CN112194776B

CN112194776B - Preparation method of hydroxyl polyurethane

Info

Publication number: CN112194776B
Application number: CN202011058734.7A
Authority: CN
Inventors: 郑思珣; 赵冰洁
Original assignee: Shanghai Jiaotong University
Current assignee: Shanghai Jiaotong University
Priority date: 2020-09-30
Filing date: 2020-09-30
Publication date: 2021-10-26
Anticipated expiration: 2040-09-30
Also published as: CN112194776A

Abstract

The invention relates to a preparation method of hydroxyl Polyurethane (PHU), which firstly adopts an isocyanate route for synthesizing the traditional Polyurethane (PU) to synthesize the PHU and comprises two steps of prepolymerization and chain extension for the preparation of linear PHU. The process is as follows: first, an excess of diisocyanate-based monomer is reacted with a macrodiol to obtain an isocyanate group-terminated prepolymer. Then, a ketal (aldehyde) -protected diol chain extender is added to react with the prepolymer to obtain PU-ketal (aldehyde), and finally, the ketal (aldehyde) protecting group in the PU-ketal (aldehyde) structure is hydrolyzed into hydroxyl under acidic conditions, thereby obtaining PHU. For the preparation of crosslinked PHU, the procedure was: and (2) reacting the linear PHU with a diisocyanate monomer, and controlling the ratio of the PHU to the diisocyanate monomer to ensure that a part of hydroxyl groups are still reserved on the PHU main chain, thereby obtaining the crosslinked PHU. Compared with the prior art, the method has the advantages of simple operation, easily obtained raw materials, low economic cost and high product yield, and is suitable for large-scale industrial production.

Description

Preparation method of hydroxyl polyurethane

Technical Field

The invention belongs to the technical field of polymer material synthesis, and relates to a preparation method of hydroxyl polyurethane.

Background

Polyurethanes (PUs) are an important class of polymeric materials, widely used in coatings, adhesives, leather, foams, elastomers, and the like, and are actively used in the fields of basic traffic, electromechanical applications, aerospace, building substrates, food processing, and the like.

Currently, the preparation of polyurethanes is carried out industrially, generally by the isocyanate route, i.e. by the stepwise polymerization of polyisocyanate monomers and polyhydroxyl monomers. In addition, there are also reported methods for synthesizing polyurethanes by the so-called non-isocyanate route. Among them, in the last 90 s, the preparation of polyurethanes by reacting cyclic carbonates with primary amines has attracted a great deal of interest. The polyurethanes synthesized by this process structurally contain additional urethane-bound hydroxyl groups and are therefore also referred to as hydroxyl Polyurethanes (PHUs). The presence of a large number of hydroxyl groups on the PHU structural unit makes it exhibit more enhanced chemical stability, non-polar solvent resistance and adhesion than conventional PU. In addition, due to the existence of hydroxyl, PHU can be subjected to various functional designs and modifications, such as intelligent reversible covalent (non-covalent) bonds, introduction of functional groups with photoelectric properties and the like, and the introduction of the groups is expected to endow polyurethane materials with more new functional properties. Therefore, in recent years, PHUs have become an industry focus, and research on the preparation and structure-performance relationship of PHUs is increasing. Recently, Fortman et al reported thermosetting PHUs prepared from bis (six-membered cyclic carbonates) and polyamines that the stress of such thermosetting PHUs can relax to zero at high temperatures due to transesterification reactions between hydroxyl groups and carbamates in their structures, i.e., that they can be reprocessed at high temperatures. Torkelson et al also reported that this reprocessability is also present in biobased thermoset hydroxyl polyurethanes. The reworking performance of the PHU is expected to improve the problem that the traditional thermosetting PU is difficult to be secondarily processed and molded, thereby realizing the recycling and processing of the thermosetting polyurethane material. Therefore, it is very significant to realize industrial mass production of PHU.

