Non-uniform long-chain network enhanced crystal cross-linked polyurethane and preparation method thereof

Abstract

The invention relates to cross-linked polyurethane with non-uniform long-chain network enhanced crystals and a preparation method of the cross-linked polyurethane. The cross-linked polyurethane disclosed by the invention has a non-uniform long-chain network structure, and the non-uniform long-chain network structure has hyperbranched cross-linking points formed by interconnection of the cross-linking agent, so that the chain length between the cross-linking points can be increased while the cross-linking degree is kept, and the performance of the material is improved. The preparation method of the cross-linked polyurethane comprises the following steps: firstly, carrying out prepolymerization reaction on dihydric alcohol and diisocyanate to obtain a prepolymer, and then further carrying out curing reaction on the prepolymer, the diisocyanate and a cross-linking agent to obtain the cross-linked polyurethane with a non-uniform long-chain network structure.

Description

Technical Field

[0001] The invention belongs to the field of polymer materials, and in particular relates to a cross-linked polyurethane with non-uniform long-chain network-enhanced crystallization and a preparation method thereof. Background Art

[0002] The effect of cross-linked networks on the properties of traditional polymer elastomers has been extensively studied. In classical polymer network theory, uniform cross-linked networks are believed to relieve stress concentration and improve mechanical properties (Non-Patent Literature 1). Researchers have made many efforts to synthesize polymers with uniform networks, however, in non-elastic networks, such as crystalline polymer systems, the effect of network uniformity on performance has been largely ignored.

[0003] The addition reaction between hydroxyl and isocyanate groups is the core chemical reaction for synthesizing polyurethane, which has the characteristics of rapidity and high selectivity. Therefore, the structure of the cross-linked network can be designed by the prepolymer method. Through prepolymerization, uniform short-chain networks and non-uniform long-chain cross-linked networks can be obtained (non-patent literature 2). If the polymer chain can crystallize, the longer chain is more likely to act as a nucleation site. This means that the long-chain non-uniform network has a higher crystallization potential than the uniform short-chain network. It is well known that the mechanical properties and gas barrier properties of crystalline polymers are closely related to their crystallinity. Therefore, regulating the structure of the cross-linked network can be used as an effective strategy to enhance the properties of crystalline polymers.

[0004] References:

[0005] Non-patent literature 1: Macromolecules 2017, 50, 8955-8964;

[0006] Non-patent literature 2: Angew. Chem. Int. Ed. 2023, 62, e202310989doi.org / 10.1002 / anie.202310989. Summary of the invention

[0007] Problem that the invention aims to solve

[0008] The methods for regulating the properties of cross-linked polyurethanes currently mainly include changing the chemical composition and adjusting the degree of cross-linking. However. In traditional chemically cross-linked polymers, the molecular weight between the cross-linking points is not high, usually in the range of several hundred to several thousand Daltons. For polymer chains of this length, crystallinity is mainly controlled by nucleation, which means that longer molecular chains between cross-linking points will be easier to crystallize. However, simply increasing the molecular weight between cross-linking points will reduce the degree of cross-linking, resulting in a significant decrease in the solvent resistance and shape memory properties of the cross-linked polymer. In addition, sufficient chemical cross-linking is also beneficial to strengthen strain hardening, thereby ensuring the strength and toughness of the material. Therefore, finding a way to increase the length of the crystallizable chain between cross-linking points while maintaining the degree of cross-linking is an important direction for improving material performance.

[0009] Currently, there is a lack of effective strategies to improve material performance by structural design of polymer networks under the conditions of the same monomer structure and ratio.

[0010] Therefore, there is an urgent need to develop a cross-linked polyurethane based on polymer network structure design and a method for enhancing its performance.

[0011] Solutions for solving problems

[0012] In view of the above problems, the inventors conducted in-depth research and found that the crystallization ability of the non-uniform long-chain network is significantly better than that of the uniform short-chain network, and more effective strain-induced crystallization can be produced during deformation. Therefore, the inventors proposed a cross-linked polyurethane having a non-uniform long-chain network structure, which has hyperbranched cross-linking points formed by interconnection of a cross-linking agent, so that the chain length between the cross-linking points can be increased while maintaining the degree of cross-linking, thereby achieving improved material performance.

