Carbon dioxide-based terpolymer as well as preparation method and application thereof

Abstract

The invention provides a carbon dioxide-based terpolymer and a preparation method and application thereof.The carbon dioxide-based terpolymer comprises a propylene carbonate structural unit and a cyclohexene carbonate structural unit, and an epoxy monomer and part of solvent in raw materials are preheated before polymerization reaction; the obtained carbon dioxide-based terpolymer has two glass transition temperatures, the relatively low glass transition temperature Tg1 is greater than or equal to 35 DEG C, the relatively high glass transition temperature Tg2 is less than or equal to 80 DEG C, and the difference between the two glass transition temperatures is limited to be 10-45 DEG C; the specific glass transition temperature can reasonably speculate that the internal structure distribution of the carbon dioxide-based terpolymer provided by the invention is between complete random distribution and complete block distribution, so that the carbon dioxide-based terpolymer has excellent mechanical properties and light transmittance.

Description

Technical Field

[0001] The invention belongs to the technical field of polymers, and in particular relates to a carbon dioxide-based terpolymer and a preparation method thereof. Background Art

[0002] Carbon dioxide (CO2) is a major greenhouse gas and also a cheap and clean carbon-oxygen resource. The copolymers prepared using carbon dioxide and epoxy compounds have good mechanical properties and barrier properties, and are also biodegradable. Therefore, the development of carbon dioxide-based copolymers that meet market demand can not only help reduce carbon emissions, but also reduce "white pollution", which has important economic and social significance.

[0003] Carbon dioxide, propylene oxide (PO), and cyclohexene oxide (CHO) ternary copolymerization can obtain a carbon dioxide-based copolymer with excellent performance. For example, CN114479043A discloses a carbon dioxide-based random copolymer synthesized by a solution one-pot method using carbon dioxide, propylene oxide, and cyclohexene oxide as raw materials in the presence of a catalyst and a solvent. The tensile strength of the random copolymer is 43.3±0.4-55.8±0.8MPa, the elongation at break is 11.5±0.4-22.1±0.4%, and the light transmittance is 88.6-90.5%. Although the random copolymer obtained by the invention has excellent mechanical properties, the transparency still needs to be improved.

[0004] For another example, CN101906208A discloses a method for synthesizing a carbon dioxide-based block copolymer by a step-by-step method using a supported zinc carboxylate catalyst, carbon dioxide, propylene oxide and cyclohexane oxide as raw materials. The preparation process requires step-by-step feeding and step-by-step reaction, and prepares a PPC-PCHC diblock copolymer and a PCHC-PPC-PCHC triblock copolymer, respectively. The tensile strength of the PPC-PCHC diblock copolymer is 36 to 43 MPa, and the tensile strength of the PCHC-PPC-PCHC triblock copolymer is 46 to 53 MPa. However, the method and process provided by the invention is relatively complicated, and the transparency of the obtained diblock copolymer or triblock copolymer also needs to be improved.

[0005] In summary, the random copolymers or block copolymers obtained by copolymerization of propylene oxide, cyclohexene oxide and carbon dioxide in the prior art including the above two inventions all have the problem of poor transparency, which seriously affects the promotion and application of carbon dioxide-based copolymers in light-transmitting products.

[0006] Therefore, in view of the above problems, it is urgent to develop a carbon dioxide-based terpolymer with excellent light transmittance. Summary of the invention

[0007] In view of the deficiencies in the prior art, the object of the present invention is to provide a carbon dioxide-based terpolymer and a preparation method and application thereof. The carbon dioxide-based terpolymer has high light transmittance and low haze, excellent light transmittance, and also has excellent mechanical properties.

[0008] The inventors of the present invention creatively discovered during the research process that the transparency of the carbon dioxide-based terpolymer obtained by copolymerization of propylene oxide, cyclohexane oxide and carbon dioxide is related to the distribution of cyclohexene carbonate (CHC) structural units and propylene carbonate (PC) structural units contained therein, and that the intrinsic structural distribution of the existing carbon dioxide-based terpolymers is either completely random distribution or completely block distribution, and both cannot obtain ideal transparency.

[0009] Since the distribution of CHC and PC structural units contained in the carbon dioxide-based terpolymer can be characterized by the glass transition temperature (Tg), it is found that: the carbon dioxide-based terpolymer with completely random distribution has only one Tg, and the CHC and PC structural units are statistically completely randomly distributed, indicating that the PCHC block and the PPC block are completely thermodynamically compatible (the transmittance of the obtained carbon dioxide-based terpolymer can reach about 90%); and the carbon dioxide-based terpolymer with completely block distribution has two Tgs, corresponding to the Tg of the PCHC block (about 100°C, which is specifically related to the ether segment content) and the Tg of the PPC block (about 29°C, which is specifically related to the ether segment content). At this time, since the main chain structure of the PCHC block contains a six-membered ring, the overall rigidity is very strong, and the main chain structure of the PPC block is a flexible segment, although both are polycarbonate structures, the compatibility of PCHC and PPC is not good, resulting in the poor transparency of the carbon dioxide-based terpolymer with completely block distribution.

[0010] Based on the above content, the inventors of the present invention reasonably speculate that: in order to improve the transparency of the carbon dioxide-based terpolymer, it is very important to change its internal distribution, and design a carbon dioxide-based terpolymer with an internal distribution between completely random distribution and completely block distribution, that is, the internal structure distribution of the carbon dioxide-based terpolymer is mainly composed of PCHC blocks containing CHC structures, supplemented by a small amount of PC structure randomly embedded in the PCHC blocks, and at the same time, it is mainly composed of PPC blocks containing PC structures, supplemented by a small amount of CHC structure randomly embedded in the PPC blocks, and the linking part of the PCHC block and the PPC block is a segment composed of CHC structure and PC structure randomly, forming a structure that is neither completely random nor completely block as a whole, which can effectively solve the above problems and significantly improve the transparency of the carbon dioxide-based terpolymer;

[0011] Furthermore, as mentioned above, since the Tg of the carbon dioxide-based terpolymer is affected by the distribution state of the PC structural units and CHC structural units contained in the molecular chain of the carbon dioxide-based terpolymer, the distribution of the CHC and PC structural units contained in the obtained carbon dioxide-based terpolymer can be characterized by Tg, and it is known from research that the more CHC structural units there are in the PPC block, the higher the Tg1, and vice versa; the more PC structural units there are in the PCHC block, the lower the Tg2, and vice versa; conversely, the higher the Tg1, the more CHC structural units there are in the PPC block, and at this time, the PPC block and the PCHC block are more distributed. The lower the Tg1, the fewer CHC structural units in the PPC block, and it tends to form a relatively more significant PPC block structure. At this time, the compatibility with the PCHC block in the molecular chain deteriorates, and the transparency decreases. Similarly, the lower the Tg2, the more PC structural units in the PCHC block, and at this time, the PCHC block and the PPC block structure are more similar, the compatibility becomes better, and the transparency becomes higher; the higher the Tg2, the fewer PC structural units in the PCHC block, and at this time, the PCHC block tends to form a relatively more significant PCHC block structure, and the compatibility with the PPC block deteriorates, and the transparency decreases.

