Low pressure variable processing ppdi-based tpu and method for preparing the same

Abstract

The application discloses a low-pressure variable processing PPDI-based TPU and a preparation method thereof. A simple preparation process is used to synthesize a thermal reversible Diels-Alder bond to overcome the shortcomings of PPDI-based elastomers, such as difficult plasticization in processing, easy degradation at high temperature and the like. The application selects p-phenylene diisocyanate as an isocyanate component, adopts a prepolymer method to pour into a shape, and realizes thermal reversible crosslinking of the PPDI-based elastomer by synthesizing a ternary alcohol monomer containing the Diels-Alder bond for chain extension. The obtained elastomer has a low compression permanent deformation and is easy to be plasticized and molded.

Description

Technical Field

[0001] This invention relates to the field of terephthalic diisocyanate (PPDI)-based thermoplastic polyurethane elastomers (TPU), specifically to a low-compression-deformation (compression permanent deformation) easily processable PPDI-based TPU and its preparation method. Background Technology

[0002] Polyurethane is a block copolymer composed of alternating soft and hard segments. It has advantages such as easy structure design and adjustable mechanical properties. Among them, the soft segments composed of oligomeric polyols with low glass transition temperatures provide elasticity to the material, while the hard segments composed of diisocyanates and small molecule chain extenders with high melting points play the role of physical crosslinking and reinforcing fillers, giving the material good dimensional stability and load-bearing capacity.

[0003] PPDI, as a special diisocyanate, has a highly symmetrical molecular structure. In the preparation of polyurethane elastomers, it easily forms dense hard segments and good microphase separation, giving polyurethane elastomers excellent thermal stability, dynamic properties and comprehensive mechanical properties.

[0004] The introduction of chemical crosslinking structures can effectively regulate the comprehensive mechanical properties of thermoplastic polyurethane elastomers (TPU). Trimethylolpropane (TMP) is often used as a crosslinking agent for TPU, which can significantly improve the modulus and deformation recovery ability, and reduce the compression set of the elastomer. The patent specification with publication number CN105037676A discloses a TMP-crosslinked low-pressure variable casting type PPDI-based polyurethane elastomer and its preparation method. The elastomer can be directly used to obtain polyurethane products by curing in a mold for 20-48 hours. However, due to the presence of irreversible crosslinking components, it is difficult to use the product for subsequent thermoplastic processing.

[0005] Diels-Alder is a cycloaddition reaction between dienes and dienophiles, which can generate cyclohexane derivatives. The forward reaction of the Diels-Alder covalent bond occurs at a relatively low temperature, while the reverse reaction occurs at high temperatures, regenerating the dienophile and diene functional groups. Introducing furan groups (dienes) and maleimide functional groups (dienophiles) into the synthesis of polyurethane elastomers can induce the Diels-Alder reaction, allowing for the presence of thermally reversible cross-linked covalent bonds in the polyurethane. This introduces a cross-linked structure while simultaneously imparting certain thermally reversible properties. Patents such as CN111440269A, CN105949469A, and CN108440735A describe methods for preparing polymer materials based on the Diels-Alder reaction. However, conventional Diels-Alder reactions suffer from cumbersome preparation processes, requiring the formation or modification of polyurethane in a solvent, resulting in low efficiency and hindering large-scale product promotion. Summary of the Invention

[0006] This invention provides a method for preparing a low-pressure, easily processable PPDI-based TPU. By using a simple preparation process to synthesize thermally reversible Diels-Alder bonds, the method overcomes the disadvantages of PPDI-based elastomers, such as difficulty in processing and plasticizing and easy degradation at high temperatures. Terephthalic diisocyanate is selected as the isocyanate component, and prepolymer casting is used for molding. By synthesizing triol monomers containing Diels-Alder bonds for chain extension, thermally reversible crosslinking of PPDI-based elastomers is achieved. The resulting elastomer has low compression set while being easy to plasticize and process.

[0007] The specific technical solution is as follows:

[0008] A method for preparing a low-pressure variable processable PPDI-based TPU involves uniformly dispersing a small molecule diol chain extender, a triol chain extender containing a Diels-Alder structure, and a catalyst into an NCO-terminated PPDI-based polyurethane prepolymer, then casting them together into a mold and curing at 100–110°C to obtain the low-pressure variable processable PPDI-based TPU.