[0013] The inventors have also proposed a method for preparing a cross-linked polyurethane, which firstly obtains a prepolymer by a prepolymerization reaction of a diol and a diisocyanate, and then further cures the prepolymer with a diisocyanate and a cross-linking agent to obtain a cross-linked polyurethane having a non-uniform long-chain network structure.

[0014] Specifically, the present invention solves the problem of the present invention through the following solutions.

[0015] [1] A cross-linked polyurethane obtained by reacting a diol, a diisocyanate and a cross-linking agent, wherein the cross-linked polyurethane comprises one or more structures represented by the following formulas (1) to (4):

[0016]

[0017]

[0018] Wherein B represents a diisocyanate residue, C represents a crosslinker residue, * represents the connection site between B and the crosslinker or diol, n, m, s, t represent the number of repetitions of the structure in brackets, n and s are independently integers of 0 to 10, and m and t are independently integers of 1 to 10.

[0019] [2] The cross-linked polyurethane according to [1], wherein the diol is one or more selected from crystalline oligomer diols; the crystalline oligomer diol is preferably one or more selected from polycaprolactone diol, polyethylene glycol, polybutylene adipate diol, and polycarbonate diol; and the number average molecular weight of the crystalline oligomer diol is 2000 to 5000.

[0020] [3] The cross-linked polyurethane according to [1], wherein the diisocyanate is one or more selected from aliphatic diisocyanates and aromatic diisocyanates; preferably one or more selected from isophorone diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, toluene diisocyanate, naphthalene diisocyanate, and dicyclohexylmethane diisocyanate.

[0021] [4] The cross-linked polyurethane according to [1], wherein the average functionality of the cross-linking agent is greater than 2 and less than 4; preferably, the cross-linking agent is a trifunctional cross-linking agent and / or a tetrafunctional cross-linking agent; preferably, the cross-linking agent is one or more selected from triols, triamines, tetraols, and tetraamines; more preferably, it is one or more selected from glycerol, trimethylolpropane, triethanolamine, trihydroxyphenylethane, castor oil, and pentaerythritol.

[0022] [5] The cross-linked polyurethane according to any one of [1] to [4], wherein the molar ratio of the diol residue, the diisocyanate residue and the cross-linking agent residue is 1: (1-4): (0.2-3), preferably 1: (1.5-3.5): (0.3-2), more preferably 1: (1.8-2.8): (0.3-1), and further preferably 1: (2-2.5): (0.3-0.8).

[0023] [6] A method for preparing a cross-linked polyurethane, comprising the following steps:

[0024] (1) subjecting a diol to a prepolymerization reaction with a diisocyanate to obtain a prepolymer;

[0025] (2) The prepolymer, diisocyanate and crosslinking agent are mixed and subjected to a curing reaction.

[0026] [7] The preparation method according to [6], wherein step (2) comprises the following sub-steps:

[0027] (2-1) mixing the prepolymer, diisocyanate and cross-linking agent to obtain a mixture;

[0028] (2-2) The mixture is placed in a mold to perform a curing reaction.

[0029] [8] The preparation method according to [6] or [7], wherein

[0030] In step (1), the molar ratio of diol to diisocyanate is 1:(1.05-1.5), preferably 1:(1.1-1.4), and more preferably 1:(1.2-1.35);

[0031] The molar ratio of the diisocyanate used in step (1) to the diisocyanate used in step (2) is 1:(0.4-2.5), preferably 1:(0.5-2);

[0032] The molar ratio of the diisocyanate to the crosslinking agent used in step (2) is 1:(0.4-1.5), preferably 1:(0.6-1.3), and more preferably 1:(0.8-1.1);

[0033] In the total amount used in steps (1) and (2), the molar ratio of diol, diisocyanate and cross-linking agent is 1: (1-4): (0.2-3), preferably 1: (1.5-3.5): (0.3-2), more preferably 1: (1.8-2.8): (0.3-1), and further preferably 1: (2-2.5): (0.3-0.8).

[0034] [9] The preparation method according to [6] or [7], wherein the prepolymerization reaction temperature is 50 to 120°C, and the prepolymerization reaction time is 0.5 to 6 hours; the curing reaction temperature is 40 to 120°C, and the curing reaction time is 6 to 48 hours.

[0035]

[10] A cross-linked polyurethane obtained by the preparation method according to any one of [5] to [8], wherein the cross-linked polyurethane has a tensile strength of 35 MPa or more, an elongation at break of 1000% or more, and a fracture toughness of 250 MJ / m 3 above.

