A method for the synthesis of narrow distribution and low molecular weight polystyrene

Abstract

The application provides a synthesis method of narrow distribution and low molecular weight polystyrene, wherein the weight average molecular weight of the polystyrene obtained by the method is in the range of 1800-12000, and the PDI is in the range of 1-1.4. The method for synthesizing narrow distribution and low molecular weight polystyrene by O / W microemulsion limited photopolymerization has the advantages of mild reaction condition, good controllability, good reproducibility, and the yield of polystyrene is not less than 85.7%. In the method for synthesizing narrow distribution and low molecular weight polystyrene by O / W microemulsion limited photopolymerization, the emulsifier and mineral oil involved can be regenerated and recycled, and almost no obvious three waste emissions are generated. In the method for synthesizing narrow distribution and low molecular weight polystyrene by O / W microemulsion limited photopolymerization, the chemical oxygen demand of the water phase after treatment by activated carbon and anion exchange resin is not more than 28.6 mg O2 / L.

Description

Technical Field

[0001] The invention relates to a method for synthesizing polystyrene, in particular to a method for synthesizing polystyrene with narrow distribution and low molecular weight with high reproducibility, and belongs to the technical field of special functional organic chemicals. Background Art

[0002] Compared to high-molecular-weight polymers, low-molecular-weight polymers often possess unique fluidity and good compatibility with substrates, while retaining the high molecular weight and low biotoxicity of higher-molecular-weight polymers. Therefore, they have broad and unique applications in fillers, adhesives, and coatings. Low-molecular-weight polystyrene (LMPS) is a precursor for the synthesis of a novel brominated polymer flame retardant, polybromostyrene. LMWPS is synthesized by direct bromination of LMWPS. Considering flame retardancy, processing properties, and product aging performance, LMWPS with a molecular weight range of 2000-12000 and a polydispersity index (PDI) below 1.4 are most suitable. However, designing a synthesis method for LMWPS with a narrow molecular weight distribution remains a challenge. The key challenge is reproducibly achieving both a molecular weight of 2000-12000 and a sufficiently narrow molecular weight distribution (PDI no greater than 1.4). To address this problem, the present invention uses microemulsion confined photopolymerization to precisely synthesize a series of polystyrenes with narrow distribution (PDI in the range of 1-1.4) and low molecular weight (weight average molecular weight in the range of 1800-12000). Previously, there was a report on the synthesis of low molecular weight polystyrenes by anionic polymerization using a scandium-based organic compound as a catalyst and a combination of boron-containing and aluminum-containing organic compounds as an activator (Macromolecules, 2020, 53, 1205-1211). The number average molecular weight of the obtained polystyrenes was in the range of 2200-5800. Only one batch of polystyrenes had a PDI of 1.3, while the PDI of the remaining polystyrenes was in the range of 1.4-2.6. In addition, there was a report on the use of benzoyl peroxide as an initiator in dichloromethane to obtain polystyrenes with a viscosity average molecular weight in the range of 1180-5735 (Journal of Functional Polymers, 1997, 10(1), 87-89). However, the PDI data of the obtained polystyrenes were not reported.There are essential differences between the known publicly available methods for synthesizing low molecular weight polystyrene and the method for synthesizing low molecular weight polystyrene by O / W microemulsion confined photopolymerization described in the present invention. The most important difference is that the PDI of the low molecular weight polystyrene reported in the literature (Macromolecules, 2020, 53, 1205-1211) is generally large, and the low molecular weight polystyrene reported in the literature (Journal of Functional Polymers, 1997, 10(1),87-89) does not provide PDI data. In addition, none of the known literatures clearly states whether the reported methods for synthesizing low molecular weight polystyrene can accurately reproduce the experimental results. None of the known literatures clearly states whether the reported methods for synthesizing low molecular weight polystyrene can accurately and reproducibly synthesize polystyrene with a molecular weight in the range of 6000~12000 and a PDI not exceeding 1.4. The methods for synthesizing low molecular weight polystyrene reported in the known literatures have obvious three waste problems. The method for synthesizing polystyrene by confined photopolymerization of O / W microemulsions described in the present invention can obtain polystyrene with a weight-average molecular weight in the range of 1800 to 12000 and a PDI in the range of 1 to 1.4. Moreover, the molecular weight and PDI of the obtained polystyrene can be highly reproducible after repeating the synthesis three times. Summary of the Invention

[0003] The present invention aims to provide a highly reproducible method for synthesizing narrow-distribution and low-molecular-weight polystyrene, addressing the technical difficulties in the current field of narrow-distribution and low-molecular-weight polystyrene synthesis, namely, the difficulty in both reproducibly controlling the weight-average molecular weight of the polystyrene within the range of 1800 to 12000 and reproducibly controlling the molecular weight distribution of the low-molecular-weight polystyrene to be sufficiently narrow (i.e., the PDI is not greater than 1.4).

