CN110982004B - Preparation method of styrene-acrylonitrile copolymer - Google Patents

Abstract

The invention provides a preparation method of styrene-acrylonitrile copolymer, which comprises the steps of mixing and cooling a styrene monomer and an acrylonitrile monomer, feeding the mixture into a first reactor, reacting in a full state, controlling the temperature, feeding the mixture into a second reactor, continuing the reaction in the full state, and finally performing devolatilization. The invention also provides a styrene-acrylonitrile copolymer prepared by the preparation method. The preparation method provided by the invention can achieve heat insulation or nearly heat insulation in the whole polymerization reaction process, can effectively control the stability of the polymerization reaction temperature without external heat transfer, further ensures the stability of the composition of the obtained copolymer, and the prepared copolymer has excellent optical performance.

Description

Preparation method of styrene-acrylonitrile copolymer

Technical Field

The invention relates to the field of styrene-acrylonitrile copolymers, in particular to a preparation method of a styrene-acrylonitrile copolymer.

Background

An acrylonitrile-styrene copolymer (also referred to AS SAN resin or AS resin) is a high molecular polymer formed by copolymerizing acrylonitrile and styrene, and has excellent processability. SAN resin has good dimensional stability, weather resistance, heat resistance, oil resistance, shock resistance and chemical stability, and is widely applied to the fields of automobiles, buildings, stationery, hardware and household appliances, modern functional materials and the like.

The industrial production of styrene-acrylonitrile copolymer adopts the third generation of continuous bulk polymerization method, and uses styrene and acrylonitrile as monomers, and adds a small amount of diluting solvent to synthesize the styrene-acrylonitrile copolymer. In the process for producing styrene-acrylonitrile copolymer by bulk polymerization, the main problem is the control of reaction heat, the theoretical heat of polymerization of acrylonitrile is 1365KJ/KG, which is much higher than that of styrene (668 KJ/KG of styrene, data from supplier product manual), and the heat release of polymerization is obviously increased along with the increase of acrylonitrile proportion after the copolymerization of styrene and acrylonitrile. Styrene and acrylonitrile both have very strong thermal polymerization ability, if the reaction heat can not be well controlled in the reaction process, the risk of implosion or local implosion occurs in the reaction is very large, which not only can influence the performance of the product, but also can cause the reaction to be out of control under more serious conditions, thereby generating potential safety hazard.

In order to control the reaction heat, generally, a monomer/solvent gasification condensation method is adopted to transfer heat, a reaction device is not completely filled, a condenser is arranged at the top, and the reaction temperature is usually above the boiling points of the monomer and the solvent, the monomer and the solvent can generate steam at the top of the reaction device in the reaction process, and the steam can take away a large amount of gasification heat after being condensed by the condenser. Furthermore, the recycling of the gaseous phase to the reaction liquid after condensation may cause local variations in monomer composition from the bulk, which may result in difficult control of the composition of the styrene-acrylonitrile copolymer. In the case of styrene-acrylonitrile copolymers, when the acrylonitrile content is not uniform among the polymers, the compatibility of the polymers is reduced, thereby affecting the transparency of the polymers. Furthermore, since the proportion of acrylonitrile in the gas-phase condensate is high and no polymerization inhibitor is contained, there is also a risk of polymerization to form polymers having a high acrylonitrile content. When the content of acrylonitrile in the polymer is high, the adjacent acrylonitrile is easy to form a ring at high temperature to form a conjugated structure, and blue light in visible light is absorbed to cause resin yellowing.

Chinese patent CN 104628925A discloses a method for producing SAN resin by two-kettle series polymerization, and the appearance and transparency of the obtained SAN resin are improved. However, the method needs to feed in two sections, each section of the feeding is different in raw material proportion, the precise control is difficult, the effective volume of a reactor of a first polymerization kettle is controlled to be 75%, and at a reaction temperature higher than the boiling point of monomers, even if no monomer evaporates and transfers heat, an evaporation gas phase area can be formed in the first polymerization kettle, and the existence of the gas phase area can cause the local generation of polymers with uneven compositions. Furthermore, the heat removal by external jacket cooling also results in non-uniform temperature in the polymerization vessel, and these factors affect the quality of SAN resin.

Therefore, in view of various aspects, there is a need to find a new method for preparing acrylonitrile-styrene copolymer, which can keep the temperature and composition of the reaction solution more stable and even during the whole polymerization process, so that the obtained copolymer has more excellent properties, especially optical properties.

Disclosure of Invention

In order to overcome the above-mentioned drawbacks of the prior art, it is an object of the present invention to provide a method for preparing a styrene-acrylonitrile copolymer having more excellent properties, especially optical properties.

It is another object of the present invention to provide a styrene-acrylonitrile copolymer.

The preparation method of the styrene-acrylonitrile copolymer provided by the invention comprises the following steps:

s1: mixing 60-90 parts by mass of styrene monomer and 10-40 parts by mass of acrylonitrile monomer, and cooling to-40-10 ℃ to obtain a mixed raw material;

s2: feeding the mixed raw materials into a first reactor, reacting in a state of keeping the first reactor full, and discharging to obtain first slurry;

s3: controlling the temperature of the first slurry to be 90-110 ℃, feeding the first slurry into a second reactor, keeping the first slurry fully filled in the second reactor, continuing to react, and discharging to obtain a second slurry, wherein the ratio of the monomer conversion rate of the first slurry to the monomer conversion rate of the second slurry is 0.4-0.9: 1; and

s4: and devolatilizing the second slurry to obtain the styrene-acrylonitrile copolymer.

The exothermic effect is obvious in the polymerization process of styrene and acrylonitrile, the exothermic reaction needs to be removed in time, the preparation method of the invention divides the polymerization process into two-section polymerization, the reaction system is in an adiabatic or nearly adiabatic state on the whole without external heat removal (such as jacket cooling, monomer gas phase condensation and other modes) by controlling the temperature of monomer raw materials and slurry and the polymerization degree of each section of polymerization process, the exothermic reaction is absorbed basically through latent heat of the monomer, the condition of non-uniform temperature cannot occur in the reactor, and the reactor runs in a full state, the gas phase monomer is not generated, and the condition of local non-uniform copolymer is avoided, therefore, the preparation method of the invention can effectively ensure the stability of the composition of the polymerization reaction liquid, and further effectively ensure the composition stability of the prepared copolymer, thereby the copolymer has more excellent performance, especially transparency, yellowing index and the like.

