Polystyrene-maleic anhydride-lactide copolymers, methods for their preparation and use

Abstract

This invention provides a polystyrene-maleic anhydride-lactide copolymer having the structure shown in the following formula, wherein R1 and R2 are independently selected from substituted or unsubstituted alkyl groups of C1-C10, substituted or unsubstituted alicyclic groups or aryl groups of C6-C30, x and y are integers from 5 to 50, n is an integer from 10 to 120, and p is an integer from 20 to 260. This invention first copolymerizes styrene with maleic anhydride to prepare low molecular weight SMA, then condenses lactic acid or lactic acid oligomers to form low molecular weight polylactic acid, which is then modified by end-hydroxylation. Finally, under the action of a chain extender, the end-hydroxylated low molecular weight polylactic acid is polymerized with SMA at high temperature to obtain the copolymer. The copolymer of this invention simultaneously possesses the rigidity and strength of polylactic acid segments and the flexibility and toughness of SMA segments, exhibiting excellent mechanical properties, heat resistance, and processing performance, thus broadening its industrial application fields.

Description

Technical Field

[0001] This invention relates to a technique for synthesizing high molecular weight polyesters by chain extension of lactic acid oligomers, and particularly to a high molecular weight polystyrene-maleic anhydride-lactide copolymer and its preparation method, belonging to the field of polymer material synthesis. Background Technology

[0002] Polylactic acid (PLA) is a biodegradable plastic produced by fermenting biomass resources to generate lactic acid, followed by lactic acid condensation to prepare lactide, and then lactide polymerization to produce PLA. This green synthesis route offers unparalleled advantages over traditional petroleum-based plastics, making PLA material preparation a hot area in polymer synthesis. PLA possesses advantages such as high strength and good processability; however, its production cost is relatively high, primarily due to low product yields during the synthesis process. On one hand, the depolymerization of lactic acid polymers to prepare lactide leaves behind some lactic acid oligomers, which have large molecular weights and are difficult to recycle for further depolymerization to form lactide. On the other hand, during the distillation and purification stage of lactide, some lactic acid oligomers are generated at the bottom of the reboiler in the distillation column, resulting in a low distillation and purification yield. The traditional method for reusing lactic acid oligomers involves hydrolyzing them into small lactic acid molecules, which are then separated, purified, and used in the preparation of lactide. However, lactide is prone to racemization during depolymerization and distillation, resulting in the presence of dextrorotatory lactic acid in the lactic acid produced by hydrolysis. Separating this portion of lactic acid is difficult and significantly increases the cost of recycling and reusing lactic acid oligomers.

[0003] The lactic acid oligomers produced during lactide preparation typically have molecular weights ranging from several thousand to tens of thousands. Compared to high molecular weight polylactic acid (PLA), lactic acid oligomers have lower melting points and strengths, making them difficult to use directly in material preparation. A common method is to perform chain extension reactions on the lactic acid oligomers to prepare relatively high molecular weight PLA materials. However, the chain extension reaction of lactic acid oligomers involves linking macromolecules, which has low reactivity and is difficult to achieve. Therefore, the PLA prepared is generally of lower molecular weight and of lower quality compared to PLA prepared by the ring-opening polymerization of lactide. Styrene-maleic anhydride copolymer (SMA), on the other hand, is prepared by binary copolymerization of styrene monomer (St) and maleic anhydride (MA). Industrially used SMA can be divided into two categories: one is low molecular weight SMA, which can be used as a surfactant or solvent for polymers; the other is high molecular weight SMA, which can be used alone as a matrix resin or blended with various polymer resins for modification. Due to the excellent properties and outstanding molecular polarity of SMA, low molecular weight SMA resin can be used as a good plasticizer for polylactic acid (PLA) and can improve the toughness of PLA to a certain extent. However, the use of SMA as a plasticizer in the preparation of materials with PLA does not fundamentally improve the performance of polyester materials, and the modification effect is not significant.

[0004] Chinese patent CN103254411A describes the synthesis of polylactic acid (PLA) materials by adding stannous octoate catalyst to lactic acid oligomers and reacting them under oil bath heating conditions. The temperature was raised to 175°C and the pressure was reduced to 100 Pa. After 10 hours of polycondensation, the reaction was stopped. In the later stage of the polycondensation reaction, the system temperature was lowered to 160°C, and 0.5% of a carbodiimide chain extender was added to carry out the chain extension reaction. After mechanical stirring for 2 hours, a PLA product with a weight-average molecular weight of 102,000 was obtained. PLA materials were successfully synthesized from lactic acid oligomers through chain extension reaction. However, the molecular weight of PLA is relatively low, resulting in poor heat resistance, high brittleness, and low toughness of the material. Chinese patent CN106344958A uses lactic acid as a raw material, dehydrates and refines it under vacuum to obtain lactic acid oligomers. These oligomers are then mixed with a catalyst and added to a reaction vessel. Under vacuum, the mixture is heated to produce polylactic acid (PLA) intermediates. Chain extender HDI is added to the reaction vessel, and the mixture is heated under vacuum to obtain PLA material. Although PLA is prepared from lactic acid oligomers via chain extension, this method does not improve the high brittleness and low toughness of PLA. Chinese patent CN104212085A uses SMA as a plasticizer, adding it to a blend of polystyrene, polyethylene, and PLA. A copolyester material is successfully prepared via twin-screw extrusion. While SMA as a plasticizer improves the compatibility of the copolyester to some extent, this simple physical blending method does not alter the thermodynamic properties of the base resin material itself.

