CN107903430B

CN107903430B - Preparation method of isocyanate-based polyimide rigid foam

Info

Publication number: CN107903430B
Application number: CN201711305372.5A
Authority: CN
Inventors: 田华峰; 姚媛媛; 项爱民
Original assignee: Beijing Technology and Business University
Current assignee: Beijing Technology and Business University
Priority date: 2017-12-05
Filing date: 2017-12-05
Publication date: 2020-10-16
Anticipated expiration: 2037-12-05
Also published as: CN107903430A

Abstract

The invention discloses a preparation method of an isocyanate group polyimide hard foam material, which is synthesized by taking aromatic dianhydride and isocyanate as main raw materials. The preparation process mainly comprises the following steps: preparing prepolymer, foaming process and controlling process of high-temperature post-treatment. The foam materials with different structures and performances are obtained by adjusting the proportion of the organic tin catalyst and the amine catalyst. Compared with other polyimide foams, the foam obtained by the invention has low manufacturing cost, simple preparation process and loose equipment requirement, not only has good mechanical property, but also shows excellent thermal stability and flame retardant property, and the limiting oxygen index is as high as 49.2%. The invention adopts deionized water as a foaming agent, prepares the polyimide foam through mechanical stirring foaming, does not generate harmful gas in the preparation process, is suitable for industrial continuous production, and the obtained terminal product is expected to be applied in large scale in the aspects of high temperature resistant heat insulation materials, flame retardant materials and the like, and has wide application prospect and great commercial value.

Description

Preparation method of isocyanate-based polyimide rigid foam

Technical Field

The invention relates to a preparation method of isocyanate group polyimide hard foam, belonging to the field of high polymer foam materials and also belonging to the field of high-performance materials.

Background

The Polyimide (PI) foam material is one of the materials with the best thermal stability in polymer foam plastics, has excellent self-flame retardant property and good mechanical property, and can be used as a structural material. But the production process is difficult to control, difficult to process and manufacture and high in production cost, is mainly applied to high-tech fields such as aerospace, electronic industry and the like, and greatly limits the wide application of the method. The isocyanate group polyimide foam material has simple preparation process, loose equipment requirement and low manufacturing cost, and is concerned in recent years. However, the polyimide formation reaction is a complex chemical reaction system, and the control of the preparation process is undoubtedly the most critical and important along with the occurrence of various reactions. The PI foam with excellent performance can be obtained by a proper preparation process, the cost can be saved, and the production maximization is realized. The type and proportion of the catalyst play an important role in the preparation process of PI foam, and the catalyst not only controls the balance between a chain extension reaction (dianhydride and isocyanate) and a foaming reaction (isocyanate and water), but also influences the foaming time and the curing time of a system, and further influences the performance of a product.

In the existing polyimide synthesis technology, the method for preparing polyimide foam mainly comprises a one-step method and a powder method. The one-step method is that the required raw materials are added in sequence and react to directly obtain the final product; the powder method is that firstly, the required raw materials are synthesized into precursor powder, and then the powder is filled into a mould to be heated and foamed to obtain the final product. The following disadvantages exist: different types of catalysts are added simultaneously, the chain growth reaction and the foaming reaction occur simultaneously, and the foam structure is not easy to control. Therefore, optimization of the polyimide foam preparation process and regulation and control of the structure and performance of the polyimide foam become important research directions.

In order to solve the problems in the prior art, the invention needs to provide a preparation method of isocyanate group polyimide rigid foam, PI foams with different structures and performances can be obtained by optimizing and regulating the existing preparation process, and the technical effects of widening the application field of the PI foams are realized.

Disclosure of Invention

The invention discloses a preparation method of isocyanate-based polyimide rigid foam, which can obtain PI foam with excellent structure and performance.