In the preparation method provided by the invention, the mixed raw material can contain 60-90 parts by mass of styrene monomer and 10-40 parts by mass of acrylonitrile monomer, based on the total mass of the monomers, when the content of the acrylonitrile monomer is lower than 10 wt%, the performance of the styrene-acrylonitrile copolymer cannot be fully embodied, and the styrene-acrylonitrile copolymer has no practical value, and when the content of the acrylonitrile monomer is higher than 40 wt%, the optical performance of the copolymer cannot meet the use requirement easily. In some preferred embodiments, the mixed raw material may include 70 to 80 parts by mass of a styrene monomer and 20 to 30 parts by mass of an acrylonitrile monomer, i.e., the acrylonitrile monomer content is 20 to 30 wt% based on the total mass of the monomers.

In the preparation method provided by the invention, the mixed raw material in the step S1 can be cooled by conventional technology in the chemical field. In some preferred embodiments, the mixed raw material can be cooled by a heat exchanger, the heat exchanger can be a plate type or a tube type heat exchanger, preferably a tube type heat exchanger, and the cooling medium of the heat exchanger can be liquid ammonia or liquid nitrogen, preferably liquid ammonia.

In the preparation method provided by the invention, the temperature of the cooled mixed raw material (namely the feeding temperature of the first reactor) needs to be controlled in a certain range to be matched with the polymerization heat of the monomer, the proper temperature range can be-40-10 ℃, when the feeding temperature is higher than 10 ℃, the latent heat quantity which can be taken away by the monomer entering the reaction liquid is less, the heat transfer in the reaction process is difficult, and when the feeding temperature is lower than-40 ℃, the monomer has the solidification risk and the heat exchange energy consumption is higher. In some preferred embodiments, the temperature of the reduced temperature mixed raw material may be-30 to-10 ℃.

In the preparation method provided by the invention, the temperature of the first slurry in the step S3 can be controlled by conventional technology in the chemical field, and the temperature control before the second-stage polymerization is mainly based on the following two considerations, namely that if the first slurry stays for too long at high temperature, side reactions are increased, the concentration of generated oligomers or branched cross-linking substances is higher, and the improvement of the optical performance of the copolymer is not facilitated; secondly, the low-temperature slurry enters a second reactor to take away a large amount of polymerization heat, through proper process control, the heat release of polymerization and the heat absorption of monomer/slurry in the second reactor can reach heat balance, the temperature of a polymerization system is more uniform, and the performance of the obtained polymer is better. In some preferred embodiments, the temperature of the first slurry can be controlled by a heat exchanger, the heat exchanger can be a plate type or a tube type heat exchanger, preferably a tube type heat exchanger, and the cooling medium of the heat exchanger can be liquid ammonia or liquid nitrogen, preferably liquid ammonia.

In the preparation method provided by the invention, the monomer conversion rate of the first slurry and the second slurry is based on the monomer dosage of the mixed raw materials, and can be obtained according to the conventional test and calculation method in the field. In some preferred embodiments, the ratio of the monomer conversion of the first slurry to the monomer conversion of the second slurry may be 0.5 to 0.8: 1.

In the preparation method provided by the invention, in step S2, the mixed raw materials are subjected to a residence reaction in the first reactor for 0.1-2 h until the monomer conversion rate is 25-45 wt%, the residence reaction time is controlled to achieve the desired monomer conversion rate, and the monomer conversion rate is based on the consideration of the control of reaction heat, when the conversion rate is less than 25 wt%, on one hand, the output of the first reactor is too low, on the other hand, a large amount of monomers need to be subsequently devolatilized, which is not suitable from the viewpoint of energy consumption, and when the conversion rate is greater than 45 wt%, the reaction system is difficult to be realized in the aspects of heat balance and uniform temperature control. In some preferred embodiments, the mixed raw materials are kept in the first reactor for reaction for 0.8 to 1.5 hours until the monomer conversion rate is 35 to 42 wt%.

In the preparation method provided by the invention, in step S3, the first slurry stays in the second reactor for reaction for 0.1-2 hours until the monomer conversion rate is 40-70 wt%, when the conversion rate is lower than 40 wt%, 60 wt% of volatile matters need to be removed, and both the energy consumption aspect and the monomer residual control aspect have great problems, and when the conversion rate is higher than 70 wt%, the viscosity of the reaction solution is high, and the mass and heat transfer in the second reactor is difficult, so that the final application performance of the product is influenced. In some preferred embodiments, the first slurry stays in the second reactor for 0.2 to 1 hour for reaction to a monomer conversion of 50 to 60 wt%.

In the preparation method provided by the invention, the first reactor is a full-mixing flow reactor, and the first slurry overflows and is discharged from the top of the full-mixing flow reactor, wherein the full-mixing flow reactor can use common equipment in the chemical industry field, such as a pressure-resistant polymerization kettle, and can be provided with an anchor type or double helical ribbon type stirrer, and the full-mixing flow reactor does not need common heat removal equipment such as a heat exchanger, a condensing device and the like. In some preferred embodiments, the first reactor is a well-insulated reactor that substantially maintains a balance between the exothermic heat of polymerization and the endothermic heat of monomer.

In the preparation method provided by the invention, the second reactor is a plug flow reactor, the first slurry is reacted in the second reactor in a full-filling state, the first slurry enters the second reactor at a lower temperature, the temperature of the first slurry is raised by the polymerization heat released by the monomers in the second reactor, and the pressure in the second reactor can be controlled within the range of 0.5-2 MPa to prevent the monomers from being gasified. In some preferred embodiments, the second reactor may be a tubular reactor, and is preferably insulated to maintain a substantial balance between exothermic polymerization heat and endothermic monomer/slurry heat.

In the preparation method provided by the invention, the temperature in the first reactor is 130-160 ℃, as mentioned above, the heat balance is achieved in the reactor through heat release during polymerization and heat absorption of monomers, in order to ensure the polymerization effect, the temperature in the reactor is controlled to be maintained in a relatively stable state through the feeding of monomer raw materials, when the temperature is lower than 130 ℃, the thermal reaction rate is low, the production efficiency is influenced, and when the reaction temperature is higher than 160 ℃, the polymerization reaction rate is too high, and the reaction liquid has the risk of local overheating and implosion, and the product performance is influenced. In some preferred embodiments, the temperature in the first reactor may be 140 to 150 ℃. In other preferred embodiments, the first reactor may also be provided with a holding device, such as a jacketed oil bath, for keeping the temperature of the first reactor stable rather than for heat removal.

In the preparation method provided by the invention, the temperature in the second reactor is 90-160 ℃, as mentioned above, the heat balance is achieved in the reactor through heat release during polymerization and heat absorption of the monomer/slurry, and in order to ensure the polymerization effect, the temperature in the reactor is controlled to be maintained in a relatively stable state through temperature control of the slurry. In some preferred embodiments, the temperature in the second reactor may be 140 to 160 ℃.

