High molecular weight narrow distribution pmma cast sheet and its controlled polymerization preparation process
Patent Information
- Application Number
- CN202611161786.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-08-03
- Publication Date
- 2026-11-03
AI Technical Summary
In existing PMMA casting processes, the molecular weight distribution is too wide, and the polydispersity index generally exceeds 2.5, which leads to warping, cracking or optical distortion of the material during post-processing, making it difficult to meet the stringent requirements of aerospace transparent parts and high-end display light guide plates.
By employing a composite initiator (a complex system of azobisisobutyronitrile and benzoyl peroxide) and iodoalkane chain transfer agents in a synergistic manner, combined with a three-stage segmented temperature regime and vacuum degassing treatment, the molecular weight and its distribution in the prepolymerization stage are controlled, ultimately achieving narrow distribution polymerization.
The polydispersity index of PMMA cast plates is ≤2.0, the molecular chain length inside the material tends to be uniform, the thermal shrinkage and rheological behavior are consistent, warping and optical distortion are avoided, the light transmittance is ≥92%, the haze is ≤1.0%, and the mechanical properties and heat resistance are improved.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of PMMA preparation technology, specifically to high molecular weight narrow distribution PMMA casting plates and a controllable polymerization preparation process for high molecular weight narrow distribution PMMA casting plates. Background Technology
[0002] PMMA, commonly known as plexiglass, is widely used in aerospace transparent components, high-end display light guide plates, and optical lenses due to its excellent optical transparency, weather resistance, and mechanical strength. Industrial upgrading has placed higher demands on the performance of sheet materials, requiring not only extremely high molecular weights to ensure mechanical and heat resistance, but also sufficiently narrow molecular weight distributions to improve the uniformity of processing flow and the dimensional stability of finished products, thus avoiding warping, cracking, or optical distortion caused by differences in molecular chain lengths during post-processing.
[0003] Traditional domestic casting processes often employ a single initiator without adding chain transfer agents, coupled with a simple heating regime. This results in a relatively crude control of free radical concentration throughout the polymerization process. Under this process, it is difficult to maintain a coordinated rate of chain growth, chain termination, and chain transfer reactions throughout the entire cycle. Consequently, the molecular weight distribution of the final polymer product is typically wide, with a polydispersity index generally exceeding 2.5. Such a wide distribution indicates the presence of numerous molecular chains of varying lengths within the material, leading to significant differences in their rheological and thermal shrinkage behaviors. This can easily cause internal stress concentration, resulting in very low yield rates during subsequent hot bending or laser cutting. Existing improvement technologies, such as adjusting the initiator or using thiol-based chain transfer agents, still struggle to overcome the technical bottleneck of a polydispersity index below 2.0 due to their simplistic mechanisms. Summary of the Invention
[0004] This invention addresses the problems in the prior art by providing high molecular weight narrow distribution PMMA casting plates and their controllable polymerization preparation process. The specific technical solution is as follows: The controlled polymerization process for preparing high molecular weight narrow distribution PMMA casting sheets includes the following steps: S1: Mix methyl methacrylate monomer, composite initiator and chain transfer agent, and carry out prepolymerization reaction under stirring conditions. Control the reaction temperature at 50~80℃ and the conversion rate at 20%~25% to obtain prepolymer slurry. The composite initiator is a mixture of azobisisobutyronitrile (AIBN) and benzoyl peroxide, with a mass ratio of AIBN to benzoyl peroxide of 1:3 to 3:1; the chain transfer agent is an iodoalkane compound, and its addition amount is 0.01% to 0.5% of the mass of methyl methacrylate monomer. S2: The prepolymer slurry obtained in step S1 is poured into a mold, and a three-stage segmented temperature regime is used for the polymerization reaction, specifically including: First stage: Hold at 60~70℃ for 2~6 hours to carry out low-temperature initiation polymerization; Second stage: Heat to 75~85℃ and hold for 4~12 hours to carry out medium-temperature growth polymerization; Third stage: Heat to 100~110℃ and hold for 1~4 hours to carry out high-temperature curing polymerization; S3: After the polymerization reaction is completed, the product is demolded, annealed, and cut to obtain PMMA casting sheet.
