CN1927911A - Preparation method of biodegradation polylactic acid based multicomponent block polymer - Google Patents

Abstract

The present invention belongs to the field of polymer material technology, and is especially preparation process of biodegradable polylactic acid based polynary block polymer. The preparation process includes the first polycondensation of lactic acid, lactic acid and small molecular dibasic alcohol, or lactic acid and small molecular dibasic carboxylic acid to obtain lactic acid prepolymer in certain molecular weight; and the subsequent adding ester oligomer and chain expander to react under N2 atmosphere at pressure below 60 Pa and temperature of 150-230 deg.c for 10-45 min to obtain the biodegradable resin with high molecular weight. The biodegradable resin has flexibility and heat resistance higher than that of lactic acid homopolymer, adjustable degradation speed, simple preparation process and wide application, and the preparation process is easy use in industrial production.

Description

Preparation method of fully biodegradable polylactic acid-based multi-block polymer

technical field

The invention belongs to the technical field of polymer materials, and in particular relates to a preparation method of fully biodegradable polylactic acid-based multi-block polymers.

Background technique

Due to its special properties such as good biodegradability, biocompatibility and absorbability, biodegradable polymer materials have developed rapidly in medicine, medicine, and the environment, especially polylactic acid polymers, the main source of lactic acid It is used in renewable resource crops, so it has become a hot spot in the field of materials science. At present, the main methods of preparing polylactic acid are ring-opening polymerization of lactide and direct polycondensation of lactic acid. The lactide ring-opening polymerization method is easy to obtain high molecular weight polylactic acid polymer materials, but the preparation of the cyclic intermediate lactide makes the synthesis route of the polymer lengthy and the cost is high, which restricts the biodegradation of polylactic acid materials. The main reason for promoting the app. Therefore, in recent years, the synthesis of polylactic acid polymer materials by the direct polycondensation method of lactic acid has attracted special attention. molecular weight polymers. Chain extension reaction is one of the important methods to increase the molecular weight in the field of polymer synthesis. It has the advantages of quickness, high efficiency, relatively simple process conditions, and easy industrial continuous production. Therefore, the chain extension synthesis of polylactic acid-based biodegradable materials is of great significance.

As early as 1982, Gogolewski et al reported the use of dihydroxy-terminated polylactide with diphenylmethane diisocyanate (MDI), 2,4-toluene diisocyanate (TDI), 4,4'-dicyclohexylmethane Chain extenders such as isocyanate (DES) and hexamethylene diisocyanate (HDI) are chain extended to obtain linear polylactic acid degradation materials, which are used to blend with polylactide polymers to prepare porous and water-permeable biomedical materials ( Makromol. Chem., Rapid Commun., 1982, 3:839-845.). Storey et al. reported that trimethylolpropane (TMP) was used as an initiator to make D, L-lactide ring-opening homopolymerization, or to make D, L-lactide and trimethylene carbonate ring-opening copolymerization to obtain three Hydroxyl-terminated prepolymer (polylactide triol), after chain extension with TDI, can synthesize amorphous biodegradable network material (Polymer, 1994, 35(4): 830-838.). Domestically, by controlling the amount of polyethylene glycol (PEG), Wu Zhong et al. opened the ring of lactide to make PLA-PEG block prepolymer, and then cross-linked with TMP after MDI chain extension to synthesize a series of polyurethane elastomers. The elastic material for the degradable urethral stent that meets the requirements can be produced (Journal of Xinyang Normal University (Natural Science Edition), 1999, 12(2): 166-169.). Song Moudao and others used PEG-PLA prepolymer to synthesize cross-linked elastomer by reacting with TDI and TMP. Animal experiments showed that the processed elastomer tube could meet the requirements of urethral support tube (Acta Polymer Sinica, 1998, (4) : 393-398.). Zhang Yanhong et al. reported the chain extension reaction of low molecular weight poly D, L-lactide, polycaprolactone oligomer, TDI, etc., which opened the ring of ethylene glycol, and synthesized an elastomer with certain strength and toughness. The performance can meet the requirements of clinical jaw fixation, avoiding the defects of direct use of PLLA in orthopedic fixation materials due to slow degradation in vivo and causing adverse reactions (Journal of Heilongjiang University (Natural Science Edition), 2000, 17(3): 77-79 .). In the above relevant studies, in the synthesis steps of lactic acid prepolymers, lactide is used as a raw material for ring-opening copolymerization to obtain various prepolymers, which is different from the method for preparing prepolymers by direct polycondensation of lactic acid used in the present invention; and the above-mentioned None of the studies involved the chain extension reaction between the lactic acid prepolymer and the prepolymerization product of the polycondensation reaction of diol and dicarboxylic acid or dicarboxylic anhydride, and the new properties of the resulting new polylactic acid-based multi-block polymer material.

