CN113754871B - Biodegradable block copolyesters based on lactide- (cycloaliphatic-co-aromatic) -lactide - Google Patents
Biodegradable block copolyesters based on lactide- (cycloaliphatic-co-aromatic) -lactide Download PDFInfo
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- C08G63/16—Dicarboxylic acids and dihydroxy compounds
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Abstract
The invention relates to the field of high polymer materials, and discloses a biodegradable block copolyester based on lactide- (alicyclic-co-aromatic) -lactide. The structural formulase:Sub>A of the biodegradable block copolyesters is B-A-B. Wherein A is an alicyclic-aromatic random copolyester chain segment, and the weight average molecular weight of the alicyclic-aromatic random copolyester chain segment is 500-150,000g/mol; b is a polylactide chain segment formed by lactide polymerization in a ring opening mode, and the weight average molecular weight of the polylactide chain segment is 500-200,000g/mol; the total weight average molecular weight of the block copolyesters is from 10,000 to 500,000g/mol. The segmented copolymer ester obtained by copolymerizing the alicyclic dibasic acid, the aromatic dibasic acid and the ethylene glycol and further opening the ring of lactide combines the degradation performance and the mechanical property of the copolyester, and can be used as an environment-friendly material and a biomedical material.
Description
Technical Field
The invention relates to the field of high polymer materials, in particular to a biodegradable block copolyester based on lactide- (alicyclic-co-aromatic) -lactide.
Background
The synthetic polymer brings unique mechanical properties and thermal properties due to various chain compositions, chain structures and aggregation state structures. The quality is stable, the long-term use is realized, and the production and the life of human beings are greatly changed. Polyester is one of the largest synthetic polymer products in global production and use, mainly polyethylene terephthalate (PET), is nontoxic, transparent and stable in thermal and mechanical properties, and is widely used in the fields of spinning, packaging, information, electronics and the like.
PET is non-toxic in itself but is stable in nature for long periods of time. PET is reported to exist in the natural environment for periods of at least 16-48 years, and bottle products can even exist for more than 450 years. The waste residue in the soil can obstruct the transmission of water and nutrient, and the waste can gradually accumulate along with the river and ocean current in the water body, thereby seriously damaging the natural environment and the ecological system. In addition, the micro-plastics formed by the polyester textile scraps can accumulate in organisms along with ecological chains and finally enter human bodies to endanger the life safety of the human bodies. These negative effects are exacerbated with the rapid development of the industry. Thus, tremendous environmental pressures place new degradation requirements on PET.
The design key points of the polyester polymer material are the molecular chain composition and the topological structure. Up to now, by adjusting the composition of the polymer molecular chains, various biodegradable copolyester products have been formed, such as poly (adipic acid)/butylene terephthalate (PBAT), poly (succinic acid)/butylene adipate (PBSA), poly (succinic acid)/butylene terephthalate (PBST), etc. However, these modified copolyesters are usually random copolymers, have a single topological structure, and the mechanical strength of the material is reduced due to the introduction of random aliphatic chain segments while the degradation performance is improved; on the other hand, there are fewer biodegradable modified products for PET polyesters.
CN 103570925a discloses a biodegradable polyester synthesized by adjusting the composition of the polyester, which comprises aliphatic, alicyclic and aromatic chain segments, but the chain structures are random copolymerization, and the tensile strength of the material is lower; CN 105732964a discloses a preparation method of dimer fatty acid polylactic acid block polyester, the method for obtaining the block structure is that aliphatic prepolymer and polylactic acid prepolymer are further polymerized under the action of catalyst, the method has less polymerization active site, and the mixture of block polyester and two prepolymers is easy to be formed; CN 101684175a discloses a biodegradable multi-block polyester copolymer, wherein the polyhydroxy acid chain segment is further chain-extended by a prepolymer and is connected with an aromatic polyester chain segment, and the problem of less chain-extended active sites exists.
