Polyester and method of preparation thereof and its use

Abstract

The present invention describes a polyester, its method of preparation, and its use. The total content of low molecular weight substances in the polyester is 0.1 to 0.6% by weight, and the GPC curve of these substances exhibits the following characteristic: the integral area of ​​the peaks with a numerical average molecular weight (Mn) greater than 400 is less than 60% of the total integral area. The present invention effectively solves the problem of the high probability of precipitation on the surface of a polyester product, and the resulting product exhibits high gloss.

Description

Polyester and method of preparation thereof and its use Technical field The present invention relates to the field of biodegradable polyesters, and specifically to a polyester having a low content of low molecular weight substances, and to a method of preparing and using the same. Background Currently, thermoplastic aromatic polyesters, widely used in industry and daily life, possess excellent thermal stability and mechanical properties, are easy to process, and are inexpensive. For example, polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) are widely used in the manufacture of fibers, membranes, and containers. However, these aromatic polyesters are difficult to degrade after use and disposal, and no direct degradation of aromatic polyesters such as PET and PBT by microorganisms has yet been observed. Aliphatic polyesters have received attention as environmentally friendly plastics. These polyesters can be obtained through esterification and melt polycondensation reactions of aliphatic dicarboxylic acids and aliphatic diols. The aliphatic dicarboxylic acids (such as succinic and adipic acids) can be produced from plant-derived glucose via fermentation, and the aliphatic diols (such as ethylene glycol, propylene glycol, and butanediol) can also be produced from plant-derived raw materials, thus conserving fossil fuel resources. Furthermore, since plants can absorb carbon dioxide from the atmosphere during growth, a significant contribution can be made to reducing carbon dioxide emissions.Furthermore, aliphatic polyesters are also known to exhibit excellent biodegradability and can therefore be considered triply environmentally friendly plastics. However, aliphatic polyester products often suffer from the problems of small molecule precipitation on surfaces, loss of gloss, and similar issues. To address these problems, JP2004107457A describes cleaning polyester particles with acetone, and JP3396537B2 describes cleaning them with methanol or isopropanol, among other methods. While these methods can improve the gloss of polyesters to some extent, they increase the number of additional multi-stage processes and raise costs. Furthermore, these organic solvents can remain on the polyester particles and cause further problems with small molecules. Additionally, the use of alcohols can lead to polyester degradation, decreased molecular weight, and similar issues.In document CN101910245B, the brightness of a polyester product is improved by controlling the surface temperature of the wall of a distillation tube of a polycondensation reactor and the internal temperature of the polycondensation reactor, but the degree of improvement remains limited. On the other hand, aliphatic polyesters have high viscosity in the molten state, and for injection molding of thin parts, problems such as short melt flow rates and similar issues easily arise. Therefore, improving the flowability of aliphatic polyesters has become an important topic for experts in the field. Document CN 113683763 A describes polyesters with low oligomer content. Summary To overcome the shortcomings of the prior art, an objective of the present invention is to provide a polyester. This polyester has a specific content of low molecular weight substances, which not only solves the problem of easy precipitation on the surfaces of polyester products, but also gives the polyester product a high gloss and improves the flowability of the polyester resin, so that the gloss and flowability of the product are maintained in a balanced state. Another objective of the present invention is to provide a method for preparing polyester. The above objectives of the present invention are achieved through the following technical solutions. A polyester includes a repeating unit derived from the following components: a first component A, based on a total molar amount of the first component A, which includes: a1) 81-100 mol%, preferably 90-100 mol% of succinic acid, or ester derivatives thereof or anhydride derivatives thereof; a2) 0-19 mol%, preferably 0-10 mol% of other binary carboxylic acids, except succinic acid, or its ester derivatives or its anhydride derivatives; a second component B, 1, 4-butanediol; Wherein, based on the total weight of the polyester, the total content of low molecular weight substances in the polyester is 0.1-0.6% by weight, preferably 0.2-0.5% by weight, and the GPC curve of the low molecular weight substances has the following characteristic: an integral area of ​​peaks having a number-average molecular weight (Mn) greater than 400 is less than 60% of the total integral area. The total content of low molecular weight substances is analyzed using the following method: Take 10 g of polyester particles and record the mass of the polyester particles as wg; place the polyester particles in 100 ml of ethanol for heating and refluxing for 4 h, perform a heat filtration to obtain a filtrate, pour the filtrate into a pre-weighed evaporating plate and record the weight of the evaporating plate as a0; place the obtained filtrate in a water bath for evaporation until almost dry, transfer the evaporating plate to an oven to dry at 105 °C for 2 h, then remove the evaporating plate, perform the weighing after cooling for 0.5 h and record the weight as a1; and obtain the content of the low molecular weight substances as (a1-a0) / w × 100 %. The low molecular weight substances of polyester are cyclic esters produced in a polyester synthesis process, and mainly include cyclic dimers and cyclic polymers with a number of repeating units greater than 2. In the present invention, by controlling the total content of the low molecular weight substances in the polyester to 0.1-0.6% by weight and the integral area of ​​the peaks (cyclic polymers) having a number average molecular weight (Mn) greater than 400 to be less than 60% of the total integral