[0036] Effects of the Invention

[0037] The cross-linked polyurethane of the present invention has excellent mechanical properties, water vapor barrier properties, etc., which are significantly improved compared with ordinary polyurethanes with short-chain uniform network structures. The preparation method of the present invention provides a new strategy for the design, preparation and application of high-performance materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Schematic diagram of the synthesis route of Example 1 and Comparative Example 1;

[0039] Figure 2 The DSC curves of the cross-linked polyurethane obtained in Example 1 and Comparative Example 1;

[0040] Figure 3 1 is the tensile curve of the cross-linked polyurethane obtained in Example 1 and Comparative Example 1;

[0041] Figure 4 In-situ stretching small angle X-ray scattering (SAXS) data of the cross-linked polyurethane obtained in Example 1 and Comparative Example 1;

[0042] Figure 5 In-situ stretched wide-angle X-ray scattering (WAXS) data of the cross-linked polyurethane obtained in Example 1 and Comparative Example 1;

[0043] Figure 6 The water vapor barrier data of the cross-linked polyurethane obtained in Example 1 and Comparative Example 1 are shown. DETAILED DESCRIPTION

[0044] The following is a detailed description of the present invention. The technical features described below are described based on representative embodiments and specific examples of the present invention, but the present invention is not limited to these embodiments and specific examples.

[0045] <Terms and Definitions>

[0046] In this specification, the numerical range expressed using "a numerical value A to a numerical value B" means a range including the endpoints numerical values ​​A and B.

[0047] In the present specification, a numerical range expressed using "above" or "below" means a numerical range including the number.

[0048] In this specification, the word "may" means both performing a certain process and not performing a certain process.

[0049] In this specification, the use of "optionally" or "optional" indicates that certain substances, components, execution steps, application conditions and other factors are used or not used.

[0050] In this specification, the unit names used are all international standard unit names, and unless otherwise stated, the "%" used indicates weight or mass percentage.

[0051] In this specification, the references to "preferred embodiments", "embodiments", etc., mean that the specific elements (e.g., features, structures, properties and / or characteristics) described in connection with the embodiments are included in at least one embodiment described herein, and may or may not exist in other embodiments. In addition, it should be understood that the elements may be combined in various embodiments in any suitable manner.

[0052] An object of the present invention is to provide a cross-linked polyurethane, characterized in that it is obtained by reacting a diol, a diisocyanate and a cross-linking agent, and the cross-linked polyurethane comprises one or more structures represented by the following formulas (1) to (4):

[0053]

[0054]

[0055] Wherein B represents a diisocyanate residue, C represents a crosslinker residue, * represents the connection site between B and the crosslinker or diol, n, m, s, t represent the number of repetitions of the structure in brackets, n and s are independently integers of 0 to 10, and m and t are independently integers of 1 to 10.

[0056] Preferably, n, m, s, t are independently 1, 2, 3, 4, 5, 6, 7, 8 or 9.

[0057] Since the polyurethane of the present invention has hyperbranched crosslinking points formed by interconnection of a crosslinking agent as shown in formulas (1) to (4), the chain length between the crosslinking points can be increased while maintaining the degree of crosslinking, thereby achieving improved material performance.

[0058] In one embodiment, the diol is one or more selected from crystalline oligomer diols.

[0059] In the present specification, the term "crystalline oligomer diol" refers to an oligomer diol that is crystalline at room temperature (23±2°C), and its melting point is usually 40°C or higher.

[0060] Preferably, the crystalline oligomer diol is one or more selected from polycaprolactone diol, polyethylene glycol, polybutylene adipate diol, and polycarbonate diol. Preferably, the number average molecular weight of the crystalline oligomer diol is 2000 to 5000. In the present invention, by using the crystalline oligomer diol as a crystallizable monomer, the crystallinity of the crystalline segment is enhanced through the non-uniform long chain network, thereby strengthening the mechanical properties of the cross-linked polyurethane.

[0061] In one embodiment, the diisocyanate is one or more selected from aliphatic diisocyanates and aromatic diisocyanates. Preferably, the diisocyanate is one or more selected from isophorone diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, toluene diisocyanate, naphthalene diisocyanate, dicyclohexylmethane diisocyanate.

