CN114262315A - Soluble norbornene-terminated imide oligomer and preparation method thereof - Google Patents
Soluble norbornene-terminated imide oligomer and preparation method thereof Download PDFInfo
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Abstract
The invention belongs to the technical field of high polymer materials, and provides a soluble norbornene-terminated imide oligomer and a preparation method thereof, aiming at solving the problems of high porosity of a thermosetting polyimide composite material prepared by taking PMR type polyimide resin and amic acid as prepregs and high raw material cost of the thermosetting polyimide composite material prepared by using ethynyl and phenylethynyl-terminated imide oligomer. The low-cost aromatic diamine and aromatic dianhydride are used as monomers, the norbornene dianhydride is used as a capping agent, and the norbornene-terminated imide oligomer is obtained through polycondensation and dehydration cyclization reactions. The obtained norbornene-based end-capped imide oligomer has the characteristics of good solubility, low solution viscosity, conversion into thermosetting polyimide at high temperature and no release of volatile micromolecules in polar solvents such as N, N-dimethylacetamide and N-methylpyrrolidone, and is suitable for preparing a pore-free composite material.
Description
Technical Field
The invention belongs to the technical field of high polymer materials, and particularly relates to a soluble norbornene-terminated imide oligomer and a preparation method thereof.
Background
The thermosetting polyimide resin is one of the matrix resins with the highest temperature resistance level at present, and the composite material based on the thermosetting polyimide resin has wide application in the fields of aerospace and the like. However, polyimide has higher melt viscosity and poorer solubility due to the rigidity of the chain and stronger intermolecular and intramolecular interaction, and the composite material directly based on polyimide has higher preparation difficulty. In the 70's of the 20 th century, the American NASA Lewis research center successfully developed PMR-15 resin, and composites based thereon could be used at 316 ℃ for a long period of time. The product adopts a monomer in-situ polymerization technology (PMR technology), aromatic dimethyl tetracarboxylic acid, aromatic diamine and norbornene dicarboxylic acid monoester are dissolved in methanol according to a certain proportion, then fiber is impregnated, resin monomers are subjected to in-situ polymerization to generate a prepolymer with low relative molecular mass when the composite material is thermally cured, and then a reticular structure is formed through high-temperature crosslinking of norbornene. The PMR-15 overcomes the problems of poor solubility and poor manufacturability of polyimide resins. Thereafter, people carried out a series of improvements on PMR-15 and prepared series products such as LaRC-160, LaRC-RP46, PMR-II-15, V-CAP, AFR-700B and the like. The development of the PMR type resin improves the problems of poor solubility and poor manufacturability of polyimide resin, but the composite material based on the PMR type resin inevitably releases small-molecule volatile substances in the preparation process, so that holes appear in the final product.
The benzyne-terminated polyimide resin (PETI) and the asymmetric dianhydride-based polyimide resin (TriA-PI) which are successively developed in the United states and Japan from the end of the 20 th century to the beginning of the 21 st century all show good toughness. However, due to the low solubility of polyimide, PETI and TriA-PI mostly adopt an amic acid form when preparing prepreg, and then are cured and molded by a high-temperature mould pressing mode; however, when the amide acid is subjected to thermal imidization, small molecular byproducts such as water and the like are generated, and the byproducts generate air holes in the composite material and are difficult to remove, so that the porosity of the final product is high, and the processing of large-size and large-thickness products becomes very difficult.
Heretofore, efforts have been made in recent decades to develop imide oligomers in a fully imidized form having high solubility in organic solvents. It has been studied that one effective way to improve the solubility of imide oligomers is to introduce flexible chains, bulky side groups and use asymmetric monomers in the imide. The method has the disadvantages of high cost and reduced thermal and mechanical properties of the prepared composite material. Another method is to synthesize an isoimide oligomer, which exhibits excellent solubility and processability due to structural asymmetry. In addition, the isoimide is easily converted into an imide structure at high temperature, and volatile small molecules are not generated in the conversion process, so that the preparation of pore-free large-size and large-thickness workpieces is facilitated. Currently, there have been used isoimide products such as IP600 (ethynyl terminated isoimide oligomer), phenylethynyl terminated isoimide oligomer, as heat-resistant adhesive and heat-resistant matrix resin for fiber composite materials, but these two products are expensive.
