An aliphatic polyester with reversible cross-linking properties, its preparation method and applications

Abstract

The present application discloses an aliphatic polyester with reversible crosslinking properties, its preparation method and application, relating to the technical field of polymer materials. The aliphatic polyester with reversible crosslinking properties is formed by chemical crosslinking of a polyester containing a furoamide group side chain and a crosslinking agent containing a maleimide group; the polyester containing a furoamide group side chain is a random copolymer composed of the following repeating units I: and II:, where both R1 and R2 are C2-C 12 alkyl groups; the molar ratio of the repeating units I and II is (0.1-1):1. The aliphatic polyester provided by the present application can not only repeatedly undergo chemical crosslinking and de-crosslinking, enabling repeated processing and reuse, but also has excellent melt thermal stability, mechanical strength and good heat aging resistance.

Description

Technical Field

[0001] This application relates to the technical field of polymer materials, and particularly relates to an aliphatic polyester with reversible cross-linking characteristics, a preparation method thereof, and an application thereof. Background Art

[0002] As is well known, aliphatic polyesters are biodegradable materials containing ester bonds in molecular repeating units. They are easily decomposed and metabolized by various microorganisms in nature or enzymes in animals and plants, and at the same time have good mechanical properties. Now they have been widely used in fields such as packaging, tableware, medical supplies, agricultural films, sustained-release materials, and biomedical materials. The development and utilization of aliphatic polyester materials is one of the effective ways to fundamentally solve the problem of white pollution. For example, the polybutanedioate series is a main aliphatic polyester produced industrially, and is favored due to its relatively high melting point, good thermal stability, and mechanical properties.

[0003] However, existing aliphatic polyester materials usually have problems such as poor melt thermal stability during molding and processing, easy generation of peculiar smells, obvious yellowing, poor color and luster quality, poor heat aging resistance of the finished product, and mechanical strength that needs to be further enhanced. Summary of the Invention

[0004] In view of the deficiencies of the above technologies, this application provides an aliphatic polyester with reversible cross-linking characteristics, a preparation method thereof, and an application thereof, which solves the problems of poor melt thermal stability, heat aging resistance, and mechanical strength of existing aliphatic polyester materials. The aliphatic polyester provided by this application can not only repeatedly undergo chemical cross-linking and de-cross-linking, enabling repeated processing and reuse, but also has excellent melt thermal stability, mechanical strength, and good heat aging resistance.

[0005] To achieve the above object, this application mainly provides the following technical solutions:

[0006] This application provides an aliphatic polyester with reversible cross-linking characteristics, which is formed by chemical cross-linking of a polyester containing a furoamide group side chain and a cross-linking agent containing a maleimide group;

[0007] The polyester containing a furoamide group side chain is a random copolymer composed of the following repeating units I and II:

[0008]

[0009] Wherein both R1 and R2 are C2-C 12 alkyl;

[0010] The molar ratio of the repeating units I and II is (0.1 - 1):1.

[0011] Preferably, the cross-linking agent containing a maleimide group has the following structure:

[0012]

[0013] Wherein n is 2, and R3 is selected from the following groups:

[0014]

[0015] Wherein m is 2 - 20.

[0016] More preferably, the crosslinking agent containing maleimide groups is selected from one or more of 4,4'-bismaleimide diphenylmethane and N,N'-m-phenylene bismaleimide.

[0017] Preferably, in the aliphatic polyester having reversible crosslinking properties, the molar ratio of the maleimide group to the furamide group is 1:(0.1 - 100).

[0018] More preferably, in the aliphatic polyester having reversible crosslinking properties, the molar ratio of the maleimide group to the furamide group is 1:(2 - 100).

[0019] This application also provides a preparation method of the above-mentioned aliphatic polyester having reversible crosslinking properties, including the following steps:

[0020] (1) Add an aliphatic dicarboxylic acid or its ester, an aliphatic diol, a monomer containing a furamide group, and a catalyst into a reactor for an esterification reaction;

[0021] (2) Raise the temperature of the reactor for a polycondensation reaction to obtain a polyester containing furamide group side chains;

[0022] (3) Mix the polyester containing furamide group side chains and a crosslinking agent containing maleimide groups evenly, and then carry out a chemical crosslinking reaction to obtain an aliphatic polyester having reversible crosslinking properties;

[0023] The monomer containing a furamide group has the following structure:

[0024]

[0025] Wherein R4 is H or an alkyl group of C1 - C3.

[0026] Preferably, the aliphatic dicarboxylic acid or its ester is a C2 - C 12 alkane saturated dicarboxylic acid or its ester; the aliphatic diol is a C2 - C 12 alkane saturated diol.

[0027] Preferably, the aliphatic dicarboxylic acid or its ester is selected from one or more of oxalic acid, malonic acid, succinic acid, dimethyl succinate, diethyl succinate, glutaric acid, dimethyl glutarate, diethyl glutarate, adipic acid, dimethyl adipate, and diethyl adipate;

[0028] The aliphatic diol is selected from one or more of ethylene glycol, 1,2 - propanediol, 1,3 - propanediol, 1,4 - butanediol, 1,5 - pentanediol, and 1,6 - hexanediol.