A preparation method of isocyanate group polyimide rigid foam is characterized by comprising the following steps: adding aromatic dianhydride and alcohol into a polar solvent according to the molar ratio of functional groups of 1: 1 to react until the mixture is clear, then gradually heating up, adding isocyanate with the molar ratio of the aromatic dianhydride functional groups of 1: 1 in the heating up process, adding an organic tin catalyst, reacting for 4-6 hours at the temperature of 80-95 ℃ to obtain a prepolymer solution, cooling to room temperature, sequentially adding isocyanate and an amine catalyst to stir for 2-4 minutes, then adding a foam stabilizer and deionized water to stir at high speed for 10-30 seconds to foam freely to prepare a foam intermediate, and finally placing the foam intermediate into a vacuum drying oven to perform step heating treatment at the temperature of 160-220 ℃ for 4-6 hours to obtain the polyimide hard foam.

Preferably, the aromatic dianhydride comprises one or more of pyromellitic dianhydride, 3 ', 4, 4' -benzophenone tetracarboxylic dianhydride, 3 ', 4, 4' -anisole tetracarboxylic dianhydride, 2-bis (3, 4-phthalic anhydride) hexafluoropropane or 1, 3-bis (3, 4-phthalic anhydride) hexafluoropropane.

Preferably, the isocyanate comprises one or more of polyphenyl polymethylene polyisocyanate, p-phenylene diisocyanate, diphenylmethane-4, 4' -diisocyanate, 1, 5-diisocyanatonaphthalene or dimethylbiphenyl diisocyanate.

Preferably, the alcohol comprises one or more of methanol, ethanol or ethylene glycol.

Preferably, the polar solvent comprises one or more of tetrahydrofuran, dimethylformamide, dimethylacetamide or N-methylpyrrolidone.

Preferably, the organic tin catalyst comprises one or more of dibutyltin diacetate, dibutyltin dilaurate or stannous octoate.

Preferably, the amine catalyst comprises one of triethanolamine, triethylamine, triethylene diamine, dimethylethanolamine and triethylene diamine.

Preferably, the foam stabilizer comprises one or more of silicone polyether copolymer, organosilicon and silicone stabilizer.

Preferably, the stirring speed during high-speed stirring is 1500-2000r/min, and the stirring time is 15-20 s.

Preferably, the organotin catalyst is dibutyltin dilaurate, and the amine catalyst is triethanolamine.

Further, the content of the dibutyl tin dilaurate is 1.85 wt%, and the content of the triethanolamine is 1.48 wt%.

Has the advantages that:

the invention adopts a method of synthesizing prepolymer and foaming in two steps to prepare the isocyanate group polyimide hard foam. Compared with a one-step method, the prepolymer synthesis method adopted by the invention has the advantages that: the foam structure can be effectively controlled, and the obtained foam has high mechanical strength, excellent self-flame resistance and good high and low temperature resistance; compared with the powder method, the method has the advantages that: controllable molecular weight, simple and convenient operation, lower requirement on equipment, low manufacturing cost, no harmful gas generation and suitability for industrial continuous production. The invention is innovative in that the structure and performance of the foam can be effectively regulated and controlled by adding the catalyst step by utilizing different functions of the catalyst.

The type and proportion of the catalyst directly affect the structure and performance of the polyimide foam. The organic tin catalyst and the tertiary amine catalyst used in the invention have different catalysis mechanisms in the polyimide foam, the organic tin catalyst is sensitive to gel reaction in the preparation process of the prepolymer, can effectively increase the chain growth reaction rate, and has obvious effects on the thermal stability and the flame retardant property of the polyimide foam; the tertiary amine catalyst is sensitive to the foaming process, can effectively promote the foaming reaction, plays a role in adjusting the shape of foam cells in the foaming engineering, and has great influence on the density and the mechanical property of the foam. The organic tin catalysts include dibutyl tin dilaurate (DBTDL) and stannous octoate, and the tertiary amine catalysts include Triethanolamine (TEOA), Triethylamine (TEA), triethylenediamine and dimethylethanolamine. In particular, the tertiary amine catalyst containing hydroxyl groups such as dimethylethanolamine and triethanolamine is easy to react with isocyanate and is tightly connected in a polymer main chain, thereby not only playing a role of catalyzing foaming, but also being a better cross-linking agent or chain extender. The catalysts of the present invention are preferably dibutyl tin dilaurate and triethanolamine. Polyimide foams with different structures and performances can be obtained by adjusting the proportion of the two catalysts. The invention adopts deionized water as a foaming agent, prepares the polyimide foam through mechanical stirring foaming, does not generate harmful gas in the preparation process, is suitable for industrial continuous production, and the obtained terminal product is expected to be applied in large scale in the aspects of high temperature resistant heat insulation materials, flame retardant materials and the like, and has wide application prospect and great commercial value.

