Preparation method of polyester and obtained polyester

Abstract

The invention discloses a preparation method of polyester and the obtained polymer.The preparation method comprises the steps that dibasic acid and esterification products of dihydric alcohol are subjected to condensation polymerization in the presence of cyclic carbonate to obtain the polyester, and the dibasic acid is selected from adipic acid and optional other dibasic acid. The cyclic carbonate is added after esterification, and the acid value of the system can be reduced, so that decarboxylation cyclization of adipic acid or a chain segment of adipic acid at a polycondensation stage under a high-temperature condition and further inhibition of polymerization side reaction are realized, and polyester (such as PBAT resin) with good quality is obtained.

Description

Technical Field

[0001] The present invention belongs to the field of polyesters, and particularly relates to a method for preparing a polyester and the obtained polyester. Background Art

[0002] The use of plastic materials has greatly improved the quality of human life. However, with the large increase in plastic waste, the soil and oceans on which humans depend for survival are also facing serious "white pollution". Therefore, it is extremely urgent to research and develop environmentally friendly biodegradable materials. Among a series of biodegradable polyesters, for example, poly(butylene adipate-co-terephthalate) (PBAT), it has good ductility and elongation at break, as well as good heat resistance and impact resistance. At the same time, it can be degraded by microorganisms into water and carbon dioxide, and can be widely used in fields such as sheets, mulch films, packaging, and foaming. It is one of the most active and best commercially applied biodegradable plastics in current research.

[0003] Then, during the preparation of polyesters containing adipic acid units (such as PBAT), adipic acid (AA) or its segments are prone to decarboxylation degradation under high-temperature conditions, as well as further polymerization of the degradation products, especially under the high-temperature conditions of polycondensation. This makes the obtained PBAT resin have a poor color and high a and b values, which greatly limits the application of PBAT.

[0004] CN113667103A discloses a method for preparing a PBAT resin, in which a titanium EDTA composite catalyst, terephthalic acid, adipic acid, and 1,4-butanediol are subjected to an esterification reaction; after the esterification reaction is completed, a reducing agent 4,4′,4″-triaminotriphenylmethane and / or L-polylysine are added, and PBAT pellets are prepared by polycondensation. The PBAT shows lower a and b values.

[0005] In the above technologies, the hue of the PBAT resin is improved by increasing the esterification rate of adipic acid or by reducing to inhibit deacidification, but there are problems such as many steps in the preparation process, relatively high cost of the reducing agent, and certain toxicity during the operation process. Summary of the Invention

[0006] In order to overcome the problems existing in the prior art, the present invention provides a method for preparing a polyester and the obtained polyester. Among them, after esterification, a cyclic carbonate is added, which can reduce the acid value of the system, thereby realizing the decarboxylation cyclization of adipic acid or its segments under high-temperature conditions in the polycondensation stage and inhibiting the further polymerization side reaction, and obtaining a polyester with good quality (such as PBAT resin).

[0007] One object of the present invention is to provide a method for preparing a polyester, comprising: subjecting an esterification product of a dibasic acid and a diol to a polycondensation reaction in the presence of a cyclic carbonate to obtain a polyester, wherein the dibasic acid is selected from adipic acid and optionally other dibasic acids.

[0008] Wherein, the other dibasic acid refers to dibasic acids other than adipic acid.

[0009] In a preferred embodiment, the other dibasic acid is selected from aromatic dibasic acids and optionally C2-C10 alkyl dibasic acids other than adipic acid.

[0010] In a further preferred embodiment, the other dibasic acid is selected from terephthalic acid and optionally C4-C10 alkyl dibasic acids other than adipic acid.

[0011] In a preferred embodiment, the dibasic acid includes terephthalic acid, adipic acid, optionally succinic acid, and optionally sebacic acid.

[0012] In a further preferred embodiment, the molar ratio of the other dibasic acid to adipic acid is (0.1-0.9):(0.1-0.9), preferably (0.4-0.6):(0.4-0.6).

[0013] For example, based on the total molar amount of the dibasic acid being 100%, wherein the other dibasic acid and the adipic acid each independently account for 10-90%, preferably 40-60%, such as 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90%.

[0014] In a preferred embodiment, the diol is selected from C2-C10 diols, preferably at least one of 1,4-butanediol, ethylene glycol, 1,3-propanediol, and 1,4-cyclohexanedimethanol.