In 1995, Woo et al. first reported the chain extension research of lactic acid homopolymer as a prepolymer. The PLLA with a _MW of 11,000 was obtained by melt polymerization, and HDI was used as a chain extender to extend the chain at 160 ° C under a nitrogen atmosphere for 10 Minutes, the M _W of the polylactic acid derivative reaches 76,000, and the molecular weight increases with the increase of the molar ratio of -NCO/-OH (Polym.Bull., 1995, 35(4): 415-421.). Domestically, Zhong Wei et al. reported that PLLA produced by melt polymerization was extended by HDI for 20 minutes, and the polymer M _W increased from 10,100 to 72,000 (Journal of Fudan University (Natural Science Edition), 1999, 38(6): 705-708 .) with MDI chain extension, 175 ° C reaction for 40 minutes, M _W increased from 09,800 to 57,000, to obtain a biodegradable material with good heat resistance (J.Appl.Polym.Sci., 1999, 74: 2546- 2551.). Feng Ruijiang et al. also reported the chain extension reaction of direct polymerized polylactic acid and the degradation performance of chain extended products. They used polylactic acid with the highest molecular weight in melt polymerization and solution polymerization as raw materials respectively, and solution polymerization polylactic acid with a M _W of 26,000 was used for chain extension. After that, the molecular weight increased to 160,000. Although the lactic acid prepolymer was prepared by the direct polycondensation method in the above research, it did not involve the chain extension reaction between the lactic acid prepolymer and the prepolymerization product of the polycondensation reaction of dihydric alcohol and dicarboxylic acid or dicarboxylic anhydride, nor expected the resulting New properties of novel polylactic acid-based multi-block polymer materials.

Hiltunen et al. conducted in-depth research on the lactic acid melt copolymerization/diisocyanate chain extension method from the synthesis of prepolymers to the degradation of polymers after chain extension. The hydroxyl-terminated prepolymer of lactic acid and 1,4-butanediol is directly melt-copolymerized as a raw material, and HDI is used to extend the chain to obtain thermoplastic Poly(ester-urethane) (PEU), when the -OH/-NCO molar ratio is 1 , when reacting for 100 minutes, the M _W of linear PEU is as high as 390,000 (J.Appl.Polym.Sci., 1997, 63:1091-1100). Feng Ruijiang and others also studied the lactic acid melt copolymerization/diisocyanate chain extension method. Through the direct condensation of lactic acid and glycerin, a series of prepolymers with different lactic acid/glycerol (molar ratios) were synthesized. Network materials (Petrochemical Industry, 2001, 30(7): 520-523.). The above research adopts the melt polycondensation method to prepare a hydroxyl-terminated lactic acid copolymer prepolymer, and then undergoes a chain extension reaction of a diisocyanate chain extender to obtain a variety of polymer materials. The end group modification of the polymer prepolymer is different from the use of a chain extender for the chain extension reaction between the prepolymerization product of the dihydric alcohol and dicarboxylic acid or dicarboxylic anhydride condensation reaction. The research does not anticipate the resulting new Materials and new properties.

