Synthesis method of narrow-distribution and low-molecular-weight polystyrene

Abstract

The invention provides a synthesis method of narrow-distribution and low-molecular-weight polystyrene, the weight-average molecular weight of the obtained polystyrene is in a range of 1800-12000, and the PDI is in a range of 1-1.4. The method for synthesizing narrow-distribution and low-molecular-weight polystyrene through O / W type microemulsion confinement photopolymerization is mild in reaction condition, good in controllability and good in reproducibility, and the yield of polystyrene is not lower than 85.7%. The emulsifier and mineral oil involved in the method for synthesizing narrow-distribution and low-molecular-weight polystyrene through O / W type microemulsion confinement photopolymerization can be regenerated and recycled, and almost no obvious three-waste emission is generated. According to the method for synthesizing narrow-distribution and low-molecular-weight polystyrene through O / W type microemulsion confinement photopolymerization, the chemical oxygen demand of a water phase treated by activated carbon and anion exchange resin does not exceed 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 with high molecular weight polymers, low molecular weight polymers often have unique fluidity and good compatibility with substrate materials, while retaining the characteristics of high molecular weight and low biological toxicity of high molecular weight materials. Therefore, they have extensive and unique applications in technical fields such as fillers, adhesives and coating materials. Among them, low molecular weight polystyrene is a precursor for synthesizing a new type of brominated polymer flame retardant - polybromostyrene. The synthesis method of low molecular weight polybromostyrene is to directly use low molecular weight polystyrene for bromination reaction. In terms of comprehensive flame retardant properties, processing properties and product aging properties, low molecular weight polystyrene with a molecular weight in the range of 2000~12000 and a dispersion index PDI within 1.4 is the most suitable. However, how to design a synthesis method for narrow distribution low molecular weight polystyrene has not been well solved. The most difficult core problem to solve is: how to achieve high reproducibility to control the molecular weight of polystyrene in the range of 2000~12000, and at the same time control the molecular weight distribution of low molecular weight polystyrene to be narrow enough (that is, PDI is not greater than 1.4). To solve this problem, the present invention uses a microemulsion confined photopolymerization method to accurately synthesize a series of narrow distribution (PDI in the range of 1-1.4) and low molecular weight (weight average molecular weight in the range of 1800-12000) polystyrenes. There have been reports of synthesizing low molecular weight polystyrene by anionic polymerization using scandium-based organic matter as a catalyst and a combination of boron-containing and aluminum-containing organic matter as an activator (Macromolecules, 2020, 53, 1205-1211). The number average molecular weight of the obtained polystyrene is in the range of 2200-5800. Only one batch of polystyrene has a PDI of 1.3, and the PDI of the remaining polystyrenes is in the range of 1.4-2.6. In addition, there are reports of obtaining polystyrene with a viscosity average molecular weight in the range of 1180-5735 in dichloromethane using benzoyl peroxide as an initiator (Journal of Functional Polymers, 1997, 10(1), 87-89), but the PDI data of the obtained polystyrene are 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 to 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 O / W microemulsion confined photopolymerization of the present invention can obtain polystyrene with a weight average molecular weight in the range of 1800-12000 and a PDI in the range of 1-1.4, and the molecular weight and PDI of the polystyrene obtained by repeating the synthesis three times can be highly reproducible. Summary of the invention

[0003] The purpose of the present invention is to provide a highly reproducible synthesis method for narrow distribution and low molecular weight polystyrene in order to solve the technical problem that it is difficult to both highly reproducibly control the weight average molecular weight of polystyrene within the range of 1800 to 12000 and to highly reproducibly control the molecular weight distribution of low molecular weight polystyrene to be sufficiently narrow (i.e., PDI is not greater than 1.4) in the current field of narrow distribution and low molecular weight polystyrene synthesis.

[0004] A highly reproducible synthesis method of narrow distribution and low molecular weight polystyrene comprises the following steps: firstly preparing styrene, 2-hydroxy-2-methylpropiophenone, mineral oil, emulsifier and water into a microemulsion, then subjecting the microemulsion to irradiation with 365 nm ultraviolet light until the reaction is complete, and then 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 then subjecting the polystyrene, mineral oil phase and water phase to separation, respectively, and subjecting the obtained water phase to treatment with ion exchange resin to obtain a regenerated water phase, and then mixing the mineral oil phase, the regenerated water phase and fresh styrene and 2-hydroxy-2-methylpropiophenone, and then adjusting the pH with an organic base to form a regenerated microemulsion system, and then subjecting the system to irradiation with 365 nm ultraviolet light for the next 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 by the 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%~1.47% and the mass percentage of the styrene-2-hydroxy-2-methylpropiophenone composition is 0.73%~1.8%.