Drawings

The invention is further illustrated with reference to the following figures and examples.

FIG. 1 is a scanning electron microscope photograph of the polyimide foam obtained in example 3.

FIG. 2 shows the thermogravimetric curves of polyimide foam prepared by the one-step method, the powder method and the prepolymer method respectively.

Detailed Description

The technical aspects of the present invention will now be described in detail below in order to clearly understand the technical features of the present invention, but the present invention is not to be construed as limiting the implementable scope of the present invention.

Example 1

Adding 100g of pyromellitic dianhydride (PMDA) and 25g of methanol into 100g N, N-Dimethylformamide (DMF) to react at a certain temperature until the mixture is clear, gradually heating, 130g of polyphenyl polymethylene polyisocyanate (PAPI) is added in the process of raising the temperature to 80 ℃, then 2g of stannous octoate catalyst is added, reacting for 3-7 hours at the temperature of 80-95 ℃ to obtain a prepolymer solution, cooling to room temperature, sequentially adding 40g of PAPI and 2g of Triethylamine (TEA), uniformly stirring, adding 30g of foam stabilizer AK-8805 and 15g of deionized water, stirring at a high speed for 10-20 s at the rotating speed of 1000-2000 r/min, and freely foaming to obtain a foam intermediate, and finally placing the foam intermediate in a vacuum drying oven for high-temperature treatment at the temperature of 160-220 ℃ for 4-6 hours to fully imidize the foam intermediate to obtain the polyimide hard foam.

Example 2

Adding 100g of PMDA and 25g of methanol into 100g of DMF, reacting at a certain temperature until the mixture is clear, gradually heating, adding 130g of PAPI when the temperature is increased to 80 ℃, adding 2g of dibutyltin dilaurate (DBTDL) catalyst, reacting at 80-95 ℃ for 3-7 hours to obtain a prepolymer solution, cooling to room temperature, sequentially adding 40g of PAPI and 2g of Triethanolamine (TEOA), uniformly stirring, adding 30g of foam stabilizer AK-8805 and 15g of deionized water, stirring at a high speed of 1000-2000 r/min for 10-20 s, freely foaming to obtain a foam intermediate, and finally placing the foam intermediate in a vacuum drying oven for high-temperature treatment at 160-220 ℃ for 4-6 hours to fully imidize the foam intermediate to obtain the polyimide hard foam.

Example 3

Adding 100g PMDA and 25g methanol into 100g DMF, reacting at a certain temperature until the mixture is clear, gradually heating, during the temperature rise to 80 ℃, 130g of PAPI was added, followed by the catalyst dibutyl tin dilaurate (content 0.74 wt%), reacting for 3-7 hours at the temperature of 80-95 ℃ to obtain prepolymer solution, cooling to room temperature, sequentially adding 40g of PAPI and triethanolamine (the content is 0.74 wt%), stirring uniformly, adding 30g of foam stabilizer AK-8805 and 15g of deionized water, stirring at a high speed for 10-20 s at the rotating speed of 1000-2000 r/min, foaming freely to obtain a foam intermediate, finally placing the foam intermediate in a vacuum drying oven, treating at the high temperature of 160-220 ℃ for 4-6 hours, a scanning electron micrograph of the foam intermediate was shown in FIG. 1, which was sufficiently imidized to obtain a polyimide rigid foam.