[0004] A highly reproducible synthesis method for polystyrene with narrow distribution and low molecular weight comprises the following steps: first, styrene, 2-hydroxy-2-methylpropiophenone, mineral oil, an emulsifier, and water are prepared into a microemulsion, then irradiated with 365 nm ultraviolet light until the reaction is complete, and then the microemulsion system after the reaction is demulsified with hydrochloric acid to obtain a three-phase system of polystyrene solid, oil phase, and water phase. After separation, polystyrene, a mineral oil phase, and a water phase are obtained respectively. The obtained water phase is treated with an ion exchange resin to obtain a regenerated water phase. The mineral oil phase, the regenerated water phase, fresh styrene, and 2-hydroxy-2-methylpropiophenone are mixed, and the pH is adjusted with an organic base to form a regenerated microemulsion system. The system is then irradiated with 365 nm ultraviolet light for another round of polymerization reaction to obtain polystyrene again.

[0005] Furthermore, the styrene, 2-hydroxy-2-methylpropiophenone, mineral oil, emulsifier and water are prepared into a microemulsion, and styrene and 2-hydroxy-2-methylpropiophenone are combined in a molar ratio of 1:0.001-0.04 to form a styrene-2-hydroxy-2-methylpropiophenone composition.

[0006] Furthermore, the styrene, 2-hydroxy-2-methylpropiophenone, mineral oil, emulsifier and water are prepared into a microemulsion, and the mineral oil is n-dodecane.

[0007] Furthermore, the styrene, 2-hydroxy-2-methylpropiophenone, mineral oil, emulsifier and water are prepared into a microemulsion, and the emulsifier is a composition of triethylamine n-dodecanoate and n-butanol in a mass ratio of 1:2.

[0008] Furthermore, in the microemulsion prepared from styrene, 2-hydroxy-2-methylpropiophenone, mineral oil, emulsifier and water, the mass percentage of the emulsifier is 20%, the mass percentage of water is 77.8%, the mass percentage of the mineral oil is 0.4% to 1.47%, and the mass percentage of the styrene-2-hydroxy-2-methylpropiophenone composition is 0.73% to 1.8%.

[0009] Furthermore, the microemulsion prepared by the styrene, 2-hydroxy-2-methylpropiophenone, mineral oil, emulsifier and water is of O / W type.

[0010] Furthermore, the temperature of the reaction with 365 nm ultraviolet light irradiation is room temperature, and the intensity of the ultraviolet light is 4 W / cm 2 , the reaction time is 1 to 6 hours.

[0011] Furthermore, hydrochloric acid is used to demulsify the microemulsion system after the reaction, and hydrochloric acid is used to adjust the pH of the system to 7.0 after the reaction is completed.

[0012] Furthermore, the polystyrene, mineral oil phase and water phase are obtained respectively after the separation by first releasing the lower water phase from the demulsification system and then separating the oil phase and the polystyrene solid from each other by vacuum filtration.

[0013] Furthermore, the obtained aqueous phase is treated with an ion exchange resin to obtain a regenerated aqueous phase, wherein the ion exchange resin is a hydroxyl anion exchange resin, and the hydroxyl anion exchange resin is mixed with the aqueous phase to be treated in a mass ratio of 1:1 for 5 minutes to make the pH of the aqueous phase reach 11.5.

[0014] Furthermore, the mineral oil phase, the regenerated water phase, fresh styrene and 2-hydroxy-2-methylpropiophenone are mixed and then the pH is adjusted with an organic base to form a regenerated microemulsion system, wherein the organic base is triethylamine and the pH is adjusted to 8.5.

[0015] Furthermore, the next round of polymerization reaction was carried out by irradiating with 365 nm ultraviolet light, the temperature of the 365 nm ultraviolet light irradiation reaction was room temperature, and the intensity of the ultraviolet light was 4 W / cm 2 , the reaction time is 1 to 6 hours.