[0009] Furthermore, the type of microemulsion prepared by the styrene, 2-hydroxy-2-methylpropiophenone, mineral oil, emulsifier and water is 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 after separation respectively 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, the organic base is triethylamine, and the pH is adjusted to 8.5.

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

[0016] The above synthesized products were detected by gel permeation chromatography (GPC), 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 product was not less than 85.7%.

[0017] The method of the present invention has the following advantages over the prior art: 1. The weight average molecular weight of the polystyrene obtained by the present invention is in the range of 1800 to 12000, and the PDI is in the range of 1 to 1.4.

[0018] 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%.

[0019] 3. The emulsifier and mineral oil involved in the method for synthesizing narrow distribution and low molecular weight polystyrene by O / W type microemulsion confined photopolymerization provided by the present invention can be recycled and reused, and there is almost no obvious discharge of three wastes.

[0020] 4. In the method for synthesizing narrow distribution and low molecular weight polystyrene by O / W type microemulsion confined photopolymerization provided by the present invention, the chemical oxygen demand of the aqueous phase after being treated with activated carbon and anion exchange resin does not exceed 28.6 mg O2 / L. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the GPC elution curve of the synthesized polystyrene (weight average molecular weight in the range of 4000-5000) in Example 1 of the present invention.

[0022] 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.

[0023] Figure 3 This is the identification result of the continuous phase dye dilution method of the microemulsion type of the synthetic polystyrene (weight average molecular weight in the range of 4000-5000) in Example 1 of the present invention before ultraviolet irradiation. DETAILED DESCRIPTION

[0024] 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.

[0025] Example 1: Highly reproducible synthesis of polystyrene with a weight average molecular weight in the range of 4000 to 5000 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, and then introduce high-purity N2 at a flow rate of 10 mL / min into the bottom of the material in the round-bottom flask 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 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 the water 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 detection ( 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.

[0026] The obtained aqueous phase was treated with OH-type anion exchange resin (the mass ratio of aqueous phase to resin was 1:1) for 5 minutes to obtain a regenerated aqueous phase. The mineral oil phase, the regenerated aqueous phase, 0.719 g of fresh styrene and 11.2 mg of 2-hydroxy-2-methylpropiophenone were mixed, and then the pH was adjusted to 8.5 with triethylamine under N2 flow (flow rate 10 mL / min) to form a regenerated microemulsion system, and then irradiated with 365 nm ultraviolet light for a second round of polymerization to obtain PS-2. This operation was repeated for a third round of polymerization to obtain PS-3. The molecular weight, PDI and yield of the polystyrene obtained in the three rounds are listed in Table 1.

[0027] Table 1 Highly reproducible synthesis results of polystyrene with a weight average molecular weight in the range of 4000-5000

[0028] Before UV irradiation, the three rounds of reaction systems described in this example were all measured by laser light scattering to measure the particle size distribution of the small droplets in the microemulsion system ( 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 is proved that the polymerization reaction in this example is indeed carried out in the 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 3 A is to dilute the dyed microemulsion with n-dodecane, Figure 3 B is to dilute the dyed microemulsion with water. Figure 3 The results show that the microemulsion described in this example is of O / W type.

[0029] After the three rounds of synthesis reaction in this embodiment are completed and the product polystyrene is separated, the obtained aqueous phase is treated with anion exchange resin and activated carbon respectively, wherein the mass ratio of the aqueous phase to the resin is 1:1, the mass ratio of the aqueous phase to the activated carbon is 1:0.5, the treatment time is 0.5 hours and 1 hour respectively, and the chemical oxygen demand value of the water is measured after treatment. The chemical oxygen demand of the aqueous phase obtained in the three rounds after treatment is 18.3 mg O2 / L, 18.1 mg O2 / L and 17.9 mg O2 / L respectively. It can be seen that the treatment effect of the wastewater obtained by the high reproducibility synthesis method of narrow distribution and low molecular weight polystyrene provided by the present invention is very simple and effective.