For the production of PHU, the precursor cyclic carbonate used is extremely important. The current synthetic routes for cyclic carbonates can be broadly divided into two categories: high pressure processes and atmospheric processes. High pressure process namely epoxy resin-CO₂Intercalation means the utilization of CO under high temperature and pressure conditions₂And (3) a supercritical technology for catalyzing the cyclic carbonate ester to be added with epoxy resin to prepare the cyclic carbonate ester. CO 2₂The insertion method is a green, fresh, environment-friendly and simple process. However, the method has severe experimental conditions, extremely high technical requirements on equipment and the danger of flammability and explosiveness. The normal pressure method mainly comprises an o-diol-ester exchange method and chloroformic acidThe ethyl ester method, the ortho-diol-ester exchange method, uses a compound with adjacent hydroxyl as a raw material, and performs ester exchange reaction with carbonic diester under the condition of alkaline catalysis to prepare cyclic carbonate. Ethyl chloroformate is a cyclic carbonate prepared by the ring closure after dehydrochlorination by reacting a diol with ethyl chloroformate. However, the atmospheric method has been slow due to the limited choice of vicinal diols and the extreme toxicity of the ethyl chloroformate used. In addition, cyclic carbonates prepared by the atmospheric method also generally cannot prepare PHU materials with better performance due to structural activity, purity, and the like. At present, no matter the cyclic carbonate is synthesized by adopting a high pressure method or a low pressure method and is further applied to synthesis in PHU, the cyclic carbonate is still in a theoretical research state, and the cyclic carbonate cannot be applied to industrial production of polyurethane.

Chinese patent CN 109354681A discloses a PHU preparation method, which comprises the steps of firstly, using bio-based mevalonic acid or mevalonic lactone as a substrate to prepare intermediate product polyol, polycarboxylic acid or multiolefin or derivatives of the three substances; then, the obtained intermediate product is subjected to oxidation, carbon dioxide addition or dehydration condensation reaction to prepare precursor multi-element cyclic carbonate; and finally, preparing the non-isocyanate polyurethane monomer from the multiple cyclic carbonate and diamine compounds. Chinese patent CN 109369462A discloses a PHU monomer and a preparation method thereof, wherein the preparation method comprises the step of obtaining the PHU monomer by carrying out two amidation reactions on a five-membered cyclic carbonate compound, a diamine compound and an acrylic acid compound. Chinese patent CN 111484613A discloses a temperature-sensitive PHU, a preparation method and application thereof, the PHU is prepared by the reaction of soybean oil cyclic carbonate and methoxy polyethylene glycol amine, and can replace the traditional polyurethane to be applied to biomedical materials. However, the reported methods disclosed in the above patents, which all employ cyclic carbonates to react with primary amine compounds to prepare PHU, are not suitable for large-scale industrial production of PHU.

Disclosure of Invention

The object of the present invention is to overcome the above-mentioned drawbacks of the prior art and to provide a method for preparing hydroxyl polyurethane which can be industrially produced on a large scale. The crosslinked PHU synthesized by the method has heavy processability and can realize the recycling and processing of materials.

The purpose of the invention can be realized by the following technical scheme: the hydroxyl polyurethane of the invention comprises linear PHU and cross-linked PHU, wherein

For the preparation of linear PHU, two steps of prepolymerization and chain extension are adopted. The process is as follows: firstly, reacting excessive diisocyanate monomers with macrodiol to obtain isocyanate-terminated prepolymer; then, adding a ketal (aldehyde) -protected glycol chain extender to react with the prepolymer to obtain PU-ketal (aldehyde); finally, the ketal (aldehyde) protecting group in the PU-ketal (aldehyde) structure is hydrolyzed to a hydroxyl group under acidic conditions, thereby obtaining PHU.