[0029] Preferably, the molar ratio of the aliphatic dicarboxylic acid or its ester, the aliphatic diol, and the monomer containing a furamide group is 1:(1 - 4):(0.1 - 1).

[0030] Preferably, the catalyst is selected from one or more of tetrabutyl titanate, antimony trioxide, magnesium oxide, zinc acetate, sodium acetate, potassium acetate, nickel acetate, manganese acetate, cobalt acetate, magnesium acetate, and silicon dioxide.

[0031] Preferably, the addition amount of the catalyst is 0.01% - 1% of the molar amount of the aliphatic dicarboxylic acid or its ester.

[0032] Preferably, the reaction temperature in step (1) is 130 - 190 °C, and the reaction temperature in step (2) is 200 - 260 °C.

[0033] Preferably, the polyester containing a furamide group side chain and the cross - linker containing a maleimide group are mixed in a static mixer.

[0034] Preferably, the static mixer includes at least two temperature gradient intervals. The temperature range of the first section is 120 - 150 °C, and the temperature range of the second section is 150 - 210 °C; the time for the mixed material to pass through each temperature gradient interval is 5 - 60 min.

[0035] Preferably, the chemical cross - linking reaction is carried out at 50 - 80 °C, and the reaction time is 2 - 20 h.

[0036] Preferably, in step (2), after the polycondensation reaction is completed, the reaction product is further subjected to devolatilization treatment;

[0037] The devolatilization treatment is carried out using a twin - screw extruder equipped with only a devolatilization section. The devolatilization treatment conditions are: treatment at 150 - 180 °C and an absolute pressure ≤ 500 Pa for 20 - 60 min.

[0038] This application also provides the application of the above - mentioned aliphatic polyester with reversible cross - linking characteristics in the fields of biodegradable plastic packaging, film materials, sustained - release materials, and biomedical materials.

[0039] One or more technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages:

[0040] (1) By introducing furfuramide groups into the copolyester chain in the present application, furan groups can be introduced into the molecular chain of the copolyester formed by aliphatic dicarboxylic acids or their esters and aliphatic diols. Utilizing the 4+2 cycloaddition reaction between the furan group and the maleimide group, that is, the Diels-Alder reaction, a reversible covalent bonding can be formed between the electron-rich furan group and the electron-deficient maleimide group, enabling the acquisition of an aliphatic polyester material with reversible crosslinking characteristics. Furthermore, it endows the material with higher mechanical strength, more excellent solvent resistance, and slightly higher heat aging resistance. When the material reaches the end of its service life, the covalent crosslinking formed between the furan group and the maleimide group can also be broken by heating, endowing it with the repeated processing performance that traditional crosslinked materials do not have, enabling the recycling and reuse of the material, effectively reducing environmental pollution and resource waste; introducing a certain crosslinked structure into the system can significantly improve the mechanical strength and heat aging resistance of the final material;

[0041] (2) By introducing phenyl groups substituted with furfuramide groups into the copolyester chain in the present application, a rigid benzene ring structure is introduced into the polyester main chain, which can improve the common problems of softness and poor heat resistance of aliphatic polyesters. The amide bonds in the polyester molecular chain can form hydrogen bond forces between and within molecules, endowing it with better glass transition temperature, melting point, and mechanical properties. At the same time, the hydrogen bonds will endow it with excellent water absorption, promoting the degradation rate of degradable polyesters and the moisture retention of degradable agricultural films and mulch films. Detailed implementation manners

[0042] To further elaborate on the technical means and effects adopted by the present application to achieve the intended application purpose, the following, in combination with preferred embodiments, details the specific implementation manners, structures, features, and their effects according to the present application as follows.

[0043] It should be noted that different "one embodiment" or "embodiments" in the present application do not necessarily refer to the same embodiment. In addition, the specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form. It should be understood that the embodiments of the present application are explanations of the solutions of the present application and do not limit the protection scope of the present application.

[0044] In the present application, a range can be expressed as a range from "about" one specific value and / or to "about" another specific value. When expressing such a range, examples include starting from a certain specific value and / or ending at another specific value. Similarly, when using the antecedent "about" to indicate that a numerical value is an approximate value, it should be understood that the specific numerical value constitutes another aspect. It should also be understood that each endpoint value of each range is meaningful both in relation to and independent of another endpoint value.

[0045] Unless otherwise stated, none of the methods described herein are intended to be understood as requiring their steps to be performed in a specific order. Accordingly, when a method claim does not actually recite that its steps follow a certain order or when it is not otherwise specifically indicated in the claims or the specification that the steps are limited to a specific order, no particular order is intended to be implied.

[0046] Although the transitional phrase "comprising" is used to disclose various features, elements or steps of a particular embodiment, it should be understood that this implies alternative embodiments that may be described by the transitional phrases "consisting of", "consisting essentially of". Thus, for example, implicit alternative embodiments of a method comprising A + B + C include embodiments where the method consists of A + B + C and embodiments where the method consists essentially of A + B + C.

[0047] The present application provides an aliphatic polyester having reversible crosslinking properties, formed by chemical crosslinking of a polyester containing furamide group side chains and a crosslinking agent containing maleimide groups;

[0048] The polyester containing furamide group side chains is a random copolymer composed of the following repeating units I and II:

[0049]

[0050] wherein both R1 and R2 are C2-C 12 alkyl;

[0051] The molar ratio of the above repeating units I and II is (0.1 - 1):1.