In the preparation method provided by the present invention, the step S3 further includes: when the content of acrylonitrile monomer is less than 25 wt% based on the total mass of the monomers in the mixed raw material, m is supplemented into the first slurry before temperature control ₁ % of the total mass of the monomers of acrylonitrile monomer; when the content of acrylonitrile monomer is more than 25 wt%, m is supplemented into the first slurry before temperature control ₂ % of the total mass of the monomers of styrene monomers,

wherein m is ₁ And m ₂ Calculated from equation (1) and equation (2), respectively:

in the formula (1) and the formula (2), f ₁ Denotes the acrylonitrile monomer content, f, based on the total mass of monomers in the mixed feed ₂ Represents the styrene monomer content based on the total mass of monomers in the mixed raw materials, and x represents the monomer conversion rate of the first slurry.

The styrene and acrylonitrile monomers have certain difference in reaction activity, the copolymer system formed by the styrene and the acrylonitrile has a constant ratio point when the acrylonitrile content is 25 wt%, the composition of the reaction liquid and the copolymer can change along with the conversion rate after deviating from the constant ratio point, and the change rule is inconsistent above and below the constant ratio point. Therefore, for the two-stage reaction of the present invention, in order to further secure the composition and properties of the copolymer, the composition of the monomers in the reaction solution can be appropriately adjusted in the second-stage reaction, specifically by adding a small amount of monomers. The present inventors have found that, depending on the process parameters of both the feed ratio of the raw material acrylonitrile and the monomer conversion of the first slurry, the optimum amount of the additional monomer as described in the formulas (1) and (2) can be obtained, thereby making the composition of the polymer formed by the two-stage reaction smaller. When the amount of the monomer added exceeds the range shown in the formula, the composition of the copolymer deviates greatly from that in the first stage reaction, and the properties of the polymer are adversely affected.

The preparation method provided by the invention can be suitable for a bulk polymerization process and can also be suitable for a solution polymerization process in the presence of a small amount of solvent. In some preferred embodiments, prior to the second stage polymerization, a suitable amount of solvent may be added to reduce the viscosity of the reaction mass and to increase the solubility of the polymer in the monomers, and the solvent may be any of those commonly used in the copolymerization process of styrene and acrylonitrile, including but not limited to toluene, ethylbenzene, cyclohexane, acetonitrile, tetrahydrofuran, N-dimethylformamide, etc., and is preferably N, N-dimethylformamide in view of its solubility in the polymer. Too high an amount of solvent is not favorable for increasing the yield of the polymer and burdens the subsequent devolatilization, while too low an amount of solvent is not effective for improving the viscosity and solubility of the polymer. In some preferred embodiments, the solvent may be added in an amount of 5 to 20 wt%, more preferably 10 to 15 wt% of the first slurry.

In the preparation method provided by the present invention, step S3 further includes: after temperature control, an initiator is added to the first slurry, and the addition of the initiator can increase the reaction rate of the monomers in the second reactor. The initiator may be any kind of initiator commonly used in the copolymerization process of styrene and acrylonitrile, and may be, for example, an organic peroxide initiator or an azo initiator, preferably an organic peroxide initiator, including, but not limited to, dibenzoyl peroxide, dilauroyl peroxide, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxyisobutyrate, 1-bis- (tert-butylperoxy) -3,3, 5-trimethylcyclohexane, tert-butylperoxy-3, 5, 5-trimethylhexanoate, and the like.

In addition, the selection of the initiator is also related to the half-life of the initiator and the addition amount, and the first slurry can be reacted in the second reactor according to the required polymerization temperature by controlling the half-life of the initiator and the concentration in the first slurry. In some preferred embodiments, the half-life of the initiator at the temperature after temperature control (i.e., at 90-110 ℃) is 1-30 min, when the half-life of the initiator is too long, the rate of free radicals generated by the initiator after entering the second reactor is too slow, and the polymerization reaction time is long, and when the half-life of the initiator is too short, the initiator is prone to local overheating caused by non-uniform mixing, and is not beneficial to control of the polymer structure and performance. In some more preferred embodiments, the initiator has a half-life of 6 to 10min at the temperature after temperature control. In other preferred embodiments, the amount of the initiator added is 10 to 100ppm, more preferably 20 to 50ppm, based on the mass of the first slurry.

In the preparation method provided by the invention, the mixed raw material for preparing the styrene-acrylonitrile copolymer can be added with a chain transfer agent to control the molecular weight of the polymer within a certain range besides two monomers of styrene and acrylonitrile. In some preferred embodiments, the chain transfer agent added is t-dodecyl mercaptan, which is better at transferring chains of both styrene and acrylonitrile. In some more preferred embodiments, the chain transfer agent is added in an amount of 0.02 to 0.2 wt%, preferably 0.05 to 0.15 wt%, based on the total mass of monomers in the raw materials for mixing, in order to control the weight average molecular weight of the copolymer in the range of 8 to 20 ten thousand.

In the preparation method provided by the invention, after the two-stage polymerization reaction is finished, the obtained second slurry is subjected to devolatilization treatment to remove volatile components in the second slurry, wherein the volatile components comprise monomers (styrene and acrylonitrile), solvents, oligomers, accumulated organic impurities in a reactor and the like. The devolatilization method of step S4 may be any devolatilization method used in a conventional copolymerization process of styrene and acrylonitrile, such as one-stage or multi-stage devolatilization. The devolatilizer may be selected from a flash tank, a falling bar devolatilizer, a flight devolatilizer, or a twin-screw extruder, and a twin-screw extruder is preferably used from the viewpoint of controlling the residual polymer content and appearance, and a twin-screw extruder having two or more vents is more preferred.

In some preferred embodiments, the second slurry of step S4 is subjected to secondary devolatilization, and the first stage devolatilization temperature is not too high because acrylonitrile is easily yellowed at high temperature, the temperature control range is 80-160 ℃, acrylonitrile is difficult to be removed when the temperature is lower than 80 ℃, and the optical properties of the copolymer are adversely affected when the temperature is higher than 160 ℃, and more preferably 100-140 ℃, and further, the first stage devolatilization has high volatile concentration, and the material is easily foamed when the vacuum degree is high, so the absolute pressure in the devolatilizer is controlled to be 10-40 KPa. The second-stage devolatilization adopts a high-temperature high-vacuum condition, residual high-boiling-point volatile components (including styrene, a solvent, oligomers formed by styrene and acrylonitrile and the like) can be removed, the second-stage devolatilization temperature is 180-240 ℃, the preferred temperature is 200-220 ℃, and the absolute pressure is lower than 1 KPa.

