Self-nucleation modified polylactic acid and preparation method thereof

Abstract

The invention relates to self-nucleation modified polylactic acid, which has the characteristics of a hydrogen bond induction effect of an amide group, an intramolecular plasticizing effect of a hydrocarbon chain, local eutectic of PDLA-PLLA and the like, so that rapid crystallization can be realized through a multiple synergistic nucleation mechanism. Therefore, rapid crystallization of polylactic acid can be realized under the condition that a nucleating agent does not need to be added. The invention further relates to a preparation method of the self-nucleation modified polylactic acid, the method can directly utilize an existing production line, a nucleating agent does not need to be added in the process through secondary processing modes such as screws and internal mixing, and the method is suitable for industrial large-scale production.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and specifically relates to a self-nucleating modified polylactic acid and a preparation method thereof. Background Art

[0002] Polylactic acid (PLA) is a semi-crystalline thermoplastic material with relatively good mechanical properties and good transparency, biocompatibility, and biodegradability. The raw material for producing PLA, lactic acid, can be prepared from biomass raw materials (such as cassava, sugar cane, straw cellulose, etc.) after microbial fermentation, and does not rely on petroleum resources. Related PLA products can be naturally decomposed into carbon dioxide and water after use. The environmentally friendly properties and transparency of PLA give it broad application prospects in food packaging and agriculture.

[0003] Although polylactic acid has been successfully industrialized and applied in the fields of medicine, there are still many problems in its production and use, which restrict the application and development of polylactic acid materials. Polylactic acid is a linear polyester, which is prone to hydrolysis and thermal degradation during production and processing, resulting in a decrease in the molecular weight of the polymer, affecting the performance of the end product. The repeating units in the main chain of the polylactic acid molecule are short and rigid, resulting in a slow crystallization rate and low crystallinity of semi-crystalline PLA. It almost does not crystallize during the actual molding process (such as extrusion and injection), resulting in a low heat deformation temperature and a long molding cycle. Therefore, how to improve the crystallization rate and crystallinity of polylactic acid is still one of the key issues that need to be solved in the current development of the polylactic acid industry.

[0004] At present, nucleating agents are usually added to PLA to improve the crystallization performance of PLA. The addition of nucleating agents can reduce the surface free energy barrier required for PLA nucleation, allowing PLA to heterogeneously nucleate, thereby shortening its crystallization time, increasing the crystallization rate, and promoting the crystallization of PLA. Currently, the commonly used nucleating agents for PLA can be roughly divided into two categories: inorganic nucleating agents and organic nucleating agents. However, the above nucleating agents are all used in the post-processing section of the finished polylactic acid resin, and physical blending is performed by means of screw extrusion or mixing. The added nucleating agents cannot be uniformly and effectively dispersed in the high-viscosity polylactic acid melt, and the secondary processing process may also cause thermal degradation of polylactic acid, resulting in performance loss of the finished resin. Summary of the invention

[0005] In order to overcome the defects in the prior art, one of the objects of the present invention is to provide a self-nucleating modified polylactic acid and a preparation method thereof, wherein the self-nucleating modified polylactic acid can obtain a high crystallization rate and a high crystallinity without adding a nucleating agent.

[0006] In one aspect, the present invention relates to a self-nucleating modified polylactic acid having a structure of the following formula (I) or (II):

[0007] A1-O-L1 Formula (I)

[0008] A2-O——L2-O——A3 Formula (II)

[0009] In formula (I),

[0010] L1 is selected from the following structures:

[0011]

[0012] in,

[0013] L 1a Selected from C 1-12 Straight hydrocarbon chain, L 1b Selected from C 10-20 Straight chain hydrocarbon group;

[0014] L 1c Selected from C 10-20 Straight hydrocarbon chain, L 1d Selected from C 1-12 Straight hydrocarbon chain, L 1e Selected from C 10-20 Straight chain hydrocarbon group;

[0015] A1 is

[0016] wherein n is an integer selected from 300-800, and n' is an integer selected from 700-2500;

[0017] In formula (II),

[0018] L2 is selected from the following structures:

[0019]

[0020] in,

[0021] L 2a Selected from C 1-12 Straight hydrocarbon chain, L 2b Selected from C 1-20 Straight hydrocarbon chain, C 3-20 branched hydrocarbon chains;

[0022] L 2c Selected from C 1-20 Straight hydrocarbon chain, C 3-20 Branched hydrocarbon chain, L 2d Selected from C 1-12 Straight hydrocarbon chain, L 2e Selected from C 1-20 Straight hydrocarbon chain, C 3-20 branched hydrocarbon chains;

[0023] A2 is And A3 is Or, A2 is And A3 is

[0024] in,

[0025] p is an integer selected from 150-400, p' is an integer selected from 350-1250, q is an integer selected from 150-400, q' is an integer selected from 350-1250, the ratio of p to q is 0.8-1.2, and the ratio of p' to q' is 0.8-1.2.

[0026] On the other hand, the present invention also relates to a method for preparing the self-nucleating modified polylactic acid according to any one of claims 1 to 4, comprising the following steps:

[0027] reacting an aliphatic amide containing a terminal hydroxyl group with a coordination catalyst to obtain an alcohol salt of the aliphatic amide;

[0028] The alkoxide of the aliphatic amide is reacted with the molten first lactide, and the alkoxide of the aliphatic amide initiates the ring-opening polymerization of the first lactide to obtain a modified polylactic acid prepolymer;

[0029] The modified polylactic acid prepolymer reacts with the molten second lactide, and the modified polylactic acid prepolymer initiates the ring-opening polymerization of the second lactide to obtain the self-nucleating modified polylactic acid;

[0030] in,

[0031] The aliphatic amide containing terminal hydroxyl groups has a structure of the following formula (III) or (IV):

[0032] HO-L1 Formula (III)

[0033] HO-L2—OH Formula (IV),

[0034] The first lactide is L-lactide and the second lactide is D-lactide, or the first lactide is D-lactide and the second lactide is L-lactide. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The DSC curves of the corresponding polymer products obtained by initiating ring-opening polymerization of L-lactide at high temperature and low temperature respectively with the modified poly (D-lactic acid) prepolymer of Comparative Example 1 and Example 1 are shown.

[0036] Figure 2 The DSC curves of isothermal crystallization at 110° C. of the samples of Example 1, Example 3 and Comparative Example 3 of the present invention are shown.

[0037] Figure 3The DSC curves of isothermal crystallization at 110° C. of the samples of Example 2, Example 4 and Comparative Example 4 of the present invention are shown.

[0038] Figure 4 DSC curves showing isothermal crystallization of samples of Examples 1-4 and Comparative Example 4 at 110°C DETAILED DESCRIPTION

[0039] General Definitions and Terminology

[0040] Unless otherwise indicated, all publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In the event of a conflict, the definitions provided herein shall prevail.

[0042] Unless otherwise indicated, all percentages, parts, ratios, etc. are by weight.

[0043] When quantity, concentration or other value or parameter is given as range, preferred range or preferred upper limit and lower limit or specific value, it should be understood as specifically disclosing all ranges formed by paired values ​​from any upper limit range or preferred value and any lower limit range or preferred value, regardless of whether the range is disclosed separately. Unless otherwise stated, when numerical range is quoted herein, the range refers to including its endpoints and integers and fractions within all such ranges. The scope of the present invention is not limited to the specific numerical value quoted when defining the range. For example, "1-8" covers 1, 2, 3, 4, 5, 6, 7, 8 and any sub-range consisting of any two values ​​therein, such as 2-6, 3-5.

[0044] The terms "about" and "approximately" when used with a numerical variable generally refer to the value of that variable and all values ​​of that variable are within experimental error (e.g., within a 95% confidence interval for the mean) or within ±10% of the specified value, or a wider range.

[0045] The terms "comprises", "includes", "has", "contains" or "involves" and other variations thereof herein are inclusive or open-ended and do not exclude other unlisted elements or method steps. It will be understood by those skilled in the art that the above terms such as "comprising" encompass the meaning of "consisting of". The expression "consisting of" excludes any element, step or ingredient not specified. The expression "consisting essentially of" means that the scope is limited to the specified elements, steps or ingredients, plus the optional presence of elements, steps or ingredients that do not substantially affect the basic and novel features of the claimed subject matter. It will be understood that the expression "comprising" encompasses the expressions "consisting essentially of" and "consisting of".

[0046] The term "selected from..." means that one or more elements in the group listed later are independently selected and may include combinations of two or more elements.

[0047] When values ​​or end-points of a range are described herein, it should be understood that the disclosure includes the specific value or end-point cited.

[0048] As used herein, the terms "one or more" or "at least one" refer to one, two, three, four, five, six, seven, eight, nine or more.

[0049] Unless otherwise specified, the terms "combination thereof" and "mixture thereof" refer to a multi-component mixture of the elements, such as a two-component mixture, a three-component mixture, a four-component mixture and the maximum possible multi-component mixture.

[0050] In addition, if the number of parts or components of the present invention is not indicated before, it means that there is no limit to the number of occurrences (or existence) of the parts or components. Therefore, it should be interpreted as including one or at least one, and the singular form of the parts or components also includes the plural form, unless the numerical value obviously represents the singular.

[0051] As used herein, the term "optional" or "optionally" means that the subsequently described event or circumstance may or may not occur, and that the description includes both occurring and not occurring of said event or circumstance.

[0052] When the lower and upper limits of a numerical range are disclosed, any numerical value and any included range falling within the range are specifically disclosed. In particular, each range of values ​​disclosed herein (in the form of "about a to b", or equivalently, "approximately a to b", or equivalently, "about ab"), should be understood to represent each numerical value and range encompassed within the broader range.