[0052] The inventors of the present application found through research that by introducing a phenyl group substituted with a furamide group into the copolyester chain, on the one hand, a furan group can be introduced into the molecular chain of the copolyester formed by an aliphatic dicarboxylic acid or its ester and an aliphatic diol. Utilizing the 4+2 cycloaddition reaction between the furan group and the maleimide group, that is, the Diels-Alder reaction, a reversible covalent bond can be formed between the electron-rich furan group and the electron-deficient maleimide group, enabling an aliphatic polyester material with reversible crosslinking characteristics to be obtained. Furthermore, the material can be endowed with higher mechanical strength, more excellent solvent resistance, and slightly higher heat aging resistance. When the material reaches the end of its service life, the covalent crosslinking formed between the furan group and the maleimide group can also be broken by heating, endowing it with the repeated processing performance that traditional crosslinked materials do not have, enabling the material to be recycled and reused, effectively reducing environmental pollution and resource waste; introducing a certain crosslinking structure into the system can significantly improve the mechanical strength and heat aging resistance of the final material. On the other hand, introducing a rigid benzene ring structure into the polyester main chain can improve the common problems of poor softness and heat resistance of aliphatic polyesters. The amide bonds in the polyester molecular chain can form hydrogen bond forces between and within molecules, endowing it with better glass transition temperature, melting point, and mechanical properties. At the same time, the hydrogen bonds will endow it with excellent water absorption, promoting the degradation rate of the biodegradable polyester and improving the moisture retention of the biodegradable agricultural film and mulch film.

[0053] Specifically, the crosslinking agent containing a maleimide group has the following structure:

[0054]

[0055] Where n is 2, and R3 is selected from the following groups:

[0056]

[0057] Where m is 2 - 20.

[0058] In the above crosslinking agent, the aliphatic chain selected for the middle linking group R3 has good flexibility, the aromatic ring can provide a certain degree of rigidity, and the methylene group, ether bond, and thioether bond all have different flexibilities and reactivities, which help to adjust the flexibility of the aliphatic polyester material.

[0059] More preferably, the crosslinking agent containing a maleimide group is selected from one or more of 4,4'-bismaleimide diphenylmethane and N,N'-m-phenylene bismaleimide.

[0060] Preferably, in the above aliphatic polyester with reversible crosslinking characteristics, the molar ratio of the maleimide group to the furamide group is 1:(0.1 - 100), and more preferably the molar ratio of the maleimide group to the furamide group is 1:(2 - 100).

[0061] The present application also provides a method for preparing the above aliphatic polyester, comprising the following steps:

[0062] (1) Adding an aliphatic dicarboxylic acid or its ester, an aliphatic diol, a monomer containing a furanamide group, and a catalyst into a reactor for an esterification reaction;

[0063] (2) Raising the temperature of the reactor for a polycondensation reaction to obtain a polyester containing a furanamide group side chain;

[0064] (3) Mixing the polyester containing a furanamide group side chain and a crosslinking agent containing a maleimide group evenly, and then carrying out a chemical crosslinking reaction to obtain an aliphatic polyester with reversible crosslinking characteristics.

[0065] The above monomer containing a furanamide group has the following structure:

[0066]

[0067] wherein R4 is H or an alkyl group of C1-C3.

[0068] In the present application, the above monomer containing a furanamide group can be prepared by an amide reaction of 5-aminoisophthalic acid or its ester with 2-furoyl chloride.

[0069] For example, the preparation process of 5-furanamidophthalic acid is as follows: Under the condition of an ice-water bath, 5-aminoisophthalic acid, 2-furoyl chloride, and triethylamine are added to dichloromethane, and stirred for reaction for 1 to 5 hours. After the reaction is completed, the dichloromethane solvent is removed under reduced pressure to obtain a product, which is washed with deionized water 3 to 5 times, and then vacuum dried at 90 °C to obtain 5-furanamidophthalic acid. Among them, the molar ratio of 5-aminoisophthalic acid, 2-furoyl chloride to triethylamine is 1:1:0.1 to 1.0; the molar concentration of 5-aminoisophthalic acid in the solvent dichloromethane is 0.01 to 3 mmol / mL.

[0070] Preferably, the above aliphatic dicarboxylic acid or its ester is a C2-C 12 alkane saturated dicarboxylic acid or its ester; the above aliphatic diol is a C2-C 12 alkane saturated diol.

[0071] More preferably, the above aliphatic dicarboxylic acid or its ester is selected from one or more of oxalic acid, malonic acid, succinic acid, dimethyl succinate, diethyl succinate, glutaric acid, dimethyl glutarate, diethyl glutarate, adipic acid, dimethyl adipate, diethyl adipate; the above aliphatic diol is selected from one or more of ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol.

[0072] Specifically, the molar ratio of the above-mentioned aliphatic dicarboxylic acid or its ester, aliphatic diol, and the monomer containing a furanamide group is 1:(1-4):(0.1-1).