area in the GPC curve of the low molecular weight substances, the flowability of the polyester can be improved while reducing the problem of polyester precipitation, and a prepared polyester product has high brightness and good flowability.When the total content of low molecular weight substances in polyester is too high, severe precipitation will occur during subsequent processing and use, resulting in poor gloss. Conversely, when the total content of low molecular weight substances is too low, the effects of a flow modifier cannot be achieved, and the improvement of the polyester's flowability will be compromised. As an additional technical solution of the present invention, the total content of the low molecular weight substances in the polyester is 0.2-0.35% by weight, and the GPC curve of the low molecular weight substances has the following characteristic: the integral area of ​​the peaks having a number average molecular weight (Mn) greater than 400 is less than 50% of the total integral area. Preferably, the first component A includes succinic acid, or ester derivatives thereof or anhydride derivatives thereof. As an example of specific selection, component a2) is selected from one or more of oxalic acid, dimethyl oxalate, malonic acid, dimethyl malonate, methylsuccinic acid, glutaric acid, dimethyl glutarate, bis(2-hydroxyethyl) glutarate, bis(3-hydroxypropyl) glutarate, bis(4-hydroxybutyl) glutarate, 2-methylglutaric acid, 3-methylglutaric acid, adipic acid, dimethyl adipate, bis(2-hydroxyethyl) adipate, bis(3-hydroxypropyl) adipate, bis(4-hydroxybutyl) adipate, 3-methyladipic acid, 2,2,5,5-tetramethyladipic acid, pimelic acid, suberic acid, azelaic acid, dimethyl azelate, acid sebacic acid, 1,11-undecanedicarboxylic acid, 1,10-decanedicarboxylic acid, undecanedioic acid, 1,12-dodecanedicarboxylic acid, hexadecanedioic acid, eicosanedioic acid, tetracosanedioic acid, dimeric acid, terephthalic acid, dimethyl terephthalate, bis(2-hydroxyethyl) terephthalate, bis(3-hydroxypropyl) terephthalate,bis(4-hydroxybutyl) terephthalate, isophthalic acid, dimethyl isophthalate, bis(2-hydroxyethyl) isophthalate, bis(3-hydroxypropyl) isophthalate, bis(4-hydroxybutyl) isophthalate, 2,6-naphthalenedicarboxylic acid, 2,6-dimethyl phthalate, 2,7-naphthalenedicarboxylic acid, 2,7-dimethyl phthalate, 3,4'-diphenyletherdicarboxylic acid, 3,4'-diphenyletherdicarboxylate dimethyl, 4,4'-diphenyletherdicarboxylic acid, 4,4'-diphenyletherdicarboxylate dimethyl, 3,4'-phenylthioetherdicarboxylate dimethyl, 4,4'-diphenylthioetherdicarboxylic acid, 4,4'-dimethyl 4,4'-phenylthioetherdicarboxylate, 3,4'-diphenylsulfonedicarboxylic acid, 3,4'-dimethyldiphenylsulfonedicarboxylate, 4,4'-diphenylsulfonedicarboxylic acid, 4, Dimethyl 4'-diphenylsulfonedicarboxylate, 3,4'-benzophenonedicarboxylic acid, dimethyl 3,4'-benzophenonedicarboxylate, 4,4'-benzophenonedicarboxylic acid, 4,4'-dimethyl 4,4'-benzophenonedicarboxylate, 1,4-naphthalenedicarboxylic acid, dimethyl 1,4-naphthalenedicarboxylate, 4,4'-methylenebis(benzoic) acid, 4,4'-methylenebis(dimethyl benzoate), or ester derivatives thereof or anhydride derivatives thereof, preferably selected from one or more of adipic acid, sebacic acid, 1,12-dodecanedicarboxylic acid, terephthalic acid, or ester derivatives thereof or anhydride derivatives thereof, more preferably selected from one or more of adipic acid, sebacic acid, terephthalic acid, or ester derivatives thereof or anhydride derivatives thereof, and most preferably, adipic acid, terephthalic acid, or ester derivatives thereof or anhydride derivatives thereof. In the present invention, when necessary, the polyester further includes a third component C, and component C is a compound containing at least three functional groups, and is preferably selected from one or more of tartaric acid, citric acid, malic acid, fumaric acid, maleic acid, trimethylolpropane, trimethylolethane, pentaerythritol, polyether triol, glycerol, 1,3,5-benzenetricarboxylic acid, 1,2,4-benzenetricarboxylic acid, 1,2,4-benzenetricarboxylic anhydride, 1,2,4,5-benzenenotetracarboxylic acid, or pyromellitic dianhydride, more preferably one or more of malic acid, citric acid, fumaric acid, maleic acid, or glycerol; and Preferably, based on the total molar amount of the first component A, the content of the third component C is 0.01-1.0% by moles, preferably 0.02-0.2% by moles. In the present invention, when necessary, the polyester further includes a fourth component D, and the fourth component D is a chain extender. The chain extender is selected from one or more of an isocyanate, an isocyanurate, a peroxide, an epoxide, oxazoline, oxazine, lactam, carbodiimide, and polycarbodiimide containing two or more functional groups, preferably an isocyanate containing two or more functional groups, and most preferably hexamethylene diisocyanate. The isocyanate containing two or more functional groups may be an aromatic isocyanate or an aliphatic isocyanate, preferably an aromatic diisocyanate or an aliphatic diisocyanate. Preferably, the aromatic diisocyanate is toluene 2,4-diisocyanate, toluene 2,6-diisocyanate, diphenylmethane 2,2'-diisocyanate, diphenylmethane 2,4'-diisocyanate, diphenylmethane 4,4'-diisocyanate, naphthalene 1,5-diisocyanate, or xylene diisocyanate. More preferably, the aromatic diisocyanate is diphenylmethane 2,2'-diisocyanate, diphenylmethane 2,4'-diisocyanate, or diphenylmethane 4,4'-diisocyanate. Preferably, the aliphatic diisocyanate is any linear or branched alkylene diisocyanate or cycloalkylene diisocyanate containing from 2 to 20 carbon atoms. More preferably, the aliphatic diisocyanate is any linear or branched alkylene diisocyanate or cycloalkylene diisocyanate containing from 3 to 12 carbon atoms. The aliphatic diisocyanate may be hexamethylene 1,6-diisocyanate, isophorone diisocyanate, or methylene bis(4-cyclohexaneisocyanate). Most preferably, the aliphatic diisocyanate is hexamethylene 1,6-diisocyanate or isophorone diisocyanate. The isocyanate containing 2 or more functional groups can also be tri(4-isocyanatophenyl)methane with three rings. Preferably, the isocyanurate containing two or more functional groups is an aliphatic isocyanurate, selected from an alkylene diisocyanate or a cycloalkylene diisocyanate containing 2 to 20 carbon atoms, preferably 3 to 12 carbon atoms, such as isophorone diisocyanate or methylene bis(4-isocyanatecyclohexane). The alkylene diisocyanate may be a linear or branched compound. In particular, isocyanurates based on cyclic