[0053] For example, the expression “C 1-12 " should be understood to include any sub-ranges and each point value therein, such as C 1-4 , C 2-4 , C3-4 , C 2-4 , C 3-4 etc., as well as C1, C2, C3, C4, etc. For example, the expression “C1- 12 ”, “C 2-18 ”, “C 2-12 ”, “C 12-18 " and the like should also be understood in a similar manner, for example, to include any sub-ranges and point values ​​contained therein.

[0054] Unless otherwise specified, as used herein, the term "hydrocarbon chain" refers to a straight or branched hydrocarbon chain consisting only of carbon and hydrogen, connecting two structural fragments, which may be saturated or contain one or more carbon-carbon double or triple bonds. a-b "Hydrocarbon chain" means a hydrocarbon chain containing a to b carbon atoms. Unless otherwise specified, as used herein, the term "alkane chain" refers to a saturated hydrocarbon chain composed only of carbon and hydrogen. "C a-b "Alkane chain" means an alkane chain containing a to b carbon atoms.

[0055] Unless otherwise specified, as used herein, the term "hydrocarbyl" includes alkyl, alkenyl, and alkynyl. The term "alkyl" refers to a saturated straight or branched chain hydrocarbon group consisting only of carbon and hydrogen atoms. The term "alkenyl" refers to a straight or branched chain hydrocarbon group consisting only of carbon and hydrogen atoms, which contains one or more carbon-carbon double bonds. The term "alkynyl" refers to a straight or branched chain hydrocarbon group consisting only of carbon and hydrogen atoms, which contains one or more carbon-carbon triple bonds. As used herein, "C a-b "Hydrocarbon" means a hydrocarbon group containing a to b carbon atoms, and "C a-b Alkyl", "C a-b Alkenyl", "C a-b The term "alkynyl" is also to be understood in this way.

[0056] Herein, when a wavy line is shown on a chemical bond in a structural fragment, it indicates that it is connected to another structure through the bond. For example: Indicates that the benzene ring is connected to another structure via a bond shown with a wavy line through it.

[0057] Unless otherwise indicated, as used herein, the term "repeating unit" refers to a combination of atoms linked in a certain manner on a polymer chain, which is a basic unit constituting a polymer.

[0058] Unless otherwise indicated, as used herein, the term "room temperature" (RT) refers to about 20 to 35°C, preferably about 25°C.

[0059] Self-nucleating modified polylactic acid

[0060] In one aspect, the present invention relates to a self-nucleating modified polylactic acid having a structure of the following formula (I) or (II):

[0061] A1-O-L1 Formula (I)

[0062] A2—O—L2—O—A3 Formula (II)

[0063] In formula (I),

[0064] L1 is selected from the following structures:

[0065]

[0066] Among them, L 1a Selected from C 1-12 Straight hydrocarbon chain, L 1b Selected from C 10-20 Straight chain hydrocarbon; L 1c Selected from C 10-20 Straight hydrocarbon chain, L 1d Selected from C 1-12 Straight hydrocarbon chain, L 1e Selected from C 10-20 Straight chain hydrocarbon group;

[0067] A1 is

[0068] wherein n is an integer selected from 300-800, and n' is an integer selected from 700-2500;

[0069] In formula (II),

[0070] L2 is selected from the following structures:

[0071]

[0072] Among them, L 2a Selected from C 1-12 Straight hydrocarbon chain, L 2b Selected from C 1-20 Straight hydrocarbon chain, C 3-20 Branched hydrocarbon chain; L 2c Selected from C 1-20 Straight hydrocarbon chain, C 3-20 Branched hydrocarbon chain, L 2d Selected from C 1-12 Straight hydrocarbon chain, L 2e Selected from C 1-20 Straight hydrocarbon chain, C 3-20 branched hydrocarbon chains;

[0073] A2 is And A3 is Or, A2 is And A3 is

[0074] wherein p is an integer selected from 150-400, p' is an integer selected from 350-1250, q is an integer selected from 150-400, q' is an integer selected from 350-1250, the ratio of p to q is 0.8-1.2, and the ratio of p' to q' is 0.8-1.2.

[0075] In a preferred embodiment, in formula (I), A1 is

[0076] In a preferred embodiment, in formula (II), A2 is And A3 is

[0077] The structure of formula (I)

[0078] The self-nucleating modified polylactic acid of the present invention may contain only a single PDLA-PLLA segment. In one embodiment, the self-nucleating modified polylactic acid of the present invention has the structure of the above formula (I), specifically the structure of the following formula (IA) or (IB):

[0079]

[0080] Structural fragment A1 is a PDLA-PLLA block structure, and such structural fragment is conducive to forming a local eutectic. A1 can be Wherein, n is an integer selected from 300-800, and n' is an integer selected from 700-2500. PDLA segments and PLLA segments with n and n' in the appropriate range can fully form a local eutectic effect. If n or n' is too small, the PDLA segment or PLLA segment is too short, the local eutectic effect is not obvious, which is not conducive to the rapid crystallization of the final polylactic acid, and the mechanical properties and thermal properties of the final polylactic acid may decrease, which is not conducive to actual processing and use. If n is too high, the molecular weight of the modified polylactic acid prepolymer is too high, which is not conducive to obtaining a modified polylactic acid prepolymer with a low melting point.

[0081] In formula (IA), the structural fragment L 1a Connecting amide groups and PDLA-PLLA structural fragment A1, structural fragment L 1b Attached to one side of the amide group.

[0082] In formula (IA), L 1a Can be selected from C 1-12 Preferably, L 1a Can be selected from C 1-12Straight alkane chains, for example -CH2-, -CH2CH2-, -CH2CH2CH2-, -CH2CH2CH2CH2-, -(CH2)5-, -(CH2)6-, -(CH2)7-, -(CH2)8-, -(CH2)9-, -(CH2) 10 -、-(CH2) 11 -、-(CH2) 12 -.L 1a More preferred is a C2 straight alkane chain, ie, -CH2CH2-.

[0083] In formula (IA), L 1b Can be selected from C 10-20 Preferably, L 1b Can be selected from C 10-20 Straight chain alkyl, more preferably C 11-17 Straight chain alkyl, such as -(CH2)9CH3, -(CH2) 10 CH3, -(CH2) 11 CH3, -(CH2) 12 CH3, -(CH2) 13 CH3, -(CH2) 14 CH3, -(CH2) 15 CH3, -(CH2) 16 CH3, -(CH2) 17 CH3, -(CH2) 18 CH3, -(CH2) 19 CH3 etc.L 1b More preferably C 11 or C 17 Straight chain alkyl, i.e., -(CH2) 10 CH3 or -(CH2) 16 CH3.

[0084] In formula (IB), the structural fragment L 1c Connecting amide groups and PDLA-PLLA structural fragment A1, structural fragment L 1d Connecting two amide groups, the structural fragment L 1e Attached to one side of the amide group.

[0085] In formula (IB), L 1c Can be selected from C 10-20 Straight hydrocarbon chain, preferably, L 1c Can be selected from C 10-20 Straight alkane chain, more preferably C 11-17 Straight alkane chains, such as -(CH2) 10 -、-(CH2) 11 -、-(CH2)12 -、-(CH2) 13 -、-(CH2) 14 -、-(CH2) 15 -、-(CH2) 16 -、-(CH2) 17 -、-(CH2) 18 -、-(CH2) 19 -、-(CH2) 20 -wait.

[0086] In formula (IB), L 1d Can be selected from C 1-12 Preferably, L 1d Can be selected from C 1-12 Straight alkane chains, for example -CH2-, -CH2CH2-, -CH2CH2CH2-, -CH2CH2CH2CH2-, -(CH2)5-, -(CH2)6-, -(CH2)7-, -(CH2)8-, -(CH2)9-, -(CH2) 10 -、-(CH2) 11 -、-(CH2) 12 -.

[0087] In formula (IB), L 1e Can be selected from C 10-20 Preferably, L 1e Can be selected from C 10-20 Straight chain alkyl, such as -(CH2)9CH3, -(CH2) 10 CH3, -(CH2) 11 CH3, -(CH2) 12 CH3, -(CH2) 13 CH3, -(CH2) 14 CH3, -(CH2) 15 CH3, -(CH2) 16 CH3, -(CH2) 17 CH3, -(CH2) 18 CH3, -(CH2) 19 CH3, etc.

[0088] Since the structure of formula (I) contains only a single PDLA-PLLA segment, the symmetry of the structure is relatively low. 1a , L 1b , L 1c , L 1d , L 1e Compared with their respective corresponding branched hydrocarbon chains (or hydrocarbon groups), L having a straight chain structure 1a , L1b , L 1c , L 1d , L 1e The flexibility of L is better, and its chain segment movement is not hindered by the branch chain. 1a , L 1b , L 1c , L 1d , L 1e The excellent flexibility can make up for the adverse effect of the lack of symmetry on the crystallization performance, thereby being beneficial for the structure of formula (I) to have excellent crystallization performance, and can also ensure a suitable internal plasticization effect, so that the modified polylactic acid prepolymer has a desired lower melting point.

[0089] The structure of formula (II)

[0090] The self-nucleating modified polylactic acid of the present invention may contain only a plurality of PDLA-PLLA segments. In one embodiment, the self-nucleating modified polylactic acid of the present invention has the structure of the above formula (II), specifically the structure of the following formula (II-A) or (II-B):

[0091]

[0092] The structural fragments A2 and A3 are PDLA-PLLA block structures, and such structural fragments are conducive to the formation of local eutectics.

[0093] In one embodiment, in formula (II), A2 is And A3 is wherein p is an integer selected from 150-400, p' is an integer selected from 350-1250, q is an integer selected from 150-400, q' is an integer selected from 350-1250, the ratio of p to q is 0.8-1.2, and the ratio of p' to q' is 0.8-1.2.