[0009] Triols containing the Diels-Alder structure act as thermally reversible crosslinking agents in chain extension reactions. During high-temperature heating and plasticization, the Diels-Alder bonds can break, avoiding excessively high crosslinking density that would lead to difficulties in material processing. At the same time, the Diels-Alder bonds can be regenerated after the material is plasticized and molded, ensuring that the material still has a crosslinked structure when used. Furthermore, the chain extension of diols can also prevent the material viscosity from being too low due to the breakage of the Diels-Alder bonds during high-temperature processing, ensuring that the material still has sufficient melt strength when injection molded.

[0010] In a preferred embodiment, the molar ratio of the small molecule diol chain extender to the triol chain extender containing the Diels-Alder structure is 1:0.2-1 in the method for preparing the low-pressure variable-processability PPDI-based TPU. Using the above-mentioned ratio of small molecule diol and triol containing the Diels-Alder structure as chain extenders ensures that the linear small molecule diol provides sufficient reactivity in the chain extension reaction, while the crosslinking density can be adjusted by the amount of triol added, thereby effectively controlling the mechanical properties and compression set.

[0011] In the method for preparing the low-pressure variable-processing PPDI-based TPU, the small molecule diol chain extender can be selected from at least one of ethylene glycol, 1,2-propanediol, 1,3-propanediol, butanediol, and hexanediol.

[0012] The catalyst in the method for preparing the low-pressure variable processable PPDI-based TPU can be selected from at least one of dibutyltin dilaurate, stannous octoate, bismuth neodecanoate, and bismuth naphthenate.

[0013] In a preferred embodiment, the method for synthesizing the triol chain extender containing the Diels-Alder structure includes: reacting furfuryl alcohol and tris(2-maleimide ethyl)amine (TMEA) under reflux in toluene at 105-110°C, and washing the resulting precipitate with diethyl ether and vacuum drying to obtain the triol chain extender containing the Diels-Alder structure.

[0014] The reaction formula for the above synthesis method can be represented as follows:

[0015]

[0016] Furthermore, the molar ratio of furfuryl alcohol to tris(2-maleimide ethyl)amine is preferably 3 to 3.5:1.

[0017] In a preferred embodiment, the method for preparing the NCO-terminated PPDI-based polyurethane prepolymer includes: reacting oligomeric polyols with PPDI at 70-80°C, and then vacuum degassing after reaching the designed NCO content to obtain the NCO-terminated PPDI-based polyurethane prepolymer.

[0018] The molecular weight of the oligomeric polyol can be 1000–2000 g / mol.

[0019] The oligomeric polyol may be selected from at least one of polytetramethylene ether polyol, polycaprolactone polyol, polycarbonate polyol, polyadipate polyol, polyether ester copolyol, polyethylene glycol, and polypropylene glycol.

[0020] In a preferred embodiment, in the preparation method of the NCO-terminated PPDI-based polyurethane prepolymer, the oligomeric polyol is first vacuum dehydrated at 100-120°C until the water content is below 200 ppm, and then cooled to 70-80°C to react with PPDI.

[0021] In the above method for preparing NCO-terminated PPDI-based polyurethane prepolymer, PPDI can be slightly in excess to ensure that the PPDI-based polyurethane prepolymer is NCO-terminated, and the hardness and processing temperature of the product can be controlled by the mass fraction of the NCO-terminated prepolymer. The mass fraction of the NCO-terminated prepolymer is preferably 3% to 8%.

[0022] The present invention also provides a low-pressure variable processable PPDI-based TPU prepared by the preparation method described above.

[0023] The R value (molar ratio of isocyanate to hydroxyl groups) of the low-pressure variable processable PPDI-based TPU prepared by this invention can be 0.9 to 1.1:1.

[0024] The low-pressure variable-processable PPDI-based TPU prepared by this invention can be further crushed into granules after demolding. After these PPDI-based TPU granules are sold to customers, the customers can further heat and plasticize them to make the desired polyurethane products.

[0025] Compared with the prior art, the beneficial effects of this invention are as follows:

[0026] 1. This invention is the first to propose using triols containing Diels-Alder structures as chain extenders. The triol monomers synthesized by the Diels-Alder reaction are directly used in the two-step prepolymer chain extension reaction of polyurethane elastomers. This avoids the disadvantages of the previous method of introducing Diels-Alder bonds into polyurethane elastomers, such as cumbersome reaction process and the need to carry it in a solvent. The synthesis process of this invention is simple, the polymerization efficiency is high, and it is easy to achieve mass production.

[0027] 2. This invention uses sufficient or even excessive amounts of furfuryl alcohol and trifunctional tris(2-maleimide ethyl)amine to carry out a Diels-Alder reaction, thereby achieving three-dimensional network crosslinking between macromolecular chains in PPDI-based polyurethane elastomers. This improves the dynamic mechanical properties of the elastomers and can effectively reduce the compression set of the material under medium and high temperature conditions.