Disclosure of Invention
In order to solve the technical problems, the invention provides the biodegradable block copolyesters based on lactide- (alicyclic-co-aromatic) -lactide, and the block copolyesters obtained by copolymerizing alicyclic diacid, aromatic diacid and glycol and further ring-opening lactide are compatible with the degradation performance and mechanical properties of the copolyesters, and can be used as environment-friendly materials and biomedical materials.
The specific technical scheme of the invention is as follows:
in a first aspect, the present invention provides a biodegradable block copolyesters based on lactide- (cycloaliphatic-co-aromatic) -lactide having the structural formula:
B-A-B
wherein A is alicyclic-aromatic random copolyester chain segment, and the weight average molecular weight is 500-150,000g/mol; b is a polylactide chain segment formed by lactide polymerization in a ring opening mode, and the weight average molecular weight of the polylactide chain segment is 500-200,000g/mol; the total weight average molecular weight of the block copolyesters is from 10,000 to 500,000g/mol.
Compared with random copolyester, the biodegradable block copolyester has higher molecular chain regularity in each block and more complete crystal morphology, thus having higher mechanical strength.
Preferably, the A is an alicyclic-aromatic random copolyester segment with a weight average molecular weight of 10,000-150,000g/mol; b is a polylactide segment formed by lactide polymerization in a ring opening mode, and the weight average molecular weight of the polylactide segment is 8,000-200,000g/mol; the total weight average molecular weight of the block copolyesters is from 30,000 to 500,000g/mol.
It should be noted that, in order to ensure the mechanical properties of the copolyester, the molecular weight of the B segment is particularly important, and the present team found through researches that, in the case that the weight average molecular weight of the A segment is in the above range, the weight average molecular weight of the B segment is 8,000-200,000g/mol, so that the mechanical properties of the copolyester can be ensured. If the molecular weight of the B chain segment is too low, the mechanical properties of the copolyester are affected, and the experimental data of the specific examples are shown in detail.
In a second aspect, the invention provides a method for preparing the biodegradable block copolyesters, which comprises the following steps:
(1) In the first reaction kettle, the alicyclic diacid, the aromatic diacid and the ethylene glycol are subjected to polycondensation reaction under the action of a catalyst A to obtain a melt of the segment A.
(2) Directly conveying the melt of the segment A to a second reaction kettle, and simultaneously adding lactide; under the action of a catalyst B, lactide performs ring-opening polymerization reaction on two sides of the segment A to generate the segment B, so as to obtain the biodegradable block copolyesters.
The melt of the chain segment A is directly conveyed into a second reaction kettle at high temperature, and can be naturally cooled to a proper temperature for ring-opening polymerization by controlling conveying distance and speed or adjusting a public engineering method, so that the temperature is not required to be reduced and then increased, and the energy is saved.
Meanwhile, the melt of the segment A and the lactide are added simultaneously, so that the mixture is more uniform compared with a mode of adding the melt and the lactide sequentially, and the segmented copolyesters with regular structures are formed. Compared with the preparation of random copolyester by a one-step method, the block copolyesters prepared by a two-step method can polymerize each block under proper conditions, and avoid the loss caused by decomposition of monomers due to unsuitable temperature.
In addition, compared with a chain extension method for preparing a segmented copolymer, the ring-opening polymerization method has more hydroxyl active sites, can realize the rapid synthesis of a block structure and has clearer and more uniform molecular chain structures.
Preferably, the alicyclic dicarboxylic acid is one or more of cis-1, 4-cyclohexane dicarboxylic acid, trans-1, 4-cyclohexane dicarboxylic acid, cis-1, 3-cyclopentane dicarboxylic acid, trans-1, 3-cyclopentane dicarboxylic acid, cis-1, 3-cyclobutane dicarboxylic acid and trans-1, 3-cyclobutane dicarboxylic acid.
Preferably, the aromatic dibasic acid is one or more of terephthalic acid, isophthalic acid and 2, 5-furandicarboxylic acid;
the lactide is one or more of L-lactide, D-lactide and D, L-lactide.