Bis(2-oxazoline) is a highly selective chain extender, which only acts on -COOH and is inert to -OH. Tuo Minen et al. used bis(2- _oxazoline ) chain extension to synthesize the thermoplastic amorphous polymer material poly (ester-amide) (PEA) (Macromolecules, 2000, 33(10): 3530-3535.). Kylmae et al. reported the joint effect of diisocyanate and bis(2-oxazoline) reactive chain extenders in lactic acid polymerization. They found that adding bis(2-oxazoline) after melt polymerization of lactic acid, and then adding HDI after a certain period of time, bis(2-oxazoline) not only effectively couples carboxyl groups, but also significantly reduces the acid value, making diisocyanate The coupling to hydroxyl can be completed at a lower temperature and in a shorter time; in addition, two (2-oxazoline) chain extensions can improve the thermal stability of the product (Polymer, 2001, 42 (8): 3333-3343 .). Recently, they also reported that high-molecular-weight polylactic acid derivatives can be obtained by adding bis(2-oxazoline) and HDI simultaneously or sequentially, but the products obtained by adding HDI before bis(2-oxazoline) are more complex than those obtained by adding the two kinds at the same time. The case of chain extenders produces more branched products (Polymer, 2002, 43(1):3-10.). The above research involves the influence of two different types of chain extenders on the chain extension reaction, as well as the synergistic effect, but its research is limited to the chain extension reaction of lactic acid copolymer prepolymers, and does not involve diols and dicarboxylic acids or dicarboxylic anhydrides. The introduction of polycondensation reaction prepolymerization products as chain extension units, as well as the formation of new materials and new properties.

Contents of the invention

The purpose of the present invention is to provide a method for preparing a fully biodegradable polylactic acid-based multi-block polymer with simple preparation method, easy industrial production, and better flexibility and heat resistance.

The preparation method of the biodegradable polylactic acid-based multi-block polymer proposed by the present invention firstly performs a one-step polycondensation reaction on the refined and purified lactic acid under the action of a catalyst to obtain a prepolymer with a certain molecular weight, and then adds a linear polyester oligomer Compound and chain extender, filled with N ₂ gas, vacuumized, reacted at 150-230°C for 10-45 minutes, discharged under N ₂ gas protection, and finally obtained the desired product. The specific steps are:

(1) Add any one of lactic acid, lactic acid and small molecule dibasic alcohol or lactic acid and small molecule dicarboxylic acid into the reactor, vacuumize, and carry out polycondensation reaction under the action of a catalyst, and control the pressure of the reactor to be 1- 2KPa, raise the temperature of the reactor to 100-120°C, react for 3-5 hours, then reduce the pressure of the reactor to below 60Pa, raise the temperature of the reactor to 140-180°C, and continue the reaction for 12-15 hours to obtain M _W =2×10 ⁴ -5×10 ⁴ lactic acid prepolymer; where,

The molar ratio of small molecule glycol to lactic acid is 1:30-1:50;

The molar ratio of small molecule dicarboxylic acid to lactic acid is 1:30-1:50;

(2) Add the lactic acid prepolymer and linear polyester oligomer obtained in step (1) respectively into the reactor, vacuumize, and carry out the polymerization reaction under the action of the chain extender, and under the _N2 atmosphere, the control system The pressure is below 60Pa, the temperature is 150-230°C, and the reaction is 10-45 minutes to obtain the desired product. The weight average molecular weight M _W of the product is 1×10 ⁵ -3×10 ⁵ ; where: The molar ratio of the compound to the lactic acid prepolymer is 1:9-9:1.

In the present invention, the lactic acid is one or more of commonly used L-lactic acid (LLA), D-lactic acid (DLA), and D,L-lactic acid (DLLA).