[0012] Based on the above content, the present invention provides the following technical solutions:

[0013] In a first aspect, the present invention provides a carbon dioxide-based terpolymer, wherein the carbon dioxide-based terpolymer comprises a propylene carbonate (PC) structural unit and a cyclohexene carbonate (CHC) structural unit;

[0014] The propylene carbonate structural unit has a structure shown in the following formula I or formula II:

[0015]

[0016] The cyclohexenyl carbonate structural unit has a structure as shown in the following formula III:

[0017]

[0018] The carbon dioxide-based terpolymer has two glass transition temperatures, a relatively low glass transition temperature is recorded as Tg1, and a relatively high glass transition temperature is recorded as Tg2, Tg1≥35°C (for example, 35°C, 36°C, 37°C, 38°C, 39°C, 40°C, 41°C, 42°C, 43°C, 45°C, 46°C, 47°C, 48°C, 49°C or 50°C, etc.), Tg2≤80°C (for example, 80°C, 79°C, 78°C, 77°C, 76°C, 75°C, 74°C, 73°C, 72°C, 71°C, 70°C, 68°C, 66°C, 64°C, 62°C or 60°C, etc.), and the difference between Tg2 and Tg1 is 10-45°C (for example, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C or 45°C, etc.). First, it can be seen that the carbon dioxide-based terpolymer provided by the present invention also contains two different Tgs, but is different from the fully block carbon dioxide-based terpolymer in that, compared with the two Tgs of the fully block carbon dioxide-based terpolymer, the relatively low Tg1 of the two Tgs of the carbon dioxide-based terpolymer provided by the present invention has a higher temperature, and the relatively high Tg2 has a lower temperature, thereby making the temperature difference between the two smaller.

[0019] Secondly, on the one hand, the present invention limits Tg1≥35°C and Tg2≤80°C, because if Tg1 is too small, its limit value is closer to the Tg of pure PPC, and the PPC block formed in the copolymer is more significant and ordered. Similarly, if Tg2 is too large, its limit value is closer to the Tg of pure PCHC, and the PCHC block formed in the copolymer is more significant and ordered. On the other hand, the present invention also limits Tg1 and Tg2 and when the difference between Tg2 and Tg1 is 10-45°C, if the difference between the two is too small, it is more inclined to random copolymerization, indicating that the blocks composed of PC structural units and CHC structural units in the structure are not significant, and the improvement of transparency is not obvious; if the difference between the two is too large, it indicates that the blocks composed of PC structural units and CHC structural units are too significant and ordered, resulting in a significant difference in the thermodynamic compatibility of the two types of blocks, and this relatively significant difference constitutes a significant decrease in transparency.

[0020] Finally, it is verified that the carbon dioxide-based terpolymer provided by the present invention has higher light transmittance and lower haze than the existing carbon dioxide-based terpolymers with completely random distribution and completely block distribution, and has better light transmittance performance and excellent mechanical properties. In order to further improve the mechanical properties and transparency of the obtained carbon dioxide-based terpolymer, the following preferred limitations are made:

[0021] Preferably, the weight average molecular weight of the carbon dioxide-based terpolymer is ≥ 100,000, such as 100,000, 110,000, 120,000, 130,000, 140,000, 150,000, 200,000, 250,000, 300,000, 350,000, 400,000, 450,000 or 500,000. If the weight average molecular weight of the carbon dioxide-based terpolymer is too small, it is easy to cause its viscosity to be too low, thereby resulting in insufficient mechanical properties.

[0022] Preferably, the molar ratio of the propylene carbonate structural unit to the cyclohexene carbonate structural unit is (0.25-4):1, such as 0.25:1, 0.5:1, 1:1, 2.5:1, 3:1 or 4:1, etc. On the one hand, if the molar ratio of the PPC structural unit is too high, Tg1 is close to the Tg value of pure PPC, the CHC structural unit is too few to form a block structure, Tg2 does not exist, and the obtained carbon dioxide-based terpolymer only shows one Tg value, and the structure is close to that of pure PPC, and the mechanical strength is poor; on the other hand, if the CHC structural unit ratio is too high, Tg2 is close to the Tg value of pure PCHC, the PPC structural unit is too few to form a block structure, Tg1 does not exist, and the obtained carbon dioxide-based terpolymer also only shows one Tg value, and the structure is close to that of pure PCHC, and the mechanical strength is high, but the toughness is poor and the elongation at break is low.

[0023] In a second aspect, the present invention provides a method for preparing a carbon dioxide-based terpolymer, the preparation method comprising the following steps:

[0024] (1) preparing materials: preparing epoxy monomer, solvent, catalyst and carbon dioxide as raw materials; the epoxy monomer includes propylene oxide and cyclohexene oxide;

[0025] (2) Feeding and preheating: Carbon dioxide is charged into the reactor, and part of the solvent, propylene oxide and cyclohexene oxide are added in sequence, the temperature of the raw materials in the reactor is controlled at 35-60° C., and the remaining part of the solvent carrying the catalyst is added into the reactor for mixing;

[0026] (3) Copolymerization: Filling the reactor with carbon dioxide again, and raising the temperature to allow the materials in the reactor to react, thereby obtaining the carbon dioxide-based terpolymer.

[0027] The preparation method of the carbon dioxide-based terpolymer provided by the present invention is a solution one-pot process, which has the advantages of simple preparation process, low reaction temperature and low energy consumption. By preheating part of the raw materials, a carbon dioxide-based terpolymer with a "micro-block" structure that meets the requirements and has an intrinsic distribution between completely random distribution and completely block distribution is successfully prepared.