[0005] As a further technical solution of the present invention, the iodoalkane chain transfer agent in step S1 is selected from at least one of ethyl iodoacetate, iodopropane, and iodobutane.
[0006] As a further technical solution of the present invention, the iodoalkane chain transfer agent is ethyl iodoalkane.
[0007] As a further technical solution of the present invention, the prepolymerization reaction temperature in step S1 is 60~75℃ and the stirring rate is 50~200 rpm.
[0008] As a further technical solution of the present invention, the amount of composite initiator added in step S1 is 0.01% to 0.5% of the mass of methyl methacrylate monomer.
[0009] As a further technical solution of the present invention, in the three-stage segmented temperature regime described in step S2, the heat preservation time of the first stage is 2 to 4 hours, the heat preservation time of the second stage is 6 to 10 hours, and the heat preservation time of the third stage is 1 to 3 hours.
[0010] As a further technical solution of the present invention, the mold mentioned in step S2 is a circulating water bath jacketed mold, and the temperature fluctuation of the mold cavity is controlled within ±1℃ by the circulating water bath.
[0011] As a further technical solution of the present invention, the prepolymer slurry is subjected to vacuum degassing treatment before casting. The vacuum degree of vacuum degassing is -0.08 to -0.1 MPa, and the degassing time is 10 to 60 minutes.
[0012] As a further technical solution of the present invention, the annealing conditions in step S3 are: heat treatment at 90~120℃ for 1~4 hours, and then naturally cooled to room temperature.
[0013] On the other hand, the present invention provides a high molecular weight narrow distribution PMMA casting plate, which is prepared by the above-mentioned controlled polymerization preparation process of high molecular weight narrow distribution PMMA casting plate. The PMMA casting plate has a weight average molecular weight ≥8×105, a polydispersity index ≤2.0, a light transmittance ≥92%, and a haze ≤1.0%.
[0014] The beneficial effects of this invention are as follows: (1) In this invention, by synergistic regulation of composite initiator and iodoalkane chain transfer agent, the molecular weight and its distribution are pre-controlled in the prepolymerization stage, and the polydispersity index of the final product can be stabilized below 2.0, which solves the technical problem that the molecular weight distribution is too wide and the polydispersity index generally exceeds 2.5 due to the fluctuation of free radical concentration and uneven chain growth opportunities in traditional casting process.
[0015] (2) In this invention, the narrow molecular weight distribution makes the molecular chain length inside the material tend to be uniform, thereby achieving consistency in thermal shrinkage behavior and rheological behavior. The warpage of the product is controlled to be no more than 0.5 mm per meter, and the stress distribution is uniform. This solves the problem that the internal stress concentration caused by the difference in chain length during the post-processing of wide-distribution plates leads to warping, cracking or optical distortion.
[0016] (3) In this invention, the micro-phase separation and light scattering center formation caused by uneven chain length are suppressed by the reversible chain transfer balance mechanism, so as to achieve excellent optical performance with light transmittance of not less than 92% and haze of not more than 1.0%. This solves the problem that traditional wide-distribution plates have poor optical uniformity and cannot meet the stringent requirements of optical-grade light guide plates and high-end display fields.
[0017] (4) In this invention, the composite initiation system maintains a stable free radical concentration throughout the polymerization cycle, achieving both high molecular weight and narrow distribution, avoiding the deterioration of mechanical properties caused by low molecular weight components, and solving the problem that traditional single initiator processes are difficult to simultaneously increase molecular weight and narrow distribution, resulting in insufficient comprehensive mechanical properties and heat resistance. Detailed Implementation
[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments.