[0015] In a preferred embodiment, the molar ratio of the total amount of the dibasic acid to the diol is 1:1.1-1:2.0, preferably 1:1.4-1:2.0, such as 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2.0.

[0016] In a preferred embodiment, the cyclic carbonate is selected from at least one of the compounds represented by formula (I), in formula (I), R is selected from a linear or branched hydrocarbon group of C2-C10 (such as C2-C5), preferably a linear or branched alkyl group of C2-C10 (such as C2-C5):

[0017]

[0018] In a further preferred embodiment, the cyclic carbonate is selected from at least one of the compounds represented by formula (II) to formula (III):

[0019]

[0020] In formula (II) and formula (III), R1 to R 5 are each independently selected from hydrogen or a C1-C5 alkyl group, preferably from hydrogen or a C1-C3 alkyl group, more preferably from hydrogen, methyl or ethyl.

[0021] Most preferably, the cyclic carbonate is selected from at least one of ethylene carbonate, propylene carbonate, and trimethylene carbonate.

[0022] In the present invention, adding a cyclic carbonate compound after esterification can play a role in stabilizing the carboxyl group through its further reaction with the carboxyl group, and reduce decarboxylation under high-temperature conditions.

[0023] In a preferred embodiment, based on the theoretical production amount of the polyester, the amount of the cyclic carbonate used is 5-200 mol / t, preferably 20-100 mol / t, for example 5 mol / t, 10 mol / t, 20 mol / t, 40 mol / t, 60 mol / t, 80 mol / t, 100 mol / t, 120 mol / t, 150 mol / t, 180 mol / t or 200 mol / t.

[0024] Among them, the theoretical production amount of the polyester is obtained as follows: the number of moles of the diacid multiplied by the molar mass of the repeating unit.

[0025] Among them, the amount of the cyclic carbonate used should not be too much. When the amount is too much, it may increase the length of the aliphatic chain segment in the polyester chain and affect the performance of the polyester.

[0026] In a preferred embodiment, the polycondensation reaction is further carried out in the presence of a phosphorus-containing compound.

[0027] In a further preferred embodiment, the phosphorus-containing compound is selected from at least one of organic phosphates, preferably from at least one of trimethyl phosphate, triethyl phosphate, tripropyl phosphate, triisopropyl phosphate, tributyl phosphate, dibutyl phosphate and triphenyl phosphate.

[0028] Among them, the phosphorus-containing compound can reduce the thermal degradation reaction rate of the polyester under high-temperature conditions and is also helpful for improving the hue of the polyester. When the content of the phosphorus-containing compound is too low, the catalyst performance cannot be effectively improved. When the content of the phosphorus-containing compound is too high, although the hue and thermal degradation rate are effectively improved, the activity of the esterification catalyst is also severely inhibited.

[0029] In a further preferred embodiment, based on 100 wt% of the theoretical production amount of the polyester, the amount of the phosphorus-containing compound is 0.002 to 0.2 wt%, preferably 0.002 to 0.12 wt%. Based on the amount of phosphorus element in the phosphorus-containing compound, for example, it is 0.002 wt%, 0.005 wt%, 0.008 wt%, 0.01 wt%, 0.02 wt%, 0.05 wt%, 0.08 wt%, 0.1 wt%, 0.12 wt%, 0.15 wt%, 0.18 wt% or 0.2 wt%.

[0030] In a preferred embodiment, the conditions of the polycondensation reaction include: the polycondensation temperature is 190 to 280 °C, the pressure is 10 to 1000 Pa absolute pressure, and the reaction time is 1 to 10 h.

[0031] Among them, the conditions of the polycondensation reaction include: the polycondensation temperature is 190 °C, 200 °C, 210 °C, 220 °C, 230 °C, 240 °C, 250 °C, 260 °C, 270 °C or 280 °C, the pressure is 10 Pa, 50 Pa, 100 Pa, 200 Pa, 400 Pa, 600 Pa, 800 Pa or 1000 Pa absolute pressure, and the reaction time is 1 h, 2 h, 4 h, 6 h, 8 h or 10 h.

[0032] In a further preferred embodiment, the conditions of the polycondensation reaction include: the polycondensation temperature is 210 to 250 °C, the pressure is 30 to 500 Pa absolute pressure, and the reaction time is 1 to 8 h.