[0094] In another embodiment, in formula (II), A2 is And A3 is wherein p is an integer selected from 150-400, p' is an integer selected from 350-1250, q is an integer selected from 150-400, q' is an integer selected from 350-1250, the ratio of p to q is 0.8-1.2, and the ratio of p' to q' is 0.8-1.2.

[0095] In formula (II), PDLA segments and PLLA segments with suitable ranges of p, p', q, and q' can fully form a local eutectic effect. In one embodiment, p is an integer selected from 150-400, such as 150, 160, 170, 180, 200, 250, 300, 310, 320, 325, etc.; p' is an integer selected from 350-1250, such as 350, 360, 370, 380, 390, 400, 450, 500, 600, 700, 800, 900, 950, 960, 970, 980, 990, 1000, 1010, 1020, 1030, 1040, 1050, 1060, 1070, 1080, 1090, 1110, 1120, 1130, 1140, 1150, 1160, 1170, 1180, 1190, 1201, 1210, 1220, 1230, 1240, 1250, 1260, 1270, 1280, 1290, 1310, 1320, 1330, 1340, 1350 000, etc.; q is an integer selected from 150-400, such as 150, 160, 170, 180, 200, 250, 300, 310, 320, 325, etc.; q' is an integer selected from 350-1250, such as 350, 360, 370, 380, 390, 400, 450, 500, 600, 700, 800, 900, 950, 960, 970, 980, 990, 1000, etc. If p, p', q or q' is too small, the PDLA segment or PLLA segment is too short, the local eutectic effect is not obvious, which is not conducive to the rapid crystallization of the modified polylactic acid, and the mechanical properties and thermal properties of the modified polylactic acid may be poor, which is not conducive to actual processing and use. If p or q is too high, the molecular weight of the modified polylactic acid prepolymer is too high, which is not conducive to obtaining a modified polylactic acid prepolymer with a low melting point.

[0096] In formula (II-A), the structural fragment L 2a Connecting amide groups and PDLA-PLLA structural fragment A2, structural fragment L 2b Connect the amide group and the PDLA-PLLA structural fragment A3.

[0097] In formula (II-A), L 2a Can be selected from C 1-12 Preferably, L 2a Can be selected from C 1-12 Straight alkane chains, for example -CH2-, -CH2CH2-, -CH2CH2CH2-, -CH2CH2CH2CH2-, -(CH2)5-, -(CH2)6-, -(CH2)7-, -(CH2)8-, -(CH2)9-, -(CH2) 10 -、-(CH2) 11 -、-(CH2) 12 -.L 2a More preferred is a C2 straight alkane chain, ie, -CH2CH2-.

[0098] In formula (II-A), L 2b Can be selected from C 1-20 Straight hydrocarbon chain, C 3-20Preferably, L 2b Can be selected from C 1-20 Straight alkane chain, C 3-20 In a specific embodiment, L 2b Can be C 17 Branched alkane chains, such as -(CH2) 10 CH(CH2CH2CH2CH2CH2CH3)-.

[0099] In formula (II-B), the structural fragment L 2c Connecting amide groups and PDLA-PLLA structural fragment A2, structural fragment L 2d Connecting two amide groups, the structural fragment L 2e Connect the amide group and the PDLA-PLLA structural fragment A3.

[0100] In formula (II-B), L 2c Can be selected from C 1-20 Straight chain, C 3-20 Branched hydrocarbon chain, preferably C 1-20 Straight alkane chain, C 3-20 In a specific embodiment, L 2c Can be C 17 Branched alkane chains, such as -(CH2) 10 CH(CH2CH2CH2CH2CH2CH3)-.

[0101] In formula (II-B), L 2d Can be selected from C 1-12 Straight hydrocarbon chain, preferably selected from C 1-12 Straight alkane chains, for example -(CH2)2-, -(CH2)3-, -(CH2)4-, -(CH2)5-, -(CH2)6-, -(CH2)7-, -(CH2)8-, -(CH2)9-, -(CH2) 10 -、-(CH2) 11 -、-(CH2) 12 -.L 2d More preferably, it is a C2 straight alkane chain, that is, -CH2CH2-. 2d It can ensure the appropriate intramolecular plasticizing effect.

[0102] In formula (II-B), L 2e Can be selected from C 1-20 Straight chain, C 3-20 Branched hydrocarbon chain, preferably C 1-20 Straight alkane chain, C 3-20 In a specific embodiment, L2e Can be C 17 Branched alkane chains, such as -(CH2) 10 CH(CH2CH2CH2CH2CH2CH3)-.

[0103] The presence of two PDLA-PLLA segments in formula (II) makes the structure have good symmetry as a whole, and such good structural symmetry enables the modified polylactic acid to obtain good performance. Therefore, for the structure of formula (II), the connecting segment L having a linear or branched structure 2b、 L 2c、 L 2e The modified polylactic acid with the desired properties (such as rapid crystallization) can be obtained. In order to further optimize the crystallization performance, the connecting segment L having a linear structure 2b、 L 2c、 L 2e In order to reduce the cost of raw materials, a connecting segment L having a branched structure can be selected. 2b、 L 2c、 L 2e .

[0104] Without being bound by theory, improving the symmetry of the structure of formula (II) is beneficial to further increase the crystallization rate and crystallization effect of the self-nucleating modified polylactic acid. The structure of formula (II) preferably has central symmetry or is substantially close to central symmetry. In one embodiment, the ratio of p and q is 0.8-1.2, preferably 0.9-1.1, and more preferably 1. In one embodiment, the ratio of p' and q' is 0.8-1.2, preferably 0.9-1.1, and more preferably 1. p and q are close to or equal, p' and q' are close to or equal, the central symmetry of the structure of formula (II) is better, and the crystallization rate and crystallization effect of the self-nucleating modified polylactic acid are better.

[0105] In one embodiment, fragment L 2c With L 2e Same. Without being bound by theory, L 2c With L 2e Having the same structure can improve the symmetry of the structure of formula (II-B), and when preparing the self-nucleating modified polylactic acid having the structure of formula (II-B), the reaction activities of the ring-opening polymerization reaction of the lactide at both ends of the reaction substrate can be closer, thereby facilitating the polymerization degree of the corresponding blocks of the PDLA-PLLA block structure on both sides of formula (II) to be close, that is, facilitating p and q to be closer or equal, and facilitating p' and q' to be close or equal.

[0106] In the self-nucleating modified polylactic acid of the present invention, the amide group and the hydrocarbon chain connected thereto can synergistically exert an intramolecular plasticizing effect, and produce a hydrogen bond induction effect to promote the crystallization process. The PDLA-PLLA fragment will form a local eutectic, and the hydrocarbon chain can produce a suitable intramolecular plasticizing effect. Such multiple synergistic nucleation mechanisms are all helpful in obtaining a self-nucleating modified polylactic acid that can be crystallized rapidly. Therefore, without the additional addition of a nucleating agent, the modified polylactic acid of the present invention can also crystallize rapidly, that is, the crystallization process is completed in a short time.

[0107] In the self-nucleating modified polylactic acid of the present invention, the amide group and the hydrocarbon chain connected thereto can synergistically produce a hydrogen bond induction effect to promote the crystallization process, and can also play an intramolecular plasticizing effect, which is conducive to reducing the melting point of the modified polylactic acid prepolymer (as described below). As the number of amide groups in the structure increases, the above effect is more obvious. For the self-nucleating modified polylactic acid of the present application, the number of amide groups and the remaining structural fragments in the molecule have a suitable combination, so that the self-nucleating modified polylactic acid can be smoothly prepared and has the desired advantageous performance.

[0108] For the self-nucleating modified polylactic acid containing only a single amide group (e.g., Formula (IA), Formula (II-A)), the present invention, especially the preferred L 1a , L 2a The structure can ensure the intramolecular plasticizing effect. In addition, during the preparation process, the corresponding aliphatic amide containing terminal hydroxyl groups can react more smoothly with the coordination catalyst, and the formed alkoxide can more efficiently initiate the ring-opening polymerization of lactide.

[0109] For the self-nucleating modified polylactic acid containing only a single amide group (e.g., Formula (IA), Formula (II-A)), the structural fragment L 1b and L 2b It is a longer and more flexible chain structure, which can be used to provide intramolecular plasticizing effect. 1b and L 2b The part of the flexible long chain close to the amide group can be easily induced into a primitive crystal nucleus by hydrogen bonding, providing a self-nucleation site and reducing the activation energy required for crystallization, thereby promoting crystallization. Since there is only a single amide group in the structure of the compound, L 1b and L 2b The chain length of L is usually longer to improve the flexibility of the chain, to increase the probability of being induced by hydrogen bonds to form a primitive nucleus, thereby ensuring sufficient self-nucleation sites. 1b and L 2b Good internal plasticization effect can also reduce the melting point of the modified polylactic acid prepolymer (as described below), which is beneficial to the preparation of the fast-crystallizing self-nucleating modified polylactic acid of the present application.

[0110] The present invention, especially preferably L 1b and L 2b It helps to obtain a modified polylactic acid prepolymer with a low melting point and can also avoid an overly strong plasticizing effect that causes a decrease in the Vicat softening temperature of the product.

[0111] For the self-nucleating modified polylactic acid containing two amide groups (e.g., formula (IB), formula (II-B)), the presence of two amide segments can provide a stronger hydrogen bond induction effect and internal plasticization effect, which reduces the effect on the chain segment L. 1c , L 1d and L 1e and L 2c , L 2d and L 2e The chain length and segment flexibility requirements of the modified polylactic acid prepolymer can usually have a desired lower melting point, and the modified polylactic acid of formula (IB) and formula (II-B) can usually have better rapid crystallization performance.