In the present invention, the small molecular dihydric alcohol has the following structure:

(I)

In the formula, n is an integer of 2-6.

In the present invention, the small molecule dicarboxylic acid has the following structure:

In the formula, n is an integer of 1-4.

In the present invention, the linear polyester oligomer is a polycondensation reaction product of dihydric alcohol and dicarboxylic acid or dicarboxylic anhydride, and has the following structure (III) or (IV):

(III) In the formula, m and q are integers of 2-10; (IV) In the formula, m is an integer of 2-10.

In the present invention, the catalyst is a polycondensation reaction catalyst, such as: stannous octoate, stannous chloride, tetrabutyl titanate, antimony trioxide, germanium chloride or tin, antimony or germanium element as the coordination center One or more of the chelates, etc., the catalyst addition is 0.05-0.1wt% of the mass of lactic acid.

In the present invention, the chain extender is any one of a diisocyanate compound or a mixture of a diisocyanate compound and bis(2-oxazoline), and has the following structure (V) or (VI):

(V) In the formula, R is one of the following groups:

In the present invention, the added amount of the chain extender is: the molar ratio of the chain extender to the sum of the lactic acid prepolymer and the linear polyester oligomer is 1:1-1.5:1.

In the present invention, in order to make the polycondensation reaction more sufficient and obtain a higher molecular weight of the prepolymer, the lactic acid is refined and purified by vacuum distillation before the polycondensation reaction.

The advantages of the present invention are:

(1) Polylactic acid materials with excellent biodegradability and good mechanical processing properties are used for chain extension reactions with linear polyesters with different structural properties to prepare high-molecular-weight biodegradable copolymers with good toughness and heat resistance. thing;

(2) The introduction of linear polyesters with different structures and properties can effectively improve the defects of single polylactic acid materials, and can control the degradation rate of copolymers;

(3) The preparation process and conditions are simple, feasible, and easy for industrialized integrated production.

The biodegradable polylactic acid-based multi-block polymer prepared by the invention can be widely used in the preparation of disposable medical devices, disposable tableware, shopping bags, packaging materials, adhesives, elastomers, sheets, films and the like. Because the raw materials are all non-toxic materials, it is especially suitable as the outer packaging material of food. The fully degradable copolymerized material of the present invention can be completely degraded in the natural environment after being used and discarded, and the degradation speed is faster under composting conditions, without producing any toxic substances, and is an environmentally friendly product.

Detailed ways

The present invention is further illustrated below by way of examples.

Example 1

(1) Put 800g of L-lactic acid purified by vacuum distillation into a vacuum reactor, add 0.8g of stannous chloride, vacuumize, control the pressure of the reactor at 1.0kPa, raise the temperature of the reactor to 100°C, and react for 5 hours ;Then the temperature of the reactor is raised to 140°C, the pressure is lowered to below 60Pa, and the reaction is continued for 15 hours to obtain a lactic acid prepolymer with a weight average molecular weight M _W =2×10 ⁴ -5×10 ⁴ ;

(2) the linear polyester oligomer polybutylene adipate (PBA), the lactic acid prepolymer (PLA) that step (1) obtains, the chain extender hexamethylene diisocyanate (HDI) respectively Put it into the reaction kettle, the molar ratio of PBA to PLA is 1:9, the molar ratio of the sum of PBA and PLA to HDI is 1:1, fill with _N2 gas, vacuumize, and after repeated operations several times, the system pressure is reduced to 60Pa Then, react at 150°C for 10 minutes, discharge under N ₂ gas protection, and obtain the desired product with a weight-average molecular weight M _W of 1×10 ⁵ -3×10 ⁵ .