A process for preparing a linear hydroxyl polyurethane comprising the steps of:

(1) preparation of pentaerythritol monoketal (aldehyde):

dissolving pentaerythritol and p-toluenesulfonic acid monohydrate in DMF at 60-100 ℃, standing and cooling to 30-50 ℃, dropwise adding a protective agent, stirring the mixture at 20-40 ℃ for 20-28h, adding trimethylamine, continuously stirring for 1-3h, removing DMF by rotary evaporation, dissolving the crude product in dichloromethane, washing with deionized water for three times, collecting an organic layer, adding anhydrous magnesium sulfate, drying, removing dichloromethane by rotary evaporation, and drying in a vacuum oven at 40 ℃ for 6h to obtain powdery pentaerythritol monoketal (aldehyde);

(2) preparation of isocyanate terminated prepolymer:

adding diisocyanate monomer and macrodiol into a reactor provided with a mechanical stirring and nitrogen introducing device, then adding dibutyltin dilaurate into the reactor, introducing nitrogen into the system for 0.5-1h, and reacting at 40-80 ℃ for 2-5h to obtain isocyanate-terminated prepolymer;

(3) preparation of linear PU-ketal (aldehyde):

dissolving pentaerythritol mono-ketal (aldehyde) prepared in the step (1) in an organic solvent, adding the pentaerythritol mono-ketal (aldehyde) into the prepolymer prepared in the step (2), continuously reacting at 50-100 ℃ for 4-8h, cooling to room temperature, pouring the mixture into a tetrafluoro mold, placing the tetrafluoro mold in a 60 ℃ oven for 12h to remove most of the solvent, and completely removing a small amount of residual solvent through a 60 ℃ vacuum oven for 48h to obtain linear PU-ketal (aldehyde);

(4) preparation of linear PHU:

and (3) dissolving the linear PU-ketal (aldehyde) prepared in the step (3) in an organic solvent, adding 1M HCl, continuously stirring the mixture for 2-6h, pouring into a tetrafluoro mold, placing in a 60 ℃ oven for 12h to remove most of the solvent, and completely removing a small amount of residual solvent through a 60 ℃ vacuum oven for 48h to obtain the linear PHU material.

Further, in the step (1),

the structure of the protective agent is as follows:

wherein R is₁、R₂、R₃、R₄、R₅And R₆Is H atom or alkyl with 1-8 carbon atoms;

the molar ratio of the pentaerythritol to the p-toluenesulfonic acid monohydrate to the protective agent is as follows: 98-102:1:100.

Further, in the step (2),

the diisocyanate monomer is one or more of diphenylmethane diisocyanate (MDI), Toluene Diisocyanate (TDI), Hexamethylene Diisocyanate (HDI), isophorone diisocyanate (IPDI), dicyclohexylmethane diisocyanate (HMDI) and Lysine Diisocyanate (LDI);

the macrodiol is one or more of polyether diol, polyester diol and polyolefin diol, including but not limited to polyethylene glycol (PEG), polypropylene glycol (PPG), polytetrahydrofuran diol (PTMG), polycaprolactone diol, polycarbonate diol and polybutadiene diol;

the molecular weight of the macroglycol is 1,000-3,000 Da;

the molar ratio of the diisocyanate monomer to the macrodiol is 1.5-3.0: 1;

the dibutyltin dilaurate accounts for 0.05-0.20% of the mass ratio of all the reactants.

The macrodiol comprises polyethylene glycol (PEG), polypropylene glycol (PPG), polytetrahydrofuran diol (PTMG), polycaprolactone diol or polycarbonate diol or polybutadiene diol.

Further, in the step (3),

the organic solvent is N, N-Dimethylformamide (DMF), N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO) or N-methylpyrrolidone (NMP);

the molar ratio of pentaerythritol mono-ketal (aldehyde) to the prepolymer is 0.8-1.2: 1.

Further, in the step (4),

the organic solvent is DMF, DMAc, DMSO or NMP.

The molar ratio of water to linear PU-ketal (aldehyde) in 1M HCl is 2-2.1: 1.

