CN107987260B - Modified polyester and preparation method thereof - Google Patents
Modified polyester and preparation method thereof Download PDFInfo
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- CN107987260B CN107987260B CN201711341927.1A CN201711341927A CN107987260B CN 107987260 B CN107987260 B CN 107987260B CN 201711341927 A CN201711341927 A CN 201711341927A CN 107987260 B CN107987260 B CN 107987260B
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
- C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
- C08G63/12—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from polycarboxylic acids and polyhydroxy compounds
- C08G63/16—Dicarboxylic acids and dihydroxy compounds
- C08G63/18—Dicarboxylic acids and dihydroxy compounds the acids or hydroxy compounds containing carbocyclic rings
- C08G63/181—Acids containing aromatic rings
- C08G63/183—Terephthalic acids
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
- C08G63/78—Preparation processes
- C08G63/82—Preparation processes characterised by the catalyst used
- C08G63/85—Germanium, tin, lead, arsenic, antimony, bismuth, titanium, zirconium, hafnium, vanadium, niobium, tantalum, or compounds thereof
- C08G63/86—Germanium, antimony, or compounds thereof
- C08G63/866—Antimony or compounds thereof
Abstract
The invention relates to a modified polyester and a preparation method thereof, wherein terephthalic acid, ethylene glycol and dihydric alcohol with branched chain are mixed uniformlyAfter being homogenized, the modified polyester is obtained by esterification reaction and polycondensation reaction in sequence, wherein the structural formula of the dihydric alcohol with the branched chain is as follows:
in the formula, R1And R2Each independently selected from linear alkylene having 1 to 3 carbon atoms, R3Selected from alkyl with 1-5 carbon atoms, R4Selected from alkyl with 2-5 carbon atoms. The molecular chain of the finally prepared modified polyester comprises a terephthalic acid chain segment, an ethylene glycol chain segment and a dihydric alcohol chain segment with a branched chain, and the content of cyclic oligomer in the modified polyester is less than or equal to 0.6 wt%. The method can obviously reduce the content of the cyclic oligomer in the polyester without influencing the performance of the polyester, and the prepared modified polyester has high molecular weight and narrow distribution and has excellent popularization value.
Description
Technical Field
The invention belongs to the field of polymer modification, and relates to modified polyester and a preparation method thereof.
Background
Polyethylene terephthalate (PET) is a polymer with excellent performance, and the PET has the advantages of high modulus, high strength, good shape retention, good barrier property and the like, so that the PET is widely applied to the fields of fibers, bottle packaging, films, sheets and the like, the yield is increased year by year, and the industrial position is remarkably improved.
However, in the polycondensation reaction for synthesizing ethylene terephthalate, especially in the case of linear high polymer, linear and cyclic oligomers are also associated due to high-temperature oxidative degradation, the cyclic oligomers are formed by the back-biting cyclization of the chain ends of macromolecules in the polycondensation stage, about 70% or more of the cyclic oligomers are cyclic trimers, and the cyclic trimers have the characteristics of easy aggregation, easy crystallization, high chemical and heat stability and the like, and the formation of the cyclic trimers has the following influence on the processing of polyester: (1) the spinning assembly can be blocked, and the service life of the melt filter and the assembly is influenced; (2) the fiber can be separated out in the process of heat setting and deposited on a heating roller, so that the friction force is increased and the heating is uneven; (3) the dyeing process takes the cyclic trimer as a center, so that the dye is gathered and adhered to the surface of the fiber, the phenomena of dye color points, spots, color flowers and the like appear on the surface of the fiber, the hand feeling and the color light of the fabric woven by the fiber are influenced, and meanwhile, the normal liquid flow velocity of a melt is limited by the cyclic oligomer filled with a pipeline and a valve, so that the fiber is unevenly dyed, and the reproducibility is poor; (4) the adhesive is adhered to the surface of the fiber, so that the winding is difficult, the phenomena of yarn breakage, uneven thickness and the like occur, the mechanical properties of the fiber such as breaking strength, breaking elongation and the like are influenced, and the product quality is seriously influenced.
With the increasing production of polyester fiber, the demand for polyester quality is increasing, so the problem of polyester post-processing caused by cyclic oligomer is attracting attention, especially with the rapid development of fine denier polyester fiber, the market puts higher demands on the dyeing of polyester fiber. In order to reduce the generation of cyclic oligomers in the polycondensation reaction of polyesters, researchers at home and abroad have conducted a great deal of research. The main methods for reducing cyclic oligomers in polyesters are: (1) pentavalent phosphorus compound or ether compound is added to combine with metal catalyst in the polyester synthesis process, or the amount of heat stabilizer is increased, so as to generate stabilization effect on polyester, and thus the generation of cyclic trimer can be inhibited under high temperature melting; (2) the residence time of the polyester melt at high temperature is reduced. However, the above-mentioned method causes a decrease in the molecular weight and a broadening of the distribution of the polyester, affecting the quality of the finally obtained fiber, while the effect of reducing the cyclic trimer oligomers is not significant.
Therefore, it is very important to develop a method for remarkably reducing the content of cyclic oligomers in the polyester without affecting the properties of the polyester itself.
Disclosure of Invention
The present invention aims to overcome the problems of the prior art that the content of cyclic oligomers in polyester cannot be significantly reduced and the adverse effect on the performance of the polyester itself is generated, and provides a method for significantly reducing the content of cyclic oligomers in polyester without the adverse effect on the performance of the polyester itself, which is mainly realized by adding branched diol with a specific structure in the raw material of the polyester.
In order to achieve the purpose, the invention adopts the technical scheme that:
the modified polyester comprises a molecular chain comprising a terephthalic acid chain segment, an ethylene glycol chain segment and a dihydric alcohol chain segment with a branched chain, wherein the structural formula of the dihydric alcohol with the branched chain is as follows:
in the formula, R1And R2Each independently selected from linear alkylene having 1 to 3 carbon atoms, R3Selected from alkyl with 1-5 carbon atoms, R4The carbon atom number is 2-5, and the purpose of carbon atom number limitation is as follows: because a branched chain structure and a long chain structure are introduced into the dihydric alcohol, the electronegativity of an alkoxy part is weakened, the number of carbon atoms of the branched chain structure is too small, the electronegativity influence on the alkoxy part is small, and the significance for reducing the generation of cyclic oligomers is not large; when the number of carbon atoms in the branched structure is too large, intermolecular entanglement occurs, which affects the molecular weight distribution.
