CN114874129B - Preparation method of low-temperature Gao Xiaojie-sealable closed isocyanate - Google Patents

Abstract

The invention discloses a preparation method of closed isocyanate capable of being sealed at low temperature Gao Xiaojie, which comprises the following preparation steps: the N-hydroxyphthalimide compound reacts with isocyanate at room temperature under the condition of no catalyst to obtain the blocked isocyanate. The blocked isocyanate prepared by the invention has dynamic thermal reversibility, is stable at room temperature, can be spontaneously dissociated into isocyanate and N-hydroxyphthalimide (class compound) when placed under the condition of more than or equal to 80 ℃, and can be dissociated into isocyanate and N-hydroxyphthalimide (class compound) by about 50% when the temperature is raised to 120 ℃ to reach dynamic balance. Namely, the blocked isocyanate prepared by the invention can realize efficient deblocking only at a lower temperature, and the deblocking rate is far higher than that of the existing oxime blocking agent, and meanwhile, the blocked isocyanate has good light stability. The preparation method has mild conditions, does not need harsh conditions, has simple process and has wide application prospect.

Description

A method for preparing blocked isocyanate capable of being deblocked at low temperature and with high efficiency

Technical Field

The invention belongs to the technical field of blocked isocyanate, and particularly relates to a method for preparing a blocked isocyanate which can be deblocked at low temperature and with high efficiency.

Background technique

Isocyanate is the main material for synthesizing polyurethane. Synthetic polyurethane products are flexible, diverse and have excellent performance. They are made into products such as foam plastics, elastomers, fibers, coatings, adhesives and synthetic leather. They are widely used in production and life, medical care, health care, and national defense. They are known as the "fifth plastic."

Isocyanate (-NCO) has a high reactivity due to its unique structure. It can not only react with compounds containing active hydrogen, but also react with itself to form dimers or trimers. As a result, isocyanate compounds have problems such as short storage period, high requirements for use conditions, and inability to produce continuously. To address this problem, isocyanate (-NCO) can be blocked by a blocking agent to form a stable blocked isocyanate, so that it loses the ability to react with other groups under storage conditions, thereby preventing the isocyanate from reacting with active hydrogen. When used, the blocked isocyanate undergoes a reverse reaction under appropriate conditions to release -NCO, allowing it to react with the target active hydrogen compound to form a polyurethane material. In recent years, blocked isocyanates have been widely used in coatings and waterborne polyurethanes.

At present, the commonly used blocking agents in practical applications can be roughly divided into the following five categories: 1) alcohol blocking agents, which have relatively high stability, but require the addition of catalysts during the blocking process, and require a higher temperature for deblocking; 2) phenol blocking agents, which have a lower deblocking temperature, but most of these blocking agents react slowly with isocyanates; 3) amines and amides, which have very high deblocking temperatures; 4) oxime blocking agents, which have much lower deblocking temperatures than phenols and alcohols due to the higher reactivity of oxime groups with isocyanate groups than alcohols and phenols, and have a wider range of applications, but have poor light stability and unsatisfactory deblocking efficiency (only 11% of oxime aminoesters return to isocyanates and oximes when equilibrium is reached at 120°C as monitored by variable temperature nuclear magnetic resonance); 5) caprolactam blocking agents, which have unsatisfactory deblocking efficiency, with only about 10% dissociating back to the raw materials when equilibrium is reached at 120°C. It can be seen that although the above-mentioned isocyanate blocking agents have made great progress, there are still many problems, such as: (a) a catalyst needs to be added during the blocking process, and generally organic metals or organic amines are used as catalysts, such as dibutyltin dilaurate, stannous octoate, triethylamine, triethyleneimine, etc. Such catalysts are often highly toxic and will bring certain restrictions to the application of the prepared polyurethane products; the deblocking temperature is high, that is, it requires high energy consumption, and also affects the stability of the polyurethane material; (b) the deblocking efficiency is low, resulting in a waste of resources; (c) the light stability is poor, which may cause the polyurethane material prepared by the blocked isocyanate to change color when used for a long time. The existence of the above problems has, to a certain extent, limited the application and promotion of polyurethane materials using isocyanate as raw materials.

