Low melt index poly(butylene oxalate) and method of making and use thereof

Abstract

The application discloses low-melting-index polybutylene oxalate and a preparation method and application thereof. The preparation method comprises the following steps: taking oxalate and 1,4-butanediol as raw materials, adding a micro-crosslinking agent, and through ester exchange reaction and polycondensation reaction under the action of intrinsic catalyst titanium oxalate and polycondensation catalyst to obtain low-melting-index polybutylene oxalate. The intrinsic catalyst titanium oxalate and the oxalate can be subjected to hydrogen bond coordination, the ester exchange reaction activity of the oxalate bond can be significantly improved, the production and removal rate of by-products methanol or ethanol in the ester exchange process can be greatly improved, and the esterification efficiency can be significantly improved; meanwhile, the addition of the micro-crosslinking agent can significantly reduce the melt index of the polybutylene oxalate; the polybutylene oxalate prepared by the application has good crystallization capacity, mechanical properties and controllable degradation rate, and has a wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of polymer material synthesis technology, and in particular relates to a polybutylene oxalate with low melt index, high mechanical strength and high hydrolysis rate that is easy to process, as well as its preparation method and application. Background Technology

[0002] Adhering to the principle that polymer materials are generated from CO2 and ultimately produce CO2, an increasing number of researchers are focusing on novel polymer monomers derived from CO2. Among these, the electrocatalytic reduction of CO2 to synthesize oxalic acid and the coal-to-ethylene glycol process for preparing the intermediate dimethyl oxalate provide new pathways for low-cost oxalate-based polymer monomers. As a linear aliphatic oxalate, poly(ethylene oxalate) has mechanical properties that meet market demands, but its low crystallinity and rapid degradation rate pose a risk of accidental degradation during shelf life. The introduction of long-chain diols has mitigated the accidental degradation of poly(hexanediol oxalate) and poly(octyl glycol oxalate), but they suffer from low strength and poor mechanical properties. Therefore, the structure of poly(butylene oxalate), which combines mechanical properties with degradation capability, has attracted widespread attention.

[0003] Patent CN102219891A discloses a method for preparing polybutylene oxalate, wherein the ratio of diethyl oxalate to butanediol is 1:1 to 1:3, oxalic acid is preferred as the catalyst, and the reaction is carried out at 80 to 170°C under N2 protection for 0.5 to 5 hours, followed by a reaction at 110 to 180°C under a vacuum of 200 to 500 Pa for 3 to 8 hours to obtain polybutylene oxalate with an intrinsic viscosity of only 0.05 to 0.45 dL / g. The low intrinsic viscosity makes it unsuitable for material application requirements.

[0004] Patent CN115677988A relates to an in-situ preparation method of polybutylene oxalate. Under the co-catalysis of titanium-sulfonic acid composite catalyst and second-type metal oxide, polybutylene oxalate is obtained through three steps: transesterification, pre-condensation and final condensation. The target product has an intrinsic viscosity of 1.4-1.8 dL / g and a weight-average molecular weight of 130-180 kDa. However, this invention requires precise control of the raw material molar ratio to 1:1, which can easily lead to a significant decrease in the molecular weight and performance deviation of the product due to the imbalance of the feed ratio.

[0005] During melt polycondensation, dimethyl oxalate or diethyl oxalate suffers from poor thermal stability and easy degradation upon heating, leading to thermal degradation in the later stages of polycondensation. This results in a decrease in molecular weight, an increase in the content of terminal and free carboxyl groups, and an increase in the acid and hydroxyl values ​​of the product. This not only reduces storage stability but also lowers mechanical properties. Furthermore, PBS itself has a high melt index, requiring chain extension or solid-state polycondensation in industry to further reduce the melt index of PBS polymerized granules to meet PBS processing requirements. Similar to PBS, due to its relatively low melting point (107°C) and the characteristic of being entirely aliphatic, the melt index of high molecular weight polybutylene oxalate obtained by conventional polymerization is excessively high, reaching more than five times that of PBAT with a similar molecular weight. This causes the melt to flow too quickly at high temperatures, which is mismatched with the melt index of currently widely used materials such as PBAT or PBS, resulting in a narrow processing window and stringent requirements.

[0006] Therefore, finding novel catalysts that enhance the thermal stability of oxalate-based polyesters, prevent thermal degradation during melt polycondensation, and significantly reduce their melt index to meet industrial requirements has become a key challenge in the synthesis of high-quality polybutylene oxalate. Summary of the Invention

[0007] The main objective of this invention is to provide a novel intrinsic catalyst for the preparation of polybutylene oxalate, as well as low melt index polybutylene oxalate and its preparation method, to overcome the shortcomings of the prior art.

[0008] Another object of the present invention is to provide the application of the low melt index polybutylene oxalate.

[0009] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0010] This invention provides a method for preparing low melt index polybutylene oxalate, comprising:

[0011] Using oxalate and 1,4-butanediol as raw materials, a micro-crosslinking agent is added, and under the action of intrinsic catalyst titanium oxalate and polycondensation catalyst, low melt index polybutylene oxalate is obtained through transesterification and polycondensation reactions.

[0012] In some embodiments, the intrinsic catalyst titanium oxalate is prepared by the following steps: under nitrogen protection at room temperature, titanium metal is used as the anode, placed in an electrolyte containing oxalic acid, and a constant current of 20-50 mA is passed through it for more than 60 minutes to obtain the intrinsic catalyst titanium oxalate.

[0013] This invention also provides a low melt index polybutylene oxalate prepared by the above preparation method, the structural formula of which is shown in formula (1):

[0014] ;

[0015] Wherein, R1 is selected from at least one structural unit of polyol compounds, and x, y, and n are all integers, x=1~20, y=1~3, and n=20~100.

[0016] In some embodiments, the polyol compound includes at least one of glycerol, pentaerythritol, 1,2,6-hexanetriol, trimethylolpropane, and trimethylolethane.

[0017] This invention also provides applications of the aforementioned low melt index polybutylene oxalate in fields such as agricultural mulch films, artificial seed coatings, drug sustained-release carriers, human implant components, or transient electronic devices.

[0018] Compared with the prior art, the beneficial effects of the present invention include:

[0019] 1) The method for preparing low melt index polybutylene oxalate provided by this invention employs intrinsic catalyst titanium oxalate to undergo hydrogen bonding coordination with oxalate ester, which can significantly improve the transesterification reactivity of oxalate ester bonds, thereby greatly increasing the generation and removal rate of byproducts methanol or ethanol during transesterification and significantly improving esterification efficiency. At the same time, the addition of micro-crosslinking agent significantly reduces the melt index of polybutylene oxalate, making it compatible with currently widely used biodegradable materials such as PBAT or PBS, providing a new material for truly achieving fully natural degradation materials. This solves the problem of excessively fast melt flow rate at high temperatures, which is incompatible with the flowability of widely used biodegradable materials such as PBAT or PBS, and broadens the processing window.