[0062] In one embodiment, the crosslinking agent is a polyol or a polyamine, and the average functionality (in terms of hydroxyl and / or amino groups) is greater than 2 and less than 4. Preferably, the crosslinking agent is a trifunctional crosslinking agent and / or a tetrafunctional crosslinking agent. More preferably, the crosslinking agent is one or more selected from triols, triamines, tetraols, and tetraamines. More preferably, the crosslinking agent is one or more selected from glycerol, trimethylolpropane, triethanolamine, trihydroxyphenylethane, castor oil (polyol, functionality 2.6), and pentaerythritol.

[0063] In one embodiment, the crosslinking agent is a trifunctional crosslinking agent, and the polyurethane of the present invention has a structure shown in formula (1) and / or formula (2). In one embodiment, the crosslinking agent is a tetrafunctional crosslinking agent, and the polyurethane of the present invention has a structure shown in formula (3) and / or formula (4). In one embodiment, the crosslinking agent is a combination of a trifunctional crosslinking agent and a tetrafunctional crosslinking agent, and the polyurethane of the present invention has one or both of the structures shown in formula (1) and formula (2), and also has one or both of the structures shown in formula (3) and formula (4).

[0064] In one embodiment, the molar ratio of the residues derived from diols (hereinafter referred to as "diol residues"), the residues derived from diisocyanates (hereinafter referred to as "diisocyanate residues") and the residues derived from crosslinkers (hereinafter referred to as "crosslinker residues") in the polyurethane of the present invention is 1: (1-4): (0.2-3), preferably 1: (1.5-3.5): (0.3-2), more preferably 1: (1.8-2.8): (0.3-1), and further preferably 1: (2-2.5): (0.3-0.8). The molar ratio within the above range is conducive to the preparation of the material and good comprehensive performance. If the content of diisocyanate residues is too low, the molecular weight will be too low and the material performance will decrease; if the content of diisocyanate residues is too high, a large amount of irreversible crosslinking will occur, destroying the preset network structure. If the amount of cross-linking agent residues is too high, that is, the cross-linking degree is too high, it will limit the crystallization ability of the crystalline segment and reduce the crystallization performance of the material. If the amount of cross-linking agent residues is too low, that is, the cross-linking degree is too low, it will have an adverse effect on the inherent properties of the cross-linked polymer such as solvent resistance and melt resistance.

[0065] In one embodiment, the ratio of the crosslinking agent residues in the structures represented by formula (1) to formula (4) relative to the total crosslinking agent residues is 50 mol % or more, preferably 60 mol % or more.

[0066] The polyurethane of the invention has excellent mechanical properties, including excellent tensile strength, elongation at break, Young's modulus and fracture toughness.

[0067] In one embodiment, the tensile strength of the polyurethane of the present invention is 35 MPa or more, preferably 48 MPa or more, more preferably 49 MPa or more, further preferably 50 MPa or more, for example 55 MPa or more, and for example 60 MPa or more.

[0068] In one embodiment, the elongation at break of the polyurethane of the present invention is 1000% or more, preferably 1300% or more, more preferably 1400% or more, further preferably 1500% or more, for example 1600% or more.

[0069] In one embodiment, the Young's modulus of the polyurethane of the present invention is 140 MPa or more, preferably 150 MPa or more, more preferably 160 MPa or more, further preferably 170 MPa or more, for example 180 MPa or more.

[0070] In one embodiment, the fracture toughness of the polyurethane of the present invention is 250 MJ / m 3 Above, preferably 300MJ / m 3 More preferably 350MJ / m 3 More preferably, 400 MJ / m 3 above.

[0071] An object of the present invention is to provide a method for preparing a cross-linked polyurethane, which comprises the following steps:

[0072] (1) subjecting a diol to a prepolymerization reaction with a diisocyanate to obtain a prepolymer;

[0073] (2) The prepolymer, diisocyanate and crosslinking agent are mixed and subjected to a curing reaction.

[0074] In one embodiment, the method for preparing the cross-linked polyurethane of the present invention is a method for preparing the cross-linked polyurethane of the present invention described above.

[0075] The various steps of the preparation method of the present invention are described below.

[0076] Step (1)

[0077] Step (1) is a prepolymerization step, in which a diol and a diisocyanate are subjected to a prepolymerization reaction to obtain a prepolymer.