Preferably, the catalyst A is one or more of antimony trioxide, antimony acetate, ethylene glycol antimony, tetrabutyl titanate and isopropyl titanate.
Preferably, the catalyst B is one or more of stannous octoate, stannous dichloride, tetraphenyltin and boron trichloride.
Preferably, in step (1): the ratio of the molar quantity of the ethylene glycol to the total acid molar quantity of the alicyclic dibasic acid and the aromatic dibasic acid is 1.05-2.5:1; wherein the molar quantity of the alicyclic dibasic acid accounts for 1.0-99.0% of the total acid molar quantity of the alicyclic dibasic acid and the aromatic dibasic acid.
Preferably, in step (1): the dosage of the catalyst A is 0.005-0.5% of the total acid molar quantity of the alicyclic dibasic acid and the aromatic dibasic acid.
Preferably, in step (1): the polycondensation reaction temperature is 230-280 ℃, the polycondensation reaction vacuum degree is 0-300Pa, and the polycondensation reaction time is 0.5-12.0h.
Further preferably, the degree of vacuum of the polycondensation reaction is 0 to 100Pa.
Preferably, in step (2): the mass of the lactide accounts for 5-95% of the total mass of the lactide and the A chain segment.
Preferably, in step (2): the dosage of the catalyst B is 0.001-0.5% of the molar quantity of lactide.
Preferably, in step (2): the ring-opening polymerization reaction temperature is 150-220 ℃, the vacuum degree of the ring-opening polymerization reaction is 0-150Pa, and the time of the ring-opening polymerization reaction is 0.5-48.0h.
Further preferably, the degree of vacuum for the ring-opening polymerization is 0 to 50Pa.
Preferably, bulk polymerization is employed in the synthesis of both the a segment and the B segment.
Compared with the prior art, the invention has the beneficial effects that:
(1) The invention prepares the biodegradable copolyester with a block structure by two-step polymerization, and combines the degradation performance and the mechanical property.
(2) The invention adopts a ring-opening polymerization method to polymerize the polylactide chain segments at the two ends of the alicyclic-aromatic copolyester chain segments, has more polymerization active sites, and the synthesized segmented copolyester has clear structure, and does not have a blend formed by monomer self-polymerization.
(3) The preparation process is bulk polymerization, does not use solvent, and does not have the problem of solvent separation.
Detailed Description
The invention is further described below with reference to examples.
General examples
Biodegradable block copolyesters based on lactide- (cycloaliphatic-co-aromatic) -lactide have the following structural formula:
B-A-B
wherein A is alicyclic-aromatic random copolyester chain segment, and the weight average molecular weight is 500-150,000g/mol; b is a polylactide chain segment formed by lactide polymerization in a ring opening mode, and the weight average molecular weight of the polylactide chain segment is 500-200,000g/mol; the total weight average molecular weight of the block copolyesters is from 10,000 to 500,000g/mol.
Preferably, the A is an alicyclic-aromatic random copolyester segment with a weight average molecular weight of 10,000-150,000g/mol; b is a polylactide segment formed by lactide polymerization in a ring opening mode, and the weight average molecular weight of the polylactide segment is 8,000-200,000g/mol; the total weight average molecular weight of the block copolyesters is from 30,000 to 500,000g/mol.
A method for preparing biodegradable block copolyesters, comprising the steps of:
(1) In the first reaction kettle, the alicyclic diacid, the aromatic diacid and the ethylene glycol are subjected to polycondensation reaction under the action of a catalyst A to obtain a melt of the segment A.
(2) Directly conveying the melt of the segment A to a second reaction kettle, and simultaneously adding lactide; under the action of a catalyst B, lactide performs ring-opening polymerization reaction on two sides of the segment A to generate the segment B, so as to obtain the biodegradable block copolyesters.
In the synthesis of both the A segment and the B segment, bulk polymerization is employed.