[0020] 2) The low melt index polybutylene oxalate prepared by this invention has higher molecular weight and mechanical properties, good crystallization ability, biocompatibility and degradation ability, and has broad application prospects in agricultural mulch films, artificial seed coatings, drug sustained release carriers, human implant components and transient electronic devices. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is the infrared FTIR spectrum of the intrinsic catalyst titanium oxalate prepared by electrocatalysis in Example 1 of this invention;

[0023] Figure 2The NMR of polybutylene oxalate prepared using titanium oxalate in Example 2 of this invention is shown. 1 H-NMR spectrum;

[0024] Figure 3 This is a DSC image of polybutylene oxalate prepared using titanium oxalate in Example 2 of the present invention.

[0025] Figure 4 This is a stress-strain diagram of polybutylene oxalate prepared using titanium oxalate in Example 2 of the present invention.

[0026] Figure 5 This is a hydrolysis mass loss diagram of polybutylene oxalate prepared using titanium oxalate in Example 2 of the present invention. Detailed Implementation

[0027] In view of the problems existing in the prior art, after long-term research and a large number of experiments, the inventors of this case propose a method for preparing low melt index polybutylene oxalate. An intrinsic catalyst, titanium oxalate, is synthesized by electrocatalysis. Under the action of a small amount of micro-crosslinking agent, the polybutylene oxalate has a high molecular weight, low acid value and hydroxyl value, and excellent mechanical properties and degradation performance. The melt index at 190℃ is 5g / 10min-20g / 10min, which is compatible with the current market bio-based plastic raw materials such as PBAT and PBS. The amount of polybutylene oxalate can be adjusted to meet the requirements of different application scenarios for the stability and degradation rate of degradable materials.

[0028] To facilitate understanding of the present invention, it will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to make the disclosure of the present invention more thorough and complete.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments or examples only and is not intended to be limiting of the invention.

[0030] As one aspect of the technical solution of the present invention, it relates to a novel intrinsic catalyst for the preparation of polybutylene oxalate, that is, the application of titanium oxalate as a catalyst in the preparation of polybutylene oxalate.

[0031] As another aspect of the technical solution of the present invention, a method for preparing a low melt index polybutylene oxalate includes: using oxalate and 1,4-butanediol as raw materials, adding a micro-crosslinking agent, and obtaining a low melt index polybutylene oxalate through transesterification and polycondensation reactions under the action of intrinsic catalyst titanium oxalate and polycondensation catalyst.

[0032] In some embodiments, the method for preparing the low melt index polybutylene oxalate includes:

[0033] Under a protective atmosphere, a first mixed reaction system containing oxalate, 1,4-butanediol, a micro-crosslinking agent and an intrinsic catalyst titanium oxalate is subjected to transesterification to obtain a micro-crosslinked polyester oligomer.

[0034] Under vacuum conditions, a second mixed reaction system containing the micro-crosslinked polyester oligomer, a polycondensation catalyst, an antioxidant, and a heat stabilizer is subjected to a polycondensation reaction to obtain low melt index polybutylene oxalate.

[0035] The main inventive concept of this invention lies in using oxalate esters such as dimethyl oxalate or diethyl oxalate and 1,4-butanediol as raw materials, adding a micro-crosslinking agent, and obtaining polybutylene oxalate through transesterification and polycondensation reactions under the action of intrinsic catalyst titanium oxalate and a polycondensation catalyst. This invention utilizes intrinsic catalyst titanium oxalate to achieve hydrogen bonding coordination with oxalate esters, which significantly enhances the transesterification reactivity of oxalate bonds, thereby greatly increasing the generation and removal rates of byproducts such as methanol or ethanol during transesterification, and significantly improving esterification efficiency.

[0036] In some embodiments, the oxalate ester may be one or more of dimethyl oxalate, diethyl oxalate, etc., but is not limited to these.

[0037] In some embodiments, the intrinsic catalyst titanium oxalate and the microcrosslinking agent are added to the reaction system prior to the transesterification reaction.

[0038] In some preferred embodiments, the intrinsic catalyst titanium oxalate is prepared by the following steps: under nitrogen protection at room temperature, titanium metal is used as the anode, placed in an electrolyte containing oxalic acid, and a constant current of 20-50 mA is passed through it for more than 60 minutes to obtain the intrinsic catalyst titanium oxalate.

[0039] In some more specific preferred embodiments, the intrinsic catalyst titanium oxalate suitable for polybutylene oxalate is prepared by the following steps:

[0040] S1: Under nitrogen protection at room temperature, titanium metal is used as the anode and placed in oxalic acid electrolyte and a constant current is passed through it for more than 60 minutes. A light yellow solid is precipitated in the electrolyte.

[0041] S2: Under nitrogen protection at room temperature, the light yellow solid is filtered and then eluted with ethanol 3-5 times to remove oxalic acid. After evaporation and crystallization, yellow prismatic crystals are obtained, which are the intrinsic catalyst titanium oxalate.

[0042] Specifically, the chemical reaction formula of the intrinsic catalyst is as follows:

[0043] .

[0044] In some implementation schemes, the molar ratio of the oxalate ester to 1,4-butanediol during feeding is 1:1.2 to 1:1.5.

[0045] In some embodiments, the microcrosslinking agent comprises a polyol compound, preferably including any one or a combination of glycerol, pentapentaerythritol, 1,2,6-hexanetriol, trimethylolpropane, and trimethylolethane, but not limited thereto. The addition of the microcrosslinking agent in this invention significantly reduces the melt index of polybutylene oxalate, making it compatible with currently widely used biodegradable materials such as PBAT or PBS. This provides a new material for truly achieving fully biodegradable materials, solving the problem of excessively fast melt flow at high temperatures and mismatch with the flowability of widely used biodegradable materials such as PBAT or PBS, thus broadening the processing window.

[0046] In some embodiments, the amount of the microcrosslinking agent is 1% to 3% of the molar fraction of the oxalate (such as dimethyl oxalate or diethyl oxalate).

[0047] In some embodiments, the molar ratio of the microcrosslinking agent to 1,4-butanediol is 1:40 to 1:150.

[0048] In some implementation schemes, the amount of titanium oxalate used as an intrinsic catalyst is 0.2‰ to 1.5‰ of the mass fraction of the oxalate ester (such as dimethyl oxalate or diethyl oxalate).