[0028] 3. The crosslinking bonds introduced by the Diels-Alder reaction in the PPDI-based elastomer of this invention are thermally reversible. At temperatures above 120°C, a reverse reaction will occur to regenerate the original groups, which changes the crosslinking network structure and can reduce the subsequent processing temperature of the material. This avoids the problems of excessively high melting point, processing difficulties, and material degradation caused by excessively high processing temperature in current PPDI-based elastomers due to increased crosslinking density. It also makes it easy to achieve plastic molding of crosslinked PPDI-based elastomers. Detailed Implementation

[0029] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0030] The triol chain extenders containing the Diels-Alder structure in the following examples were all prepared by the following method:

[0031] 386g of tris(2-maleimide ethyl)amine (TMEA) was added to a 2L three-necked flask equipped with a condenser and a magnetic stirrer. Anhydrous toluene was added until TMEA was completely dissolved. Then, 323g of furfuryl alcohol was added, and the mixture was refluxed at 110°C for 24 hours until the Diels-Alder reaction was complete. After the reaction solution was cooled to room temperature, the precipitate was washed several times with anhydrous diethyl ether. Finally, the obtained product was placed in a vacuum oven at 40°C for 5 days to completely remove residual solvent. After that, it was ground and dried to obtain a triol monomer containing the Diels-Alder structure.

[0032] Example 1

[0033] (a) Take 1000g of polytetramethylene ether polyol with a molecular weight of 2000g / mol and dehydrate it under vacuum at 100℃ for 2h to reduce the moisture content to below 200ppm. After cooling to 70℃, add 194g of PPDI and control the experimental temperature in the range of 70-80℃ to react for 3h. After the NCO content reaches 5wt%, degas under vacuum to obtain NCO-terminated PPDI-based prepolymer.

[0034] (b) 202.3g of triol chain extender containing Diels-Alder structure was added to 1000g of prepolymer and stirred evenly. Then 26.8g of butanediol and 0.25g of stannous octoate were added and stirred evenly. The mixture was then quickly poured into a preheated mold and cured at 100°C for 24h. The mold was then removed and demolded to obtain PPDI-based TPU containing thermally reversible crosslinking bonds.

[0035] Example 2

[0036] (a) Take 1000g of polytetramethylene ether polyol with a molecular weight of 1000g / mol and dehydrate it under vacuum at 100℃ for 2h to reduce the moisture content to below 200ppm. After cooling to 70℃, add 230g of PPDI and control the experimental temperature in the range of 70-80℃ to react for 3h. After the NCO content reaches 3wt%, degas under vacuum to obtain NCO-terminated PPDI-based prepolymer.

[0037] (b) 77.1g of a triol chain extender containing a Diels-Alder structure was added to 1000g of prepolymer and stirred until homogeneous. Then, 26.8g of hexanediol and 0.3g of dibutyltin dilaurate were added and stirred quickly until homogeneous. The mixture was then rapidly poured into a preheated mold and cured at 100°C for 24 hours before being removed from the mold to obtain PPDI-based TPU containing thermally reversible crosslinking bonds.

[0038] Example 3

[0039] (a) Take 1000g of polycaprolactone polyol with a molecular weight of 2000g / mol and dehydrate it under vacuum at 120℃ for 2h to reduce the moisture content to below 200ppm. After cooling to 70℃, add 194g of PPDI and control the experimental temperature within the range of 70-80℃ to react for 2h. After the NCO content reaches 5wt%, degas under vacuum to obtain NCO-terminated PPDI-based prepolymer.

[0040] (b) 202.3g of triol chain extender containing Diels-Alder structure was added to 1000g of prepolymer and stirred evenly. Then, 26.8g of butanediol and 0.2g of stannous octoate were added and stirred evenly. The mixture was then quickly poured into a preheated mold and cured at 100°C for 24 hours before being removed from the mold. Finally, PPDI-based TPU containing thermally reversible crosslinking bonds was obtained.

[0041] Example 4

[0042] (a) Take 1000g of polybutylene adipate polyol with a molecular weight of 2000g / mol and dehydrate it under vacuum at 100℃ for 2h to reduce the moisture content to below 200ppm. After cooling to 70℃, add 219g of PPDI and control the experimental temperature in the range of 70-80℃ for 2h. After the NCO content reaches 6wt%, degas under vacuum to obtain NCO-terminated PPDI-based prepolymer.