Disclosure of Invention
The invention provides a soluble norbornene-terminated imide oligomer and a preparation method thereof, aiming at solving the problems of high porosity of thermosetting polyimide composite materials prepared by taking PMR type polyimide resin and amic acid as prepregs and high raw material cost of thermosetting polyimide composite materials prepared by ethynyl and phenylethynyl-terminated imide oligomers.
The invention is realized by the following technical scheme: a soluble norbornenyl-terminated imide oligomer is prepared by adopting low-cost aromatic diamine monomers, aromatic dianhydride monomers and norbornenic anhydride end capping agents to carry out polycondensation and dehydration cyclization reactions to obtain the norbornenyl-terminated imide oligomer, wherein the structural formula of the oligomer is as follows:
(ii) a Wherein Ar has 4 structures, Ar' has 3 structures, and the structures are respectively as follows:
。
a method of preparing said soluble norbornenyl terminated imide oligomer comprising the steps of:
(1) dissolving an aromatic diamine monomer in an N-methyl pyrrolidone or N, N-dimethyl acetamide solvent under an inert gas environment;
(2) dissolving an aromatic dianhydride monomer in an N-methyl pyrrolidone or N, N-dimethyl acetamide solvent, and then dropwise adding the aromatic dianhydride monomer into the aromatic diamine solution prepared in the step (1) to react for 4-12 h to obtain an amine-terminated amic acid solution; wherein the molar ratio of dianhydride to diamine monomer is 1:2-6: 7;
(3) dissolving nadic anhydride in N-methyl pyrrolidone or N, N-dimethyl acetamide solvent, and then dropwise adding the nadic anhydride into the amine-terminated amic acid solution prepared in the step (2) to react for 6-24 hours to obtain a norbornenyl-terminated amic acid solution;
(4) dropwise adding a dehydrating agent into the solution obtained in the step (3) for cyclization reaction for 2-24 hours to obtain a norbornene-terminated imide oligomer solution;
(5) precipitating the norbornene-terminated imide oligomer solution by using a precipitant, continuously washing the solution by using the precipitant until the filtrate is neutral, drying the filtrate to constant weight, and crushing the filtrate to obtain the soluble norbornene-terminated imide oligomer.
In the step (1), the aromatic diamine monomer is any one of p-phenylenediamine, 4' -diaminodiphenylmethane, 4' -diaminodiphenyl ether or 3,4' -diaminodiphenyl ether; the inert gas is nitrogen atmosphere.
In the step (2), the aromatic dianhydride monomer is any one of 3,3',4,4' -benzophenone tetracarboxylic dianhydride, 3',4,4' -biphenyl tetracarboxylic dianhydride or 4,4' -biphenyl ether dianhydride.
The molar ratio of the nadic anhydride in the step (3) to the amino end group in the amine-terminated amic acid solution in the step (2) is 1: 1-1.2: 1.
In the step (4), the dehydrating agent is trifluoroacetic anhydride or N, N' -dicyclohexylcarbodiimide, and the molar ratio of the dehydrating agent to the diamine monomer is 2: 1-2.5: 1.
And (5) the precipitating agent is any one of acetone, ethanol or isopropanol, and the volume ratio of the norbornene-terminated imide oligomer solution to the precipitating agent is 1: 2-1: 5.
The temperature of the reaction system in the steps (1) to (4) is-10 ℃ to 40 ℃; the drying temperature in the step (5) is 50-150 ℃.
The solid content of the norbornene-based end-capped imide oligomer solution obtained in the step (4) is 15-22 wt%; the polymerization degree of the soluble norbornene-based end-capped imide oligomer obtained in the step (5) is 1 to 6.
The norbornene-based end-capped imide oligomer obtained by the invention has the characteristics of good solubility, low solution viscosity, conversion into thermosetting polyimide at high temperature and no release of volatile micromolecules in polar solvents such as N, N-dimethylacetamide and N-methylpyrrolidone.