Summary of the invention

In view of the problems existing in existing blocking agents, such as the need for a catalyst during blocking, low unblocking efficiency and poor light stability, the present invention proposes to use N-hydroxyphthalimide compounds as blocking agents to block isocyanate, and prepare a blocked isocyanate that can be unblocked efficiently at low temperature. Specifically, the nitrogen hydroxyl group in the N-hydroxyphthalimide compounds is reacted with the isocyanate group (NCO) to achieve the blocking of the isocyanate group.

To achieve the above purpose, the technical solution adopted by the present invention is as follows:

A method for preparing a blocked isocyanate that can be efficiently unblocked at low temperature, comprising the steps of: reacting an N-hydroxyphthalimide compound represented by the following general formula (II) with an isocyanate in the absence of a catalyst to obtain a blocked isocyanate, the general structural formula of which is shown in formula (I):

In the formula, R1 is independently selected from H, an unsubstituted or substituted alkyl group, an unsubstituted or substituted aromatic group, an unsubstituted or substituted alkoxy group, and an unsubstituted or substituted heteroatom substituent; R2 is independently selected from a polyisocyanate formed by one or more of aliphatic isocyanate, alicyclic isocyanate, aromatic aliphatic isocyanate, aromatic isocyanate and heterocyclic isocyanate, wherein the isocyanate group is removed; and x is independently selected from an integer of 1 to 10.

Preferably, the molar ratio of the N-hydroxyphthalimide compound to the isocyanate is 1 to 3:1.

Preferably, the reaction is carried out at room temperature.

Preferably, the alkyl group is a hydrocarbon group having 1 to 20 carbon atoms, and more preferably an alkyl group having 1 to 12 carbon atoms and an aryl group having 6 to 12 carbon atoms; particularly preferably, a chain alkyl group having 1 to 12 carbon atoms and a cyclic alkyl group having 3 to 12 carbon atoms; as the chain alkyl group having 1 to 12 carbon atoms, examples include straight-chain or branched chain alkyl groups having 1 to 12 carbon atoms, for example, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, isopentyl, hexyl, heptyl, octyl, nonyl, isononyl, decyl, undecyl, dodecyl and the like.

Preferably, the aliphatic isocyanate is a linear aliphatic monoisocyanate or polyisocyanate having 3 to 10 carbon atoms; for example, n-octyl isocyanate, n-butyl isocyanate, propyl isocyanate, hexamethylene diisocyanate, 1,3-propylene diisocyanate, 1,2-propylene diisocyanate, 1,4-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, 1,6-hexamethylene diisocyanate, etc.

Preferably, the aromatic isocyanate is any one of 2-phenylethyl isocyanate, toluene diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, diphenylmethane diisocyanate, 4,4'-toluidine diisocyanate, and 4,4'-diphenyl ether diisocyanate.

Preferably, the alicyclic isocyanate is any one of isophorone diisocyanate, 1,3-cyclopentane diisocyanate, 1,3-cyclopentene diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, and norbornane diisocyanate.

Preferably, the aromatic aliphatic isocyanate is any one of xylylene diisocyanate and tetramethylxylylene diisocyanate.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The present invention uses N-hydroxyphthalimide compounds as blocking agents to react with isocyanate at room temperature without a catalyst to prepare blocked isocyanate that can be unblocked at low temperature and efficiently, namely, N-hydroxyphthalimide amino ester compounds. The N-hydroxyphthalimide amino ester compounds have dynamic thermal reversibility and are relatively stable at room temperature. When placed under conditions of ≥80°C, they can spontaneously dissociate into isocyanate and N-hydroxyphthalimide (compounds). When the temperature is raised to 120°C to reach equilibrium, about 50% of the blocked isocyanate dissociates into isocyanate and N-hydroxyphthalimide (compounds). That is, the blocked isocyanate prepared by the present invention can be unblocked efficiently at a relatively low temperature, and the unblocking rate is much higher than that of the existing oxime blocking agents (unblocking efficiency is 11%), and also has good light stability.