trimers, pentamers, or higher oligomers of hexamethylene diisocyanates, such as hexamethylene 1,6-diisocyanate, are preferred. Preferably, the peroxide containing 2 or more functional groups is preferably benzoyl peroxide, 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-di(tert-butylperoxy)methylcyclododecane, 4,4-di(n-butylperoxy)valerate, dicumyl peroxide, tert-butyl peroxybenzoate, dibutyl peroxide, -di(tert-butylperoxy)diisopropylbenzene, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexan-3-acetylene or tert-butylperoxycumene. Preferably, the epoxide containing 2 or more functional groups is preferably hydroquinone, diglycidyl ether, resorcinol diglycidyl ether, 1,6-hexanediol diglycidyl ether, hydrobisphenol A diglycidyl ether, diglycidyl terephthalate, diglycidyl tetrahydrophthalate, diglycidyl hexahydrophthalate, dimethyldiglycidyl phthalate, phenylenediglycidyl ether, ethylenediglycidyl ether, trimethylenediglycidyl ether, tetramethylenediglycidyl ether, hexamethylenediglycidyl ether, sorbitoldiglycidyl ether, polyglycerolpolyglycidyl ether, pentaerythritolpolyglycidyl ether, diglycerolpolyglycidyl ether, glycerolpolyglycidyl ether, trimethylolpropanepolyglycidyl ether, resorcinoldiglycidyl ether, neopentylglycoldiglycidyl ether, ethyleneglycoldiglycidyl ether, diethyleneglycoldiglycidyl ether, polyethyleneglycoldiglycidyl ether, propyleneglycoldiglycidyl ether, dipropyleneglycoldiglycidyl ether, polypropyleneglycoldiglycidyl ether or polybutyleneglycoldiglycidyl ether. The epoxide containing two or more functional groups is also preferably a copolymer based on styrene, an acrylate, and / or a methacrylate, and contains an epoxy group, the epoxy group being preferably glycidyl methacrylate. Advantageous compounds have been shown to be copolymers in which the proportion of glycidyl methacrylate is greater than 20 wt%, more preferably greater than 30 wt%, and more preferably greater than 50 wt%. The weight equivalent of the epoxy group in these copolymers is preferably from 150 to 3,000 g / eq, more preferably from 200 to 500 g / eq. The weight average molecular weight (Mw) of the copolymer is preferably from 2,000 to 25,000, more preferably from 3,000 to 8,000. The number average molecular weight (Mn) of the copolymer is preferably from 400 to 6,000, more preferably from 1,000 to 4,000. The polydispersity index (Q=Mw / Mn) is preferably from 1.5 to 5. Oxazoline or oxazine containing 2 or more functional groups is preferably dioxazoline or dioxazine, and a bridging part is a single bond, (CH2) z-alkylene, where z equals 2, 3 or 4, such as methylene, ethyl-1, 2-diyl, propyl-1, 3-diyl or propyl-1,2-diyl or phenylene. Specifically, dioxazoline is 2,2'-bis(2-oxazoline), bis(2-oxazolinyl)methane, 1,2-bis(2-oxazolinyl)ethane, 1,3-bis(2-oxazolinyl)propane, 1,4-bis(2-oxazolinyl)butane, 2,2'-bis(2-oxazoline), 2, 2'-bis(4-methyl-2-oxazoline), 2,2'-bis(4,4'-dimethyl-2-oxazoline), 2,2'-bis(4-ethyl-2-oxazoline), 2,2'-bis(4,4'-diethyl-2-oxazoline), 2,2'-bis(4-propyl-2-oxazoline) , 2, 2'-bis (4-butyl-2-oxazoline) , 2,2'-bis(4-hexyl-2-oxazoline), 2,2'-bis(4-phenyl-2-oxazoline), 2,2'-bis(4-cyclohexyl-2-oxazoline), 2,2'-bis(4-phenylmethyl-2-oxazoline), 2,2'-p-phenylenebis (4-methyl-2-oxazoline), 2, 2'-p-phenylenebis (4, 4'-dimethyl-2-oxazoline), 2,2'-m-phenylenobis-bis(4-methyl-2-oxazoline), 2, 2'-mphenylenobis (4, 4'-dimethyl-2-oxazoline), 2, 2'-hexamethylenebis (2-oxazoline), 2, 2'-octamethylenebis (2-oxazoline), 2, 2. 2'-decamethylenebis(2-oxazoline), 2,2'-ethylenebis(4-methyl-2-oxazoline), 2,2'-tetramethylenebis(4,4'-dimethyl-2-oxazoline), 2,2'-9,9'-diphenoxyethanobis(2-oxazoline), 2,2. 2′-cyclohexylenobis(2-oxazoline) or 2,2′-diphenylene(2-oxazoline)., Specifically, the dioxazine is 2,2'-bis(2-dioxazin) , bis(2-dioxazinyl)methane, 1,2-bis(2-dioxazinyl)ethane, 1,3-bis(2-dioxazinyl)propane, 1,4-bis(2-dioxazinyl)butane, 1,4-bis (2-dioxazinyl)benzene, 1,2-bis(2-dioxazinyl)benzene or 1,3-bis(2-dioxazinyl)benzene. The carbodiimida or polycarbodiimida which contains 2 or more of 2 functional groups is preferably N, N'-di-2, 6-diisopropylphenylcarbodiimida, N, N'-di-o-tolylcarbodiimida, N, N'-diphenylcarbodiimida, N, N'-dioctyldecylcarbodiimida, N, N'-di-2, 6-dimethylphenylcarbodiimida, N-tolyl-N'-cyclohexylcarbodiimida, N, N'-di-2, 6-di-terc-butylphenylcarbodiimida, N-tolyl-N'-phenylcarbodiimida, N, N'-di-p-nitrophenylcarbodiimida, N, N'-di-p-aminophenylcarbodiimida, N, N'-di-hydroxyphenylcarbodiimida, N,N'-dicyclohexylcarbodiimida, N,N'-di-p-tolylcarbodiimida, p-phenyleno-bis(di-otolylcarbodiimida), p-phenyleno-bis(dicyclohexylcarbodiimida), hexamethylene-bis(dicyclohexylcarbodiimida), 4,4'-dicyclohexylmethanecarbodiimida, ethylene-bis(diphenylcarbodiimida), N,N'-phenylmethyl-carbodiimida, N-octadecyl-N'-phenylcarbodiimida, N-bencyl-N'-phenylcarbodiimida, N-octadecyl-N'-tolylcarbodiimida, N-cyclohexyl-N'-tolylcarbodiimida, N-phenyl-N'-tolylcarbodiimida, N-bencyl-N'-tolylcarbodiimida, N,N'-di-o-ethylphenylcarbodiimida, N,N'-di-p-ethylphenylcarbodiimida, N,N'-di-o-isopropylphenylcarbodiimida, N,N'-di-p-isopropylphenylcarbodiimida, N,N'-di-o-isobutylphenylcarbodiimida, N,N'-di-pisobutylphenylcarbodiimida, N,N'-di-2, 6-diethylphenylcarbodiimida, N,N'-di-2-ethyl-6-isopropylphenylcarbodiimida, N,N'-di-2-isobutyl-6-isopropylphenylcarbodiimida, N,N'-di-2, 4, 6-trimethylphenylcarbodiimida, N,N'-di-2, 4, 6-triisopropylphenylcarbodiimida, N, N'-di-2, 4, 6-triisobutylphenylcarbodiimida, diisopropylcarbodiimida, dimethylcarbodiimida, diisobutylcarbodiimida, dioctylcarbodiimida, tert-butylisopropylcarbodiimida, di-ß-naphthylcarbodiimida or di-tert-butylcarbodiimida., Preferably, based on the total molar content of the primer component A, the content of the fourth component D is 0.01-5.0 % in moles. Preferably, the viscosity of the polyester determined in a phenol / o-dichlorobenzene solution at a weight ratio of 1:1 in a water bath at a constant temperature of 25 ± 0.05 °C, as specified according to document GB / T 17931-1999, is 100-350 ml / g. The present invention further provides a method for preparing the polyester, which includes the following steps: S1: mixing the first component A, the second component B and a part of a catalyst, and performing heating in an esterification reactor at 180-260 °C to carry out an esterification reaction for 1-4 h to obtain an esterification product AB; S2: allowing the AB esterification product from step S1 to undergo a primary polycondensation reaction at a reaction temperature of 200-240 °C for a reaction time of 2-6 