[0028] Specifically, the inventors of the present invention found during the research process that: if the raw materials are not preheated but directly added to the reactor, and then the temperature is raised from room temperature to the reaction temperature for polymerization, the obtained carbon dioxide-based terpolymer is a random copolymer with only one Tg, while the obtained carbon dioxide-based terpolymer can have two Tgs by preheating the epoxy monomer and part of the solvent and then adding the catalyst for polymerization, but it is not a complete block structure (different from the two Tgs of the complete block structure), and it is further speculated that the preheating treatment can cause CHC and PC to produce certain microblocks; specifically, before the catalyst is added to the reactor, the epoxy monomer and part of the solvent in the raw materials are preferentially heated to 35-60°C. At 35-60°C, the reaction rates of the ring-opening alternating copolymerization of CHO and PO in the epoxy monomer with CO2 are significantly different. Generally, the reaction rate of CHO is faster, and molecular chains with more CHC structural units will be preferentially produced. As the reaction proceeds, the CHO concentration decreases, and the formation of molecular chains with more PC structural units will dominate. As the reaction continues, a certain amount of ternary random copolymer structure will be generated in the system, and finally the carbon dioxide-based ternary copolymer containing specific Tg1 and Tg2 and having a specific "micro-block" structure as described in the present invention will be formed. At the same time, if the preheating temperature is greater than 60°C, it is easy to cause the difference between the two Tgs to be too large, and even a random copolymer product with a single Tg is obtained, so that the transparency of the obtained carbon dioxide-based ternary copolymer is reduced; if no preheating is performed, after the feeding is completed, the time required for heating to the predetermined reaction temperature is usually 2 to 3 hours. In this process, although there is still a problem of reaction rate difference, this reaction rate difference is smaller when the temperature is low. The reactions are carried out simultaneously during the heating process. In this process, a large amount of oligomers with a ternary random copolymer structure will be obtained at the initial stage of the reaction. After the temperature is raised to a suitable reaction temperature, the oligomers of the ternary random polymer generated during the heating process will adjust the overall polymer structure by chain transfer, and no micro-block structure will be obtained, thereby forming a carbon dioxide-based ternary copolymer with a completely random structure.

[0029] In the present invention, the amount of the solvent in the raw material is not particularly limited, and can be selected according to the actual situation; in general, if the amount of the solvent is too low, the concentration of the epoxy monomer will be too high, resulting in a too fast reaction speed and difficulty in control, and prone to over-temperature and over-pressure implosion, while if the amount of the solvent is too high, the concentration of the epoxy monomer will be too low, resulting in a too slow reaction and reduced production efficiency. Therefore, in order to make the reaction proceed more smoothly, it is preferred to limit the volume ratio of the epoxy monomer to the solvent in step (1) to 1: (1 to 4), such as 1: 1, 1: 1.5, 1: 2, 1: 2.5, 1: 3, 1: 3.5 or 1: 4, etc.

[0030] Similarly, in the present invention, there is no particular limitation on the specific type of the solvent in the raw material. Those skilled in the art can select a conventional solvent suitable for the copolymerization of carbon dioxide and epoxy monomer based on their own requirements, including but not limited to any one or more combinations of tetrahydrofuran, dioxolane, dioxane, chloroalkanes, acetone, methyl ethyl ketone or propylene carbonate.

[0031] Preferably, the mass ratio of propylene oxide to cyclohexene oxide in step (1) is (13-70):(87-30), such as 13:87, 15:85, 20:80, 25:75, 30:70, 35:65, 40:60, 45:55, 60:40, 65:35 or 70:30, etc. If the mass ratio of propylene oxide to cyclohexene oxide is too large or too small, one side will have too little monomer, resulting in failure to achieve the desired block effect, which is manifested as Tg characteristics failing to reach the target value, and the transparency of the obtained carbon dioxide-based terpolymer decreases.

[0032] In the present invention, there is no special requirement for the amount of catalyst in the raw material. Generally, too much catalyst will cause too fast reaction and easy explosion, while too little catalyst will cause too slow reaction speed and too low production efficiency. Therefore, in order to make the reaction proceed more smoothly, preferably, the mass of the catalyst is 0.005-1.8%, such as 0.005%, 0.05%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6% or 1.8%, etc., based on the mass of the epoxy monomer in step (1) as 100%.

[0033] Preferably, the catalyst comprises a double metal cyanide catalyst and / or a modified double metal cyanide catalyst.

[0034] In the present invention, the double metal cyanide catalyst refers to a type of zinc-cobalt double metal cyanide catalyst, and the general chemical formula can be described as (Zn) a [Co(CN) b ] c Cl d (tBA) e (OH) f (H2O) g , wherein tBA is tert-butyl alcohol, a-g are all positive numbers, and 2a+3c=b×c+d+f, a:e=0.1:10, a:g=0.01-5. The modified double metal cyanide catalyst refers to the basic structure of the aforementioned double metal cyanide catalyst, which is further modified by using organic ligands such as small molecule alcohols, ethers, acids or polymers. The general chemical formula can be described as (Zn) a [Co(CN) b ] c Cld (L) e (tBA) f (OH) g (H2O) h , where tBA is tert-butyl alcohol, a~h are all positive numbers, 2a+3c=b×c+d+g, a:(e+f)=0.05~10, a:h=0.01~5, and L represents an organic ligand.

[0035] Furthermore, the inventors creatively discovered that compared with the unmodified double metal cyanide catalyst, the transmittance of the carbon dioxide-based terpolymer catalyzed by the modified double metal cyanide catalyst modified with the organic ligand is significantly improved. It is speculated that this may be because the double metal cyanide catalyst modified with the organic ligand has a higher compatibility with the organic matrix, thereby minimizing the effect of the catalyst itself on the haze of the polymer.

[0036] Preferably, the mass percentage of the total water content in the epoxy monomer, solvent and catalyst in step (1) is ≤200ppm, such as 200ppm, 190ppm, 180ppm, 170ppm, 160ppm, 150ppm, 140ppm, 130ppm, 120ppm, 100ppm, 90ppm, 80ppm, 70ppm, 60ppm, 50ppm, 40ppm, 30ppm, 20ppm or 10ppm, etc., more preferably ≤100ppm. If the total water content in the epoxy monomer, solvent and catalyst is too high, the reaction will be very slow or even impossible to proceed, so it is necessary to control the water content. In actual operation, the epoxy monomer and solvent can be dried before feeding, and since the amount of catalyst added is very small, it is usually not necessary to dry it.

[0037] Similarly, since the dew point of carbon dioxide corresponds to its moisture content, the dew point temperature of the carbon dioxide in step (1) is preferably ≤ -40°C (for example, -41°C, -42°C, -43°C, -44°C, -45°C, -46°C, -47°C, -48°C, -49°C, -50°C, -60°C, -70°C, -80°C or -90°C, etc.), and is further preferably ≤ -50°C, so that the moisture content of all raw materials meets the requirements.