Compared with the prior art, the invention has the characteristics and beneficial effects that:
(1) the invention adopts low-cost aromatic diamine monomer, aromatic dianhydride monomer and nadic anhydride end capping agent to prepare the norbornene-terminated imide oligomer through polycondensation and dehydration cyclization reactions. Compared with the imide oligomer blocked by ethynyl and phenylacetylene blocking agents with the unit price of 2-5 ten thousand yuan/kg, the invention adopts the nadic anhydride with the unit price of about 400 yuan/kg as the blocking agent, thereby greatly reducing the cost of raw materials.
(2) The norbornene-terminated imide oligomer provided by the invention has an asymmetric structure, strong disorder of molecular chains, difficulty in crystallization, good solubility in polar solvents such as N, N-dimethylacetamide and N-methylpyrrolidone, and low solution viscosity; in addition, the iso-imide structure in the norbornene-based end-capped iso-imide oligomer is a kinetic product, is thermodynamically unstable, is easily isomerized by heating to form a thermodynamically stable imide structure (the transformation process is shown in figure 1), does not release small molecular substances in the transformation process, and is more suitable for preparing a non-porous thermosetting polyimide composite material compared with PMR type polyimide resin with high porosity of a final product and PETI resin and TriA-PI resin which are used as prepreg by using precursor amic acid due to release of small molecular substances in the curing process. Based on the characteristics, the norbornene-based end-capped imide oligomer provided by the invention can be applied to the fields of aerospace, national defense and military industry, civil use and the like.
Drawings
FIG. 1 is a diagram showing a process of converting an isoimide structure into an imide structure in an isoimide oligomer;
FIG. 2 is a chart of the infrared spectrum of a norbornene-based terminated imide oligomer prepared in example 1;
FIG. 3 is a DSC temperature rise profile of norbornene-based end-capped imide oligomer prepared in example 1;
FIG. 4 is a graph showing the thermogravimetry of a norbornene-based terminated imide oligomer prepared in example 1;
FIG. 5 is a DMA profile of norbornene-based end-capped imide oligomer prepared in example 1;
FIG. 6 is a chart of the infrared spectrum of norbornene-based terminated imide oligomer prepared in example 1 after curing by crosslinking at 280 ℃;
FIG. 7 is a representation of a sample prepared in example 1 after curing by crosslinking the norbornene-based terminated imide oligomer at 280 ℃;
FIG. 8 is a thermal decomposition profile of norbornene-based terminated imide oligomer prepared in example 1 after curing by crosslinking at 280 ℃.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments; all other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs and the disclosures and references cited herein and the materials to which they refer are incorporated by reference.
Those skilled in the art will recognize that equivalents to the specific embodiments described, as may be learned by routine experimentation, are intended to be encompassed by the present application.
The experimental procedures in the following examples are conventional unless otherwise specified. The instruments used in the following examples are, unless otherwise specified, laboratory-standard instruments; the experimental materials used in the following examples were purchased from a conventional biochemical reagent store unless otherwise specified. The norbornene-terminated imide oligomer and the preparation method thereof designed by the present invention will be further described below.
In the following examples, each of the raw materials is commercially available, and each raw material is abbreviated as follows: 4,4' -diaminodiphenylmethane, MDA; 4,4' -diaminodiphenyl ether, ODA; 3,4' -diaminodiphenyl ether, mODA; p-phenylenediamine, p-PDA; 3,3',4,4' -benzophenonetetracarboxylic dianhydride, s-BTDA; 3,3',4,4' -biphenyl tetracarboxylic dianhydride (s-BPDA); 4,4' -diphenyl ether dianhydride, ODPA; nadic anhydride, i.e., NA; n-methylpyrrolidone, NMP; n, N-dimethylacetamide (DMAc); trifluoroacetic anhydride, i.e., TFAA; n, N' -Dicyclohexylcarbodiimide (DCC).
