CN105111418A - Method for preparing sterically regular polylactic acid on mild conditions - Google Patents

Abstract

The invention relates to a preparation method of stereoregular polylactic acid. The steps are as follows: adding a composite catalyst and racemic lactide into a reaction vessel, adding an appropriate amount of solvent for dissolution, and reacting the obtained reaction solution at 0-25°C for 20min-4 Hours, after the reaction was completed, methanol solution of hydrochloric acid was added to terminate the reaction, and the resulting product was washed and precipitated with methanol to obtain stereoregular polylactic acid. The present invention catalyzes the ring-opening polymerization of racemic lactide under relatively mild conditions, and the monomer conversion rate is greater than 90%; the polylactic acid obtained according to the preparation method of the present invention has a stereoregular structure and isotactic structure The content is greater than 70%.

Description

A kind of preparation method of stereoregular polylactic acid under mild condition

technical field

The invention relates to the technical field of macromolecules, in particular to a method for preparing stereoregular polylactic acid through racemic lactide polymerization.

Background technique

Polylactic acid is a polymer with good biodegradability. The raw material comes from biomass resources such as corn. It is energy-saving and environmentally friendly. It can replace polyethylene and polyvinyl chloride in agricultural films and packaging materials to solve the problem of "white pollution". It can also be used in biomedicine, such as absorbable surgical sutures, degradable implant materials and support materials in vivo, drug slow-release carriers, etc., which has aroused widespread interest. There are chiral carbons in the structural units of polylactic acid, and the arrangement of chiral carbons will generate various stereoisomerisms, including amorphous, isotactic, heteroisomeric, syndiotactic, etc. The difference in stereostructure will directly affect its performance. Polylactic acid with amorphous structure has a low glass transition temperature of 50-60°C, poor mechanical properties, and is easy to degrade. Stereoregular polylactic acid (poly L-lactide or poly D-lactide) will form a crystalline structure, and the crystallization temperature High (greater than 170°C), good mechanical properties, long degradation cycle. Moreover, when poly-L-lactide and poly-D-lactide form a stereo-complex, the crystallization temperature is higher, which can reach 220°C. It has been reported in the literature that various Schiff base alkyl/alkoxy metal catalysts can catalyze the ring-opening polymerization of racemic lactide to prepare polylactic acid with high stereoregularity, but the general reaction temperature is high (greater than 70 ° C), and the reaction time Long (several hours), CN104211929A has reported that a kind of organozinc catalyst can catalyze the ring-opening polymerization of racemic lactide to prepare polylactic acid, and this catalyst has the characteristics of higher isotropic selectivity and higher activity at room temperature, but The preparation of the catalyst is cumbersome, and the requirements for the polymerization conditions are also very strict, requiring anhydrous and oxygen-free.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for preparing stereoregular polylactic acid by using racemic lactide under mild conditions in view of the above-mentioned deficiencies in the prior art. The obtained stereoregular polylactic acid is identical The stereo content exceeds 70%.

In order to solve the problems of the technologies described above, the technical solution provided by the invention is:

A method for preparing stereoregular polylactic acid under mild conditions is provided, the steps of which are as follows: add a composite catalyst and racemic lactide into a reaction vessel, add a solvent to dissolve, and react the obtained reaction solution at 0-25°C for 20min-4 Hours, add methanol hydrochloride to terminate the reaction after the reaction is over, and the resulting product is washed and precipitated with methanol to obtain stereoregular polylactic acid;

The composite catalyst is composed of a main catalyst and a co-catalyst, the molar ratio of the main catalyst and the co-catalyst is 1:0.5-2, wherein the main catalyst is metal salen M(III)-salen (M=Cr, Co) or metal porphyrin M (III)-porphyrin (M = Al, Cr, Co), the cocatalyst is bis-(triphenylphosphoryl) ammonium chloride (PPNCl), dimethylaminopyridine (DMAP), 2,6- One of lutidine;

The structural formula of the metal salen M(III)-salen (M=Cr, Co) is:

M=Cr or Co; R ₁ =oC ₆ H ₄ , 1,2-cyclohexenyl, -CH ₂ CH ₂ - or -CH(CH ₃ )CH ₂ -; R ₂ and R ₃ are independently selected from Hydrogen, chlorine, bromine, chlorine-substituted or bromine-substituted aliphatic groups; X is -Cl, -Br, CCl ₃ COO-, CF ₃ COO-, 2,4-dinitrophenoloxy, 3,5- One of dinitrophenoxy and 2,4,6-trinitrophenoxy;