[0112] In the present invention, the advantages of the modified polylactic acid prepolymer with a low melting point are mainly as follows: in the process of the modified polylactic acid prepolymer and the second lactide undergoing the second ring-opening reaction, it is necessary to carry out a homogeneous ring-opening polymerization reaction at a temperature at which all the raw materials can be melted. The modified polylactic acid prepolymer with a low melting point can be melted at a relatively low temperature, thereby reducing or avoiding the self-polymerization reaction of lactide, promoting the polylactic acid prepolymer and lactide to form a block copolymer such as formula (I) or (II), so that the self-nucleating modified polylactic acid of the present invention can be obtained smoothly and efficiently. If the melting point of the modified polylactic acid prepolymer is too high, in order to ensure that all raw materials are melted to promote the formation of a homogeneous system, the ring-opening reaction of lactide initiated by the modified polylactic acid prepolymer needs to be carried out at a relatively high reaction temperature, which may aggravate the self-polymerization reaction of lactide, and even cause the implosion of lactide, resulting in the appearance of a blended product, which is not conducive to the generation of the block copolymer of formula (I) or (II) of the target.

[0113] For conventional polylactic acid resin, its melting point is positively correlated with optical purity and molecular weight within a certain range. The melting point of polylactic acid will increase with the increase of optical purity. The melting point of polylactic acid will also increase with the increase of its molecular weight. Therefore, conventional high optical purity PDLA or PLLA has a higher melting point (usually ≥170°C). The modified polylactic acid prepolymer of the present application has a plasticizing effect brought by a suitable molecular weight and a specific structure, which can maintain the high crystallinity brought by the high optical purity of the PDLA segment or PLLA segment, and it also has a lower melting point. Therefore, the polylactic acid prepolymer of the present application can react with lactide at a lower temperature and successfully realize the ring-opening polymerization of lactide.

[0114] In one embodiment, the self-nucleating modified polylactic acid has a structure shown in formula (I-1):

[0115]

[0116] In formula (I-1), n ​​is an integer selected from 300-800, and n' is an integer selected from 700-2500.

[0117] In one embodiment, the self-nucleating modified polylactic acid has a structure shown in formula (I-2):

[0118]

[0119] In formula (I-2), n is an integer selected from 300-800, and n' is an integer selected from 700-2500.

[0120] In one embodiment, the self-nucleating modified polylactic acid has a structure shown in formula (I-3):

[0121]

[0122] In formula (I-3), n is an integer selected from 300-800, and n' is an integer selected from 700-2500.

[0123] In one embodiment, the self-nucleating modified polylactic acid has a structure shown in formula (I-4):

[0124]

[0125] In one embodiment, the self-nucleating modified polylactic acid has a structure shown in formula (II-1):

[0126]

[0127] In formula (II-1), p is an integer selected from 150-400, p' is an integer selected from 350-1250, q is an integer selected from 150-400, and q' is an integer selected from 350-1250.

[0128] In one embodiment, the self-nucleating modified polylactic acid has a structure shown in formula (II-2):

[0129]

[0130] In formula (II-2), p is an integer selected from 150-400, p' is an integer selected from 350-1250, q is an integer selected from 150-400, and q' is an integer selected from 350-1250.

[0131] In one embodiment, the self-nucleating modified polylactic acid has a structure shown in formula (II-3):

[0132]

[0133] In formula (II-3), p is an integer selected from 150-400, p' is an integer selected from 350-1250, q is an integer selected from 150-400, and q' is an integer selected from 350-1250.

[0134] In one embodiment, the self-nucleating modified polylactic acid has a structure shown in formula (II-4):

[0135]

[0136]

[0137] In formula (II-4), p is an integer selected from 150-400, p' is an integer selected from 350-1250, q is an integer selected from 150-400, and q' is an integer selected from 350-1250.

[0138] Preparation method

[0139] In another aspect, the present invention relates to a method for self-nucleating modified polylactic acid of the present application as described above, comprising the following steps:

[0140] The aliphatic amide containing terminal hydroxyl groups is reacted with a coordination catalyst to obtain an alcohol salt of the aliphatic amide;

[0141] The alkoxide of aliphatic amide is reacted with the molten first lactide, and the alkoxide of aliphatic amide initiates the ring-opening polymerization of the first lactide to obtain a modified polylactic acid prepolymer;

[0142] The modified polylactic acid prepolymer is reacted with a coordination catalyst to obtain the modified polylactic acid prepolymer;

[0143] The modified polylactic acid prepolymer reacts with the molten second lactide, and the modified polylactic acid prepolymer initiates the ring-opening polymerization of the second lactide to obtain the self-nucleating modified polylactic acid of the present invention;

[0144] Wherein, the aliphatic amide containing terminal hydroxyl groups has the structure of the following formula (III) or (IV):

[0145] HO-L1 Formula (III),

[0146] HO——L2——OH Formula (IV),

[0147] The first lactide is L-lactide and the second lactide is D-lactide, or the first lactide is D-lactide and the second lactide is L-lactide.

[0148] The present application method is further described below according to specific steps.

[0149] Step 1 : The aliphatic amide containing terminal hydroxyl groups is reacted with a coordination catalyst to obtain the alcohol salt of the aliphatic amide.

[0150] In one embodiment, the aliphatic amide containing terminal hydroxyl groups has the structure of the following formula (III) or (IV):

[0151] HO-L1 Formula (III),

[0152] HO-L2—OH Formula (IV),

[0153] Wherein, L1 and L2 are as defined above.

[0154] The structure of the coordination catalyst may be RMR, and the coordination catalyst reacts with the terminal hydroxyl group of the aliphatic amide containing the terminal hydroxyl group to form the corresponding alcohol salt.

[0155] The reaction mechanism of the aliphatic amide containing a single terminal hydroxyl group of formula (III) and the coordination catalyst is as follows:

[0156]

[0157] The reaction mechanism of the aliphatic amide containing two terminal hydroxyl groups of formula (IV) and the coordination catalyst is as follows:

[0158]

[0159] In one embodiment, M is selected from a divalent coordinating metal, preferably zinc, tin or magnesium. In one embodiment, R is selected from an organic monovalent acid radical, preferably octanoate, isooctanoate, decanoate or acetate. In a specific embodiment, the coordination catalyst is stannous octoate. For the aliphatic amide containing terminal hydroxyl groups of the present invention, the preferred coordination catalyst type has better adaptability and catalytic activity, which is conducive to the preparation of the corresponding alkoxide.

[0160] In the reaction of the aliphatic amide containing terminal hydroxyl groups and the coordination catalyst, the appropriate feed ratio of the aliphatic amide containing terminal hydroxyl groups and the coordination catalyst is conducive to the formation of the alcohol salt of the aliphatic amide containing terminal hydroxyl groups, and is also conducive to reserving a sufficient amount of alcohol salt in the modified polylactic acid prepolymer to catalyze the ring-opening polymerization reaction of the second lactide. In one embodiment, the molar ratio of the aliphatic amide containing terminal hydroxyl groups and the coordination catalyst is (5:5)-(3:7), for example, 5:5, 4:6, 3.5:6.5, 6:7, 5:7, 4:7, 3:7, etc. If the ratio is too high, it is not conducive to the preparation of the alcohol salt; if the ratio is too low, it may cause excessive residues of the coordination catalyst and lead to a decrease in the performance of the product.

[0161] In one embodiment, the temperature T1 at which the aliphatic amide containing terminal hydroxyl groups reacts with the coordination catalyst is 140-150° C. A suitable reaction temperature is conducive to the smooth generation of the alcohol salt of the aliphatic amide containing terminal hydroxyl groups. Too high a reaction temperature will increase the energy consumption during the reaction and may also cause the decomposition of the reactants; too low a reaction temperature is not conducive to the occurrence of the reaction and the reaction rate is reduced.

[0162] In one embodiment, the reaction time of the terminal hydroxyl group-containing aliphatic amide and the coordination catalyst is about 20-40 minutes, such as about 20 minutes, about 25 minutes, about 30 minutes, about 35 minutes, about 40 minutes. Too short a reaction time will result in incomplete reaction; too long a reaction time will increase the energy consumption during the reaction.

[0163] Step 2 The alkoxide of aliphatic amide is reacted with the molten first lactide, and the alkoxide of aliphatic amide initiates the ring-opening polymerization of the first lactide to obtain a modified polylactic acid prepolymer.

[0164] After the first lactide is heated to melt, an alcohol salt of aliphatic amide is added to initiate the ring-opening polymerization of lactide. When the polymerization is completed, a modified polylactic acid prepolymer can be obtained. In this process, the active alcohol salt of aliphatic amide can induce the ring-opening of lactide, and then the hydroxyamide structure is introduced into the polylactic acid segment, and at the same time, the coordination catalyst (such as stannous octoate) is reduced.

[0165] The first lactide can be L-lactide or D-lactide. The concentration of free acid in the first lactide needs to be controlled within a relatively low range so that the ring-opening polymerization can proceed smoothly. In one embodiment, the free acid of the first lactide is about 10 mmol / kg or less, for example, about 1 mmol / kg, 2 mmol / kg, 3 mmol / kg, 5 mmol / kg, 6 mmol / kg, 8 mmol / kg, 10 mmol / kg, etc. The PLLA or PDLA block of a single chirality prepared using the first lactide of high optical purity can increase the regularity of the self-nucleated modified polylactic acid structure, which is conducive to rapid crystallization. In one embodiment, the optical purity of the first lactide is ≥98.5%.

[0166] In the reaction of the alcohol salt of aliphatic amide and the molten first lactide, the appropriate feed weight ratio of the alcohol salt of aliphatic amide to the first lactide is conducive to the formation of the modified polylactic acid prepolymer. The feed weight ratio of the alcohol salt of aliphatic amide to the first lactide is about 0.005-0.01, for example, about 0.005, 0.006, 0.007, 0.008, 0.009, 0.010, etc.