Example 4

Adding 100g of PMDA and 25g of methanol into 100g of DMF, reacting at a certain temperature until the mixture is clear, gradually heating, adding 130g of PAPI when the temperature is increased to 80 ℃, adding a catalyst dibutyl tin dilaurate (the content is 1.11 wt%), reacting at 80-95 ℃ for 3-7 hours to obtain a prepolymer solution, cooling to room temperature, sequentially adding 40g of PAPI and triethanolamine (the content is 0.74 wt%), uniformly stirring, adding 30g of foam stabilizer AK-8805 and 15g of deionized water, stirring at a high speed of 1000-2000 r/min for 10-20 seconds, freely foaming to obtain a foam intermediate, and finally placing the foam intermediate in a vacuum drying oven for high-temperature treatment at 160-220 ℃ for 4-6 hours to fully imidize the foam intermediate to obtain the polyimide rigid foam.

Example 5

Adding 100g of PMDA and 25g of methanol into 100g of DMF, reacting at a certain temperature until the mixture is clear, gradually heating, adding 130g of PAPI when the temperature is increased to 80 ℃, adding a catalyst dibutyl tin dilaurate (the content is 1.48 wt%), reacting at 80-95 ℃ for 3-7 hours to obtain a prepolymer solution, cooling to room temperature, sequentially adding 40g of PAPI and triethanolamine (the content is 0.74 wt%), uniformly stirring, adding 30g of foam stabilizer AK-8805 and 15g of deionized water, stirring at a high speed of 1000-2000 r/min for 10-20 seconds, freely foaming to obtain a foam intermediate, and finally placing the foam intermediate in a vacuum drying oven for high-temperature treatment at 160-220 ℃ for 4-6 hours to fully imidize the foam intermediate to obtain the polyimide rigid foam.

Example 6

Adding 100g of PMDA and 25g of methanol into 100g of DMF, reacting at a certain temperature until the mixture is clear, gradually heating, adding 130g of PAPI when the temperature is increased to 80 ℃, adding a catalyst dibutyl tin dilaurate (the content is 1.85 wt%), reacting at 80-95 ℃ for 3-7 hours to obtain a prepolymer solution, cooling to room temperature, sequentially adding 40g of PAPI and triethanolamine (the content is 0.74 wt%), uniformly stirring, adding 30g of foam stabilizer AK-8805 and 15g of deionized water, stirring at a high speed of 1000-2000 r/min for 10-20 seconds, freely foaming to obtain a foam intermediate, and finally placing the foam intermediate in a vacuum drying oven for high-temperature treatment at 160-220 ℃ for 4-6 hours to fully imidize the foam intermediate to obtain the polyimide rigid foam.

Example 7

Adding 100g of PMDA and 25g of methanol into 100g of DMF, reacting at a certain temperature until the mixture is clear, gradually heating, adding 130g of PAPI when the temperature is increased to 80 ℃, adding a catalyst dibutyl tin dilaurate (the content is 0.74 wt%), reacting at 80-95 ℃ for 3-7 hours to obtain a prepolymer solution, cooling to room temperature, sequentially adding 40g of PAPI and triethanolamine (the content is 1.11 wt%), uniformly stirring, adding 30g of foam stabilizer AK-8805 and 15g of deionized water, stirring at a high speed of 1000-2000 r/min for 10-20 seconds, freely foaming to obtain a foam intermediate, and finally placing the foam intermediate in a vacuum drying oven for high-temperature treatment at 160-220 ℃ for 4-6 hours to fully imidize the foam intermediate to obtain the polyimide rigid foam.

Example 8

Adding 100g of PMDA and 25g of methanol into 100g of DMF, reacting at a certain temperature until the mixture is clear, gradually heating, adding 130g of PAPI when the temperature is increased to 80 ℃, adding a catalyst dibutyl tin dilaurate (the content is 0.74 wt%), reacting at 80-95 ℃ for 3-7 hours to obtain a prepolymer solution, cooling to room temperature, sequentially adding 40g of PAPI and triethanolamine (the content is 1.48 wt%), uniformly stirring, adding 30g of foam stabilizer AK-8805 and 15g of deionized water, stirring at a high speed of 1000-2000 r/min for 10-20 seconds, freely foaming to obtain a foam intermediate, and finally placing the foam intermediate in a vacuum drying oven for high-temperature treatment at 160-220 ℃ for 4-6 hours to fully imidize the foam intermediate to obtain the polyimide rigid foam.