[0005] In summary, the current methods for recycling and reusing lactic acid oligomers mainly have the following problems: (1) Hydrolyzing lactic acid oligomers into small lactic acid molecules and then preparing polylactic acid from lactic acid can recycle lactic acid oligomers, but the cost of separating small lactic acid molecules is too high, which is not conducive to industrial application. (2) If polylactic acid is prepared from lactic acid oligomers through a simple self-chain extension reaction, it is difficult to prepare high molecular weight, high quality polylactic acid materials due to the low reactivity between macromolecular chains and the difficulty of linking. (3) Polylactic acid materials prepared from recycled lactic acid oligomers have poor heat resistance and low toughness, and require modification processing before industrial application. Summary of the Invention

[0006] To address the above shortcomings, this invention provides a high molecular weight polystyrene-maleic anhydride-lactide copolymer, which is prepared using lactic acid oligomers as raw materials and a reaction route different from existing technologies. The prepared copolymer has the rigidity and strength of polylactic acid segments, the flexibility and toughness of SMA segments, excellent heat resistance and processing performance, is biodegradable, and is easy to industrialize.

[0007] To achieve the above technical objectives, the technical solution adopted by this invention is as follows:

[0008] The first aspect of the present invention aims to provide a polystyrene-maleic anhydride-lactide copolymer having the structure of general formula I:

[0009]

[0010] R1 and R2 are independently selected from substituted or unsubstituted alkyl groups of C1-C10, substituted or unsubstituted alicyclic groups or aryl groups of C6-C30; preferably substituted or unsubstituted alkyl groups of C2-C6, alicyclic groups or aryl groups of C6-C15.

[0011] x is an integer from 5 to 50, preferably an integer from 15 to 25; y is an integer from 5 to 50, preferably an integer from 15 to 25; n is an integer from 10 to 120, preferably an integer from 40 to 100; p is an integer from 20 to 260, preferably an integer from 60 to 120.

[0012] Furthermore, as a more specific implementation, R1 is selected from -CH2CH2CH2CH2-, -CH2CH2CH2CH2CH2-, -CH2CH2CH2CH2CH2CH2-,

[0013] One of the groups.

[0014] Furthermore, as a more specific implementation, R2 is selected from -CH2CH2-, -CH2CH2CH2-, -CH(CH3)CH2-, CH2CH2CH2CH2- and One of the groups.

[0015] Furthermore, the polystyrene-maleic anhydride-lactide copolymer has a weight-average molecular weight of 1.0 × 10⁻⁶. 5 -3.5×10 5 2.0×10 is preferred. 5 -3.0×10 5 .

[0016] Furthermore, the right-angle tear strength of the polystyrene-maleic anhydride-lactide copolymer is not less than 90 kN / m, preferably 100-120 kN / m; and the elongation at break is not less than 75%, preferably 80-105%.

[0017] Furthermore, the glass transition temperature of the polystyrene-maleic anhydride-lactide copolymer is 120-150°C.

[0018] In this invention, the right-angle tear strength and elongation at break are measured by a universal mechanical testing machine; the weight-average molecular weight is measured by gel chromatography; and the glass transition temperature is measured by differential scanning calorimetry. These are described in detail below.

[0019] The second aspect of the present invention aims to provide a method for preparing a polystyrene-maleic anhydride-lactide copolymer, comprising the following:

[0020] (1) Maleic anhydride and styrene are polymerized to obtain a low molecular weight SMA polymer.

[0021] (2) Low molecular weight polylactic acid is obtained by prepolymerizing lactic acid or lactic acid oligomers at low temperature in the presence of a catalyst, and then by adding diol to end-hydroxylate the low molecular weight polylactic acid to obtain end-hydroxylated low molecular weight polylactic acid.

[0022] (3) The hydroxylated low molecular weight polylactic acid obtained in step (2) is heated and melted, and the low molecular weight SMA polymer obtained in step (1) is added to the melt. During the reaction, diisocyanate is continuously added dropwise, and the polystyrene-maleic anhydride-lactide copolymer is prepared by high-temperature polymerization.

