A process for the preparation of a pentamethylene diisocyanate trimer

Abstract

The present application relates to the technical field of paint chemical industry, and particularly relates to a preparation method of pentamethylene diisocyanate trimer, which comprises the following steps: (1) pre-catalysis: antioxidants and part of catalysts are put into pentamethylene diisocyanate for stirring at normal temperature, and vacuum degassing is carried out under negative pressure; (2) self-polymerization reaction: the remaining catalysts are added drop by drop into the monomer after degassing to initiate isocyanate self-polymerization; (3) fixed-point polymerization inhibition intervention: when the reaction reaches a certain specified conversion rate, a small amount of polymerization inhibitor is added to realize selective inhibition of the polymerization reaction; (4) termination treatment: when the stable polymerization reaches the end point, the polymerization is terminated by supplementing the polymerization inhibitor, and a thin film evaporator and a short path molecular still are used for purification. The preparation method has the advantages of high catalytic efficiency, stable polymerization and controllable product quality, the trimer content is higher than 60%, the residual monomer content is lower than 0.3%, and the green environmental protection requirement is met.

Description

Technical Field

[0001] This invention relates to the field of coatings and chemical technology, and in particular to a method for preparing pentamethylene diisocyanate trimer. Background Technology

[0002] Polyurethane coatings are characterized by good film appearance, excellent mechanical properties, and chemical resistance, and are widely used in the coating and protection of wood, automobiles, construction, railways, and other industries, showing great promise. Isocyanate curing agents are a key component of polyurethane coatings, and pentamethylene diisocyanate trimer is one of the important development directions for isocyanate curing agents. It has a six-membered ring structure of isocyanurate, good thermal stability, and excellent anti-yellowing properties.

[0003] Currently, the preparation of pentamethylene diisocyanate trimers still faces several problems: 1) Inappropriate catalyst selection and complex catalytic processes often require the addition of large amounts of catalyst at high temperatures to initiate polymerization, which is not only inefficient but also leads to temperature runaway and loss of control in the production process; 2) The self-polymerization of isocyanates is a continuously exothermic reaction, and the system will continuously heat up, requiring real-time manual temperature monitoring and preparation for cooling, which is cumbersome; 3) When the temperature drops below the catalyst's initiation temperature, the monomer will stop self-polymerizing, requiring rapid external heating or additional catalyst to continue the reaction, making the preparation method inefficient and difficult to control; 4) Under normal monomer conversion rates, the prepared trimer content is low; or a low conversion rate is required to prepare a high-content trimer curing agent, resulting in inefficient production. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the present invention provides a highly efficient and stable method for preparing pentamethylene diisocyanate trimer, the steps of which are as follows:

[0005] (1) Precatalysis

[0006] Under vacuum conditions, catalyst A is added to pentamethylene diisocyanate monomer and mixed thoroughly at room temperature. The amount of catalyst A added is 0.03 to 0.3% of the mass of pentamethylene diisocyanate monomer.

[0007] (2) Self-polymerization reaction

[0008] Release the negative pressure in step (1), heat the mixture obtained in step (1) to the initial reaction temperature of 35-75°C under a protective atmosphere, and continuously and slowly add catalyst B to carry out the self-polymerization reaction;

[0009] (3) Intervention to inhibit aggregation

[0010] When the isocyanate content in the reaction system of step (2) reaches 35-55%, or when the temperature of the reaction system of step (2) exceeds the initial reaction temperature by 5-25°C, add polymerization inhibitor A to it. The amount of polymerization inhibitor A added is 1 / 40 to 1 / 4 of the sum of the molar numbers of catalyst A and catalyst B.

[0011] (4) Reaction terminated

[0012] When the isocyanate content in the reaction system of step (3) decreases to a certain extent, polymerization inhibitor B is added to terminate the reaction. The amount of polymerization inhibitor B added is 1 to 2 times the sum of the molar numbers of catalyst A and catalyst B. Pentamethylene diisocyanate trimer is obtained by purification in the terminated reaction system.

[0013] Preferably, in step (1), the amount of catalyst A added is 0.06 to 0.1% of the mass of pentamethylene diisocyanate monomer.