[0167] In one embodiment, the alcohol salt prepared from the aliphatic amide containing a single terminal hydroxyl group of formula (III) initiates the ring-opening polymerization of L-lactide to obtain a modified polylactic acid prepolymer having the structure of the following formula (V-1):

[0168]

[0169] wherein L1 is as defined above.

[0170] In one embodiment, the alcohol salt prepared from the aliphatic amide containing a single terminal hydroxyl group of formula (III) initiates the ring-opening polymerization of D-lactide to obtain a modified polylactic acid prepolymer having the structure of the following formula (V-2):

[0171]

[0172] wherein L1 is as defined above.

[0173] In one embodiment, the alcohol salt prepared from the aliphatic amide containing two terminal hydroxyl groups of formula (IV) initiates the ring-opening polymerization of D-lactide to obtain a modified polylactic acid prepolymer having the structure of the following formula (VI-1):

[0174]

[0175] Wherein, L2, p, q are as defined above.

[0176] In one embodiment, the alcohol salt prepared from the aliphatic amide containing two terminal hydroxyl groups of formula (IV) initiates the ring-opening polymerization of L-lactide to obtain a modified polylactic acid prepolymer having the structure of the following formula (VI-2):

[0177]

[0178] Wherein, L2, p, q are as defined above.

[0179] In one embodiment, the number average molecular weight Mn of the modified polylactic acid prepolymer is about 25000-45000Da, for example, about 25000Da, 30000Da, 35000Da, 40000Da, 45000Da, 31800Da, 35105Da, 40120, 43060Da, etc. If the number average molecular weight is too low, local eutectics are not easy to form in the final modified polylactic acid; if the number average molecular weight is too high, the activity of the modified polylactic acid prepolymer may decrease in subsequent reactions, and the melting point of the modified polylactic acid prepolymer will increase, which is not conducive to the smooth progress of the subsequent desired polymerization reaction and the rapid crystallization of the final modified polylactic acid.

[0180] In one embodiment, the melting point of the modified polylactic acid prepolymer is 145-155°C, for example, 145°C, 146°C, 147°C, 148°C, 149°C, 150°C, 151°C, 152°C, 153°C, 154°C, 155°C, etc. The advantages of the low-melting-point modified polylactic acid prepolymer are as described above. The formed modified polylactic acid prepolymer has a low melting point and can be melted at a lower temperature, thereby reducing or avoiding the self-polymerization reaction of lactide, promoting the polylactic acid prepolymer and lactide to form a block copolymer such as formula (I) or (II), so that the self-nucleating modified polylactic acid of the present invention can be obtained smoothly and efficiently.

[0181] Step 3 The modified polylactic acid prepolymer reacts with the molten second lactide, and the modified polylactic acid prepolymer initiates the ring-opening polymerization of the second lactide to obtain the self-nucleating modified polylactic acid of the present invention.

[0182] The modified polylactic acid prepolymer acts as a macromolecular hydroxyl initiator, and the second lactide undergoes ring-opening polymerization under the catalysis of the coordination catalyst (such as stannous octoate) reduced in the system in the above step 2.

[0183] The second lactide can be L-lactide or D-lactide, and the second lactide has an opposite chirality to the first lactide, which is conducive to the formation of a local eutectic. In one embodiment, the first lactide is L-lactide and the second lactide is D-lactide. In one embodiment, the first lactide is D-lactide and the second lactide is L-lactide.

[0184] Preferably, the first lactide is D-lactide and the second lactide is L-lactide, which is conducive to further optimizing the crystallization rate of the obtained self-nucleating modified polylactic acid. Without being bound by theory, the alcohol salt of the aliphatic amide initiates the ring-opening polymerization of D-lactide to obtain a modified polylactic acid prepolymer containing a PDLA segment, and then the modified polylactic acid prepolymer containing a PDLA segment initiates the ring-opening polymerization of L-lactide to obtain the final self-nucleating modified polylactic acid, and the relatively fast crystallization rate of the PDLA segment is conducive to improving the crystallization rate of the PLLA segment.

[0185] The concentration of free acid in the second lactide needs to be controlled within a relatively low range so that the ring-opening polymerization can proceed smoothly. In one embodiment, the free acid of the second lactide is about 20 mmol / kg or less, for example, about 1 mmol / kg, 2 mmol / kg, 5 mmol / kg, 8 mmol / kg, 10 mmol / kg, 12 mmol / kg, 15 mmol / kg, 18 mmol / kg, 20 mmol / kg, etc. The use of a high optical purity second lactide can increase the regularity of the self-nucleating modified polylactic acid structure obtained, which is conducive to rapid crystallization. In one embodiment, the optical purity of the second lactide is ≥98.5%.

[0186] In the reaction of the modified polylactic acid prepolymer and the molten second lactide, the weight ratio of the modified polylactic acid prepolymer to the second lactide is 0.01-0.1, for example, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, etc.

[0187] During the reaction of the modified polylactic acid prepolymer and the molten second lactide, a suitable reaction temperature can melt the raw materials, promote the formation of a homogeneous system, and facilitate the ring-opening polymerization reaction. In one embodiment, the reaction temperature T2 of the modified polylactic acid prepolymer and the molten second lactide is 140-150°C. Too high a reaction temperature will increase the energy consumption during the reaction and may also cause undesirable thermal decomposition; too low a reaction temperature is not conducive to the occurrence of the reaction and the reaction rate is reduced.

[0188] The reaction of the present application can be carried out in conventional instruments and equipment in the art, including but not limited to a reactor. Conventional methods in the art can be used to ensure the smooth progress of the reaction, including but not limited to: drying and dehydrating the reaction system, placing the reaction system in an inert atmosphere (such as a nitrogen atmosphere), etc.

[0189] Beneficial Effects

[0190] The invention prepares a modified polylactic acid prepolymer with high optical purity and low melting point by initiating the ring-opening polymerization of lactide with the alcohol salt of aliphatic amide containing terminal hydroxyl groups. By controlling the molecular weight of the prepolymer and utilizing the plasticizing effect of a specific aliphatic amide, the modified polylactic acid prepolymer has a lower melting point, which is beneficial to initiating the ring-opening polymerization of lactide in the subsequent molten state; the higher optical purity of the modified polylactic acid prepolymer is beneficial to maintaining the structural regularity of polylactic acid to achieve rapid crystallization of polylactic acid.

[0191] The preparation method of the present invention can directly utilize the existing production line, and does not need to add a nucleating agent during the process through secondary processing such as screw and internal mixing, and is suitable for industrial large-scale production.

[0192] The self-nucleating polylactic acid resin of the present invention has the characteristics of hydrogen bond induction effect of amide groups, intramolecular plasticization effect of hydrocarbon chains and local eutectic of PDLA-PLLA, and such multiple synergistic nucleation mechanisms are helpful to obtain self-nucleating modified polylactic acid that can crystallize rapidly.

[0193] Example

[0194] The solution of the present invention is further described in detail below in conjunction with specific embodiments.

[0195] It should be noted that the following examples are merely examples for clearly illustrating the technical solutions of the present invention, and are not intended to limit the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description, and it is not necessary and impossible to exhaustively list all the embodiments here, and the obvious changes or modifications derived therefrom are still within the scope of protection of the present invention. Unless otherwise specified, the instruments, equipment, and reagents used herein are all commercially available.

[0196] Material

[0197] D-Lactide: purchased from Corbijn-Prak, The Netherlands.

[0198] L-Lactide: purchased from Zhejiang Hisun Biomaterials Co., Ltd.

[0199] Stannous octoate: purchased from Shanghai Aishu New Material Technology Co., Ltd.

[0200] N-(2-Hydroxyethyl) stearamide: CAS number: 111-57-9; purchased from Shanghai En Chemical Technology Co., Ltd.

[0201] Ethylene bis-12-hydroxystearamide:

[0202] CAS number: 123-26-2; purchased from Hubei Xinghengye Technology Co., Ltd.

[0203] Cocoyl monoethanolamine: CAS number: 68140-00-1; purchased from Shanghai Yuanye Biotechnology Co., Ltd.

[0204] 12-Hydroxy-N-(2-hydroxyethyl)octadecanoamide: CAS number: 106-15-0; purchased from Wuhan Huaxiang Kejie Biotechnology Co., Ltd.

[0205] Monohydroxyoctadecyl alcohol: CAS number: 112-92-5, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0206] Dihydroxyoctadecyl glycol: CAS number: 3155-43-9, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0207] preparation

[0208] The samples of the embodiments and comparative examples were prepared according to the following steps:

[0209] Example 1

[0210] Example 1 was prepared by the following preparation method:

[0211] Stannous octoate and N-(2-hydroxyethyl) stearamide are placed in a reaction container in a molar ratio of 6:4, N2 is purged 2-3 times to provide a nitrogen atmosphere, the system is heated to 140°C, and the reaction is carried out for 20 minutes to obtain an alcohol salt of N-(2-hydroxyethyl) stearamide;

[0212] D-lactide was added into a polymerization reactor and the temperature was raised to 150° C. After the D-lactide was melted, 0.9 wt % (based on the weight of the D-lactide) of an alcohol salt of N-(2-hydroxyethyl) stearamide was added to initiate the ring-opening polymerization of the D-lactide. After the polymerization reaction was completed, a modified D-polylactic acid prepolymer (No. E1-A) was obtained;

[0213] The prepared modified poly D-lactic acid prepolymer (based on the total weight of the modified poly D-lactic acid prepolymer and L-lactide, the amount of the modified poly D-lactic acid prepolymer is 5wt%) and L-lactide are put into another reactor, and the system is heated to 155°C. After the modified poly D-lactic acid prepolymer and L-lactide are completely melted, the reactor is heated to 200°C. After the reaction is completed, a sample of the self-nucleating polylactic acid resin of Example 1 is obtained (No. E1-B).