[0023] Furthermore, in step (1), maleic anhydride and styrene are polymerized in the presence of an initiator selected from at least one of dicumyl peroxide or azobisisobutyronitrile, preferably dicumyl peroxide.

[0024] Further, the specific process of step (1) is as follows: maleic anhydride is dissolved in an organic solvent, and an initiator is added and heated at a constant temperature. Styrene monomer is added dropwise to the reaction solution, and the reaction is continued to be heated. After the reaction is completed, a precipitant is added, and after filtration and drying, a low molecular weight SMA polymer is obtained. The organic solvent is selected from at least one of butyl acetate, n-heptane and acetone, preferably acetone. The precipitant is selected from at least one of diethyl ether, anhydrous methanol and anhydrous ethanol, preferably anhydrous ethanol.

[0025] Furthermore, by weight, the amount of initiator added in step (1) is 0.1-5% of maleic anhydride, preferably 0.5-2.0%, and the amount of styrene added is 100-300% of maleic anhydride, preferably 150-250%.

[0026] Furthermore, step (1) is a constant-temperature reaction under an inert atmosphere, preferably a nitrogen gas flow, with a reaction temperature of 50-150℃, preferably 80-120℃; a reaction time of 1-8h, preferably 2-6h; and a flow rate of the inert atmosphere protective gas of 0.5-6m / s, preferably 2-4m / s.

[0027] The main reaction that occurs in step (1) is shown in the following equation:

[0028]

[0029] Furthermore, the molecular weight of the low molecular weight SMA polymer mentioned in step (1) is 1000-10000, preferably 3000-5000.

[0030] Furthermore, the lactic acid oligomer in step (2) is preferably a lactide depolymerization substrate or a distillation substrate, preferably a lactide distillation substrate; the catalyst is selected from one or more of stannous octoate, zinc lactate, trialkylaluminum, triisobutylaluminum and stannous chloride, preferably stannous octoate; the diol is selected from one or more of ethylene glycol, 1,3-propanediol, 1,2-propanediol, bisphenol A or 1,4-butanediol, preferably 1,4-butanediol.

[0031] Furthermore, in step (2), the amount of catalyst added is 0.01-1% by weight of lactic acid or lactic acid oligomer, preferably 0.05-0.5%; the amount of diol added is 0.01-0.1% by weight of lactic acid or lactic acid oligomer, preferably 0.02-0.08%.

[0032] Furthermore, step (2) involves low-temperature polymerization under an inert atmosphere, preferably a nitrogen gas flow. The polymerization temperature is 100-150℃, preferably 120-140℃; the reaction pressure is 100-1000 kPa, preferably 200-500 kPa; the flow rate of the inert atmosphere is 0.5-6 m / s, preferably 2-4 m / s; the polymerization time is 2-15 h, preferably 3-8 h; and the terminal hydroxylation reaction time is 1-8 h, preferably 2-6 h.

[0033] In this invention, unless otherwise stated, all pressures refer to absolute pressure.

[0034] Furthermore, the molecular weight of the terminally hydroxylated low molecular weight polylactic acid obtained in step (2) is 2000-20000, preferably 5000-10000.

[0035] Further, the diisocyanate mentioned in step (3) is one or more of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI) or hexamethylene diisocyanate (HDI), preferably hexamethylene diisocyanate (HDI). By weight, the amount of diisocyanate added is 0.01-0.1% of the hydroxylated low molecular weight polylactic acid, preferably 0.02-0.08%, and the amount of SMA added is 20-80% of the hydroxylated low molecular weight polylactic acid, preferably 30-60%.

[0036] The main reaction process in step (3) is shown in the following equation:

[0037]

[0038] Furthermore, step (3) involves polymerization under an inert atmosphere, preferably a nitrogen gas flow, with a polymerization temperature of 100-200℃, preferably 120-180℃; a reaction pressure of 100-1000 kPa, preferably 200-500 kPa; a flow rate of the inert atmosphere protective gas of 0.5-6 m / s, preferably 2-4 m / s; and a polymerization reaction time of 4-20 h, preferably 6-18 h.

[0039] The technical objective of the third aspect of this invention is to provide applications of polystyrene-maleic anhydride-lactide copolymer, which is used in automotive interiors, coatings, textiles, printing and dyeing, and medical supplies.

[0040] Compared with existing technologies, the present invention has the following advantages:

[0041] (1) Compared with the prior art, the present invention provides a novel route for synthesizing polystyrene-maleic anhydride-lactide copolymer. First, styrene and maleic anhydride are copolymerized to prepare low molecular weight polystyrene-maleic anhydride (SMA). Then, lactic acid or lactic acid oligomers are further condensed to form low molecular weight polylactic acid. The obtained low molecular weight polylactic acid is modified by end-hydroxylation. Finally, under the action of a chain extender, the end-hydroxylated low molecular weight polylactic acid and SMA are polymerized at high temperature to prepare polystyrene-maleic anhydride-lactide copolymer.