As a preferred technical scheme:
according to the modified polyester, the content of cyclic oligomer in the modified polyester is less than or equal to 0.6 wt%, the amount of cyclic oligomer in the polyester prepared by the prior art is 1.5-2.1 wt%, and compared with the prior art, the generation amount of cyclic oligomer is remarkably reduced.
The modified polyester has the number average molecular weight of 20000-27000 and the molecular weight distribution index of 1.8-2.2, is high in molecular weight and narrow in molecular weight distribution, can meet the requirements of spinning processing, and is beneficial to preparing fibers with excellent performance.
According to the modified polyester, the molar content of the dihydric alcohol chain segment with the branched chain in the modified polyester is 3-5% of that of the terephthalic acid chain segment, and the molar content of the dihydric alcohol chain segment with the branched chain in the modified polyester is low, so that the excellent performance of the polyester is favorably maintained.
The modified polyester as described above, wherein the branched diol is 2-ethyl-2-methyl-1, 3-propanediol, 2-diethyl-1, 3-propanediol, 2-butyl-2-ethyl-1, 3-propanediol, 3-diethyl-1, 5-pentanediol, 4-diethyl-1, 7-heptanediol, 4-bis (1, -methylethyl) -1, 7-heptanediol, 3-dipropyl-1, 5-pentanediol, 4-dipropyl-1, 7-heptanediol, 4-methyl-4- (1, 1-dimethylethyl) -1, 7-heptanediol, 3-methyl-3-pentyl-1, 6-hexanediol or 3, 3-dipentyl-1, 5-pentanediol.
The invention also provides a method for preparing the modified polyester, which comprises the steps of uniformly mixing terephthalic acid, ethylene glycol and the dihydric alcohol with the branched chain, and then carrying out esterification reaction and polycondensation reaction in sequence to obtain the modified polyester.
As a preferred technical scheme:
the method comprises the following specific steps:
(1) performing esterification reaction;
preparing terephthalic acid, ethylene glycol and the dihydric alcohol with the branched chain into slurry, adding a catalyst, a delustering agent and a stabilizer, uniformly mixing, pressurizing in a nitrogen atmosphere to perform esterification reaction, wherein the pressurizing pressure is normal pressure to 0.3MPa, the esterification reaction temperature is 250-260 ℃, and the esterification reaction endpoint is determined when the distilled amount of water in the esterification reaction reaches more than 90% of a theoretical value;
(2) performing polycondensation reaction;
and after the esterification reaction is finished, starting the polycondensation reaction in a low vacuum stage under the negative pressure condition, stably pumping the pressure in the low vacuum stage from normal pressure to below 500Pa in 30-50 min at the reaction temperature of 260-270 ℃ for 30-50 min, then continuously pumping the vacuum to perform the polycondensation reaction in a high vacuum stage, further reducing the reaction pressure to below 100Pa, controlling the reaction temperature to 275-285 ℃ and the reaction time to be 50-90 min, and thus obtaining the modified polyester.
In the method, in the step (1), the molar ratio of the terephthalic acid to the ethylene glycol to the branched diol is 1: 1.2-2.0: 0.03-0.06, the addition amount of the catalyst is 0.01-0.05% of the weight of the terephthalic acid, the addition amount of the flatting agent is 0.20-0.25% of the weight of the terephthalic acid, and the addition amount of the stabilizer is 0.01-0.05% of the weight of the terephthalic acid.
In the method, the catalyst is antimony trioxide, ethylene glycol antimony or antimony acetate, the flatting agent is titanium dioxide, and the stabilizer is triphenyl phosphate, trimethyl phosphate or trimethyl phosphite.
The invention mechanism is as follows:
in organic compounds, the angle between two chemical bonds formed by the same atom in a molecule is called the bond angle, which is usually expressed in degrees, and the electronegativity of the central atom and the coordinating atom in the molecule of the organic compound affects the bond angle of the molecule. When the electronegativity of the coordinating atom bonded to the central atom is increased, the electron-withdrawing ability of the coordinating atom is increased, the bonding electron pair moves toward the ligand and is farther away from the central atom, so that the bond pairs are closer to each other due to the decrease in repulsive force, and the bond angle is decreased, and conversely, when the electronegativity of the coordinating atom bonded to the central atom is decreased, the electron-donating ability of the coordinating atom is increased, the bonding electron pair moves toward the central atom and is closer to the central atom, so that the bond pairs are farther away from each other due to the increase in repulsive force, and the bond angle is increased.
According to Pauling electronegativity scale, the electronegativity of C, H and O atoms are 2.55, 2.20 and 3.44, respectively, and according to valence electron energy equilibrium theory, the calculation formula of the group electronegativity is shown as follows:
in the formula, xiIs the electronegativity of the neutral atom of the i atom prior to bonding,
is the number of valence electrons in the i atom, niIs the number of i atoms in the molecule. The calculation steps for the electronegativity of more complex groups are mainly: the electronegativity of the simple group is firstly calculated, then the electronegativity of the more complex group is calculated by taking the simple group as a quasi atom, and the electronegativity of the target group is finally obtained through successive iteration. In calculating the electronegativity of a quasi-atom, the valence electron that is not bonded in a radical atom (for example, the radical atom of a group-OH is an O atom) is regarded as the valence electron of the quasi-atom.
In the invention, after C-O bond of carboxyl in terephthalic acid is broken, C atom is combined with O atom of hydroxyl in dihydric alcohol to form new C-O bond in ester group, bond angle between C-C bond formed by C atom in ester group and C atom on benzene ring and newly formed chemical bond C-O is marked as alpha, change of bond angle alpha can affect ring forming reaction, when alpha is less than 109 ℃, the molecule is easy to form ring, and with increase of alpha, the ring forming probability of the molecule is reduced. The invention introduces dihydric alcohol with branched chain, and the structural formula is shown as the following formula:
in the formula, R1And R2Each independently selected from linear alkylene having 1 to 3 carbon atoms, R3Selected from alkyl with 1-5 carbon atoms, R4Selected from alkyl with 2-5 carbon atoms. The diol structure is introduced with a branched chain structure and a long chain structure, so that the electronegativity of an alkoxy part of the diol structure is weakened, and the electronegativity of a group connected with a carbonyl group in diacid in the diol structure is 2.59-2.79 according to a calculation formula of the electronegativity of the group, and a group-OCH (OCH) group connected with the carbonyl group in the diacid in ethylene glycol2CH2Electronegativity of-was 3.04, so that the alkoxy group was in comparison with-OCH in ethylene glycol2CH2The bond-forming electron pairs on the newly formed chemical bond C-O bond are moved to the central C atom and are closer to the central atom, so that the bond angles alpha are larger than 109 degrees and the probability of forming linear polymers is increased, thereby reducing the generation of cyclic oligomers.