[0016] The above-synthesized products were tested by gel permeation chromatography (GPC) technology, and the weight average molecular weight was in the range of 1800-12000, and the PDI was in the range of 1-1.4, and the yield of the products was not less than 85.7%.

[0017] The method of the present invention has the following advantages over the prior art:

[0018] 1. The weight average molecular weight of the polystyrene obtained in the present invention is in the range of 1800 to 12000, and the PDI is in the range of 1 to 1.4.

[0019] 2. The method for synthesizing narrow distribution and low molecular weight polystyrene by O / W microemulsion confined photopolymerization provided by the present invention has mild reaction conditions, good controllability, good reproducibility, and the yield of polystyrene is not less than 85.7%.

[0020] 3. The emulsifier and mineral oil involved in the method for synthesizing narrow distribution and low molecular weight polystyrene by O / W microemulsion confined photopolymerization provided by the present invention can be recycled and reused, and there is almost no obvious discharge of three wastes.

[0021] 4. In the method for synthesizing narrow distribution and low molecular weight polystyrene by O / W microemulsion confined photopolymerization provided by the present invention, the chemical oxygen demand of the aqueous phase after treatment with activated carbon and anion exchange resin does not exceed 28.6 mg O2 / L. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the GPC elution curve of the polystyrene (weight average molecular weight in the range of 4000-5000) synthesized in Example 1 of the present invention.

[0023] Figure 2 This is a laser light scattering diagram of the microemulsion system of the synthesized polystyrene (weight average molecular weight in the range of 4000-5000) before ultraviolet irradiation in Example 1 of the present invention.

[0024] Figure 3 This is the identification result of the continuous phase dye dilution method of the microemulsion type of the synthesized polystyrene (weight average molecular weight in the range of 4000-5000) in Example 1 of the present invention before ultraviolet irradiation. DETAILED DESCRIPTION

[0025] The following is a further description of the process for synthesizing polystyrene, the reproducibility effect, the regeneration and recycling of the reaction medium, and the wastewater treatment effect of the present invention through specific examples.

[0026] Example 1: Highly reproducible synthesis of polystyrene with a weight average molecular weight in the range of 4000 to 5000

[0027] Take 0.719 g of styrene, 11.2 mg of 2-hydroxy-2-methylpropiophenone and 1.47 g of n-dodecane and add them to a 250 mL round-bottom flask. Then add 77.8 g of water, 4.43 g of n-dodecanoic acid, 2.24 g of triethylamine and 13.33 g of n-butanol. Then, high-purity nitrogen is introduced into the bottom of the material in the round-bottom flask at a flow rate of 10 mL / min until all the materials in the round-bottom flask are evenly mixed and the appearance is clear and transparent. Then, use 365 nm ultraviolet light (4 W / cm 2 ) irradiation was carried out at room temperature for 6 hours. Hydrochloric acid was then added to adjust the pH to 7.0 to completely demulsify the microemulsion system after the reaction, and the product polystyrene (PS-1) and the mineral oil phase and aqueous phase were separated. The obtained PS-1 was washed with a small amount of methanol and dried to obtain a white solid powder with a yield of 89.1%. Using standard polystyrene as a control, GPC analysis ( Figure 1 ) The weight average molecular weight of the obtained PS-1 ( M w ) is 4380, the number average molecular weight ( M n ) is 3650 and PDI is 1.2.

[0028] The resulting aqueous phase was treated with an OH-type anion exchange resin (a 1:1 aqueous phase to resin mass ratio) for 5 minutes to obtain a regenerated aqueous phase. The mineral oil phase, regenerated aqueous phase, 0.719 g of fresh styrene, and 11.2 mg of 2-hydroxy-2-methylpropiophenone were mixed. The pH was then adjusted to 8.5 with triethylamine under nitrogen flow (10 mL / min) to form a regenerated microemulsion. A second round of polymerization was then carried out under 365 nm UV irradiation to obtain PS-2. This process was repeated for a third round of polymerization to obtain PS-3. The molecular weight, PDI, and yield of the polystyrenes obtained from these three rounds are listed in Table 1.