[0078] In one embodiment, in step (1), the molar ratio of diol to diisocyanate is 1:(1.05-1.5), preferably 1:(1.1-1.4), and more preferably 1:(1.2-1.35). By adjusting the molar ratio of diol to diisocyanate in the prepolymerization step, the molecular weight of the polymer chain between the crosslinking points can be controlled. If the molecular weight is too small, it is not conducive to crystallization. If it is too large, the viscosity of the prepolymer becomes large and the degree of crosslinking decreases. When the molar ratio of diol to diisocyanate is within the above range, the molecular weight of the polymer chain between the crosslinking points is appropriate, so that crystallinity, preparation convenience and crosslinking degree can be taken into account.

[0079] In one embodiment, the temperature of the prepolymerization reaction is 50-120°C, preferably 60-110°C, more preferably 70-100°C, such as 80-95°C.

[0080] In one embodiment, the prepolymerization reaction time is 0.5 to 6 hours, preferably 0.8 to 5 hours, and more preferably 1 to 4 hours.

[0081] The prepolymerization reaction can be carried out in the form of solution polymerization or bulk polymerization, preferably in the form of bulk polymerization. In the embodiment of solution polymerization, the solvent described below for sub-step (2-1) can be used.

[0082] Step (2)

[0083] In step (2), the prepolymer, diisocyanate and crosslinking agent obtained in step (1) are mixed and subjected to a curing reaction to obtain the polyurethane of the present invention.

[0084] The preparation method of the present invention further uses diisocyanate in step (2), so that the network structure of the obtained cross-linked polyurethane has hyperbranched cross-linking points formed by interconnection of the cross-linking agent.

[0085] In one embodiment, the molar ratio of the diisocyanate used in step (1) to the diisocyanate used in step (2) is 1:(0.4-2.5), preferably 1:(0.5-2).

[0086] In one embodiment, the molar ratio of the diisocyanate to the cross-linking agent used in step (2) is 1:(0.4-1.5), preferably 1:(0.6-1.3), and more preferably 1:(0.8-1.1).

[0087] In one embodiment, in the total amount used in steps (1) and (2), the molar ratio of diol, diisocyanate and cross-linking agent is 1: (1-4): (0.2-3), preferably 1: (1.5-3.5): (0.3-2), more preferably 1: (1.8-2.8): (0.3-1), and further preferably 1: (2-2.5): (0.3-0.8).

[0088] In one embodiment, the curing reaction temperature is 40 to 120°C, preferably 60 to 110°C, and more preferably 70 to 100°C.

[0089] In one embodiment, the curing reaction time is 6 to 48 hours, preferably 8 to 40 hours, and more preferably 10 to 20 hours.

[0090] In one embodiment, step (2) comprises the sub-steps of:

[0091] (2-1) mixing the prepolymer, diisocyanate and cross-linking agent to obtain a mixture;

[0092] (2-2) The mixture is placed in a mold to perform a curing reaction.

[0093] Preferably, in sub-step (2-1), the diisocyanate and the cross-linking agent are dissolved in a solvent and then mixed with the prepolymer obtained in step (1) to obtain a mixture. By dissolving the diisocyanate and the cross-linking agent in a solvent, the three raw materials can be mixed more fully.

[0094] The solvent may be any suitable organic solvent that can dissolve diisocyanate and crosslinking agent and does not react chemically with the raw materials, preferably one or more selected from tetrahydrofuran, dioxane, N,N'-dimethylformamide, N,N'-dimethylacetamide, acetone and butanone.

[0095] In one embodiment, the mass amount of the solvent is 0.5 to 2 times the mass of the diol in step (1).

[0096] The mold used in sub-step (2-2) can be selected as needed, and the present invention has no particular restrictions on the shape, material and size of the mold. For example, the shape of the mold can be a sheet shape such as a square or a circle, or a three-dimensional shape such as a sphere. For another example, the material of the mold can be stainless steel, tetrafluoroethylene, etc.

[0097] The present invention also correspondingly relates to the cross-linked polyurethane obtained by the preparation method of the present invention.

[0098] Example

[0099] The present invention is further described by enumerating specific embodiments below. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content recorded in the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the present invention equally.

[0100] Among the reagents used in the following examples: polycaprolactone diol (molecular weight 3000), polybutylene adipate diol (molecular weight 4000), polycarbonate diol (molecular weight 3000) were purchased from Huakai Resin Company; isophorone diisocyanate, diphenylmethane diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, and castor oil were produced by Admas-beta Company; glycerol and trihydroxyphenylethane were purchased from TCI Company. Tetrahydrofuran was purchased from Aladdin Company.