[0030] Example 2: Highly reproducible synthesis of polystyrene with a weight average molecular weight in the range of 1800 to 2000 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, and then introduce high-purity N2 at a flow rate of 10 mL / min into the bottom of the material in the round-bottom flask until all the materials in the round-bottom flask 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 1 hour to complete the reaction. 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-4) and the mineral oil phase and the water phase were separated. The obtained PS-4 was washed with a small amount of methanol and dried to obtain 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 was determined by GPC ( M w ) is 1880, the number average molecular weight ( M n ) is 1710 and PDI is 1.1.

[0031] The obtained aqueous phase was treated with OH-type anion exchange resin (the ratio of aqueous phase mass to resin mass was 1:1) for 5 minutes to obtain a regenerated aqueous phase. The mineral oil phase, the regenerated aqueous phase, and 1236.6 mg of fresh styrene and 77.4 mg of 2-hydroxy-2-methylpropiophenone were mixed, and then the pH was adjusted to 8.5 with triethylamine under N2 flow (flow rate 10 mL / min) to form a regenerated microemulsion system, and then irradiated with 365 nm ultraviolet light for a second round of polymerization to obtain PS-5. This operation was repeated for a third round of polymerization to obtain PS-6. The molecular weight, PDI, and yield of the polystyrene obtained in the three rounds are listed in Table 2.

[0032] Table 2 Highly reproducible synthesis results of polystyrene with a weight average molecular weight in the range of 1800-2000

[0033] Before ultraviolet irradiation, the radius of the small droplets in the microemulsion system in the first round of reaction system described in this example was measured by laser light scattering to be about 11.9 nm, and combined with the clear and transparent appearance, it was proved that the polymerization reaction in this example was indeed carried out in the microemulsion system. The continuous phase dye dilution method was used to verify that the type of microemulsion described in this example was O / W type.

[0034] In this embodiment, after the three rounds of synthesis reaction were completed and the product polystyrene was separated, the obtained 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, and the treatment time was 0.5 hour and 1 hour, respectively. After the treatment, the chemical oxygen demand value of the water was measured, and the chemical oxygen demand of the aqueous phase obtained in the three rounds after treatment was 28.3 mg O2 / L, 28.6 mg O2 / L and 27.9 mg O2 / L, respectively.

[0035] Example 3: Highly reproducible synthesis of polystyrene with a weight average molecular weight in the range of 2000 to 3000 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, and then introduce high-purity N2 at a flow rate of 10 mL / min into the bottom of the material in the round-bottom flask 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 the water 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%. Using standard polystyrene as a control, the weight average molecular weight of the obtained PS-7 was determined by GPC ( M w ) is 2510, the number average molecular weight ( M n ) is 2000 and PDI is 1.26.

[0036] The obtained aqueous phase was treated with OH-type anion exchange resin (the mass ratio of aqueous phase to resin was 1:1) for 5 minutes to obtain a regenerated aqueous phase. The mineral oil phase, the regenerated aqueous phase, and 2921.8 mg of fresh styrene and 138.2 mg of 2-hydroxy-2-methylpropiophenone were mixed, and then the pH was adjusted to 8.5 with triethylamine under N2 flow (flow rate 10 mL / min) to form a regenerated microemulsion system, and then irradiated with 365 nm ultraviolet light for a second round of polymerization to obtain PS-8. This operation 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 polystyrene obtained in the six rounds are listed in Table 3.

[0037] Table 3 Highly reproducible synthesis results of polystyrene with a weight average molecular weight in the range of 2000-3000

[0038] Before ultraviolet irradiation, the radius of the small droplets in the microemulsion system of the fourth round of reaction system described in this example was measured by laser light scattering to be about 24.9 nm, and combined with the clear and transparent appearance, it was proved that the polymerization reaction in this example was indeed carried out in the microemulsion system. The continuous phase dye dilution method was used to verify that the type of microemulsion described in this example was O / W type.

[0039] After the sixth round of synthesis reaction in this embodiment is completed and the product polystyrene is separated, the obtained aqueous phase is treated with anion exchange resin and activated carbon, respectively, wherein the mass ratio of the aqueous phase to the resin is 1:1, and the mass ratio of the aqueous phase to the activated carbon is 1:0.5, and the treatment time is 0.5 hour and 1 hour, respectively. After treatment, the chemical oxygen demand value of the water is measured to be 24.4 mgO2 / L.