Example 2

(1) Add 800 g of D, L-lactic acid purified by vacuum distillation into a vacuum reactor, add 0.4 g of stannous octoate, vacuumize, control the pressure of the reactor at 1.5 kPa, raise the temperature of the reactor to 110 ° C, and react 4 hours; then the temperature of the reactor rose to 160°C, the pressure dropped below 60Pa, and the reaction was continued for 14 hours to obtain a lactic acid prepolymer with a weight average molecular weight M _W =2×10 ⁴ -5×10 ⁴ ;

(2) Lactic acid prepolymer (PLA), linear polyester oligomer polybutylene succinate (PBS), chain extender diphenylmethane diisocyanate (MDI) obtained in step (1) PBS and PLA molar ratio is 1:1, PBS, PLA molar sum and MDI molar ratio is 1:1.3, fill with _N2 gas, vacuumize, after repeated operation several times, make the system pressure drop to Below 60Pa, then react at 180°C for 20 minutes, and discharge under N ₂ gas protection to obtain the desired product, whose weight average molecular weight M _W is 1×10 ⁵ -3×10 ⁵ .

Example 3

(1) 400g of L-lactic acid purified by vacuum distillation, D, 400g of L-lactic acid are added to a vacuum reactor, 0.8g of germanium chloride is added, vacuumized, the pressure of the reactor is controlled at 2.0KPa, and the temperature of the reactor is raised to 120°C, react for 3 hours; the temperature of the reactor is raised to 180°C, the pressure drops below 60Pa, and the reaction is continued for 12 hours to obtain a lactic acid prepolymer with a weight average molecular weight _Mw = 2×10 ⁴ -5×10 ⁴ ;

(2) Lactic acid prepolymer (PLA), linear polyester oligomer polyhexamethylene adipate (PHA) obtained in step (1), chain extender 4,4'-dicyclohexylmethane Add isocyanate (DES) into the reaction kettle respectively, the molar ratio of PHA to PLA is 9:1, the molar ratio of the sum of PHA and PLA to DES is 1:1.5, fill with _N2 gas, vacuumize, and after repeated operations several times, make The pressure of the system was lowered to below 60Pa, and then reacted at 200°C for 30 minutes, and discharged under the protection of N ₂ gas to obtain the desired product with a weight-average molecular weight M _W of 1×10 ⁵ -3×10 ⁵ .

Example 4

(1) 600g of L-lactic acid purified by vacuum distillation, D, and 200g of L-lactic acid are added to the vacuum reactor, 0.4g of antimony trioxide is added, vacuumized, the pressure of the reactor is controlled at 1.0KPa, and the temperature of the reactor is raised to 120°C, react for 5 hours; then raise the temperature of the reactor to 160°C, lower the pressure to below 60Pa, and continue to react for 15 hours to obtain a lactic acid prepolymer with a weight-average molecular weight M _W =2×10 ⁴ -5×10 ⁴ ;

(2) Lactic acid prepolymer (PLA), linear polyester oligomer polybutylene adipate (PBA), chain extender diphenylmethane diisocyanate (MDI) obtained in step (1) and bis(2-oxazoline) (BOX) were added to the reactor respectively, the molar ratio of PBA to PLA was 3:7, the sum of the molar weights of PBA and PLA to the sum of the molar weights of MDI and BOX was 1:1.2, and the MDI The molar ratio to BOX is 1:1, filled with N ₂ gas, vacuumized, and after repeated operations several times, the system pressure was reduced to below 60Pa, and then reacted at 180°C for 45 minutes, and discharged under the protection of N ₂ gas to obtain The desired product has a weight average molecular weight M _W of 1×10 ⁵ -3×10 ⁵ .

