Preparation method of polymethacrylimide foam with high foaming ratio

Abstract

The invention relates to a preparation method of polymethacrylimide foam, in particular to a preparation method of polymethacrylimide foam with high foaming ratio. The invention aims to solve the problems that the preparation process of the existing polymethacrylimide foam is complicated, the forming process window is narrow, and the polymethacrylimide foam with high foaming ratio cannot be obtained. The method comprises the following steps: 1, weighing; 2, prepolymerization; 3, polymerizing; and 4, foaming. Formamide, tert-butyl alcohol and 1-nitrile propyl-3-methylimidazolium hexafluorophosphate are used as a composite foaming agent, the foaming agent has good intersolubility with a main monomer butyl methacrylate and cannot be separated out in a prepolymerization stage and a post-polymerization stage, and the prepared copolymerization plate is uniform and transparent; the foaming ratio of the polymethacrylimide foam with the high foaming ratio prepared by the preparation method disclosed by the invention can reach 15.8 times; the compression strength can reach 1.03 MPa, and the bending strength can reach 1.82 MPa.

Description

Technical Field

[0001] The present invention relates to a method for preparing polymethacrylimide foam. Background Art

[0002] With the development of fields such as aviation, aerospace, navigation, railway, highway, and wind energy, in addition to meeting the requirement of light weight, foam plastics also need to meet the special needs of these fields for material strength, stiffness, and heat resistance, which requires continuous improvement of the performance of foam plastics. Therefore, high performance has become a new direction and hotspot in the research of foam plastics. Currently, foreign countries have used high-performance foam plastics as load-bearing structural materials in fields such as aviation, aerospace, and transportation, such as the framework of satellite solar cells, the fairing at the front end of rockets, the vertical tail of unmanned aircraft, the airframe and wings of cruise missiles, and the large radome of ships.

[0003] Polymethacrylimide refers to a polymer having a cyclic structure as shown in Structural Formula I, and some people also call it methyl polyisophthalimide. It is obtained by imidization of homopolymers or copolymers of methacrylic acid derivatives (such as methyl methacrylate, methacrylic acid, methacrylamide, methacrylonitrile, etc.) with amines at high temperature. It can be seen from the structure that the imide ring with a methyl group provides very strong rigidity for the material. When the content of the cyclic structure reaches a certain level, the material can have excellent heat resistance, good weather resistance, high modulus, strength, and other excellent mechanical properties.

[0004] The performance of foam plastics depends on factors such as the performance of the polymer, cell structure, cell size, foaming ratio, and molding method and molding conditions. The research approaches for high-performance foam plastics include the development of new foam plastics and the regulation of cell structure. However, currently, the preparation process of PMI foam is complex, the molding process window is narrow, and the existing methods cannot obtain polymethacrylimide foam with a high foaming ratio. Therefore, it is of great significance to provide a method for preparing polymethacrylimide foam with a high foaming ratio. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems that the preparation process of existing polymethacrylimide foam is complex, the molding process window is narrow, and polymethacrylimide foam with a high foaming ratio cannot be obtained, and to provide a method for preparing polymethacrylimide foam with a high foaming ratio.

[0006] A method for preparing polymethacrylimide foam with a high foaming ratio is specifically completed according to the following steps:

[0007] I. Weighing materials:

[0008] ① Weigh butyl methacrylate and acrylamide to obtain Raw Material I;

[0009] In Step 1①, the mass ratio of butyl methacrylate to acrylamide is 68:32;

[0010] ② Weigh the initiator, foaming agent and crosslinking agent to obtain Raw Material II;

[0011] In Step 1②, the foaming agent is formamide, tert-butanol and 1-cyanopropyl-3-methylimidazolium hexafluorophosphate, and the mass ratio of formamide, tert-butanol and 1-cyanopropyl-3-methylimidazolium hexafluorophosphate is 1:3:1;

[0012] In Step 1②, the initiator is azobisisobutyronitrile;

[0013] In Step 1②, the crosslinking agent is N,N-methylenebisacrylamide;

[0014] ③ Mix Raw Material I and Raw Material II to obtain Raw Material III;

[0015] II. Pre-polymerization:

[0016] Place Raw Material III in a high-temperature water bath at 80-95°C for pre-polymerization reaction. The liquid in the system becomes a colorless, transparent and viscous liquid, obtaining the pre-polymerized system;

[0017] III. Polymerization:

[0018] Use the casting method to pour the pre-polymerized system into a closed mold with nitrogen protection, and then place the mold in a constant-temperature water bath for polymerization reaction for a period of time. The water bath temperature is controlled at 45°C - 54°C, and the mold is removed to obtain a transparent copolymer resin sheet;

[0019] IV. Foaming:

[0020] Place the transparent copolymer resin sheet in a flat vulcanizing machine at 180-200°C for foaming for a period of time to obtain a poly(methacrylimide) foam with a high foaming ratio.