[0042] (2) As polystyrene-maleic anhydride-lactide copolymer has both the rigidity and strength of polylactic acid segments and the flexibility and toughness of SMA segments, it has excellent mechanical properties, heat resistance and processing performance, which broadens the field of industrial application.

[0043] (3) The copolymerization process of SMA and terminally hydroxylated low molecular weight polylactic acid does not generate small molecules, the polymerization speed is fast and the time is short, and it is easy to industrialize.

[0044] (4) In this invention, lactic acid oligomers can be used directly as raw materials, eliminating the process of hydrolysis, recycling and reuse of lactic acid oligomers. The lactic acid oligomers can be directly used to prepare copolyester materials, providing a new way to use lactic acid oligomers generated in the depolymerization and distillation stages of lactide, and greatly reducing production costs.

[0045] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0046] Figure 1 Fourier transform infrared spectra of pure PLA (polylactic acid) and polystyrene-maleic anhydride-lactide copolyester (PLSMA) prepared in Example 1. Detailed Implementation

[0047] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way. Unless otherwise specified, the reagents, materials, and instruments involved in the following embodiments can be obtained through legitimate commercial channels. Unless otherwise specified, the testing and inspection methods involved in the following embodiments are existing testing and inspection methods in the prior art. The following embodiments clearly and completely describe the technical solutions of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. All obvious variations or modifications derived from the present invention still fall within the scope of protection of the present invention.

[0048] The following are the test methods involving performance parameters in the embodiments:

[0049] (1) Right-angle tear strength and elongation at break: measured by a universal testing machine in accordance with GB / T1039-1992 standard.

[0050] (2) Glass transition temperature: Measured using a differential scanning calorimeter (DSC) (DSC 204, Netzsch, Germany). The test conditions were as follows: 5–10 mg of sample was heated from room temperature to 200 °C at a heating rate of 10 °C / min and held at isothermal temperature for 5 min to eliminate the thermal history of the sample; then the sample was rapidly cooled to -20 °C, and then heated from -20 °C to 200 °C at a heating rate of 10 °C / min; nitrogen gas was introduced as a protective gas throughout the test, with a flow rate of 50 mL / min.

[0051] (3) Polymer weight-average molecular weight: Measured by gel permeation chromatography (GPC). The molecular weight of the polylactic acid graft copolymer samples was characterized using gel permeation chromatography (GPC Waters 1515 system). Chromatographically pure THF was used as the mobile phase at a flow rate of 1.0 mL / min and a column temperature of 35 °C. Before testing, the sample was dissolved in THF at a concentration of 5 mg / mL, filtered through a 0.22 μm polytetrafluoroethylene (PTFE) membrane, and injected. Calibration was performed using narrow-distribution polystyrene (PS) standards.

[0052] Example 1

[0053] (1) Maleic anhydride and acetone solvent were added to a reaction vessel, along with dicumyl peroxide as the initiator. Simultaneously, styrene monomer was added dropwise to the reaction vessel. The reaction was carried out under constant temperature conditions with a nitrogen flow. After the reaction was complete, anhydrous ethanol was added as a precipitant. The mixture was then filtered and dried to obtain a low molecular weight SMA polymer. The constant temperature reaction was 80°C, and the reaction time was 3 hours. The flow rate of the nitrogen-protected gas was 3 m / s. Based on the weight of maleic anhydride, the amount of dicumyl peroxide added as the initiator was 2% of the maleic anhydride, and the amount of styrene added was 180% of the maleic anhydride.

[0054] (2) Lactic acid oligomers were mixed with stannous octoate and prepolymerized at low temperature under nitrogen flow and negative pressure to obtain low molecular weight polylactic acid. 1,4-Butanediol was added to end-hydroxylate the low molecular weight polylactic acid to obtain hydroxylated low molecular weight polylactic acid. The polymerization temperature was 120℃ and the reaction pressure was 300 kPa; the gas flow rate of the nitrogen flow was 3 m / s, the polymerization reaction time was 4 h, and the end-hydroxylation reaction time was 3 h; based on the weight of the lactic acid oligomers, the amount of stannous octoate added was 0.1% of the lactic acid oligomers; the amount of 1,4-butanediol added was 0.03% of the lactic acid oligomers.