h to obtain a primary polycondensation product Pre-AB; and S3: Transfer the primary polycondensation product Pre-AB obtained in step S2 and the remaining catalyst to a final polymerization reactor to carry out a continuous polycondensation reaction at a temperature of 210-270 °C until a determined reaction product in a phenol / o-dichlorobenzene solution at a weight ratio of 1:1 in a water bath at a constant temperature of 25 ± 0.05 °C, as specified according to GB / T 17931-1999, reaches a viscosity of 100-350 ml / g. Preferably, in step S1, the amount of addition of the second component, 1,4-butanediol, is normally 1.3-3.0 times (molar amount) of the first component A, a diacid, preferably 1.5-2.5 times (molar amount). Preferably, in step S1, during the preparation of the AB esterification product, the catalyst is added at a rate of 0.001–1% by weight of the final polyester. Ideally, the catalyst addition rate is 0.02–0.2% by weight of the final polyester. The catalyst addition rate in step S1 is typically 10–40% by weight of the total catalyst used. Controlling the catalyst addition rate can result in a more stable downstream processing operation. Furthermore, the catalyst can be a tin compound, an antimony compound, a cobalt compound, a lead compound, a zinc compound, an aluminum compound, or a titanium compound, most preferably a zinc compound, an aluminum compound, or a titanium compound.Titanium compounds, such as tetrabutyl orthotitanate or tetraisopropyl orthotitanate, have the advantage that the residual amount remaining in a product or in a downstream product is less toxic compared to other compounds. This property is particularly important in biodegradable polyesters because biodegradable polyesters go directly into the environment in the form of compost bags or mulch films. In stage S2, the reaction temperature is preferably 210-230 °C. In stage S2, the initial pressure is normally set at 0.1 to 0.5 bar, preferably 0.2 to 0.4 bar, and the pressure at the end of S2 is normally set at 5 to 200 mbar, more preferably 10 to 100 mbar. According to a process of the present invention, by adding a specific amount of catalyst in a polycondensation step S3, the polymerization of cyclic esters in the high molecular weight linear polyester can be catalyzed in this step, thereby effectively reducing the content of cyclic esters, especially the content of cyclic polymers with a number of repeating units greater than 2, so that the total content of low molecular weight substances in the polyester does not exceed 0.6% by weight. Furthermore, the integral area of ​​the peaks (cyclic dimers) having a number-average molecular weight (Mn) greater than 400 can be simultaneously controlled to be less than 60% of the total integral area on the GPC curve of the low molecular weight substances. Research into the present invention shows that the amount of catalyst added in step S3 directly affects the total content of low molecular weight substances in the polyester. If the amount of catalyst added in step S3 is too small, it cannot effectively reduce the total content of these substances. Preferably, in step S3, the amount of catalyst added should be 60-90% by weight of the total amount of catalyst used. In stage S3, the reaction temperature for continuous polycondensation is preferably 230–260 °C. In stage S3, the initial pressure is typically controlled between 0.2 and 5 mbar, more preferably between 0.5 and 3 mbar. The reaction time for continuous polycondensation is preferably 2–7 h, more preferably 3–6 h. The carboxyl content in the polyester after the reaction in S3 is preferably 20–60 mmol / kg. When necessary, once step S3 is completed, step S4 is performed: adding the polyester obtained in step S3 to a twin-screw extruder, together with the chain extender as the fourth component D in an amount of 0.01-5.0% by moles (depending on the total molar amount of the first component A), at a reaction temperature of 200-270 °C for a residence time of 0.5-15 minutes to obtain a polyester, wherein the polyester is determined in a phenol / o-dichlorobenzene solution in a weight ratio of 1:1 in a water bath at a constant temperature of 25 ± 0.05 °C, as specified according to document GB / T 17931-1999, having a viscosity of 150-350 ml / g. In another aspect, the present invention further provides a polyester molding composition, calculated as a percentage by weight, which includes the following components: 5-95% by weight of polyester; 5-95% by weight of an additive and / or other polymers; and 0-70% by weight of a reinforcing material and / or a load. As a specific selection, the additive and / or other polymers may include at least one or more of the components selected from aliphatic polyesters, polycaprolactones, starch, cellulose, polyhydroxyalkanoates, and polylactic acid. In another aspect, the present invention further provides for the use of polyester in the preparation of compostable degradable products, and the compostable degradable products may include fibers, films or containers, etc. The present invention also provides for the use of polyester in the preparation of suction tubes. Compared to the prior art, the present invention has the following beneficial effects: The present invention provides a polyester. By controlling the total content of low molecular weight substances in the polyester to 0.1-0.6% by weight and the integral area of ​​the peaks having a number-average molecular weight (Mn) greater than 400 to be less than 60% of the total integral area in the GPC curve of the low molecular weight substances, not only can the problem of easy precipitation on the surfaces of polyester products be solved, but a prepared polyester product can also have a high gloss and the flowability of a polyester resin can be improved, so that the gloss and flowability of the product are maintained in a balanced state. Brief description of the drawings Figure 1 shows a GPC curve for low molecular weight substances in Example 1 of the present invention. Figure 2 shows a GPC curve for low molecular weight substances in Comparative Example 1 of the present invention. Detailed description of the achievements Unless otherwise specified, the raw materials, reagents, and solvents used in the present invention are all commercially available without any treatment. The present invention is described in more detail below, along with examples, but embodiments of the present invention are not limited by the following examples, and any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention shall be considered equivalent modes of replacement and are included within the scope of protection of the present invention. Furthermore, "part" and "%" used in the description, unless otherwise specified, represent "part by mass" and "% by mass," respectively. The raw materials used in the examples and comparative examples of the present invention are all acquired on the market. Testing methods: Viscosity of a polyester: As specified according to document GB / T 17931-1999, the determination was carried out in a phenol / o-dichlorobenzene solution at a weight ratio of 1:1 in a water bath at a constant temperature of 25 ± 0.05 °C, and the sample concentration was 5 mg / ml. Content of low molecular weight substances: Approximately 10 g of polyester particles were taken and the mass of the polyester particles was recorded as wg; the polyester particles were placed in 100 ml of ethanol for heating and refluxing for 4 h, filtration was carried out with heat to obtain a filtrate and the filtrate was poured onto a previously weighed evaporating plate (recorded as a0); the filtrate obtained was placed in a water bath to evaporate until almost dry, the evaporating plate was transferred to an oven to dry at 105 °C for 2 h, then the evaporating plate was removed, cooled for 0.5 h and weighed (recorded as a1); and the content of low molecular weight substances was obtained as (a1-a0) / w × 100 %. GPC testing of low molecular weight substances: The GPC was tested using the Waters ACQUITY APC™ system at a test temperature of 40 °C. XT45, XT200, and XT459 chromatographic columns were used, tetrahydrofuran was used as the solvent, and the mobile phase flow rate was 0.5 mL / min. A polystyrene standard was used as the sample. Approximately 10 g of polyester particles were placed in 100 mL of ethanol, heated, and refluxed for 4 h. The filtrate was then heated and poured onto an evaporating plate, which was then placed in a water bath to evaporate until almost dry. The evaporating plate was then transferred to an oven to dry at 105 °C for 2 h, removed, and cooled for 0.5 h.The substances on the evaporation plate were low molecular weight substances, and these low molecular weight substances were prepared in a solution of approximately 0.5 mg / mL for the test. Brightness test: After drying at 80 °C for 5 h, the polyester particles were injection molded at 160 °C to obtain a 100*100*2 mm square plate, and then the L value of the square plate was tested with an X-Rite Color Eye 7000A desktop spectrophotometer. The larger L value indicates greater brightness. MFR: With reference to document GB / T 3682.1-2018 Plastics-Determination of the melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of thermoplastics-Part 1: Standard method, the melt flow rate (MRF) of a polyester was tested. The test temperature was 190 °C, the load was 2.16 kg, and the melting time was 5 min. Example 1 S1: 800 kg / h of butanedioic acid (succinic acid), 1038 kg / h of 1,4-butanediol, 0.93 kg / h of glycerol and 0.104 kg / h of tetrabutyl orthotitanate were physically mixed in an esterification reactor at normal temperature, and then the mixture was allowed to undergo an esterification reaction at 200 °C for 60-120 min to obtain an esterification product AB. S2: The AB esterification product was passed through a static mixer and then introduced into a vertical stirred, thoroughly mixed reactor at an initial pressure of 0.3 bar, heated to 220 °C for a reaction time of 3-5 h, the pressure was reduced to 100 mbar and most of the excess 1,4-butanediol was removed by distillation to obtain a Pre-AB prepolymerization product. S3: The prepolymerization product Pre-AB and 0.587 kg / h of tetrabutyl orthotitanate were transferred to a final polymerization reactor for further polycondensation at 240 °C and 1 mbar for 3–5 h, and the remaining excess 1,4-butanediol and other byproducts were removed by distillation. A polyester was then granulated using a submerged granulator and subsequently dried to obtain a final polyester product. Table 1 shows the integral proportions of various peaks on a GPC curve of low-molecular-weight substances, and Table 3 shows the yield results. Table 1 Integral proportions of several peaks in a GPC curve Example 2 S1: 800 kg / h of butanedioic acid, 1038 kg / h of 1,4-butanediol, 0.93 kg / h of glycerol and 0.207 kg / h of tetrabutyl orthotitanate were physically mixed in an esterification reactor at normal temperature, and then the mixture was allowed to undergo an esterification reaction at 200 °C for 60-120 min to obtain an esterification product AB. S2: The AB esterification product was passed through a static mixer and then introduced into a vertical stirred, thoroughly mixed reactor at an initial pressure of 0.3 bar, heated to 220 °C for a reaction time of 3-5 h, the pressure was reduced to 100 mbar and most of the excess 1,4-butanediol was removed by distillation to obtain a Pre-AB prepolymerization product. S3: The prepolymerization product Pre-AB and 0.483 kg / h of tetrabutyl orthotitanate were transferred to a final polymerization reactor for further polycondensation at 240 °C and 1 mbar for 3–5 h, and the remaining excess 1,4-butanediol and other byproducts were removed by distillation. A polyester was then granulated using a submersible granulator and subsequently dried to obtain a final polyester product. The yield results are shown in Table 3. Example 3 S1: 800 kg / h of butanedioic acid, 1038 kg / h of 1,4-butanediol, 0.93 kg / h of glycerol and 0.207 kg / h of tetrabutyl orthotitanate were physically mixed in an esterification reactor at normal temperature, and then the mixture was allowed to undergo an esterification reaction at 200 °C for 60-120 min to obtain an esterification product AB. S2: The AB esterification product was passed through a static mixer and then introduced into a vertical stirred, thoroughly mixed reactor at an initial pressure of 0.3 bar, heated to 220 °C for a reaction time of 3-5 h, the pressure was reduced to 100 mbar and most of the excess 1,4-butanediol was removed by distillation to obtain a Pre-AB prepolymerization product. S3: The prepolymerization product Pre-AB and 0.483 kg / h of tetrabutyl orthotitanate were transferred to a final polymerization reactor for further polycondensation at a temperature of 240 °C and a pressure of 1 mbar for 3-5 h, and the remaining excess of 1,4-butanediol and other byproducts were removed by distillation to obtain a final polymer Poly-AB. S4: The