[0021] Principle of the present invention:

[0022] I. The present invention uses formamide, tert-butanol and 1-cyanopropyl-3-methylimidazolium hexafluorophosphate as a composite foaming agent. This foaming agent has good solubility with the main monomer butyl methacrylate and will not separate out during the pre-polymerization stage and the post-polymerization stage. The prepared copolymer plate is uniform and transparent;

[0023] II. The present invention innovatively discovers that when the mass ratio of butyl methacrylate to acrylamide is 68:32 and the mass ratio of formamide, tert-butanol and 1-cyanopropyl-3-methylimidazolium hexafluorophosphate is 1:3:1, a poly(methacrylimide) foam with a high foaming ratio can be obtained;

[0024] III. The foaming ratio of the polymethacrylimide foam prepared by the present invention can reach 15.8 times; the compressive strength can reach 1.03 MPa, and the flexural strength can reach 1.82 MPa.

[0025] The present invention can obtain a polymethacrylimide foam with a high foaming ratio. Description of the Drawings

[0026] Figure 1 SEM images of the polymethacrylimide foams prepared in Examples 1 to 3. In the figure, (a) is Example 2, (b) is Example 1, and (c) is Example 3;

[0027] Figure 2 Pore size, density, and foaming ratio diagrams of the polymethacrylimide foams prepared in Examples 1 to 3. In the figure, 1 is Example 2, 2 is Example 1, and 3 is Example 3. Detailed Embodiments

[0028] Detailed Embodiment 1: A method for preparing a polymethacrylimide foam with a high foaming ratio is specifically completed according to the following steps:

[0029] A method for preparing a polymethacrylimide foam with a high foaming ratio is specifically completed according to the following steps:

[0030] I. Weighing materials:

[0031] ① Weigh butyl methacrylate and acrylamide to obtain Raw Material I;

[0032] In step ① of step I, the mass ratio of butyl methacrylate to acrylamide is 68:32;

[0033] ② Weigh an initiator, a foaming agent, and a crosslinking agent to obtain Raw Material II;

[0034] In step ② of step I, the foaming agent is formamide, tert-butanol, and 1-cyanopropyl-3-methylimidazolium hexafluorophosphate, and the mass ratio of formamide, tert-butanol, and 1-cyanopropyl-3-methylimidazolium hexafluorophosphate is 1:3:1;

[0035] In step ② of step I, the initiator is azobisisobutyronitrile;

[0036] In step ② of step I, the crosslinking agent is N,N-methylenebisacrylamide;

[0037] ③ Mix Raw Material I and Raw Material II to obtain Raw Material III;

[0038] II. Prepolymerization:

[0039] The raw material Ⅲ is placed in a high-temperature water bath at 80-95 °C for pre-polymerization reaction. The liquid in the system becomes a colorless, transparent and viscous liquid, and the pre-polymerized system is obtained.

[0040] III. Polymerization:

[0041] The pre-polymerized system is cast into a closed mold with nitrogen protection by the casting method, and then the mold is placed in a constant-temperature water bath for polymerization reaction for a period of time. The water bath temperature is controlled at 45 °C - 54 °C. The mold is removed to obtain a transparent copolymer resin sheet.

[0042] IV. Foaming:

[0043] The transparent copolymer resin sheet is placed in a flat vulcanizing machine at 180-200 °C for foaming for a period of time to obtain a polymethacrylimide foam with a high foaming ratio.

[0044] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that in the raw material Ⅲ described in step ①③, the mass ratio of the foaming agent to the raw material Ⅰ is (4 g - 12 g):100. Other steps are the same as those in Specific Embodiment 1.

[0045] Specific Embodiment 3: The difference between this embodiment and one of Specific Embodiments 1 or 2 is that in the raw material Ⅲ described in step ①③, the mass ratio of the initiator to the raw material Ⅰ is (0.1 g - 0.3 g):100. Other steps are the same as those in Specific Embodiment 1 or 2.

[0046] Specific Embodiment 4: The difference between this embodiment and one of Specific Embodiments 1 to 3 is that in the raw material Ⅲ described in step ①③, the mass ratio of the cross-linking agent to the raw material Ⅰ is (1 g - 3 g):100. Other steps are the same as those in Specific Embodiments 1 to 3.