[0055] (3) The hydroxylated low molecular weight polylactic acid obtained in step (2) was heated and melted. The low molecular weight SMA polymer obtained in step (1) was added to the melt. Hexamethylene diisocyanate was continuously added dropwise during the reaction. Polystyrene-maleic anhydride-lactide copolyester (PLSMA) was prepared by high-temperature polymerization under nitrogen flow and negative pressure conditions. The polymerization temperature was 150℃; the reaction pressure was 300 kPa; the gas flow rate of the nitrogen flow was 3 m / s; the polymerization reaction time was 8 h; based on the weight of the hydroxylated low molecular weight polylactic acid, the amount of hexamethylene diisocyanate added was 0.03% of the hydroxylated low molecular weight polylactic acid, and the amount of SMA added was 40% of the hydroxylated low molecular weight polylactic acid.

[0056] Performance characterization: The right-angle tear strength of the polystyrene-maleic anhydride-lactide copolymer was measured to be 100 kN / m, the elongation at break was 80%, the glass transition temperature was 125℃, the weight-average molecular weight of the hydroxyl-terminated low molecular weight polylactic acid was 5500, the weight-average molecular weight of the low molecular weight SMA was 3200, and the weight-average molecular weight of the polystyrene-maleic anhydride-lactide copolyester was 1.91 × 10⁻⁶. 5 .

[0057] Figure 1 Fourier transform infrared spectra of pure PLA (polylactic acid) and polystyrene-maleic anhydride-lactide copolyester (PLSMA) prepared in Example 1, from the attached... Figure 1 As can be seen from the infrared spectrum of pure PLA, at 1750 cm⁻¹ -1 1186cm-1 The peaks at 1380 cm⁻¹ represent the strong characteristic absorption peaks of the C=O group and the stretching vibration peak of CO, respectively. Compared to pure PLA, the infrared spectrum of PLASMA shows a stronger characteristic absorption peak at 1380 cm⁻¹. -1 1020cm -1 The presence of the characteristic absorption peak of CN and the stretching vibration peak of CH on the benzene ring indicates that SMA copolymer segments have been introduced into the PLA macromolecular chain.

[0058] Example 2

[0059] (1) Maleic anhydride and acetone solvent were added to a reaction vessel, along with dicumyl peroxide as the initiator. Simultaneously, styrene monomer was added dropwise to the reaction vessel. The reaction was carried out under constant temperature conditions with a nitrogen flow. After the reaction was complete, anhydrous ethanol was added as a precipitant. The mixture was then filtered and dried to obtain a low molecular weight SMA polymer. The constant temperature reaction was 90°C, and the reaction time was 4 hours. The flow rate of the nitrogen-protected gas was 3 m / s. Based on the weight of maleic anhydride, the amount of dicumyl peroxide added as the initiator was 1.5% of the maleic anhydride, and the amount of styrene added was 200% of the maleic anhydride.

[0060] (2) Lactic acid oligomers were mixed with stannous octoate and prepolymerized at low temperature under nitrogen flow and negative pressure to obtain low molecular weight polylactic acid. 1,4-Butanediol was added to end-hydroxylate the low molecular weight polylactic acid to obtain hydroxylated low molecular weight polylactic acid. The polymerization temperature was 125℃ and the reaction pressure was 300 kPa; the gas flow rate of the nitrogen flow was 3 m / s, the polymerization reaction time was 5 h, and the end-hydroxylation reaction time was 4 h; based on the weight of the lactic acid oligomers, the amount of stannous octoate added was 0.2% of the lactic acid oligomers; the amount of 1,4-butanediol added was 0.04% of the lactic acid oligomers.

[0061] (3) The hydroxylated low molecular weight polylactic acid obtained in step (2) was heated and melted. The low molecular weight SMA polymer obtained in step (1) was added to the melt. Hexamethylene diisocyanate was continuously added dropwise during the reaction. Polystyrene-maleic anhydride-lactide copolyester (PLSMA) was prepared by high-temperature polymerization under nitrogen flow and negative pressure conditions. The polymerization temperature was 160℃; the reaction pressure was 300 kPa; the gas flow rate of the nitrogen flow was 3 m / s; the polymerization time was 10 h; based on the weight of the hydroxylated low molecular weight polylactic acid, the amount of hexamethylene diisocyanate added was 0.04% of the hydroxylated low molecular weight polylactic acid, and the amount of SMA added was 45% of the hydroxylated low molecular weight polylactic acid.

[0062] Performance characterization: The measured right-angle tear strength of the polystyrene-maleic anhydride-lactide copolyester material was 108 kN / m, the elongation at break was 85%, the glass transition temperature was 132℃, the weight-average molecular weight of the hydroxyl-terminated low molecular weight polylactic acid was 6200, the weight-average molecular weight of the low molecular weight SMA was 3600, and the weight-average molecular weight of the polystyrene-maleic anhydride-lactide copolyester was 2.16 × 10⁻⁶. 5 .