[0101] In order to compare the effects of the invention, a chemical combination ratio with the same component content was used to prepare the cross-linked polyurethane 1 of Example 1 of the heterogeneous long-chain network preparation strategy proposed in the present invention, and Comparative Example 1 was prepared according to a conventional method as a control material.

[0102] Example 1

[0103] Preparation of cross-linked polyurethane 1

[0104] Polycaprolactone diol (molecular weight 3000) and hexamethylene diisocyanate were mixed in a molar ratio of 4:5, and prepolymerized at 90°C for 2 hours to obtain a prepolymer. Hexamethylene diisocyanate and trihydroxyphenylethane dissolved in tetrahydrofuran (the mass is the same as that of polycaprolactone diol) were added to the prepolymer so that the molar ratio of polycaprolactone diol, hexamethylene diisocyanate, and trihydroxyphenylethane was 1:2:2 / 3, and mixed evenly to obtain a raw material composition. The raw material composition was poured into a square polytetrafluoroethylene mold, and a polymerization reaction was carried out at a temperature of 80°C for 12 hours to obtain a cross-linked polyurethane sheet with a thickness of 1 mm.

[0105] Example 2

[0106] Preparation of cross-linked polyurethane 2

[0107] Polybutylene adipate diol (molecular weight 4000) and isophorone diisocyanate were mixed in a molar ratio of 5:6, and prepolymerized at 90°C for 3 hours to obtain a prepolymer. Isophorone diisocyanate and propylene glycol dissolved in tetrahydrofuran (same mass as polybutylene adipate diol) were added to the prepolymer so that the molar ratio of polybutylene adipate diol, isophorone diisocyanate and propylene glycol was 1:3:4 / 3, and mixed evenly to obtain a raw material composition. The raw material composition was poured into a square polytetrafluoroethylene mold, and a polymerization reaction was carried out at a temperature of 90°C for 24 hours to obtain a cross-linked polyurethane sheet with a thickness of 2 mm.

[0108] Example 3

[0109] Preparation of cross-linked polyurethane 3

[0110] Polybutylene adipate diol (molecular weight 4000) and diphenylmethane diisocyanate were mixed in a molar ratio of 3:4, and prepolymerized at 90°C for 1 hour to obtain a prepolymer. Diphenylmethane diisocyanate and castor oil dissolved in tetrahydrofuran (same mass as polybutylene adipate diol) were added to the prepolymer so that the molar ratio of polybutylene adipate diol, diphenylmethane diisocyanate and castor oil was 1:2:2 / 3, and mixed evenly to obtain a raw material composition. The raw material composition was poured into a square polytetrafluoroethylene mold, and a polymerization reaction was carried out at a temperature of 90°C for 16 hours to obtain a cross-linked polyurethane sheet with a thickness of 2 mm.

[0111] Example 4

[0112] Preparation of cross-linked polyurethane 4

[0113] Polycarbonate diol (molecular weight 3000) and toluene diisocyanate were mixed in a molar ratio of 3:4, and prepolymerized at 90°C for 1 hour to obtain a prepolymer. Toluene diisocyanate and triethanolamine dissolved in tetrahydrofuran (same mass as polycarbonate diol) were added to the prepolymer so that the molar ratio of polycarbonate diol, toluene diisocyanate and triethanolamine was 1:2:2 / 3, and mixed evenly to obtain a raw material composition. The raw material composition was poured into a square polytetrafluoroethylene mold, and a polymerization reaction was carried out at a temperature of 90°C for 12 hours to obtain a cross-linked polyurethane sheet with a thickness of 2 mm.

[0114] Comparative Example 1

[0115] Polycaprolactone diol (molecular weight 3000) and hexamethylene diisocyanate were mixed in a molar ratio of 1:2, and prepolymerized at 90°C for 2 hours to obtain a prepolymer. Trihydroxyphenylethane dissolved in tetrahydrofuran was added to the prepolymer so that the molar ratio of polycaprolactone diol, hexamethylene diisocyanate and trihydroxyphenylethane was 1:2:2 / 3, and mixed evenly to obtain a raw material composition. The raw material composition was poured into a square polytetrafluoroethylene mold, and a polymerization reaction was carried out at a temperature of 80°C for 12 hours to obtain a cross-linked polyurethane sheet with a thickness of 1 mm.