[0038] In the present invention, there is no special restriction on the amount of the partial solvent in step (2), as long as it can satisfy the sufficient dispersion of the epoxy monomer. Exemplarily, the mass of the partial solvent in step (2) is 40-60% of the mass of all solvents, for example, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58% or 60%, etc.

[0039] In the present invention, the heating method of step (2) is not particularly limited. The epoxy monomer and part of the solvent may be preheated in a heat exchanger and then added to the reactor and mixed with the catalyst. Alternatively, the epoxy monomer and part of the solvent may be directly added to the reactor for preheating and then added with the catalyst for mixing. Alternatively, the epoxy monomer and part of the solvent may be preheated by corresponding devices before and after being added to the reactor and then mixed with the catalyst. However, no matter which preheating method is used, it is necessary to ensure that the temperature of the epoxy monomer and part of the solvent after preheating and after being added to the reactor is maintained at 35-60°C.

[0040] Preferably, after the carbon dioxide is charged into the reactor in step (2), the pressure in the reactor is ≤6MPa, such as 2MPa, 3MPa, 3.5MPa, 4MPa, 4.5MPa, 5MPa, 5.5MPa or 6MPa, and more preferably 1-6MPa. In principle, the carbon dioxide may not be charged into the step (2), but in industry, carbon dioxide is generally charged into the reactor to make the pressure in the reactor reach 1-2MPa in consideration of economic efficiency.

[0041] Preferably, in step (3), the pressure in the reactor is 3-7 MPa after the carbon dioxide is introduced into the reactor again, such as 3 MPa, 3.5 MPa, 4 MPa, 4.5 MPa, 5 MPa, 5.5 MPa, 6 MPa, 6.5 MPa or 7 MPa. If the pressure in the reactor meets the requirements at this time, carbon dioxide may not be added. However, if the amount of carbon dioxide added in this step is too small, the carbon dioxide-based terpolymer of the target structure cannot be obtained. If the amount of carbon dioxide added in this step is too large, the subsequent reaction pressure will be too high, and the safety will be reduced.

[0042] Preferably, the temperature of the reaction in step (3) is 50-60°C (e.g., 50°C, 52°C, 54°C, 56°C, 57°C or 60°C, etc.), and the pressure is 3-7MPa (e.g., 3MPa, 3.5MPa, 4MPa, 4.5MPa, 5MPa, 5.5MPa, 6MPa, 6.5MPa or 7MPa, etc.). If the reaction temperature is too low, the reaction may be very slow or even non-reactive, affecting production efficiency, while if the reaction temperature is too high, the ether content in the final product may be too high; similarly, if the reaction pressure is too low, the reaction may be very slow or even non-reactive, and the content of ether structure in the product may be too high, while if the reaction pressure is too high, safety may be reduced.

[0043] Preferably, the reaction in step (3) ends when the viscosity of the system no longer increases, and the required time is 8 to 16 hours, for example, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours or 16 hours.

[0044] Preferably, after the reaction in step (3) is completed, a step of devolatilizing to remove the solvent is also included.

[0045] In a third aspect, the present invention provides a use of the carbon dioxide-based terpolymer as described in the first aspect or the carbon dioxide-based terpolymer prepared by the preparation method as described in the second aspect in the preparation of a light-transmitting product.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] The carbon dioxide-based terpolymer provided by the present invention comprises a propylene carbonate structural unit and a cyclohexene carbonate structural unit. By preheating the epoxy monomer and part of the solvent in the raw material before the polymerization reaction, the obtained carbon dioxide-based terpolymer has two glass transition temperatures, wherein the relatively low glass transition temperature Tg1 is ≥35°C, and the relatively high glass transition temperature Tg2 is ≤80°C, and the difference between the two is 10-45°C. It can be reasonably inferred from the above glass transition temperatures that its internal structural distribution is between completely random distribution and completely block distribution, so that it can have both excellent mechanical properties and transparent properties, and can make the light transmittance ≥92%, the haze ≤0.5%, and at the same time ensure that the tensile strength is ≥31MPa and the elongation at break is ≥11%. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 The DSC spectrum of the carbon dioxide-based terpolymer provided in Example 1;

[0049] Figure 2 The DSC spectrum of the carbon dioxide-based terpolymer provided in Example 5;

[0050] Figure 3 The DSC spectrum of the block carbon dioxide-based terpolymer provided in Comparative Example 1;

[0051] Figure 4 The DSC spectrum of the random carbon dioxide-based terpolymer provided for Comparative Example 2;

[0052] Figure 5 The DSC spectrum of the carbon dioxide-based terpolymer provided for Comparative Example 6. DETAILED DESCRIPTION

[0053] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0054] Test method:

[0055] (1) Molar ratio of PO to CHO: The molar ratio of PO to CHO was measured using a Bruker AVANCE III 600 MHz NMR spectrometer with CDCl3 as solvent and TMS as internal standard. 1 The molar ratio of PO to CHO in the carbon dioxide-based terpolymer was determined by H-NMR test.

[0056] (2) Weight average molecular weight: The weight average molecular weight was measured by gel permeation chromatography (GPC), with dichloromethane as the mobile phase and polystyrene (PDI=1.02) as the standard.

[0057] (3) Moisture content: Tested according to the method provided in GB / T 6283-2008.

[0058] (4) Tg: The test was conducted in accordance with the method provided in the national standard GB / T 19466.2-2004 using a TA company's Q2000 differential scanning calorimeter. The thermal history was eliminated before the test and the heating rate was set to 10°C / min.

[0059] Preparation Example 1

[0060] A modified double metal cyanide catalyst is prepared by referring to the method disclosed in Example 1 of CN101440159A, the only difference being that the organic ligand is a mixture of tert-butyl alcohol and diethylene glycol dimethyl ether, and the molar ratio of the two is 1:1. The prepared modified double metal cyanide catalyst is named DMCC-1.

[0061] Preparation Example 2

[0062] A modified double metal cyanide catalyst is prepared by referring to the method disclosed in Example 2 of CN101928390A. The prepared modified double metal cyanide catalyst is named DMCC-2.

[0063] Preparation Example 3

[0064] A modified double metal cyanide catalyst is prepared by referring to the method disclosed in Example 1 of CN105820326A. The prepared modified double metal cyanide catalyst is named DMCC-3.

[0065] Preparation Example 4

[0066] A double metal cyanide catalyst is prepared by referring to the method disclosed in Comparative Example 1 in CN102432857A. The prepared double metal cyanide catalyst is named DMC-4.