Example 5

(1) 500g of L-lactic acid purified by vacuum distillation, D, and 300g of L-lactic acid are added to a vacuum reactor, 0.8g of tetrabutyl titanate is added, vacuumized, and the pressure of the reactor is controlled at 1.0KPa. Raise to 120°C, react for 5 hours; raise the temperature of the reactor to 160°C, drop the pressure below 60Pa, continue to react for 15 hours, and obtain a lactic acid prepolymer with a weight average molecular weight _Mw = 2×10 ⁴ -5×10 ⁴ ;

(2) Lactic acid prepolymer (PLA), linear polyester oligomer polybutylene terephthalate (PBT), chain extender diphenylmethane diisocyanate (MDI) obtained in step (1) ) and bis(2-oxazoline) (BOX) were added to the reactor respectively, the molar ratio of PBT and PLA was 1:4, the sum of PBT and PLA molar weights and the sum ratio of MDI and BOX molar weights were 1:1.2, The molar ratio of MDI to BOX is 1:1, fill with _N2 gas, vacuumize, and after repeated operations several times, the system pressure drops below 60Pa, then react at 230°C for 40 minutes, and discharge under the protection of _N2 gas, that is The desired product is obtained, and its weight-average molecular weight M _W is 1×10 ⁵ -3×10 ⁵ .

Example 6

(1) 900g of L-lactic acid and 0.33mol ethylene glycol will be added to the vacuum reactor by vacuum distillation, add 0.9g stannous chloride, vacuumize, control the pressure of the reactor at 1.0kPa, and the temperature of the reactor will be raised to 100°C, react for 5 hours; the temperature of the reactor is raised to 140°C, the pressure drops below 60Pa, and the reaction is continued for 15 hours to obtain a lactic acid prepolymer with a weight average molecular weight _Mw = 2×10 ⁴ -5×10 ⁴ ;

(2) Lactic acid prepolymer (PLA), linear polyester oligomer polybutylene adipate (PBA), chain extender hexamethylene diisocyanate (HDI) obtained in step (1) Add to the reaction kettle respectively, the molar ratio of PBA and PLA is 1:9, the molar ratio of the sum of PBA and PLA to HDI is 1:1, fill with _N2 gas, vacuumize, and after repeated operations several times, the system pressure drops to Below 60Pa, then react at 150°C for 10 minutes, and discharge under N ₂ gas protection to obtain the desired product, whose weight-average molecular weight M _W is 1×10 ⁵ -3×10 ⁵ .

Example 7

(1) Will adopt the D of vacuum distillation method purification, L-lactic acid 900g and 0.25mol 1,4-butanediol are added vacuum reactor, add 0.45g stannous octoate, vacuumize, control reactor pressure at 1.5kPa, will The temperature of the reactor was raised to 110°C, and the reaction was carried out for 4 hours; the temperature of the reactor was raised to 160°C, the pressure was lowered to below ^60Pa , and the reaction was continued _for ¹⁴ hours to obtain lactic acid pre- Polymer;

(2) Lactic acid prepolymer (PLA), linear polyester oligomer polybutylene succinate (PBS), chain extender diphenylmethane diisocyanate (MDI) obtained in step (1) PBS and PLA molar ratio is 1:1, PBS, PLA molar sum and MDI molar ratio is 1:1.3, fill with _N2 gas, vacuumize, after repeated operation several times, make the system pressure drop to Below 60Pa, then react at 180°C for 20 minutes, and discharge under N ₂ gas protection to obtain the desired product, whose weight-average molecular weight M _W is 1×10 ⁵ -3×10 ⁵ .

Example 8

(1) Put 500g of L-lactic acid purified by vacuum distillation, 400g of D, L-lactic acid and 0.2mol 1,6-hexanediol into a vacuum reactor, add 0.9g of germanium chloride, vacuumize, and control the pressure of the reactor At 2.0kPa, raise the temperature of the reactor to 120°C, react for 3 hours; raise the temperature of the reactor to 180°C, lower the pressure to below 60Pa, continue the reaction for 12 hours, and obtain the weight average molecular weight M _W =2×10 ⁴ -5× 10 ⁴ lactic acid prepolymers;

(2) Lactic acid prepolymer (PLA), linear polyester oligomer polyhexamethylene adipate (PHA) obtained in step (1), chain extender 4,4'-dicyclohexylmethane Add isocyanate (DES) into the reaction kettle respectively, the molar ratio of PHA to PLA is 9:1, the molar ratio of the sum of PHA and PLA to DES is 1:1.5, fill with _N2 gas, vacuumize, and after repeated operations several times, make The pressure of the system was lowered to below 60Pa, and then reacted at 200°C for 30 minutes, and discharged under the protection of N ₂ gas to obtain the desired product, whose weight-average molecular weight M _W was 1×10 ⁵ -3×10 ⁵ .