The invention also provides a preparation method of the crosslinked PHU, which comprises the following steps: and (3) reacting the PHU with a diisocyanate monomer, and controlling the ratio of the PHU to the diisocyanate monomer to ensure that a part of hydroxyl groups are still reserved on the PHU main chain, thereby obtaining the crosslinked PHU. The specific synthesis method comprises the following steps:

the linear PHU material prepared in the step (4) is further prepared into a cross-linked PHU through the following reaction: and (5) dissolving the linear PHU material prepared in the step (4) and diisocyanate monomer in an organic solvent, adding the organic solvent into a reactor provided with a mechanical stirring device and a nitrogen introducing device, then adding dibutyltin dilaurate into the reactor, introducing nitrogen into the system for 0.5-1h, reacting at 40-80 ℃ until gel is formed, taking out the gel, placing the gel in a 60 ℃ oven for 12h to remove most of the solvent, and completely removing the residual solvent by a 60 ℃ vacuum oven for 48h to obtain the crosslinked PHU.

Further, in the step (5), the diisocyanate monomer is MDI, TDI, HDI, IPDI, HMDI or LDI;

the organic solvent is DMF, DMAc, DMSO or NMP.

The molar ratio of hydroxyl to diisocyanate monomer in the linear PHU material structure is 1.00: 0.01-0.99.

Compared with the prior art, the invention has the advantages that:

1. the preparation method of PHU provided by the invention is simple to operate, the raw materials are easy to obtain, the economic cost is low, the product yield is high, and the method is suitable for large-scale industrial production.

2. The preparation method of the PHU provided by the invention adopts the existing industrially mature isocyanate route, can utilize the existing industrially prepared PU synthesis process, and does not need additional design.

3. The PHU prepared by the method has better performance due to higher purity and activity of the raw materials.

4. The method for preparing the PHU can flexibly adjust the performance of the prepared PHU by changing raw materials, the feed ratio and the like, and has wide application range.

5. The linear PHU provided by the invention can be subjected to various functional designs due to the existence of a large number of hydroxyl groups on the structure, and is expected to endow PHU with more and new functional characteristics.

6. The cross-linked PHU prepared by the method has the advantages that the cross-linked PHU structurally has the reworking performance due to the ester exchange reaction between hydroxyl and a carbamate bond, the problem that the traditional thermosetting polyurethane is difficult to perform secondary processing and molding can be solved, and the recycling and processing of the thermosetting polyurethane are realized, so that the cross-linked PHU has good practical significance and application prospect.

Drawings

FIG. 1 is a route for the preparation of linear PHU;

FIG. 2 is a route for the preparation of crosslinked PHU;

FIG. 3 is the NMR spectrum of pentaerythritol monoketal prepared in example 1;

FIG. 4 is the NMR spectra of linear M-PU-ketal and M-PHU prepared in example 1;

FIG. 5 is an infrared spectrum of the linear M-PU-ketal and M-PHU prepared in example 1;

FIG. 6 is a GPC curve of linear M-PU-ketal and M-PHU prepared in example 1;

FIG. 7 is a photograph showing a rework process of the crosslinked M-PHU prepared in example 2;

FIG. 8 is a stress-strain curve of the initial and three-fold reworked samples of the cross-linked M-PHU prepared in example 2.

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments.

Example 1:

the preparation route of the linear PHU is shown in figure 1, and the specific steps are as follows:

(1) preparation of pentaerythritol monoketal:

dissolving 30.00g of pentaerythritol and 0.42g of p-toluenesulfonic acid monohydrate in DMF at 80 ℃, standing and cooling to 40 ℃, dropwise adding 22.95g of 2, 2-dimethyloxypropane, stirring the mixture at 25 ℃ for 24h, adding 0.13g of trimethylamine, continuously stirring for 2h, removing DMF by rotary evaporation, dissolving the crude product in dichloromethane, washing with deionized water for three times, collecting an organic layer, adding anhydrous magnesium sulfate, drying, removing dichloromethane by rotary evaporation, and drying in a vacuum oven at 40 ℃ for 6h to obtain powdery pentaerythritol monoketal.