In the preparation method provided by the invention, any type of auxiliary agent with any content commonly used in the field can be added in the process according to the required copolymer performance, including but not limited to a release agent, an ultraviolet absorbent, an antioxidant, a coloring agent and the like.

By controlling the process conditions, the prepared styrene-acrylonitrile copolymer has good mechanical properties (such as tensile strength, bending strength, impact strength and the like) and good optical properties. Therefore, the invention also provides a styrene-acrylonitrile copolymer prepared by the preparation method of any one of the technical schemes.

In some preferred embodiments, the styrene-acrylonitrile copolymers provided herein have one or more of the following properties: the total light transmittance is more than or equal to 91 percent (test standard ISO 13486), the haze is less than or equal to 2 percent (test standard ISO 13486) or the yellowing index of an injection-molded 3mm membrane is less than or equal to 2 (test standard ASTM D1925). In some more preferred embodiments, the styrene-acrylonitrile copolymer provided by the present invention can achieve the above three optical performance criteria simultaneously.

In the styrene-acrylonitrile copolymer provided by the invention, the acrylonitrile content in the finally obtained copolymer can be changed according to the addition amount of the acrylonitrile monomer. In some preferred embodiments, the styrene-acrylonitrile copolymer provided by the invention has an acrylonitrile content of 10 to 30 wt%; more preferably, the acrylonitrile content is 20 to 30 wt%. The styrene-acrylonitrile copolymer provided by the invention can be prepared into common products in any form and any type according to a common processing and forming process, can be suitable for any common application field or application occasion, and is particularly suitable for application fields such as food containers, refrigerator fresh-keeping boxes, dust covers, lighters, transparent parts of household appliances and the like.

The preparation method of the styrene-acrylonitrile copolymer provided by the invention can achieve thermal insulation or nearly thermal insulation in the whole polymerization reaction process, can effectively control the stability of the polymerization reaction temperature without common external heat transfer modes such as monomer gasification condensation, jacket cooling and the like, and further ensures the stability of the composition of the obtained copolymer. In addition, the preparation method of the invention has simple and convenient process, is easy to control, does not need complex equipment, and is very suitable for large-scale industrial production.

Drawings

FIG. 1 is a schematic view of a system for producing a styrene-acrylonitrile copolymer according to an embodiment of the present invention;

wherein the reference numbers are as follows:

1. a dosing tank; 2. a first heat exchanger; 3. a melt booster pump; 4. a fully mixed flow polymerizer; 5. a second heat exchanger; 6. a static mixer; 7. a tubular reactor; 8. a twin screw extruder; 9. monomer and solvent feed lines; 10. an initiator feed line.

Detailed Description

The technical solution of the present invention is further described in detail with reference to the following specific examples.

In the examples of the present invention and the comparative examples, the sources of the raw materials are shown in table 1.

Table 1 raw material source information

Name of raw materials	For short	Rank of	Suppliers of goods
				Styrene (meth) acrylic acid ester	SM	Industrial grade	Qilu petrochemical
Acrylonitrile	AN	Industrial grade	Jilin petrochemical
				Tert-dodecyl mercaptan	t-DDM	Industrial grade	Chemistry of pear tree
N, N-dimethylformamide	DMF	Reagent grade	Aladdin
				Dibenzoyl peroxide	BPO	Industrial grade	Akema

In the examples and comparative examples of the present invention, the methods for measuring the molecular weight, solid content and monomer conversion of the polymer were as follows:

molecular weight measurement

The molecular weight was measured by liquid gel chromatography (GPC), mobile phase Tetrahydrofuran (THF), detector using a parallax refractometer, and monodisperse polystyrene as a standard.

Solid content and monomer conversion test

Samples were taken from the first reactor and second reactor outlets, respectively, by samplers to test solids content. The test method is as follows: weighing about 1g of reaction solution, placing the reaction solution into tin foil paper (the tin foil paper is weighed in advance), placing the tin foil paper in a vacuum oven at 160 ℃, controlling absolute pressure to be less than 1KPa, vacuumizing for 0.5h, taking out the tin foil paper, cooling the tin foil paper at room temperature, and weighing the dried dry-based resin. The solids content can be calculated by dividing the mass of the dry resin by the mass of the reaction solution. The solids content was repeated three times per sample and averaged.

The monomer conversion is obtained by dividing the solid content by the monomer content in the reaction solution (i.e. the total monomer mass divided by the total reaction solution mass). And calculating the monomer conversion rate of the second slurry by taking the total mass of the originally added monomers as a reference, and when the monomers are supplemented, adding the mass of the supplemented monomers into the total mass of the monomers.

The polymer properties were measured as shown in Table 2.

TABLE 2 Polymer Performance test standards and conditions

Test items	Test standard	Test conditions
			Light transmittance	ISO 13486	3mm
Haze degree	ISO 14782	3mm
			Melt Flow Rate (MFR)	ISO 1133	220℃，10KG
Heat Distortion Temperature (HDT) load	ISO 75	1.8MPa, annealing
			Charpy impact Strength	ISO 179	1eU, no gap
Tensile strength	ISO 527	1A/5
			Elongation at break	ISO 527	1A/5
Bending strength	ISO 527	1A/5
			Yellowing index	ASTM D1925	C/2，3mm

The preparation system is shown in figure 1 and is connected through pipelines for conveying materials, and comprises a dosing tank 1, a first heat exchanger 2, a melt booster pump 3, a fully mixed flow polymerizer 4 (namely a first reactor), a second heat exchanger 5, a static mixer 6, a tubular reactor 7 (namely a second reactor) and a twin-screw extruder 8 which are connected in sequence.

Wherein, a pipeline between the complete mixed flow polymerizer 3 and the second heat exchanger 5 is also connected with a monomer and solvent feeding pipeline 9 for supplementing monomer and/or solvent; the line between the second heat exchanger 5 and the static mixer 6 is also connected to an initiator feed line 10 for the addition of initiator.

Example 1

75Kg of Styrene (SM), 25Kg of Acrylonitrile (AN) and 0.065Kg of chain transfer agent, tert-dodecyl mercaptan, were added to 200L of the compounding tank 1, and after being uniformly mixed, they were cooled to-20 ℃ by the first heat exchanger 2.

Continuously conveying the raw material mixed liquor into a fully mixed flow polymerization kettle 4 with the volume of 10L and good heat insulation through a melt booster pump 3 at the feeding speed of 10L/h, reacting the kettle body in a fully filled state, controlling the temperature in the kettle to be about 150 ℃ by adjusting the feeding temperature of the raw material mixed liquor, controlling the average retention time of materials in the kettle to be 1h, and overflowing and discharging the materials from the top of the kettle to obtain slurry A. The monomer conversion at one stage was tested to be 39%.