[0033] In a preferred embodiment, the esterification product is obtained as follows: the dibasic acid and the diol are subjected to an esterification reaction in the presence of a catalyst to obtain the esterification product.

[0034] In a further preferred embodiment, the catalyst is selected from titanium-containing catalysts, preferably titanates, more preferably at least one of the titanates having a structure as shown in Ti(OR) 4 wherein R is selected from C2 to C10 (preferably C2 to C6).

[0035] For example, the titanium-containing catalyst is selected from at least one of tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate and tetramethyl titanate.

[0036] In a more preferred embodiment, based on the theoretical production amount of the polyester, the amount of the catalyst is 50 to 200 mg / kg. Based on the amount of titanium element in the catalyst, for example, it is 50 mg / kg, 60 mg / kg, 80 mg / kg, 100 mg / kg, 120 mg / kg, 140 mg / kg, 160 mg / kg, 180 mg / kg or 200 mg / kg.

[0037] In a preferred embodiment, the conditions for the esterification reaction include: a pressure of 0 to 0.5 MPa, a temperature of 160 to 240 °C, and a time of 60 to 300 min.

[0038] Among them, the conditions for the esterification reaction include: a pressure of 0 MPa, 0.1 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa, or 0.5 MPa, a temperature of 160 °C, 170 °C, 180 °C, 190 °C, 200 °C, 210 °C, 220 °C, 230 °C, or 240 °C, and a time of 60 min, 100 min, 150 min, 200 min, 250 min, or 300 min.

[0039] In a further preferred embodiment, the conditions for the esterification reaction include: normal pressure, a temperature of 180 to 230 °C, and a time of 120 to 180 min.

[0040] In a preferred embodiment, the preparation method includes:

[0041] 1) Directly adding or preparing into a slurry and adding the dibasic acid (such as terephthalic acid, adipic acid), the diol (such as 1,4-butanediol), and the catalyst into a reaction kettle, and carrying out an esterification reaction to obtain an esterification product;

[0042] 2) Adding a cyclic carbonate and a phosphorus-containing compound to the above esterification product, continuously stirring and reacting, and then carrying out a polycondensation reaction to obtain polybutylene terephthalate-adipate with good hue.

[0043] The second object of the present invention is to provide a polyester obtained by using the preparation method described in the first object of the present invention.

[0044] Among them, the intrinsic viscosity of the polyester > 1.2 dl / g, the b value is less than 10, and the a value is less than 2.

[0045] In the ranges disclosed in the present invention, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in this article. In the following text, in principle, various technical solutions can be combined with each other to obtain new technical solutions, which should also be regarded as specifically disclosed in this article.

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

[0047] (1) By adding cyclic titanate after esterification, the present invention can effectively reduce the acid value of the system, thereby well improving the hue of the resin, obtaining PBAT resin with a low color value, and having little influence on the polymerization activity, and can obtain a resin with an intrinsic viscosity > 1.2 dl / g, having good technical effects.

[0048] (2) The preparation method described in the present invention is simple and feasible, and can be applied to large-scale production. Detailed Embodiments

[0049] The present invention will be specifically described below in conjunction with specific embodiments. It is necessary to point out here that the following embodiments are only for further illustration of the present invention and cannot be understood as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention still fall within the protection scope of the present invention.

[0050] In addition, it should be noted that the various specific technical features described in the following detailed embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0051] Furthermore, any combination can be made between different embodiments of the present invention as long as it does not violate the idea of the present invention. The technical solutions formed thereby belong to a part of the original public content of this specification and also fall within the protection scope of the present invention.

[0052] The raw materials used in the examples and comparative examples, if not specifically limited, are all disclosed in the prior art, for example, can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0053] In the present invention, the intrinsic viscosity, hue, etc. of the polyester are tested by the following methods:

[0054] (1) Intrinsic viscosity: Measured with an Ubbelohde viscometer at 25 °C using a mixed solution of phenol and tetrachloroethane as the solvent.

[0055] (2) Hue: After the pellet sample is treated at 80 °C for 1 hour, its Hunter L value (brightness), a value (hue of red - green), and b value (hue of yellow - blue) are measured with a color - view automatic color difference meter from BYK Gardner. Among them, the higher the L value, the greater the brightness; the higher the a value, the polyester chips are more reddish, and the higher the b value, the polyester chips are more yellowish. For the present invention, a high L value and a low a / b value are desired.