[0214] Example 2

[0215] Example 2 was prepared by the following preparation method:

[0216] Stannous octoate and ethylene bis-12-hydroxystearamide are placed in a reaction container in a molar ratio of 5:5, N2 is purged 2-3 times to provide a nitrogen atmosphere, the system is heated to 150° C., and the reaction is carried out for 30 minutes to obtain an alcohol salt of ethylene bis-12-hydroxystearamide;

[0217] D-lactide was added into a polymerization reactor and the temperature was raised to 150° C. After the D-lactide was melted, 0.6 wt % (based on the weight of the D-lactide) of ethylene bis-12-hydroxystearamide alcohol salt was added to initiate the ring-opening polymerization of the D-lactide. After the polymerization reaction was completed, a modified poly D-lactic acid prepolymer (numbered E1-A) was obtained;

[0218] The prepared modified poly D-lactic acid prepolymer (the amount of poly D-lactic acid prepolymer is 7wt% based on the total weight of the modified poly D-lactic acid prepolymer and L-lactide) and L-lactide are put into another reactor, and the system is heated to 155°C. After the modified polylactic acid prepolymer and L-lactide are completely melted, the reactor is heated to 200°C. After the reaction is completed, a sample of the self-nucleating polylactic acid resin of Example 2 is obtained (No. E2-B).

[0219] Example 3

[0220] Example 3 was prepared by the following preparation method:

[0221] Stannous octoate and cocoyl monoethanolamine are placed in a reaction container in a molar ratio of 6:4, N2 is purged 2-3 times to provide a nitrogen atmosphere, the system is heated to 140° C., and the reaction is carried out for 20 minutes to obtain the alcohol salt of cocoyl monoethanolamine;

[0222] D-lactide is added into a polymerization reactor and the temperature is raised to 150° C. After the D-lactide is melted, 0.9 wt % (based on the weight of the D-lactide) of ethanol salt of coconut oil acyl monoethanolamine is added to initiate the ring-opening polymerization of the D-lactide. After the polymerization reaction is completed, a modified D-polylactic acid prepolymer (numbered E3-A) is obtained;

[0223] The prepared modified poly D-lactic acid prepolymer (the amount of poly D-lactic acid prepolymer is 5wt% based on the total weight of the modified poly D-lactic acid prepolymer and L-lactide) and L-lactide are put into another reactor, and the system is heated to 155°C. After the modified poly D-lactic acid prepolymer and L-lactide are completely melted, the reactor is heated to 200°C. After the reaction is completed, a sample of the self-nucleating polylactic acid resin of Example 3 is obtained (No. E3-B).

[0224] Example 4

[0225] Example 4 was prepared by the following preparation method:

[0226] Stannous octoate and 12-hydroxy-N-(2-hydroxyethyl) octadecanoic acid amide are placed in a reaction container at a molar ratio of 5:5, N2 is purged 2-3 times to provide a nitrogen atmosphere, the system is heated to 150°C, and the reaction is carried out for 30 minutes to obtain an alcohol salt of 12-hydroxy-N-(2-hydroxyethyl) octadecanoic acid amide;

[0227] D-lactide was added into a polymerization reactor and the temperature was raised to 150° C. After the D-lactide was melted, 0.6 wt % (based on the weight of the D-lactide) of 12-hydroxy-N-(2-hydroxyethyl) octadecanoic acid amide alcohol salt was added to initiate the ring-opening polymerization of the D-lactide. After the polymerization reaction was completed, a modified poly D-lactic acid prepolymer (No. E4-A) was obtained;

[0228] The prepared modified poly D-lactic acid prepolymer (the amount of poly D-lactic acid prepolymer is 7wt% based on the total weight of the modified poly D-lactic acid prepolymer and L-lactide) and L-lactide are put into another reactor, and the system is heated to 155°C. After the modified polylactic acid prepolymer and L-lactide are completely melted, the reactor is heated to 200°C. After the reaction is completed, a sample of the self-nucleating polylactic acid resin of Example 4 is obtained (No. E4-B).

[0229] Comparative Example 1

[0230] Comparative Example 1 was prepared by the following preparation method:

[0231] Stannous octoate and monohydroxyoctadecyl alcohol are placed in a reaction container in a molar ratio of 6:4, N2 is purged 2-3 times to provide a nitrogen atmosphere, the system is heated to 140°C, and the reaction is carried out for 20 minutes to obtain an alcoholate of monohydroxyoctadecyl alcohol;

[0232] D-lactide was added into a polymerization reactor and the temperature was raised to 150° C. After the D-lactide was melted, 0.9 wt % (based on the weight of the D-lactide) of alkoxide of monohydroxyoctadecyl alcohol was added to initiate the ring-opening polymerization of the D-lactide. After the polymerization reaction was completed, a modified D-polylactic acid prepolymer (No. CE1-A) was obtained;

[0233] The prepared modified poly D-lactic acid prepolymer (the amount of poly D-lactic acid prepolymer is 5wt% based on the total weight of the modified poly D-lactic acid prepolymer and L-lactide) and L-lactide are put into another reactor, and the system is heated to 155°C. After the melting condition of the system is stabilized, the reactor is heated to 200°C. After the reaction is completed, a sample of the self-nucleating polylactic acid resin of Comparative Example 1 is obtained (No. CE1-B).

[0234] Comparative Example 2

[0235] Comparative Example 2 was prepared by the following preparation method:

[0236] Stannous octoate and dihydroxyoctadecyl alcohol are placed in a reaction container at a molar ratio of 5:5, N2 is purged 2-3 times to provide a nitrogen atmosphere, the system is heated to 150° C., and the reaction is carried out for 30 minutes to obtain an alcoholate of dihydroxyoctadecyl alcohol;

[0237] D-lactide was added into a polymerization reactor and the temperature was raised to 150° C. After the D-lactide was melted, 0.6 wt % (based on the weight of the D-lactide) of alcohol salt of dihydroxyoctadecyl alcohol was added to initiate the ring-opening polymerization of the D-lactide. After the polymerization reaction was completed, a modified poly D-lactic acid prepolymer (No. CE1-A) was obtained;

[0238] The prepared modified poly D-lactic acid prepolymer (the amount of poly D-lactic acid prepolymer is 7wt% based on the total weight of the modified poly D-lactic acid prepolymer and L-lactide) and L-lactide are put into another reactor, and the system is heated to 155°C. After the melting condition of the system is stabilized, the reactor is heated to 200°C. After the reaction is completed, a sample of the self-nucleating polylactic acid resin of Comparative Example 2 is obtained (No. CE2-B).

[0239] Comparative Example 3

[0240] Comparative Example 3 was prepared by the following preparation method:

[0241] Stannous octoate and N-(2-hydroxyethyl) stearamide are placed in a reaction container in a molar ratio of 6:4, N2 is purged 2-3 times to provide a nitrogen atmosphere, the system is heated to 140°C, and the reaction is carried out for 20 minutes to obtain an alcohol salt of N-(2-hydroxyethyl) stearamide;

[0242] The prepared alcohol salt of N-(2-hydroxyethyl) stearamide (based on the total weight of the alcohol salt of N-(2-hydroxyethyl) stearamide and L-lactide, the amount of the alcohol salt of N-(2-hydroxyethyl) stearamide is 0.045wt%, which corresponds to: in the reaction of the modified poly D-lactic acid prepolymer and L-lactide in Example 1, the actual content of the active alcohol salt contained in the modified poly D-lactic acid prepolymer) and L-lactide are put into a reactor, and the system is heated to 155°C. After the L-lactide is completely melted, the reactor is heated to 200°C. After the reaction is completed, the poly-L-lactic acid resin sample of Comparative Example 1 (No. CE3) is obtained.

[0243] Comparative Example 4

[0244] Comparative Example 4 was prepared by the following preparation method:

[0245] Stannous octoate and ethylene bis-12-hydroxystearamide are placed in a reaction container in a molar ratio of 5:5, N2 is purged 2-3 times to provide a nitrogen atmosphere, the system is heated to 150° C., and the reaction is carried out for 30 minutes to obtain an alcohol salt of ethylene bis-12-hydroxystearamide;

[0246] The prepared ethanol salt of ethylene bis-12-hydroxystearamide (based on the total weight of the ethanol salt of ethylene bis-12-hydroxystearamide and L-lactide, the amount of the ethanol salt of ethylene bis-12-hydroxystearamide is 0.042wt%, which corresponds to: in the reaction of the modified poly D-lactic acid prepolymer and L-lactide in Example 2, the actual content of the active ethanol salt contained in the modified poly D-lactic acid prepolymer) and L-lactide are put into a reactor, and the system is heated to 155°C. After the L-lactide is completely melted, the reactor is heated to 200°C. After the reaction is completed, the poly-L-lactic acid resin sample of Comparative Example 2 (No. CE4) is obtained.

[0247] Comparative Example 5

[0248] Comparative Example 5 was prepared by the following preparation method:

[0249] N-(2-hydroxyethyl)stearamide and polylactic acid resin (polylactic acid brand: Haizheng R190; number average molecular weight: 100,000) were uniformly mixed and granulated by twin-screw extrusion to obtain a physically dispersed polylactic acid resin sample of comparative example 5 (numbered CE5), wherein the amount of N-(2-hydroxyethyl)stearamide added was determined in the following manner: the content of N-(2-hydroxyethyl)stearamide in the sample of comparative example 5 was kept consistent with the content of the corresponding structure of N-(2-hydroxyethyl)stearamide present in the sample of Example 1.