[0029] Table 1 Highly reproducible synthesis results of polystyrene with a weight average molecular weight in the range of 4000-5000

[0030]

[0031] Before UV irradiation, the particle size distribution of the droplets in the microemulsion system was measured by laser light scattering in the three rounds of reaction systems described in this example ( Figure 2 ), the radius of the microemulsion droplets before the three rounds of reaction was approximately 10.8 nm, 12.3 nm, and 14.8 nm, respectively. Combined with the clear and transparent appearance, it was confirmed that the polymerization reaction in this example was indeed carried out in a microemulsion system. Identification by continuous phase dye dilution method ( Figure 3 ), in order to make the interface clearly identifiable during the dilution process, the microemulsion was pre-dyed with a water-soluble dye methylene blue before dilution. Figure 3A is to dilute the dyed microemulsion with n-dodecane, Figure 3 B is to dilute the dyed microemulsion with water, Figure 3 The results showed that the microemulsion in this example was of O / W type.

[0032] In this example, after the three rounds of synthesis reaction were completed and the polystyrene product was isolated, the resulting aqueous phases were treated with anion exchange resin and activated carbon, respectively, in a 1:1 aqueous phase to resin mass ratio and a 1:0.5 aqueous phase to activated carbon mass ratio, for 0.5 hours and 1 hour, respectively. The chemical oxygen demand (COD) values ​​of the water after treatment were measured, and the COD values ​​of the treated aqueous phases from the three rounds were 18.3 mg O2 / L, 18.1 mg O2 / L, and 17.9 mg O2 / L, respectively. This demonstrates that the treatment of wastewater obtained by the highly reproducible synthesis method for narrowly distributed and low molecular weight polystyrene provided by the present invention is very simple and effective.

[0033] Example 2: Highly reproducible synthesis of polystyrene with a weight average molecular weight in the range of 1800 to 2000

[0034] Take 1236.6 mg of styrene, 77.4 mg of 2-hydroxy-2-methylpropiophenone and 2.65 g of n-dodecane and add them to a 500 mL round-bottom flask. Then add 140 g of water, 7.97 g of n-dodecanoic acid, 4.03 g of triethylamine and 24 g of n-butanol. Then, high-purity nitrogen is introduced into the bottom of the material in the round-bottom flask at a flow rate of 10 mL / min until all the materials in the round-bottom flask are evenly mixed and the appearance is clear and transparent. Then, use 365 nm ultraviolet light (4 W / cm 2 ) irradiated and reacted at room temperature for 1 hour. Hydrochloric acid was then added to adjust the pH to 7.0 to completely demulsify the microemulsion system, separating the product polystyrene (PS-4), the mineral oil phase, and the aqueous phase. The resulting PS-4 was washed with a small amount of methanol and dried to a white solid powder with a yield of 85.7%. Using standard polystyrene as a control, the weight-average molecular weight of the obtained PS-4 ( M w ) is 1880, the number average molecular weight ( M n ) is 1710 and PDI is 1.1.

[0035] The resulting aqueous phase was treated with an OH-type anion exchange resin (a 1:1 aqueous phase to resin mass ratio) for 5 minutes to obtain a regenerated aqueous phase. The mineral oil phase, the regenerated aqueous phase, 1236.6 mg of fresh styrene, and 77.4 mg of 2-hydroxy-2-methylpropiophenone were mixed. The pH was then adjusted to 8.5 with triethylamine under nitrogen flow (10 mL / min) to form a regenerated microemulsion. A second round of polymerization was then carried out under 365 nm UV irradiation to obtain PS-5. This process was repeated for a third round of polymerization to obtain PS-6. The molecular weight, PDI, and yield of the polystyrenes obtained from these three rounds are listed in Table 2.

[0036] Table 2 Highly reproducible synthesis results of polystyrene with a weight-average molecular weight in the range of 1800-2000

[0037]

[0038] Before UV irradiation, laser light scattering measurements of the microemulsion droplet radius in the first reaction cycle described in this example revealed an approximate 11.9 nm radius. This, combined with the clear, transparent appearance, confirms that the polymerization reaction in this example was indeed carried out within the microemulsion. Continuous phase dye dilution analysis confirmed that the microemulsions described in this example were all O / W-type.

[0039] In this example, after the three rounds of synthesis reaction were completed and the product polystyrene was separated, the resulting aqueous phases were treated with anion exchange resin and activated carbon, respectively, wherein the mass ratio of the aqueous phase to the resin was 1:1, and the mass ratio of the aqueous phase to the activated carbon was 1:0.5. The treatment times were 0.5 hour and 1 hour, respectively. After treatment, the chemical oxygen demand of the water was measured. The chemical oxygen demand of the aqueous phases obtained after treatment was 28.3 mg O2 / L, 28.6 mg O2 / L, and 27.9 mg O2 / L, respectively.