[0067] Example 1

[0068] A method for preparing a carbon dioxide-based terpolymer comprises the following steps:

[0069] (1) Preparation of materials: Propylene oxide and cyclohexene oxide are selected as epoxy monomers, dichloromethane is used as a solvent, the modified double metal cyanide catalyst DMCC-1 provided in Preparation Example 1 is used as a catalyst, and carbon dioxide with a dew point of -60°C is selected; and propylene oxide, cyclohexene oxide and dichloromethane are dried to make the total mass percentage of water in the three to be 100 ppm;

[0070] Wherein, the volume ratio of epoxy monomer to dichloromethane is 1:3, the mass ratio of propylene oxide to cyclohexene oxide is 50:50, and based on the total mass of epoxy monomer as 100%, the mass of the modified double metal cyanide catalyst DMCC-1 provided in Preparation Example 1 is 1%;

[0071] (2) Feeding and preheating: 2m 3 Carbon dioxide was charged into the autoclave to raise the pressure in the autoclave to 4 MPa, and 50% (mass percentage of all dichloromethane) of dichloromethane, propylene oxide and cyclohexene oxide were added in sequence. 3 After the temperature of the autoclave was raised to 45°C, the modified double metal cyanide catalyst DMCC-1 provided in Preparation Example 1 was flushed into the autoclave using the remaining 50% of dichloromethane. 3 Mixing with other materials in a high-pressure reactor;

[0072] (3) Copolymerization: Again to 2m 3 Carbon dioxide is filled into the high-pressure reactor to raise the pressure in the reactor to 5.5 MPa, and the temperature in the reactor is raised to 55°C. The pressure in the reactor is maintained at 5.5 MPa and the temperature is maintained at 55°C for 10 hours until the viscosity of the material in the reactor no longer increases. After stopping the reaction, the material is unloaded into a buffer tank, and the material is passed through a twin-shaft self-cleaning reactor and a twin-screw extruder under high vacuum conditions to remove dichloromethane and perform underwater pelletizing to obtain the carbon dioxide-based terpolymer.

[0073] The molar ratio of PO to CHO in the carbon dioxide-based terpolymer prepared in Example 1 was 1.69:1, and the weight average molecular weight was 566,000. The carbon dioxide-based terpolymer provided in this example was further tested using a TA Q2000 differential scanning calorimeter at a test temperature range of -30 to 130°C, and the DSC spectrum of the carbon dioxide-based terpolymer provided in Example 1 was obtained as shown in FIG. Figure 1 As shown, from Figure 1 It can be seen that the carbon dioxide-based terpolymer prepared in Example 1 contains two Tgs, wherein Tg1 is 38°C and Tg2 is 62°C, and the difference between the two is 24°C.

[0074] Example 2

[0075] A method for preparing a carbon dioxide-based terpolymer comprises the following steps:

[0076] (1) Preparation of materials: propylene oxide and cyclohexene oxide are selected as epoxy monomers, dichloromethane is used as a solvent, the modified double metal cyanide catalyst DMCC-2 provided in Preparation Example 2 is used as a catalyst, and carbon dioxide with a dew point of -50°C is selected; and propylene oxide, cyclohexene oxide and dichloromethane are dried to make the total mass percentage of water in the three to be 200 ppm;

[0077] Wherein, the volume ratio of epoxy monomer to dichloromethane is 1:1.5, the mass ratio of propylene oxide to cyclohexene oxide is 15:85, and based on the total mass of epoxy monomer as 100%, the mass of the modified double metal cyanide catalyst DMCC-2 provided in Preparation Example 2 is 0.05%;

[0078] (2) Feeding and preheating: 2m 3 Carbon dioxide was charged into the autoclave to raise the pressure in the autoclave to 5.5 MPa, and 40% (in terms of the mass percentage of all dichloromethane) of dichloromethane, propylene oxide and cyclohexene oxide were added in sequence. 3 The autoclave is heated to 58° C., and then the modified double metal cyanide catalyst DMCC-2 provided in Preparation Example 2 is flushed into the autoclave using the remaining 60% of dichloromethane to mix with other materials;

[0079] (3) Copolymerization: Carbon dioxide is again charged into the autoclave to maintain the pressure in the autoclave at 5.5 MPa, and the temperature in the autoclave is maintained at 58° C. for 15 hours until the viscosity of the material in the autoclave no longer increases. After stopping the reaction, the material is unloaded into a buffer tank, and the material is passed through a twin-shaft self-cleaning reactor and a twin-screw extruder under high vacuum conditions to remove dichloromethane and perform underwater pelletizing to obtain the carbon dioxide-based terpolymer.

[0080] The molar ratio of PO and CHO in the carbon dioxide-based terpolymer prepared in Example 2 is 0.3:1, and the weight-average molecular weight is 451,000; and referring to the testing method of Example 1, the test shows that the carbon dioxide-based terpolymer prepared in Example 2 also contains two Tgs, wherein Tg1 is 36°C and Tg2 is 79°C, and the difference between the two is 43°C.

[0081] Example 3

[0082] A method for preparing a carbon dioxide-based terpolymer comprises the following steps:

[0083] (1) Preparation of materials: propylene oxide and cyclohexene oxide are selected as epoxy monomers, dichloromethane is used as a solvent, the modified double metal cyanide catalyst DMCC-3 provided in Preparation Example 3 is used as a catalyst, and carbon dioxide with a dew point of -40°C is selected; and propylene oxide, cyclohexene oxide and dichloromethane are dried to make the total mass percentage of water in the three materials 80 ppm;

[0084] Wherein, the volume ratio of epoxy monomer to dichloromethane is 1:4, the mass ratio of propylene oxide to cyclohexene oxide is 70:30, and based on the total mass of epoxy monomer as 100%, the mass of the modified double metal cyanide catalyst DMCC-3 provided in Preparation Example 3 is 1.8%;

[0085] (2) Feeding and preheating: Carbon dioxide was charged into the autoclave to raise the pressure in the autoclave to 2 MPa, and 60% (in terms of the mass percentage of all dichloromethane) of dichloromethane, propylene oxide and cyclohexene oxide were added in sequence. 3 After the temperature of the autoclave is raised and the temperature of the raw materials in the autoclave is controlled to reach 35° C., the modified double metal cyanide catalyst DMCC-3 provided in Preparation Example 3 is flushed into the autoclave using the remaining 40% of dichloromethane to mix with other materials;

[0086] (3) Copolymerization: Fill the autoclave with carbon dioxide again to raise the pressure inside the autoclave to 3 MPa, and raise the temperature inside the autoclave to 50° C., maintain the pressure inside the autoclave at 3 MPa and the temperature at 50° C. for 8 hours, until the viscosity of the material in the autoclave no longer increases. After stopping the reaction, unload the material into a buffer tank, pass the material through a twin-shaft self-cleaning reactor and a twin-screw extruder under high vacuum conditions to remove dichloromethane and perform underwater pelletizing to obtain the carbon dioxide-based terpolymer.