Example 1: 19.83g (0.1 mol) of MDA and 29.75g of NMP are added into a three-neck flask with magnetic stirring and at the temperature of 20 ℃ for dissolution under the nitrogen environment; then 21.49g (0.067 mol) s-BTDA is dissolved in 222.62g NMP and is dripped into the MDA solution to react for 8h, so that an amine-terminated amic acid solution is obtained; dissolving 10.93g (0.067 mol) of NA in 43.72g of NMP, and dropwise adding the solution into an amine-terminated amic acid solution to react for 15 hours to obtain a norbornene-based terminated amic acid solution with a solid content of 15 wt%; 52.51g (0.25 mol) of TFAA was added dropwise to the norbornene-based terminated amic acid solution for reaction for 12 hours to give a norbornene-based terminated imide oligomer solution. Finally, the norbornene-group-terminated imide oligomer solution is poured into acetone for precipitation (the volume ratio of the oligomer solution to the acetone is 1: 2), the precipitate is collected by filtration, and the precipitate is washed to be neutral by the acetone. The precipitate washed to neutrality is dried in a forced air oven at 50 ℃ until the product weight is constant.
The prepared norbornene-based end-capped imide oligomer is characterized by structure, performance and the like, and the results are shown in fig. 2-5. Preheating the prepared norbornene-based end-capped imide oligomer at 210 ℃ for 1h by using a vulcanizer, then hot-pressing at 280 ℃ for 1h under the pressure of 6MPa and at 320 ℃ for 1h to prepare a thermosetting polyimide standard sample strip, and carrying out structural, performance and other representations on the standard sample strip, wherein the results are shown in FIGS. 6-8.
FIG. 2 is an infrared spectrum of the prepared norbornene-based terminated imide oligomer. As can be seen from FIG. 2, 1805cm-1、1690cm-1、933 cm-1The characteristic peak of the imidolactone of the isoimide appears, which indicates that the norbornene-group-terminated isoimide oligomer is generated; furthermore, 1546cm-1C-NH vibration peak of amide II, 1668cm-1the-C = O-oscillation peak of amide i disappeared completely, indicating that the amic acid was all converted to the isoimide.
FIG. 3 is a DSC graph showing the temperature rise of the prepared norbornene-based terminated imide oligomer under a nitrogen atmosphere. As can be seen from FIG. 3, a broad exothermic peak occurs at 185 ℃ to 300 ℃, which is caused by the crosslinking and curing of norbornene and the conversion of the imide structure to the imide structure; based on FIG. 2, the structural transition temperature and curing temperature of the norbornene-based end-capped imide oligomer can be selected from 185 ℃ to 300 ℃.
FIG. 4 is a graph showing the thermogravimetry of the prepared norbornene-based terminated imide oligomer under nitrogen atmosphere, and it can be seen from FIG. 4 that the norbornene-based terminated imide oligomer prepared according to the present invention has T in nitrogen atmosphere5%And T10%The carbon residue rates are respectively 285 ℃, 360 ℃ and 800 ℃ and are 49.0 percent; the thermal weight loss of the norbornene-based end-capped imide oligomer before 285 ℃ is mainly caused by decomposition of low molecular weight substances, and the thermal weight loss of 285 ℃ to 500 ℃ is mainly caused by decomposition of partial condensation polymers due to low crosslinking density and poor thermal stability caused by insufficient crosslinking.
FIG. 5 is a graph showing the mechanical loss with temperature of the norbornene-based terminated imide oligomer prepared in example 1 measured by a three-point bending method. As can be seen from FIG. 5, the curve peaked at 360 ℃ to illustrate that the glass transition temperature of the thermoset polyimide obtained by crosslinking and curing the norbornene-based terminated imide oligomer prepared in example 1 was 360 ℃ at which the polymer state was changed from a glassy state to a highly elastic state.
FIG. 6 is a chart showing the infrared spectrum of the prepared norbornene-based terminated imide oligomer after crosslinking curing at 280 ℃. As can be seen from FIG. 6, 1805cm-1、1690cm-1、933 cm-1The characteristic peak of the imino lactone of the isoimide disappears, and 1780cm appears-1imide-C = O-asymmetric stretching vibration peak, 1720cm-1imide-C = O-symmetric stretching vibration peak, 1380cm-1And (3) an imide C-N stretching vibration peak, which shows that after the crosslinking and curing at 280 ℃, the system is completely converted into an imide structure from an isoimide structure to obtain the thermosetting polyimide.