[0047] Specific Embodiment 5: The difference between this embodiment and one of Specific Embodiments 1 to 4 is that the pre-polymerization reaction time described in step ② is 5 min - 30 min. Other steps are the same as those in Specific Embodiments 1 to 4.

[0048] Specific Embodiment 6: The difference between this embodiment and one of Specific Embodiments 1 to 5 is that the polymerization reaction time described in step ③ is 40 h - 48 h. Other steps are the same as those in Specific Embodiments 1 to 5.

[0049] Specific Embodiment 7: The difference between this embodiment and one of Specific Embodiments 1 to 6 is that the foaming time described in step ④ is 30 min - 60 min. Other steps are the same as those in Specific Embodiments 1 to 6.

[0050] The following examples are used to verify the beneficial effects of the present invention:

[0051] Example 1: A preparation method of poly (methacrylimide) foam with high foaming ratio is specifically completed according to the following steps:

[0052] I. Weighing materials:

[0053] ① Weigh 68 g of butyl methacrylate (BMA) and 32 g of acrylamide (AM) to obtain raw material I;

[0054] ② Weigh 0.2 g of initiator, 12 g of foaming agent and 2 g of crosslinking agent to obtain raw material II;

[0055] The foaming agent described in step I ② is formamide, tert-butanol and 1-cyanopropyl-3-methylimidazolium hexafluorophosphate, and the mass ratio of formamide, tert-butanol and 1-cyanopropyl-3-methylimidazolium hexafluorophosphate is 1:3:1;

[0056] The initiator described in step I ② is azobisisobutyronitrile;

[0057] The crosslinking agent described in step I ② is N,N'-methylenebisacrylamide;

[0058] ③ Mix raw material I and raw material II to obtain raw material III;

[0059] II. Prepolymerization:

[0060] Place raw material III in a high-temperature water bath at 95 °C for a prepolymerization reaction for 20 min. The liquid in the system becomes a colorless and transparent viscous liquid to obtain the prepolymerized system;

[0061] III. Polymerization:

[0062] Adopt the casting method to pour the prepolymerized system into a closed mold with nitrogen protection, and then place the mold in a constant-temperature water bath for a polymerization reaction for 48 h. The water bath temperature is controlled at 50 °C, and the mold is removed to obtain a transparent copolymer resin sheet;

[0063] IV. Place the transparent copolymer resin sheet in a flat vulcanizer at 200 °C for foaming for a period of time to obtain poly (methacrylimide) foam (PMI foam) with high foaming ratio.

[0064] Example 2: The difference between this example and Example 1 is that in step I ①, 60 g of butyl methacrylate and 40 g of acrylamide are weighed to obtain raw material I. Other steps and parameters are the same as those in Example 1.

[0065] Example 3: The difference between this example and Example 1 is that in step I ①, 75 g of butyl methacrylate and 25 g of acrylamide are weighed to obtain raw material I. Other steps and parameters are the same as those in Example 1.

[0066] Example 4: The difference between this example and Example 1 is that: the foaming agent described in Step 1 ② is formamide and tert-butanol, and the mass ratio of formamide to tert-butanol is 1:3. Other steps and parameters are the same as those in Example 1.

[0067] Example 5: The difference between this example and Example 1 is that: the foaming agent described in Step 1 ② is formamide, tert-butanol and 1-cyanopropyl-3-methylimidazolium hexafluorophosphate, and the mass ratio of formamide, tert-butanol and 1-cyanopropyl-3-methylimidazolium hexafluorophosphate is 1:1:1. Other steps and parameters are the same as those in Example 1.

[0068] Figure 1 SEM images of the poly(methacrylimide) foams prepared in Examples 1-3, where (a) is Example 2, (b) is Example 1, and (c) is Example 3;

[0069] From Figure 1 it can be seen that: as the content of BMA monomer increases, the cell size shows a trend of first decreasing and then increasing. At the same time, the cell number also shows a change of first increasing and then decreasing.