[0049] In some embodiments, the transesterification reaction is carried out at a temperature of 130°C to 150°C for a duration of 120 min to 180 min.

[0050] In some embodiments, the preparation method includes adding intrinsic catalyst titanium oxalate and microcrosslinking agent to the reaction system prior to the transesterification reaction.

[0051] In some more preferred embodiments, the preparation method includes: before the transesterification reaction, placing oxalate (such as dimethyl oxalate or diethyl oxalate), 1,4-butanediol, intrinsic catalyst titanium oxalate, and micro-crosslinking agent together in a reaction chamber (such as a reaction vessel), heating to 130°C~150°C within 30 minutes and continuously stirring mechanically to carry out the transesterification reaction. The timing is set at the point where one drop of small-molecule methanol or ethanol is collected, and the endpoint of the transesterification reaction is defined as when the mass of collected methanol or ethanol is more than 95% of the theoretical value. The transesterification reaction time is 120 minutes~180 minutes.

[0052] In some embodiments, the polycondensation catalyst is an organometallic compound. This invention uses a combination of organometallic compounds such as antimony-based catalysts, titanium-based catalysts, tin-based catalysts, and germanium-based catalysts as polycondensation agents, which significantly improves the thermal stability of polybutylene oxalate, reduces the content of free carboxyl and hydroxyl groups, improves stability, avoids the degradation of polybutylene oxalate in melt polycondensation reaction, and has higher molecular weight and mechanical properties, good crystallization ability, biocompatibility and degradation ability.

[0053] Furthermore, the antimony-based catalyst can be any one or a combination of antimony trioxide, antimony acetate, antimony glycol, triethyl antimonate, etc., but is not limited to these.

[0054] Furthermore, the titanium-based catalyst can be any one or a combination of titanium isopropoxide, tetrabutyl titanate, and tetraethyl titanate, but is not limited to these.

[0055] Furthermore, the tin-based catalyst may be any one or a combination of stannous chloride, stannous oxalate, dibutyltin oxide, stannous octanoate, and stannous trifluoromethanesulfonate, but is not limited thereto.

[0056] Furthermore, the germanium-based catalyst may be any one or a combination of germanium dioxide, germanium chloride, triethylgermanate, tetraethylgermanate, and tetrabutylgermanate, but is not limited thereto.

[0057] In some embodiments, the amount of the polycondensation catalyst is 0.5‰ to 2‰ of the mass fraction of the oxalate (such as dimethyl oxalate or diethyl oxalate).

[0058] In some embodiments, the amount of the antioxidant is 1‰ to 2‰ of the molar mass of the oxalate (such as dimethyl oxalate or diethyl oxalate).

[0059] In some preferred embodiments, the antioxidant is selected from phenolic antioxidants, wherein the phenolic antioxidant may include at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 2,6-di-tert-butyl-4-cresol, 2,2-methylenebis(4-methyl-6-tert-butylphenol), etc., but is not limited thereto.

[0060] In some embodiments, the heat stabilizer is selected from phosphorus-based stabilizers, which may include at least one of phosphorous acid, diphenyl phosphate, triphenyl phosphate, and triphenyl phosphite, but are not limited thereto.

[0061] In some embodiments, the amount of heat stabilizer is 1‰ to 5‰ of the molar mass of the oxalate (such as dimethyl oxalate or diethyl oxalate).

[0062] In some embodiments, the preparation method includes adding a polycondensation catalyst, an antioxidant, and a heat stabilizer before carrying out the polycondensation reaction.

[0063] In some preferred embodiments, the temperature of the polycondensation reaction is 190℃~210℃, the pressure in the early stage of polycondensation is 200~1000Pa, and the time in the early stage of polycondensation is 60min~90min; the pressure in the middle stage of polycondensation is 50~200Pa, and the time in the middle stage of polycondensation is 30min~60min; the pressure in the later stage of polycondensation is below 10Pa, and the time in the later stage of polycondensation is 60min~90min.

[0064] As one aspect of the technical solution of the present invention, it involves the low melt index polybutylene oxalate prepared by the aforementioned preparation method.

[0065] Furthermore, the structural formula of the low melt index polybutylene oxalate is shown in formula (1):

[0066] ;

[0067] Wherein, R1 is selected from at least one structural unit of polyol compounds, and x, y, and n are all integers, x=1~20, y=1~3, and n=20~100.

[0068] In some embodiments, the polyol compound includes at least one of glycerol, pentaerythritol, 1,2,6-hexanetriol, trimethylolpropane, and trimethylolethane.

[0069] In some embodiments, the low melt index polybutylene oxalate has an intrinsic viscosity of 1.4 dL / g to 1.7 dL / g, a weight-average molecular weight of 120,000 g / mol to 180,000 g / mol, an acid value of 15 mol / t to 25 mol / t, a hydroxyl value of 30 KOH mg to 40 KOH mg / g, a melt index of 5 g / 10 min to 20 g / 10 min at 190°C, and an initial thermal decomposition temperature of 310°C to 340°C.

[0070] In some embodiments, the low melt index polybutylene oxalate has a glass transition temperature of -23°C to 21°C, a melting point of 104°C to 106°C, an elastic modulus of 500 to 550 MPa, a tensile strength of 50 MPa to 60 MPa, and an elongation at break of 300% to 500%. The water contact angle of the polybutylene oxalate film prepared by hot pressing is 30° to 40°, the CO2 transmittance is 1 barrer to 3 barrer, and the O2 transmittance is 2.5 barrer to 4 barrer. The mass loss after 35 days of hydrolysis is 80% to 95%, and the remaining mass after 35 days of seawater degradation is 40% to 60%.

[0071] As one aspect of the technical solution of the present invention, it relates to the application of the aforementioned low melt index polybutylene oxalate.

[0072] Furthermore, the low melt index polybutylene oxalate has good crystallization ability and mechanical properties as well as a controllable degradation rate, and has broad application prospects in agricultural mulch films, artificial seed coatings, drug sustained-release carriers, human implant components, and transient electronic devices.

[0073] To facilitate understanding of the present invention, it will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to make the disclosure of the present invention more thorough and complete.

[0074] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments or examples only and is not intended to be limiting of the invention.

[0075] The low melt index polybutylene oxalate will be further described below through specific embodiments.

[0076] In the examples, nuclear magnetic resonance hydrogen spectrum (NMR) 1H-NMR was measured on a Bruker 400 AVANCE Ⅲ Spectrometer instrument at a frequency of 400 MHz, using trifluoroacetic acid (TFA) as the solvent.

[0077] In the examples, gel permeation chromatography (GPC) (Agilent PL-GPC220) was performed at 40°C using chromatographic grade chloroform as the eluent at a flow rate of 1.0 mL / min. -1 Select polystyrene as the standard for molecular weight calibration.