[0014] Preferably, in step (1), catalyst A is a quaternary ammonium base and / or a quaternary ammonium salt. The quaternary ammonium base includes one or a combination of tetraethylammonium hydroxide, trimethylhydroxypropylammonium hydroxide, and benzyltrimethylammonium hydroxide. The quaternary ammonium salt includes one or a combination of N-(2-hydroxypropyl)-N,N,N-trimethylammonium-2-ethylhexanoate, N-(2-hydroxypropyl)-N,N,N-trimethylammonium-2-carboxylate, and N,N,N-tetramethylammonium octanoate.

[0015] Preferably, in step (1), catalyst A is added in the form of a diluent, and the diluent used is a solvent that is inert to isocyanate groups, including one or a mixture of several of butyl acetate, ethyl acetate, propylene glycol methyl ether acetate, dimethyl succinate, tetrahydrofuran, diethylene glycol dimethyl ether, and xylene, and the mass percentage of catalyst A in the diluent is 1 to 20%.

[0016] As a preferred embodiment, in step (1), in addition to adding catalyst A to the pentamethylene diisocyanate monomer, an antioxidant is also added. The antioxidant is liquid and / or solid, including one or a combination of several of hindered phenolic antioxidants, hindered amine antioxidants, phosphite antioxidants, thiodipropionate antioxidants, and thiol antioxidants. The amount added is 0.05 to 0.5% of the mass of the pentamethylene diisocyanate monomer.

[0017] As a preferred option, in step (1), the pressure of the vacuum environment is 50 to 500 Pa.

[0018] In step (2), catalyst B can be the same as or different from catalyst A.

[0019] Preferably, in step (2), catalyst B is added dropwise in the form of a diluent at a rate of 0.3–3 g / min. The diluent used in the diluent is a solvent inert to isocyanate groups, including one or a mixture of several of butyl acetate, ethyl acetate, propylene glycol methyl ether acetate, dimethyl succinate, tetrahydrofuran, diethylene glycol dimethyl ether, and xylene. Alternatively, the diluent may be a solvent with low reactivity to isocyanate groups, such as monofunctional alcohols, N-monosubstituted amides, including one or a mixture of several of ethanol, n-propanol, isooctyl alcohol, n-butanol, ether alcohols, ester alcohols, allyl alcohol, benzyl alcohol, and 2-pyrrolidone. The mass percentage of catalyst B in the diluent is 5–10%.

[0020] Preferably, in step (2), the amount of catalyst B added is 1 / 10 to 1 / 3 of the mass of catalyst A.

[0021] Further: In step (2), the amount of catalyst B added is 1 / 8 to 1 / 4 of the mass of catalyst A.

[0022] As a preferred option: In step (3), the polymerization inhibitor A is one or a combination of several of dibutyl phosphate, monochloroacetic acid, dodecylbenzene sulfonic acid, benzoyl chloride, methanesulfonic acid, and p-toluenesulfonic acid. The polymerization inhibitor A can be added directly or in the form of a diluent. The diluent used is pentamethylene diisocyanate monomer.

[0023] In step (4), the polymerization inhibitor B can be the same as or different from the polymerization inhibitor A.

[0024] As a preferred option: in step (4), after terminating the reaction, the reaction system is passed sequentially through a thin-film evaporator and a short-path molecular distillation apparatus, and the pentamethylene diisocyanate trimer product is collected.

[0025] Furthermore, the operating temperature of both the thin-film evaporator and the short-path molecular distillation apparatus is 100–200℃, and the scraping speed is 100–800 rpm. The vacuum absolute pressure of the thin-film evaporator is 100–1000 Pa, and the vacuum absolute pressure of the short-path molecular distillation apparatus is 5–500 Pa.

[0026] The beneficial effects of this invention are as follows:

[0027] Using a pre-catalytic process, most of the catalyst is fully dispersed in the pentamethylene diisocyanate monomer at room temperature. Although catalyst A cannot catalyze the polymerization reaction of the isocyanate monomer at room temperature, this part of the catalyst disperses in the monomer to form all-round polymerization sites, stimulating the potential activity of the monomer. When the remaining catalyst is added dropwise, the monomer self-polymerization can be fully initiated without high temperature, saving catalytic time and making the catalytic process highly efficient.

[0028] By employing targeted polymerization inhibition measures, a specific amount of polymerization inhibitor is added at a specific stage of the isocyanate self-polymerization reaction, which can specifically inhibit the further polymerization conversion of trimer to polymer, but will not terminate the normal polymerization reaction. While ensuring monomer conversion rate, it can stably generate as many trimers as possible.