[0056] (3) Acid value: The esterified product is dissolved with dichloromethane, titrated with a KOH / ethanol solution using phenolphthalein as the indicator, and the average value is taken after measuring 3 times.

[0057]

Example 1

[0058] 230 g of terephthalic acid, 200 g of adipic acid, 400 g of 1,4-butanediol and tetrabutyl titanate (the weight of titanium atoms is 100 ppm based on the amount of polyester produced) were mixed to form a slurry, which was added to a polymerization kettle for esterification reaction. The esterification temperature was gradually increased from 190 to 230 °C at atmospheric pressure, and the water generated by the reaction was discharged through a rectification device. After the esterification was completed (150 min), 2.6 g of ethylene carbonate and triethyl phosphate (the addition amount of triethyl phosphate based on the amount of polyester produced and calculated as phosphorus element was 0.006 wt%) were added, and stirring was continued for 10 minutes. Then, a small amount of esterified product sample was taken. After that, the pressure was reduced to below 130 Pa by vacuum pumping, and the temperature was gradually increased to 250 °C at the same time. When the system reaction reached 150 min, the reaction was stopped. Then, the product was extruded from the bottom of the polymerization kettle, cooled, and pelletized for performance testing.

[0059] The test results are listed in Table 1.

[0060]

Example 2

[0061] 230 g of terephthalic acid, 200 g of adipic acid, 400 g of 1,4-butanediol and tetrabutyl titanate (the weight of titanium atoms is 100 ppm based on the amount of polyester produced) were mixed to form a slurry, which was added to a polymerization kettle for esterification reaction. The esterification temperature was gradually increased from 190 to 230 °C at atmospheric pressure, and the water generated by the reaction was discharged through a rectification device. After the esterification was completed (150 min), 5.1 g of ethylene carbonate and triethyl phosphate (the addition amount of triethyl phosphate based on the amount of polyester produced and calculated as phosphorus element was 0.006 wt%) were added, and stirring was continued for 10 minutes. Then, a small amount of esterified product sample was taken. After that, the pressure was reduced to below 130 Pa by vacuum pumping, and the temperature was gradually increased to 250 °C at the same time. When the system reaction reached 150 min, the reaction was stopped. Then, the product was extruded from the bottom of the polymerization kettle, cooled, and pelletized for performance testing.

[0062] The test results are listed in Table 1.

[0063]

Example 3

[0064] 230 g of terephthalic acid, 200 g of adipic acid, 400 g of 1,4-butanediol and tetrabutyl titanate (the weight of titanium atoms is 100 ppm based on the amount of polyester produced) were mixed to form a slurry, which was added to a polymerization kettle for esterification reaction. The esterification temperature was gradually increased from 190 to 230 °C at atmospheric pressure, and the water generated by the reaction was discharged through a rectification device. After the esterification was completed (150 min), 1.3 g of ethylene carbonate and triethyl phosphate (the addition amount of triethyl phosphate based on the amount of polyester produced and calculated as phosphorus element was 0.006 wt%) were added, and stirring was continued for 10 minutes. Then, a small amount of esterified product sample was taken. After that, the pressure was reduced by vacuum to a system pressure below 130 Pa, and the temperature was gradually increased to 250 °C at the same time. When the system reaction reached 150 min, the reaction was stopped. Then, the product was extruded from the bottom of the polymerization kettle, cooled and pelletized for performance testing.

[0065] The test results are listed in Table 1.

[0066]

Example 4

[0067] 230 g of terephthalic acid, 200 g of adipic acid, 400 g of 1,4-butanediol and tetrabutyl titanate (the weight of titanium atoms is 100 ppm based on the amount of polyester produced) were mixed to form a slurry, which was added to a polymerization kettle for esterification reaction. The esterification temperature was gradually increased from 190 to 230 °C at atmospheric pressure, and the water generated by the reaction was discharged through a rectification device. After the esterification was completed (150 min), 3.0 g of trimethylene carbonate and triethyl phosphate (the addition amount of triethyl phosphate based on the amount of polyester produced and calculated as phosphorus element was 0.006 wt%) were added, and stirring was continued for 10 minutes. Then, a small amount of esterified product sample was taken. After that, the pressure was reduced by vacuum to a system pressure below 130 Pa, and the temperature was gradually increased to 250 °C at the same time. When the system reaction reached 150 min, the reaction was stopped. Then, the product was extruded from the bottom of the polymerization kettle, cooled and pelletized for performance testing.