[0040] Example 4: Highly reproducible synthesis of polystyrene with a weight average molecular weight in the range of 3000 to 4000 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, and then introduce high-purity N2 at a flow rate of 10 mL / min into the bottom of the material in the round-bottom flask 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 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 the water 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 control, the weight average molecular weight of the obtained PS-13 was determined by GPC ( M w ) is 3590, the number average molecular weight ( M n ) is 2970 and PDI is 1.21.

[0041] The obtained aqueous phase was treated with OH-type anion exchange resin (the mass ratio of aqueous phase to resin was 1:1) for 5 minutes to obtain a regenerated aqueous phase. The mineral oil phase, the regenerated aqueous phase, and 2239.4 mg of fresh styrene and 70.6 mg of 2-hydroxy-2-methylpropiophenone were mixed, and then the pH was adjusted to 8.5 with triethylamine under N2 flow (flow rate 10 mL / min) to form a regenerated microemulsion system, and then irradiated with 365 nm ultraviolet light for a second round of polymerization to obtain PS-14. This operation 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 polystyrene obtained in the five rounds are listed in Table 4.

[0042] Table 4 Highly reproducible synthesis results of polystyrene with a weight average molecular weight in the range of 3000-4000

[0043] Before ultraviolet irradiation, the radius of the small droplets in the microemulsion system measured by laser light scattering in the third round of reaction system described in this example was about 20.9 nm, combined with the clear and transparent appearance, it was proved that the polymerization reaction in this example was indeed carried out in the microemulsion system. The continuous phase dye dilution method was used to verify that the type of microemulsion described in this example was O / W type.

[0044] Example 5: Highly reproducible synthesis of polystyrene with a weight average molecular weight in the range of 5000 to 7000 Take 17831.3 mg of styrene, 168.7 mg of 2-hydroxy-2-methylpropiophenone and 8.4 g of n-dodecane and add them to a 2.5 L reactor. Then add 933.6 g of water, 53.2 g of n-dodecanoic acid, 26.9 g of triethylamine and 160.1 g of n-butanol. Then, introduce high-purity nitrogen into the bottom of the reactor at a flow rate of 72 mL / min until all the materials in the reactor 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-18) and the mineral oil phase and the water 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 control, the weight average molecular weight of the obtained PS-18 was determined by GPC ( M w ) is 6380, the number average molecular weight ( M n ) is 5110 and PDI is 1.25.

[0045] The obtained aqueous phase was treated with OH-type anion exchange resin (the ratio of aqueous phase mass to resin mass was 1:1) for 5 minutes to obtain a regenerated aqueous phase. The mineral oil phase, the regenerated aqueous phase, and 17831.3 mg of fresh styrene and 168.7 mg of 2-hydroxy-2-methylpropiophenone were mixed, and then the pH was adjusted to 8.5 with triethylamine under N2 flow (flow rate 50 mL / min) to form a regenerated microemulsion system, and then irradiated with 365 nm ultraviolet light for a second round of polymerization to obtain PS-19. This operation was repeated for a third round of polymerization to obtain PS-20. The molecular weight, PDI, and yield of the polystyrene obtained in the three rounds are listed in Table 5.

[0046] Table 5 Highly reproducible synthesis results of polystyrene with a weight average molecular weight in the range of 5000-7000

[0047] Before ultraviolet irradiation, the radius of the small droplets in the microemulsion system measured by laser light scattering in the third round of reaction system described in this example was about 32.9 nm, combined with the clear and transparent appearance, it was proved that the polymerization reaction in this example was indeed carried out in the microemulsion system. The continuous phase dye dilution method was used to verify that the type of microemulsion described in this example was O / W type.

[0048] After the third round of synthesis reaction in this embodiment was completed and the product polystyrene was separated, the obtained 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, and the treatment time was 0.5 hour and 1 hour, respectively. After treatment, the chemical oxygen demand value of the water was measured to be 28.1 mgO2 / L.

[0049] Example 6: Highly reproducible synthesis of polystyrene with a weight average molecular weight in the range of 7000 to 9000 Take 29858.7 mg of styrene, 141.3 mg of 2-hydroxy-2-methylpropiophenone and 14 g of n-dodecane into 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 introduce high-purity nitrogen 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 the water 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 control, the weight average molecular weight of the obtained PS-21 was determined by GPC ( M w ) is 8100, the number average molecular weight ( M n ) is 7160 and PDI is 1.13.