(2) The preparation method of the present invention has mild conditions and does not require harsh reaction conditions (such as high temperature, organic base and metal catalyst, etc.). The process is simple and has broad application prospects.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

FIG1 is a schematic diagram of the general structural formula of a blocked isocyanate prepared in the present invention;

FIG2 is a variable temperature H-NMR spectrum of the blocked isocyanate prepared in the present invention under thermal stimulation conditions in a thermal dissociation experiment;

FIG3 is the NMR spectra of various substances in the dynamic exchange experiment;

FIG4 is a hydrogen NMR spectrum of the blocked isocyanate prepared in the present invention under thermal stimulation conditions in a dynamic exchange experiment.

Detailed ways

In the following description, for the purpose of illustration rather than limitation, specific details such as specific system structures and technologies are provided to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may also be implemented in other embodiments without these specific details.

Example 1

N-hydroxyphthalimide (163.0 mg, 1.0 mmol) was dissolved in 20 mmL of anhydrous tetrahydrofuran, and an equivalent amount of 2-phenylethyl isocyanate (147.0 mg, 1.0 mmol) was added. After stirring at room temperature for 3 h, the solvent was removed by distillation under reduced pressure to obtain a white solid BI-1, 308.0 g, with a yield of 99%.

Characterization results: ¹ H NMR (400 MHz, CDCl ₃ , ppm) δ8.30 (br, 1H), 8.22-8.16 (m, 5H), 8.04-7.95 (m, 4H), 3.22-3.06 (m, 2H), 1.83-1.77 (m, 2H); ESI-HRMS Calcd for C ₁₇ H ₁₄ N ₂ O ₄ Na[M+H] ⁺ : 333.0851, Found: 333.0856, Error: 0.5ppm.

Example 2

N-hydroxyphthalimide (163.0 mg, 1.0 mmol) was dissolved in 20 mmL anhydrous tetrahydrofuran, and an equivalent amount of n-octyl isocyanate (155.2 mg, 1.0 mmol) was added. After stirring at room temperature for 3 h, the solvent was removed by distillation under reduced pressure to obtain a white solid BI-2, 311.0 g, with a yield of 98%.

Characterization results: ¹ H NMR (500 MHz, DMSO-d ₆ , ppm) δ 8.29 (br, 1H), 7.96-7.92 (m, 4H), 3.11-3.08 (m, 2H), 1.49-1.47 (m, 2H), 1.29-1.27 (m, 10H), 0.88 (t, J=6.5 Hz, 3H); ESI-HRMS Calcd for C ₁₇ H ₂₂ N ₂ O ₄ Na[M+H] ⁺ : 341.1477, Found: 341.1479, Error: 0.2 ppm.

Example 3

4-Methyl-N-hydroxyphthalimide (179.0 mg, 1.0 mmol) was dissolved in 20 mmL anhydrous tetrahydrofuran, and an equivalent amount of n-octyl isocyanate (155.2 mg, 1.0 mmol) was added. After stirring at room temperature for 3 h, the solvent was removed by distillation under reduced pressure to obtain a white solid BI-3, 325.0 g, with a yield of 98%.

Characterization results: ¹ H NMR (500 MHz, DMSO-d ₆ , ppm) δ 8.32 (br, 1H), 7.83 (d, J=12 1H), 7.78 (s, 1H), 3.29 (s, 3H), 3.13-3.09 (m, 2H), 1.48-1.47 (m, 2H), 1.29-1.27 (m, 10H), 0.88 (t, J=6.5 Hz, 3H); ESI-HRMS Calcd for C ₁₇ H ₂₄ N ₂ O ₄ Na[M+H] ⁺ 355.3898, Found: 355.3894, Error: 0.4 ppm.