[0019] The detection method of the present invention is as follows: Molecular weight and molecular weight distribution: Determined by gel permeation chromatography with tetrahydrofuran as the mobile phase and column temperature of 35℃. The weight-average molecular weight, number-average molecular weight and polydispersity index were calculated using narrow-distribution polystyrene standard.
[0020] Transmittance and haze: Tested using a transmittance / haze meter according to GB / T7134-2008 standard, with a sample thickness of 3 mm.
[0021] Mechanical properties: tensile strength, impact strength and heat distortion temperature were all measured in accordance with GB / T7134-2008 standard.
[0022] Internal stress and warpage: The uniformity of interference fringes was observed using a polarizing stress meter. Warpage was determined by placing the sheet material on a horizontal platform and measuring the maximum difference in height between the four corners and the ground.
[0023] The following are specific embodiments; Example 1
[0024] Step S1: 10 kg of methyl methacrylate monomer, after depressurized distillation to remove polymerization inhibitors, was added to the reactor. A mixture of azobisisobutyronitrile (AIBN) and benzoyl peroxide (mass ratio 1:1) as a composite initiator was added, totaling 0.1% of the monomer (i.e., 10 g); and 5 g of ethyl iodobutyl iodide as a chain transfer agent was added, accounting for 0.05% of the monomer. Under nitrogen protection, the mixture was stirred at 100 rpm and reacted at 65°C. The refractive index was monitored to calculate the conversion rate. When the conversion rate reached 22%, the reaction was rapidly terminated by cooling. A slurry sample was taken for gel permeation chromatography analysis, and the weight-average molecular weight of the prepolymer was 3.2 × 10⁻⁶. 5 The polydispersity index is 1.72.
[0025] Step S2: The prepolymer slurry was degassed under vacuum at -0.095 MPa for 30 minutes, and then injected into a circulating water bath jacketed mold with a cavity size of 2 m × 1.5 m × 0.01 m. A three-stage temperature regime was implemented: the first stage was held at 65℃ for 3 hours; the second stage was raised to 80℃ and held for 8 hours; and the third stage was raised to 105℃ and held for 2 hours. During the polymerization process, the temperature fluctuation in the mold cavity was controlled within ±0.8℃.
[0026] Step S3: After polymerization, cool to below 80°C to demold, anneal the board at 110°C for 2 hours, cool with the furnace, and cut to obtain the finished product.
[0027] Example 2
[0028] Step S1: Take 10 kg of methyl methacrylate monomer after alkali washing, water washing, and drying. Add 20 g of a mixture of azobisisobutyronitrile and benzoyl peroxide in a mass ratio of 2:1, and 10 g of iodopropane. React at 70℃, and terminate when the conversion rate reaches 25%.
[0029] Step S2: After degassing the slurry at -0.09MPa for 20 minutes, inject it into the jacketed mold. Temperature regime: 70℃ for 2 hours, 85℃ for 6 hours, 110℃ for 1.5 hours, mold cavity temperature control ±0.9℃.
[0030] Step S3: Demold at 80℃ and anneal at 120℃ for 1.5 hours.
[0031] Finished product properties: Weight-average molecular weight 8.8 × 10⁻⁶ 5 Polydispersity index 1.90, light transmittance 92.5%, haze 0.8%, tensile strength 76.2 MPa, impact strength 17.8 kJ / m 2 Heat distortion temperature 100℃.
[0032] Example 3
[0033] Step S1: 10 kg of monomer obtained by vacuum distillation is added to 8 g of a mixture of azobisisobutyronitrile and benzoyl peroxide in a mass ratio of 1:2, and 3 g of ethyl iodoacetate. The reaction is carried out at 60 °C and terminated when the conversion rate reaches 20%.
[0034] Step S2: Degas the slurry at -0.1MPa for 40 minutes. Temperature regime: 60℃ for 4 hours, 75℃ for 10 hours, 100℃ for 3 hours, mold cavity temperature control ±0.7℃.