[0087] The molar ratio of PO and CHO in the carbon dioxide-based terpolymer prepared in Example 3 is 4:1, and the weight-average molecular weight is 624,000; and referring to the testing method of Example 1, the test shows that the carbon dioxide-based terpolymer prepared in Example 3 contains two Tgs, wherein Tg1 is 39°C and Tg2 is 49°C, and the difference between the two is 10°C.

[0088] Example 4

[0089] A method for preparing a carbon dioxide-based terpolymer comprises the following steps:

[0090] (1) Preparation of materials: Propylene oxide and cyclohexene oxide are selected as epoxy monomers, dichloromethane is used as a solvent, the modified double metal cyanide catalyst DMCC-2 provided in Preparation Example 2 is used as a catalyst, and carbon dioxide with a dew point of -60°C is selected; and propylene oxide, cyclohexene oxide and dichloromethane are dried so that the total mass percentage of water in the three is 100 ppm;

[0091] Wherein, the volume ratio of epoxy monomer to dichloromethane is 1:1, the mass ratio of propylene oxide to cyclohexene oxide is 13:87, and based on the total mass of epoxy monomer as 100%, the mass of the modified double metal cyanide catalyst DMCC-2 provided in Preparation Example 2 is 0.005%;

[0092] (2) Feeding and preheating: 2m 3 Carbon dioxide was charged into the autoclave to raise the pressure in the autoclave to 6 MPa, and 50% (mass percentage of all dichloromethane) of dichloromethane, propylene oxide and cyclohexene oxide were added in sequence. 3 After the temperature of the autoclave was raised to 60°C, the modified double metal cyanide catalyst DMCC-2 provided in Preparation Example 4 was flushed into the autoclave using the remaining 50% of dichloromethane. 3 Mixing with other materials in a high-pressure reactor;

[0093] (3) Copolymerization: Again to 2m 3 Carbon dioxide is filled into the high-pressure reactor to raise the pressure in the reactor to 7 MPa, and the temperature in the reactor is maintained at 60°C. The pressure in the reactor is maintained at 7 MPa and the temperature is maintained at 60°C for 16 hours until the viscosity of the material in the reactor no longer increases. After stopping the reaction, the material is unloaded into a buffer tank, and the material is passed through a double-shaft self-cleaning reactor and a twin-screw extruder under high vacuum conditions to remove dichloromethane and perform underwater pelletizing to obtain the carbon dioxide-based terpolymer.

[0094] The molar ratio of PO and CHO in the carbon dioxide-based terpolymer prepared in Example 4 is 0.25:1, and the weight-average molecular weight is 432,000; and referring to the test method provided in Example 1, the test shows that the carbon dioxide-based terpolymer prepared in Example 4 contains two Tgs, wherein Tg1 is 35°C and Tg2 is 80°C, and the difference between the two is 45°C.

[0095] Example 5

[0096] A method for preparing a carbon dioxide-based terpolymer, which differs from Example 1 in that the double metal cyanide catalyst DMC-4 provided in Preparation Example 4 is used to replace the modified double metal cyanide catalyst DMCC-1 provided in Preparation Example 1, and other substances, amounts and steps are the same as in Example 1.

[0097] The molar ratio of PO to CHO in the carbon dioxide-based terpolymer prepared in Example 5 is 1.69:1, and the weight average molecular weight is 540,000; and the carbon dioxide-based terpolymer provided in Example 5 is tested using a TA company Q2000 differential scanning calorimeter, and the test temperature range is -40 to 130°C, and the DSC spectrum of the carbon dioxide-based terpolymer provided in Example 5 is obtained as shown in Figure 2 As shown, from Figure 2 It can be seen that the carbon dioxide-based terpolymer prepared in Example 5 contains two Tgs, wherein Tg1 is 39°C and Tg2 is 57°C, and the difference between the two is 18°C.

[0098] Comparative Example 1

[0099] A method for preparing a block carbon dioxide-based terpolymer comprises the following steps:

[0100] Under normal temperature conditions, 3 In the high-pressure reactor, 400 kg of dichloromethane and 108 kg of propylene oxide were pumped into the reactor in sequence, and then 50 g of the modified double metal cyanide catalyst DMCC-1 provided in Preparation Example 1 was flushed into the reactor using 200 kg of dichloromethane, and then carbon dioxide was used to pressurize to 4 MPa, and then the temperature and pressure were controlled to 55° C. and 5.5 MPa for reaction for 12 hours. After the viscosity no longer increased, 150 kg of cyclohexene oxide and 550 kg of dichloromethane were pumped in, and the reaction was continued at 55° C. and 5.5 MPa for 12 hours until the viscosity no longer increased, and the material was unloaded into a buffer tank, and the dichloromethane was removed through a devolatilization section and underwater pelletization was performed to obtain the block carbon dioxide-based terpolymer.

[0101] The molar ratio of PO to CHO in the block carbon dioxide-based terpolymer provided in Comparative Example 1 is 1.69:1, and the weight average molecular weight is 687,000; and the block carbon dioxide-based terpolymer provided in Comparative Example 1 is tested using a TA company Q2000 differential scanning calorimeter, and the test temperature range is -50 to 130 ° C. The DSC spectrum of the block carbon dioxide-based terpolymer provided in Comparative Example 1 is as follows Figure 3 As shown, from Figure 3 It can be seen that the block carbon dioxide-based terpolymer provided in Comparative Example 1 contains two Tgs, wherein Tg1 is 29°C and Tg2 is 100°C, and the difference between the two is 71°C.

[0102] Comparative Example 2

[0103] A method for preparing a random carbon dioxide-based terpolymer comprises the following steps:

[0104] Under normal temperature conditions, 3Into the high-pressure reactor, 690 kg of dichloromethane, 150 kg of propylene oxide and 150 kg of cyclohexane oxide were pumped in sequence, and then 460 kg of dichloromethane was used to flush 50 g of the modified double metal cyanide catalyst DMCC-1 provided in Preparation Example 1 into the reactor, and then carbon dioxide was used to pressurize to 4.0 MPa, and then the temperature and pressure were controlled to 55 ° C and 5.5 MPa for 12 hours. The viscosity in the reactor no longer increased, and the material was unloaded into a buffer tank, and dichloromethane was removed through a devolatilization section and underwater pelletization was performed to obtain the random carbon dioxide-based terpolymer.