[0040] Example 3: Highly Reproducible Synthesis of Polystyrene with a Weight Average Molecular Weight in the Range of 2000-3000

[0041] Take 2921.8 mg of styrene, 138.2 mg of 2-hydroxy-2-methylpropiophenone and 0.68 g of n-dodecane and add them to a 250 mL round-bottom flask. Then add 132.3 g of water, 7.53 g of n-dodecanoic acid, 3.81 g of triethylamine and 22.66 g of n-butanol. Then, high-purity nitrogen is introduced into the bottom of the material in the round-bottom flask at a flow rate of 10 mL / min until all the materials in the round-bottom flask are evenly mixed and visually clear and transparent. Then, use 365 nm ultraviolet light (4 W / cm 2) irradiation was carried out at room temperature for 3.5 hours. Hydrochloric acid was then added to adjust the pH to 7.0 to completely demulsify the microemulsion system after the reaction, and the product polystyrene (PS-7) and the mineral oil phase and aqueous phase were separated. The obtained PS-7 was washed with a small amount of methanol and dried to obtain a white solid powder with a yield of 86.0%. The weight average molecular weight of the obtained PS-7 ( M w ) is 2510, the number average molecular weight ( M n ) is 2000 and PDI is 1.26.

[0042] The resulting aqueous phase was treated with OH-type anion exchange resin (a 1:1 aqueous phase to resin mass ratio) for 5 minutes to obtain a regenerated aqueous phase. The mineral oil phase, the regenerated aqueous phase, 2921.8 mg of fresh styrene, and 138.2 mg of 2-hydroxy-2-methylpropiophenone were mixed. The pH was then adjusted to 8.5 with triethylamine under nitrogen flow (10 mL / min) to form a regenerated microemulsion. A second round of polymerization was then carried out under 365 nm UV irradiation to obtain PS-8. This process was repeated for the third to sixth rounds of polymerization to obtain PS-9 to PS-12, respectively. The molecular weight, PDI, and yield of the polystyrenes obtained from these six rounds are listed in Table 3.

[0043] Table 3 Highly reproducible synthesis results of polystyrene with a weight average molecular weight in the range of 2000-3000

[0044]

[0045] Before UV irradiation, laser light scattering measurements of the microemulsion droplet radius in the fourth reaction run described in this example revealed a microemulsion system with a clear, transparent appearance, confirming that the polymerization reaction in this example was indeed carried out within the microemulsion system. Continuous phase dye dilution confirmed that the microemulsions described in this example were all O / W-type.

[0046] In this example, after the sixth round of synthesis reaction was completed and the product polystyrene was separated, the resulting aqueous phase was treated with anion exchange resin and activated carbon, respectively, wherein the mass ratio of the aqueous phase to the resin was 1:1 and the mass ratio of the aqueous phase to the activated carbon was 1:0.5. The treatment times were 0.5 hour and 1 hour, respectively. After treatment, the chemical oxygen demand of the water was measured to be 24.4 mgO2 / L.

[0047] Example 4: Highly Reproducible Synthesis of Polystyrene with a Weight Average Molecular Weight in the Range of 3000-4000

[0048] Take 2239.4 mg of styrene, 70.6 mg of 2-hydroxy-2-methylpropiophenone and 2.32 g of n-dodecane and add them to a 250 mL round-bottom flask. Then add 163.4 g of water, 9.3 g of n-dodecanoic acid, 4.71 g of triethylamine and 27.98 g of n-butanol. Then, high-purity nitrogen is introduced into the bottom of the material in the round-bottom flask at a flow rate of 10 mL / min until all the materials in the round-bottom flask are evenly mixed and the appearance is clear and transparent. Then, use 365 nm ultraviolet light (4 W / cm 2 ) irradiation was carried out at room temperature for 5.5 hours. Hydrochloric acid was then added to adjust the pH to 7.0 to completely demulsify the microemulsion system after the reaction, and the product polystyrene (PS-13) and the mineral oil phase and aqueous phase were separated. The obtained PS-13 was washed with a small amount of methanol and dried to obtain a white solid powder with a yield of 87.7%. Using standard polystyrene as a reference, the weight average molecular weight of the obtained PS-13 ( M w ) is 3590, the number average molecular weight ( M n ) is 2970 and PDI is 1.21.