FIG. 3 is the NMR spectrum of the pentaerythritol monoketal. Specifically, the proton peaks at 4.48ppm, 3.58 ppm and 3.66ppm, and the proton peaks at the methylene group bonded to oxygen in the acetal structure, and the proton peaks at 1.32ppm, respectively, are the proton peaks of the methyl group in the acetal structure, indicating that the pentaerythritol monoketal compound is successfully obtained by the method.

(2) Preparation of isocyanate terminated prepolymer:

10.00g of diphenylmethane diisocyanate (MDI) and 20.00g of polytetrahydrofuran diol (PTMG, Mn. RTM. 1,000Da) were charged into a reaction vessel equipped with a mechanical stirring and nitrogen-introducing device, and dibutyltin dilaurate (0.05% by mass of the total reaction) was then charged into the flask, and after 0.5 hour of introduction of nitrogen gas into the system, the reaction was carried out at 50 ℃ for 4 hours to obtain an isocyanate-terminated prepolymer.

(3) Preparation of linear M-PU-ketal:

3.50g of pentaerythritol monoketal was dissolved in an organic solvent, added to the prepolymer obtained above, and the reaction was continued at 70 ℃ for 6 hours. After cooling to room temperature, the mixture was poured into a tetrafluoro mold and placed in a 60 ℃ oven for 12h to remove most of the solvent, and the remaining small amount of solvent was completely removed by a 60 ℃ vacuum oven for 48h to obtain linear M-PU-ketal.

(4) Preparation of linear M-PHU:

dissolving 10.00g of linear M-PU-ketal in an organic solvent, adding 0.20ml of 1M HCl, continuously stirring the mixture for 4h, pouring the mixture into a tetrafluoro mold, placing the tetrafluoro mold in a 60 ℃ oven for 12h to remove most of the solvent, and completely removing the residual small amount of the solvent through a 60 ℃ vacuum oven for 48h to obtain the linear M-PHU material.

FIG. 4 shows the NMR spectra of M-PU-ketal and M-PHU. As can be seen, for M-PU-ketal, proton peaks at 9.49 and 8.54ppm on the urethane bond; proton peaks at 7.30 and 7.11ppm on the benzene ring of the MDI component; proton peaks at 4.06 and 3.23ppm on the methylene of the ketal component; 3.78ppm is the proton peak on the methylene group of the MDI component connected to the benzene ring; 3.31 and 1.49ppm are proton peaks on methylene of PTMG component; at 1.22ppm is the proton peak on the methyl group of the ketal component. For M-PHU, the proton peak at 1.22ppm methyl on the ketal component disappeared, and the proton peak at 5.28ppm hydroxyl appeared, as seen from the nuclear magnetic results, demonstrating complete removal of the ketal protecting group.

FIG. 5 shows the IR spectrum of M-PU-ketal and M-PHU. As can be seen from the figure, first, both are at 2260cm^-1The stretching vibration peak of the characteristic of NCO group disappears completely, which indicates that the chain extension reaction is completely carried out. Secondly, 3310cm for M-PU-ketal^-1Is a stretching vibration peak of an N-H bond on the carbamate; 1736 and 1710cm^-1Respectively is a stretching vibration peak of C ═ O on an amido bond and an ester bond; 1221 and 1081cm^-1Is a C-O bond stretching vibration peak on the ester group; in the case of M-PHU, the stretching vibration of newly added O-H bond due to the formation of a large number of hydroxyl groups after removing the protecting group makes it 3310cm^-1The signal peak at the position is obviously enhanced, and a newly increased position of 1010cm-1 appearsThe C-O bond stretching vibration peak on the primary alcohol of (1).

FIG. 6 shows GPC curves of M-PU-ketal and M-PHU, respectively, and it can be seen that the number average molecular weight of the sample is 47,000Da and the molecular weight distribution index is 1.49, which indicates that the method of the present invention successfully prepares M-PHU material with high molecular weight, and the molecular weight and distribution of the sample are consistent before and after the deprotection process.

The nuclear magnetic resonance hydrogen spectrum, the infrared spectrum and the GPC result show that the linear M-PHU material with high molecular weight is successfully prepared by the method provided by the invention.