[0063] Example 3

[0064] (1) Maleic anhydride and acetone solvent were added to a reaction vessel, along with dicumyl peroxide as the initiator. Simultaneously, styrene monomer was added dropwise to the reaction vessel. The reaction was carried out under constant temperature conditions with a nitrogen flow. After the reaction was complete, anhydrous ethanol was added as a precipitant. The mixture was then filtered and dried to obtain a low molecular weight SMA polymer. The constant temperature reaction was 100°C, and the reaction time was 5 hours. The flow rate of the nitrogen-protected gas was 3 m / s. Based on the weight of maleic anhydride, the amount of dicumyl peroxide as the initiator was 1.5% of the maleic anhydride, and the amount of styrene added was 220% of the maleic anhydride.

[0065] (2) Lactic acid oligomers were mixed with stannous octoate and prepolymerized at low temperature under nitrogen flow and negative pressure to obtain low molecular weight polylactic acid. 1,4-Butanediol was added to end-hydroxylate the low molecular weight polylactic acid to obtain hydroxylated low molecular weight polylactic acid. The polymerization temperature was 130℃ and the reaction pressure was 300 kPa; the gas flow rate of the nitrogen flow was 3 m / s, the polymerization reaction time was 6 h, and the end-hydroxylation reaction time was 4 h; based on the weight of the lactic acid oligomers, the amount of stannous octoate added was 0.3% of the lactic acid oligomers; the amount of 1,4-butanediol added was 0.04% of the lactic acid oligomers.

[0066] (3) The hydroxylated low molecular weight polylactic acid obtained in step (2) was heated and melted. The low molecular weight SMA polymer obtained in step (1) was added to the melt. Hexamethylene diisocyanate was continuously added dropwise during the reaction. Polystyrene-maleic anhydride-lactide copolyester (PLSMA) was prepared by high-temperature polymerization under nitrogen flow and negative pressure conditions. The polymerization temperature was 165℃; the reaction pressure was 300 kPa; the gas flow rate of the nitrogen flow was 3 m / s; the polymerization time was 12 h; based on the weight of the hydroxylated low molecular weight polylactic acid, the amount of hexamethylene diisocyanate added was 0.05% of the hydroxylated low molecular weight polylactic acid, and the amount of SMA added was 50% of the hydroxylated low molecular weight polylactic acid.

[0067] Performance characterization: The measured right-angle tear strength of the polystyrene-maleic anhydride-lactide copolyester material was 116 KN / m, the elongation at break was 91%, the glass transition temperature was 138℃, the weight-average molecular weight of the hydroxyl-terminated low molecular weight polylactic acid was 7100, the weight-average molecular weight of the low molecular weight SMA was 4000, and the weight-average molecular weight of the polystyrene-maleic anhydride-lactide copolyester was 2.33 × 10⁻⁶. 5 .

[0068] Example 4

[0069] (1) Maleic anhydride and acetone solvent were added to a reaction vessel, along with dicumyl peroxide as the initiator. Simultaneously, styrene monomer was added dropwise to the reaction vessel. The reaction was carried out under constant temperature conditions with a nitrogen flow. After the reaction was complete, anhydrous ethanol was added as a precipitant. The mixture was then filtered and dried to obtain a low molecular weight SMA polymer. The constant temperature reaction was 110°C, and the reaction time was 6 hours. The flow rate of the nitrogen-protected gas was 3 m / s. Based on the weight of maleic anhydride, the amount of dicumyl peroxide as the initiator was 2% of the maleic anhydride, and the amount of styrene added was 250% of the maleic anhydride.

[0070] (2) Lactic acid oligomers were mixed with stannous octoate and prepolymerized at low temperature under nitrogen flow and negative pressure to obtain low molecular weight polylactic acid. 1,4-Butanediol was added to end-hydroxylate the low molecular weight polylactic acid to obtain hydroxylated low molecular weight polylactic acid. The polymerization temperature was 140℃ and the reaction pressure was 300 kPa; the gas flow rate of the nitrogen flow was 3 m / s, the polymerization reaction time was 8 h, and the end-hydroxylation reaction time was 5 h; based on the weight of the lactic acid oligomers, the amount of stannous octoate added was 0.4% of the lactic acid oligomers; the amount of 1,4-butanediol added was 0.06% of the lactic acid oligomers.

[0071] (3) The hydroxylated low molecular weight polylactic acid obtained in step (2) was heated and melted. The low molecular weight SMA polymer obtained in step (1) was added to the melt. Hexamethylene diisocyanate was continuously added dropwise during the reaction. Polystyrene-maleic anhydride-lactide copolyester (PLSMA) was prepared by high-temperature polymerization under nitrogen flow and negative pressure conditions. The polymerization temperature was 165℃; the reaction pressure was 300 kPa; the gas flow rate of the nitrogen flow was 3 m / s; the polymerization reaction time was 12 h; based on the weight of the hydroxylated low molecular weight polylactic acid, the amount of hexamethylene diisocyanate added was 0.06% of the hydroxylated low molecular weight polylactic acid, and the amount of SMA added was 55% of the hydroxylated low molecular weight polylactic acid.