The alicyclic dicarboxylic acid is one or more of cis-1, 4-cyclohexane dicarboxylic acid, trans-1, 4-cyclohexane dicarboxylic acid, cis-1, 3-cyclopentane dicarboxylic acid, trans-1, 3-cyclopentane dicarboxylic acid, cis-1, 3-cyclobutane dicarboxylic acid and trans-1, 3-cyclobutane dicarboxylic acid. The aromatic dibasic acid is one or more of terephthalic acid, isophthalic acid and 2, 5-furandicarboxylic acid; the lactide is one or more of L-lactide, D-lactide and D, L-lactide. The catalyst A is one or more of antimony trioxide, antimony acetate, ethylene glycol antimony, tetrabutyl titanate and isopropyl titanate. The catalyst B is one or more of stannous octoate, stannous dichloride, tetraphenyltin and boron trichloride.
In the step (1), the ratio of the molar quantity of the ethylene glycol to the total acid molar quantity of the alicyclic dibasic acid and the aromatic dibasic acid is 1.05-2.5:1; wherein the molar quantity of the alicyclic dibasic acid accounts for 1.0-99.0% of the total acid molar quantity of the alicyclic dibasic acid and the aromatic dibasic acid. The dosage of the catalyst A is 0.005-0.5% of the total acid molar quantity of the alicyclic dibasic acid and the aromatic dibasic acid. The polycondensation reaction temperature is 230-280 ℃, the polycondensation reaction vacuum degree is 0-300Pa, and the polycondensation reaction time is 0.5-12.0h. Further preferably, the degree of vacuum of the polycondensation reaction is 0 to 100Pa.
In the step (2), the mass of the lactide accounts for 5-95% of the total mass of the lactide and the A chain segment. The dosage of the catalyst B is 0.001-0.5% of the molar quantity of lactide. The ring-opening polymerization reaction temperature is 150-220 ℃, the vacuum degree of the ring-opening polymerization reaction is 0-150Pa, and the time of the ring-opening polymerization reaction is 0.5-48.0h. Further preferably, the degree of vacuum for the ring-opening polymerization is 0 to 50Pa.
Example 1
(1) Synthesis of A chain segment
Delivering 0.1mol of trans-1, 4-cyclohexanedicarboxylic acid, 0.9mol of terephthalic acid and 1.1mol of ethylene glycol into a first reaction kettle, mixing to obtain slurry, adding 0.001mol of ethylene glycol antimony, and polycondensing at 260 ℃ and 50Pa for 1h after esterification to obtain a segment A.
(2) Synthesis of block copolyesters
And (3) conveying the segment A to a second reaction kettle, adding stannous octoate with the molar quantity of 0.05% of L-lactide and L-lactide accounting for 100% of the mass of the segment A, and performing ring-opening polymerization for 4 hours at 200 ℃ and 70Pa to generate a segment B, thereby obtaining the block copolyesters.
The copolyester can be completely degraded in an industrial composting environment for 90 days.
Example 2
(1) Synthesis of A chain segment
Delivering 0.1mol of cis-1, 4-cyclohexanedicarboxylic acid, 0.2mol of trans-1, 4-cyclohexanedicarboxylic acid, 0.7mol of furandicarboxylic acid and 1.4mol of ethylene glycol into a first reaction kettle, mixing to obtain slurry, adding 0.005mol of antimony trioxide, esterifying, and polycondensing at 265 ℃ under 30Pa for 4 hours to obtain a segment A.
(2) Synthesis of block copolyesters
Conveying the segment A to a second reaction kettle, adding D, L-lactide with the mass of 800% of the segment A and tin dichloride with the molar quantity of 0.4% of the D, L-lactide, and carrying out ring-opening polymerization for 20h at 180 ℃ under the condition of 35Pa to generate a segment B, thereby obtaining the block copolyesters.
The copolyester can be completely degraded in an industrial composting environment for 182 days.