Example 4

4-Chloro-N-hydroxyphthalimide (199.5 mg, 1.0 mmol) was dissolved in 30 mmL of anhydrous tetrahydrofuran, and an equivalent amount of n-octyl isocyanate (155.2 mg, 1.0 mmol) was added. After stirring at room temperature for 3.5 h, the solvent was removed by distillation under reduced pressure to obtain a white solid BI-4, 321.5 g, with a yield of 97%.

Characterization results: ¹ H NMR (500 MHz, DMSO-d ₆ , ppm) δ 8.29 (br, 1H), 7.85 (d, J = 12.0 1H), 7.79 (s, 1H), 3.14-3.10 (m, 2H), 1.52-1.49 (m, 2H), 1.33-1.29 (m, 10H), 0.89 (t, J = 6.5 Hz, 3H); ESI-HRMS Calcd for C ₁₇ H ₂₁ ClN ₂ O ₄ Na [M + H] ⁺ 375.1088, Found: 375.1086, Error: 0.2 ppm.

Example 5

4-Phenyl-N-hydroxyphthalimide (241.1 mg, 1.0 mmol) was dissolved in 30 mmL of anhydrous tetrahydrofuran, and an equivalent amount of n-octyl isocyanate (155.2 mg, 1.0 mmol) was added. After stirring at room temperature for 3.5 h, the solvent was removed by distillation under reduced pressure to obtain a white solid BI-5, 318.3 g, with a yield of 96%.

Characterization results: ¹ H NMR (500 MHz, DMSO-d ₆ , ppm) δ 8.29 (br, 1H), 7.85 (d, J = 12.0 1H), 7.79 (s, 1H), 7.33-7.52 (m, 5H), 3.14-3.10 (m, 2H), 1.52-1.49 (m, 2H), 1.33-1.29 (m, 10H), 0.89 (t, J = 6.5 Hz, 3H); ESI-HRMS Calcd for C ₁₇ H ₂₁ ClN ₂ O ₄ Na [M + H] ⁺ 417.1790, Found: 417.1793, Error: 0.3 ppm.

Example 6

4-Nitro-N-hydroxyphthalimide (210.0 mg, 1.0 mmol) was dissolved in 30 mmL of anhydrous tetrahydrofuran, and an equivalent amount of n-octyl isocyanate (155.2 mg, 1.0 mmol) was added. After stirring at room temperature for 3.5 h, the solvent was removed by distillation under reduced pressure to obtain a white solid BI-6, 315.1 g, with a yield of 95%.

Characterization results: ¹ H NMR (500 MHz, DMSO-d ₆ , ppm) δ 8.29 (br, 1H), 8.12 (d, J = 12.0 1H), 7.92 (s, 1H), 3.14-3.10 (m, 2H), 1.55-1.52 (m, 2H), 1.34-1.30 (m, 10H), 0.93 (t, J = 6.5 Hz, 3H); ESI-HRMS Calcd for C ₁₇ H ₂₁ ClN ₂ O ₄ Na [M + H] ⁺ 417.1790, Found: 417.1793, Error: 0.3 ppm.

Performance Testing

(1) Thermal dissociation performance

The response behavior of the prepared blocked isocyanate, namely N-hydroxyphthalimide amino ester compound, under thermal stimulation conditions was monitored by in situ variable temperature nuclear magnetic resonance detection.

Specifically, the blocked isocyanate BI-2 prepared in Example 2 was used as the research object. 0.1 mmol of BI-2 (31.8 mg) was added to 0.6 mL of anhydrous deuterated dimethyl sulfoxide (DMSO-d ₆ ) in a glove box. After being sealed, the mixture was placed in an in-situ variable temperature nuclear magnetic resonance monitoring instrument and heated from room temperature to 120° C. by programmed temperature increase. Equilibrium was reached after about 20 minutes of each temperature increase. The nuclear magnetic hydrogen spectrum (1H NMR) was measured once before and after the temperature increase, and then the next stage of temperature increase was carried out. The experimental results are shown in FIG2 .