[0035] Step S3: After cold demolding, anneal at 100℃ for 3 hours.
[0036] Finished product properties: Weight-average molecular weight 1.02 × 10⁻⁶ 6 Polydispersity index 1.78, light transmittance 93.5%, haze 0.5%, tensile strength 80.1 MPa, impact strength 19.2 kJ / m 2 The heat distortion temperature is 104℃.
[0037] Comparative Example 1 Using only 15 grams of azobisisobutyronitrile (AIBN) as a single initiator, without adding chain transfer agents, prepolymerization was carried out at 70°C to a conversion rate of 22%. A standard mold and a single-stage heating process were used: direct programmed heating to 85°C for 10 hours, followed by curing at 105°C for 2 hours. Post-treatment was the same as in Example 1.
[0038] Results: Weight-average molecular weight 7.2 × 10⁻⁶ 5 Polydispersity index 2.68, light transmittance 90.8%, haze 1.8%, tensile strength 68.5 MPa, impact strength 14.2 kJ / m 2 The heat distortion temperature is 94℃, the warpage is about 1.8 mm / m, and the polarized stress stripes are obviously uneven.
[0039] Comparative Example 2 The initiator and temperature regime were the same as in Example 1, but no chain transfer agent was added.
[0040] Results: Weight-average molecular weight 8.5 × 10⁻⁶ 5 It has a polydispersity index of 2.31, a light transmittance of 91.2%, a haze of 1.4%, and a warpage of approximately 1.2 mm / m.
[0041] Comparative Example 3 Using only 10 grams of azobisisobutyronitrile and 5 grams of ethyl iodoacetate, the rest was exactly the same as in Example 1.
[0042] Results: Weight-average molecular weight 7.8 × 10⁻⁶ 5 It has a polydispersity index of 2.18, a light transmittance of 91.8%, a haze of 1.2%, and a warpage of approximately 1.0 mm / m.
[0043] The plates prepared in Examples 1-3 and Comparative Examples 1-3 were tested, and the test results are shown in Table 1.
[0044]
[0045] Table 1 As can be clearly seen from Table 1, the polydispersity index of all three embodiments of the present invention is below 1.90, which is far superior to the 2.68 of the conventional process in Comparative Example 1, and achieves an overwhelming advantage in optical performance and dimensional stability.
[0046] Comparing Example 1 and Comparative Example 2, it can be seen that, with the same composite initiator and segmentation temperature, the polydispersity index increased sharply from 1.83 to 2.31 in the absence of the iodoalkane chain transfer agent, and the warpage also increased significantly. This strongly demonstrates the crucial role of the reversible chain transfer equilibrium mechanism in achieving an extremely narrow distribution.
[0047] Comparing Example 1 and Comparative Example 3, it can be seen that, with the presence of a chain transfer agent and a suitable segmentation temperature, using a single azobisisobutyronitrile initiator instead of a composite initiator increased the polydispersity index from 1.83 to 2.18, and the molecular weight also increased from 9.6 × 10⁻⁶. 5 Reduced to 7.8×10 5 This demonstrates that the composite initiation system makes an irreplaceable synergistic contribution to maintaining stable free radical concentration, simultaneously increasing molecular weight, and narrowing distribution.
[0048] Synergistic effect verification: The polydispersity index (PDI) was 2.31 when the composite initiator was used alone, and 2.18 when the chain transfer agent was used alone, both failing to break the 2.0 threshold. Only when both were used in combination did the PDI plummet to 1.83. This "1+1>2" effect fully demonstrates the necessity and advancement of the dual regulatory mechanism of "free radical concentration stabilization" and "reversible chain transfer balance" in this invention.
[0049] Example 3 achieved optimal overall performance with a weight-average molecular weight of over one million and a polydispersity index as low as 1.78 by using a 1:2 ratio of composite initiator, a lower prepolymerization temperature of 60°C, and an appropriate amount of chain transfer agent.