[0029] Throughout the reaction process, the reaction system releases heat steadily without the need for manual temperature control, effectively preventing runaway polymerization and greatly improving process safety and operability. Attached Figure Description

[0030] Figure 1 The image shows a gel permeation chromatogram of the pentamethylene diisocyanate trimer prepared in Example 1. Detailed Implementation

[0031] To better understand the present invention, the present invention is further described below with reference to embodiments and comparative examples, but these do not constitute a limitation on the scope of protection of the claims of the present invention. Other technical solutions obtained by those skilled in the art based on the embodiments without creative effort are all within the scope of protection of the present invention.

[0032] A highly efficient and stable method for preparing pentamethylene diisocyanate trimer, comprising the following steps in sequence:

[0033] (1) Precatalysis

[0034] Catalyst A and an antioxidant were added to pentamethylene diisocyanate monomer under a vacuum environment with a pressure of 50–500 Pa, and mixed thoroughly at room temperature. The amount of catalyst A added was 0.03–0.3% of the mass of pentamethylene diisocyanate monomer.

[0035] Catalyst A is a quaternary ammonium base and / or a quaternary ammonium salt. The quaternary ammonium base includes one or more of tetraethylammonium hydroxide, trimethylhydroxypropylammonium hydroxide, and benzyltrimethylammonium hydroxide, and the quaternary ammonium salt includes one or more of N-(2-hydroxypropyl)-N,N,N-trimethylammonium-2-ethylhexanoate, N-(2-hydroxypropyl)-N,N,N-trimethylammonium-2-carboxylate, and N,N,N-tetramethylammonium octanoate.

[0036] Catalyst A is added in the form of a diluted solution. The diluent used is a solvent inert to isocyanate groups, including one or a mixture of several of butyl acetate, ethyl acetate, propylene glycol methyl ether acetate, dimethyl succinate, tetrahydrofuran, diethylene glycol dimethyl ether, and xylene. The mass percentage of catalyst A in the diluted solution is 1-20%.

[0037] The antioxidant is in liquid and / or solid form, including one or a combination of several of hindered phenolic antioxidants, hindered amine antioxidants, phosphite antioxidants, thiodipropionate antioxidants, and thiol antioxidants, and is added in an amount of 0.05 to 0.5% of the mass of pentamethylene diisocyanate monomer;

[0038] (2) Self-polymerization reaction

[0039] Release the negative pressure in step (1), and heat the mixture obtained in step (1) to the initial reaction temperature of 35-75°C under a protective atmosphere. Then, continuously and slowly add catalyst B to it to carry out the self-polymerization reaction.

[0040] Catalyst B can be the same as or different from catalyst A. The amount of catalyst B added is 1 / 10 to 1 / 3 of the mass of catalyst A.

[0041] Catalyst B is added dropwise in the form of a diluted solution at a rate of 0.3–3 g / min. The diluent used in the diluted solution is a solvent inert to isocyanate groups, including one or a mixture of several of butyl acetate, ethyl acetate, propylene glycol methyl ether acetate, dimethyl succinate, tetrahydrofuran, diethylene glycol dimethyl ether, and xylene. Alternatively, the diluent may be a solvent with low reactivity to isocyanate groups, such as monofunctional alcohols or N-monosubstituted amides, including one or a mixture of several of ethanol, n-propanol, isooctanol, n-butanol, ether alcohols, ester alcohols, allyl alcohol, benzyl alcohol, and 2-pyrrolidone. The mass percentage of catalyst B in the diluted solution is 5–10%.

[0042] (3) Intervention to inhibit aggregation

[0043] When the isocyanate content in the reaction system of step (2) reaches 35-55%, or when the temperature of the reaction system of step (2) exceeds the initial reaction temperature by 5-25°C, polymerization inhibitor A is added. The amount of polymerization inhibitor A added is 1 / 40 to 1 / 4 of the sum of the molar numbers of catalyst A and catalyst B.

[0044] Polymer inhibitor A is one or a combination of several of dibutyl phosphate, monochloroacetic acid, dodecylbenzenesulfonic acid, benzoyl chloride, methanesulfonic acid, and p-toluenesulfonic acid. Polymer inhibitor A can be added directly or in the form of a diluted solution. The diluent used is pentamethylene diisocyanate monomer.

[0045] (4) Reaction terminated

[0046] When the isocyanate content in the reaction system of step (3) decreases to a certain level, polymerization inhibitor B is added to terminate the reaction. The amount of polymerization inhibitor B added is 1 to 2 times the sum of the molar numbers of catalyst A and catalyst B. The pentamethylene diisocyanate trimer is then purified from the terminated reaction system.