Example 9

(1) 900g of L-lactic acid and 0.33mol malonic acid to be purified by vacuum distillation are added to a vacuum reactor, 0.9g of tin protochloride is added, vacuumized, the pressure of the reactor is controlled at 1.0kPa, and the temperature of the reactor is raised to 100°C, react for 5 hours; the temperature of the reactor is raised to 140°C, the pressure drops below 60Pa, and the reaction is continued for 15 hours to obtain a lactic acid prepolymer with a weight average molecular weight _Mw = 2×10 ⁴ -5×10 ⁴ ;

(2) Lactic acid prepolymer (PLA), linear polyester oligomer polybutylene adipate (PBA), chain extender diphenylmethane diisocyanate (MDI) obtained in step (1) and bis(2-oxazoline) (BOX) were added to the reactor respectively, the molar ratio of PBA to PLA was 1:9, the sum of the molar weights of PBA and PLA to the sum of the molar weights of MDI and BOX was 1:1.1, and the molar ratio of MDI The molar ratio to BOX is 1:1, fill with N ₂ gas, vacuumize, and after repeated operations several times, the system pressure drops below 60Pa, then react at 150°C for 10 minutes, and discharge the material under the protection of N ₂ gas to obtain The desired product has a weight average molecular weight M _W of 1×10 ⁵ -3×10 ⁵ .

Example 10

(1) Will adopt the D of vacuum distillation method purification, L-lactic acid 900g and 0.25mol succinic acid are added vacuum reactor, add 0.45g stannous octoate, vacuumize, control reactor pressure at 1.5kPa, the temperature of reactor is raised To 110°C, react for 4 hours; the temperature of the reactor is raised to 160°C, the pressure drops below 60Pa, and the reaction is continued for 14 hours to obtain a lactic acid prepolymer with a weight average molecular weight _Mw = 2×10 ⁴ -5×10 ⁴ ;

(2) Lactic acid prepolymer (PLA), linear polyester oligomer polybutylene succinate (PBS), chain extender hexamethylene diisocyanate (HDI) obtained in step (1) and bis(2-oxazoline) (BOX) were added to the reactor respectively, the molar ratio of PBS and PLA was 1:1, the sum of the molar weights of PBS and PLA and the sum of the molar weights of HDI and BOX were 1:1.2, and the ratio of HDI The molar ratio to BOX is 1:1, fill with _N2 gas, vacuumize, and repeat the operation several times until the system pressure drops below 60Pa, then react at 180°C for 20 minutes, and discharge the material under the protection of N2 gas to obtain the obtained The desired product has a weight average molecular weight M _W of 1×10 ⁵ -3×10 ⁵ .

Example 11

(1) 500g of L-lactic acid purified by vacuum distillation, D, 400g of L-lactic acid and 0.2mol adipic acid are added to a vacuum reactor, 0.9g of germanium chloride is added, vacuumized, and the pressure of the reactor is controlled at 2.0kPa, Raise the temperature of the reactor to 120°C, and react for 3 hours; raise the temperature of the reactor to 180°C, lower the pressure to below 60Pa, and continue the reaction for 12 hours to obtain lactic acid with a weight average molecular weight M _W =2×10 ⁴ -5×10 ⁴ Prepolymer;