[0078] In this embodiment, the melt flow rate was measured using an electric melt flow rate meter of model YK-3651A. According to the test standard ASTM D 1238, the mass of melt flowed within 10 minutes at 190°C and 2.16 kg pressure was measured, and the unit was g / 10 min.

[0079] In the example, the acid value was measured by volumetric titration. The sample was dissolved under reflux in a phenol-chloroform mixed solvent (volume ratio 2:3), cooled, and then titrated with a potassium hydroxide-ethanol standard titrant (c(KOH) = 0.05 mol / L) using a 0.1% bromophenol blue ethanol solution as an indicator. The content of terminal carboxyl groups was calculated based on the volume of standard titrant consumed.

[0080] In the example, the hydroxyl value was measured by volumetric titration. The sample was dissolved under reflux in an acetylated mixed solution, and titrated with a 1 mol / L sodium hydroxide standard solution while hot, using phenolphthalein as an indicator. The hydroxyl content was calculated based on the volume of standard titration solution consumed.

[0081] In this embodiment, thermal analysis was performed using differential scanning calorimetry (Mettler Toledo DSC) at a heating rate of 10 °C / min in an N2 atmosphere, with a temperature range of -50 °C to 150 °C.

[0082] In this embodiment, the mechanical properties were tested using an Instron 5567 universal testing machine. The sample dimensions were 35.0 mm in length, 2.0 mm in width, and 1.0 mm in thickness, and the tensile speed was 20 mm / min.

[0083] In this embodiment, the water contact angle (CA) was measured at room temperature and normal pressure using a WCA analyzer OCA20 (Dataphysics Ltd., Germany).

[0084] In this embodiment, the barrier performance of O2 and CO2 was tested using a Labthink VAC-V2. O2 and CO2 were used as gas sources, and measurements were conducted at a temperature of 23°C and a humidity of 50% RH. The sample size was Φ=97mm, and the permeable area was 38.5cm².2 .

[0085] In the example, phosphate buffer solution was used as the degradation solvent, and hydrolysis degradation test was carried out in a constant temperature water shaker at 37°C. The sample was 10 mm long, 10 mm wide, and 0.5 mm thick.

[0086] In the example, 35g of sea salt was used for calibration in a 1L volumetric flask, and seawater degradation tests were conducted at 8-18℃. The sample was 10mm long, 10mm wide, and 0.5mm thick.

[0087] Example 1 (Preparation of intrinsic catalyst titanium oxalate)

[0088] Under nitrogen protection at 25°C, titanium metal was used as the anode, and a 0.5 mol / L oxalic acid-ethanol solution was added. The redox potential was set to 1.00 V, and a constant current of 20 mA was applied for 60 min. A pale yellow solid precipitated in the ethanol solution. After filtering the pale yellow solid, the solid was eluted five times with ethanol to remove the oxalic acid present in the solid. The temperature was raised to 15°C above the boiling point of ethanol, and excess ethanol was evaporated. The solution was then allowed to cool naturally to room temperature (25°C) to obtain yellow prismatic crystals, which is the intrinsic catalyst titanium oxalate. The FTIR structure is shown below. Figure 1 .

[0089] Comparative Example 1

[0090] Add 3 ml of TiCl4 hydrochloric acid solution (molar ratio 1:2) dropwise to a 5% w / v oxalic acid aqueous solution and stir continuously for 60 min. Gradually add the reaction solution to an excess of cold saturated ethanol solution and stir continuously for 30 min. Let it stand for 5 h to allow it to settle completely. Wash the solution 3-5 times with ethanol by vacuum filtration and dry it in a vacuum oven at 50℃ for 5 h to obtain a solid powder, which is titanium oxalate.

[0091] Example 2 (Preparation of polybutylene oxalate)

[0092] Dimethyl oxalate and 1,4-butanediol were added to the reactor at molar amounts of 0.30 mol and 0.36 mol, respectively. Then, the intrinsic catalyst titanium oxalate (0.3‰ of the total molar mass of all acid raw materials) prepared in Example 1 and the micro-crosslinking agent pentaerythritol (1% of the total molar mass of all acid raw materials) were added. Under nitrogen protection, the temperature was raised to 140 °C within 30 min for transesterification reaction. The mechanical stirring speed was 140 r. After 2 h of reaction, micro-crosslinked polyester oligomers were obtained.

[0093] Under nitrogen protection and continuous stirring, tetrabutyl germanate (1.2‰ of the total molar mass of all acid raw materials), triphenyl phosphite (1.5‰ of the total molar mass of all acid raw materials), and octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (2‰ of the total molar mass of all acid raw materials) were added as a polycondensation catalyst. The temperature was gradually increased to 195℃, and the vacuum was gradually reduced to 200 Pa for 90 min. The vacuum was then further reduced to 50 Pa for 60 min, and the vacuum was further reduced to below 10 Pa for 60 min. The target polybutylene oxalate was obtained by discharging the product under nitrogen protection.

[0094] NMR spectroscopy of the polybutylene oxalate prepared in this embodiment 1 H-NMR such as Figure 2 As shown, the structure of the obtained polybutylene oxalate is clear; the DSC curve of the polybutylene oxalate is as follows. Figure 3 As shown, polybutylene oxalate has a glass transition temperature of -23.2℃ and a melting point of 104.4℃; the stress-strain curve of this polybutylene oxalate is shown below. Figure 4 As shown, the elastic modulus is 528 MPa, the tensile strength is 53.4 MPa, and the elongation at break is 325%.

[0095] The polybutylene oxalate prepared in this embodiment has the following properties: intrinsic viscosity 1.43 dL / g, weight-average molecular weight 123000 g / mol, acid value 24 mol / t, hydroxyl value 38 KOH mg / g, melt index 11 g / 10 min, initial thermal decomposition temperature 332℃, water contact angle 32°, CO2 permeability 1.63 barrer, O2 permeability 3.12 barrer, 90% mass loss after 35 days of degradation in phosphate buffer, and 48% mass loss after 35 days of degradation in seawater. Figure 5 As shown.

[0096] Comparative Example 2

[0097] Dimethyl oxalate and 1,4-butanediol were added to the reactor at molar amounts of 0.30 mol and 0.36 mol, respectively. Then, pentaerythritol (1% of the total molar mass of all acid raw materials) was added as a micro-crosslinking agent. Under nitrogen protection, the temperature was raised to 140 °C within 30 min for esterification. The mechanical stirring speed was 140 r, and the reaction was carried out for 3 h to obtain polyester oligomers.