FIG. 7 is a cross-sectional view and a surface view of a prepared norbornene-based terminated imide oligomer after crosslinking curing at 280 ℃. As can be seen in FIG. 7, the hot-pressed bars were smooth in cross-section and surface and free of voids. Illustrating that the thermoset polyimide article prepared from the norbornene-based terminated imide oligomer prepared in accordance with the present invention is void-free.
FIG. 8 is a graph showing the thermogravimetric analysis of the prepared norbornene-based terminated imide oligomer after crosslinking curing at 280 ℃. As can be seen from FIG. 8, T in a nitrogen atmosphere of a thermosetting polyimide obtained after crosslinking and curing of an isoimide oligomer5%And T10%The carbon residue rates of 480 ℃, 546 ℃ and 750 ℃ are 72.0 percent respectively, and the alloy has better heat resistance. The weight loss by heat before 546 ℃ is mainly due to the low crosslinking density and poor thermal stability of the partial polycondensate caused by insufficient crosslinking, so that the partial polycondensate is decomposed. The thermal weight loss after 546 ℃ is mainly caused by thermal decomposition of the thermosetting polyimide.
Example 2: and finally, pouring the norbornene-group-terminated imide oligomer solution into ethanol for precipitation (the volume ratio of the oligomer solution to the ethanol is 1: 2), filtering and collecting precipitates, and washing the precipitates to be neutral by using the ethanol. The precipitate washed to neutrality is dried in a forced air oven at 50 ℃ until the product weight is constant. The rest of the procedure is as described in example 1.
Example 3: finally, the norbornene-group-terminated imide oligomer solution is poured into isopropanol to precipitate (the volume ratio of the oligomer solution to the isopropanol is 1: 2), the precipitate is collected by filtration, and the precipitate is washed to be neutral by the isopropanol. The precipitate washed to neutrality is dried in a forced air oven at 50 ℃ until the product weight is constant. The rest of the procedure is as described in example 1.
Example 4: in a nitrogen atmosphere, 20.02g (0.1 mol) of ODA and 30.03g of NMP are added into a three-neck flask with magnetic stirring and at the temperature of 20 ℃ for dissolution; then 19.62g (0.067 mol) s-BPDA was dissolved in 212.81g NMP and added dropwise to the ODA solution for reaction for 8h to obtain an amine-terminated amic acid solution; dissolving 10.93g (0.067 mol) of NA in 43.72g of NMP, and dropwise adding the solution into an amine-terminated amic acid solution to react for 15 hours to obtain a norbornene-based terminated amic acid solution with a solid content of 15 wt%; 52.51g (0.25 mol) of TFAA was added dropwise to the norbornene-based terminated amic acid solution for reaction for 12 hours to give a norbornene-based terminated imide oligomer solution. And finally, pouring the norbornene-group-terminated imide oligomer solution into ethanol for precipitation (the volume ratio of the oligomer solution to the ethanol is 1: 2), filtering and collecting precipitates, and washing the precipitates to be neutral by using the ethanol. The precipitate washed to neutrality is dried in a forced air oven at 50 ℃ until the product weight is constant.
Example 5: in a nitrogen atmosphere, 20.02g (0.1 mol) of mODA and 30.03g of NMP are added into a three-neck flask with magnetic stirring and at the temperature of 20 ℃ for dissolution; then 19.62g (0.067 mol) s-BPDA is dissolved in 212.81g NMP and is dripped into the mODA solution to react for 8h, so as to obtain amine-terminated amic acid solution; dissolving 10.93g (0.067 mol) of NA in 43.72g of NMP, and dropwise adding the solution into an amine-terminated amic acid solution to react for 15 hours to obtain a norbornene-based terminated amic acid solution with a solid content of 15 wt%; 52.51g (0.25 mol) of TFAA was added dropwise to the norbornene-based terminated amic acid solution for reaction for 12 hours to give a norbornene-based terminated imide oligomer solution. And finally, pouring the norbornene-group-terminated imide oligomer solution into ethanol for precipitation (the volume ratio of the oligomer solution to the ethanol is 1: 2), filtering and collecting precipitates, and washing the precipitates to be neutral by using the ethanol. The precipitate washed to neutrality is dried in a forced air oven at 50 ℃ until the product weight is constant.