[0049] The resulting aqueous phase was treated with an OH-type anion exchange resin (a 1:1 aqueous phase to resin mass ratio) for 5 minutes to obtain a regenerated aqueous phase. The mineral oil phase, the regenerated aqueous phase, 2239.4 mg of fresh styrene, and 70.6 mg of 2-hydroxy-2-methylpropiophenone were mixed. The pH was then adjusted to 8.5 with triethylamine under nitrogen flow (10 mL / min) to form a regenerated microemulsion. A second round of polymerization was then carried out under 365 nm UV irradiation to obtain PS-14. This process was repeated for the third to fifth rounds of polymerization to obtain PS-15 to PS-17, respectively. The molecular weight, PDI, and yield of the polystyrenes obtained from these five rounds are listed in Table 4.

[0050] Table 4 Highly reproducible synthesis results of polystyrene with a weight average molecular weight in the range of 3000-4000

[0051]

[0052] Before UV irradiation, laser light scattering measurements of the microemulsion droplet radius in the third reaction run described in this example revealed a microemulsion system with a clear, transparent appearance, confirming that the polymerization reaction in this example was indeed carried out within the microemulsion system. Continuous phase dye dilution confirmed that the microemulsions described in this example were all O / W-type.

[0053] Example 5: Highly Reproducible Synthesis of Polystyrene with a Weight Average Molecular Weight in the Range of 5000-7000

[0054] 17831.3 mg of styrene, 168.7 mg of 2-hydroxy-2-methylpropiophenone and 8.4 g of n-dodecane were added to a 2.5 L reactor, followed by 933.6 g of water, 53.2 g of n-dodecanoic acid, 26.9 g of triethylamine and 160.1 g of n-butanol. High-purity nitrogen was then introduced into the bottom of the reactor at a flow rate of 72 mL / min until all the materials in the reactor were evenly mixed and visually clear. The mixture was then irradiated with 365 nm ultraviolet light (4 W / cm 2 ) irradiation was carried out at room temperature for 6 hours. Hydrochloric acid was then added to adjust the pH to 7.0 to completely demulsify the microemulsion system after the reaction, and the product polystyrene (PS-18) and the mineral oil phase and aqueous phase were separated. The obtained PS-18 was washed with a small amount of methanol and dried to obtain a white solid powder with a yield of 85.9%. Using standard polystyrene as a reference, the weight average molecular weight of the obtained PS-18 ( M w ) is 6380, the number average molecular weight ( M n ) is 5110 and PDI is 1.25.

[0055] The resulting aqueous phase was treated with OH-type anion exchange resin (a 1:1 aqueous phase to resin mass ratio) for 5 minutes to obtain a regenerated aqueous phase. The mineral oil phase, the regenerated aqueous phase, 17,831.3 mg of fresh styrene, and 168.7 mg of 2-hydroxy-2-methylpropiophenone were mixed. The pH was then adjusted to 8.5 with triethylamine under nitrogen flow (50 mL / min) to form a regenerated microemulsion. A second round of polymerization was then carried out under 365 nm UV irradiation to obtain PS-19. This process was repeated for a third round of polymerization to obtain PS-20. The molecular weight, PDI, and yield of the polystyrene obtained from the three rounds are listed in Table 5.

[0056] Table 5 Highly reproducible synthesis results of polystyrene with a weight average molecular weight range of 5000-7000

[0057]

[0058] Before UV irradiation, laser light scattering measurements of the microemulsion droplet radius in the third reaction run described in this example revealed a microemulsion system with a clear, transparent appearance, confirming that the polymerization reaction in this example was indeed carried out within the microemulsion system. Continuous phase dye dilution confirmed that the microemulsions described in this example were all O / W-type.

[0059] In this example, after the third round of synthesis reaction was completed and the product polystyrene was separated, the resulting aqueous phase was treated with anion exchange resin and activated carbon, respectively, wherein the mass ratio of the aqueous phase to the resin was 1:1 and the mass ratio of the aqueous phase to the activated carbon was 1:0.5. The treatment times were 0.5 hour and 1 hour, respectively. After treatment, the chemical oxygen demand of the water was measured to be 28.1 mgO2 / L.