Example 3
(1) Synthesis of A chain segment
Delivering 0.6mol of trans-1, 3-cyclopentane dicarboxylic acid, 0.25mol of cis-1, 3-cyclopentane dicarboxylic acid, 0.15mol of isophthalic acid and 2.1mol of ethylene glycol into a first reaction kettle, mixing to obtain slurry, adding 0.0001mol of tetrabutyl titanate and 0.0001mol of isopropyl titanate, and polycondensing at 230 ℃ and 65Pa for 2.5h after esterification to obtain the segment A.
(2) Synthesis of block copolyesters
And (3) conveying the segment A to a second reaction kettle, adding 0.002% tetraphenyltin of L-lactide and L-lactide with the mass of 300% of that of the segment A, and performing ring-opening polymerization for 3h at 160 ℃ and 150Pa to generate a segment B, thereby obtaining the block copolyesters.
The copolyester can be completely degraded in an industrial composting environment for 124 days.
Example 4
(1) Synthesis of A chain segment
Delivering 0.05mol of trans-1, 3-cyclobutanedicarboxylic acid, 0.95mol of terephthalic acid and 1.25mol of ethylene glycol into a first reaction kettle, mixing to obtain slurry, adding 0.004mol of antimony acetate, and polycondensing at 260 ℃ and 50Pa for 4.5 hours after esterification to obtain the segment A.
(2) Synthesis of block copolyesters
And (3) conveying the segment A to a second reaction kettle, adding stannous octoate with 1800% of the mass of the segment A and 0.5% of the molar quantity of the L-lactide, and performing ring-opening polymerization for 42h at 210 ℃ and 30Pa to generate the segment B to obtain the block copolyesters.
The copolyester can be completely degraded in 278 days under an industrial composting environment.
Comparative example 1
Delivering 0.1mol of trans-1, 4-cyclohexanedicarboxylic acid, 0.9mol of terephthalic acid and 1.1mol of ethylene glycol into a first reaction kettle, mixing to obtain slurry, adding 0.001mol of ethylene glycol antimony, and polycondensing at 260 ℃ and 50Pa for 1h after esterification to obtain a segment A.
The copolyester can be completely degraded in an industrial composting environment for 48 days.
Comparative example 2
Delivering 0.1mol of trans-1, 4-cyclohexanedicarboxylic acid, 0.9mol of terephthalic acid and 1.1mol of ethylene glycol into a first reaction kettle, mixing to obtain slurry, adding 0.001mol of ethylene glycol antimony, and polycondensing at 260 ℃ and 50Pa for 3h after esterification to obtain a segment A.
The copolyester can be completely degraded in 146 days under an industrial composting environment.
Comparative example 3
Delivering 0.8mol of trans-1, 4-cyclohexanedicarboxylic acid, 0.2mol of terephthalic acid and 1.1mol of ethylene glycol into a first reaction kettle, mixing to obtain slurry, adding 0.001mol of ethylene glycol antimony, and polycondensing at 260 ℃ and 50Pa for 5h after esterification to obtain a segment A.
The copolyester can be completely degraded in an industrial composting environment for 76 days.
Comparative example 4
(1) Synthesis of A chain segment
Delivering 0.1mol of cis-1, 4-cyclohexanedicarboxylic acid, 0.2mol of trans-1, 4-cyclohexanedicarboxylic acid, 0.7mol of furandicarboxylic acid and 1.4mol of ethylene glycol into a first reaction kettle, mixing to obtain slurry, adding 0.005mol of antimony trioxide, esterifying, and polycondensing at 265 ℃ under 30Pa for 4 hours to obtain a segment A.
(2) Synthesis of block copolyesters
Conveying the segment A to a second reaction kettle, adding D, L-lactide with the mass of 800% of the segment A and tin dichloride with the molar quantity of 0.4% of the D, L-lactide, and carrying out ring-opening polymerization for 3h at 180 ℃ under the condition of 35Pa to generate a segment B, thereby obtaining the block copolyesters.