Example 6: in a nitrogen atmosphere, 10.81g (0.1 mol) of p-PDA and 16.22g of NMP are added into a three-neck flask with magnetic stirring and at the temperature of 20 ℃ for dissolution; then 20.69g (0.067 mol) of ODPA is dissolved in 180.50g of NMP and is dripped into the p-PDA solution to react for 8h, so as to obtain an amine-terminated amic acid solution; dissolving 10.93g (0.067 mol) of NA in 43.72g of NMP, and dropwise adding the solution into an amine-terminated amic acid solution to react for 15 hours to obtain a norbornene-based terminated amic acid solution with a solid content of 15 wt%; 52.51g (0.25 mol) of TFAA was added dropwise to the norbornene-based terminated amic acid solution for reaction for 12 hours to give a norbornene-based terminated imide oligomer solution. And finally, pouring the norbornene-group-terminated imide oligomer solution into ethanol for precipitation (the volume ratio of the oligomer solution to the ethanol is 1: 2), filtering and collecting precipitates, and washing the precipitates to be neutral by using the ethanol. The precipitate washed to neutrality is dried in a forced air oven at 50 ℃ until the product weight is constant.
Example 7: 19.83g (0.1 mol) of MDA and 29.75g of NMP are added into a three-neck flask with magnetic stirring and at the temperature of 20 ℃ for dissolution under the nitrogen environment; then 16.11g (0.05 mol) s-BTDA was dissolved in 201.25g NMP and added dropwise to the MDA solution to react for 8h to give an amine-terminated amic acid solution; dissolving 16.40g (0.1 mol) of NA in 65.60g of NMP, and dropwise adding the solution into an amine-terminated amic acid solution to react for 15 hours to obtain a norbornene-based terminated amic acid solution with a solid content of 15 wt%; 52.51g (0.25 mol) of TFAA was added dropwise to the norbornene-based terminated amic acid solution for reaction for 12 hours to give a norbornene-based terminated imide oligomer solution. And finally, pouring the norbornene-group-terminated imide oligomer solution into ethanol for precipitation (the volume ratio of the oligomer solution to the ethanol is 1: 2), filtering and collecting precipitates, and washing the precipitates to be neutral by using the ethanol. The precipitate washed to neutrality is dried in a forced air oven at 50 ℃ until the product weight is constant.
Example 8: 19.83g (0.1 mol) of MDA and 29.75g of NMP are added into a three-neck flask with magnetic stirring and at the temperature of 20 ℃ for dissolution under the nitrogen environment; then 27.71g (0.086 mol) of s-BTDA was dissolved in 247.48g of NMP and added dropwise to the MDA solution for reaction for 8h to obtain an amine-terminated amic acid solution; dissolving 4.69g (0.029 mol) of NA in 18.75g of NMP, and dropwise adding the solution into an amine-terminated amic acid solution to react for 15 hours to obtain a norbornene-terminated amic acid solution with the solid content of 15 wt%; 52.51g (0.25 mol) of TFAA was added dropwise to the norbornene-based terminated amic acid solution for reaction for 12 hours to give a norbornene-based terminated imide oligomer solution. And finally, pouring the norbornene-group-terminated imide oligomer solution into ethanol for precipitation (the volume ratio of the oligomer solution to the ethanol is 1: 2), filtering and collecting precipitates, and washing the precipitates to be neutral by using the ethanol. The precipitate washed to neutrality is dried in a forced air oven at 50 ℃ until the product weight is constant.
