea.

6. The preparation method according to claim 5, characterized in that: In the step (1), the molar ratio of the polylactic acid diol, the T-type chain extender and the diisocyanate is 1-20:1-10:3-30.

7. The preparation method according to claim 5, characterized in that: In the step (1), the amount of the catalyst added is 0.01-0.1% of the total mass of the polylactic acid diol, the diisocyanate and the T-type chain extender.

8. The preparation method according to claim 5, characterized in that: The organic solvent A is selected from one or more of dichloromethane, chloroform, 1,2-dichloroethane, acetone, dimethyl sulfoxide, N,N-dimethylformamide and N,N-dimethylacetamide.

9. The preparation method according to claim 5, characterized in that: The organic solvent B is selected from n-hexane, n-heptane, isohexane, isoheptane, cyclohexane or diethyl ether.

10. A polylactic acid-based polyurethane urea film, characterized in that: The polyurethane urea is prepared from the ultra-stretched polylactic acid-based polyurethane urea based on the internal plasticizing effect of the T-type chain extender as described in any one of claims 1 to 4.

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