The copolyester can be completely degraded in 138 days under the industrial composting environment.
Comparative example 5
The method comprises the steps of conveying 0.1mol of trans-1, 4-cyclohexanedicarboxylic acid, 0.9mol of terephthalic acid and 1.1mol of ethylene glycol into a first reaction kettle to be mixed to obtain slurry, and adding L-lactide accounting for 100% of the total mass of the trans-1, 4-cyclohexanedicarboxylic acid, the terephthalic acid and the ethylene glycol to be mixed. Adding 0.001mol of ethylene glycol antimony and 0.05mol of stannous octoate with the molar quantity of L-lactide, and polymerizing for 4 hours at 260 ℃ and 50Pa after esterification to obtain the copolyester.
The copolyester can be completely degraded in an industrial composting environment for 32 days.
Comparative example 6
(1) Synthesis of A chain segment
Delivering 0.6mol of trans-1, 3-cyclopentane dicarboxylic acid, 0.25mol of cis-1, 3-cyclopentane dicarboxylic acid, 0.15mol of isophthalic acid and 2.1mol of ethylene glycol into a first reaction kettle, mixing to obtain slurry, adding 0.0001mol of tetrabutyl titanate and 0.0001mol of isopropyl titanate, and polycondensing at 230 ℃ and 65Pa for 8h after esterification to obtain the segment A.
(2) Synthesis of block copolyesters
And (3) conveying the segment A to a second reaction kettle, adding 0.002% tetraphenyltin of L-lactide and L-lactide with the mass of 50% of that of the segment A, and performing ring-opening polymerization for 1h at 160 ℃ and 150Pa to generate a segment B, thereby obtaining the block copolyesters.
The copolyester can be completely degraded in an industrial composting environment for 130 days.
Comparative example 7
(1) Synthesis of A chain segment
Delivering 0.1mol of trans-1, 4-cyclohexanedicarboxylic acid, 0.9mol of terephthalic acid and 1.1mol of ethylene glycol into a first reaction kettle, mixing to obtain slurry, adding 0.001mol of ethylene glycol antimony, and polycondensing at 260 ℃ and 300Pa for 12h after esterification to obtain a segment A.
(2) Synthesis of block copolyesters
And (3) conveying the segment A to a second reaction kettle, adding stannous octoate with the molar quantity of 0.05% of L-lactide and L-lactide accounting for 100% of the mass of the segment A, and performing ring-opening polymerization for 4 hours at 200 ℃ and 70Pa to generate a segment B, thereby obtaining the block copolyesters.
The copolyester can be completely degraded in an industrial composting environment for 82 days.
Comparative example 8
(1) Synthesis of A chain segment
0.15mol of cis-1, 4-cyclohexanedicarboxylic acid, 0.85mol of terephthalic acid and 1.2mol of ethylene glycol which are equivalent to 0.15mol are conveyed into a first reaction kettle to be mixed to obtain slurry, antimony acetate which is equivalent to 0.0005mol is added, and after esterification, the A chain segment is obtained by polycondensation for 1.5 hours under the condition of 275 ℃ and 120 Pa.
(2) Synthesis of block copolyesters
And (3) conveying the segment A to a second reaction kettle, adding 10% of D-lactide and 0.005% of tin dichloride by mole of the D-lactide in the mass of the segment A, and performing ring-opening polymerization for 2 hours at 200 ℃ and 40Pa to generate the segment B, thereby obtaining the block copolyesters.
The copolyester can be completely degraded in an industrial composting environment for 30 days.
The copolyesters obtained in examples 1 to 4 and comparative examples 1 to 8 were tested for molecular weight and tensile strength, and the results are shown in Table 1.