Example 9: under nitrogen atmosphere, 19.83g (0.1 mol) of MDA and 24.24g of DMAc are added into a three-neck flask with magnetic stirring and at the temperature of-10 ℃ for dissolution; then 21.49g (0.067 mol) of s-BTDA is dissolved in 138.4g of DMAc, and is dripped into the MDA solution to react for 12h, so as to obtain an amine-terminated amic acid solution; dissolving 13.12g (0.08 mol) of NA in 30.60g of DMAc, and dropwise adding the solution into an amine-terminated amic acid solution to react for 24 hours to obtain a norbornene-based terminated amic acid solution with the solid content of 22 wt%; 42.01g (0.2 mol) of TFAA was added dropwise to the norbornene-based terminated amic acid solution for reaction for 24 hours to obtain a norbornene-based terminated imide oligomer solution. Finally, the norbornene-group-terminated imide oligomer solution is poured into ethanol for precipitation (the volume ratio of the oligomer solution to the ethanol is 1: 5), the precipitate is collected by filtration, and the precipitate is washed to be neutral by the ethanol. And drying the precipitate washed to be neutral in a blast oven at 150 ℃ until the product is constant in weight.
Example 10: 19.83g (0.1 mol) of MDA and 29.75g of NMP are added into a three-neck flask with magnetic stirring and at the temperature of 40 ℃ for dissolution under the nitrogen environment; then 21.49g (0.067 mol) s-BTDA is dissolved in 222.62g NMP and is dripped into the MDA solution to react for 4h, so that an amine-terminated amic acid solution is obtained; dissolving 10.93g (0.067 mol) of NA in 43.72g of NMP, and dropwise adding the solution into an amine-terminated amic acid solution to react for 6 hours to obtain a norbornene-based terminated amic acid solution with a solid content of 15 wt%; 47.45g (0.23 mol) of DCC was added to the norbornene-based terminated amic acid solution for 2 hours to obtain a norbornene-based terminated imide oligomer solution. And finally, pouring the norbornene-group-terminated imide oligomer solution into ethanol for precipitation (the volume ratio of the oligomer solution to the ethanol is 1: 2), filtering and collecting precipitates, and washing the precipitates to be neutral by using the ethanol. The precipitate washed to neutrality is dried in a blast oven at 85 ℃ until the product weight is constant.
The system, monomer ratio and process parameters of each example in examples 1 to 10 are shown in tables 1 and 2.
TABLE 1 example systems and monomer ratios
TABLE 2 Process parameters of the examples
The norbornene-based terminated imide oligomer prepared in the above example was subjected to dissolution and viscosity tests; the mechanical property test is carried out by preparing a thermosetting polyimide standard sample strip through hot die pressing molding (equipment: a vulcanizing machine; process: preheating for 1h at 210 ℃, then hot pressing for 1h at 280 ℃ and hot pressing for 1h at 320 ℃ under the pressure of 6 MPa), and the specific test method is as follows:
solubility and viscosity testing: the isoimide oligomer was formulated as a DMAc solution at 20wt% solids, the solution viscosity was tested using GB/T2794-.
Glass transition temperature (T)g): the glass transition temperature of thermoset polyimides was tested using the DMA three point bend test, according to ASTM D5418 test standards.
Mechanical properties: testing the tensile strength and tensile modulus of the thermosetting polyimide by adopting the GB/T1040.2-2006 standard; testing the bending strength and the bending modulus of the thermosetting polyimide by adopting the GB/T9341-2008 standard; the compression strength of the thermosetting polyimide is tested by adopting the GB/T1041-2008 standard. The test results are shown in tables 3 and 4.
Table 3 results of solubility and viscosity tests for each example
TABLE 4 mechanical Properties of the hot-pressed sample strips of the examples
As can be seen from Table 3, the norbornene-based end-capped imide oligomer prepared by the method is light yellow powder, a DMAc solution with the solid content of 20wt% is a yellow clear solution, and the viscosity of the DMAc solution is less than 100mPa.s, which shows that the norbornene-based end-capped imide oligomer has the characteristics of good solubility and low solution viscosity in aprotic polar solvents such as DMAc and can meet the requirements of a prepreg during preparation of a composite material.