[0072] Performance characterization: The right-angle tear strength of the polystyrene-maleic anhydride-lactide copolyester material was measured to be 120 kN / m, the elongation at break was 101%, the glass transition temperature was 145℃, the weight-average molecular weight of the hydroxyl-terminated low molecular weight polylactic acid was 8000, the weight-average molecular weight of the low molecular weight SMA was 5200, and the weight-average molecular weight of the polystyrene-maleic anhydride-lactide copolyester was 2.51 × 10⁻⁶. 5 .

[0073] Example 5

[0074] (1) Maleic anhydride and acetone solvent were added to a reaction vessel, along with dicumyl peroxide as the initiator. Simultaneously, styrene monomer was added dropwise to the reaction vessel. The reaction was carried out under constant temperature conditions with a nitrogen flow. After the reaction was complete, anhydrous ethanol was added as a precipitant. The mixture was then filtered and dried to obtain a low molecular weight SMA polymer. The constant temperature reaction was 120°C, and the reaction time was 6 hours. The flow rate of the nitrogen-protected gas was 3 m / s. Based on the weight of maleic anhydride, the amount of dicumyl peroxide as the initiator was 2% of the maleic anhydride, and the amount of styrene added was 250% of the maleic anhydride.

[0075] (2) Lactic acid oligomers were mixed with stannous octoate and prepolymerized at low temperature under nitrogen flow and negative pressure to obtain low molecular weight polylactic acid. 1,4-Butanediol was added to end-hydroxylate the low molecular weight polylactic acid to obtain hydroxylated low molecular weight polylactic acid. The polymerization temperature was 140℃ and the reaction pressure was 300 kPa; the gas flow rate of the nitrogen flow was 3 m / s, the polymerization reaction time was 8 h, and the end-hydroxylation reaction time was 6 h; based on the weight of the lactic acid oligomers, the amount of stannous octoate added was 0.5% of the lactic acid oligomers; the amount of 1,4-butanediol added was 0.08% of the lactic acid oligomers.

[0076] (3) The hydroxylated low molecular weight polylactic acid obtained in step (2) was heated and melted. The low molecular weight SMA polymer obtained in step (1) was added to the melt. Hexamethylene diisocyanate was continuously added dropwise during the reaction. Polystyrene-maleic anhydride-lactide copolyester (PLSMA) was prepared by high-temperature polymerization under nitrogen flow and negative pressure conditions. The polymerization temperature was 170℃; the reaction pressure was 300 kPa; the gas flow rate of the nitrogen flow was 3 m / s; the polymerization reaction time was 16 h; based on the weight of the hydroxylated low molecular weight polylactic acid, the amount of hexamethylene diisocyanate added was 0.08% of the hydroxylated low molecular weight polylactic acid, and the amount of SMA added was 60% of the hydroxylated low molecular weight polylactic acid.

[0077] Performance characterization: The right-angle tear strength of the polystyrene-maleic anhydride-lactide copolyester material was measured to be 105 kN / m, the elongation at break was 83%, the glass transition temperature was 128℃, the weight-average molecular weight of the hydroxyl-terminated low molecular weight polylactic acid was 10600, the weight-average molecular weight of the low molecular weight SMA was 8100, and the weight-average molecular weight of the polystyrene-maleic anhydride-lactide copolyester was 2.05 × 10⁻⁶. 5 .

Claims

1. A polystyrene-maleic anhydride-lactide copolymer, characterized in that, It has the structure of general formula I: Ⅰ R1 and R2 are independently selected from substituted or unsubstituted alkyl groups of C1-C10, substituted or unsubstituted alicyclic groups or aryl groups of C6-C30; x is an integer between 5 and 50, y is an integer between 5 and 50, n is an integer between 10 and 120, and p is an integer between 20 and 260. The polystyrene-maleic anhydride-lactide copolymer has a weight-average molecular weight of 1.0 × 10⁻⁶. 5 -3.5×10 5 Its right-angle tear strength is not less than 90kN / m, its elongation at break is not less than 75%, and its glass transition temperature is 120-150℃.

2. The polystyrene-maleic anhydride-lactide copolymer according to claim 1, characterized in that, R1 and R2 are independently selected from substituted or unsubstituted alkyl groups of C2-C6, alicyclic groups or aryl groups of C6-C15; x is an integer from 15 to 25; y is an integer from 15 to 25; n is an integer from 40 to 100; and p is an integer from 60 to 120.