[0043] (b) 227.2g of a triol chain extender containing a Diels-Alder structure was added to 1000g of prepolymer and stirred until homogeneous. Then, 37.6g of butanediol and 0.3g of bismuth neodecanoate were added and stirred quickly until homogeneous. The mixture was then rapidly poured into a preheated mold and cured at 100°C for 24 hours before being removed from the mold. Finally, PPDI-based TPU containing thermally reversible crosslinking bonds was obtained.

[0044] Example 5

[0045] (a) Take 1000g of polycarbonate polyol with a molecular weight of 2000g / mol and dehydrate it under vacuum at 120℃ for 2h to reduce the moisture content to below 200ppm. After cooling to 70℃, add 274g of PPDI and control the experimental temperature within the range of 70-80℃ to react for 2h. After the NCO content reaches 8wt%, degas under vacuum to obtain NCO-terminated PPDI-based prepolymer.

[0046] (b) 330.4g of a triol chain extender containing a Diels-Alder structure was added to 1000g of prepolymer and stirred until homogeneous. Then, 30.2g of ethylene glycol and 0.2g of stannous octoate were added and stirred quickly until homogeneous. The mixture was then rapidly poured into a preheated mold and cured at 100°C for 24 hours before being removed from the mold. Finally, PPDI-based TPU containing thermally reversible crosslinking bonds was obtained.

[0047] Example 6

[0048] (a) Take 1000g of polypropylene glycol with a molecular weight of 1000g / mol and dehydrate it under vacuum at 100℃ for 2h to reduce the moisture content to below 200ppm. After cooling to 70℃, add 230g of PPDI and control the experimental temperature in the range of 70-80℃ to react for 3h. After the NCO content reaches 3wt%, degas under vacuum to obtain NCO-terminated PPDI-based prepolymer.

[0049] (b) 36.8g of a triol chain extender containing a Diels-Alder structure was added to 1000g of prepolymer and stirred evenly. Then, 24.4g of butanediol and 0.25g of stannous octoate were added and stirred evenly. The mixture was then quickly poured into a preheated mold and cured at 100°C for 24 hours before being removed from the mold. Finally, PPDI-based TPU containing thermally reversible crosslinking bonds was obtained.

[0050] Comparative Example 1

[0051] (a) 356 g of N,N-bismaleimide diphenylmethane (BMI) was added to a 2 L three-necked flask equipped with a condenser and magnetic stirrer. Anhydrous toluene was added until the BMI was completely dissolved. Then, 216 g of furfuryl alcohol was added, and the mixture was refluxed at 110 °C for 24 h until the Diels-Alder reaction was complete. After the reaction solution was cooled to room temperature, the precipitate was washed several times with anhydrous diethyl ether. Finally, the obtained product was placed in a vacuum oven at 40 °C for 5 days to completely remove residual solvent. After that, it was ground and dried to obtain a diol monomer containing the Diels-Alder structure.

[0052] (b) Take 1000g of polytetramethylene ether polyol with a molecular weight of 2000g / mol and dehydrate it under vacuum at 100℃ for 2h to reduce the moisture content to below 200ppm. After cooling to 70℃, add 194g of PPDI and control the experimental temperature in the range of 70-80℃ to react for 3h. After the NCO content reaches 5wt%, degas under vacuum to obtain NCO-terminated PPDI-based prepolymer.

[0053] (c) 330g of a diol chain extender containing a Diels-Alder structure was added to 1000g of prepolymer and stirred evenly. Then 0.25g of stannous octoate was added and stirred rapidly. The mixture was then quickly poured into a preheated mold and cured at 100°C for 24 hours before being removed from the mold. Finally, PPDI-based TPU containing thermally reversible crosslinking bonds was obtained.

[0054] Comparative Example 2

[0055] (a) Take 1000g of polytetramethylene ether polyol with a molecular weight of 2000g / mol and dehydrate it under vacuum at 100℃ for 2h to reduce the moisture content to below 200ppm. After cooling to 70℃, add 194g of PPDI and control the experimental temperature in the range of 70-80℃ to react for 3h. After the NCO content reaches 5wt%, degas under vacuum to obtain PPDI-based prepolymer.

[0056] (b) Weigh 53.6g of butanediol and 0.25g of stannous octoate and add them to 1000g of prepolymer. Stir quickly until homogeneous, then pour into a preheated mold. After curing at 100°C for 24 hours, remove from the mold to obtain PPDI-based TPU.