The overflowed slurry A is continuously conveyed to the rear section, N-dimethylformamide is continuously added into a pipeline for conveying the slurry A at the feeding speed of 1L/h through a monomer and solvent feeding pipeline 9, the temperature of the obtained mixture is controlled to be 100 ℃ through a second heat exchanger 5, after the temperature is controlled, 35ppm of initiator dibenzoyl peroxide (the concentration is based on the mass of the slurry A, the half life period is 8min at the temperature of 100 ℃) is continuously injected into the mixed material through an initiator feeding pipeline 10, then the mixed material is uniformly mixed through a static mixer 6 and enters a tubular reactor 7, the total volume of the tubular reactor 7 is 6.6L, the retention time of the mixed material is 0.6h, the outlet temperature is 160 ℃, the slurry B is obtained, and the monomer conversion rate of the second section is 55% through tests.

And (3) feeding the slurry B into a double-screw extruder 8, controlling the first devolatilization port temperature to be 120 ℃, the pressure to be 30KPa, the second devolatilization port temperature to be 210 ℃, the pressure to be 200Pa, and molding the devolatilized material to obtain a styrene-acrylonitrile copolymer (SAN resin) product. The product structure and performance test results are shown in table 3.

Example 2

80Kg of styrene, 20Kg of acrylonitrile and 0.06Kg of chain transfer agent tert-dodecyl mercaptan are added into a 200L batching tank 1, and after being uniformly mixed, the mixture is cooled to-25 ℃ by a first heat exchanger 2.

The raw material mixed liquor is continuously conveyed into a fully mixed flow polymerization kettle 4 with the volume of 10L and good heat preservation through a melt booster pump 3 at the feeding speed of 6.6L/h, the kettle body reacts under the full-filling state, and the temperature in the kettle is controlled to be maintained at about 140 ℃ by adjusting the feeding temperature of the raw material mixed liquor. The average residence time of the materials in the kettle is 1.5h, and the materials overflow from the top of the kettle and are discharged to obtain slurry A. The monomer conversion for one stage was tested to be 42%.

Continuously conveying the overflowed slurry A to a rear section, continuously adding N, N-dimethylformamide into a pipeline for conveying the slurry A at a feeding speed of 0.66L/h through a monomer and solvent feeding pipeline 9, continuously supplementing acrylonitrile at a feeding speed of 0.06L/h (the acrylonitrile addition amount is 0.9 wt% of the total amount of the monomers), then controlling the temperature of the obtained mixture to be 100 ℃ through a second heat exchanger 5, controlling the temperature, continuously injecting 35ppm of initiator dibenzoyl peroxide (the concentration is based on the mass of the slurry A, the half life period is 8min at the temperature of 100 ℃) into the mixture through an initiator feeding pipeline 10, then uniformly mixing the mixture through a static mixer 6, then feeding the mixture into a tubular reactor 7, wherein the total volume of the tubular reactor 7 is 4.4L, the retention time of the mixture in the tubular reactor 7 is 0.6h, the outlet temperature is 160 ℃, slurry B was obtained and found to have a monomer conversion of 55% in the second stage.

And (3) feeding the slurry B into a double-screw extruder 8, controlling the temperature of a first devolatilization port to be 120 ℃, the pressure to be 30KPa, the temperature of a second devolatilization port to be 210 ℃, the pressure to be 200Pa, and forming the devolatilized materials to obtain the SAN resin product. The product structure and performance test results are shown in table 3.

Example 3

80Kg of styrene, 20Kg of acrylonitrile and 0.06Kg of chain transfer agent tert-dodecyl mercaptan are added into a 200L batching tank 1, and after being uniformly mixed, the mixture is cooled to-10 ℃ by a first heat exchanger 2.

The raw material mixed liquor is continuously conveyed into a fully mixed flow polymerization kettle 4 with the volume of 10L and good heat preservation through a melt booster pump 3 at the feeding speed of 12.5L/h, the kettle body reacts under the full-filling state, and the temperature in the kettle is controlled to be maintained at about 150 ℃ by adjusting the feeding temperature of the raw material mixed liquor. The average residence time of the materials in the kettle is 0.8h, and the materials overflow from the top of the kettle and are discharged to obtain slurry A. The monomer conversion at one stage was tested to be 35%.

Continuously conveying the overflowed slurry A to a rear section, continuously adding N, N-dimethylformamide into a pipeline for conveying the slurry A at a feeding speed of 1.26L/h through a monomer and solvent feeding pipeline 9, continuously supplementing acrylonitrile at a feeding speed of 0.088L/h (the acrylonitrile addition amount is 0.7 wt% of the total amount of the monomers), then controlling the temperature of the obtained mixture to 90 ℃ through a second heat exchanger 5, controlling the temperature, continuously injecting 50ppm of initiator dibenzoyl peroxide into the mixture through an initiator feeding pipeline 10 (the concentration is based on the mass of the slurry A, the half life period is 10min at the temperature of 90 ℃), then uniformly mixing the mixture through a static mixer 6, then feeding the mixture into a tubular reactor 7, wherein the total volume of the tubular reactor 7 is 13.8L, and the retention time of the mixture in the tubular reactor 7 is 1h, the exit temperature was 160 ℃ to give slurry B, which was tested to have a monomer conversion of 60% in the second stage.

And (3) feeding the slurry B into a double-screw extruder 8, controlling the temperature of a first devolatilization port to be 120 ℃, the pressure to be 30KPa, the temperature of a second devolatilization port to be 210 ℃, the pressure to be 200Pa, and forming the devolatilized materials to obtain the SAN resin product. The product structure and performance test results are shown in table 3.

Example 4

70Kg of styrene, 30Kg of acrylonitrile and 0.07Kg of chain transfer agent tert-dodecyl mercaptan are added into a 200L batching tank 1, and after being uniformly mixed, the mixture is cooled to-30 ℃ by a first heat exchanger 2.

The raw material mixed liquor is continuously conveyed into a fully mixed flow polymerization kettle 4 with the volume of 10L and good heat preservation through a melt booster pump 3 at the feeding speed of 12.5L/h, the kettle body reacts under the full-filling state, and the temperature in the kettle is controlled to be kept at about 145 ℃ by adjusting the feeding temperature of the raw material mixed liquor. The average residence time of the materials in the kettle is 0.8h, and the materials overflow from the top of the kettle and are discharged to obtain slurry A. The monomer conversion at one stage was tested to be 35%.