[0060] Example 6: Highly Reproducible Synthesis of Polystyrene with a Weight Average Molecular Weight in the Range of 7000-9000

[0061] Take 29858.7 mg of styrene, 141.3 mg of 2-hydroxy-2-methylpropiophenone and 14 g of n-dodecane and add them to a 5L reactor, then add 1556 g of water, 88.6 g of n-dodecanoic acid, 44.8 g of triethylamine and 266.67 g of n-butanol, and then use high-purity nitrogen to flow into the bottom of the reactor at a flow rate of 100 mL / min until all the materials in the reactor are mixed evenly and the appearance is clear and transparent. Then use 365 nm ultraviolet light (4 W / cm 2 ) irradiation was carried out at room temperature for 6 hours. Hydrochloric acid was then added to adjust the pH to 7.0 to completely demulsify the microemulsion system after the reaction, and the product polystyrene (PS-21) and the mineral oil phase and aqueous phase were separated. The obtained PS-21 was washed with a small amount of methanol and dried to obtain a white solid powder with a yield of 87.8%. Using standard polystyrene as a reference, the weight average molecular weight of the obtained PS-21 ( M w ) is 8100, the number average molecular weight ( M n ) is 7160 and PDI is 1.13.

[0062] The resulting aqueous phase was treated with an OH-type anion exchange resin (a 1:1 aqueous phase to resin mass ratio) for 5 minutes to obtain a regenerated aqueous phase. The mineral oil phase, the regenerated aqueous phase, 29,858.7 mg of fresh styrene, and 141.3 mg of 2-hydroxy-2-methylpropiophenone were mixed. The pH was then adjusted to 8.5 with triethylamine under nitrogen flow (100 mL / min) to form a regenerated microemulsion. A second round of polymerization was then carried out under 365 nm UV irradiation to obtain PS-22. This process was repeated for the third to seventh rounds of polymerization to obtain PS-23 to PS-27, respectively. The molecular weight, PDI, and yield of the polystyrenes obtained from these seven rounds are listed in Table 6.

[0063] Table 6 Highly reproducible synthesis results of polystyrene with a weight average molecular weight range of 7000-9000

[0064]

[0065] Before UV irradiation, laser light scattering measurements of the microemulsion droplet radius in the third reaction run described in this example revealed a microemulsion system with a clear, transparent appearance, confirming that the polymerization reaction in this example was indeed carried out within the microemulsion system. Continuous phase dye dilution confirmed that the microemulsions described in this example were all O / W-type.

[0066] In this example, after the fifth to seventh rounds of synthesis reactions were completed and the polystyrene product was separated, the resulting aqueous phases were treated with anion exchange resin and activated carbon, respectively, wherein the mass ratio of the aqueous phase to the resin was 1:1 and the mass ratio of the aqueous phase to the activated carbon was 1:0.5. The treatment times were 0.5 hour and 1 hour, respectively. The chemical oxygen demand values ​​of the water after treatment were measured to be 24.9 mg O2 / L, 26.6 mg O2 / L, and 25.2 mg O2 / L, respectively.

[0067] Example 7: Highly Reproducible Synthesis of Polystyrene with a Weight Average Molecular Weight in the Range of 9000 to 12000

[0068] 109826.8 mg of styrene, 173.2 mg of 2-hydroxy-2-methylpropiophenone and 110.1 g of n-dodecane were added to a 15 L reactor, followed by 7780.7 g of water, 443.3 g of n-dodecanoic acid, 224.2 g of triethylamine and 1333.1 g of n-butanol. High-purity nitrogen was then introduced into the bottom of the reactor at a flow rate of 100 mL / min until all the materials in the reactor were evenly mixed and visually clear. The reaction mixture was then irradiated with 365 nm ultraviolet light (4 W / cm 2 ) irradiation was carried out at room temperature for 2.6 hours. Hydrochloric acid was then added to adjust the pH to 7.0 to completely demulsify the microemulsion system after the reaction, and the product polystyrene (PS-28) and the mineral oil phase and aqueous phase were separated. The obtained PS-28 was washed with a small amount of methanol and dried to obtain a white solid powder with a yield of 89.3%. Using standard polystyrene as a reference, the weight average molecular weight of the obtained PS-28 ( M w ) is 11500, the number average molecular weight ( M n ) is 10010 and PDI is 1.15.