[0047] Inhibitor B can be the same as or different from inhibitor A.

[0048] After the reaction was terminated, the reaction system was purified and the pentamethylene diisocyanate trimer product was collected by passing it sequentially through a thin-film evaporator and a short-path molecular distillation apparatus. The operating temperature of the thin-film evaporator and the short-path molecular distillation apparatus was 100-200℃, and the scraping speed was 100-800 rpm. The absolute pressure of the vacuum in the thin-film evaporator was 100-1000 Pa, and the absolute pressure of the vacuum in the short-path molecular distillation apparatus was 5-500 Pa.

[0049] Example 1

[0050] (1) Precatalysis

[0051] Under conditions of vacuum and stirring degassing (vacuum pressure maintained at 300 Pa), 0.8 parts by weight of antioxidant pentaerythritol tetrakis(β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) and 0.8 parts by weight of catalyst AN-(2-hydroxypropyl)-N,N,N-trimethylammonium-2-ethylhexanoate (catalyst A was dispersed in xylene at 20% by mass before being added) were added to 1000 parts by weight of pentamethylene diisocyanate monomer, and mixed thoroughly at room temperature (25°C).

[0052] (2) Self-polymerization reaction

[0053] Release the negative pressure in step (1), purge the mixture obtained in step (1) with nitrogen, heat it to the initial reaction temperature of 40°C and keep it at that temperature, and then add 0.1 parts by weight of catalyst B N-(2-hydroxypropyl)-N,N,N-trimethylammonium-2-carboxylate (catalyst B is dispersed in isooctanol at a mass fraction of 10% and then added dropwise) at a rate of 0.6 g / min to carry out the self-polymerization reaction;

[0054] (3) Intervention to inhibit aggregation

[0055] When the temperature of the reaction system in step (2) rises to 60°C (at this time, the isocyanate content in the reaction system drops to 45%, and the isocyanate content = the current mass of isocyanate in the reaction system ÷ the current total mass of the reaction system × 100%, the same below), 0.08 parts by weight of benzoyl chloride (benzoyl chloride is added after being dispersed in pentamethylene diisocyanate monomer at a mass fraction of 50%) is added at once, and the system automatically and slowly cools down to 40-45°C and continues to react;

[0056] (4) Reaction terminated

[0057] When the isocyanate content in the reaction system of step (3) drops to 42%, 0.8 parts by weight of dibutyl phosphate is added to terminate the reaction. The resulting reaction mixture is first passed through a thin-film evaporator at 160°C and 1000 Pa absolute pressure, and then through a short-path molecular distillation apparatus at 150°C and 80 Pa absolute pressure. The collected heavy components are pentamethylene diisocyanate trimers.

[0058] Example 2

[0059] (1) Precatalysis

[0060] Under conditions of vacuum and stirring degassing (vacuum pressure maintained at 200 Pa), 1.5 parts by weight of antioxidant pentaerythritol tetrakis(β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) and 0.6 parts by weight of catalyst AN-(2-hydroxypropyl)-N,N,N-trimethylammonium-2-ethylhexanoate (catalyst A was dispersed in butyl acetate at a mass fraction of 15% before being added) were added to 1000 parts by weight of pentamethylene diisocyanate monomer, and the mixture was thoroughly mixed at room temperature.

[0061] (2) Self-polymerization reaction

[0062] Release the negative pressure in step (1), purge the mixture obtained in step (1) with nitrogen, heat it to the initial reaction temperature of 50°C and keep it at that temperature, and then add 0.06 parts by weight of catalyst B N-(2-hydroxypropyl)-N,N,N-trimethylammonium-2-carboxylate (catalyst B is dispersed in benzyl alcohol at a mass fraction of 10% and then added dropwise) at a rate of 1.2 g / min to carry out the self-polymerization reaction;

[0063] (3) Intervention to inhibit aggregation

[0064] When the isocyanate content in the reaction system of step (2) drops to 45%, 0.08 parts by weight of benzoyl chloride (benzoyl chloride is added after being dispersed in pentamethylene diisocyanate monomer at a mass fraction of 50%) is added at once. The system automatically and slowly cools down to 50-55°C and continues to react.