[0068] The test results are listed in Table 1.

[0069]

Example 5

[0070] 230 g of terephthalic acid, 200 g of adipic acid, 400 g of 1,4-butanediol and tetrabutyl titanate (the weight of titanium atoms is 100 ppm based on the amount of polyester produced) were mixed to form a slurry, which was added to a polymerization kettle for esterification reaction. The esterification temperature was raised from 190 to 230 °C at atmospheric pressure, and the water generated by the reaction was discharged through a rectification device. After the esterification was completed (150 min), 0.5 g of ethylene carbonate and triethyl phosphate (the addition amount of triethyl phosphate based on the amount of polyester produced and calculated by phosphorus element was 0.006 wt%) were added, and stirring was continued for 10 minutes. Then a small amount of esterified product sample was taken. After that, the pressure was reduced to below 130 Pa by vacuum pumping, and the temperature was gradually raised to 250 °C at the same time. When the system reaction reached 150 min, the reaction was stopped. Then the product was extruded from the bottom of the polymerization kettle, cooled and pelletized for performance testing.

[0071] The test results are listed in Table 1.

[0072]

Example 6

[0073] 206 g of terephthalic acid, 221 g of adipic acid, 490 g of 1,4-butanediol and tetrabutyl titanate (the weight of titanium atoms is 110 ppm based on the amount of polyester produced) were mixed to form a slurry, which was added to a polymerization kettle for esterification reaction. The esterification temperature was gradually raised from 190 to 230 °C at atmospheric pressure, and the water generated by the reaction was discharged through a rectification device. After the esterification was completed (150 min), 4.7 g of propylene carbonate and triphenyl phosphate (the addition amount of triphenyl phosphate based on the amount of polyester produced and calculated by phosphorus element was 0.005 wt%) were added, and stirring was continued for 10 minutes. Then a small amount of esterified product sample was taken. After that, the pressure was reduced to below 130 Pa by vacuum pumping, and the temperature was gradually raised to 250 °C at the same time. When the system reaction reached 150 min, the reaction was stopped. Then the product was extruded from the bottom of the polymerization kettle, cooled and pelletized for performance testing.

[0074] The test results are listed in Table 1.

[0075]

Example 7

[0076] 251 g of terephthalic acid, 181 g of adipic acid, 350 g of 1,4-butanediol and tetrabutyl titanate (the weight of titanium atoms is 120 ppm based on the amount of polyester produced) were mixed to form a slurry, which was added to a polymerization kettle for esterification reaction. The esterification temperature gradually increased from 190 to 230 °C at atmospheric pressure, and the water generated by the reaction was discharged through a rectification device. After the esterification was completed (150 min), 4 g of butylene carbonate and trimethyl phosphate (the addition amount of trimethyl phosphate based on the amount of polyester produced and calculated as phosphorus element was 0.008 wt%) were added, and stirring continued for 10 minutes. Then, a small amount of esterified product sample was taken. After that, the pressure was reduced to below 130 Pa by vacuum pumping, and the temperature was gradually increased to 250 °C at the same time. When the system reaction reached 150 min, the reaction was stopped. Then, the product was extruded from the bottom of the polymerization kettle, cooled and pelletized for performance testing.

[0077] The test results are listed in Table 1.

[0078]

Comparative Example 1

[0079] 230 g of terephthalic acid, 200 g of adipic acid, 400 g of 1,4-butanediol and tetrabutyl titanate (the weight of titanium atoms is 100 ppm based on the amount of polyester produced) were mixed to form a slurry, which was added to a polymerization kettle for esterification reaction. The esterification temperature increased from 190 to 230 °C at atmospheric pressure, and the water generated by the reaction was discharged through a rectification device. After the esterification was completed (150 min), triethyl phosphate (the addition amount of triethyl phosphate based on the amount of polyester produced and calculated as phosphorus element was 0.006%) was added, and after stirring for 10 min, a small amount of esterified product sample was taken. Then, the pressure was reduced to below 130 Pa by vacuum pumping, and the temperature was gradually increased to 250 °C at the same time. When the system reaction reached 150 min, the reaction was stopped. Then, the product was extruded from the bottom of the polymerization kettle, cooled and pelletized for performance testing.