[0098] Under nitrogen protection and continuous stirring, tetrabutyl germanate (1.2‰ of the total molar mass of all acid raw materials), triphenyl phosphite (1.5‰ of the total molar mass of all acid raw materials), and octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (0.5‰ of the total molar mass of all acid raw materials) were added as a polycondensation catalyst. The temperature was gradually increased to 195℃, and the vacuum was gradually reduced to 200 Pa for 90 min. The vacuum was then further reduced to 50 Pa for 60 min, and the vacuum was further reduced to below 10 Pa for 60 min. The target polybutylene oxalate was obtained by discharging the product under nitrogen protection.

[0099] The polybutylene oxalate prepared in this comparative example has the following intrinsic viscosity: 0.83 dL / g; weight-average molecular weight: 86000 g / mol; acid value: 30 mol / t; hydroxyl value: 52 KOH mg / g; melt index: 28 g / 10 min; glass transition temperature: -22.8℃; melting point: 105.7℃; initial thermal decomposition temperature: 320℃; elastic modulus: 525 MPa; tensile strength: 38.2 MPa; elongation at break: 185%; water contact angle of the film: 35°; CO2 permeability: 1.78 barrer; O2 permeability: 3.84 barrer; mass loss after 35 days of degradation in phosphate buffer: 95%; mass loss after 35 days of degradation in seawater: 67%.

[0100] Comparative Example 3

[0101] Dimethyl oxalate and 1,4-butanediol were added to the reactor at molar amounts of 0.30 mol and 0.36 mol, respectively. Then, titanium oxalate (0.3‰ of the total molar mass of all acid raw materials) prepared in Comparative Example 1 and pentaerythritol (1% of the total molar mass of all acid raw materials) were added. Under nitrogen protection, the temperature was raised to 140 °C within 30 min for esterification. The mechanical stirring speed was 140 r, and the reaction was carried out for 3 h to obtain polyester oligomers.

[0102] Under nitrogen protection and continuous stirring, tetrabutyl germanate (1.2‰ of the total molar mass of all acid raw materials), triphenyl phosphite (1.5‰ of the total molar mass of all acid raw materials), and octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (0.5‰ of the total molar mass of all acid raw materials) were added as a polycondensation catalyst. The temperature was gradually increased to 195℃, and the vacuum was gradually reduced to 200 Pa for 90 min. The vacuum was then further reduced to 50 Pa for 60 min, and the vacuum was further reduced to below 10 Pa for 60 min. The target polybutylene oxalate was obtained by discharging the product under nitrogen protection.

[0103] The polybutylene oxalate prepared in this comparative example has the following intrinsic viscosity: 0.74 dL / g; weight-average molecular weight: 78000 g / mol; acid value: 35 mol / t; hydroxyl value: 54 KOH mg / g; melt index: 38 g / 10 min; glass transition temperature: -23.6℃; melting point: 106.8℃; initial thermal decomposition temperature: 292℃; elastic modulus: 482 MPa; tensile strength: 22 MPa; elongation at break: 167%; water contact angle of the film: 35°; CO2 permeability: 2.35 barrer; O2 permeability: 3.87 barrer; mass loss after 35 days of degradation in phosphate buffer: 94%; mass loss after 35 days of degradation in seawater: 69%.

[0104] Comparative Example 4

[0105] Dimethyl oxalate and 1,4-butanediol were added to the reactor at molar amounts of 0.30 mol and 0.36 mol, respectively. Under nitrogen protection, the temperature was raised to 140 °C within 30 min for esterification. The mechanical stirring speed was 140 r, and the reaction was carried out for 6 h to obtain polyester oligomers.

[0106] Under nitrogen protection and continuous stirring, tetrabutyl germanate (1.2‰ of the total molar mass of all acid raw materials), triphenyl phosphite (1.5‰ of the total molar mass of all acid raw materials), and octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (0.5‰ of the total molar mass of all acid raw materials) were added as a polycondensation catalyst. The temperature was gradually increased to 195℃, and the vacuum was gradually reduced to 200 Pa for 120 min. The vacuum was then further reduced to 50 Pa for 120 min, and the reaction was continued for 240 min. The target polybutylene oxalate was obtained by discharging the product under nitrogen protection.

[0107] The polybutylene oxalate prepared in this comparative example has the following intrinsic viscosity: 0.54 dL / g; weight-average molecular weight: 52000 g / mol; acid value: 32 mol / t; hydroxyl value: 44 KOH mg / g; melt index: 75 g / 10 min; glass transition temperature: -21.2℃; melting point: 105.8℃; initial thermal decomposition temperature: 280℃; elastic modulus: 454 MPa; tensile strength: 55.4 MPa; elongation at break: 342%; water contact angle of the film: 35°; CO2 permeability: 1.77 barrer; O2 permeability: 3.45 barrer; mass loss after 35 days of degradation in phosphate buffer: 87%; mass loss after 35 days of degradation in seawater: 56%.

[0108] Comparative Example 5

[0109] Dimethyl oxalate and 1,4-butanediol were added to the reactor at molar amounts of 0.30 mol and 0.36 mol, respectively. Then, the intrinsic catalyst titanium oxalate (0.3‰ of the total molar mass of all acid raw materials) prepared in Example 1 and the micro-crosslinking agent pentaerythritol (1% of the total molar mass of all acid raw materials) were added. Under nitrogen protection, the temperature was raised to 140 °C within 30 min for transesterification reaction. The mechanical stirring speed was 140 r. After 3 h of reaction, micro-crosslinked polyester oligomers were obtained.

[0110] Under nitrogen protection and continuous stirring, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (1‰ of the total molar mass of all acid feedstocks), triphenyl phosphite (1.5‰ of the total molar mass of all acid feedstocks), and β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (2‰ of the total molar mass of all acid feedstocks) were added as an organic base polycondensation catalyst. The temperature was gradually increased to 195℃, and the vacuum was gradually reduced to 200 Pa for 90 min. The vacuum was then further reduced to 50 Pa for 60 min, and the vacuum was further reduced to below 10 Pa for 60 min. The target polybutylene oxalate was obtained by discharging the product under nitrogen protection.

[0111] The polybutylene oxalate prepared in this comparative example has the following intrinsic viscosity: 0.53 dL / g; weight-average molecular weight: 62000 g / mol; acid value: 48 mol / t; hydroxyl value: 64 KOH mg / g; melt index: 55 g / 10 min; glass transition temperature: -23.2℃; melting point: 106.3℃; initial thermal decomposition temperature: 288℃; elastic modulus: 475 MPa; tensile strength: 21 MPa; elongation at break: 179%; water contact angle of the film: 36°; CO2 permeability: 1.96 barrer; O2 permeability: 3.28 barrer; mass loss after 35 days of degradation in phosphate buffer: 87%; mass loss after 35 days of degradation in seawater: 58%.