[0116] <Evaluation>

[0117] 1. Crystallization performance analysis

[0118] The cross-linked polyurethane obtained in Example 1 and Comparative Example 1 was tested using a TA DSC 250 differential scanning calorimeter. The thermal history was eliminated at 70°C, and the heating and cooling rate was 10°C / min. The cooling and secondary heating curves of Example 1 and Comparative Example 1 are as follows: Figure 2 shown.

[0119] Depend on Figure 2 It can be seen that the cross-linked polyurethane 1 of Example 1 has a higher crystallization temperature and a higher melting point, which means that it has stronger crystallization performance, which is mainly due to the longer polymer chains between the cross-linking points.

[0120] 2. Mechanical properties evaluation

[0121] A UTM-1432 electronic universal testing machine (Chengde Jinjian) was used. According to GB / T 528-1998 standard, the tensile speed was 50 mm / min, the marking spacing of the tensile specimen was 20.0 ± 0.2 mm, the width was 4.0 ± 0.1 mm, and the standard thickness was 2.0 ± 0.2 mm.

[0122] The cross-linked polyurethanes obtained in Examples 1 to 4 and Comparative Example 1 were subjected to tensile property tests. Comparative Example 1 and Example 1 were compared with each other. The results of the tensile test are shown in Table 1. The tensile curves of Example 1 and Comparative Example 1 are shown in Table 1. Figure 3 shown.

[0123] Table 1

[0124] Tensile strength(MPa) Elongation at break (%) Young's modulus (MPa) <![CDATA[Toughness (MJ / m 3 )]]> Example 1 63.5±2.9 1423±55 179±8 365±16.6 Comparative Example 1 46.2±3.3 1211±39 130±9 225±20.4 Example 2 39.9±5.1 1039±58 190±12 267±36.2 Example 3 51.1±3.9 1689±66 179±9 403±25.9 Example 4 49.7±6.1 1321±41 166±5 331±29.7

[0125] From the results in Table 1, it can be seen that the cross-linked polyurethanes prepared in Examples 1 to 4 have significantly improved excellent mechanical properties compared with Comparative Example 1. In traditional elastic polymers, non-uniform cross-linked networks are not conducive to mechanical properties, but in the present invention, it is found that non-uniform long-chain networks can improve the mechanical properties of the material. This is an important innovation of the present invention.

[0126] 3. In situ stretching small-angle X-ray scattering and wide-angle X-ray scattering

[0127] Small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) tests were carried out at the 1W2A beamline of the Beijing Synchrotron Radiation Source with an exposure time of 1 min. Silver behenate, polypropylene, and zinc oxide were used for peak position calibration.

[0128] The SAXS and WAXS results of the cross-linked polyurethanes of Comparative Example 1 and Example 1 are as follows: Figure 4 and Figure 5 As shown. The SAXS results show that the scattering signal (mainly caused by crystals) of the sample is significantly weakened after yielding (at 200% strain). The WAXS results also correspond to this process. In the cross-linked polyurethane of Comparative Example 1, the weakening of the SAXS scattering signal is more serious, while it is relatively slight in Example 1. This difference may be due to the earlier stretching recrystallization of the cross-linked polyurethane of Example 1. At 800% strain, the SAXS scattering signal of the cross-linked polyurethane of Comparative Example 1 shows recovery relative to 200% strain, which is due to its recrystallization. At 800% strain, the SAXS scattering signal of the cross-linked polyurethane of Example 1 exceeds 0% strain, showing stronger stretching recrystallization than Comparative Example 1. On the WAXS curve, the recrystallization signal of Example 1 at 800% strain is also better than that of Comparative Example 1. It can be seen that for polymers with strong crystallization ability, enhancing their crystallization properties through a non-uniform long chain network can offset their sensitivity to stress concentration, thereby improving their mechanical properties.

[0129] 4. Water vapor barrier test

[0130] The water vapor barrier properties were measured using the N530G gas permeability tester (GBPI). All permeability data are the average of at least three measurements. Figure 6 The water vapor barrier test data of the cross-linked polyurethane of Example 1 and Comparative Example 1. Due to the enhancement of crystallinity, the water vapor permeability of Example 1 is 2.15*10 -13 g*cm / (cm 2 *s*Pa) is 30% lower than that of comparative example 1, and its absolute value is better than that of the common polyester material PBAT (about 4.0*10 -13 g*cm / (cm 2 *s*Pa)).