[0105] The molar ratio of PO to CHO in the random carbon dioxide-based terpolymer prepared in Comparative Example 2 is 1.69:1, and the weight average molecular weight is 649,000; and the carbon dioxide-based terpolymer provided in Comparative Example 2 is tested using a TA company Q2000 differential scanning calorimeter, and the test temperature range is -30 to 130 ° C. The DSC spectrum of the random carbon dioxide-based terpolymer provided in Comparative Example 2 is as follows Figure 4 As shown, from Figure 4 It can be seen that the random carbon dioxide-based terpolymer provided by Comparative Example 2 contains only one Tg, which is 62°C.

[0106] Comparative Example 3

[0107] A method for preparing a carbon dioxide-based terpolymer, which differs from Example 1 in that, in step (3) copolymerization, carbon dioxide is again charged into the high-pressure reactor to raise the pressure in the reactor to 2.5 MPa, and the pressure in the reactor is maintained at 2.5 MPa for reaction, and other substances, amounts and steps are the same as those in Example 1.

[0108] The molar ratio of PO and CHO in the carbon dioxide-based terpolymer prepared in Comparative Example 3 is 1.69:1, and the weight-average molecular weight is 573,000; and referring to the test method provided in Example 1, the test shows that the carbon dioxide-based terpolymer prepared in Comparative Example 3 contains two Tgs, wherein Tg1 is 31°C and Tg2 is 49°C, and the difference between the two is 18°C.

[0109] Comparative Example 4

[0110] A method for preparing a carbon dioxide-based terpolymer, which differs from Example 1 in that in the material preparation of step (1), the mass ratio of propylene oxide to cyclohexene oxide is 10:90, and other substances, amounts and steps are the same as those in Example 1.

[0111] The molar ratio of PO and CHO in the carbon dioxide-based terpolymer prepared in Comparative Example 4 is 0.19:1, and the weight-average molecular weight is 407,000; and referring to the test method provided in Example 1, the test shows that the carbon dioxide-based terpolymer prepared in Comparative Example 4 contains two Tgs, wherein Tg1 is 36°C and Tg2 is 86°C, and the difference between the two is 50°C.

[0112] Comparative Example 5

[0113] A method for preparing a carbon dioxide-based terpolymer, which differs from Example 1 in that the mass ratio of propylene oxide to cyclohexene oxide is 75:25, and other substances, amounts and steps are the same as those in Example 1.

[0114] The molar ratio of PO and CHO in the carbon dioxide-based terpolymer prepared in Comparative Example 5 is 5.07:1, and the weight-average molecular weight is 663,000; and referring to the test method provided in Example 1, the test shows that the carbon dioxide-based terpolymer prepared in Comparative Example 5 contains two Tgs, wherein Tg1 is 32°C and Tg2 is 51°C, and the difference between the two is 19°C.

[0115] Comparative Example 6

[0116] A method for preparing a carbon dioxide-based terpolymer comprises the following steps:

[0117] (1) Preparation of materials: propylene oxide and cyclohexene oxide are selected as epoxy monomers, dichloromethane is used as a solvent, the modified double metal cyanide catalyst DMCC-1 provided in Preparation Example 1 is used as a catalyst, and carbon dioxide with a dew point of -60°C is selected; and propylene oxide, cyclohexene oxide and dichloromethane are dried to make the mass percentage of water in the three materials 100 ppm in total;

[0118] Wherein, the volume ratio of epoxy monomer to dichloromethane is 1:3, the mass ratio of propylene oxide to cyclohexene oxide is 50:50, and based on the total mass of epoxy monomer as 100%, the mass of the modified double metal cyanide catalyst DMCC-1 provided in Preparation Example 1 is 1%;

[0119] (2) Feeding: 2m 3 Carbon dioxide was charged into the autoclave to raise the pressure in the autoclave to 4 MPa, and 50% (mass percentage of all dichloromethane) of dichloromethane, propylene oxide and cyclohexene oxide were added in sequence, and the modified double metal cyanide catalyst DMCC-1 provided in Preparation Example 1 was flushed into 2 m 3 Mixing with other materials in a high-pressure reactor;

[0120] (3) Copolymerization: Again to 2m 3Carbon dioxide is filled into the high-pressure reactor to raise the pressure in the reactor to 5.5 MPa, and the temperature in the reactor is raised to 55°C. The pressure in the reactor is maintained at 5.5 MPa and the temperature is maintained at 55°C for 10 hours until the viscosity of the material in the reactor no longer increases. After stopping the reaction, the material is unloaded into a buffer tank, and the material is passed through a twin-shaft self-cleaning reactor and a twin-screw extruder under high vacuum conditions to remove dichloromethane and perform underwater pelletizing to obtain the carbon dioxide-based terpolymer.

[0121] The molar ratio of PO to CHO in the carbon dioxide-based terpolymer prepared in Comparative Example 6 is 1.69:1, and the weight average molecular weight is 583,000; and the carbon dioxide-based terpolymer provided in Comparative Example 6 is tested using a TA company Q2000 differential scanning calorimeter, and the test temperature range is -50 to 110 ° C. The DSC spectrum of the carbon dioxide-based terpolymer provided in Comparative Example 6 is as follows Figure 5 As shown, from Figure 5 It can be seen that the carbon dioxide-based terpolymer provided in Comparative Example 6 contains only one Tg of 64°C.

[0122] Comparative Example 7

[0123] A method for preparing a carbon dioxide-based terpolymer, which differs from Example 1 in that, during the feeding and preheating of step (2), 2m 3 The temperature of the autoclave was raised to 32° C. The other substances, amounts and steps were the same as those in Example 1.

[0124] The molar ratio of PO and CHO in the carbon dioxide-based terpolymer prepared in Comparative Example 7 is 1.69:1, the weight average molecular weight is 580,000, and referring to the test method provided in Example 1, the test shows that the carbon dioxide-based terpolymer prepared in Comparative Example 7 contains only one Tg, which is 64°C.

[0125] Comparative Example 8

[0126] A method for preparing a carbon dioxide-based terpolymer, which differs from Example 1 in that, during the feeding and preheating of step (2), 2m 3 The temperature of the autoclave was raised to 65° C. The other substances, amounts and steps were the same as those in Example 1.

[0127] The molar ratio of PO and CHO in the random carbon dioxide-based terpolymer prepared in Comparative Example 8 is 1.69:1, the weight average molecular weight is 574,000, and referring to the test method provided in Example 1, the test shows that the carbon dioxide-based terpolymer prepared in Comparative Example 8 contains only one Tg, which is 63°C.