[0080] The test results are listed in Table 1.

[0081]

Comparative Example 2

[0082] 230 g of terephthalic acid, 200 g of adipic acid, 400 g of 1,4-butanediol and tetrabutyl titanate (the weight of titanium atoms is 100 ppm based on the amount of polyester produced) were mixed to form a slurry, which was added to a polymerization kettle for esterification reaction. The esterification temperature increased from 190 to 230 °C at atmospheric pressure, and the water generated by the reaction was discharged through a rectification device. After the esterification was completed (150 min), a small amount of esterified product sample was taken. Then, the pressure was further reduced to below 130 Pa by vacuum pumping, and the temperature was gradually increased to 250 °C at the same time. When the system reaction reached 150 min, the reaction was stopped. Then, the product was extruded from the bottom of the polymerization kettle, cooled and pelletized for performance testing.

[0083] The test results are listed in Table 1.

[0084]

Comparative Example 3

[0085] 230 g of terephthalic acid, 200 g of adipic acid, 400 g of 1,4-butanediol, tetrabutyl titanate (the weight of titanium atoms is 100 ppm based on the amount of polyester produced), and 2.6 g of ethylene carbonate were mixed to form a slurry, which was added to a polymerization kettle for esterification reaction. The esterification temperature was raised from 190 to 230 °C, the pressure was atmospheric pressure, and the water generated by the reaction was discharged through a rectification device. After the esterification was completed (150 min), triethyl phosphate (the addition amount was 0.006 wt% based on the amount of polyester produced and calculated as phosphorus element) was added. After stirring for 10 min, a small amount of esterified product sample was taken, and then the vacuum was reduced to a system pressure below 130 Pa while gradually raising the temperature to 250 °C. When the system reaction reached 150 min, the reaction was stopped. Then the product was extruded from the bottom of the polymerization kettle, cooled, and pelletized for performance testing.

[0086] The test results are listed in Table 1.

[0087]

Comparative Example 4

[0088] 230 g of terephthalic acid, 200 g of adipic acid, 400 g of 1,4-butanediol and tetrabutyl titanate (the weight of titanium atoms is 100 ppm based on the amount of polyester produced) were mixed to form a slurry, which was added to a polymerization kettle for esterification reaction. The esterification temperature was gradually raised from 190 to 230 °C, the pressure was atmospheric pressure, and the water generated by the reaction was discharged through a rectification device. After the esterification was completed (150 min), 2.6 g of ethylene carbonate was added, and stirring was continued for 10 minutes. Then a small amount of esterified product sample was taken. After that, the vacuum was reduced to a system pressure below 130 Pa while gradually raising the temperature to 250 °C. When the system reaction reached 150 min, the reaction was stopped. Then the product was extruded from the bottom of the polymerization kettle, cooled, and pelletized for performance testing.

[0089] The test results are listed in Table 1.

[0090]

Comparative Example 5

[0091] The process of Example 1 was repeated, except that 2.6 g of dimethyl carbonate was used to replace ethylene carbonate, and other conditions remained unchanged.

[0092] Table 1:

[0093]

[0094]

[0095] It can be seen from Table 1 that:

[0096] (1) Compared with Comparative Example 1, in Examples 1-5 (especially Examples 1-4), adding an appropriate amount of cyclic carbonate after esterification effectively reduced the acid value of the esterified product, achieved the stabilization of carboxyl groups, thereby reducing side reactions such as decarboxylation during the polycondensation process, and the obtained chips had excellent hue.

[0097] (2) Compared with Comparative Example 2, in Comparative Example 4, adding cyclic carbonate could reduce the acid value of the system. Although it could improve the hue of the polyester, since the phosphorus stabilizer was not added, the hue of the obtained chips was still poor.

[0098] (3) Compared with Example 1, adding cyclic carbonate too early in Comparative Example 3 could not effectively reduce the acid value. This was because at the initial stage of the reaction, there were a large number of carboxyl groups in the system, which would consume the highly active cyclic carbonate first, thus unable to effectively reduce the acid value.

[0099] In summary, adding a certain amount of cyclic carbonate and phosphorus-containing compound after esterification as described in the present invention effectively improved the color of the resin, and polybutylene terephthalate-adipate with good quality could be obtained, having good technical effects.