Example 2:

preparation of crosslinked M-PHU: the synthesis route diagram is shown in fig. 2, and the specific steps are as follows:

10.00g of the linear M-PHU obtained in example 1 and 0.75g of MDI were dissolved in DMF and charged into a reaction vessel equipped with a mechanical stirring and nitrogen introducing device, and then dibutyltin dilaurate (0.05% based on the total reaction mass) was added to the flask, and after introducing nitrogen into the system for 0.5 hour, the reaction was carried out at 60 ℃ until gel formation. And (3) taking out the gel, placing the gel in a 60 ℃ oven for 12h to remove most of the solvent, and completely removing the residual small amount of the solvent through a 60 ℃ vacuum oven for 48h to obtain the cross-linked M-PHU material.

FIG. 7 is a photograph of a rework process of a cross-linked M-PHU material, wherein a sample of a block of the cross-linked M-PHU material was selected and sheared to find that the sheared sample could be hot-pressed into a complete piece again under certain temperature and pressure conditions (as shown in FIG. 7). This initially demonstrates the reworkability of the cross-linked M-PHU material prepared according to the present invention at high temperatures.

In order to further prove the reworking performance of the cross-linked M-PHU prepared by the invention, the mechanical properties of the sample after multiple times of hot pressing are compared with those of the initial sample, and FIG. 8 shows the stress-strain curves of the initial sample of the cross-linked M-PHU material and the sample after multiple times of hot pressing, and it is found that even after three times of reworking, the Young modulus, the breaking strength and the breaking elongation of the sample can still return to more than 95% of the initial sample, which indicates that the M-PHU material prepared by the invention can hardly cause the loss of the mechanical properties even after multiple times of reworking and has excellent reworking performance.

Example 3:

(1) preparation of pentaerythritol monoketal:

(2) Preparation of isocyanate terminated prepolymer:

10.00g of diphenylmethane diisocyanate (MDI) and 26.67g of polytetrahydrofuran diol (PTMG, Mn. RTM. 1,000Da) were charged into a reaction vessel equipped with a mechanical stirrer and a nitrogen-introducing device, and dibutyltin dilaurate (0.05% by mass of the total reaction) was then charged into the flask, and after 0.5 hour of introduction of nitrogen gas into the system, the reaction was carried out at 50 ℃ for 4 hours to obtain an isocyanate-terminated prepolymer.

(3) Preparation of linear M-PU-ketal:

2.35g of pentaerythritol monoketal was dissolved in an organic solvent, added to the prepolymer obtained above, and the reaction was continued at 70 ℃ for 6 hours. After cooling to room temperature, the mixture was poured into a tetrafluoro mold and placed in a 60 ℃ oven for 12h to remove most of the solvent, and the remaining small amount of solvent was completely removed by a 60 ℃ vacuum oven for 48h to obtain a linear PU-ketal.

(4) Preparation of linear M-PHU:

dissolving 10.00g of linear M-PU-ketal in an organic solvent, adding 0.12ml of 1M HCl, continuously stirring the mixture for 4h, pouring the mixture into a tetrafluoro mold, placing the tetrafluoro mold in a 60 ℃ oven for 12h to remove most of the solvent, and completely removing the residual small amount of the solvent through a 60 ℃ vacuum oven for 48h to obtain the linear M-PHU material.

Example 4:

preparation of crosslinked M-PHU:

10g of the linear M-PHU obtained in example 3 and 0.43g of MDI were dissolved in DMF and charged into a reaction vessel equipped with a mechanical stirring and nitrogen introducing device, and then dibutyltin dilaurate (0.05% based on the total reaction mass) was added to the flask, and after introducing nitrogen into the system for 0.5 hour, the reaction was carried out at 60 ℃ until gel formation. And (3) taking out the gel, placing the gel in a 60 ℃ oven for 12h to remove most of the solvent, and completely removing the residual small amount of the solvent through a 60 ℃ vacuum oven for 48h to obtain the cross-linked M-PHU material.