Continuously conveying the overflowed slurry A to a rear section, continuously adding N, N-dimethylformamide into a pipeline for conveying the slurry A at a feeding speed of 1.26L/h through a monomer and solvent feeding pipeline 9, continuously supplementing styrene at a feeding speed of 0.132L/h (the styrene supplementing amount is 1.05 wt% of the total amount of the monomers), then controlling the temperature of the obtained mixture to be 100 ℃ through a second heat exchanger 5, controlling the temperature, continuously injecting 35ppm of initiator dibenzoyl peroxide into the mixture through an initiator feeding pipeline 10 (the concentration is based on the mass of the slurry A, the half life period is 8min at the temperature of 100 ℃) after the temperature is controlled, then uniformly mixing the mixture through a static mixer 6, then feeding the mixture into a tubular reactor 7, wherein the full volume of the tubular reactor 7 is 8.4L, the retention time of the mixture in the tubular reactor 7 is 0.6h, the exit temperature was 155 ℃ to give slurry B, which was tested to have a monomer conversion of 50% in the second stage.

And (3) feeding the slurry B into a double-screw extruder 8, controlling the temperature of a first devolatilization port to be 120 ℃, the pressure to be 30KPa, the temperature of a second devolatilization port to be 210 ℃, the pressure to be 200Pa, and forming the devolatilized materials to obtain the SAN resin product. The product structure and performance test results are shown in table 3.

Example 5

70Kg of styrene, 30Kg of acrylonitrile and 0.07Kg of chain transfer agent, tert-dodecyl mercaptan, were added to 200L of the batching tank 1, and after being uniformly mixed, they were cooled to-30 ℃ by the first heat exchanger 2.

The raw material mixed liquor is continuously conveyed into a fully mixed flow polymerization kettle 4 with the volume of 10L and good heat preservation through a melt booster pump 3 at the feeding speed of 10L/h, the kettle body reacts under the full-filling state, and the temperature in the kettle is controlled to be maintained at about 150 ℃ by adjusting the feeding temperature of the raw material mixed liquor. The average residence time of the materials in the kettle is 1h, and the materials are discharged from the top of the kettle in an overflowing manner to obtain slurry A. The monomer conversion for one stage was tested to be 42%.

Continuously conveying the overflowed slurry A to a rear section, continuously adding N, N-dimethylformamide into a pipeline for conveying the slurry A at a feeding speed of 1L/h through a monomer and solvent feeding pipeline 9, continuously supplementing styrene at a feeding speed of 0.12L/h (the styrene supplementation amount is 1.2 wt% of the total monomers), then controlling the temperature of the obtained mixture to be 110 ℃ through a second heat exchanger 5, controlling the temperature, continuously injecting 25ppm of initiator dibenzoyl peroxide (the concentration is based on the mass of the slurry A, and the half-life period is 6min at the temperature of 110 ℃) into the mixture through an initiator feeding pipeline 10, then uniformly mixing the mixture through a static mixer 6, then feeding the mixture into a tubular reactor 7, wherein the total volume of the tubular reactor 7 is 4.4L, the retention time of the mixture in the tubular reactor 7 is 0.4h, the outlet temperature is 150 ℃, slurry B was obtained and the monomer conversion of the second stage was tested to be 50%.

And (3) feeding the slurry B into a double-screw extruder 8, controlling the temperature of a first devolatilization port to be 120 ℃, the pressure to be 30KPa, the temperature of a second devolatilization port to be 210 ℃, the pressure to be 200Pa, and forming the devolatilized materials to obtain the SAN resin product. The product structure and performance test results are shown in table 3.

Example 6

80Kg of styrene, 20Kg of acrylonitrile and 0.06Kg of chain transfer agent tert-dodecyl mercaptan are added into a 200L batching tank 1, and after being uniformly mixed, the mixture is cooled to-25 ℃ by a first heat exchanger 2.

The raw material mixed solution is continuously conveyed into a fully mixed flow polymerization kettle 4 with the volume of 10L and good heat preservation through a melt booster pump 3 at the feeding speed of 6.7L/h, the kettle body reacts in a fully filled state, and the temperature in the kettle is controlled to be about 140 ℃ by adjusting the feeding temperature of the raw material mixed solution. The average residence time of the materials in the kettle is 1.5h, and the materials overflow from the top of the kettle and are discharged to obtain slurry A. The monomer conversion for one stage was tested to be 42%.

The overflowed slurry A is continuously conveyed to the rear section, N-dimethylformamide is continuously added into a pipeline for conveying the slurry A at a feeding speed of 0.67L/h through a monomer and solvent feeding pipeline 9, the temperature of the obtained mixture is controlled to be 100 ℃ through a second heat exchanger 5, 35ppm of initiator dibenzoyl peroxide (the concentration is based on the mass of the slurry A, the half-life period is 8min at the temperature of 100 ℃) is continuously injected into the mixed material through an initiator feeding pipeline 10 after the temperature is controlled, then the mixed material is uniformly mixed through a static mixer 6 and enters a tubular reactor 7, the total volume of the tubular reactor 7 is 4.4L, the retention time of the mixed material in the tubular reactor 7 is 0.6h, the outlet temperature is 155 ℃, the slurry B is obtained, and the monomer conversion rate of the second section is 60% through tests.

And (3) feeding the slurry B into a double-screw extruder 8, controlling the temperature of a first devolatilization port to be 120 ℃, the pressure to be 30KPa, the temperature of a second devolatilization port to be 210 ℃, the pressure to be 200Pa, and forming the devolatilized materials to obtain the SAN resin product. The product structure and performance test results are shown in table 3.

Example 7

70Kg of styrene, 30Kg of acrylonitrile and 0.07Kg of chain transfer agent tert-dodecyl mercaptan are added into a 200L batching tank 1, and after being uniformly mixed, the mixture is cooled to-30 ℃ by a first heat exchanger 2.

The raw material mixed liquor is continuously conveyed into a fully mixed flow polymerization kettle 4 with the volume of 10L and good heat preservation through a melt booster pump 3 at the feeding speed of 12.5L/h, the kettle body reacts under the full-filling state, and the temperature in the kettle is controlled to be kept at about 145 ℃ by adjusting the feeding temperature of the raw material mixed liquor. The average residence time of the materials in the kettle is 0.8h, and the materials overflow from the top of the kettle and are discharged to obtain slurry A. The monomer conversion at one stage was tested to be 35%.

The overflowed slurry A is continuously conveyed to the rear section, N-dimethylformamide is continuously added into a pipeline for conveying the slurry A at a feeding speed of 1.25L/h through a monomer and solvent feeding pipeline 9, the temperature of the obtained mixture is controlled to be 100 ℃ through a second heat exchanger 5, 35ppm of initiator dibenzoyl peroxide (the concentration is based on the mass of the slurry A, the half-life period is 8min at the temperature of 100 ℃) is continuously injected into the mixed material through an initiator feeding pipeline 10 after the temperature is controlled, then the mixed material is uniformly mixed through a static mixer 6 and enters a tubular reactor 7, the total volume of the tubular reactor 7 is 8.25L, the retention time of the mixed material in the tubular reactor 7 is 0.6h, the outlet temperature is 155 ℃, the slurry B is obtained, and the monomer conversion rate of the second section is 60% through tests.