[0073] Specifically, in the above step (1), the catalyst is selected from one or more of tetrabutyl titanate, antimony trioxide, magnesium oxide, zinc acetate, sodium acetate, potassium acetate, nickel acetate, manganese acetate, cobalt acetate, magnesium acetate, and silicon dioxide. Preferably, the addition amount of these catalysts is 0.01%-1% of the molar amount of the aliphatic dicarboxylic acid or its ester, and more preferably 0.1%-0.3%.

[0074] Specifically, the reaction temperature of step (1) is 130-190 °C, and the reaction temperature of step (2) is 200-260 °C.

[0075] Preferably, in step (2), after the polycondensation reaction is completed, the reaction product is further subjected to devolatilization treatment. Specifically, a twin-screw extruder equipped only with a devolatilization section is used for devolatilization treatment. The specific devolatilization treatment conditions are: treatment at 150-180 °C and an absolute pressure ≤ 500 Pa for 20-60 min. Conducting devolatilization treatment after the polycondensation reaction is completed can increase the molecular weight of the aliphatic polyester, reduce the residual monomers and ash content, thereby improving the strength, elongation, and material quality of the polyester.

[0076] Preferably, the polyester containing a furanamide group side chain and a crosslinking agent containing a maleimide group are mixed in a static mixer; the static mixer is selected from an SK type static mixer, an SX type static mixer, or an SV type static mixer.

[0077] Due to the limited heat transfer and stirring effects of a conventional stirred reactor, it is difficult for the Diels-Alder reaction to occur between the maleimide group and the furan group in a timely and effective manner, and the stirring and disturbing effect in the stirred reactor is limited, making it impossible to transfer the heat in local areas inside the polyester melt in a timely manner, resulting in too high a temperature in local areas and triggering side reactions such as thermal oxidative degradation, so that the finally obtained material has a problem of slight yellowing, which will also have an adverse impact on the melt thermal stability, mechanical strength, and heat aging resistance of the material. Using a static mixer instead of a conventional stirred reactor can avoid the above problems, thereby improving the melt thermal stability, mechanical strength, and heat aging resistance of the thermoplastic polyester material.

[0078] Preferably, the above static mixer includes at least two temperature gradient intervals. The temperature range of the first stage is 120-150°C, and the temperature range of the second stage is 150-210°C. It is also possible to use three or more temperature gradient intervals. For example, the temperature range of the first stage is 120-130°C, the temperature range of the second stage is 130-150°C, and the temperature range of the third stage is 150-210°C. The residence time of the reaction material at each temperature is 5-60 min, which can be specifically adjusted according to the types of different polyesters and the temperature of each temperature interval. Since the polyester and the cross-linking agent need to be mixed evenly at a temperature higher than the melting point of the polyester, and long-term high temperature will cause problems such as thermal degradation of the polyester, multi-stage gradient heating is carried out during mixing with the static mixer, which can avoid problems such as thermal degradation of the polyester caused by too long a high-temperature stage, thereby improving the product quality of the aliphatic polyester.

[0079] Specifically, the mixed material of the polyester containing furamide group side chains and the cross-linking agent containing maleimide groups, which is mixed and homogenized by the static mixer, undergoes a cross-linking reaction at 50-80°C for 2-20 h to obtain an aliphatic polyester with reversible cross-linking characteristics.

[0080] The above-mentioned aliphatic polyester with reversible cross-linking characteristics provided by the present application can undergo a de-cross-linking reaction under certain conditions and can be chemically cross-linked again, thereby realizing repeatable processing. Specifically, the above-mentioned aliphatic polyester with reversible cross-linking characteristics can undergo a de-cross-linking reaction at 90-180°C for 10-150 min, and then repeat the above chemical cross-linking process to re-obtain the product.

[0081] The present application also provides the application of the above-mentioned aliphatic polyester with reversible cross-linking characteristics in the fields of biodegradable plastic packaging, film materials, sustained-release materials, and biomedical materials.

[0082] Specifically, the above-mentioned aliphatic polyester with reversible cross-linking characteristics can also be used for the preparation of recyclable plastics or elastomer materials. When the recyclable plastics or elastomer materials made of the aliphatic polyester with reversible cross-linking characteristics provided by the present application are used, the recycled plastics or elastomer materials are subjected to a de-cross-linking reaction at 90-180°C for 10-150 min, and then subjected to a cross-linking reaction at 50-80°C for 2-20 h to re-prepare new products, thereby realizing recycling and reuse.

[0083] Example 1

[0084] This example provides the preparation process of the aliphatic polyester:

[0085] (1) Succinic acid, ethylene glycol, and 5-furfurylamidophthalic acid were added to an atmospheric reactor (such as a conventional stirred reactor) at a molar ratio of 1:1.65:0.1. Then, tetrabutyl titanate at 0.3% of the molar amount of succinic acid was added. Subsequently, an esterification reaction was carried out under an inert atmosphere and at atmospheric pressure, with the reaction temperature being 165 °C until no more small molecule fractions were distilled out.

[0086] (2) The material obtained in step (1) was transferred to a vacuum reactor (such as a conventional stirred reactor). The temperature of the reactor was raised to 220 °C, and the pressure was reduced to an absolute pressure of 50 Pa. A polycondensation reaction was carried out until the intrinsic viscosity of the material in the reactor no longer increased. The material in the reactor was transferred to a twin-screw extruder equipped only with a devolatilization section. Under the conditions of 150 °C and an absolute pressure ≤ 500 Pa, devolatilization treatment was carried out for 35 min, thus obtaining a polyester containing a furfurylamide side group.