[0057] Comparative Example 3

[0058] (a) Take 1000g of polytetramethylene ether polyol with a molecular weight of 2000g / mol and dehydrate it under vacuum at 100℃ for 2h to reduce the moisture content to below 200ppm. After cooling to 70℃, add 194g of PPDI and control the experimental temperature in the range of 70-80℃ to react for 3h. After the NCO content reaches 5wt%, degas under vacuum to obtain PPDI-based prepolymer.

[0059] (b) Weigh 26.8g butanediol, 39.9g trimethylolpropane (TMP) and 0.25g stannous octoate and add them to 1000g of prepolymer. Stir quickly until homogeneous, then pour into a preheated mold. After curing at 100°C for 24 hours, remove from the mold to obtain PPDI-based TPU.

[0060] The PPDI-based TPU obtained in each embodiment and comparative example was crushed into granules and thoroughly dried. The granules were then injection molded into polyurethane products of the desired shape, and the performance was tested. The results are shown in Table 1.

[0061] Table 1

[0062]

[0063] As can be seen from the performance data of each embodiment and comparative example, introducing a triol containing a Diels-Alder structure as a chain extender into PPDI-based TPU results in a lower processing temperature. Compared with the diol with the same structure introduced in Comparative Example 1 and the conventional linear diol chain extender in Comparative Example 2, the triol chain extender can effectively reduce the compressive strength of the material. Furthermore, the PPDI-based TPU containing the Diels-Alder triol structure not only exhibits excellent compressive strength at low and medium temperatures of 70°C, but also maintains very low compressive strength when tested at high temperatures of 100°C. This is of great significance for expanding its practical application range and increasing its durability at high temperatures. Compared with the thermosetting TMP chain extender in Comparative Example 3, the thermally reversibly crosslinked Diels-Alder triol has better processing performance and can be processed and molded at lower temperatures, avoiding performance degradation due to material degradation.

Claims

1. A method for preparing a low-pressure, easily processable PPDI-based TPU, characterized in that, Small molecule diol chain extender, triol containing Diels-Alder structure and catalyst are uniformly dispersed into NCO-terminated PPDI-based polyurethane prepolymer, and then poured together into a mold and cured at 100-110°C to obtain the low-pressure variable processable PPDI-based TPU. The molar ratio of the small molecule diol chain extender to the triol containing the Diels-Alder structure is 1:0.2 to 1; The method for synthesizing the triol containing the Diels-Alder structure includes: refluxing furfuryl alcohol and tris(2-maleimide ethyl)amine in toluene at 105-110°C, washing the resulting precipitate with diethyl ether and drying under vacuum to obtain the triol containing the Diels-Alder structure; the molar ratio of furfuryl alcohol to tris(2-maleimide ethyl)amine is 3-3.5:

1.

2. The method for preparing low-pressure variable-processing PPDI-based TPU according to claim 1, characterized in that, The small molecule diol chain extender is selected from at least one of ethylene glycol, 1,2-propanediol, 1,3-propanediol, butanediol, and hexanediol.

3. The method for preparing low-pressure variable-processing PPDI-based TPU according to claim 1, characterized in that, The catalyst is selected from at least one of dibutyltin dilaurate, stannous octoate, bismuth neodecanoate, and bismuth naphthenate.

4. The method for preparing low-pressure variable-processing PPDI-based TPU according to claim 1, characterized in that, The preparation method of the NCO-terminated PPDI-based polyurethane prepolymer includes: reacting oligomeric polyol with PPDI at 70-80°C, and then vacuum degassing after reaching the designed NCO content to obtain the NCO-terminated PPDI-based polyurethane prepolymer; the mass fraction of the NCO terminator is 3%-8%.

5. The method for preparing low-pressure variable-processing PPDI-based TPU according to claim 4, characterized in that, The molecular weight of the oligomeric polyol is 1000-2000 g / mol; The oligomeric polyol is selected from at least one of polytetramethylene ether polyol, polycaprolactone polyol, polycarbonate polyol, polyadipate polyol, polyether ester copolyol, polyethylene glycol, and polypropylene glycol.

6. The method for preparing low-pressure variable-processing PPDI-based TPU according to claim 4 or 5, characterized in that, In the preparation method of the NCO-terminated PPDI-based polyurethane prepolymer, the oligomeric polyol is first vacuum dehydrated at 100-120°C until the water content is below 200 ppm, and then cooled to 70-80°C to react with PPDI.

7. The low-pressure variable-processable PPDI-based TPU prepared by the preparation method according to any one of claims 1 to 6.

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