[0100] The present invention has been described in detail above in combination with specific embodiments and exemplary examples, but these descriptions should not be construed as limiting the present invention. Those skilled in the art understand that without departing from the spirit and scope of the present invention, various equivalent substitutions, modifications or improvements can be made to the technical solutions and their implementation manners of the present invention, and all of these fall within the scope of the present invention. The protection scope of the present invention is subject to the appended claims.

Claims

1. A method for preparing a polyester, comprising: subjecting an esterification product of a dibasic acid and a diol to a polycondensation reaction in the presence of a cyclic carbonate to obtain a polyester, wherein the dibasic acid is selected from adipic acid and optional other dibasic acids.

2. The preparation method according to claim 1, characterized in that the other dibasic acids are selected from aromatic dibasic acids and optional C2-C10 alkyl dibasic acids other than adipic acid, preferably terephthalic acid and optional C4-C10 alkyl dibasic acids other than adipic acid; and / or, the diol is selected from C2-C10 diols, preferably at least one of 1,4-butanediol, ethylene glycol, 1,3-propanediol, 1,4-cyclohexanedimethanol.

3. The preparation method according to claim 1, characterized in that the molar ratio of the other dibasic acids to adipic acid is (0.1-0.9):(0.1-0.9), preferably (0.4-0.6):(0.4-0.6); and / or, the molar ratio of the total amount of the dibasic acid to the diol is 1:1.1-1:2.0, preferably 1:1.4-1:2.

0.

4. The preparation method according to claim 1, characterized in that the cyclic carbonate is selected from at least one of the compounds represented by formula (I), in formula (I), R is selected from C2-C10 straight-chain or branched hydrocarbon groups, preferably C2-C10 straight-chain or branched alkyl groups: Preferably, the cyclic carbonate is selected from at least one of the compounds represented by formula (II) to formula (III): In formulas (II) and (III), R 1 ~R 5 are each independently selected from hydrogen or C1-C5 alkyl, preferably from hydrogen or C1-C3 alkyl.

5. The preparation method according to claim 1, characterized in that based on the theoretical production amount of the polyester, the amount of the cyclic carbonate used is 5-200 mol / t, preferably 20-100 mol / t.

6. The preparation method according to claim 1, characterized in that the polycondensation reaction is further carried out in the presence of a phosphorus-containing compound; preferably, based on 100 wt% of the theoretical production amount of the polyester, the amount of the phosphorus-containing compound used is 0.002-0.2 wt%, preferably 0.002-0.12 wt%, calculated based on the amount of phosphorus element in the phosphorus-containing compound.

7. The preparation method according to claim 6, characterized in that the phosphorus-containing compound is selected from at least one of organic phosphoric acid esters, preferably at least one of trimethyl phosphate, triethyl phosphate, tripropyl phosphate, triisopropyl phosphate, tributyl phosphate, dibutyl phosphate and triphenyl phosphate.

8. The preparation method according to any one of claims 1-7, characterized in that the conditions of the polycondensation reaction include: the polycondensation temperature is 190-280 °C, the pressure is an absolute pressure of 10-1000 Pa, and the reaction time is 1-10 h; preferably, the polycondensation temperature is 210-250 °C, the pressure is an absolute pressure of 30-500 Pa, and the reaction time is 1-8 h.

9. The preparation method according to any one of claims 1-7, characterized in that the esterification product is obtained as follows: the dibasic acid and the diol are subjected to an esterification reaction in the presence of a catalyst to obtain the esterification product.

10. The preparation method according to claim 9, characterized in that The catalyst is selected from titanium-containing catalysts, preferably from titanates, more preferably from at least one of the titanates having a structure as shown in Ti(OR) 4 wherein R is selected from C2 to C10; more preferably, based on the theoretical production amount of the polyester, the dosage of the catalyst is 50 to 200 mg / kg in terms of the amount of titanium element in the catalyst.

11. The preparation method according to claim 9, characterized in that the conditions of the esterification reaction include: the pressure is 0 to 0.5 MPa, the temperature is 160 to 240 °C, and the time is 60 to 300 min; preferably, the pressure is atmospheric pressure, the temperature is 180 to 230 °C, and the time is 120 to 180 min.

12. The polyester obtained by using the preparation method according to any one of claims 1 to 11, preferably, the intrinsic viscosity of the polyester > 1.2 dl / g, the b value is less than 10, and the a value is less than 2.

Images