[0087] (3) Then, the polyester containing a furfurylamide side group prepared in step (2) was cooled to 120 °C, and then conveyed to an SK-type static mixer. 4,4'-bismaleimide diphenylmethane was added at the starting end of the static mixer, and the addition amount of 4,4'-bismaleimide diphenylmethane was 10% of the molar amount of 5-furfurylamidophthalic acid. The inside of the static mixer was at atmospheric pressure and was divided into three sections. The temperature of the first section was 120 °C, the temperature of the second section was 136 °C, and the temperature of the third section was 150 °C. The time for the material to pass through the first section was 5 min, the time to pass through the second section was 10 min, and the time to pass through the third section was 15 min. The mixed material derived from the static mixer was subjected to a chemical cross-linking reaction at 70 °C for 5 h, and then extruded and granulated to obtain an aliphatic polyester with reversible cross-linking characteristics.

[0088] Example 2

[0089] This example provides the preparation process of an aliphatic polyester with reversible cross-linking characteristics:

[0090] (1) Succinic acid, ethylene glycol, and 5-furfurylamidophthalic acid were added to an atmospheric reactor (such as a conventional stirred reactor) at a molar ratio of 1:1.65:0.2. Then, antimony trioxide at 0.1% of the molar amount of succinic acid was added. Subsequently, an esterification reaction was carried out under an inert atmosphere and at atmospheric pressure, with the reaction temperature being 130 °C until no more small molecule fractions were distilled out.

[0091] (2) Transfer the material obtained in step (1) to a vacuum reactor (such as a conventional stirred reactor), raise the reactor temperature to 200 °C, and reduce the pressure to an absolute pressure of 100 Pa, and carry out polycondensation reaction until the intrinsic viscosity of the material in the reactor no longer increases. Then transfer the material in the reactor to a twin-screw extruder equipped only with a devolatilization section, and carry out devolatilization treatment for 60 min under the conditions of 165 °C and an absolute pressure ≤ 500 Pa, thus obtaining a polyester containing a furoamide-based side group;

[0092] (3) Then cool the polyester containing a furoamide-based side group prepared in step (2) to 125 °C, then convey it to an SK-type static mixer, and add 4,4'-bismaleimide diphenylmethane at the starting end of the static mixer. The addition amount of 4,4'-bismaleimide diphenylmethane is 1% of the molar amount of 5-furoamide isophthalic acid. The inside of the static mixer is at normal pressure and is divided into three sections. The temperature of the first section is 130 °C, the temperature of the second section is 150 °C, and the temperature of the third section is 165 °C. The time for the material to pass through the first section is 10 min, the time to pass through the second section is 20 min, and the time to pass through the third section is 30 min. The mixed material derived from the static mixer is subjected to a chemical cross-linking reaction at 80 °C for 4 h, and then extruded and pelletized to obtain an aliphatic polyester with reversible cross-linking characteristics.

[0093] Example 3

[0094] This example provides a preparation process of an aliphatic polyester with reversible cross-linking characteristics:

[0095] (1) Add succinic acid, ethylene glycol and 5-furoamide isophthalic acid in a molar ratio of 1:1.65:0.5 to an atmospheric pressure reactor (such as a conventional stirred reactor), then add tetrabutyl titanate accounting for 0.3% of the molar amount of succinic acid, and then carry out an esterification reaction under an inert atmosphere and normal pressure at a reaction temperature of 170 °C until no more small molecule fractions are distilled out;

[0096] (2) Transfer the material obtained in step (1) to a vacuum reactor (such as a conventional stirred reactor), raise the reactor temperature to 240 °C, and reduce the pressure to an absolute pressure of 100 Pa, and carry out polycondensation reaction until the intrinsic viscosity of the material in the reactor no longer increases. Then transfer the material in the reactor to a twin-screw extruder equipped only with a devolatilization section, and carry out devolatilization treatment for 20 min under the conditions of 168 °C and an absolute pressure ≤ 500 Pa, thus obtaining a polyester containing a furoamide-based side group;

[0097] (3) Then cool the polyester containing the furanamide group side chain prepared in step (2) to 140 °C, then transfer it to an SK type static mixer, and add 4,4'-bismaleimide diphenylmethane at the starting end of the static mixer. The addition amount of 4,4'-bismaleimide diphenylmethane is 25% of the molar amount of 5-furanamide isophthalic acid; the inside of the static mixer is at normal pressure and is divided into two sections. The temperature of the first section is 150 °C, and the temperature of the second section is 208 °C. The material passes through the first section for 5 min and through the second section for 15 min; the mixed material exported from the static mixer undergoes a chemical cross-linking reaction at 60 °C for 10 h, and after extrusion granulation, an aliphatic polyester with reversible cross-linking characteristics is obtained.

[0098] Example 4

[0099] This example provides the preparation process of an aliphatic polyester with reversible cross-linking characteristics:

[0100] (1) Add dimethyl succinate, ethylene glycol, and 5-furanamide isophthalic acid to an atmospheric pressure reactor (such as a conventional stirred reactor) in a molar ratio of 1:1.65:0.3, then add antimony trioxide accounting for 0.2% of the molar amount of dimethyl succinate, and then carry out an esterification reaction under an inert atmosphere and normal pressure at a reaction temperature of 140 °C until no more small molecule fractions are distilled out.