final polymer, Poly-AB, was continuously fed into a twin-screw extruder. Simultaneously, 6.3 kg / h of hexamethylene diisocyanate (HDI) was added per dose, and the temperature was set at 240 °C. After a residence time of 3 minutes, a polyester pellet was granulated using an underwater granulator and then dried to obtain a final polyester product. The yield results are shown in Table 3. Example 4 Tetraisopropyl orthotitanate was used as a catalyst; the amount of catalyst addition in stage S1 was 0.087 kg / h and the amount of catalyst addition in stage S3 was 0.490 kg / h. Others were the same as in example 1. Table 3 shows the performance results. Example 5 S1: 800 kg / h of butanedioic acid, 855 kg / h of 1,4-butanediol, 0.93 kg / h of glycerol and 0.207 kg / h of tetrabutyl orthotitanate were physically mixed in an esterification reactor at normal temperature, and then the mixture was allowed to undergo an esterification reaction at 200 °C for 60-120 min to obtain an AB esterification product. S2: The AB esterification product was passed through a static mixer and then introduced into a vertical stirred, thoroughly mixed reactor at an initial pressure of 0.3 bar, heated to 220 °C for a reaction time of 3-5 h, the pressure was reduced to 100 mbar and most of the excess 1,4-butanediol was removed by distillation to obtain a Pre-AB prepolymerization product. S3: The prepolymerization product Pre-AB and 0.483 kg / h of tetrabutyl orthotitanate were transferred to a final polymerization reactor for further polycondensation at 240 °C and 1 mbar for 3–5 h, and the remaining excess 1,4-butanediol and other byproducts were removed by distillation. A polyester was then granulated using a submersible granulator and subsequently dried to obtain a final polyester product. The yield results are shown in Table 3. Example 6 S1: 800 kg / h of butanedioic acid, 1,526 kg / h of 1,4-butanediol, 0,93 kg / h of glycerol and 0,207 kg / h of tetrabutyl orthotitanate were physically mixed in an esterification reactor at normal temperature, and then the mixture was allowed to undergo an esterification reaction at 200 °C for 60-120 min to obtain an AB esterification product. S2: The AB esterification product was passed through a static mixer and then introduced into a vertical stirred, thoroughly mixed reactor at an initial pressure of 0.3 bar, heated to 220 °C for a reaction time of 3-5 h, the pressure was reduced to 100 mbar and most of the excess 1,4-butanediol was removed by distillation to obtain a Pre-AB prepolymerization product. S3: The prepolymerization product Pre-AB and 0.483 kg / h of tetrabutyl orthotitanate were transferred to a final polymerization reactor for further polycondensation at 240 °C and 1 mbar for 3–5 h, and the remaining excess 1,4-butanediol and other byproducts were removed by distillation. A polyester was then granulated using a submersible granulator and subsequently dried to obtain a final polyester product. The yield results are shown in Table 3. Example 7 The amount of catalyst added in stage S1 was 0.242 kg / h, and the amount of catalyst added in stage S3 was 0.449 kg / h. Others were the same as in example 5. Table 3 shows the performance results. Comparative Example 1 S1: 800 kg / h of butanedioic acid, 1038 kg / h of 1,4-butanediol, 0.93 kg / h of glycerol and 0.449 kg / h of tetrabutyl orthotitanate were physically mixed in an esterification reactor at normal temperature, and then the mixture was allowed to undergo an esterification reaction at 200 °C for 60-120 min to obtain an AB esterification product. S2: The AB esterification product was passed through a static mixer and then introduced into a vertical stirred, thoroughly mixed reactor at an initial pressure of 0.3 bar, heated to 220 °C, 0.242 kg / h of tetrabutyl orthotitanate was added to the reactor for a reaction time of 3-5 h, the pressure was reduced to 100 mbar and most of the excess 1,4-butanediol was removed by distillation to obtain a Pre-AB prepolymerization product. S3: The Pre-AB prepolymerization product was transferred to a final polymerization reactor for further polycondensation at 240 °C and 1 mbar for 3–5 h, and the remaining excess 1,4-butanediol and other byproducts were removed by distillation. A polyester was then granulated using a submerged granulator and subsequently dried to obtain a final polyester product. Table 2 shows the integral proportions of various peaks on a GPC curve of low molecular weight substances, and Table 3 shows the yield results. Table 2 Integral proportions of several peaks in a GPC curve Comparative Example 2 A PBS resin obtained in comparative example 1 was subjected to a solvent extraction operation using a countercurrent ultrasonic extraction machine (ND-400, produced by Jiangsu Huatai Heavy Industry and Equipment Co., Ltd.). The key process parameters are as follows: a feeding capacity: 500 kg / h; a solvent: ethanol / water in a volumetric ratio of 80 / 20; an extraction temperature of 70 °C; and a residence time: 2.5 h. After unloading, drying and cooling were carried out to obtain a PBS resin with a low content of low molecular weight substances, and it was detected that the resin had an ethanol content of 70 ppm. Test Method: 1.2000 ± 0.0200 g of sample was weighed, added to a sample flask, and quantified using an Agilent 7697A-7890A static top-space chromatograph as the test equipment. The concentrations were expressed in ppm relative to the sample mass. The static top-space conditions were 105 °C for 2 h. The chromatographic column was a J&W 122-7032: 250 °C: 30 m × 250 µm × 0.25 µm. The GC heating procedure was as follows: initial temperature: 50 °C, retention time: 3 min; followed by heating to 200 °C at a heating rate of 12 °C / min, retention time: 4 min. Comparative Example 3 S1: 800 kg / h of butanedioic acid, 1038 kg / h of 1,4-butanediol, 0.93 kg / h of glycerol and 0.207 kg / h of tetrabutyl orthotitanate were physically mixed in an esterification reactor at normal temperature, and then the mixture was allowed to undergo an esterification reaction at 200 °C for 60-120 min to obtain an esterification product AB. S2: The AB esterification product was passed through a static mixer and then introduced into a vertical stirred, thoroughly mixed reactor at an initial pressure of 0.3 bar, heated to 220 °C, 0.483 kg / h of tetrabutyl orthotitanate was added to the reactor for a reaction time of 3-5 h, the pressure was reduced to 100 mbar and most of the excess 1,4-butanediol was removed by distillation to obtain