[0065] (4) Reaction terminated

[0066] When the isocyanate content in the reaction system of step (3) drops to 42%, 0.8 parts by weight of dibutyl phosphate is added to terminate the reaction. The resulting reaction mixture is first passed through a thin-film evaporator at 160°C and 800 Pa absolute pressure, and then through a short-path molecular distillation apparatus at 140°C and 50 Pa absolute pressure. The collected heavy components are pentamethylene diisocyanate trimers.

[0067] Example 3

[0068] (1) Precatalysis

[0069] While degassing under vacuum (with the vacuum pressure maintained at 200 Pa), 1.5 parts by weight of antioxidant dodecyl thiodipropionate and 0.8 parts by weight of catalyst A benzyltrimethylammonium hydroxide (catalyst A was dispersed in diethylene glycol dimethyl ether at a mass fraction of 15% before being added) were added to 1000 parts by weight of pentamethylene diisocyanate monomer, and mixed thoroughly at room temperature.

[0070] (2) Self-polymerization reaction

[0071] Release the negative pressure in step (1), purge the mixture obtained in step (1) with nitrogen, heat it to the initial reaction temperature of 55°C and keep it at that temperature, and then add 0.02 parts by weight of catalyst B N-(2-hydroxypropyl)-N,N,N-trimethylammonium-2-carboxylate (catalyst B is dispersed in n-butanol at a mass fraction of 5% and then added dropwise) at a rate of 2.5 g / min to carry out the self-polymerization reaction;

[0072] (3) Intervention to inhibit aggregation

[0073] When the temperature of the reaction system in step (2) rises to 75°C, 0.08 parts by weight of p-toluenesulfonic acid (p-toluenesulfonic acid is added after being dispersed in pentamethylene diisocyanate monomer at a mass fraction of 20%) is added at once. The system automatically and slowly cools down to 55-60°C and continues to react.

[0074] (4) Reaction terminated

[0075] When the isocyanate content in the reaction system of step (3) drops to 40%, 0.8 parts by weight of dibutyl phosphate is added to terminate the reaction. The resulting reaction mixture is first passed through a thin-film evaporator at 160°C and 800 Pa absolute pressure, and then through a short-path molecular distillation apparatus at 140°C and 50 Pa absolute pressure. The collected heavy components are pentamethylene diisocyanate trimers.

[0076] Comparative Example 1

[0077] In step (3), when the isocyanate content in the reaction system drops to 45%, no polymerization inhibitor is added. Instead, external physical cooling (such as blowing cold air or a cold water bath) is used to maintain the temperature of the reaction system back within the range of 40-45°C until the final reaction is terminated. The remaining operations are the same as in Example 1.

[0078] (1) Precatalysis

[0079] Under conditions of vacuum and stirring degassing (vacuum pressure maintained at 300 Pa), 0.8 parts by weight of antioxidant pentaerythritol tetrakis(β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) and 0.8 parts by weight of catalyst AN-(2-hydroxypropyl)-N,N,N-trimethylammonium-2-ethylhexanoate (catalyst A was dispersed in xylene at 20% by mass before being added) were added to 1000 parts by weight of pentamethylene diisocyanate monomer, and the mixture was thoroughly mixed at room temperature.

[0080] (2) Self-polymerization reaction

[0081] Release the negative pressure in step (1), purge the mixture obtained in step (1) with nitrogen, heat it to the initial reaction temperature of 40°C and keep it at that temperature, and then add 0.1 parts by weight of catalyst B N-(2-hydroxypropyl)-N,N,N-trimethylammonium-2-carboxylate (catalyst B is dispersed in isooctanol at a mass fraction of 10% and then added dropwise) at a rate of 0.6 g / min to carry out the self-polymerization reaction;

[0082] (3) Intervention to inhibit aggregation

[0083] When the temperature of the reaction system in step (2) rises to 60°C (at this time, the isocyanate content in the reaction system drops to 45%), the temperature of the reaction system is kept at 40-45°C again by external physical cooling (cold water bath) to continue the reaction until the reaction in step (4) is terminated.

[0084] (4) Reaction terminated

[0085] When the isocyanate content in the reaction system of step (3) drops to 42%, 0.8 parts by weight of dibutyl phosphate is added to terminate the reaction. The resulting reaction mixture is first passed through a thin-film evaporator at 160°C and 1000 Pa absolute pressure, and then through a short-path molecular distillation apparatus at 150°C and 80 Pa absolute pressure. The collected heavy components are pentamethylene diisocyanate trimers.