[0101] (2) Transfer the material obtained in step (1) to a vacuum reactor (such as a conventional stirred reactor), raise the reactor temperature to 236 °C, and reduce the pressure to an absolute pressure of 60 Pa to carry out a polycondensation reaction until the intrinsic viscosity of the material in the reactor no longer increases. Transfer the material in the reactor to a twin-screw extruder equipped with only a devolatilization section and carry out devolatilization treatment at 180 °C and an absolute pressure of ≤500 Pa for 20 min to obtain a polyester containing a furanamide group side chain.

[0102] (3) Then cool the polyester containing the furanamide group side chain prepared in step (2) to 135 °C, then transfer it to an SK type static mixer, and add 4,4'-bismaleimide diphenylmethane at the starting end of the static mixer. The addition amount of 4,4'-bismaleimide diphenylmethane is 20% of the molar amount of 5-furanamide isophthalic acid; the inside of the static mixer is at normal pressure and is divided into three sections. The temperature of the first section is 140 °C, the temperature of the second section is 162 °C, and the temperature of the third section is 172 °C. The material passes through the first section for 8 min, through the second section for 22 min, and through the third section for 60 min; the mixed material exported from the static mixer undergoes a chemical cross-linking reaction at 65 °C for 9 h, and after extrusion granulation, an aliphatic polyester with reversible cross-linking characteristics is obtained.

[0103] Example 5

[0104] This example provides a preparation process of an aliphatic polyester with reversible crosslinking properties:

[0105] (1) Dimethyl succinate, ethylene glycol and 5-furamide isophthalic acid are added to an atmospheric reactor (such as a conventional stirred reactor) in a molar ratio of 1:1.65:0.4. Then, magnesium oxide accounting for 0.3% of the molar amount of dimethyl succinate is added. Subsequently, an esterification reaction is carried out under an inert atmosphere and at atmospheric pressure, with the reaction temperature being 190 °C until no more small molecule fractions are distilled out;

[0106] (2) The material obtained in step (1) is transferred to a vacuum reactor (such as a conventional stirred reactor). The reactor temperature is raised to 260 °C, and the pressure is reduced to an absolute pressure of 100 Pa. A polycondensation reaction is carried out until the intrinsic viscosity of the material in the reactor no longer increases. Then, the material in the reactor is transferred to a twin-screw extruder equipped only with a devolatilization section. Under the conditions of 180 °C and an absolute pressure ≤ 500 Pa, devolatilization treatment is carried out for 20 min, thus obtaining a polyester containing furamide side groups;

[0107] (3) Then, the polyester containing furamide side groups prepared in step (2) is cooled to 140 °C, and then conveyed to an SK-type static mixer. N,N'-m-phenylene bismaleimide is added at the starting end of the static mixer, and the addition amount of N,N'-m-phenylene bismaleimide is 50% of the molar amount of 5-furamide isophthalic acid. The inside of the static mixer is at atmospheric pressure and is divided into five sections. The temperature of the first section is 145 °C, the temperature of the second section is 180 °C, the temperature of the third section is 198 °C, the temperature of the fourth section is 206 °C, and the temperature of the fifth section is 210 °C. The residence time of the material in the first section is 5 min, the residence time in the second section is 5 min, the residence time in the third section is 15 min, the residence time in the fourth section is 20 min, and the residence time in the fifth section is 30 min. The mixed material derived from the static mixer undergoes a chemical crosslinking reaction at 70 °C for 8 h, and then is extruded and pelletized to obtain an aliphatic polyester with reversible crosslinking properties.

[0108] Example 6

[0109] This example provides a preparation process of an aliphatic polyester with reversible crosslinking properties:

[0110] (1) Adipic acid, 1,4-butanediol and dimethyl 5-furamide isophthalate are added to an atmospheric reactor (such as a conventional stirred reactor) in a molar ratio of 1:1.65:0.5. Then, tetrabutyl titanate accounting for 0.2% of the molar amount of adipic acid is added. Subsequently, an esterification reaction is carried out under an inert atmosphere and at atmospheric pressure, with the reaction temperature being 180 °C until no more small molecule fractions are distilled out;

[0111] (2) Transfer the material obtained in step (1) to a vacuum reactor (such as a conventional stirred reactor), raise the reactor temperature to 250 °C, and reduce the pressure to an absolute pressure of 100 Pa. Conduct a polycondensation reaction until the intrinsic viscosity of the material in the reactor no longer increases. Then transfer the material in the reactor to a twin-screw extruder equipped with only a devolatilization section, and conduct devolatilization treatment for 20 min under the conditions of 170 °C and an absolute pressure ≤ 500 Pa, thus obtaining a polyester containing a furanamide-based side group.