a Pre-AB prepolymerization product. S3: The Pre-AB prepolymerization product was transferred to a final polymerization reactor for further polycondensation at 240 °C and 1 mbar for 3–5 h, and the remaining excess 1,4-butanediol and other byproducts were removed by distillation. A polyester was then granulated using a submersible granulator and subsequently dried to obtain a final polyester product. The yield results are shown in Table 3. Comparative example 4 With reference to a polymerization process in example 1 of document CN101910245B, the following experiment was carried out: S1: 800 kg / h of butanedioic acid, 916 kg / h of 1,4-butanediol and 3.0 kg / h of malic acid were physically mixed in an esterification reactor at normal temperature, and then the mixture was allowed to undergo an esterification reaction at 200 °C for 60-120 min to obtain an esterification product AB. S2: The AB esterification product was passed through a static mixer and then introduced into a vertical stirred, thoroughly mixed reactor at an initial pressure of 0.3 bar, heated to 220 °C, 0.46 kg / h of tetrabutyl orthotitanate was added to the reactor for a reaction time of 3-5 h, the pressure was reduced to 100 mbar and most of the excess 1,4-butanediol was removed by distillation to obtain a Pre-AB prepolymerization product. S3: The Pre-AB prepolymerization product was transferred to a final polymerization reactor for further polycondensation at a temperature (internal reactor temperature t2) of 240 °C and a pressure of 1 mbar for 3–5 h. The remaining excess 1,4-butanediol and other byproducts were removed by distillation, where the surface temperature of the distillate tube wall T was 200 °C. After condensation, a distillate was fed to the esterification reactor at a rate of 4.2 kg / ha through a pipe insulated with a heated jacket (130 °C). A polyester was then granulated using an underwater granulator and subsequently dried to obtain a final polyester product. The yield results are shown in Table 3. Comparative Example 5 S1: 800 kg / h of butanedioic acid, 1038 kg / h of 1,4-butanediol, 0.93 kg / h of glycerol and 0.449 kg / h of tetrabutyl orthotitanate were physically mixed in an esterification reactor at normal temperature, and then the mixture was allowed to undergo an esterification reaction at 200 °C for 60-120 min to obtain an AB esterification product. S2: The AB esterification product was passed through a static mixer and then introduced into a vertical stirred, thoroughly mixed reactor at an initial pressure of 0.3 bar, heated to 220 °C for a reaction time of 3-5 h, the pressure was reduced to 100 mbar and most of the excess 1,4-butanediol was removed by distillation to obtain a Pre-AB prepolymerization product. S3: The prepolymerization product Pre-AB and 0.242 kg / h of tetrabutyl orthotitanate were transferred to a final polymerization reactor for further polycondensation at 240 °C and 1 mbar for 3–5 h, and the remaining excess 1,4-butanediol and other byproducts were removed by distillation. A polyester was then granulated using a submersible granulator and subsequently dried to obtain a final polyester product. The yield results are shown in Table 3. Table 3 Performance Results Table 3, continued As can be seen from the results in Table 3, in Examples 1-7 of the present invention, by controlling the total content of low molecular weight substances to 0.1-0.6% by weight and by controlling the integral area of ​​the parts (cyclic polymers) having a number average molecular weight greater than 400 to be less than 60% of the total integral area on a GPC curve of the low molecular weight substances, the brightness (L) of the prepared polyester products can reach 79 or more, the brightness is high and the flowability is good, so that the brightness and flowability are kept in a balanced state. In Comparative Examples 1 or 3, using a traditional catalyst addition process consisting of adding all the catalyst in steps S1 and S2, the content of low molecular weight substances cannot be effectively reduced. The total content of low molecular weight substances in the prepared polyesters and the integrated area of ​​parts (cyclic polymers) with a number-average molecular weight greater than 400 on a GPC curve of low molecular weight substances are outside the scope of the present invention. Although the flowability is good, the gloss of the resulting polyester products is poor, so a balance between flowability and gloss cannot be achieved. In Comparative Example 2, using a mixed ethanol / water solvent to clean the PBS resin obtained in Comparative Example 1 effectively reduces the total content of low molecular weight substances. However, the content of these substances is too low, resulting in poor product flowability and preventing the achievement of a balance between flowability and gloss. Furthermore, the resin contains more ethanol, leading to secondary contamination. In Comparative Example 4, referring to the polymerization process of Example 1 of document CN101910245B and controlling the temperature of a relevant process equipment in the final polymerization reactor, the total content of low molecular weight substances in the prepared polyester is controlled to 0.51%. However, since this process control mainly addresses cyclic dimers and is relatively limited to reducing cyclic polymers and the integral area of ​​the parts (cyclic polymers) with a number-average molecular weight greater than 400 on a GPC curve of low molecular weight substances is also outside the scope of the present invention, the brightness of the resulting polyester product is also deficient. In Comparative Example 5, the total content of low molecular weight substances and the integrated area of ​​the parts (cyclic polymers) having an average molecular weight in number greater than 400 on a GPC curve are high, and the brightness of the polyester product obtained is also deficient, so that a balance between flowability and brightness cannot be achieved. As can be seen from the results of Example 1-7 and Comparative Examples 1-5, the prepared polyester products cannot simultaneously meet the conditions that the total content of low molecular weight substances is in the range of 0.1-0.6% by weight and the proportion of the integral area of ​​the peaks having a number-average molecular weight (Mn) greater than 400 with respect to the total integral area on a GPC curve is less than 60%, so that the brightness and flow of the polyester products obtained cannot be balanced.