[0086] Comparative Example 2

[0087] Add polymerization inhibitor A to the reaction system in advance, and perform the remaining operations as in Example 1:

[0088] (1) Precatalysis

[0089] Under conditions of vacuum and stirring degassing (vacuum pressure maintained at 300 Pa), 0.8 parts by weight of antioxidant pentaerythritol tetrakis(β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) and 0.8 parts by weight of catalyst AN-(2-hydroxypropyl)-N,N,N-trimethylammonium-2-ethylhexanoate (catalyst A was dispersed in xylene at 20% by mass before being added) were added to 1000 parts by weight of pentamethylene diisocyanate monomer, and mixed thoroughly at room temperature (25°C).

[0090] (2) Self-polymerization reaction

[0091] After releasing the negative pressure in step (1), the mixed system obtained in step (1) was protected by nitrogen gas, heated to the initial reaction temperature of 40°C and kept at that temperature, and then 0.1 parts by weight of catalyst B N-(2-hydroxypropyl)-N,N,N-trimethylammonium-2-carboxylate (catalyst B was dispersed in isooctanol at a mass fraction of 10% before being added) was added dropwise at a rate of 0.6 g / min to carry out the self-polymerization reaction. After the addition was completed, 0.08 parts by weight of benzoyl chloride (benzoyl chloride was dispersed in pentamethylene diisocyanate monomer at a mass fraction of 50% before being added) was added at once. As the self-polymerization reaction proceeded, the temperature of the reaction system still rose to above 60°C and remained there for a period of time.

[0092] (3) Reaction terminated

[0093] When the isocyanate content in the reaction system of step (2) drops to 42%, 0.8 parts by weight of dibutyl phosphate is added to terminate the reaction. The resulting reaction mixture is first passed through a thin-film evaporator at 160°C and 1000 Pa absolute pressure, and then through a short-path molecular distillation apparatus at 150°C and 80 Pa absolute pressure. The collected heavy components are pentamethylene diisocyanate trimers.

[0094] Comparative Example 3

[0095] Catalyst A was not added in step (1), but was added dropwise to the reaction system together with catalyst B in step (2). The rest of the operation was the same as in Example 2.

[0096] (1) Under the condition of vacuuming and stirring degassing (the pressure of the vacuum environment is maintained at 200 Pa), 1.5 parts by weight of antioxidant tetrakis(β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid) pentaerythritol ester is added to 1000 parts by weight of pentamethylene diisocyanate monomer in one go, and mixed thoroughly at room temperature.

[0097] (2) Self-polymerization reaction

[0098] Release the negative pressure in step (1), purge the mixture obtained in step (1) with nitrogen, heat it to the initial reaction temperature of 50°C and keep it at that temperature, then add 0.06 parts by weight of catalyst B N-(2-hydroxypropyl)-N,N,N-trimethylammonium-2-carboxylate (catalyst B is dispersed in benzyl alcohol at a mass fraction of 10% and then added dropwise) at a rate of 1.2 g / min, and at the same time add 0.6 parts by weight of catalyst AN-(2-hydroxypropyl)-N,N,N-trimethylammonium-2-ethylhexanoate (catalyst A is dispersed in butyl acetate at a mass fraction of 15% and then added dropwise) at a rate of 1.2 g / min to carry out the self-polymerization reaction;

[0099] (3) Intervention to inhibit aggregation

[0100] When the isocyanate content in the reaction system of step (2) drops to 45%, 0.08 parts by weight of benzoyl chloride (benzoyl chloride is added after being dispersed in pentamethylene diisocyanate monomer at a mass fraction of 50%) is added at once. The system automatically and slowly cools down to 50-55°C and continues to react.

[0101] (4) Reaction terminated

[0102] When the isocyanate content in the reaction system of step (3) drops to 42%, 0.8 parts by weight of dibutyl phosphate is added to terminate the reaction. The resulting reaction mixture is first passed through a thin-film evaporator at 160°C and 800 Pa absolute pressure, and then through a short-path molecular distillation apparatus at 140°C and 50 Pa absolute pressure. The collected heavy components are pentamethylene diisocyanate trimers.

[0103] Comparative Example 4

[0104] Catalyst B and catalyst A were added together in step (1) and mixed at room temperature. All other operations were the same as in Example 2.