[0112] (3) Then cool the polyester containing a furanamide-based side group prepared in step (2) to 130 °C, and then transfer it to an SK-type static mixer. Add 4,4'-bismaleimide diphenylmethane at the starting end of the static mixer, where the addition amount of 4,4'-bismaleimide diphenylmethane is 20% of the molar amount of 5-furanamide isophthalic acid. The inside of the static mixer is at atmospheric pressure and is divided into two sections. The temperature of the first section is 140 °C, and the temperature of the second section is 200 °C. The residence time of the material in the first section is 5 min, and the residence time in the second section is 20 min. The mixed material derived from the static mixer undergoes a chemical cross-linking reaction at 60 °C for 12 h, and then through extrusion granulation, an aliphatic polyester with reversible cross-linking characteristics is obtained.

[0113] Comparative Example 1

[0114] This comparative example provides the preparation process of an aliphatic polyester without reversible cross-linking characteristics:

[0115] (1) Add succinic acid and ethylene glycol in a molar ratio of 1:1.65 to an atmospheric-pressure reactor (such as a conventional stirred reactor), and then add tetrabutyl titanate in an amount of 0.3% of the molar amount of succinic acid. Then conduct an esterification reaction under an inert atmosphere and atmospheric pressure at a reaction temperature of 165 °C until no more small-molecule fractions are distilled out.

[0116] (2) Transfer the material obtained in step (1) to a vacuum reactor (such as a conventional stirred reactor), raise the reactor temperature to 220 °C, and reduce the pressure to an absolute pressure of 50 Pa. Conduct a polycondensation reaction until the intrinsic viscosity of the material in the reactor no longer increases. Then transfer the material in the reactor to a twin-screw extruder equipped with only a devolatilization section, and conduct devolatilization treatment for 35 min under the conditions of 150 °C and an absolute pressure ≤ 500 Pa. Through extrusion granulation, an aliphatic polyester is obtained.

[0117] Comparative Example 2

[0118] This comparative example is different from Example 1 in that in step (3) of this comparative example, a conventional stirred reactor is used for the chemical cross-linking reaction, that is: after cooling the polyester containing furamide-based side groups prepared in step (2) to 120 °C, it is transported to a conventional stirred reactor, and 4,4'-bismaleimide diphenylmethane accounting for 10% of the molar amount of 5-furamide isophthalic acid is added, and the reaction is stirred at a temperature of 142 °C for 30 min. Except for this, the other preparation processes are the same.

[0119] Comparative Example 3

[0120] This comparative example is different from Example 1 in that after the polycondensation reaction is completed in step (2) of this comparative example, the reaction material is not subjected to devolatilization treatment and directly proceeds to the preparation process of step (3).

[0121] The aliphatic polyesters prepared in the above examples and comparative examples were subjected to performance tests according to the following methods, and the test results are shown in Table 1.

[0122] (1) Whether there is an odor: Place the sample to be tested in a constant temperature and humidity chamber at 30 °C and a relative humidity of 50%, let it stand for 24 hours, then take out the sample and observe whether there is an odor and whether the odor is obvious;

[0123] (2) Melt thermal stability: Test the melt flow rate MFR of the sample according to GB / T 3682-2000;

[0124] (3) Tensile strength: Test the tensile strength according to GB / T 1040.1-2006 (tensile speed is 50 mm / min); Test 5 specimens for each sample and take the average value;

[0125] (4) Impact strength: Test the impact strength according to GB / T 1843-2008, ISO 180-2000 / Amd 2-2013; Test 5 specimens for each sample and take the average value;

[0126] (5) Thermal air aging test: Let it stand for 21 days under the conditions of 55 °C and a relative humidity of 80%.

[0127] Table 1. Performance test results of aliphatic polyesters

[0128]

[0129]

[0130] As can be seen from Table 1, compared with the aliphatic polyesters prepared in Comparative Examples 1-3, the aliphatic polyesters with reversible cross-linking properties prepared in Examples 1-6 of the present application have no odor, good color quality, low melt index MFR, high tensile strength and impact strength, and low change rate of tensile strength and impact strength after hot air aging, indicating good heat aging resistance.

[0131] By comparing Example 1 and Comparative Example 1, it can be seen that when the aliphatic polyester in Comparative Example 1 is not chemically cross-linked, it not only has a slight odor, but also has yellowing, and the melt index MFR is much higher than that of Example 1, and the mechanical strength and heat aging resistance are also significantly inferior to those of Example 1, indicating that introducing a cross-linking structure into the aliphatic polyester system is beneficial to significantly improve the mechanical strength, heat aging resistance and color quality of the aliphatic polyester.

[0132] By comparing Example 1 and Comparative Example 2, it can be seen that in Comparative Example 2, a conventional stirred reactor is used to mix the polyester and the cross-linking agent, resulting in slight yellowing of the final aliphatic polyester material, and an adverse effect on the melt thermal stability, mechanical strength and heat aging resistance of the material. This shows that the static mixer used in Example 1 can avoid the adverse effects of insufficient stirring and poor heat transfer effect of the conventional stirred reactor on the product color quality, mechanical strength and heat aging resistance.

[0133] By comparing Example 1 and Comparative Example 3, it can be seen that in step (2), the devolatilization treatment is not performed in Comparative Example 3, resulting in a slight odor and a slightly yellowish color in the final aliphatic polyester material, and the mechanical strength and heat aging resistance of the material are deteriorated. This is because when the devolatilization treatment is not performed, a large amount of small molecular monomers or monomer oligomers that are not bonded to the polymer molecular chain remain in the final obtained material, and these substances are easily oxidized and deteriorated, thereby affecting the color quality, mechanical strength and heat aging resistance.