[0250] Comparative Example 6

[0251] Comparative Example 6 was prepared by the following preparation method:

[0252] After ethylene bis-12-hydroxystearamide and polylactic acid resin (polylactic acid brand: Haizheng R190; number average molecular weight: 100,000) are uniformly mixed, granulation is carried out by twin-screw extrusion to obtain a physically dispersed polylactic acid resin sample of Comparative Example 6 (No. CE6), wherein the amount of ethylene bis-12-hydroxystearamide added is determined in the following manner: the content of ethylene bis-12-hydroxystearamide in the sample of Comparative Example 6 is consistent with the content of the corresponding structure of ethylene bis-12-hydroxystearamide present in the sample of Example 2.

[0253] Performance Testing

[0254] The number average molecular weight and melt index of Examples 1-4 and Comparative Examples 1-4 were measured in the following manner:

[0255] Number average molecular weight:

[0256] Equipment name: Liquid chromatograph;

[0257] Equipment model: Shimadzu LC-16;

[0258] Detector: RID-20A;

[0259] Equipment manufacturer: Shimadzu Corporation of Japan;

[0260] According to GB / T29284-2012 and GB / T27843-2011, two Shodex LF-804 columns in series were used to dissolve the polystyrene standard sample in dichloromethane to prepare the standard solution; the experimental sample was also dissolved in dichloromethane to prepare a 1% concentration solution, and carefully oscillated to fully dissolve it. The mobile phase was dichloromethane, the column temperature was 40°C, and the flow rate was 1.0ml / min. 20μL of the sample solution was manually injected into the chromatographic column to form a sharp band, and the Shimadzu GPC data processing software was used for data analysis to determine the number average molecular weight of the sample.

[0261] Melt Index:

[0262] Equipment name: melt flow rate meter;

[0263] Equipment model: MFI-1211;

[0264] Equipment manufacturer: Chengde Jinjian Testing Instrument Co., Ltd.

[0265] National standard: Determined according to GB / T29284-2012;

[0266] The melt mass flow rate is carried out according to GB / T29284-2012, the test temperature is 190°C, and the nominal load is 2.16 kg. Take 50g of sample and bake it in a vacuum oven at 90°C for 4 hours, take it out and test it immediately to obtain the melt mass flow rate.

[0267] The test results are shown in Table 1-2 below.

[0268] Table 1

[0269]

[0270] It can be seen from Examples 1-4 in Table 1 that the self-nucleating modified polylactic acid with a relatively high molecular weight can be successfully prepared by the preparation method of the present invention.

[0271] The melt index, molecular weight and molecular weight distribution of the sample E1-B prepared using monohydroxyamide as raw material in Example 1 are similar to those of the sample CE3 prepared using monohydroxy alcohol as raw material in Comparative Example 3. The melt index, molecular weight and molecular weight distribution of the sample E2-B prepared using bishydroxyamide as raw material in Example 2 are also consistent with those of the sample CE4 prepared using bishydroxy alcohol as raw material in Comparative Example 4.

[0272] The modified poly D-lactic acid prepolymers (No. E1-A, E2-A, E3-A, E4-A) of Examples 1-4 have relatively low melting points (all below 155°C). At a temperature of less than 160°C, the modified poly D-lactic acid prepolymers (No. E1-A, E2-A, E3-A, E4-A) of Examples 1-4 can smoothly initiate the ring-opening polymerization of L-lactide to successfully obtain self-nucleating modified polylactic acid.

[0273] The modified poly D-lactic acid prepolymers (numbered CE1-A, CE2-A) prepared by using alkyl alcohol in Comparative Examples 1-2 have relatively high melting points, which are 170°C and 172°C, respectively. At a temperature of 155°C, the modified poly D-lactic acid prepolymers (numbered CE1-A, CE2-A) of Comparative Examples 1-2 cannot melt and cannot initiate the ring-opening polymerization of L-lactide. Further experiments show that at any temperature within 160°C, the modified poly D-lactic acid prepolymers (numbered CE1-A, CE2-A) of Comparative Examples 1-2 cannot initiate the ring-opening polymerization of L-lactide, and the polymerization reaction cannot be successfully completed.

[0274] Effect of Temperature on the Initiation of Ring-Opening Polymerization of L-Lactide

[0275] In order to study the effect of temperature on the ring-opening polymerization of L-lactide, modified poly (D-lactic acid) prepolymer was used to initiate the ring-opening polymerization of L-lactide at high and low temperatures.

[0276] The modified poly (D-lactic acid) prepolymer (No. CE1-A) of Comparative Example 1 was subjected to forced initiation of L-lactide ring-opening polymerization at a high temperature of 180° C. The DSC test results of the obtained polymer product are as follows: Figure 1 As shown (the legend is the curve of "high temperature initiation"). There are two melting peaks in the DSC curve, one is the melting point peak of PLLA or PDLA (168°C), and the other is the eutectic melting peak (236°C) after the stereocomplex of the two. It can be seen that at high temperature, the modified poly D-lactic acid prepolymer (No. CE1-A) of Comparative Example 1 is used to forcibly initiate the ring-opening polymerization of L-lactide, and L-lactide undergoes implosion, resulting in a large amount of blended PDLA and PLLA, rather than a block polymer of PDLA-PLLA, and the blended PDLA and PLLA form a composite stereocrystal.

[0277] The modified poly (D-lactic acid) prepolymer (No. E1-A) of Example 1 can initiate the ring-opening of L-lactide at low temperature, effectively control the reaction process, and smoothly prepare the PDLA / PLLA block polymer. The DSC test results of the self-nucleated modified poly (lactic acid) sample (No. E1-B) of Example 1 are as follows: Figure 1 As shown (the legend is the "low temperature initiation" curve). There is only one melting point peak (174°C) in this DSC curve. It can be seen that there is almost no blended PDLA and PLLA in the self-nucleating modified polylactic acid sample (No. E1-B) of Example 1, and it is basically a polymer of PDLA / PLLA block copolymer.

[0278] Anti-migration effect

[0279] Migration test: Referring to GB / T 5009.156-2016, the sample strips finally obtained in the embodiment and the comparative example (the strips are prepared according to GB / T 1843-2008, type A size, length 80±2 mm, width 10.0±0.2 mm, thickness 4.0±0.2 mm) are contacted with a 50% ethanol solution (which is obtained by mixing 250.0 ml of anhydrous ethanol with 250 ml of water) at 70°C for 2 hours, and measured by a balance. Referring to Regulation 6.1 of GB 31604.8-2021, the total migration amount is calculated by the following formula:

[0280]

[0281] Where:

[0282] X1—Total migration, in milligrams per square decimeter (mg / dm 2 );

[0283] m1—the mass of the immersion liquid residue used for sample determination, in milligrams (mg);

[0284] m2—residue mass of blank soaking solution, in milligrams (mg);

[0285] V—total volume of sample immersion solution obtained in migration test, in milliliters (mL);

[0286] V1-volume of immersion solution for determination, in milliliters (mL);

[0287] S—the area of ​​contact between the sample and the immersion liquid, in square decimeters (dm 2 ).

[0288] The total migration amounts of the samples of Examples 1-4 (No. E1-B, E2-B, E3-B, E4-B) and the samples of Comparative Examples 3-6 (No. CE3, CE4, CE5, CE6) are shown in Table 2. In Comparative Example 1-2, since the modified poly (D-lactic acid) prepolymer cannot initiate the ring-opening polymerization of L-lactide, the migration amount test is not performed.

[0289] Table 2

[0290]

[0291] According to Table 2, the total migration amount of the samples of Comparative Examples 5-6 (numbered CE5 and CE6) (obtained by physically blending the hydroxyamide functionalized additive with pure polylactic acid resin by screw extrusion) is high, all of which are greater than 10 mg / dm 2 The samples of Examples 1-4 and Comparative Examples 3-4 (No. E1-B, E2-B, E3-B, E4-B) (all obtained by embedding functionalized amide into the main chain of polylactic acid by chemical polymerization) have low total migration amount and excellent anti-migration effect.

[0292] Crystallization rate

[0293] Crystallization rate test: DSC is used to test the half-crystallization time of the sample at 110°C isothermal crystallization. The shorter the half-crystallization time, the faster the crystallization rate of the sample. When the temperature is lowered to the set isothermal crystallization temperature (i.e. 110°C) by program, the corresponding time is taken as t0-starting point (t0=0min), and the crystallization exothermic peak corresponds to time t 1 / 2 For samples with a fast crystallization rate, which completes exothermic crystallization during the cooling stage, the half-crystallization time is recorded as < 0.5 min for the convenience of expression.

[0294] In Comparative Example 1-2, since the modified poly (D-lactic acid) prepolymer cannot initiate the ring-opening polymerization of L-lactide, the DSC test was not performed.

[0295] In the samples of Comparative Examples 5-6 (No. CE5, CE6), the dispersion of the additives in the materials is not uniform, resulting in large deviations in the test data of random sampling, and it is impossible to count valid data.

[0296] Figure 2 The DSC curves of the samples of Examples 1 and 3 and Comparative Example 3 (No. E1-B, E3-B, CE3) are shown. Figure 3 The DSC curves of the samples (No. E2-B, E4-B, CE4) of Examples 2, 4 and Comparative Example 4 are shown. The half crystallization times of the Examples and Comparative Examples are shown in Table 3 below.

[0297] Table 3

[0298]

[0299] from Figure 2-3 From the DSC curves of the self-nucleating modified polylactic acid samples of Examples 1-4, it can be seen that no obvious crystallization exothermic peak appears after t0, which shows that the self-nucleating modified polylactic acid samples of Examples 1-4 have completed exothermic crystallization in the cooling stage (i.e., "② cooling stage" in Table 3), and the half-crystallization time is recorded as <0.5min. The samples of Comparative Examples 3-4 have crystallization exothermic peaks at 11.4min and 7.0min, respectively.