[0105] (1) Precatalysis

[0106] Under conditions of vacuum and stirring degassing (vacuum pressure maintained at 200 Pa), 1.5 parts by weight of antioxidant pentaerythritol tetrakis(β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), 0.6 parts by weight of catalyst AN-(2-hydroxypropyl)-N,N,N-trimethylammonium-2-ethylhexanoate (catalyst A was dispersed in butyl acetate at 15% by mass before being added), and 0.06 parts by weight of catalyst B N-(2-hydroxypropyl)-N,N,N-trimethylammonium-2-carboxylate (catalyst B was dispersed in benzyl alcohol at 10% by mass before being added dropwise) were added to 1000 parts by weight of pentamethylene diisocyanate monomer, and the mixture was thoroughly mixed at room temperature.

[0107] (2) Self-polymerization reaction

[0108] Release the negative pressure in step (1), purify the mixed system obtained in step (1) with nitrogen, heat it to the initial reaction temperature of 50°C and keep it at the temperature to carry out the self-polymerization reaction;

[0109] (3) Intervention to inhibit aggregation

[0110] When the isocyanate content in the reaction system of step (2) drops to 45%, 0.08 parts by weight of benzoyl chloride (benzoyl chloride is added after being dispersed in pentamethylene diisocyanate monomer at a mass fraction of 50%) is added at once. The system automatically and slowly cools down to 50-55°C and continues to react.

[0111] (4) Reaction terminated

[0112] When the isocyanate content in the reaction system of step (3) drops to 42%, 0.8 parts by weight of dibutyl phosphate is added to terminate the reaction. The resulting reaction mixture is first passed through a thin-film evaporator at 160°C and 800 Pa absolute pressure, and then through a short-path molecular distillation apparatus at 140°C and 50 Pa absolute pressure. The collected heavy components are pentamethylene diisocyanate trimers.

[0113] The products obtained in the above embodiments and comparative examples were analyzed by gel permeation chromatography. The monomer and trimer contents in the products were counted, and the preparation time (starting from the addition of the catalyst to the reactant monomer and ending at step (4) when the polymerization inhibitor was added to terminate the reaction) and the appearance of the products were evaluated. The results are shown in Table 1.

[0114] Table 1

[0115]

[0116] As shown in Table 1, the product prepared in Example 1 contained 65% trimer and 0.15% monomer, and the preparation time was 5.2 hours, which achieved the objective of the present invention quite well. However, in Comparative Example 1, the trimer content decreased significantly to only 55%. This is because when the system was found to have significant exothermic reaction in step (3) of Comparative Example 1 (exceeding the initial reaction temperature by 20°C), no site-specific polymerization inhibition measures were taken. Instead, physical temperature control was used. As a result, since the catalytic activity was not selectively inhibited, although the reaction temperature was lower, there were still trimers in the reaction system that continued to transform into pentamers, resulting in a smaller accumulation of trimers in the final product, which could not achieve the stable preparation effect of Example 1. At the same time, after controlling the reaction temperature lower in Comparative Example 1, the overall reaction rate slowed down and the reaction time was extended.

[0117] In Comparative Example 2, polymerization inhibitor A was added to the reaction system immediately after catalyst B was added. At this time, the self-polymerization reaction of the monomer in the system had not been going on for long. Since the amount of polymerization inhibitor A was small, although it would not stop the polymerization reaction, it greatly delayed the preparation time. Furthermore, due to the incorrect timing of the addition of polymerization inhibitor A, the polymerization inhibitor selectivity in Example 1 could not be reflected. In the system after the reaction, the content of the target product trimer was significantly different from that in Example 1.

[0118] In Comparative Example 3, no pre-catalytic process was used to form multi-directional polymerization sites at room temperature. In step (2) at the beginning of the polymerization reaction, since the reaction system has been heated to the polymerization reaction temperature of 50°C, if catalyst A is added all at once, it may cause the reaction system to explode and run out of control, generating large molecular insoluble polymers. Therefore, catalyst A can only be added slowly like catalyst B, which makes the whole preparation process time-consuming and inefficient.

[0119] In Comparative Example 4, all catalysts (catalyst A and catalyst B) were added to the monomer at room temperature in step (1) and dispersed. The same heating operation was then performed, but the preparation time was significantly longer. In contrast, regarding Example 2 of this scheme, the applicant believes that for the monomer mixture system in step (1) of Example 2 where catalyst A is dispersed, the polymerization reaction has already occurred when the system is heated to 50°C. At this point, the immediate addition of catalyst B further activates the catalytic polymerization, indicating that although catalyst A, when dispersed in the reactant monomer at room temperature, does not catalyze polymerization, it forms a certain potential activity in the monomer. In Comparative Example 4, all catalysts were initially added to the monomer without being added during the polymerization reaction. Even if potential activity existed, it was not effectively activated during the polymerization process.