Example 9

Adding 100g of PMDA and 25g of methanol into 100g of DMF, reacting at a certain temperature until the mixture is clear, gradually heating, adding 130g of PAPI when the temperature is increased to 80 ℃, adding a catalyst dibutyl tin dilaurate (the content is 0.74 wt%), reacting at 80-95 ℃ for 3-7 hours to obtain a prepolymer solution, cooling to room temperature, sequentially adding 40g of PAPI and triethanolamine (the content is 1.85 wt%), uniformly stirring, adding 30g of foam stabilizer AK-8805 and 15g of deionized water, stirring at a high speed of 1000-2000 r/min for 10-20 seconds, freely foaming to obtain a foam intermediate, and finally placing the foam intermediate in a vacuum drying oven for high-temperature treatment at 160-220 ℃ for 4-6 hours to fully imidize the foam intermediate to obtain the polyimide rigid foam.

Example 10

Adding 100g PMDA and 25g methanol into 100g DMF, reacting at a certain temperature until the mixture is clear, gradually heating, during the temperature rise to 80 ℃, 130g of PAPI was added, followed by the catalyst dibutyltin dilaurate (content: 1.85% by weight), reacting for 3-7 hours at the temperature of 80-95 ℃ to obtain prepolymer solution, cooling to room temperature, sequentially adding 40g of PAPI and triethanolamine (content is 1.48 wt%), stirring uniformly, adding 30g of foam stabilizer AK-8805 and 15g of deionized water, stirring at high speed for 10-20 s at the rotating speed of 1000-2000 r/min, foaming freely to obtain a foam intermediate, finally placing the foam intermediate in a vacuum drying oven for high-temperature treatment at the temperature of 160-220 ℃ for 4-6 hours, the foam intermediate was fully imidized to obtain a thermal weight loss curve of the polyimide rigid foam as shown in FIG. 2 (prepolymer method).

Comparative example 1

Adding 100g of PMDA and 25g of methanol into 100g of DMF, reacting at a certain temperature until the mixture is clear, adding 2g of dibutyltin dilaurate, 2g of triethanolamine, 30g of foam stabilizer AK-8805 and 15g of deionized water, stirring uniformly, adding 170g of PAPI, stirring at a high speed under the condition of a rotating speed of 1000-2000 r/min, foaming freely to obtain a foam intermediate, and finally placing the foam intermediate in a vacuum drying oven for high-temperature treatment at 160-220 ℃ for 4-6 hours to ensure that the foam intermediate is fully imidized, so as to obtain a thermal weight loss curve of polyimide foam as shown in FIG. 2 (one-step method).

Comparative example 2

Adding 100g of 3, 3 ', 4, 4 ' -Benzophenone Tetracarboxylic Dianhydride (BTDA) and 25g of methanol into 100g of DMF, reacting at a certain temperature until the mixture is clear, heating and refluxing to obtain diacid diester, cooling, adding 110g of 4, 4 ' -diaminodiphenyl ether (ODA), 2g of dibutyl tin dilaurate, 2g of triethanolamine and 20g of foam stabilizer AK-8805, mixing and reacting to obtain a precursor solution, drying and crushing the precursor solution to obtain solid precursor powder, and then putting the precursor powder into a mold for heating and foaming to obtain the thermal weight loss curve of the polyimide foam material as shown in figure 2 (powder method).

Table 1.

Group of	Example 3	Example 4	Example 5	Example 6	Example 10
						Limiting oxygen index	41.7％	47.3％	48.6％	49.2％	49.1％

Table 2.