3. The polystyrene-maleic anhydride-lactide copolymer according to claim 2, characterized in that, R1 is selected from -CH2CH2CH2CH2-, -CH2CH2CH2CH2CH2-, -CH2CH2CH2CH2CH2CH2-, , , , , , , , , One of the groups.

4. The polystyrene-maleic anhydride-lactide copolymer according to claim 2, characterized in that, R2 is selected from -CH2CH2-, -CH2CH2CH2-, -CH(CH3)CH2-, CH2CH2CH2CH2- and One of the groups.

5. The polystyrene-maleic anhydride-lactide copolymer according to claim 1, characterized in that, Its weight-average molecular weight is 2.0 × 10⁻⁶. 5 -3.0×10 5 .

6. The polystyrene-maleic anhydride-lactide copolymer according to claim 1, characterized in that, Its right-angle tear strength is not less than 100-120kN / m; its elongation at break is 80-105%.

7. The method for preparing the polystyrene-maleic anhydride-lactide copolymer according to claim 1, comprising the following: (1) Maleic anhydride and styrene are polymerized to obtain a low molecular weight SMA polymer with a molecular weight of 1,000-10,000. (2) Low molecular weight polylactic acid is obtained by prepolymerizing lactic acid or lactic acid oligomers at low temperature in the presence of a catalyst, and then by adding diol to end-hydroxylate the low molecular weight polylactic acid to obtain end-hydroxylated low molecular weight polylactic acid with a molecular weight of 2000-20000. (3) The hydroxylated low molecular weight polylactic acid obtained in step (2) is heated and melted, and the low molecular weight SMA polymer obtained in step (1) is added to the melt. During the reaction, diisocyanate is continuously added dropwise, and the polystyrene-maleic anhydride-lactide copolymer is prepared by high-temperature polymerization.

8. The preparation method according to claim 7, characterized in that, In step (1), maleic anhydride and styrene are polymerized in the presence of an initiator selected from at least one of dicumyl peroxide or azobisisobutyronitrile. The amount of initiator added is 0.1-5% of maleic anhydride by weight, and the amount of styrene added is 100-300% of maleic anhydride.

9. The preparation method according to claim 7, characterized in that, The specific process of step (1) is as follows: maleic anhydride is dissolved in an organic solvent, and an initiator is added and heated at a constant temperature. Styrene monomer is added dropwise to the reaction solution, and the reaction is continued to be heated. After the reaction is completed, a precipitant is added, and after filtration and drying, a low molecular weight SMA polymer is obtained. The organic solvent is selected from at least one of butyl acetate, n-heptane and acetone, and the precipitant is selected from at least one of diethyl ether, anhydrous methanol and anhydrous ethanol.

10. The preparation method according to claim 7, characterized in that, Step (1) is a constant temperature reaction under an inert atmosphere, with a reaction temperature of 50-150℃ and a reaction time of 1-8h.

11. The preparation method according to claim 7, characterized in that, The catalyst mentioned in step (2) is selected from one or more of stannous octoate, zinc lactate, trialkylaluminum, triisobutylaluminum and stannous chloride, and the amount of catalyst added is 0.01-1% of lactic acid or lactic acid oligomer by weight.

12. The preparation method according to claim 7, characterized in that, The diol mentioned in step (2) is selected from one or more of ethylene glycol, 1,3-propanediol, 1,2-propanediol, bisphenol A or 1,4-butanediol, and the amount of diol added is 0.01-0.1% by weight of lactic acid or lactic acid oligomer.

13. The preparation method according to claim 7, characterized in that, Step (2) is low-temperature polymerization under an inert atmosphere. The polymerization temperature is 100-150℃, the reaction pressure is 100-1000kpa, and the polymerization time is 2-15h.

14. The preparation method according to claim 7, characterized in that, The reaction time for the terminal hydroxylation in step (2) is 1-8 hours.

15. The preparation method according to claim 7, characterized in that, The diisocyanate mentioned in step (3) is one or more of toluene diisocyanate, diphenylmethane diisocyanate or hexamethylene diisocyanate, and the amount of diisocyanate added is 0.01-0.1% of the hydroxylated low molecular weight polylactic acid by weight.

16. The preparation method according to claim 7, characterized in that, In step (3), the amount of SMA added is 20-80% of the hydroxylated low molecular weight polylactic acid.

17. The preparation method according to claim 7, characterized in that, Step (3) is polymerization under an inert atmosphere. The polymerization temperature is 100-200℃, the reaction pressure is 100-1000kpa, and the polymerization time is 4-20h.

18. The application of the polystyrene-maleic anhydride-lactide copolymer of claim 1, wherein the polystyrene-maleic anhydride-lactide copolymer is used in the fields of automotive interiors, coatings, textiles, printing and dyeing, and medical products.

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