[0050] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it.
Claims
1. A controlled polymerization process for preparing high molecular weight narrow distribution PMMA cast sheets, characterized in that, Includes the following steps: S1: Mix methyl methacrylate monomer, composite initiator and chain transfer agent, and carry out prepolymerization reaction under stirring conditions. Control the reaction temperature at 50~80℃ and the conversion rate at 20%~25% to obtain prepolymer slurry. The composite initiator is a mixture of azobisisobutyronitrile (AIBN) and benzoyl peroxide, with a mass ratio of AIBN to benzoyl peroxide of 1:3 to 3:1; the chain transfer agent is an iodoalkane compound, and its addition amount is 0.01% to 0.5% of the mass of methyl methacrylate monomer. S2: The prepolymer slurry obtained in step S1 is poured into a mold, and a three-stage segmented temperature regime is used for the polymerization reaction, specifically including: First stage: Hold at 60~70℃ for 2~6 hours to carry out low-temperature initiation polymerization; Second stage: Heat to 75~85℃ and hold for 4~12 hours to carry out medium-temperature growth polymerization; Third stage: Heat to 100~110℃ and hold for 1~4 hours to carry out high-temperature curing polymerization; S3: After the polymerization reaction is completed, the product is demolded, annealed, and cut to obtain PMMA casting sheet.
2. The controllable polymerization preparation process for high molecular weight narrow distribution PMMA casting plates according to claim 1, characterized in that: The iodoalkane chain transfer agent mentioned in step S1 is selected from at least one of ethyl iodoacetate, iodopropane, and iodobutane.
3. The controllable polymerization preparation process for high molecular weight narrow distribution PMMA casting plates according to claim 2, characterized in that: The iodoalkane chain transfer agent is ethyl iodoalkane.
4. The controllable polymerization preparation process for high molecular weight narrow distribution PMMA casting plates according to claim 1, characterized in that: The prepolymerization reaction temperature in step S1 is 60~75℃, and the stirring rate is 50~200 rpm.
5. The controllable polymerization preparation process for high molecular weight narrow distribution PMMA casting plates according to claim 1, characterized in that: The amount of composite initiator added in step S1 is 0.01% to 0.5% of the mass of methyl methacrylate monomer.
6. The controllable polymerization preparation process for high molecular weight narrow distribution PMMA casting plates according to claim 1, characterized in that: In the three-stage temperature regime described in step S2, the heat preservation time in the first stage is 2 to 4 hours, the heat preservation time in the second stage is 6 to 10 hours, and the heat preservation time in the third stage is 1 to 3 hours.
7. The controllable polymerization preparation process for high molecular weight narrow distribution PMMA casting plates according to claim 1, characterized in that: The mold mentioned in step S2 is a circulating water bath jacketed mold, and the temperature fluctuation of the mold cavity is controlled within ±1℃ by the circulating water bath.
8. The controllable polymerization preparation process for high molecular weight narrow distribution PMMA casting plates according to claim 1, characterized in that: Before casting, the prepolymer slurry is subjected to vacuum degassing treatment. The vacuum degree of vacuum degassing is -0.08 to -0.1 MPa, and the degassing time is 10 to 60 minutes.
9. The controllable polymerization preparation process for high molecular weight narrow distribution PMMA casting plates according to claim 1, characterized in that: The annealing conditions described in step S3 are: heat treatment at 90~120℃ for 1~4 hours, and then naturally cooled to room temperature.
10. High molecular weight narrow distribution PMMA cast sheet, characterized in that: The PMMA casting sheet is prepared using the controlled polymerization process described in any one of claims 1 to 9, wherein the weight-average molecular weight of the PMMA casting sheet is ≥8 × 10⁻⁶. 5 Polydispersity index ≤ 2.0, transmittance ≥ 92%, haze ≤ 1.0%.