[0070] Figure 2 Cell size, density and foaming ratio diagrams of the poly(methacrylimide) foams prepared in Examples 1-3, where 1 is Example 2, 2 is Example 1, and 3 is Example 3;

[0071] From Figure 2 it can be seen that: as the ratio of BMA monomer to AM monomer increases from 60 / 40 to 68 / 32 and then to 75 / 25, the cell size of the PMI foam decreases from 871 μm to 523 μm first and then increases to 781 μm. At the same time, the cell density increases from 7.3×10 3 kg / cm 3 to 1.0×10 4 kg / cm 3 first and then decreases to 5.4×10 3 kg / cm 3 , and the foaming ratio of the PMI foam also increases from 11.3 times to 15.8 times first and then decreases to 10.1 times. When the ratio of BMA and AM monomers is 68 / 32, the PMI foam has the smallest cell size, the highest cell density and the largest foaming ratio. Therefore, the ratio of BMA monomer to AM monomer of 68 / 32 has the highest foaming ratio.

[0072] For the poly(methacrylimide) foams prepared in Examples 1-3

[0073] the compressive strength and flexural strength were tested, and the specific test methods are as follows:

[0074] Compressive strength:

[0075] According to GB / T8813-2008, a standard test specimen with dimensions of 50mm×50mm×25mm was cut from the foam board at a compression rate of 1mm / min to determine the compression strength of the foam material.

[0076] Flexural strength:

[0077] According to GB / T8812-2007, a standard test specimen with dimensions of 120mm×25mm×20mm was cut from the foam board at a flexural rate of 2mm / min to determine the flexural strength of the foam material.

[0078] The above test results are shown in Table 1;

[0079] Table 1

[0080]

[0081]

[0082] The cell size, density and expansion ratio of the polymethacrylimide foams prepared in Examples 1, 4 and 5 are listed in Table 2;

[0083] Table 2

[0084]

[0085] It can be seen from Table 2 that when the blowing agents are formamide, tert-butanol and 1-cyanopropyl-3-methylimidazolium hexafluorophosphate, and the mass ratio of formamide, tert-butanol and 1-cyanopropyl-3-methylimidazolium hexafluorophosphate is 1:3:1, the polymethacrylimide foam prepared has the highest expansion ratio.

Claims

1. A preparation method of polymethacrylimide foam with high foaming ratio, characterized in that The preparation method is specifically completed according to the following steps: I. Weighing materials: ① Weigh butyl methacrylate and acrylamide to obtain raw material I; In step I①, the mass ratio of butyl methacrylate to acrylamide is 68:32; ② Weigh an initiator, a foaming agent and a crosslinking agent to obtain raw material II; In step I②, the foaming agent is formamide, tert-butanol and 1-cyanopropyl-3-methylimidazolium hexafluorophosphate, and the mass ratio of formamide, tert-butanol and 1-cyanopropyl-3-methylimidazolium hexafluorophosphate is 1:3:1; In step I②, the initiator is azobisisobutyronitrile; In step I②, the crosslinking agent is N,N-methylenebisacrylamide; ③ Mix raw material I and raw material II to obtain raw material III; II. Pre-polymerization: Place raw material III in a high-temperature water bath at 80 - 95°C for pre-polymerization reaction until the liquid in the system becomes a colorless, transparent and viscous liquid to obtain the pre-polymerized system; III. Polymerization: Use the casting method to pour the pre-polymerized system into a closed mold with nitrogen protection, then place the mold in a constant-temperature water bath for polymerization reaction for a period of time, control the water bath temperature at 45°C - 54°C, and remove the mold to obtain a transparent copolymer resin sheet; IV. Foaming: Place the transparent copolymer resin sheet in a flat vulcanizing machine at 180 - 200°C for foaming for a period of time to obtain a poly(methacrylimide) foam with a high foaming ratio.

2. The preparation method of a polymethacrylimide foam with a high foaming ratio according to claim 1, characterized in that In step I③, the mass ratio of the foaming agent in raw material III to raw material I is (4g - 12g):

100.

3. The preparation method of a polymethacrylimide foam with a high foaming ratio according to claim 1, characterized in that In step I③, the mass ratio of the initiator in raw material III to raw material I is (0.1g - 0.3g):

100.

4. The preparation method of a polymethacrylimide foam with a high foaming ratio according to claim 1, characterized in that In step I③, the mass ratio of the crosslinking agent in raw material III to raw material I is (1g - 3g):

100.

5. The preparation method of a polymethacrylimide foam with a high foaming ratio according to claim 1, characterized in that In step II, the time of the pre-polymerization reaction is 5min - 30min.

6. The preparation method of a polymethacrylimide foam with a high foaming ratio according to claim 1, characterized in that In step III, the time of the polymerization reaction is 40h - 48h.

7. The preparation method of a polymethacrylimide foam with a high foaming ratio according to claim 1, characterized in that In step IV, the time of the foaming is 30min - 60min.

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