[0128] Performance Testing:

[0129] (1) Tensile strength and elongation at break: The test was conducted in accordance with GB / T1040.1-2018 “Determination of tensile properties of plastics Part 1: General” and GB / T1040.2-2022 “Determination of tensile properties of plastics Part 2: Test conditions for molded and extruded plastics”, with a tensile rate of 50 mm / min.

[0130] (2) Light transmittance and haze: The test was conducted in accordance with GB / T 2410-2008 “Determination of light transmittance and haze of transparent plastics”, with a sample thickness of 30 μm.

[0131] The carbon dioxide-based terpolymers provided in Examples 1 to 5 and Comparative Examples 1 to 8 were tested according to the above test method. The test results are shown in Table 1:

[0132] Table 1

[0133]

[0134]

[0135] From the data in Table 1, we can see that:

[0136] (1) The carbon dioxide-based terpolymers provided in Examples 1 to 5 have both excellent mechanical properties and light transmittance. In particular, the carbon dioxide-based terpolymers provided in Examples 1 to 4 have a light transmittance of 92.9 to 93.5% and a haze of 0%, achieving the best light transmittance. However, the double metal cyanide catalyst used in Example 5 may have an adverse effect on the light transmittance, which leads to a slight decrease in the light transmittance of the obtained carbon dioxide-based terpolymer, a slight increase in the haze, and a slight deterioration in the light transmittance. However, it is still better than Comparative Examples 1 to 8.

[0137] (2) The preparation method provided in Comparative Example 1 obtains a completely block carbon dioxide-based terpolymer, which has a very low light transmittance and a very high haze, and has very poor light transmittance; while the preparation method provided in Comparative Example 2 obtains a completely random carbon dioxide-based terpolymer, and its light transmittance is improved compared with that of Comparative Example 1, but still lower than that of Examples 1 to 5.

[0138] (3) Compared with Example 1, the preparation method provided in Comparative Example 3 injects too little carbon dioxide in the copolymerization in step (3), resulting in a low pressure in the reactor, which in turn makes the Tg1 of the prepared carbon dioxide-based terpolymer low, and the carbon dioxide-based terpolymer of the target structure cannot be prepared, resulting in poor light transmittance.

[0139] (4) Compared with Example 1, the preparation methods provided in Comparative Examples 4 to 5 will result in too little monomer on one side due to the mass ratio of propylene oxide to cyclohexene oxide being too large or too small, and thus the desired block effect cannot be achieved, which is manifested as the Tg characteristic failing to reach the target value, and also resulting in a decrease in the transparency of the obtained carbon dioxide-based terpolymer.

[0140] (5) Compared with Example 1, in Comparative Example 6, the materials were not preheated before the reaction. Although Comparative Example 7 was preheated, the preheating temperature was too low. As a result, the Tg characteristics of the obtained carbon dioxide-based terpolymer did not reach the target value, and thus the target structure could not be achieved, resulting in a significant decrease in light transmittance.

[0141] (6) Compared with Example 1, the preheating temperature in Comparative Example 8 is too high, which will cause the difference between the two Tg values ​​of the obtained carbon dioxide-based terpolymer to become smaller, and it is even likely to obtain a random copolymer product with a single Tg, resulting in an increase in the polyether content, which will also cause the transparency of the obtained carbon dioxide-based terpolymer to decrease significantly.

[0142] The applicant declares that the present invention illustrates a carbon dioxide-based terpolymer and its preparation method and application through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned process steps, that is, it does not mean that the present invention must rely on the above-mentioned process steps to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the raw materials selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A carbon dioxide-based terpolymer, characterized in that The carbon dioxide-based terpolymer comprises propylene carbonate structural units and cyclohexene carbonate structural units; The propylene carbonate structural unit has a structure shown in the following formula I or formula II: The cyclohexenyl carbonate structural unit has a structure as shown in the following formula III: The carbon dioxide-based terpolymer has two glass transition temperatures, a relatively low glass transition temperature is recorded as Tg1, and a relatively high glass transition temperature is recorded as Tg2, Tg1≥35°C, Tg2≤80°C, and the difference between Tg2 and Tg1 is 10-45°C.

2. The carbon dioxide-based terpolymer according to claim 1, characterized in that The weight average molecular weight of the carbon dioxide-based terpolymer is ≥100,000.

3. The carbon dioxide-based terpolymer according to claim 1 or 2, characterized in that: The molar ratio of the propylene carbonate structural unit to the cyclohexene carbonate structural unit is (0.25-4):

1.

4. A method for preparing a carbon dioxide-based terpolymer, characterized in that: The preparation method comprises the following steps: (1) preparing materials: preparing epoxy monomer, solvent, catalyst and carbon dioxide as raw materials; the epoxy monomer includes propylene oxide and cyclohexene oxide; (2) Feeding and preheating: Carbon dioxide is charged into the reactor, and part of the solvent, propylene oxide and cyclohexene oxide are added in sequence, the temperature of the raw materials in the reactor is controlled at 35-60° C., and the remaining part of the solvent carrying the catalyst is added into the reactor for mixing; (3) Copolymerization: Filling the reactor with carbon dioxide again, and raising the temperature to allow the materials in the reactor to react, thereby obtaining the carbon dioxide-based terpolymer.

5. The preparation method according to claim 4, characterized in that: The volume ratio of the epoxy monomer to the solvent in step (1) is 1:(1-4); Preferably, the mass ratio of propylene oxide to cyclohexene oxide in step (1) is (13-70):(87-30); Preferably, based on the total mass of the epoxy monomer in step (1) being 100%, the mass of the catalyst is 0.005 to 1.8%; Preferably, the catalyst comprises a double metal cyanide catalyst and / or a modified double metal cyanide catalyst.

6. The preparation method according to claim 4 or 5, characterized in that: The mass percentage of total water in the epoxy monomer, solvent and catalyst in step (1) is ≤200 ppm, preferably ≤100 ppm; Preferably, the dew point temperature of the carbon dioxide in step (1) is ≤-40°C.

7. The preparation method according to any one of claims 4 to 6, characterized in that: After the carbon dioxide is charged into the reactor in step (2), the pressure in the reactor is ≤6MPa, preferably 1-6MPa.

8. The preparation method according to any one of claims 4 to 7, characterized in that: After the carbon dioxide is introduced into the reactor again in step (3), the pressure in the reactor is 3-7 MPa.

9. The preparation method according to any one of claims 4 to 8, characterized in that: The reaction temperature in step (3) is 50-60° C. and the reaction time is 8-16 hours.

10. Use of the carbon dioxide based terpolymer as claimed in any one of claims 1 to 3 or the carbon dioxide based terpolymer prepared by the preparation method as claimed in any one of claims 4 to 9 in the preparation of light-transmitting products.

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