Example 5:

(1) preparation of pentaerythritol monoketal:

(2) Preparation of isocyanate terminated prepolymer:

10.00g of diphenylmethane diisocyanate (MDI) and 13.33g of polytetrahydrofuran diol (PTMG, Mn. RTM. 1,000Da) were charged into a reaction vessel equipped with a mechanical stirrer and a nitrogen-introducing device, and dibutyltin dilaurate (0.05% by mass of the whole reaction) was then charged into the flask, and after 0.5 hour of introduction of nitrogen gas into the system, the reaction was carried out at 50 ℃ for 4 hours to obtain an isocyanate-terminated prepolymer.

(3) Preparation of linear M-PU-ketal:

4.70g of pentaerythritol monoketal was dissolved in an organic solvent, added to the prepolymer obtained above, and the reaction was continued at 70 ℃ for 6 hours. After cooling to room temperature, the mixture was poured into a tetrafluoro mold and placed in a 60 ℃ oven for 12h to remove most of the solvent, and the remaining small amount of solvent was completely removed by a 60 ℃ vacuum oven for 48h to obtain a linear PU-ketal.

(4) Preparation of linear M-PHU:

dissolving 10.00g of linear M-PU-ketal in an organic solvent, adding 0.34ml of 1M HCl, continuously stirring the mixture for 4h, pouring the mixture into a tetrafluoro mold, placing the tetrafluoro mold in a 60 ℃ oven for 12h to remove most of the solvent, and completely removing the residual small amount of the solvent through a 60 ℃ vacuum oven for 48h to obtain the linear M-PHU material.

Example 6:

preparation of crosslinked M-PHU:

10g of the linear M-PHU obtained in example 5 and 1.19g of MDI were dissolved in DMF and charged into a reaction vessel equipped with a mechanical stirrer and a nitrogen introducing device, and then dibutyltin dilaurate (0.05% based on the total reaction mass) was added to the flask, and after introducing nitrogen into the system for 0.5 hour, the reaction was carried out at 60 ℃ until gel formation. And (3) taking out the gel, placing the gel in a 60 ℃ oven for 12h to remove most of the solvent, and completely removing the residual small amount of the solvent through a 60 ℃ vacuum oven for 48h to obtain the cross-linked M-PHU material.

Examples 7 to 11:

MDI was replaced by TDI, HDI, IPDI, HMDI and LDI, respectively, and the other conditions were the same as in example 1.

Examples 12 to 16:

the PTMG was replaced with PEG, PPG, polycaprolactone diol, polycarbonate diol and polybutadiene diol, respectively, and the other conditions were the same as in example 1.

Examples 17 to 21:

MDI was replaced by TDI, HDI, IPDI, HMDI and LDI, respectively, and the other conditions were the same as in example 2.

The properties of the products obtained in the examples are shown in the table below:

the results in the table show that both linear and crosslinked PHUs prepared by the method have good mechanical properties and can reach the performance level of industrial polyurethane elastomers. Wherein, the Young modulus range of the linear PHU is 20.16-28.21MPa, the breaking strength is 9.72-16.31MPa, and the breaking elongation is 521.84-973.63%. The Young modulus range of the crosslinked PHU is 22.96-48.32MPa, the breaking strength is 12.32-21.97MPa, and the breaking elongation is 321.39-724.72%. In addition, the prior art uses a cyclic carbonate and primary amine reaction route, and the yield is only a laboratory pilot test. The invention adopts the traditional industrial isocyanate route, and the raw materials are simple and easy to obtain, so the yield can reach the industrial grade, and the large-scale industrial production can be carried out. And the crosslinked PHU provided by the invention can be processed and formed for the second time, thereby realizing the recycling and processing of the thermosetting polyurethane material.