As can be seen from Table 4, the glass transition temperature of the thermosetting polyimide obtained by crosslinking and curing the norbornene-terminated imide oligomer prepared by the invention is higher than 330 ℃, the tensile strength is higher than 38MPa, the tensile modulus is higher than 2.5GPa, the bending strength is higher than 55MPa, the bending modulus is higher than 3.5GPa, and the compressive strength is higher than 55MPa, which shows that the thermosetting polyimide obtained by crosslinking and curing the norbornene-terminated imide oligomer prepared by the invention has better comprehensive mechanical properties.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (9)
1. A soluble norbornenyl terminated imide oligomer, characterized by: the norbornene-terminated imide oligomer is prepared by adopting low-cost aromatic diamine monomer, aromatic dianhydride monomer and norbornene dianhydride terminating agent through polycondensation and dehydration cyclization reaction, and the structural formula of the oligomer is as follows:
(ii) a Wherein Ar has 4 structures, Ar' has 3 structures, and the structures are respectively as follows:
。
2. a method of preparing the soluble norbornenyl terminated imide oligomer of claim 1 wherein: the method comprises the following steps:
(1) dissolving an aromatic diamine monomer in an N-methyl pyrrolidone or N, N-dimethyl acetamide solvent under an inert gas environment;
(2) dissolving an aromatic dianhydride monomer in an N-methyl pyrrolidone or N, N-dimethyl acetamide solvent, and then dropwise adding the aromatic dianhydride monomer into the aromatic diamine solution prepared in the step (1) to react for 4-12 h to obtain an amine-terminated amic acid solution; wherein the molar ratio of dianhydride to diamine monomer is 1:2-6: 7;
(3) dissolving nadic anhydride in N-methyl pyrrolidone or N, N-dimethyl acetamide solvent, and then dropwise adding the nadic anhydride into the amine-terminated amic acid solution prepared in the step (2) to react for 6-24 hours to obtain a norbornenyl-terminated amic acid solution;
(4) dropwise adding a dehydrating agent into the solution obtained in the step (3) for cyclization reaction for 2-24 hours to obtain a norbornene-terminated imide oligomer solution;
(5) precipitating the norbornene-terminated imide oligomer solution by using a precipitant, continuously washing the solution by using the precipitant until the filtrate is neutral, drying the filtrate to constant weight, and crushing the filtrate to obtain the soluble norbornene-terminated imide oligomer.
3. The method of preparing a soluble norbornenyl terminated imide oligomer as recited in claim 2 wherein: in the step (1), the aromatic diamine monomer is any one of p-phenylenediamine, 4' -diaminodiphenylmethane, 4' -diaminodiphenyl ether or 3,4' -diaminodiphenyl ether; the inert gas is nitrogen atmosphere.
4. The method of preparing a soluble norbornenyl terminated imide oligomer as recited in claim 2 wherein: in the step (2), the aromatic dianhydride monomer is any one of 3,3',4,4' -benzophenone tetracarboxylic dianhydride, 3',4,4' -biphenyl tetracarboxylic dianhydride or 4,4' -biphenyl ether dianhydride.
5. The method of preparing a soluble norbornenyl terminated imide oligomer as recited in claim 2 wherein: the molar ratio of the nadic anhydride in the step (3) to the amino end group in the amine-terminated amic acid solution in the step (2) is 1: 1-1.2: 1.
6. The method of preparing a soluble norbornenyl terminated imide oligomer as recited in claim 2 wherein: in the step (4), the dehydrating agent is trifluoroacetic anhydride or N, N' -dicyclohexylcarbodiimide, and the molar ratio of the dehydrating agent to the diamine monomer is 2: 1-2.5: 1.
7. The method of preparing a soluble norbornenyl terminated imide oligomer as recited in claim 2 wherein: and (5) the precipitating agent is any one of acetone, ethanol or isopropanol, and the volume ratio of the norbornene-terminated imide oligomer solution to the precipitating agent is 1: 2-1: 5.
8. The method of preparing a soluble norbornenyl terminated imide oligomer as recited in claim 2 wherein: the temperature of the reaction system in the steps (1) to (4) is-10 ℃ to 40 ℃; the drying temperature in the step (5) is 50-150 ℃.
9. The method of preparing a soluble norbornenyl terminated imide oligomer as recited in claim 2 wherein: the solid content of the norbornene-based end-capped imide oligomer solution obtained in the step (4) is 15-22 wt%; the polymerization degree of the soluble norbornene-based end-capped imide oligomer obtained in the step (5) is 1 to 6.
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