[0050] The obtained aqueous phase was treated with OH-type anion exchange resin (the mass ratio of aqueous phase to resin was 1:1) for 5 minutes to obtain a regenerated aqueous phase. The mineral oil phase, the regenerated aqueous phase, and 29858.7 mg of fresh styrene and 141.3 mg of 2-hydroxy-2-methylpropiophenone were mixed, and then the pH was adjusted to 8.5 with triethylamine under N2 flow (flow rate 100 mL / min) to form a regenerated microemulsion system, and then irradiated with 365 nm ultraviolet light for a second round of polymerization to obtain PS-22. This operation 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 polystyrene obtained in the seven rounds are listed in Table 6.

[0051] Table 6 Highly reproducible synthesis results of polystyrene with a weight average molecular weight in the range of 7000 to 9000

[0052] Before UV irradiation, the radius of the small droplets in the microemulsion system measured by laser light scattering in the third round of reaction system described in this example was about 29.9 nm, combined with the clear and transparent appearance, it was proved that the polymerization reaction in this example was indeed carried out in the microemulsion system. The continuous phase dye dilution method was used to verify that the type of microemulsion described in this example was O / W type.

[0053] After the fifth to seventh rounds of synthesis reactions in this embodiment were 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, and the treatment times were 0.5 hours and 1 hour, respectively. After treatment, the chemical oxygen demand values ​​of the water were measured to be 24.9 mg O2 / L, 26.6 mg O2 / L and 25.2 mg O2 / L, respectively.

[0054] Example 7: Highly reproducible synthesis of polystyrene with a weight average molecular weight in the range of 9000 to 12000 Take 109826.8 mg of styrene, 173.2 mg of 2-hydroxy-2-methylpropiophenone and 110.1 g of n-dodecane and add them to a 15L reactor, then add 7780.7 g of water, 443.3 g of n-dodecanoic acid, 224.2 g of triethylamine and 1333.1 g of n-butanol, and then introduce high-purity nitrogen 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 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 the water 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 control, the weight average molecular weight of the obtained PS-28 was determined by GPC ( M w ) is 11500, the number average molecular weight ( M n ) is 10010 and the PDI is 1.15.

[0055] The obtained aqueous phase was treated with OH-type anion exchange resin (the ratio of aqueous phase mass to resin mass was 1:1) for 5 minutes to obtain a regenerated aqueous phase. The mineral oil phase, the regenerated aqueous phase, and 109826.8 mg of fresh styrene and 173.2 mg of 2-hydroxy-2-methylpropiophenone were mixed, and then the pH was adjusted to 8.5 with triethylamine under N2 flow (flow rate 100 mL / min) to form a regenerated microemulsion system, and then irradiated with 365 nm ultraviolet light for a second round of polymerization to obtain PS-29. This operation 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 polystyrene obtained in the eight rounds are listed in Table 7.

[0056] Table 7 Highly reproducible synthesis results of polystyrene with a weight average molecular weight in the range of 9000 to 12000

[0057] Before UV irradiation, the radius of the small droplets in the microemulsion system measured by laser light scattering in the second round of reaction system described in this example was about 14.1 nm, combined with the clear and transparent appearance, it was proved that the polymerization reaction in this example was indeed carried out in the microemulsion system. The continuous phase dye dilution method was used to verify that the type of microemulsion described in this example was O / W type.

[0058] After the seventh and eighth rounds of synthesis reactions in this embodiment 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, and the treatment times were 0.5 hours and 1 hour, respectively. After treatment, the chemical oxygen demand values ​​of the water were measured to be 27.9 mg O2 / L and 27.4 mg O2 / L, respectively.

[0059] 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. Any person familiar with the present invention can easily change or replace the components after the present invention is disclosed, 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 narrow distribution and low molecular weight polystyrene, characterized in that: The steps include: First, 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 completed; 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, and polystyrene, mineral oil phase and water phase are obtained after separation; Step 2) The obtained aqueous phase is treated with an ion exchange resin to obtain a regenerated aqueous phase. The mineral oil phase, the regenerated water 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, which is then irradiated with 365 nm ultraviolet light for the next round of polymerization to obtain polystyrene with narrow distribution and low molecular weight.

2. The method for synthesizing polystyrene according to claim 1, characterized in that: In the step 1) and the step 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, characterized in that: The mineral oil is n-dodecane.

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

7. The method for synthesizing polystyrene according to claim 1, characterized in that: The temperature of the ultraviolet light 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 system after the microemulsion system is demulsified 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, by first releasing the lower water phase from the demulsification system, and then separating the oil phase and polystyrene solid from each other by vacuum filtration.

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

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