[0112] Example 3

[0113] Dimethyl oxalate and 1,4-butanediol were added to the reactor at molar amounts of 0.30 mol and 0.36 mol, respectively. Then, the intrinsic catalyst titanium oxalate (1‰ of the total molar mass of all acid feedstocks) prepared in Example 1 and the micro-crosslinking agent trimethylolpropane (1.5% of the total molar mass of all acid feedstocks) were added. Under nitrogen protection, the temperature was raised to 150 °C within 30 min for transesterification reaction. The mechanical stirring speed was 140 r, and the reaction was carried out for 2.5 h to obtain micro-crosslinked polyester oligomers.

[0114] Under nitrogen protection and continuous stirring, stannous trifluoromethanesulfonate (1.5‰ of the total molar mass of all acid raw materials), triphenyl phosphate (3‰ of the total molar mass of all acid raw materials), and 2,6-di-tert-butyl-4-cresol (2‰ of the total molar mass of all acid raw materials) were added as a polycondensation catalyst. The temperature was gradually increased to 210℃, and the vacuum was gradually reduced to 200 Pa for 60 min. The vacuum was then further reduced to 50 Pa for 30 min, and the vacuum was further reduced to below 10 Pa for 60 min. The target polybutylene oxalate was obtained by discharging the product under nitrogen protection.

[0115] The polybutylene oxalate prepared in this embodiment has the following intrinsic viscosity: 1.62 dL / g; weight-average molecular weight: 158,000 g / mol; acid value: 17 mol / t; hydroxyl value: 32 KOH mg / g; melt index: 7 g / 10 min; glass transition temperature: -22.9℃; melting point: 105.4℃; initial thermal decomposition temperature: 338℃; elastic modulus: 539 MPa; tensile strength: 54.8 MPa; elongation at break: 375%; water contact angle of the film: 37°; CO2 permeability: 1.34 barrer; O2 permeability: 2.92 barrer; mass loss after 35 days of degradation in phosphate buffer: 84%; and mass loss after 35 days of degradation in seawater: 49%.

[0116] Example 4

[0117] Diethyl oxalate and 1,4-butanediol were added to the reactor at molar amounts of 0.30 mol and 0.36 mol, respectively. Then, the intrinsic catalyst titanium oxalate (1.5‰ of the total molar mass of all acid raw materials) prepared in Example 1 and the micro-crosslinking agent glycerol (1.5% of the total molar mass of all acid raw materials) were added. Under nitrogen protection, the temperature was raised to 145 °C within 30 min for transesterification reaction. The mechanical stirring speed was 140 r, and the reaction was carried out for 2.5 h to obtain micro-crosslinked polyester oligomers.

[0118] Under nitrogen protection and continuous stirring, titanium isopropoxide (1.3‰ of the total molar mass of all acid feedstocks), diphenyl phosphate (2.5‰ of the total molar mass of all acid feedstocks), and 2,2-methylenebis(4-methyl-6-tert-butylphenol) (1.5‰ of the total molar mass of all acid feedstocks) were added as a polycondensation catalyst. The temperature was gradually increased to 205℃, and the vacuum was gradually reduced to 200 Pa for 60 min. The vacuum was then further reduced to 50 Pa for 30 min, and the vacuum was further reduced to below 10 Pa for 60 min. The target polybutylene oxalate was obtained by discharging the product under nitrogen protection.

[0119] The polybutylene oxalate prepared in this embodiment has the following intrinsic viscosity: 1.68 dL / g; weight-average molecular weight: 173,000 g / mol; acid value: 19 mol / t; hydroxyl value: 35 KOH mg / g; melt index: 9 g / 10 min; glass transition temperature: -22.7℃; melting point: 104.8℃; initial thermal decomposition temperature: 334℃; elastic modulus: 528 MPa; tensile strength: 58.4 MPa; elongation at break: 390%; water contact angle of the film: 38°; CO2 permeability: 1.33 barrer; O2 permeability: 2.85 barrer; mass loss after 35 days of degradation in phosphate buffer: 82%; and mass loss after 35 days of degradation in seawater: 43%.

[0120] Example 5

[0121] Diethyl oxalate and 1,4-butanediol were added to the reactor at molar amounts of 0.30 mol and 0.42 mol, respectively. Then, the intrinsic catalyst titanium oxalate (0.5‰ of the total molar mass of all acid raw materials) prepared in Example 1 and the micro-crosslinking agent 1,2,6-hexanetriol (1% of the total molar mass of all acid raw materials) were added. Under nitrogen protection, the temperature was raised to 150 °C within 30 min for transesterification reaction. The mechanical stirring speed was 140 r. After 2 h of reaction, micro-crosslinked polyester oligomers were obtained.

[0122] Under nitrogen protection and continuous stirring, triethyl antimonyate (1‰ of the total molar mass of all acid raw materials), diphenyl phosphate (2.5‰ of the total molar mass of all acid raw materials), and 2,2-methylenebis(4-methyl-6-tert-butylphenol) (1‰ of the total molar mass of all acid raw materials) were added as a polycondensation catalyst. The temperature was gradually increased to 210℃, and the vacuum was gradually reduced to 200 Pa for 60 min. The vacuum was then further reduced to 50 Pa for 60 min, and the reaction was continued for 60 min. Finally, the vacuum was further reduced to below 10 Pa for 60 min. The target polybutylene oxalate was obtained by discharging the product under nitrogen protection.

[0123] The polybutylene oxalate prepared in this embodiment has the following intrinsic viscosity: 1.52 dL / g; weight-average molecular weight: 143,000 g / mol; acid value: 16 mol / t; hydroxyl value: 32 KOH mg / g; melt index: 16 g / 10 min; glass transition temperature: -21.9℃; melting point: 105.4℃; initial thermal decomposition temperature: 329℃; elastic modulus: 529 MPa; tensile strength: 54.9 MPa; elongation at break: 357%; water contact angle of the film: 31°; CO2 permeability: 2.31 barrer; O2 permeability: 3.85 barrer; mass loss after 35 days of degradation in phosphate buffer: 87%; and mass loss after 35 days of degradation in seawater: 52%.

[0124] Example 6

[0125] Diethyl oxalate and 1,4-butanediol were added to the reactor at molar amounts of 0.30 mol and 0.45 mol, respectively. Then, the intrinsic catalyst titanium oxalate (0.3‰ of the total molar mass of all acid raw materials) prepared in Example 1 and the micro-crosslinking agent pentaerythritol (1.5% of the total molar mass of all acid raw materials) were added. Under nitrogen protection, the temperature was raised to 140 °C within 30 min for transesterification reaction. The mechanical stirring speed was 140 r. After 3 h of reaction, micro-crosslinked polyester oligomers were obtained.