[0069] The resulting aqueous phase was treated with OH-type anion exchange resin (a 1:1 aqueous phase to resin mass ratio) for 5 minutes to obtain a regenerated aqueous phase. The mineral oil phase, the regenerated aqueous phase, 109,826.8 mg of fresh styrene, and 173.2 mg of 2-hydroxy-2-methylpropiophenone were mixed. The pH was then adjusted to 8.5 with triethylamine under nitrogen flow (100 mL / min) to form a regenerated microemulsion system. A second round of polymerization was then carried out under 365 nm UV irradiation to obtain PS-29. This process was repeated for the third to eighth rounds of polymerization to obtain PS-30 to PS-35, respectively. The molecular weight, PDI, and yield of the polystyrenes obtained from these eight rounds are listed in Table 7.

[0070] Table 7 Highly reproducible synthesis results of polystyrene with a weight average molecular weight range of 9000-12000

[0071]

[0072] Before UV irradiation, laser light scattering measurements of the microemulsion droplet radius in the second-run reaction system described in this example revealed a microemulsion system with a clear, transparent appearance, confirming that the polymerization reaction in this example was indeed carried out within the microemulsion system. Continuous phase dye dilution confirmed that the microemulsions described in this example were all O / W-type.

[0073] In this example, after the seventh and eighth rounds of synthesis reactions were completed and the polystyrene product was separated, the resulting aqueous phases were treated with anion exchange resin and activated carbon, respectively, in a water-to-resin mass ratio of 1:1 and a water-to-activated carbon mass ratio of 1:0.5. The treatment times were 0.5 hour and 1 hour, respectively. The chemical oxygen demand (COD) values ​​of the water after treatment were measured to be 27.9 mg O2 / L and 27.4 mg O2 / L, respectively.

[0074] The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. After the disclosure of the present invention, any person skilled in the art can easily change or replace the components, and all technical improvements that do not depart from the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for synthesizing narrowly distributed and low molecular weight polystyrene, characterized in that: The steps include: Step 1) Styrene, 2-hydroxy-2-methylpropiophenone, mineral oil, emulsifier and water are prepared into a microemulsion, and then irradiated with 365 nm ultraviolet light until the reaction is complete; Step 2) Demulsifying the microemulsion system after the reaction with hydrochloric acid to obtain a three-phase system of polystyrene solid, oil phase and water phase, and separating to obtain polystyrene, mineral oil phase and water phase respectively; Step 3) The obtained aqueous phase is treated with ion exchange resin to obtain a regenerated aqueous phase. Step 4) The mineral oil phase, the regenerated aqueous phase obtained in step 3), styrene, and 2-hydroxy-2-methylpropiophenone are mixed, and the pH is adjusted with an organic base to form a regenerated microemulsion system. The system is then irradiated with 365 nm ultraviolet light for another round of polymerization to obtain polystyrene with narrow distribution and low molecular weight.

2. The method for synthesizing polystyrene according to claim 1, wherein: In the steps 1) and 4), styrene and 2-hydroxy-2-methylpropiophenone are combined in a molar ratio of 1:0.001-0.04 to form a styrene-2-hydroxy-2-methylpropiophenone composition.

3. The method for synthesizing polystyrene according to claim 1, wherein: The mineral oil is n-dodecane.

4. The method for synthesizing polystyrene according to claim 1, wherein: The emulsifier is a composition of triethylamine n-dodecanoate and n-butanol in a mass ratio of 1:

2.

5. The method for synthesizing polystyrene according to claim 2, wherein: In the microemulsion formed in step 1), the mass percentage of the emulsifier is 20%, the mass percentage of water is 77.8%, the mass percentage of the mineral oil is 0.4% to 1.47%, and the mass percentage of the styrene-2-hydroxy-2-methylpropiophenone composition is 0.73% to 1.8%.

6. The method for synthesizing polystyrene according to claim 1, characterized in that: The microemulsion formed in step 1) is of O / W type.

7. The method for synthesizing polystyrene according to claim 1, characterized in that: The temperature of the ultraviolet irradiation reaction in step 1) and step 4) is room temperature, and the intensity of the ultraviolet light is 4 W / cm 2 , the reaction time is 1 to 6 hours.

8. The method for synthesizing polystyrene according to claim 1, characterized in that: In the step 2), the pH of the microemulsion system after demulsification reaches 7.

0.

9. The method for synthesizing polystyrene according to claim 1, characterized in that: After separation in step 2), polystyrene, mineral oil phase and water phase are obtained respectively. The lower water phase is first released from the demulsification system, and then the oil phase and polystyrene solid are separated from each other by vacuum filtration.

10. The method for synthesizing polystyrene according to claim 1, characterized in that: In step 4), the organic base is triethylamine, and the pH is adjusted to 8.5.

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