Has the advantages that:
(1) the modified polyester has high molecular weight and narrow distribution, and can be used for preparing fibers with excellent dyeing property and mechanical property.
(2) According to the preparation method of the modified polyester, the dihydric alcohol with the branched chain is introduced, so that the bond angle of the polyester molecule is changed, and the generation of cyclic oligomer in the polyester synthesis process is obviously reduced.
(3) The preparation method of the modified polyester is simple and reasonable in preparation process, does not have adverse effect on the performance of the polyester, and has excellent popularization value.
Detailed Description
The invention will be further illustrated with reference to specific embodiments. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.
Example 1
The preparation method of the modified polyester comprises the following specific steps:
(1) performing esterification reaction;
preparing terephthalic acid, ethylene glycol and 2-ethyl-2-methyl-1, 3-propanediol with a molar ratio of 1:1.2:0.03 into slurry, adding antimony trioxide, titanium dioxide and triphenyl phosphate, uniformly mixing, pressurizing in a nitrogen atmosphere to perform esterification reaction, wherein the pressurizing pressure is normal pressure, the esterification reaction temperature is 250 ℃, and the esterification reaction end point is when the distilled water amount in the esterification reaction reaches 90% of a theoretical value, wherein the adding amount of the antimony trioxide is 0.01% of the weight of the terephthalic acid, the adding amount of the titanium dioxide is 0.20% of the weight of the terephthalic acid, and the adding amount of the triphenyl phosphate is 0.05% of the weight of the terephthalic acid, wherein the structural formula of the 2-ethyl-2-methyl-1, 3-propanediol is as follows:
(2) performing polycondensation reaction;
after the esterification reaction is finished, starting the polycondensation reaction in the low vacuum stage under the condition of negative pressure, smoothly pumping the pressure from normal pressure to the absolute pressure of 500Pa within 30min, controlling the reaction temperature to be 260 ℃ and the reaction time to be 40min, then continuing to pump the vacuum, and carrying out the polycondensation reaction in the high vacuum stage to further reduce the reaction pressure to the absolute pressure of 100Pa, control the reaction temperature to be 275 ℃ and control the reaction time to be 70min, thus obtaining the modified polyester.
The molecular chain of the finally prepared modified polyester comprises a terephthalic acid chain segment, a glycol chain segment and a 2-ethyl-2-methyl-1, 3-propanediol chain segment, the content of cyclic oligomer in the modified polyester is 0.6 wt%, the number average molecular weight is 20000, the molecular weight distribution index is 2.0, and the molar content of the 2-ethyl-2-methyl-1, 3-propanediol chain segment in the modified polyester is 3% of the molar content of the terephthalic acid chain segment.
Comparative example 1
A process for the preparation of a polyester substantially as in example 1, comprising the steps of:
(1) performing esterification reaction;
preparing terephthalic acid and ethylene glycol with a molar ratio of 1:1.2 into slurry, adding antimony trioxide, titanium dioxide and triphenyl phosphate, uniformly mixing, pressurizing in a nitrogen atmosphere to perform esterification reaction, wherein the pressurizing pressure is normal pressure, the esterification reaction temperature is 250 ℃, and the esterification reaction endpoint is when the distilled amount of water in the esterification reaction reaches 90% of a theoretical value, wherein the adding amount of the antimony trioxide is 0.01% of the weight of the terephthalic acid, the adding amount of the titanium dioxide is 0.20% of the weight of the terephthalic acid, and the adding amount of the triphenyl phosphate is 0.05% of the weight of the terephthalic acid;
(2) performing polycondensation reaction;
after the esterification reaction is finished, starting the polycondensation reaction in the low vacuum stage under the condition of negative pressure, smoothly pumping the pressure from normal pressure to the absolute pressure of 500Pa within 30min, controlling the reaction temperature to be 260 ℃ and the reaction time to be 40min, then continuing to pump the vacuum, and carrying out the polycondensation reaction in the high vacuum stage, so that the reaction pressure is further reduced to the absolute pressure of 100Pa, the reaction temperature is 275 ℃ and the reaction time is 70 min.
The content of cyclic oligomer in the obtained polyester was 2.1% by weight, the number average molecular weight was 25000, and the molecular weight distribution index was 1.92. Compared with the example 1, the invention introduces the branched diol with a specific structure into the polyester molecule to prepare the modified polyester, and the prepared modified polyester obviously reduces the generation amount of the cyclic oligomer.
Comparative example 2
A process for the preparation of a modified polyester substantially as in example 1, comprising the steps of:
(1) performing esterification reaction;
preparing terephthalic acid, ethylene glycol and 2-amyl-1, 3-propanediol with a molar ratio of 1:1.2:0.03 into slurry, adding antimony trioxide, titanium dioxide and triphenyl phosphate, uniformly mixing, and pressurizing in a nitrogen atmosphere to perform esterification reaction, wherein the pressurizing pressure is normal pressure, the esterification reaction temperature is 250 ℃, and the esterification reaction end point is determined when the water distillation amount in the esterification reaction reaches 90% of a theoretical value, wherein the adding amount of the antimony trioxide is 0.01% of the weight of the terephthalic acid, the adding amount of the titanium dioxide is 0.20% of the weight of the terephthalic acid, and the adding amount of the triphenyl phosphate is 0.05% of the weight of the terephthalic acid;
(2) performing polycondensation reaction;
after the esterification reaction is finished, starting the polycondensation reaction in the low vacuum stage under the condition of negative pressure, smoothly pumping the pressure from normal pressure to the absolute pressure of 500Pa within 30min, controlling the reaction temperature to be 260 ℃ and the reaction time to be 40min, then continuing to pump the vacuum, and carrying out the polycondensation reaction in the high vacuum stage to further reduce the reaction pressure to the absolute pressure of 100Pa, control the reaction temperature to be 275 ℃ and control the reaction time to be 70min, thus obtaining the modified polyester.
The content of cyclic oligomer in the prepared modified polyester is higher than 1.5 wt%, the number average molecular weight is 15000, and the molecular weight distribution index is 1.95, and compared with example 1, the two preparation methods are characterized in that the types of the dihydric alcohol with the branched chain introduced into the slurry are different, and the generation amount of the cyclic oligomer in the molecular structure of the prepared modified polyester is also different, so that the preparation method of the modified polyester can remarkably reduce the generation amount of the cyclic oligomer in the molecular structure, and the application prospect is very considerable.