TABLE 1
| M w (g/mol) | M w-B (g/mol) | PDI | Tensile Strength (MPa) | |
| Example 1 | 36000 | 8400 | 1.98 | 52.2 |
| Example 2 | 132100 | 51000 | 2.21 | 64.1 |
| Example 3 | 63200 | 18100 | 2.17 | 60.3 |
| Example 4 | 413000 | 175500 | 2.32 | 78.2 |
| Comparative example 1 | 19200 | 0 | 1.61 | 25.4 |
| Comparative example 2 | 40600 | 0 | 1.72 | 38.6 |
| Comparative example 3 | 46300 | 0 | 2.03 | 29.7 |
| Comparative example 4 | 51200 | 5600 | 2.32 | 32.4 |
| Comparative example 5 | 16200 | 0 | 2.78 | 20.3 |
| Comparative example 6 | 67000 | 5000 | 2.01 | 42.0 |
| Comparative example 7 | 26100 | 8200 | 1.67 | 32.4 |
| Comparative example 8 | 11600 | 3000 | 1.94 | 47.2 |
As can be seen from Table 1, the tensile strengths of examples 1 to 4 are significantly higher than those of comparative examples 1 to 8. The above results indicate that: (1) Further ring-opening polymerization to form a polylactide segment (example 1) on the basis of the alicyclic-aromatic copolyester (comparative example 1) can effectively improve molecular weight and tensile strength. The reason is that the ring-opening polymerized polylactide chain segment has good molecular chain structure regularity, can form a crystalline structure, and has higher tensile strength, so that the segmented copolyester has higher mechanical property than the original random copolyester.
(2) The block copolyesters (example 1) are able to exhibit higher tensile strength at lower molecular weights than the cycloaliphatic-aromatic copolyesters having a larger molecular weight (comparative example 2). The reason for this is the same as described above, in that the polylactide segment contributes to the mechanical properties.
(3) Even at relatively low molecular weights, reducing the cycloaliphatic segment content (comparative example 2) helps to increase the tensile strength of the copolyester compared to the copolyester having a higher cycloaliphatic segment content (comparative example 3). This is because, on the one hand, the mechanical properties of the alicyclic segment are weak, and on the other hand, the introduction of a large amount of alicyclic segments breaks the regularity of the original aromatic segment, so that the crystallization condition becomes weak, thereby reducing the tensile strength.
(4) Increasing the molecular weight of the polylactide segments (example 2) helps to increase the tensile strength of the material compared to block copolyesters having lower molecular weight polylactide segments (comparative examples 4 and 8). The reason is that the degree of regularity of the polylactic acid chain segment is higher, the degree of crystallization is better, and the tensile strength is improved.
(5) The two-stage polymerization process (example 1) gives polymers with greater molecular weights and higher tensile strengths than if the entire monomer and catalyst were added in one step (comparative example 5). The reason for this is that one-step polymerization forms a blend of polycondensation products and ring-opening polymerization products at the same time due to the variety of monomers, different reactivity of functional groups and different polymerization mechanisms, and two-step polymerization can give block copolyesters having a narrow molecular weight distribution.
(6) The block copolyesters with a shorter polycondensation time and a longer ring-opening polymerization time (example 3) have higher tensile strength than the block copolyesters with a longer polycondensation time and a shorter ring-opening polymerization time (comparative example 6). The segmented copolymer has the advantages that the molecular weight of the randomly copolymerized A chain segment is smaller due to the shortened polycondensation time, the molecular weight of the B chain segment is larger due to the prolonged ring-opening polymerization time, and compared with the randomly copolymerized A chain segment, the segmented copolymer has a regular structure, and the easily crystallized B chain segment shows higher mechanical properties, so that the segmented copolymer has higher tensile strength.
(7) Compared with a block copolyesters having a segment A obtained by a higher polycondensation pressure for a longer polycondensation time (comparative example 7), a lower polycondensation pressure can polycondense in a shorter time (example 1) and give a block copolyesters having a larger molecular weight and a higher tensile strength. Therefore, in order to ensure excellent mechanical properties of the copolyester, it is necessary to control the molecular weight of the polylactide to be 8000 or more. If the molecular weight of the polylactide is too low, a copolyester having high tensile strength cannot be obtained.