Claims

1. A preparation method of hydroxyl polyurethane is characterized by comprising the following steps:

(1) preparation of pentaerythritol monoketal or aldehyde:

dissolving pentaerythritol and p-toluenesulfonic acid monohydrate in DMF at 60-100 ℃, standing and cooling to 30-50 ℃, dropwise adding a protective agent, stirring the mixture at 20-40 ℃ for 20-28h, adding trimethylamine, continuously stirring for 1-3h, removing DMF by rotary evaporation, dissolving the crude product in dichloromethane, washing with deionized water for three times, collecting an organic layer, adding anhydrous magnesium sulfate, drying, removing dichloromethane by rotary evaporation, and drying in a vacuum oven at 40 ℃ for 6h to obtain powdered pentaerythritol monoketal or aldehyde;

(2) preparation of isocyanate terminated prepolymer:

(3) preparation of linear PU-ketals or aldehydes:

dissolving pentaerythritol mono-ketal or aldehyde prepared in the step (1) in an organic solvent, adding the pentaerythritol mono-ketal or aldehyde into the prepolymer prepared in the step (2), continuously reacting at 50-100 ℃ for 4-8h, cooling to room temperature, pouring the mixture into a tetrafluoro mold, placing the tetrafluoro mold in a 60 ℃ oven for 12h to remove most of the solvent, and completely removing a small amount of residual solvent through a 60 ℃ vacuum oven for 48h to obtain linear PU-ketal or aldehyde;

(4) preparation of linear PHU:

and (3) dissolving the linear PU-ketal or aldehyde prepared in the step (3) in an organic solvent, adding 1M HCl, continuously stirring the mixture for 2-6h, pouring into a tetrafluoro mold, placing in a 60 ℃ oven for 12h to remove most of the solvent, and completely removing a small amount of residual solvent through a 60 ℃ vacuum oven for 48h to obtain the linear PHU material.

2. The process of claim 1, wherein in step (1),

the structure of the protective agent is as follows:

or

Wherein R is₁、R₂、R₃、R₄、 R₅And R₆Is H atom or alkyl with 1-8 carbon atoms;

the molar ratio of the pentaerythritol to the p-toluenesulfonic acid monohydrate to the protective agent is as follows: 98-102:1: 100.

3. The process of claim 1, wherein in step (2),

the macrodiol is one or more of polyether diol, polyester diol and polyolefin diol, and comprises polyethylene glycol (PEG), polypropylene glycol (PPG), polytetrahydrofuran diol (PTMG), polycaprolactone diol, polycarbonate diol or polybutadiene diol;

the molecular weight of the macroglycol is 1,000-3,000 Da;

the molar ratio of the diisocyanate monomer to the macrodiol is 1.5-3.0: 1;

4. The method of claim 3, wherein the macrodiol is polyethylene glycol (PEG), polypropylene glycol (PPG), polytetrahydrofuran glycol (PTMG), polycaprolactone diol or polycarbonate diol or polybutadiene diol.

5. The process of claim 1, wherein in step (3),

the molar ratio of the pentaerythritol monoketal or aldehyde to the prepolymer is 0.8-1.2: 1.

6. The process of claim 1, wherein in step (4),

the organic solvent is DMF, DMAc, DMSO or NMP;

the molar ratio of water to linear PU-ketal or aldehyde in the 1M HCl is 2-2.1: 1.

7. A method for further preparing a crosslinked PHU based on the preparation method of hydroxyl polyurethane as claimed in claim 1, wherein the linear PHU material prepared in step (4) is further prepared into a crosslinked PHU by the following reaction:

dissolving the linear PHU material prepared in the step (4) and diisocyanate monomer in an organic solvent, adding the organic solvent and diisocyanate monomer into a reactor provided with a mechanical stirring device and a nitrogen introducing device, then adding dibutyltin dilaurate into the reactor, introducing nitrogen into the system for 0.5-1h, reacting at 40-80 ℃ until gel is formed, taking out the gel, placing the gel in a 60 ℃ drying oven for 12h to remove most of the solvent, and completely removing a small amount of residual solvent through a 60 ℃ vacuum drying oven for 48h to obtain the crosslinked PHU.

8. The method of claim 7, wherein the linear PHU material has a hydroxyl to diisocyanate monomer molar ratio of 1.00: 0.01-0.99.