Example 2
The preparation method of the modified polyester comprises the following specific steps:
(1) performing esterification reaction;
preparing terephthalic acid, ethylene glycol and 2, 2-diethyl-1, 3-propanediol with a molar ratio of 1:1.3:0.04 into slurry, adding ethylene glycol antimony, titanium dioxide and trimethyl phosphate, uniformly mixing, pressurizing in a nitrogen atmosphere to perform esterification reaction, wherein the pressurizing pressure is normal pressure, the esterification reaction temperature is 260 ℃, and the esterification reaction end point is when the distilled water amount in the esterification reaction reaches 91% of a theoretical value, wherein the adding amount of the ethylene glycol antimony is 0.02% of the weight of the terephthalic acid, the adding amount of the titanium dioxide is 0.21% of the weight of the terephthalic acid, and the adding amount of the trimethyl phosphate is 0.03% of the weight of the terephthalic acid, wherein the structural formula of the 2, 2-diethyl-1, 3-propanediol is as follows:
(2) performing polycondensation reaction;
after the esterification reaction is finished, starting the polycondensation reaction in the low vacuum stage under the condition of negative pressure, smoothly pumping the pressure from normal pressure to absolute pressure of 490Pa within 35min, controlling the reaction temperature to 261 ℃ and the reaction time to 30min, then continuing to pump the vacuum, and carrying out the polycondensation reaction in the high vacuum stage, so that the reaction pressure is further reduced to absolute pressure of 100Pa, the reaction temperature is 277 ℃ and the reaction time is 85min, thus obtaining the modified polyester.
The molecular chain of the finally prepared modified polyester comprises a terephthalic acid chain segment, a glycol chain segment and a 2, 2-diethyl-1, 3-propanediol chain segment, the content of cyclic oligomer in the modified polyester is 0.6 wt%, the number average molecular weight is 27000, the molecular weight distribution index is 1.8, and the molar content of the 2, 2-diethyl-1, 3-propanediol chain segment in the modified polyester is 5% of the molar content of the terephthalic acid chain segment.
Comparative example 3
A process for the preparation of a modified polyester substantially as in example 2, comprising the steps of:
(1) performing esterification reaction;
preparing terephthalic acid, ethylene glycol and 2-hexyl-1, 3-propanediol with the molar ratio of 1:1.3:0.04 into slurry, adding ethylene glycol antimony, titanium dioxide and trimethyl phosphate, uniformly mixing, pressurizing in a nitrogen atmosphere to perform esterification reaction, wherein the pressurizing pressure is normal pressure, the esterification reaction temperature is 260 ℃, and the esterification reaction end point is when the water distillation amount in the esterification reaction reaches 91% of a theoretical value, wherein the adding amount of the ethylene glycol antimony is 0.02% of the weight of the terephthalic acid, the adding amount of the titanium dioxide is 0.21% of the weight of the terephthalic acid, and the adding amount of the trimethyl phosphate is 0.03% of the weight of the terephthalic acid;
(2) performing polycondensation reaction;
after the esterification reaction is finished, starting the polycondensation reaction in the low vacuum stage under the condition of negative pressure, smoothly pumping the pressure from normal pressure to absolute pressure of 490Pa within 35min, controlling the reaction temperature to 261 ℃ and the reaction time to 30min, then continuing to pump the vacuum, and carrying out the polycondensation reaction in the high vacuum stage, so that the reaction pressure is further reduced to absolute pressure of 100Pa, the reaction temperature is 277 ℃ and the reaction time is 85min, thus obtaining the modified polyester.
The content of cyclic oligomer in the prepared modified polyester is higher than 1.8 wt%, the number average molecular weight is 16000, and the molecular weight distribution index is 2.03, and compared with example 2, the two preparation methods are characterized in that the types of the dihydric alcohol with the branched chain introduced into the slurry are different, and the generation amount of the cyclic oligomer in the molecular structure of the prepared modified polyester is also different, so that the preparation method of the modified polyester can remarkably reduce the generation amount of the cyclic oligomer in the molecular structure, and has a very good application prospect.
Example 3
The preparation method of the modified polyester comprises the following specific steps:
(1) performing esterification reaction;
preparing terephthalic acid, ethylene glycol and 2-butyl-2-ethyl-1, 3-propanediol with a molar ratio of 1:1.4:0.05 into slurry, adding antimony acetate, titanium dioxide and trimethyl phosphite, uniformly mixing, pressurizing in a nitrogen atmosphere to perform esterification reaction, wherein the pressurizing pressure is 0.1MPa, the esterification reaction temperature is 252 ℃, and the esterification reaction end point is when the distilled water amount in the esterification reaction reaches 92% of a theoretical value, wherein the adding amount of the antimony acetate is 0.03% of the weight of the terephthalic acid, the adding amount of the titanium dioxide is 0.23% of the weight of the terephthalic acid, and the adding amount of the trimethyl phosphite is 0.01% of the weight of the terephthalic acid, wherein the structural formula of the 2-butyl-2-ethyl-1, 3-propanediol is as follows:
(2) performing polycondensation reaction;
after the esterification reaction is finished, starting the polycondensation reaction in the low vacuum stage under the negative pressure condition, smoothly pumping the pressure from normal pressure to absolute pressure of 495Pa, the reaction temperature of 263 ℃ and the reaction time of 45min within 40min, then continuing to pump vacuum, and carrying out the polycondensation reaction in the high vacuum stage, so that the reaction pressure is further reduced to absolute pressure of 95Pa, the reaction temperature of 278 ℃ and the reaction time of 60min, thus obtaining the modified polyester.
The molecular chain of the finally prepared modified polyester comprises a terephthalic acid chain segment, a glycol chain segment and a 2-butyl-2-ethyl-1, 3-propanediol chain segment, the content of cyclic oligomer in the modified polyester is 0.5 wt%, the number average molecular weight is 21000, the molecular weight distribution index is 2.2, and the molar content of the 2-butyl-2-ethyl-1, 3-propanediol chain segment in the modified polyester is 4% of the molar content of the terephthalic acid chain segment.
Comparative example 4
A process for the preparation of a modified polyester substantially as in example 3, comprising the steps of:
(1) performing esterification reaction;
preparing terephthalic acid, ethylene glycol and 2-heptyl-1, 3-propanediol with the molar ratio of 1:1.4:0.05 into slurry, adding antimony acetate, titanium dioxide and trimethyl phosphite, uniformly mixing, and pressurizing in a nitrogen atmosphere to perform esterification reaction, wherein the pressurizing pressure is 0.1MPa, the esterification reaction temperature is 252 ℃, and the esterification reaction end point is determined when the water distillation amount in the esterification reaction reaches 92% of a theoretical value, wherein the adding amount of antimony acetate is 0.03% of the weight of the terephthalic acid, the adding amount of titanium dioxide is 0.23% of the weight of the terephthalic acid, and the adding amount of trimethyl phosphite is 0.01% of the weight of the terephthalic acid;
(2) performing polycondensation reaction;
after the esterification reaction is finished, starting the polycondensation reaction in the low vacuum stage under the negative pressure condition, smoothly pumping the pressure from normal pressure to absolute pressure of 495Pa, the reaction temperature of 263 ℃ and the reaction time of 45min within 40min, then continuing to pump vacuum, and carrying out the polycondensation reaction in the high vacuum stage, so that the reaction pressure is further reduced to absolute pressure of 95Pa, the reaction temperature of 278 ℃ and the reaction time of 60min, thus obtaining the modified polyester.