[0131] Industrial Applicability

[0132] The polyurethane material of the present invention can be widely used in packaging, structural materials, protective coatings and the like.

Claims

1. A cross-linked polyurethane, characterized in that: The cross-linked polyurethane is obtained by reacting a diol, a diisocyanate and a cross-linking agent, wherein the cross-linked polyurethane comprises one or more structures represented by the following formulas (1) to (4): Wherein B represents a diisocyanate residue, C represents a crosslinker residue, * represents the connection site between B and the crosslinker or diol, n, m, s, t represent the number of repetitions of the structure in brackets, n and s are independently integers of 0 to 10, and m and t are independently integers of 1 to 10.

2. The cross-linked polyurethane according to claim 1, characterized in that The diol is one or more selected from crystalline oligomer diols; the crystalline oligomer diol is preferably one or more selected from polycaprolactone diol, polyethylene glycol, polybutylene adipate diol, and polycarbonate diol; the number average molecular weight of the crystalline oligomer diol is 2000-5000.

3. The cross-linked polyurethane according to claim 1, characterized in that The diisocyanate is one or more selected from aliphatic diisocyanates and aromatic diisocyanates; preferably one or more selected from isophorone diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate, toluene diisocyanate, naphthalene diisocyanate, and dicyclohexylmethane diisocyanate.

4. The cross-linked polyurethane according to claim 1, characterized in that The average functionality of the cross-linking agent is greater than 2 and less than 4; preferably, the cross-linking agent is a trifunctional cross-linking agent and / or a tetrafunctional cross-linking agent; preferably, the cross-linking agent is one or more selected from triols, triamines, tetraols, and tetraamines; more preferably, it is one or more selected from glycerol, trimethylolpropane, triethanolamine, trihydroxyphenylethane, castor oil, and pentaerythritol.

5. The cross-linked polyurethane according to any one of claims 1 to 4, characterized in that The molar ratio of diol residues, diisocyanate residues and crosslinking agent residues is 1: (1-4): (0.2-3), preferably 1: (1.5-3.5): (0.3-2), more preferably 1: (1.8-2.8): (0.3-1), and further preferably 1: (2-2.5): (0.3-0.8).

6. A method for preparing a cross-linked polyurethane, characterized in that: The following steps are involved: (1) subjecting a diol to a prepolymerization reaction with a diisocyanate to obtain a prepolymer; (2) The prepolymer, diisocyanate and crosslinking agent are mixed and subjected to a curing reaction.

7. The preparation method according to claim 6, characterized in that: Step (2) includes the following sub-steps: (2-1) mixing the prepolymer, diisocyanate and cross-linking agent to obtain a mixture; (2-2) The mixture is placed in a mold to perform a curing reaction.

8. The preparation method according to claim 6 or 7, characterized in that: In step (1), the molar ratio of diol to diisocyanate is 1:(1.05-1.5), preferably 1:(1.1-1.4), and more preferably 1:(1.2-1.35); The molar ratio of the diisocyanate used in step (1) to the diisocyanate used in step (2) is 1:(0.4-2.5), preferably 1:(0.5-2); The molar ratio of the diisocyanate to the crosslinking agent used in step (2) is 1:(0.4-1.5), preferably 1:(0.6-1.3), and more preferably 1:(0.8-1.1); In the total amount used in steps (1) and (2), the molar ratio of diol, diisocyanate and cross-linking agent is 1: (1-4): (0.2-3), preferably 1: (1.5-3.5): (0.3-2), more preferably 1: (1.8-2.8): (0.3-1), and further preferably 1: (2-2.5): (0.3-0.8).

9. The preparation method according to claim 6 or 7, characterized in that: The temperature of the prepolymerization reaction is 50-120° C., and the time of the prepolymerization reaction is 0.5-6 hours; the temperature of the curing reaction is 40-120° C., and the time of the curing reaction is 6-48 hours.

10. The cross-linked polyurethane obtained by the preparation method according to any one of claims 5 to 8, characterized in that: The tensile strength of the cross-linked polyurethane is more than 35MPa, the elongation at break is more than 1000%, and the fracture toughness is 250MJ / m 3 above.

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