The raw materials and equipment used in the invention are common raw materials and equipment in the field unless specified otherwise; the methods used in the present invention are conventional in the art unless otherwise specified.
The foregoing description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and any simple modification, variation and equivalent transformation of the above embodiment according to the technical substance of the present invention still fall within the scope of the technical solution of the present invention.
Claims (10)
1. A method for improving the mechanical properties of biodegradable block copolyesters is characterized by comprising the following steps:
the method comprises the following steps:
(1) In a first reaction kettle, performing polycondensation reaction on alicyclic dibasic acid, aromatic dibasic acid and ethylene glycol under the action of a catalyst A to obtain a melt of the segment A; the alicyclic dicarboxylic acid is one or more of cis-1, 4-cyclohexane dicarboxylic acid, trans-1, 4-cyclohexane dicarboxylic acid, cis-1, 3-cyclopentane dicarboxylic acid, trans-1, 3-cyclopentane dicarboxylic acid, cis-1, 3-cyclobutane dicarboxylic acid and trans-1, 3-cyclobutane dicarboxylic acid; the aromatic dibasic acid is one or more of terephthalic acid, isophthalic acid and 2, 5-furandicarboxylic acid;
(2) Directly conveying the melt of the segment A to a second reaction kettle, and simultaneously adding lactide; under the action of a catalyst B, lactide performs ring-opening polymerization reaction on two sides of the segment A to generate the segment B, so as to obtain the biodegradable block copolyesters with the following structural formula:
B——A——B
wherein A is alicyclic-aromatic random copolyester chain segment, and the weight average molecular weight is 10000-150,000g/mol; b is a polylactide chain segment formed by lactide polymerizing in a ring opening mode, and the weight average molecular weight of the polylactide chain segment is 8000-51,000g/mol; the total weight average molecular weight of the block copolyesters is 3,0000-132100g/mol.
2. The method of claim 1, wherein: the lactide is one or more of L-lactide, D-lactide and D, L-lactide.
3. The method of claim 1, wherein:
the catalyst A is one or more of antimony trioxide, antimony acetate, ethylene glycol antimony, tetrabutyl titanate and isopropyl titanate;
the catalyst B is one or more of stannous octoate, stannous dichloride, tetraphenyltin and boron trichloride.
4. A method according to claim 1 or 2, characterized in that: in step (1): the ratio of the molar quantity of the ethylene glycol to the total acid molar quantity of the alicyclic dibasic acid and the aromatic dibasic acid is 1.05-2.5:1; wherein the molar quantity of the alicyclic dibasic acid accounts for 1.0-99.0% of the total acid molar quantity of the alicyclic dibasic acid and the aromatic dibasic acid.
5. A method according to claim 1 or 2, characterized in that: in step (1): the polycondensation reaction temperature is 230-280 ℃, the polycondensation reaction vacuum degree is 0-300Pa, and the polycondensation reaction time is 0.5-12.0h.
6. A method according to claim 1 or 2, characterized in that: in the step (2): the mass of the lactide accounts for 5-95% of the total mass of the lactide and the A chain segment.
7. A method according to claim 1 or 2, characterized in that: in step (1): the dosage of the catalyst A is 0.005-0.5% of the total acid molar quantity of the alicyclic dibasic acid and the aromatic dibasic acid.
8. A method according to claim 1 or 2, characterized in that: in the step (2): the dosage of the catalyst B is 0.001-0.5% of the molar quantity of lactide.
9. A method according to claim 1 or 2, characterized in that: in the step (2): the ring-opening polymerization reaction temperature is 150-220 ℃, the vacuum degree of the ring-opening polymerization reaction is 0-150Pa, and the time of the ring-opening polymerization reaction is 0.5-48.0h.
10. A method according to claim 1 or 2, characterized in that: in the synthesis of both the A segment and the B segment, bulk polymerization is employed.
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