The content of cyclic oligomer in the prepared modified polyester is higher by 2.1 wt%, the number average molecular weight is 15900, and the molecular weight distribution index is 1.98, as compared with example 3, it can be known that the generation amount of cyclic oligomer in the molecular structure of the prepared modified polyester is different because the types of the dihydric alcohol with branched chain introduced in the two preparation methods are different, so that the preparation method of the modified polyester of the present invention can significantly reduce the generation amount of cyclic oligomer in the molecular structure.
Example 4
The preparation method of the modified polyester comprises the following specific steps:
(1) preparing 3, 3-diethyl-1, 5-pentanediol;
reacting 3, 3-diethyl-propionaldehyde, acetaldehyde and triethylamine for 20min at 90-95 ℃ under nitrogen atmosphere, then adding the concentrated solution into a hydrogenation reactor with a Raney nickel catalyst, reacting at the hydrogen pressure of 2.914MPa and the temperature of 100 ℃, cooling after the reaction is finished, separating out the catalyst, treating the solution with ion exchange resin, evaporating water under reduced pressure, separating and purifying to obtain 3, 3-diethyl-1, 5-pentanediol, wherein the structural formula of the 3, 3-diethyl-1, 5-pentanediol is as follows:
(2) performing esterification reaction;
preparing terephthalic acid, ethylene glycol and 3, 3-diethyl-1, 5-pentanediol with the molar ratio of 1:1.5:0.06 into slurry, adding antimony trioxide, titanium dioxide and triphenyl phosphate, uniformly mixing, pressurizing in a nitrogen atmosphere to perform esterification reaction, wherein the pressurizing pressure is 0.3MPa, the esterification reaction temperature is 255 ℃, and the esterification reaction end point is when the distilled amount of water in the esterification reaction reaches 95% of a theoretical value, wherein the adding amount of the antimony trioxide is 0.04% of the weight of the terephthalic acid, the adding amount of the titanium dioxide is 0.25% of the weight of the terephthalic acid, and the adding amount of the triphenyl phosphate is 0.01% of the weight of the terephthalic acid;
(3) performing polycondensation reaction;
after the esterification reaction is finished, starting the polycondensation reaction in the low vacuum stage under the condition of negative pressure, smoothly pumping the pressure from normal pressure to the absolute pressure of 400Pa within 50min, controlling the reaction temperature to be 265 ℃ and the reaction time to be 33min, then continuing to pump the vacuum, and carrying out the polycondensation reaction in the high vacuum stage to further reduce the reaction pressure to the absolute pressure of 90Pa, control the reaction temperature to be 280 ℃ and control the reaction time to be 50min, thus obtaining the modified polyester.
The molecular chain of the finally prepared modified polyester comprises a terephthalic acid chain segment, an ethylene glycol chain segment and a 3, 3-diethyl-1, 5-pentanediol chain segment, the content of cyclic oligomers in the modified polyester is 0.2 wt%, the number average molecular weight is 23000, the molecular weight distribution index is 1.9, and the molar content of the 3, 3-diethyl-1, 5-pentanediol chain segment in the modified polyester is 3.5% of the molar content of the terephthalic acid chain segment.
Example 5
The preparation method of the modified polyester comprises the following specific steps:
(1) preparing 4, 4-diethyl-1, 7-heptanediol;
reacting 4, 4-diethyl-butyraldehyde, propionaldehyde and triethylamine for 20min at 90-95 ℃ under nitrogen atmosphere, then adding the concentrated solution into a hydrogenation reactor with a Raney nickel catalyst, reacting at the hydrogen pressure of 2.914MPa and the temperature of 100 ℃, cooling after the reaction is finished, separating out the catalyst, treating the solution with ion exchange resin, evaporating water under reduced pressure, separating and purifying to obtain 4, 4-diethyl-1, 7-heptanediol, wherein the structural formula of the 4, 4-diethyl-1, 7-heptanediol is as follows:
(2) performing esterification reaction;
preparing terephthalic acid, ethylene glycol and 4, 4-diethyl-1, 7-heptanediol with a molar ratio of 1:1.6:0.03 into slurry, adding ethylene glycol antimony, titanium dioxide and trimethyl phosphate, uniformly mixing, and pressurizing in a nitrogen atmosphere to perform esterification reaction, wherein the pressurizing pressure is normal pressure, the esterification reaction temperature is 257 ℃, and the esterification reaction end point is when the distilled amount of water in the esterification reaction reaches 92% of a theoretical value, wherein the adding amount of the ethylene glycol antimony is 0.05% of the weight of the terephthalic acid, the adding amount of the titanium dioxide is 0.20% of the weight of the terephthalic acid, and the adding amount of the trimethyl phosphate is 0.04% of the weight of the terephthalic acid;
(3) performing polycondensation reaction;
after the esterification reaction is finished, starting the polycondensation reaction in the low vacuum stage under the condition of negative pressure, smoothly pumping the pressure from normal pressure to the absolute pressure of 450Pa within 33min, controlling the reaction temperature to be 270 ℃ and the reaction time to be 30min, then continuing to pump the vacuum, and carrying out the polycondensation reaction in the high vacuum stage to further reduce the reaction pressure to the absolute pressure of 95Pa, control the reaction temperature to be 275 ℃ and control the reaction time to be 60min, thus obtaining the modified polyester.
The molecular chain of the finally prepared modified polyester comprises a terephthalic acid chain segment, an ethylene glycol chain segment and a 4, 4-diethyl-1, 7-heptanediol chain segment, the content of cyclic oligomers in the modified polyester is 0.5 wt%, the number average molecular weight is 25000, the molecular weight distribution index is 2.1, and the molar content of the 4, 4-diethyl-1, 7-heptanediol chain segment in the modified polyester is 5% of the molar content of the terephthalic acid chain segment.