[0126] Under nitrogen protection and continuous stirring, stannous oxalate (2‰ of the total molar mass of all acid raw materials), triphenyl phosphate (1‰ of the total molar mass of all acid raw materials), and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (1‰ of the total molar mass of all acid raw materials) were added as a polycondensation catalyst. The temperature was gradually increased to 195℃, and the vacuum was gradually reduced to 200 Pa for 90 min. The vacuum was then further reduced to 50 Pa for 60 min, and the vacuum was further reduced to below 10 Pa for 90 min. The target polybutylene oxalate was obtained by discharging the product under nitrogen protection.

[0127] The polybutylene oxalate prepared in this embodiment has the following intrinsic viscosity: 1.59 dL / g; weight-average molecular weight: 153,000 g / mol; acid value: 24 mol / t; hydroxyl value: 38 KOH mg / g; melt index: 18 g / 10 min; glass transition temperature: -23℃; melting point: 104.7℃; initial thermal decomposition temperature: 339℃; elastic modulus: 546 MPa; tensile strength: 55.4 MPa; elongation at break: 320%; water contact angle of the film: 39°; CO2 permeability: 1.27 barrer; O2 permeability: 2.68 barrer; mass loss after 35 days of degradation in phosphate buffer: 92%; mass loss after 35 days of degradation in seawater: 52%.

[0128] Example 7

[0129] Dimethyl oxalate and 1,4-butanediol were added to the reactor at molar amounts of 0.30 mol and 0.45 mol, respectively. Then, the intrinsic catalyst titanium oxalate (1.2‰ of the total molar mass of all acid raw materials) prepared in Example 1 and the micro-crosslinking agents glycerol and pentaerythritol (1.5% of the total molar mass of all acid raw materials) were added. Under nitrogen protection, the temperature was raised to 150 °C within 30 min for transesterification reaction. The mechanical stirring speed was 140 r. After 3 h of reaction, micro-crosslinked polyester oligomers were obtained.

[0130] Under nitrogen protection and continuous stirring, titanium isopropoxide (a polycondensation catalyst) and methyl triethylgermanate (1.5‰ of the total molar mass of all acid raw materials), triphenyl phosphite (a stabilizer) (1.5‰ of the total molar mass of all acid raw materials), and 2,2-methylenebis(4-methyl-6-tert-butylphenol) (an antioxidant) (1.5‰ of the total molar mass of all acid raw materials) were added. The temperature was gradually increased to 210℃, and the vacuum was gradually reduced to 200 Pa for 60 min. The vacuum was then further reduced to 50 Pa for 30 min, and the vacuum was further reduced to below 10 Pa for 60 min. The target polybutylene oxalate was obtained by discharging the product under nitrogen protection.

[0131] The polybutylene oxalate prepared in this embodiment has the following intrinsic viscosity: 1.49 dL / g; weight-average molecular weight: 152000 g / mol; acid value: 16 mol / t; hydroxyl value: 30 KOH mg / g; melt index: 7 g / 10 min; glass transition temperature: -21.3℃; melting point: 105.7℃; initial thermal decomposition temperature: 336℃; elastic modulus: 517 MPa; tensile strength: 58.7 MPa; elongation at break: 385%; water contact angle of the film: 36°; CO2 permeability: 2.38 barrer; O2 permeability: 3.55 barrer; mass loss after 35 days of degradation in phosphate buffer: 85%; and mass loss after 35 days of degradation in seawater: 49%.

[0132] Example 8

[0133] Diethyl oxalate and 1,4-butanediol were added to the reactor at molar amounts of 0.30 mol and 0.36 mol, respectively. Then, the intrinsic catalyst titanium oxalate (1‰ of the total molar mass of all acid raw materials) prepared in Example 1 and the micro-crosslinking agents trimethylolpropane and glycerol (3% of the total molar mass of all acid raw materials) were added. Under nitrogen protection, the temperature was raised to 140 °C within 30 min for transesterification reaction. The mechanical stirring speed was 140 r. After 3 h of reaction, micro-crosslinked polyester oligomers were obtained.

[0134] Under nitrogen protection and continuous stirring, tetrabutyl titanate (1.5‰ of the total molar mass of all acid raw materials), antimony trioxide (1.5‰ of the total molar mass of all acid raw materials), diphenyl phosphate (2.5‰ of the total molar mass of all acid raw materials), and 2,2-methylenebis(4-methyl-6-tert-butylphenol) (1‰ of the total molar mass of all acid raw materials) (1‰ of the total molar mass of all acid raw materials) were added as a polycondensation catalyst. The temperature was gradually increased to 210℃, and the vacuum was gradually reduced to 200 Pa for 90 min. The vacuum was then further reduced to 50 Pa for 60 min, and the vacuum was further reduced to below 10 Pa for 60 min. The target polybutylene oxalate was obtained by discharging the product under nitrogen protection.

[0135] The polybutylene oxalate prepared in this embodiment has the following intrinsic viscosity: 1.47 dL / g; weight-average molecular weight: 136,000 g / mol; acid value: 24 mol / t; hydroxyl value: 39 KOH mg / g; melt index: 18 g / 10 min; glass transition temperature: -22.4℃; melting point: 104.9℃; initial thermal decomposition temperature: 315℃; elastic modulus: 550 MPa; tensile strength: 54.6 MPa; elongation at break: 357%; water contact angle of the film: 35°; CO2 permeability: 1.86 barrer; O2 permeability: 3.57 barrer; mass loss after 35 days of degradation in phosphate buffer: 85%; and mass loss after 35 days of degradation in seawater: 56%.

[0136] Example 9

[0137] Dimethyl oxalate and 1,4-butanediol were added to the reactor at molar amounts of 0.30 mol and 0.36 mol, respectively. Then, the intrinsic catalyst titanium oxalate (0.2‰ of the total molar mass of all acid raw materials) prepared in Example 1 and the micro-crosslinking agent trimethylolethane (1% of the total molar mass of all acid raw materials) were added. Under nitrogen protection, the temperature was raised to 130 °C within 30 min for transesterification reaction. The mechanical stirring speed was 140 r. After 3 h of reaction, micro-crosslinked polyester oligomers were obtained.