[0134] The above description shows that the preparation method provided in the present application can significantly improve the chromaticity quality of aliphatic polyester materials, can effectively eliminate or avoid the odor of aliphatic polyester products, and has good melt thermal stability, excellent mechanical strength and good heat aging resistance.

[0135] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application and are not intended to limit it. Although the present application has been described in detail with reference to the preferred embodiments, a person of ordinary skill in the art should understand that the technical solution of the present application can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present application, which should be included in the scope of the claims of the present application.

Claims

1. An aliphatic polyester with reversible cross-linking properties, characterized in that, The aliphatic polyester with reversible crosslinking properties is formed by chemical crosslinking of a polyester containing a furoamide group side chain and a crosslinking agent containing a maleimide group; The polyester containing a furoamide group side chain is a random copolymer composed of the following repeating units I and II: wherein both R1 and R2 are C2-C 12 alkyl; The molar ratio of the repeating units I and II is (0.1 - 1):

1.

2. The aliphatic polyester according to claim 1, characterized in that, The crosslinking agent containing a maleimide group has the following structure: where n is 2, and R3 is selected from the following groups: Where m is from 2 to 20.

3. The aliphatic polyester according to claim 1, characterized in that, In the aliphatic polyester with reversible crosslinking properties, the molar ratio of the maleimide group to the furoamide group is 1:(0.1 - 100).

4. A method for preparing the aliphatic polyester with reversible cross-linking properties according to any one of claims 1-3, characterized in that, It includes the following steps: (1) Add an aliphatic dicarboxylic acid or its ester, an aliphatic diol, a monomer containing a furoamide group, and a catalyst into a reactor for an esterification reaction; (2) Raise the temperature of the reactor for a polycondensation reaction to obtain a polyester containing a furoamide group side chain; (3) Mix the polyester containing a furoamide group side chain and the crosslinking agent containing a maleimide group evenly, and then carry out a chemical crosslinking reaction to obtain an aliphatic polyester with reversible crosslinking properties; The monomer containing a furoamide group has the following structure: where R4 is H or an alkyl group with C1 - C3.

5. The method for preparing the aliphatic polyester according to claim 4, characterized in that, The aliphatic dicarboxylic acid or its ester is a C2-C 12 alkane saturated dicarboxylic acid or its ester; The aliphatic diol is a C2-C 12 alkane-saturated diol.

6. The method for preparing the aliphatic polyester according to claim 4, characterized in that, The aliphatic dicarboxylic acid or its ester is selected from one or more of oxalic acid, malonic acid, succinic acid, dimethyl succinate, diethyl succinate, glutaric acid, dimethyl glutarate, diethyl glutarate, adipic acid, dimethyl adipate, diethyl adipate; The aliphatic diol is selected from one or more of ethylene glycol, 1,2 - propanediol, 1,3 - propanediol, 1,4 - butanediol, 1,5 - pentanediol, 1,6 - hexanediol.

7. The method for preparing the aliphatic polyester according to claim 4, characterized in that, The molar ratio of the aliphatic dicarboxylic acid or its ester, the aliphatic diol, and the monomer containing a furoamide group is 1:(1 - 4):(0.1 - 1).

8. The method for preparing the aliphatic polyester according to claim 4, characterized in that, The catalyst is selected from one or more of tetrabutyl titanate, antimony trioxide, magnesium oxide, zinc acetate, sodium acetate, potassium acetate, nickel acetate, manganese acetate, cobalt acetate, magnesium acetate, silicon dioxide.

9. The method for preparing the aliphatic polyester according to claim 4, characterized in that, The addition amount of the catalyst is 0.01% - 1% of the molar amount of the aliphatic dicarboxylic acid or its ester.

10. The method for preparing an aliphatic polyester according to claim 4, characterized in that, The reaction temperature of step (1) is 130 - 190 °C, and the reaction temperature of step (2) is 200 - 260 °C.

11. The method for preparing an aliphatic polyester according to claim 4, characterized in that, The polyester containing a furoamide group side chain and the crosslinking agent containing a maleimide group are mixed in a static mixer.

12. The method for preparing an aliphatic polyester according to claim 11, characterized in that, The static mixer includes at least two temperature gradient intervals. The temperature range of the first section is 120 - 150 °C, and the temperature range of the second section is 150 - 210 °C; the time for the mixed material to pass through each temperature gradient interval is 5 - 60 min.

13. The method for preparing an aliphatic polyester according to claim 4, characterized in that, The chemical crosslinking reaction is carried out at 50 - 80 °C, and the reaction time is 2 - 20 h.

14. The method for preparing an aliphatic polyester according to claim 4, characterized in that, In step (2), after the polycondensation reaction is completed, the reaction product is further subjected to devolatilization treatment; The devolatilization treatment is carried out using a twin - screw extruder equipped with only a devolatilization section. The devolatilization treatment conditions are: treating at 150 - 180 °C and an absolute pressure ≤ 500 Pa for 20 - 60 min.

15. Use of the aliphatic polyester having reversible crosslinking properties according to any one of claims 1 - 3 in the fields of biodegradable plastic packaging, film materials, sustained release materials, and biomedical materials.

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