The results in Figure 2 show that when the temperature rises to 80°C, characteristic peaks of isocyanate appear in the nuclear magnetic hydrogen spectrum. When the temperature rises to 100°C, about 30% of the blocked isocyanate BI-2 dissociates back to the raw material. When the temperature rises to 120°C and stabilizes, about 54% of the blocked isocyanate BI-2 dissociates back to the raw material, namely N-hydroxyphthalimide and n-octyl isocyanate. This shows that the reaction between N-hydroxyphthalimide and isocyanate is a dynamic thermal reversible reaction. The blocked isocyanate BI-2 can dissociate into n-octyl isocyanate and N-hydroxyphthalimide (NHPI) under heating conditions. The dissociation reaction formula is shown in the following formula (i):

(2) Dynamic exchange reaction experiment

Dynamic exchange experiments were performed to verify the response behavior of the prepared blocked isocyanate under thermal stimulation conditions.

Specifically, in conjunction with Figures 3-4, 4-methyl-N-hydroxyphthalimide (0.5 mmol, 88.5 mg) and an equivalent amount of blocked isocyanate BI-2 (4ab, 0.5 mmol, 159.0 mg) prepared in Example 2 were added to 5 mL of anhydrous DMSO- _d6 in a glove box, heated to 100°C for 1 h under nitrogen protection, and then continued to react at 50°C for 24 h. The reaction solution was taken for nuclear magnetic hydrogen spectrum testing. The 1H The components of the reaction solution were analyzed by NMR, and the results of nuclear magnetic hydrogen spectrum are shown in Figure 4. The results in Figure 4 show that some N-hydroxyphthalimide (NHPI) is generated in the system, and the molar ratio of NHPI to 4-methyl-N-hydroxyphthalimide is close to 1:1, and a new N-hydroxyphthalimide amino ester compound, namely BI-3, is generated. The specific reaction formula is shown in the following formula (ii), and the molar ratio of the new N-hydroxyphthalimide amino ester compound to the blocked isocyanate BI-2 is also close to 1:1. It can be determined that the blocked isocyanate prepared by the present invention, namely the N-hydroxyphthalimide amino ester compound, undergoes a dynamic exchange reaction under heating conditions.

Combined with the above-mentioned variable temperature H-NMR spectrum results, it is fully proved that the reaction between N-hydroxyphthalimide (type compound) and isocyanate is a dynamic thermal reversible reaction, which further fully confirms that N-hydroxyphthalimide (type compound) is a highly efficient isocyanate blocking agent.

(3) Photostability

The blocked isocyanate BI-1 prepared in Example 1 was placed under a fluorescent lamp for one month, and the sample did not show any yellowing or other signs, indicating that the blocked isocyanate prepared in the present invention has good light stability.

The present invention is not limited to the above-mentioned specific implementation modes. Various changes made by ordinary technicians in this field based on the above-mentioned concepts without creative work are all within the protection scope of the present invention.

Claims (3)

1. A method for preparing a blocked isocyanate that can be efficiently unblocked at low temperature, characterized in that the steps are: reacting an N-hydroxyphthalimide compound represented by the following general formula (II) with an isocyanate in the absence of a catalyst to obtain a blocked isocyanate, the structural formula of which is shown in Formula I: In the formula, R1 is independently selected from H, alkyl, aromatic, alkoxy, and halogen; R2 is selected from the residue of aliphatic isocyanate without isocyanate group; x is 1; The molar ratio of the N-hydroxyphthalimide compound to the isocyanate is 1:1; The reaction is carried out at room temperature. 2 . The method for preparing a blocked isocyanate according to claim 1 , wherein the alkyl group is a hydrocarbon group having 1 to 20 carbon atoms. 3. The method for preparing a blocked isocyanate according to claim 1, wherein the aliphatic isocyanate is any one of n-octyl isocyanate, n-butyl isocyanate, and propyl isocyanate.