Group of	Example 3	Example 7	Example 8	Example 9	Example 10
						Average cell diameter	422μm	374μm	352μm	321μm	320μm

Examples 1 and 2 vary the type of catalyst, with dibutyl tin dilaurate and triethanolamine being preferred; the limiting oxygen index values of the polyimide foams obtained in examples 3, 4, 5, 6 and 10 are shown in table 1, and it can be seen that the flame retardant property of the material can be effectively improved by increasing the content of the catalyst dibutyltin dilaurate; the average cell diameters of the polyimide foams obtained in examples 3, 7, 8, 9 and 10 are shown in table 2, and it can be seen that when the triethanolamine content is increased, the cell morphology is more dense, and the mechanical properties are improved therewith; in example 10, the thermal weight loss curves of the polyimide foams obtained by the three different preparation methods of comparative example 1 and comparative example 2 are shown in fig. 2, the thermal stability of the polyimide foams prepared by the prepolymer method is far higher than that of the polyimide foams prepared by the one-step method, and the thermal stability of the polyimide foams prepared by the complex powder method is not greatly different from that of the polyimide foams prepared by the complex powder method.

The polyimide foam prepared by the invention has the shape shown in figure 1, and most of foam holes are open-cell structures; the thermal stability and the flame retardant property of the polyimide foam can be effectively improved by the catalyst dibutyl tin dilaurate, the catalyst triethanolamine plays a role of a cross-linking agent or a chain extender in the foaming process, so that the foam morphology is compact, the mechanical property is greatly improved, and the polyimide foams with different structures and properties can be prepared by adjusting the contents of the dibutyl tin dilaurate and the triethanolamine. Within the research range of the invention, when the content of dibutyltin dilaurate is 1.85 wt% and the content of triethanolamine is 1.48 wt%, the polyimide foam has good thermal stability and flame retardant property, and has compact foam pore morphology, excellent mechanical property and optimal comprehensive performance.

Claims

1. A preparation method of isocyanate group polyimide rigid foam is characterized by comprising the following steps: adding aromatic dianhydride and alcohol into a polar solvent according to the molar ratio of functional groups of 1: 1 to react until the mixture is clear, then gradually heating up, adding isocyanate with the molar ratio of the aromatic dianhydride functional groups of 1: 1 in the heating up process, adding an organic tin catalyst, reacting for 4-6 hours at the temperature of 80-95 ℃ to obtain a prepolymer solution, cooling to room temperature, sequentially adding isocyanate and a tertiary amine catalyst, stirring for 2-4 minutes, then adding a foam stabilizer and deionized water, stirring for 10-30 seconds at high speed to foam freely, preparing a foam intermediate, and finally placing the foam intermediate into a vacuum drying oven to perform stepped heating treatment at the temperature of 160-220 ℃ for 4-6 hours to obtain the polyimide hard foam.

2. The method of claim 1, wherein the aromatic dianhydride comprises one or more of pyromellitic dianhydride, 3 ', 4, 4' -benzophenone tetracarboxylic dianhydride, 3 ', 4, 4' -anisole tetracarboxylic dianhydride, 2-bis (3, 4-phthalic anhydride) hexafluoropropane, or 1, 3-bis (3, 4-phthalic anhydride) hexafluoropropane.

3. The method of claim 1, wherein the isocyanate comprises one or more of polyphenyl polymethylene polyisocyanate, p-phenylene diisocyanate, diphenylmethane-4, 4' -diisocyanate, 1, 5-diisocyanatonaphthalene, or dimethylbiphenyl diisocyanate.

4. The method of claim 1, wherein the alcohol comprises one or more of methanol, ethanol, or ethylene glycol.

5. The method of claim 1, wherein the polar solvent comprises one or more of tetrahydrofuran, dimethylformamide, dimethylacetamide, or N-methylpyrrolidone.

6. The method of claim 1, wherein the organotin-based catalyst comprises one or more of dibutyltin diacetate, dibutyltin dilaurate or stannous octoate.

7. The method of claim 1, wherein the tertiary amine catalyst comprises one or more of triethanolamine, triethylamine, triethylenediamine, dimethylethanolamine, and triethylenediamine.

8. The method of claim 1, wherein the foam stabilizer comprises one or more of silicone polyether copolymer, silicone stabilizer.

9. The method for preparing rigid foams of isocyanate-based polyimides as claimed in claim 1, wherein the stirring speed is 1500-2000r/min and the stirring time is 15-20 s.

10. The method of claim 1, wherein the organotin catalyst is dibutyltin dilaurate and the tertiary amine catalyst is triethanolamine.