(2) Lactic acid prepolymer (PLA), linear polyester oligomer polyhexamethylene adipate (PHA) obtained in step (1), chain extender 4,4'-dicyclohexylmethane Add isocyanate (DES) and bis(2-oxazoline) (BOX) into the reactor respectively, the molar ratio of PHA to PLA is 9:1, and the ratio of the sum of the moles of PHA and PLA to the sum of the moles of DES and BOX is 1 : 1.2, the molar ratio of DES to BOX is 1: 1, fill with _N2 gas, vacuumize, and after repeated operations several times, the system pressure is reduced to below 60Pa, then react at 200°C for 30 minutes, and discharge under the protection of _N2 gas The desired product is obtained, and its weight-average molecular weight M _W is 1×10 ⁵ -3×10 ⁵ .

Claims (8)

1. A preparation method for fully biodegradable polylactic acid-based multi-block polymers, characterized in that: (1) Add any one of lactic acid, lactic acid and small molecule dibasic alcohol or lactic acid and small molecule dicarboxylic acid into the reactor, vacuumize, and carry out polycondensation reaction under the action of a catalyst, and control the pressure of the reactor to be 1- 2KPa, raise the temperature of the reactor to 100-120°C, react for 3-5 hours, then lower the pressure of the reactor to below 60Pa, raise the temperature of the reactor to 140-180°C, and continue the reaction for 12-15 hours to obtain _Mw =2×10 ⁴ -5×10 ⁴ lactic acid prepolymer; where, The molar ratio of small molecule glycol to lactic acid is 1:30-1:50; The molar ratio of small molecule dicarboxylic acid to lactic acid is 1:30-1:50; (2) Add the lactic acid prepolymer and linear polyester oligomer obtained in step (1) respectively into the reactor, vacuumize, and carry out the polymerization reaction under the action of the chain extender, and under the _N2 atmosphere, the control system The pressure is below 60Pa, the temperature is 150-230°C, and the reaction is for 10-45 minutes to obtain the desired product. The weight-average molecular weight _Mw of the product is 1×10 ⁵ -3×10 ⁵ ; The molar ratio of the compound to the lactic acid prepolymer is 1:9-9:1. 2. The method for preparing biodegradable polylactic acid-based multi-block polymers according to claim 1, wherein the small molecular diol has the following structure: In the formula, n is an integer of 2-6. 3. The method for preparing biodegradable polylactic acid-based multi-block polymers according to claim 1, wherein the small molecule dicarboxylic acid has the following structure: In the formula, n is an integer of 1-4. 4. The method for preparing biodegradable polylactic acid-based multi-block polymers according to claim 1, characterized in that the linear polyester oligomer is polycondensation reaction of dihydric alcohol and dicarboxylic acid or dicarboxylic anhydride Product, has following structure (III) or (IV):

(III) In the formula, m and q are integers of 2-10; (IV) In the formula, m is an integer of 2-10. 5. The preparation method of biodegradable polylactic acid-based multi-block polymer according to claim 1 or 2, characterized in that the catalyst is stannous octoate, stannous chloride, tetrabutyl titanate, trioxide One or more of diantimony, germanium chloride or a chelate formed with tin, antimony or germanium as a coordination center, the amount of catalyst added is 0.05-0.1 wt% of the mass of lactic acid. 6. The method for preparing biodegradable polylactic acid-based multi-block polymers according to claim 1, wherein the chain extender is a diisocyanate compound or an isocyanate compound and bis(2-oxazoline) One of the mixtures, the chain extender has the following structure (V) or (VI): Wherein, R in formula (V) is any one of the following groups:

7. The method for preparing biodegradable polylactic acid-based multi-block polymers according to claim 1, characterized in that the amount of chain extender added is: chain extender and lactic acid prepolymer and linear polyester oligomerization The molar ratio of the sum of the compounds is 1:1-1.5:1. 8. The method for preparing biodegradable polylactic acid-based multi-block polymers according to claim 1, characterized in that the lactic acid is refined and purified by vacuum distillation before the polycondensation reaction.