Example 6
The preparation method of the modified polyester comprises the following specific steps:
(1) preparing 4, 4-di (1-methylethyl) -1, 7-heptanediol;
reacting 4, 4-di (1-methylethyl) -butyraldehyde, propionaldehyde and triethylamine for 20min at 90-95 ℃ under nitrogen atmosphere, adding the concentrated solution into a hydrogenation reactor with a Raney nickel catalyst, reacting at the hydrogen pressure of 2.914MPa and the temperature of 100 ℃, and cooling to separate out the catalyst after the reaction. After the solution is treated by ion exchange resin, water is evaporated under reduced pressure, and the 4, 4-di (1-methylethyl) -1, 7-heptanediol is separated and purified, wherein the structural formula of the 4, 4-di (1-methylethyl) -1, 7-heptanediol is as follows:
(2) performing esterification reaction;
preparing terephthalic acid, ethylene glycol and 4, 4-di (1-methylethyl) -1, 7-heptanediol into slurry with the molar ratio of 1:1.7:0.05, adding antimony acetate, titanium dioxide and trimethyl phosphite, uniformly mixing, and pressurizing in a nitrogen atmosphere to perform esterification reaction, wherein the pressurizing pressure is 0.2MPa, the temperature of the esterification reaction is 253 ℃, and the end point of the esterification reaction is determined when the distilled amount of water in the esterification reaction reaches 96% of a theoretical value, wherein the adding amount of the antimony acetate is 0.01% of the weight of the terephthalic acid, the adding amount of the titanium dioxide is 0.20% of the weight of the terephthalic acid, and the adding amount of the trimethyl phosphite is 0.05% of the weight of the terephthalic acid;
(3) performing polycondensation reaction;
after the esterification reaction is finished, starting the polycondensation reaction in the low vacuum stage under the condition of negative pressure, smoothly pumping the pressure from normal pressure to absolute pressure of 480Pa within 38min, controlling the reaction temperature to be 262 ℃, controlling the reaction time to be 38min, then continuing to pump the vacuum, and carrying out the polycondensation reaction in the high vacuum stage, so that the reaction pressure is further reduced to absolute pressure of 98Pa, the reaction temperature is 279 ℃, and the reaction time is 80min, thus obtaining the modified polyester.
The molecular chain of the finally prepared modified polyester comprises a terephthalic acid chain segment, a glycol chain segment and a 4, 4-bis (1-methylethyl) -1, 7-heptanediol chain segment, the content of cyclic oligomers in the modified polyester is 0.55 wt%, the number average molecular weight is 27000, the molecular weight distribution index is 2.2, and the molar content of the 4, 4-bis (1-methylethyl) -1, 7-heptanediol chain segment in the modified polyester is 4% of the molar content of the terephthalic acid chain segment.
Example 7
The preparation method of the modified polyester comprises the following specific steps:
(1) preparing 3, 3-dipropyl-1, 5-pentanediol;
reacting 3, 3-dipropyl-propionaldehyde, acetaldehyde and triethylamine for 20min at 90-95 ℃ under nitrogen atmosphere, then adding the concentrated solution into a hydrogenation reactor with a Raney nickel catalyst, reacting at the hydrogen pressure of 2.914MPa and the temperature of 100 ℃, cooling after the reaction is finished, and separating out the catalyst. After the solution is treated by ion exchange resin, water is evaporated under reduced pressure, and the 3, 3-dipropyl-1, 5-pentanediol is separated and purified, wherein the structural formula of the 3, 3-dipropyl-1, 5-pentanediol is as follows:
(2) performing esterification reaction;
preparing terephthalic acid, ethylene glycol and 3, 3-dipropyl-1, 5-pentanediol with the molar ratio of 1:1.8:0.03 into slurry, adding antimony trioxide, titanium dioxide and triphenyl phosphate, uniformly mixing, pressurizing in a nitrogen atmosphere to perform esterification reaction, wherein the pressurizing pressure is 0.3MPa, the esterification reaction temperature is 250 ℃, and the esterification reaction end point is when the distilled amount of water in the esterification reaction reaches 90% of a theoretical value, wherein the adding amount of the antimony trioxide is 0.03% of the weight of the terephthalic acid, the adding amount of the titanium dioxide is 0.24% of the weight of the terephthalic acid, and the adding amount of the triphenyl phosphate is 0.02% of the weight of the terephthalic acid;
(3) performing polycondensation reaction;
after the esterification reaction is finished, starting the polycondensation reaction in the low vacuum stage under the negative pressure condition, smoothly pumping the pressure from normal pressure to the absolute pressure of 455Pa within 42min, the reaction temperature of 264 ℃ and the reaction time of 45min, then continuing to pump vacuum, and carrying out the polycondensation reaction in the high vacuum stage to further reduce the reaction pressure to the absolute pressure of 85Pa, the reaction temperature of 285 ℃ and the reaction time of 75min, thus obtaining the modified polyester.
The molecular chain of the finally prepared modified polyester comprises a terephthalic acid chain segment, an ethylene glycol chain segment and a 3, 3-dipropyl-1, 5-pentanediol chain segment, the content of cyclic oligomers in the modified polyester is 0.45 wt%, the number average molecular weight is 26500, the molecular weight distribution index is 2.2, and the molar content of the 3, 3-dipropyl-1, 5-pentanediol chain segment in the modified polyester is 4.5% of the molar content of the terephthalic acid chain segment.
Example 8
The preparation method of the modified polyester comprises the following specific steps:
(1) preparing 4, 4-dipropyl-1, 7-heptanediol;
reacting 4, 4-dipropyl-butyraldehyde, acetaldehyde and triethylamine for 20min at 90-95 ℃ under nitrogen atmosphere, adding the concentrated solution into a hydrogenation reactor with a Raney nickel catalyst, reacting at the hydrogen pressure of 2.914MPa and the temperature of 100 ℃, cooling after the reaction is finished, and separating out the catalyst. Treating the solution with ion exchange resin, evaporating water under reduced pressure, separating, and purifying to obtain 4, 4-dipropyl-1, 7-heptanediol, wherein the structural formula of the 4, 4-dipropyl-1, 7-heptanediol is as follows:
(2) performing esterification reaction;
preparing terephthalic acid, ethylene glycol and 4, 4-dipropyl-1, 7-heptanediol with a molar ratio of 1:1.9:0.04 into slurry, adding ethylene glycol antimony, titanium dioxide and trimethyl phosphate, uniformly mixing, pressurizing in a nitrogen atmosphere to perform esterification reaction, wherein the pressurizing pressure is 0.3MPa, the esterification reaction temperature is 260 ℃, and the esterification reaction endpoint is determined when the water distillation amount in the esterification reaction reaches 93% of a theoretical value, wherein the adding amount of the ethylene glycol antimony is 0.04% of the weight of the terephthalic acid, the adding amount of the titanium dioxide is 0.21% of the weight of the terephthalic acid, and the adding amount of the trimethyl phosphate is 0.03% of the weight of the terephthalic acid;
(3) performing polycondensation reaction;
after the esterification reaction is finished, starting the polycondensation reaction in the low vacuum stage under the negative pressure condition, smoothly pumping the pressure from normal pressure to absolute pressure of 475Pa within 45min, the reaction temperature of 265 ℃ and the reaction time of 48min, then continuing to pump vacuum, and carrying out the polycondensation reaction in the high vacuum stage, so that the reaction pressure is further reduced to absolute pressure of 88Pa, the reaction temperature of 283 ℃ and the reaction time of 80min, thus obtaining the modified polyester.