Claims

1. A polyester comprising a repeating unit derived from the following components: a first component A, based on a total molar amount of the first component A, comprising: a1) 81-100 mol%, preferably 90-100 mol% of succinic acid, or ester derivatives thereof or anhydride derivatives thereof; a2) 0-19 mol%, preferably 0-10 mol% of other binary carboxylic acids, other than succinic acid, or its ester derivatives or anhydride derivatives; a second component B, 1,4-butanediol; characterized in that, based on the total weight of the polyester, the total content of low molecular weight substances in the polyester is 0.1-0.6 wt%, preferably 0.2-0.5 wt%,and the GPC curve of the low molecular weight substances has the following characteristic: an integral area of ​​peaks having a number-average molecular weight (Mn) greater than 400 is less than 60% of the total integral area, and where the GPC measurement is performed according to the method defined in the descriptive report; and the total content of the low molecular weight substances is analyzed by the following method: weigh 10 g of polyester particles and record the mass of the polyester particles as wg; place the polyester particles in 100 ml of ethanol for heating and refluxing for 4 h, perform a heated filtration to obtain a filtrate, pour the filtrate onto a previously weighed evaporating plate and record the weight of the evaporating plate as a0; place the obtained filtrate in a water bath for evaporation until almost dry, transfer the evaporating plate to an oven to dry at 105 °C for 2 h,Next, remove the evaporation plate, weigh it after cooling for 0.5 h and record the weight as a1; and obtain the content of the low molecular weight substances as (a1-a0) / w × 100%.

2. The polyester according to claim 1, characterized in that the total content of the low molecular weight substances in the polyester is 0.2-0.35% by weight, and the GPC curve of the low molecular weight substances has the following characteristic: the integral area of ​​the peaks having a number-average molecular weight (Mn) greater than 400 is less than 50% of the total integral area.

3. The polyester according to claim 1, characterized in that the first component A comprises succinic acid or ester derivatives thereof or anhydride derivatives thereof.

4. The polyester according to claim 1, characterized in that the polyester further comprises a third component C,and component C is a compound containing at least three functional groups; and based on the total molar amount of the first component A, the content of the third component C is 0.01-1.0 mol%, preferably 0.02-0.2 mol%.

5. The polyester according to claim 4, characterized in that component C is selected from one or more of tartaric acid, citric acid, malic acid, fumaric acid, maleic acid, trimethylolpropane, trimethylolethane, pentaerythritol, polyether triol, glycerol, 1,3,5-benzenetricarboxylic acid, 1,2,4-benzenetricarboxylic acid, 1,2,4-benzenetricarboxylic anhydride, 1,2,4,5-benzenenotetracarboxylic acid, or pyromellitic dianhydride, preferably one or more of malic acid, citric acid, fumaric acid, maleic acid, or glycerol.

6. The polyester according to claim 1, characterized in that the polyester further comprises a fourth component D,and the fourth component D is a chain extender; and based on the total molar amount of the first component A, the content of the fourth component D is 0.01-5.0% by moles.

7. The polyester according to claim 6, characterized in that the fourth component D is selected from one or more of an isocyanate, an isocyanurate, a peroxide, an epoxide, oxazoline, oxazine, lactam, carbodiimide, and polycarbodiimide containing two or more functional groups, preferably an isocyanate containing two or more functional groups, and more preferably hexamethylene diisocyanate.

8. The polyester according to claim 1, characterized in that the viscosity of the polyester is determined in a phenol / o-dichlorobenzene solution at a weight ratio of 1:1 in a water bath at a constant temperature of 25 ± 0.05 °C, as specified according to document GB / T 17931-1999,is 100-350 ml / g.

9. A method of preparing the polyester according to any one of claims 1-8, characterized in that the method comprises the following steps: S1: mixing the first component A, the second component B and a portion of a catalyst,and perform heating in an esterification reactor at 180-260 °C to carry out an esterification reaction for 1-4 h to obtain an esterification product AB; S2: allow the esterification product AB in step S1 to undergo a primary polycondensation reaction at a reaction temperature of 200-240 °C for a reaction time of 2-6 h to obtain a primary polycondensation product Pre-AB; and S3: transfer the primary polycondensation product Pre-AB obtained in step S2 and the remaining catalyst to a final polymerization reactor to carry out a continuous polycondensation reaction at a temperature of 210-270 °C until the determined reaction product is in a phenol / odichlorobenzene solution at a weight ratio of 1:1 in a water bath at a constant temperature of 25 ± 0.05 °C, as specified according to document GB / T 17931-1999,achieves a viscosity of 100-350 ml / g; wherein the amount of catalyst added in step S1 is 10-40% by weight of the total amount of catalyst used, and the amount of catalyst added in step S3 is 60-90% by weight of the total amount of catalyst used.

10. The method of preparing the polyester according to claim 9, characterized in that the catalyst comprises one or more of a tin compound, an antimony compound, a cobalt compound, a lead compound, a zinc compound, an aluminum compound, or a titanium compound, preferably one or more of a zinc compound, an aluminum compound, or a titanium compound, and more preferably tetrabutyl orthotitanate and / or tetraisopropyl orthotitanate.

11. A polyester molding composition, characterized in that, calculated as a weight percent,The polyester molding composition comprises the following components: 5-95% by weight of polyester according to any one of claims 1-8; 5-95% by weight of an additive and / or other polymers; and 0-70% by weight of a reinforcing material and / or filler.

12. Use of polyester according to any one of claims 1-8 in the preparation of degradable compostable products, characterized in that the degradable compostable products comprise fibers, films, or containers.

13. Use of polyester according to any one of claims 1-8 in the preparation of suction tubes.

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