[0120] All embodiments of this invention employ a pre-catalytic process and a site-directed polymerization inhibition intervention process, achieving the expected beneficial effects compared to traditional preparation techniques. The system exhibits stable exothermic activity, eliminating the need for manual temperature control and effectively preventing runaway polymerization, thus significantly improving process safety and operability. The product contains more than 60% trimer and less than 0.3% residual monomers, meeting green and environmentally friendly requirements.

Claims

1. A method for preparing pentamethylene diisocyanate trimer, characterized in that: The preparation method, in the order of operation, is as follows: (1) Precatalysis Under vacuum, catalyst A is added to pentamethylene diisocyanate monomer and mixed thoroughly at room temperature. The amount of catalyst A added is 0.03-0.3% of the mass of the pentamethylene diisocyanate monomer. (2) Self-polymerization reaction Release the negative pressure in step (1), heat the mixture obtained in step (1) to the initial reaction temperature of 35-75°C under a protective atmosphere, and continuously and slowly add catalyst B to carry out the self-polymerization reaction; (3) Intervention to prevent polymerization When the isocyanate content in the reaction system of step (2) reaches 35-55%, or when the temperature of the reaction system of step (2) exceeds the initial reaction temperature by 5-25°C, polymerization inhibitor A is added to it. The amount of polymerization inhibitor A added is 1 / 40 to 1 / 4 of the sum of the molar numbers of catalyst A and catalyst B. (4) Reaction terminated When the isocyanate content in the reaction system of step (3) decreases to a certain level, polymerization inhibitor B is added to terminate the reaction. The amount of polymerization inhibitor B added is 1 to 2 times the sum of the molar numbers of catalyst A and catalyst B. The pentamethylene diisocyanate trimer is obtained by purification in the terminated reaction system. In step (3), the polymerization inhibitor A is one or a combination of several of the following: dibutyl phosphate, monochloroacetic acid, dodecylbenzenesulfonic acid, benzoyl chloride, methanesulfonic acid, and p-toluenesulfonic acid. The catalyst B may be the same as or different from the catalyst A; the polymerization inhibitor B may be the same as or different from the polymerization inhibitor A.

2. The method for preparing the pentamethylene diisocyanate trimer according to claim 1, characterized in that: In step (1), catalyst A is added in the form of a diluent, the diluent of which includes one or a mixture of several of butyl acetate, ethyl acetate, propylene glycol methyl ether acetate, dimethyl succinate, tetrahydrofuran, diethylene glycol dimethyl ether, and xylene, and the mass percentage of catalyst A in the diluent is 1 to 20%.

3. The method for preparing the pentamethylene diisocyanate trimer as described in claim 1, characterized in that: In step (1), the amount of antioxidant added is 0.05 to 0.5% of the mass of the pentamethylene diisocyanate monomer.

4. The method for preparing the pentamethylene diisocyanate trimer according to claim 1, characterized in that: In step (2), the amount of catalyst B added is 1 / 10 to 1 / 3 of the mass of catalyst A. Catalyst B is added dropwise in the form of a diluent at a rate of 0.3 to 3 g / min. The diluent includes one or a mixture of several of the following: butyl acetate, ethyl acetate, propylene glycol methyl ether acetate, dimethyl succinate, tetrahydrofuran, diethylene glycol dimethyl ether, xylene, ethanol, n-propanol, isooctyl alcohol, n-butanol, ether alcohol, ester alcohol, allyl alcohol, benzyl alcohol, and 2-pyrrolidone. The mass percentage of catalyst B in the diluent is 5 to 10%.

5. The method for preparing the pentamethylene diisocyanate trimer according to claim 1, characterized in that: In step (4), after the reaction is terminated, the reaction system is passed through a thin-film evaporator and a short-path molecular distillation apparatus in sequence, and the pentamethylene diisocyanate trimer is collected.

6. The method for preparing the pentamethylene diisocyanate trimer as described in claim 5, characterized in that: The operating temperature of both the thin-film evaporator and the short-path molecular distillation apparatus is 100–200°C, and the scraping speed is 100–800 rpm. The absolute vacuum pressure of the thin-film evaporator is 100–1000 Pa, and the absolute vacuum pressure of the short-path molecular distillation apparatus is 5–500 Pa.

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