The molecular chain of the finally prepared modified polyester comprises a terephthalic acid chain segment, an ethylene glycol chain segment and a 4, 4-dipropyl-1, 7-heptanediol chain segment, the content of cyclic oligomers in the modified polyester is 0.6 wt%, the number average molecular weight is 23000, the molecular weight distribution index is 2.0, and the molar content of the 4, 4-dipropyl-1, 7-heptanediol chain segment in the modified polyester is 3% of the molar content of the terephthalic acid chain segment.
Example 9
The preparation method of the modified polyester comprises the following specific steps:
(1) preparing 4-methyl-4- (1, 1-dimethylethyl) -1, 7-heptanediol;
reacting 4-methyl-4- (1, 1-dimethylethyl) -butyraldehyde, propionaldehyde and triethylamine for 20min at 90-95 ℃ under a nitrogen atmosphere, then adding the concentrated solution into a hydrogenation reactor with a Raney nickel catalyst, reacting at the hydrogen pressure of 2.914MPa and the temperature of 100 ℃, cooling after the reaction is finished, separating out the catalyst, treating the solution with ion exchange resin, evaporating water under reduced pressure, separating and purifying to obtain 4-methyl-4- (1, 1-dimethylethyl) -1, 7-heptanediol, wherein the structural formula of the 4-methyl-4- (1, 1-dimethylethyl) -1, 7-heptanediol is as follows:
(2) performing esterification reaction;
preparing terephthalic acid, ethylene glycol and 4-methyl-4- (1, 1-dimethylethyl) -1, 7-heptanediol with the molar ratio of 1:2.0:0.05 into slurry, adding antimony acetate, titanium dioxide and trimethyl phosphate, uniformly mixing, pressurizing in a nitrogen atmosphere to perform esterification reaction, wherein the pressurizing pressure is normal pressure MPa, the esterification reaction temperature is 251 ℃, and the esterification reaction end point is determined when the distilled amount of water in the esterification reaction reaches 96% of a theoretical value, wherein the adding amount of the antimony acetate is 0.05% of the weight of the terephthalic acid, the adding amount of the titanium dioxide is 0.22% of the weight of the terephthalic acid, and the adding amount of the trimethyl phosphate is 0.04% of the weight of the terephthalic acid;
(3) performing polycondensation reaction;
after the esterification reaction is finished, starting the polycondensation reaction in the low vacuum stage under the condition of negative pressure, smoothly pumping the pressure from normal pressure to the absolute pressure of 420Pa within 30min, controlling the reaction temperature to 267 ℃, controlling the reaction time to 50min, then continuing to pump the vacuum, and carrying out the polycondensation reaction in the high vacuum stage, so that the reaction pressure is further reduced to the absolute pressure of 80Pa, the reaction temperature is 280 ℃, and the reaction time is 90min, thus obtaining the modified polyester.
The molecular chain of the finally prepared modified polyester comprises a terephthalic acid chain segment, a glycol chain segment and a 4-methyl-4- (1, 1-dimethylethyl) -1, 7-heptanediol chain segment, the content of cyclic oligomers in the modified polyester is 0.25 wt%, the number average molecular weight is 24000, the molecular weight distribution index is 2.2, and the molar content of the 4-methyl-4- (1, 1-dimethylethyl) -1, 7-heptanediol chain segment in the modified polyester is 4% of the molar content of the terephthalic acid chain segment.
Example 10
The preparation method of the modified polyester comprises the following specific steps:
(1) preparing 3-methyl-3-pentyl-1, 6-hexanediol;
reacting 3-methyl-3-pentyl-propionaldehyde, propionaldehyde and triethylamine for 20min at 90-95 ℃ under nitrogen atmosphere, adding the concentrated solution into a hydrogenation reactor with a Raney nickel catalyst, reacting at the hydrogen pressure of 2.914MPa and the temperature of 100 ℃, cooling after the reaction is finished, and separating out the catalyst. After the solution is treated by ion exchange resin, water is evaporated under reduced pressure, and the 3-methyl-3-pentyl-1, 6-hexanediol is obtained through separation and purification, wherein the structural formula of the 3-methyl-3-pentyl-1, 6-hexanediol is as follows:
(2) performing esterification reaction;
preparing terephthalic acid, ethylene glycol and 3-methyl-3-pentyl-1, 6-hexanediol into slurry with a molar ratio of 1:1.2:0.06, adding ethylene glycol antimony, titanium dioxide and trimethyl phosphite, uniformly mixing, and pressurizing in a nitrogen atmosphere to perform esterification reaction, wherein the pressurizing pressure is 0.1MPa, the esterification reaction temperature is 255 ℃, and the esterification reaction end point is when the water distillation amount in the esterification reaction reaches 92% of a theoretical value, wherein the adding amount of the ethylene glycol antimony is 0.01% of the weight of the terephthalic acid, the adding amount of the titanium dioxide is 0.20% of the weight of the terephthalic acid, and the adding amount of the trimethyl phosphite is 0.01% of the weight of the terephthalic acid;
(3) performing polycondensation reaction;
after the esterification reaction is finished, starting the polycondensation reaction in the low vacuum stage under the condition of negative pressure, smoothly pumping the pressure from normal pressure to absolute pressure of 490Pa within 50min, the reaction temperature of 269 ℃, the reaction time of 30min, then continuing to pump vacuum, and carrying out the polycondensation reaction in the high vacuum stage, so that the reaction pressure is further reduced to absolute pressure of 100Pa, the reaction temperature of 281 ℃, and the reaction time of 55min, thus obtaining the modified polyester.