[0138] Under nitrogen protection and continuous stirring, tetrabutyl germanate (0.5‰ of the total molar mass of all acid raw materials), triphenyl phosphite (5‰ of the total molar mass of all acid raw materials), and octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (2‰ of the total molar mass of all acid raw materials) were added as a polycondensation catalyst. The temperature was gradually increased to 190℃, and the vacuum was gradually reduced to 200 Pa for 90 min. The vacuum was then further reduced to 50 Pa for 60 min, and the vacuum was further reduced to below 10 Pa for 60 min. The target polybutylene oxalate was obtained by discharging the product under nitrogen protection.

[0139] The polybutylene oxalate prepared in this embodiment has the following intrinsic viscosity: 1.45 dL / g; weight-average molecular weight: 129000 g / mol; acid value: 23 mol / t; hydroxyl value: 37 KOH mg / g; melt index: 16 g / 10 min; glass transition temperature: -21.8℃; melting point: 103.4℃; initial thermal decomposition temperature: 320℃; elastic modulus: 540 MPa; tensile strength: 55.8 MPa; elongation at break: 349%; water contact angle of the film: 37°; CO2 permeability: 1.82 barrer; O2 permeability: 3.64 barrer; mass loss after 35 days of degradation in phosphate buffer: 83%; and mass loss after 35 days of degradation in seawater: 52%.

[0140] Compared to Comparative Example 2, the intrinsic catalyst titanium oxalate of this invention can significantly improve esterification efficiency, and the synthesized polybutylene oxalate has a higher molecular weight and excellent mechanical properties and stability. Compared to Comparative Example 3, titanium oxalate prepared by electrocatalysis has more stable hydrolysis resistance and can form higher quality polybutylene oxalate. Compared to Comparative Example 4, the addition of micro-crosslinking agent significantly reduces the melt index, making it compatible with currently mass-produced biodegradable polyesters and providing a wider processing window. Compared to Comparative Example 5, the polybutylene oxalate prepared by organic base polycondensation catalyst has a lower molecular weight and a higher acid value, and may be accompanied by thermal degradation during the reaction.

[0141] In addition, the inventors of this case also conducted experiments with other raw materials and conditions listed in this specification, referring to the aforementioned embodiments, and similarly obtained low melt index polybutylene oxalate with good crystallization ability, mechanical properties and controllable degradation rate.

[0142] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0143] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing low melt index polybutylene oxalate, characterized in that, include: Under a protective atmosphere, a first mixed reaction system containing oxalate, 1,4-butanediol, a micro-crosslinking agent, and an intrinsic catalyst, titanium oxalate, is subjected to a transesterification reaction to obtain a micro-crosslinked polyester oligomer. The intrinsic catalyst, titanium oxalate, and the micro-crosslinking agent are added to the reaction system before the transesterification reaction. The temperature of the transesterification reaction is 130°C to 150°C, and the reaction time is 120 min to 180 min. Under vacuum conditions, a second mixed reaction system containing the micro-crosslinked polyester oligomer, polycondensation catalyst, antioxidant and heat stabilizer is subjected to a polycondensation reaction to obtain low melt index polybutylene oxalate. The micro-crosslinking agent is a polyol compound selected from any one or more combinations of glycerol, pentaerythritol, 1,2,6-hexanetriol, trimethylolpropane, and trimethylolethane. The amount of the micro-crosslinking agent is 1% to 3% of the molar fraction of oxalate. The molar ratio of the micro-crosslinking agent to 1,4-butanediol is 1:40 to 1:

150. The polycondensation catalyst is an organometallic compound selected from any one or more combinations of antimony-based catalysts, titanium-based catalysts, tin-based catalysts, and germanium-based catalysts. The intrinsic catalyst titanium oxalate is prepared by the following steps: under nitrogen protection at room temperature, titanium metal is used as the anode, placed in an electrolyte containing oxalic acid, and a constant current of 20~50mA is passed through it for more than 60 minutes to obtain the intrinsic catalyst titanium oxalate.

2. The preparation method according to claim 1, characterized in that: The antimony-based catalyst is selected from any one or more combinations of antimony trioxide, antimony acetate, antimony glycolate, and triethyl antimonate; the titanium-based catalyst is selected from any one or more combinations of titanium isopropoxide, tetrabutyl titanate, and tetraethyl titanate; the tin-based catalyst is selected from any one or more combinations of stannous chloride, stannous oxalate, dibutyltin oxide, stannous octoate, and stannous trifluoromethanesulfonate; the germanium-based catalyst is selected from any one or more combinations of germanium dioxide, germanium chloride, methyl triethyl germanate, tetraethyl germanate, and tetrabutyl germanate.

3. The preparation method according to claim 1, characterized in that: The oxalate ester is selected from dimethyl oxalate and / or diethyl oxalate.

4. The preparation method according to claim 1, characterized in that: The molar ratio of oxalate to 1,4-butanediol is 1:1.2 to 1:1.

5.

5. The preparation method according to claim 1, characterized in that: The intrinsic catalyst titanium oxalate is used in an amount of 0.2‰ to 1.5‰ of the mass fraction of oxalate.

6. The preparation method according to claim 1, characterized in that... include: Before the transesterification reaction, oxalate, 1,4-butanediol, intrinsic catalyst titanium oxalate, and micro-crosslinking agent were placed together in the reaction chamber. The temperature was raised to 130℃~150℃ within 30 minutes and mechanically stirred continuously. The transesterification reaction time was 120min~180min.

7. The preparation method according to claim 1, characterized in that: The amount of the polycondensation catalyst is 0.5‰ to 2‰ of the mass fraction of oxalate.

8. The preparation method according to claim 1, characterized in that: The antioxidant is a phenolic antioxidant, which is selected from at least one of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 2,6-di-tert-butyl-4-cresol, and 2,2-methylenebis(4-methyl-6-tert-butylphenol).

9. The preparation method according to claim 1, characterized in that: The amount of the antioxidant is 1‰ to 2‰ of the molar mass of the oxalate.

10. The preparation method according to claim 1, characterized in that: The heat stabilizer is a phosphorus-based stabilizer, which is selected from at least one of phosphorous acid, diphenyl phosphate, triphenyl phosphate, and triphenyl phosphite.

11. The preparation method according to claim 1, characterized in that: The amount of the heat stabilizer is 1‰ to 5‰ of the molar mass of the oxalate ester.

12. The preparation method according to claim 1, characterized in that, include: Before the polycondensation reaction, a polycondensation catalyst, antioxidant, and heat stabilizer are added.

13. The preparation method according to claim 1, characterized in that: The polycondensation reaction is carried out at a temperature of 190℃~210℃, with a pressure of 200~1000Pa in the early stage of polycondensation and a duration of 60min~90min; a pressure of 50~200Pa in the middle stage of polycondensation and a duration of 30min~60min; and a pressure of less than 10Pa in the later stage of polycondensation and a duration of 60min~90min.

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