And (3) feeding the slurry B into a double-screw extruder 8, controlling the temperature of a first devolatilization port to be 120 ℃, the pressure to be 30KPa, the temperature of a second devolatilization port to be 210 ℃, the pressure to be 200Pa, and forming the devolatilized materials to obtain the SAN resin product. The product structure and performance test results are shown in table 3.

Comparative example 1

75Kg of styrene, 25Kg of acrylonitrile and 0.065Kg of chain transfer agent, tert-dodecyl mercaptan, were added to a 200L compounding tank and mixed at room temperature to give a mixture having a temperature of 20 ℃.

The raw material mixed liquor is continuously conveyed into a fully mixed flow polymerization kettle with the volume of 25L and good heat preservation at the feeding speed of 10L/h, the filling coefficient of the kettle body is 40 percent, a shell and tube heat exchanger is arranged at the upper part of the kettle top, and the temperature in the polymerization kettle is controlled to be maintained at about 150 ℃ by gas phase condensation of monomers. The average residence time of the materials in the kettle is 1h, and slurry A is obtained. The monomer conversion was tested to be 42%.

And (3) feeding the slurry A into a double-screw extruder, controlling the temperature of a first devolatilization port to be 120 ℃, the pressure to be 30KPa, the temperature of a second devolatilization port to be 210 ℃, and the pressure to be 200Pa, and forming the devolatilized material to obtain the SAN resin product. The product structure and performance test results are shown in table 3.

Comparative example 2

Into a 200L batch tank were charged 75Kg of styrene, 25Kg of acrylonitrile, and 0.065Kg of a chain transfer agent, tert-dodecyl mercaptan. Mixing at room temperature, and cooling the mixture to 20 deg.C.

The raw material mixed solution is continuously conveyed into a fully mixed flow polymerization kettle with the volume of 10L and good heat preservation through a melt booster pump at the feeding speed of 10L/h, the kettle body is reacted in a fully filled state, the temperature of a jacket oil bath in the polymerization kettle is 120 ℃, and the polymerization temperature is controlled by the jacket oil bath to be stabilized at about 150 ℃. The average residence time of the materials in the kettle is 1h, and the materials overflow from the top of the kettle to be discharged, so that slurry A is obtained. The monomer conversion was tested to be 42%.

And (3) feeding the slurry A into a double-screw extruder, controlling the temperature of a first devolatilization port to be 120 ℃, the pressure to be 30KPa, the temperature of a second devolatilization port to be 210 ℃, and the pressure to be 200Pa, and forming the devolatilized material to obtain the SAN resin product. The product structure and performance test results are shown in table 3.

Comparative example 3

The same procedure as in example 2 was repeated, except that the amount of acrylonitrile monomer added was 1.5% by weight based on the total amount of the monomers. The product structure and performance test results of the obtained SAN resin are shown in Table 3.

Comparative example 4

The same procedure as in example 4 was repeated, except that the styrene content was changed to 2% by weight based on the total amount of the monomers. The product structure and performance test results of the obtained SAN resin are shown in Table 3.

Comparative example 5

75Kg of styrene, 25Kg of acrylonitrile and 0.065Kg of chain transfer agent tert-dodecyl mercaptan are added into a 200L batching tank 1, and after being uniformly mixed, the mixture is cooled to-20 ℃ by a first heat exchanger 2.

The raw material mixed liquor is continuously conveyed into a fully mixed flow polymerization kettle 4 with the volume of 10L and good heat preservation through a melt booster pump 3 at the feeding speed of 10L/h, the kettle body is fully filled for reaction, the temperature in the kettle is maintained at about 150 ℃, and the temperature in the kettle is controlled to be maintained at about 150 ℃ by adjusting the feeding temperature of the raw material mixed liquor. The average residence time of the materials in the kettle is 1h, and the materials overflow from the top of the kettle to be discharged, so that slurry A is obtained. The monomer conversion at one stage was tested to be 39%.

The overflowed slurry A is continuously conveyed to the rear section, N-dimethylformamide is continuously added into a pipeline for conveying the slurry A at the feeding speed of 1L/h through a monomer and solvent feeding pipeline 9, then 35ppm of initiator dibenzoyl peroxide (the half life is less than 1min at the temperature of 150 ℃) is continuously injected into a mixed material through an initiator feeding pipeline 10, the concentration is based on the mass of the slurry A, then the mixed material is uniformly mixed through a static mixer 6 and then enters a tubular reactor 7, the full volume of the tubular reactor 7 is 6.6L, the retention time of the mixed material in the tubular reactor 7 is 0.6h, the outlet temperature is 190 ℃, and the slurry B is obtained, and the monomer conversion rate of the second section is 71% through tests.

And (3) feeding the slurry B into a double-screw extruder 8, controlling the temperature of a first devolatilization port to be 120 ℃, the pressure to be 30KPa, the temperature of a second devolatilization port to be 210 ℃, the pressure to be 200Pa, and forming the devolatilized materials to obtain the SAN resin product. The product structure and performance test results are shown in table 3.

TABLE 3 SAN resin structures and Performance test results of examples and comparative examples

From examples 1 to 7, it can be seen that the styrene-acrylonitrile copolymer prepared by the preparation method of the present invention has good optical properties (light transmittance of 91% or more, haze of 2% or less, yellowing index of 2 or less), and also maintains good mechanical properties.

As can be seen from the comparison of example 1 with comparative example 1, the polymer prepared by the present invention has obvious advantages in terms of optical properties compared with the conventional monomer condensation heat transfer process, mainly because some polymers with high acrylonitrile content are inevitably generated during the monomer gas phase condensation process, and the polymers are easily colored during the high temperature devolatilization process, thereby affecting the optical properties of the polymers.

It can be seen from the comparison between example 1 and comparative example 2 that the polymer prepared by the present invention is also superior in optical properties and other application properties compared to the conventional jacket cooling heat transfer method, mainly because the jacket heat transfer is adopted in comparative example 2, the problem of uneven heating is inevitable in the reaction solution, the deterioration of polymer properties is caused by the existence of local hot spots, the polymerization heat is carried away by the latent heat of the monomers in the present invention, no heat transfer is needed in the reaction process, the temperature of each part of the reaction system can be uniform, the temperature difference is small, the polymer structure formed in this way is more uniform, the risk of local implosion is reduced, the side reaction of the monomers or between the monomers can be effectively inhibited, and further, the better optical properties and mechanical properties can be obtained.