The molecular chain of the finally prepared modified polyester comprises a terephthalic acid chain segment, an ethylene glycol chain segment and a 3-methyl-3-amyl-1, 6-hexanediol chain segment, the content of cyclic oligomer in the modified polyester is 0.1 wt%, the number average molecular weight is 20000, the molecular weight distribution index is 1.9, and the molar content of the 3-methyl-3-amyl-1, 6-hexanediol chain segment in the modified polyester is 3.5 percent of the molar content of the terephthalic acid chain segment.
Example 11
The preparation method of the modified polyester comprises the following specific steps:
(1) preparing 3, 3-diamyl-1, 5-pentanediol;
reacting 3, 3-diamyl-propionaldehyde, acetaldehyde and triethylamine for 20min at 90-95 ℃ under nitrogen atmosphere, then adding the concentrated solution into a hydrogenation reactor with a Raney nickel catalyst, reacting at the hydrogen pressure of 2.914MPa and the temperature of 100 ℃, cooling after the reaction is finished, and separating out the catalyst. After the solution is treated by ion exchange resin, water is evaporated under reduced pressure, and the 3, 3-diamyl-1, 5-pentanediol is obtained by separation and purification, wherein the structural formula of the 3, 3-diamyl-1, 5-pentanediol is as follows:
(2) performing esterification reaction;
preparing terephthalic acid, ethylene glycol and 3, 3-diamyl-1, 5-pentanediol with the molar ratio of 1:2.0:0.03 into slurry, adding antimony acetate, titanium dioxide and trimethyl phosphite, uniformly mixing, pressurizing in a nitrogen atmosphere to perform esterification reaction, wherein the pressurizing pressure is 0.2MPa, the esterification reaction temperature is 250 ℃, and the esterification reaction end point is when the distilled amount of water in the esterification reaction reaches 97% of a theoretical value, wherein the adding amount of the antimony acetate is 0.01% of the weight of the terephthalic acid, the adding amount of the titanium dioxide is 0.23% of the weight of the terephthalic acid, and the adding amount of the trimethyl phosphite is 0.05% of the weight of the terephthalic acid;
(3) performing polycondensation reaction;
after the esterification reaction is finished, starting the polycondensation reaction in the low vacuum stage under the condition of negative pressure, smoothly pumping the pressure from normal pressure to the absolute pressure of 500Pa within 45min, controlling the reaction temperature to be 260 ℃ and the reaction time to be 40min, then continuing to pump the vacuum, and carrying out the polycondensation reaction in the high vacuum stage, so that the reaction pressure is further reduced to the absolute pressure of 92Pa, the reaction temperature is 277 ℃ and the reaction time is 80min, thus obtaining the modified polyester.
The molecular chain of the finally prepared modified polyester comprises a terephthalic acid chain segment, an ethylene glycol chain segment and a 3, 3-diamyl-1, 5-pentanediol chain segment, the content of cyclic oligomer in the modified polyester is 0.35 wt%, the number average molecular weight is 25500, the molecular weight distribution index is 1.8, and the molar content of the 3, 3-diamyl-1, 5-pentanediol chain segment in the modified polyester is 5% of the molar content of the terephthalic acid chain segment.
Claims (6)
1. Modified polyester, characterized in that: the molecular chain of the modified polyester comprises a terephthalic acid chain segment, an ethylene glycol chain segment and a dihydric alcohol chain segment with a branched chain, wherein the structural formula of the dihydric alcohol with the branched chain is as follows:
in the formula, R1And R2Each independently selected from linear alkylene having 1 to 3 carbon atoms, R3Selected from alkyl with 1-5 carbon atoms, R4Selected from alkyl with 2-5 carbon atoms;
the modified polyester has a number average molecular weight of 20000 to 27000 and a molecular weight distribution index of 1.8 to 2.2;
the molar content of the dihydric alcohol chain segment with the branched chain in the modified polyester is 3-5% of that of the terephthalic acid chain segment;
the content of cyclic oligomer in the modified polyester is less than or equal to 0.6 wt%.
2. The modified polyester according to claim 1, wherein the branched diol is 2-ethyl-2-methyl-1, 3-propanediol, 2-diethyl-1, 3-propanediol, 2-butyl-2-ethyl-1, 3-propanediol, 3-diethyl-1, 5-pentanediol, 4-diethyl-1, 7-heptanediol, 4-bis (1, -methylethyl) -1, 7-heptanediol, 3-dipropyl-1, 5-pentanediol, 4-dipropyl-1, 7-heptanediol, 4-methyl-4- (1, 1-dimethylethyl) -1, 7-heptanediol, 3-methyl-3-pentyl-1, 6-hexanediol or 3, 3-diamyl-1, 5-pentanediol.
3. A process for preparing a modified polyester as claimed in claim 1 or 2, characterized in that: uniformly mixing terephthalic acid, ethylene glycol and the dihydric alcohol with the branched chain, and then carrying out esterification reaction and polycondensation reaction in sequence to obtain the modified polyester.
4. The method according to claim 3, characterized by the following specific steps:
(1) performing esterification reaction;
preparing terephthalic acid, ethylene glycol and the dihydric alcohol with the branched chain into slurry, adding a catalyst, a delustering agent and a stabilizer, uniformly mixing, pressurizing in a nitrogen atmosphere to perform esterification reaction, wherein the pressurizing pressure is normal pressure to 0.3MPa, the esterification reaction temperature is 250-260 ℃, and the esterification reaction endpoint is determined when the distilled amount of water in the esterification reaction reaches more than 90% of a theoretical value;
(2) performing polycondensation reaction;
and after the esterification reaction is finished, starting the polycondensation reaction in a low vacuum stage under the negative pressure condition, stably pumping the pressure in the low vacuum stage from normal pressure to below 500Pa in 30-50 min at the reaction temperature of 260-270 ℃ for 30-50 min, then continuously pumping the vacuum to perform the polycondensation reaction in a high vacuum stage, further reducing the reaction pressure to below 100Pa, controlling the reaction temperature to 275-285 ℃ and the reaction time to be 50-90 min, and thus obtaining the modified polyester.
5. The method according to claim 4, wherein in the step (1), the molar ratio of the terephthalic acid to the ethylene glycol to the branched diol is 1:1.2 to 2.0:0.03 to 0.06, the catalyst is added in an amount of 0.01 to 0.05% by weight based on the terephthalic acid, the matting agent is added in an amount of 0.20 to 0.25% by weight based on the terephthalic acid, and the stabilizer is added in an amount of 0.01 to 0.05% by weight based on the terephthalic acid.
6. The method of claim 5, wherein the catalyst is antimony trioxide, ethylene glycol antimony, or antimony acetate, the matting agent is titanium dioxide, and the stabilizer is triphenyl phosphate, trimethyl phosphate, or trimethyl phosphite.
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