[0300] The crystallization rates of the self-nucleating modified polylactic acid samples of Examples 1-4 are very fast, and the half-crystallization times are all less than 0.5 min, which are much lower than the half-crystallization times of the samples of Comparative Examples 3-4.

[0301] The samples of Examples 1-4 and Comparative Examples 3-4 (numbered E1-B, E2-B, E3-B, E4-B, CE3, CE4) were further analyzed by polarizing microscope. The specific instruments and measurement methods used are as follows.

[0302] Equipment name: Metallographic microscope;

[0303] Device model: Axiolab 5;

[0304] Equipment manufacturer: ZEISS, Germany;

[0305] After preheating the temperature of the hot plate of the electric furnace to 190°C, take 10 mg of the sample and place it on the glass slide that has been kept at a constant temperature on the hot plate of the electric furnace. After the sample melts, add a cover glass and press it into a film. After keeping warm for two minutes, cool the hot plate to 110°C at a rate of 50°C / min. Subsequently, turn on the image acquisition function of the acquisition software corresponding to the camera, and place the sample (which is located between the glass slide and the cover glass) on the stage of the microscope. While observing the eyepiece of the microscope with your eyes, rotate the coarse and fine adjustment focusing mechanism of the microscope by hand to focus, and further adjust the fine adjustment knob to the preview state until a clear image can be seen. Further adjust the exposure, contrast, saturation and other functions of the image acquisition software so that the collected image is basically consistent with the image observed under the eyepiece. Manually time and observe the crystallization of the sample, and save the image at time intervals until the sample is completely crystallized. The images of each sample at different times are shown in Figure 4 Shown in.

[0306] Figure 4 In the figure, 0min indicates the image taken when the sample is just placed on the stage; 0.5min indicates the image taken 0.5min after the sample is placed on the stage; 5min indicates the image taken 5min after the sample is placed on the stage.

[0307] In polarizing microscope images, crystals appear as white spots, that is, the more white spots there are in a relative period of time, the faster the crystallization rate. Figure 4 It can be seen that at t = 0.5 min, a large amount of crystals already exist in the samples of Examples 1-4 (No. E1-B, E2-B, E3-B, E4-B), while almost no crystals exist in the samples of Comparative Examples 3-4 (No. CE3, CE4). At t = 5 min, a small amount of crystals can be observed in the samples of Comparative Examples 3-4 (No. CE3, CE4). Figure 4 It can be seen that the crystallization rates of the samples of Examples 1-4 are significantly higher than those of the samples of Comparative Examples 3-4 (No. CE3, CE4).

[0308] The above embodiments are only preferred embodiments of the present invention. For those skilled in the art, any obvious changes and improvements made without departing from the spirit of the present invention should be regarded as part of the present invention.

Claims

1. A self-nucleating modified polylactic acid having a structure of the following formula (I) or (II): A1-O-L1 formula (I A2-O-L2-O-A3 Formula (II) In formula (I), L1 is selected from the following structures: in, L 1a Selected from C 1-12 Straight hydrocarbon chain, L 1b Selected from C 10-20 Straight chain hydrocarbon group; L 1c Selected from C 10-20 Straight hydrocarbon chain, L 1d Selected from C 1-12 Straight hydrocarbon chain, L 1e Selected from C 10-20 Straight chain hydrocarbon group; A1 is wherein n is an integer selected from 300-800, and n' is an integer selected from 700-2500; In formula (II), L2 is selected from the following structures: in, L 2a Selected from C 1-12 Straight hydrocarbon chain, L 2b Selected from C 1-20 Straight hydrocarbon chain, C 3-20 branched hydrocarbon chains; L 2c Selected from C 1-20 Straight hydrocarbon chain, C 3-20 Branched hydrocarbon chain, L 2d Selected from C 1-12 Straight hydrocarbon chain, L 2e Selected from C 1-20 Straight hydrocarbon chain, C 3-20 branched hydrocarbon chains; A2 is And A3 is Or, A2 is And A3 is in, p is an integer selected from 150-400, p' is an integer selected from 350-1250, q is an integer selected from 150-400, q' is an integer selected from 350-1250, the ratio of p to q is 0.8-1.2, and the ratio of p' to q' is 0.8-1.

2.

2. The self-nucleating modified polylactic acid according to claim 1, wherein L 1a Selected from C 1-12 A straight alkane chain, preferably a C2 straight alkane chain; and / or L 1b Selected from C 10-20 Straight chain alkyl, preferably C 11-17 Straight chain alkyl, more preferably C 11 or C 17 Straight chain alkyl; and / or L 1c Selected from C 10-20 Straight alkane chains, and / or L 1d Selected from C 1-12 Straight alkane chain; and / or L 1e Selected from C 10-20 Straight chain alkyl; and / or L 2a Selected from C 1-12 A straight alkane chain, preferably a C2 straight alkane chain; and / or L 2b Selected from C 1-20 Straight alkane chain, C 3-20 Branched alkane chain, preferably C 17 Branched alkane chain, more preferably -(CH2) 10 CH(CH2CH2CH2CH2CH2CH3)-; and / or L 2c Selected from C 1-20 Straight alkane chain, C 3-20 Branched alkane chain, preferably C 17 Branched alkane chain, more preferably -(CH2) 10 CH(CH2CH2CH2CH2CH2CH3)-; and / or L 2d Selected from C 1-12 A straight alkane chain, preferably a C2 straight alkane chain; and / or L 2e Selected from C 1-20 Straight alkane chain, C 3-20 Branched alkane chain, preferably C 17 Branched alkane chain, more preferably -(CH2) 10 CH(CH2CH2CH2CH2CH2CH3)-.

3. The self-nucleating modified polylactic acid according to claim 1 or 2, wherein The ratio of p to q is 0.9-1.1, preferably 1; and / or The ratio of p' to q' is 0.9-1.1, preferably 1.

4. The self-nucleating modified polylactic acid according to any one of claims 1 to 3, wherein The self-nucleating modified polylactic acid has one of the following structures: In formula (I-1), n ​​is an integer selected from 300-800, and n' is an integer selected from 700-2500; In formula (I-2), n is an integer selected from 300-800, and n' is an integer selected from 700-2500; In formula (I-3), n is an integer selected from 300-800, and n' is an integer selected from 700-2500; In formula (I-4), n is an integer selected from 300-800, and n' is an integer selected from 700-2500; In formula (II-1), p is an integer selected from 150-400, p' is an integer selected from 350-1250, q is an integer selected from 150-400, and q' is an integer selected from 350-1250; In formula (II-2), p is an integer selected from 150-400, p' is an integer selected from 350-1250, q is an integer selected from 150-400, and q' is an integer selected from 350-1250; In formula (II-3), p is an integer selected from 150-400, p' is an integer selected from 350-1250, q is an integer selected from 150-400, and q' is an integer selected from 350-1250; In formula (II-4), p is an integer selected from 150-400, p' is an integer selected from 350-1250, q is an integer selected from 150-400, and q' is an integer selected from 350-1250.

5. A method for preparing the self-nucleating modified polylactic acid according to any one of claims 1 to 4, comprising the following steps: reacting an aliphatic amide containing a terminal hydroxyl group with a coordination catalyst to obtain an alcohol salt of the aliphatic amide; The alkoxide of the aliphatic amide is reacted with the molten first lactide, and the alkoxide of the aliphatic amide initiates the ring-opening polymerization of the first lactide to obtain a modified polylactic acid prepolymer; The modified polylactic acid prepolymer reacts with the molten second lactide, and the modified polylactic acid prepolymer initiates the ring-opening polymerization of the second lactide to obtain the self-nucleating modified polylactic acid; in, The aliphatic amide containing terminal hydroxyl groups has a structure of the following formula (III) or (IV): HO-L1 Formula (III) HO-L2-OH Formula (IV), The first lactide is L-lactide and the second lactide is D-lactide, or the first lactide is D-lactide and the second lactide is L-lactide; Preferably, The first lactide is D-lactide and the second lactide is L-lactide.

6. The method of claim 5, wherein: The number average molecular weight Mn of the modified polylactic acid prepolymer is 25000-45000Da; The melting point of the modified polylactic acid prepolymer is 145-155°C.

7. The method according to claim 5 or 6, wherein The structure of the coordination catalyst is RMR, in, M is selected from a divalent coordinating metal, preferably zinc, tin or magnesium; R is selected from organic monovalent acid radicals, preferably octanoate, isooctanoate, decanoate or acetate.

8. The method according to any one of claims 5 to 7, wherein The free acid of the first lactide is 10 mmol / kg or less; and / or The optical purity of the first lactide is ≥98.5%; and / or The free acid of the second lactide is 20 mmol / kg or less; and / or The optical purity of the second lactide is ≥98.5%.

9. The method according to any one of claims 5 to 8, wherein In the reaction of the aliphatic amide containing terminal hydroxyl groups and the coordination catalyst, the molar ratio of the aliphatic amide containing terminal hydroxyl groups to the coordination catalyst is 5:5 to 3:7; and / or The reaction temperature T1 of the reaction between the terminal hydroxyl group-containing aliphatic amide and the coordination catalyst is 140-150° C.; and / or The reaction time of the terminal hydroxyl group-containing aliphatic amide and the coordination catalyst is 20-40 minutes.

10. The method according to any one of claims 5 to 9, wherein In the reaction of the alcohol salt of aliphatic amide and the molten first lactide, the weight ratio of the alcohol salt of aliphatic amide to the first lactide is 0.005-0.

01.

11. The method according to any one of claims 5 to 10, wherein In the reaction of the modified polylactic acid prepolymer and the molten second lactide, the weight ratio of the modified polylactic acid prepolymer to the second lactide is 0.01-0.1; and / or The reaction temperature T2 of the modified polylactic acid prepolymer and the molten second lactide is 140-150°C.

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