As can be seen from the comparison of examples 2, 3 and 6 with comparative example 3 and the comparison of examples 4, 5 and 7 with comparative example 4, the addition of additional monomer to the second reactor and the control of the amount of additional monomer within a suitable range also contribute to obtaining a polymer with better optical properties, avoiding adverse effects on optical properties due to non-uniform polymer composition in the two-stage reaction.

As can be seen from the comparison of example 1 with comparative example 5, controlling the feeding temperature in the second stage reaction within a proper range can balance the heat release of the second stage polymerization process, and the stability of the polymerization temperature can ensure that the final product performance, especially the optical performance, is more excellent, mainly because, when the initial temperature of the slurry entering the second reactor is too high, the polymerization reaction rate is too fast, the heat release rate is also very fast, the temperature reached by the self-polymerization heat release is too high, and when the reaction rate is too fast, hot spots are formed locally in the reactor, which causes the non-uniformity of the polymer composition and the coloring problem.

In conclusion, the invention comprehensively considers each influence factor of the styrene-acrylonitrile copolymerization reaction process, and the finally obtained preparation method can comprehensively and effectively avoid the problems of nonuniform composition, coloring and the like of the polymer, so that the obtained polymer has excellent optical property and mechanical property, the application range of the product is expanded, the product competitiveness is improved, and the polymer has industrial practical value.

Unless otherwise defined, all terms used herein have the meanings commonly understood by those skilled in the art.

The described embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of the present invention, and those skilled in the art may make various other substitutions, alterations, and modifications within the scope of the present invention, and thus, the present invention is not limited to the above-described embodiments but only by the claims.

Claims (18)

1. A preparation method of styrene-acrylonitrile copolymer is characterized by comprising the following steps:

s1: mixing 60-90 parts by mass of styrene monomer and 10-40 parts by mass of acrylonitrile monomer, and cooling to-40-10 ℃ to obtain a mixed raw material;

s2: feeding the mixed raw materials into a first reactor, reacting in a state of keeping the first reactor full of the mixed raw materials until the monomer conversion rate is 25-45 wt%, wherein the temperature in the first reactor is 130-160 ℃, and discharging to obtain a first slurry;

s3: controlling the temperature of the first slurry to be 90-110 ℃, feeding the first slurry into a second reactor, continuously reacting under the state of keeping the second reactor full, controlling the temperature in the second reactor to be 90-160 ℃, and discharging to obtain second slurry, wherein the ratio of the monomer conversion rate of the first slurry to the monomer conversion rate of the second slurry is 0.4-0.9: 1; and

s4: and devolatilizing the second slurry to obtain the styrene-acrylonitrile copolymer.

2. The method of claim 1, wherein in the step S2, the mixed raw materials are reacted in the first reactor for 0.8-1.5 h to obtain a monomer conversion rate of 35-42 wt%.

3. The method of claim 1, wherein in step S3, the first slurry stays in the second reactor for 0.1-2 h to reach a monomer conversion of 40-70 wt%.

4. The method according to claim 3, wherein in the step S3, the first slurry stays in the second reactor for 0.2-1 h to reach a monomer conversion of 50-60 wt%.

5. The production method according to claim 1, wherein the first reactor is a fully mixed flow reactor, and the first slurry is discharged by overflowing from the top of the fully mixed flow reactor; and/or

The second reactor is a plug flow reactor.

6. The method of claim 5, wherein the second reactor is a tubular reactor.

7. The preparation method according to claim 1, wherein the temperature in the first reactor is 140-150 ℃; and/or

The temperature in the second reactor is 140-160 ℃.

8. The method for preparing a composite material according to claim 1, wherein the step S3 further includes: when the content of acrylonitrile monomer is less than 25 wt% based on the total mass of the monomers in the mixed raw material, m is supplemented into the first slurry before temperature control ₁ % of the total mass of the monomers of acrylonitrile monomer; when the content of acrylonitrile monomer is more than 25 wt%, m is supplemented into the first slurry before temperature control ₂ % of the total mass of the monomers of styrene monomers,

wherein m is ₁ And m ₂ Calculated from equation (1) and equation (2), respectively:

in the formulas (1) and (2), f ₁ Denotes the acrylonitrile monomer content, f, based on the total mass of monomers in the mixed feed ₂ Represents the styrene monomer content based on the total mass of monomers in the mixed raw materials, and x represents the monomer conversion rate of the first slurry.

9. The method for preparing a composite material according to claim 1, wherein the step S3 further includes: adding a solvent into the first slurry before temperature control, wherein the solvent is one or more of toluene, ethylbenzene, cyclohexane, acetonitrile, tetrahydrofuran and N, N-dimethylformamide; the addition amount of the solvent is 5-20 wt% of the first slurry.

10. The method according to claim 9, wherein the solvent is added in an amount of 10 to 15 wt% based on the first slurry.

11. The method for preparing a composite material according to claim 1, wherein the step S3 further includes: adding an initiator into the first slurry after temperature control, wherein the initiator is an organic peroxide initiator or an azo initiator; the addition amount of the initiator is 10-100 ppm based on the mass of the first slurry.

12. The production method according to claim 11, wherein the amount of the initiator added is 20 to 50ppm based on the mass of the first slurry.

13. The preparation method according to claim 1, wherein the mixed raw material further comprises tert-dodecyl mercaptan as a chain transfer agent, and the amount of the chain transfer agent is 0.02 to 0.2 wt% based on the total mass of the monomers in the mixed raw material.

14. The production method according to claim 13, wherein the amount of the chain transfer agent added is 0.05 to 0.15 wt% based on the total mass of the monomers in the raw materials mixture.

15. The method according to any one of claims 1 to 14, wherein in step S4, the second slurry is subjected to secondary devolatilization, the primary devolatilization temperature is 80 to 160 ℃, and the absolute pressure is 10 to 40 KPa; the second-stage devolatilization temperature is 180-240 ℃, and the absolute pressure is lower than 1 KPa.

16. The preparation method of claim 15, wherein the first-stage devolatilization temperature is 100 to 140 ℃; the second-stage devolatilization temperature is 200-220 ℃.

17. A styrene-acrylonitrile copolymer produced by the production method according to any one of claims 1 to 16.

18. The styrene-acrylonitrile copolymer of claim 17, wherein the styrene-acrylonitrile copolymer has one or more of the following properties: the total light transmittance is more than or equal to 91 percent, the haze is less than or equal to 2 percent or the yellowing index of the injection-molded 3mm membrane is less than or equal to 2.

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