The structural formula of the metalloporphyrin M(III)-porphyrin (M=Al, Cr, Co) is:

M=Cr or Co or Al, R ₂ , R ₃ , R ₄ are independently selected from hydrogen, fluorine, chlorine, bromine, chlorine-substituted or bromine-substituted aliphatic groups; X is -Cl, -OCH ₂ CH ₃ , -OCH(CH ₃ ) ₂ , -Br, CCl ₃ COO-, CF ₃ COO-, 2,4-dinitrophenoxy, 3,5-dinitrophenoxy, 2,4,6- One of the trinitrophenoloxy groups;

The solvent is an epoxy compound or a mixed solvent containing an epoxy compound, and the mixed solvent containing an epoxy compound is a mixture of an epoxy compound and tetrahydrofuran (THF), or a mixture of an epoxy compound and methylene chloride, or The mixture of oxygen compound and toluene, or the mixture of epoxy compound and dioxane, in the mixed solvent containing epoxy compound, the volume ratio of epoxy compound to the mixed solvent is ≥ 10%.

Preferably, the molar ratio of the main catalyst and the co-catalyst is 1:1.

Preferably, the cocatalyst is dimethylaminopyridine (PPNCl).

According to the above scheme, the molar ratio of the main catalyst to racemic lactide is 1:100-500.

According to the above scheme, the epoxy compound is one of propylene oxide, ethylene oxide, and cyclohexane oxide.

According to the above scheme, the mass volume concentration of the racemic lactide in the epoxy compound or the mixed solvent containing the epoxy compound is 0.01-0.1 g/mL.

According to the above scheme, the conversion rate of said racemic lactide is ≥90%.

The present invention also provides the stereoregular polylactic acid prepared according to the above method, the number average molecular weight of the stereoregular polylactic acid is 2500-10000, the molecular weight distribution is 1.1-1.5, and the isotactic content in the polylactic acid is 70-85 %.

The synthesis process route of the metal salen M(III)-salen (M=Co, Cr) of the present invention is as follows:

I+MY ₂ +O ₂ →M(III)-salen-Y

Its preparation method is:

Preparation of metal salen M(III)-salen (M=Cr, Co): Dissolve substituted salicylaldehyde and diamine monomer in ethanol (molar concentration of substituted salicylaldehyde is 0.01-0.03M, replace salicylaldehyde The molar ratio to the diamine monomer is 2:1), adding 2-3 drops of formic acid, reacting at room temperature or reflux for 24 hours, settling and filtering to obtain a precipitate, washing the precipitate with water and ethanol in turn, and vacuum drying to obtain the Saren ligand, and then Dissolve the Salem ligand in dichloromethane, add the metal salt cobaltous acetate or chromous chloride (the molar concentration of the Salen ligand is 0.05-0.1M, and the molar ratio of the Salen ligand to the metal salt is 1:1.5 ), first react at room temperature under nitrogen atmosphere for 24h, add halogenated metal salt or substituted organic acid or substituted phenol (Salen ligand: halogenated metal salt or substituted organic acid or substituted phenol=1:1.5 (molar ratio)), React for 24 h under air atmosphere, remove the solvent, wash with water or ethanol and dry in vacuum to obtain a metal-Salen (SalenM, M=Cr, Co) catalyst.

The synthetic route of metalloporphyrin M(III)-porphyrin (M=Al, Cr, Co) of the present invention is:

II+MY ₂ +O ₂ →Metal-porphyrin-YM＝Cr,Co

II+AlEt ₂ Cl→Al-porphyrin-Cl

II+AlMe ₃ →Al-porphyrin-Me

Al-porphyrin-Me+Y-H→Al-porphyrin-Y

Its preparation method is:

Add benzaldehyde or substituted benzaldehyde and pyrrole to propionic acid solvent (the molar concentration of benzaldehyde or substituted benzaldehyde is 0.4-0.5M, the molar ratio of pyrrole to benzaldehyde or substituted benzaldehyde is 1:1.2), and reflux reaction for 24h , after the reflux reaction, the solution was concentrated to half of the original volume, and then an equal volume of methanol was added, and after mixing, it was left at 0°C for 24 hours, filtered by suction, dried in vacuum, and purified by column to prepare the porphyrin ligand, and then the following a Or b step obtains metalloporphyrin catalyst:

a. the preparation of metalloporphyrin (PorphyrinM, M=Cr, Co) catalyst: porphyrin ligand and chromous chloride or cobaltous chloride are added in the solvent dimethyl formamide (the molar concentration of porphyrin ligand is 0.01-0.02M, the molar ratio of chromous chloride or cobaltous chloride to porphyrin ligand is 1.5:1), react at 150-170°C, take a small amount of reaction solution after 2 hours, use ultraviolet detection, if porphyrin If the ligand has not reacted completely, add metal salt chromous chloride or cobaltous chloride, and the molar ratio of added chromous chloride or cobaltous chloride to the porphyrin ligand is 1.5:1 until the porphyrin ligand Complete conversion, then cooled to room temperature, added hydrochloric acid, then added a large amount of ice water, settled at 0°C for 24 hours, filtered, washed with water or ethanol, dried in vacuo, and separated by column chromatography to obtain metalloporphyrin (PorphyrinM, M=Cr, Co) catalyst;

b. Preparation of metalloporphyrin (PorphyrinM, M=Al) catalyst: under a nitrogen atmosphere, dissolve the porphyrin ligand in methylene chloride solvent (molar concentration is 0.05-0.1M), add diethylaluminum chloride or three Hexane solution of methylaluminum (molar concentration is 1-2M), the molar ratio of porphyrin ligand to diethylaluminum chloride or trimethylaluminum is 1:1.5, react at room temperature for 24h, remove dichloromethane under reduced pressure , washed 3 times with n-pentane, and vacuum-dried to obtain porphyrin aluminum chloride catalyst PorphyrinAlCl or porphyrin methylated aluminum PorphyrinAlMe, adding alcohols or replacing organic acid or Substituted phenol (the molar concentration of PorphyrinAlMe is 0.05-0.1M, the molar ratio of PorphyrinAlMe and alcohols or substituted organic acids or substituted phenol is 1:1.5), reflux reaction for 24h, washed with ethanol, and vacuum dried to obtain other aluminum metal porphyrins (PorphyrinM , M=Al) catalyst.

The beneficial effects of the present invention are: 1. The present invention catalyzes the ring-opening polymerization of racemic lactide under relatively mild conditions (under air conditions, 0-25° C.), and the monomer conversion rate can be greater than 90%; 2. The polylactic acid obtained according to the preparation method of the present invention has a stereoregular structure, and the content of the isotactic structure is greater than 70%.

Description of drawings

Fig. 1 is the homogeneous decoupling ¹ H NMR spectrum of the polylactic acid prepared in Example 1 (the -CH- part in the structural unit -CH(CH ₃ )COO- of polylactic acid PLA).

Detailed ways

In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below in conjunction with the accompanying drawings.

The lactide used in the present invention is racemic lactide.

Example 1

Preparation of the main catalyst: Dissolve 7.7g benzaldehyde (72.6mmol) and 4.2g pyrrole (62.6mmol) in 180mL propionic acid solvent under nitrogen atmosphere, reflux reaction for 24h, after the reflux reaction, concentrate the solution to half of the original volume , and then add an equal volume of methanol, mix and stand at 0°C for 24 hours, filter with suction, dry in vacuum, and column purify to obtain tetraphenylporphyrin TPPH ₂ . Dissolve 1 g of tetraphenylporphyrin (1.6 mmol) in 20 mL of dichloromethane solvent, add 2.4 mL of 1M diethylaluminum chloride in hexane (2.4 mmol), stir at room temperature for 24 h, and remove the solvent under reduced pressure , washed with n-pentane for 3 times, the solvent was taken out, and vacuum-dried to obtain tetraphenylporphyrin aluminum chloride catalyst TPPAlCl, the structural formula is as follows:

Add 23.6mg (0.035mmol) of the above-mentioned TPPA1Cl catalyst, 20mg (0.035mmol) of the promoter PPNCl, 0.504g of lactide, 5mL of propylene oxide, and 5mL of dioxane into the glass bottle respectively (TPPA1Cl catalyst: promoter: lactide =1:1:100 (molar ratio)), stirred at room temperature 25°C for 1 h, added 10 mL of methanolic hydrochloride (1% concentration of HCl by mass) to terminate, and removed the solvent under reduced pressure. The polymer was washed with a large amount of methanol and dried under vacuum to obtain PLA, a white aliphatic polyester. The conversion rate of racemic lactide ≥ 90%, the number average molecular weight of polylactic acid is 2,500, the molecular weight distribution is 1.3, and the isotactic content Pm=0.78 in the product (wherein the parameter Pm is the probability of forming an isotactic bond, namely -RRRRRR-bond or -SSSSSS-bond connection probability, after the complex triggers an L-LA (or D-LA) ring opening, the probability of continuing to polymerize into a monomer with the same configuration, Pr means heterotactic bond connection The probability of forming a RRSSRRSS type connection, m represents the same connection, r represents the heterogeneous connection, and the quadruples in the polymer obtained by the ring-opening polymerization of racemic lactide will also have five connection methods, which are rmr and rmm , mmr, mmm and mrm, they will also appear five groups of peaks in the homogeneous decoupling ¹ HNMR spectrum, and the chemical shift values are 5.22, 5.20, 5.17, 5.16, 5.15ppm respectively; according to the integral area of each group of peaks and the Markov equation Calculation: [mmm]=P ² _m +(1-Pm)Pm/2, [mmr]=[rmm]=(1-Pm)Pm/2, [rmr]=[(1-Pm) ² ]/2 ,[mrm]=[(1-Pm) ² +Pm(1-Pm)]/2 can calculate Pm; Figure 1 shows the homogeneous decoupling of polylactic acid obtained by the polymerization of racemic lactide catalyzed by the catalyst in this ^example1 HNMR spectrum (the -CH- part in the structural unit -CH(CH ₃ )COO- of polylactic acid PLA, the distribution of [mmm], [rmm], [rmr] is shown in Figure 1).

Example 2

Preparation of the main catalyst: under a nitrogen atmosphere, 9.87g p-methoxybenzaldehyde (72.6mmol) and 4.2g pyrrole (62.6mmol) were dissolved in 180mL propionic acid solvent, refluxed for 24h, and the solution was concentrated to Half of the original volume was added, and an equal volume of methanol was added. After mixing, the mixture was left standing at 0° C. for 24 h, filtered with suction, dried in vacuo, and purified by column to obtain tetrakis(methoxyphenyl)porphyrin. Under a nitrogen atmosphere, 1 g (1.36 mmol) of tetrakis(methoxyphenyl) porphyrin obtained was dissolved in 20 mL of dichloromethane solvent, and 1 mL (2 mmol) of a hexane solution of trimethylaluminum with a concentration of 2M was added, and stirred at room temperature for 24 h , remove the solvent under reduced pressure, add 50 mL of n-pentane to wash 3 times, remove the solvent, add 20 mL of dichloromethane to dissolve, add 0.37 g (72.6 mmol) of 2,4-dinitrophenol, reflux for 24 h, remove the solvent under reduced pressure, Wash with ethanol for 3 times, remove the solvent, and dry in vacuo to obtain a PorphyrinAl(O(C ₆ H ₃ (NO ₂ ) ₂ ) catalyst, the structural formula of which is as follows:

Add 26.6mg (0.035mmol) of the above-mentioned PorphyrinAl(O(C ₆ H ₃ (NO ₂ ) ₂ ) catalyst, 8.54mg (0.07mmol) of the cocatalyst DMAP, 50mL of ethylene oxide and 2.52g of lactide into the glass bottle (PorphyrinAl(O(C ₆ H ₃ (NO ₂ ) ₂ ) catalyst: cocatalyst: lactide = 1:2:500 (molar ratio)), stirred at room temperature for 4 hours at 25°C, added 50 mL of methanolic hydrochloride (the mass of HCl Percentage concentration is 1%) termination, and solvent is removed under reduced pressure. Polymer is washed with a large amount of methanol, and vacuum drying obtains white aliphatic polyester PLA. Polymerization yield is greater than 90%, and the number-average molecular weight of polylactic acid 1,0000, molecular weight distribution 1.5, the product Pm=0.7 (see Example 1 for the calculation method of Pm, the distribution of [mmm] is similar to that in Figure 1, and the figure is omitted).

Example 3

Preparation of the main catalyst: Dissolve 14.23g of pentafluorobenzaldehyde (72.6mmol) and 4.2g of pyrrole (62.6mmol) in 180mL of propionic acid solvent under a nitrogen atmosphere, reflux for 24 hours, and concentrate the solution to its original volume after the reflux reaction half of the mixture, then add an equal volume of methanol, mix and let stand at 0°C for 24 hours, filter with suction, purify by column, and dry in vacuo to obtain tetrakis(pentafluorophenyl)porphyrin. 1 g (1.03 mmol) of the obtained tetrakis(pentafluorophenyl) porphyrin ligand was dissolved in 100 mL of DMF solvent, 0.189 g of anhydrous chromous chloride (1.54 mmol) was added, refluxed at 150-170° C. for 2 hours, and ultraviolet detection of tetra( Whether the reaction of pentafluorophenyl) porphyrin is complete, if not, add 0.189g (1.54mmol) of chromous chloride until there is no tetrakis (pentafluorophenyl) porphyrin in ultraviolet detection, cool to room temperature, add 50mL hydrochloric acid, Then add 300mL of ice water, settle at 0°C for 24 hours, filter, wash with a large amount of water, dry, and use alumina column chromatography to separate and purify to obtain a porphyrin chromium PorphyrinCrCl catalyst, the structural formula is as follows:

Add 37.6mg (0.035mmol) of the above-mentioned PorphyrinCrCl catalyst, 3.75mg (0.035mmol) of the cocatalyst 2,6-lutidine, 5mL of propylene oxide, 0.504g of lactide, and 45mL of the solvent dioxane into the glass bottle (PorphyrinCrCl catalyst: cocatalyst: lactide = 1:1:100 (molar ratio)), room temperature 25 ℃ stirring reaction 4h, add 20mL hydrochloric acid methanol (the mass percent concentration of HCl is 1%) stop, remove solvent under reduced pressure . The polymer was washed with a large amount of methanol and dried under vacuum to obtain PLA, a white aliphatic polyester. The polymerization yield is greater than 90%, the number-average molecular weight of polylactic acid is 5,500, the molecular weight distribution is 1.4, and the product Pm=0.8 (see Example 1 for the calculation method of Pm, and the distribution of [mmm] is similar to that in Figure 1, and the figure is omitted).

Example 4

Preparation of the main catalyst: The tetrakis(pentafluorophenyl)porphyrin ligand was prepared according to the method described in Example 3. 1 g (1.03 mmol) of the obtained tetrakis(pentafluorophenyl) porphyrin ligand was dissolved in 100 mL of DMF solvent, 0.19 g of anhydrous cobaltous chloride (1.54 mmol) was added, and the reaction was carried out under reflux at 150-170° C. for 2 hours. Whether the reaction of pentafluorophenyl) porphyrin is complete, if not, add 0.19g (1.54mmol) of cobaltous chloride until there is no tetrakis (pentafluorophenyl) porphyrin in ultraviolet detection, cool to room temperature, add 50mL hydrochloric acid, Then add 300mL of ice water, settle at 0°C for 24 hours, filter, wash with a large amount of water, dry, and use silica gel column chromatography to separate and purify to obtain a porphyrin cobalt PorphyrinCoCl catalyst, the structural formula is as follows:

Add 37.3 mg (0.035 mmol) of the above-mentioned PorphyrinCoCl catalyst, 40 mg (0.07 mmol) of the promoter PPNCl, 10 mL of ethylene oxide, and 0.504 g (3.5 mmol) of lactide into the glass bottle respectively (PorphyrinCoCl catalyst: promoter: lactide = 1:2:100 (molar ratio)), stirred and reacted at room temperature 25°C for 4h, added 10mL of methanol hydrochloride (the mass percent concentration of HCl was 1%) to terminate, and removed the solvent under reduced pressure. The polymer was washed with a large amount of methanol and dried under vacuum to obtain PLA, a white aliphatic polyester. The polymerization yield is greater than 90%, the number average molecular weight of polylactic acid is 4,500, the molecular weight distribution is 1.3, and the product Pm=0.8 (see Example 1 for the calculation method of Pm, and the distribution of [mmm] is similar to that in Figure 1, and the figure is omitted).

Example 5

Prepare the main catalyst: under nitrogen atmosphere, dissolve 13.43g p-bromobenzaldehyde (72.6mmol) and 4.2g pyrrole (62.6mmol) in 180mL propionic acid solvent, reflux reaction for 24h, and concentrate the solution to the original volume after the reflux reaction half of the mixture, then add an equal volume of methanol, mix and let stand at 0°C for 24 hours, filter with suction, and dry in vacuo to obtain tetrakis(p-bromophenyl)porphyrin. Under a nitrogen atmosphere, 1 g (1.07 mmol) of the obtained tetrakis(p-bromophenyl) porphyrin was dissolved in 20 mL of dichloromethane solvent, and 0.8 mL (1.6 mmol) of a hexane solution of trimethylaluminum having a concentration of 2M was added, and stirred at room temperature React for 24 hours, remove the solvent under reduced pressure, add 50 mL of n-pentane to wash 3 times, remove the solvent, add 20 mL of dichloromethane to dissolve, add 0.26 g (1.6 mmol) of trichloroacetic acid, reflux for 24 hours, remove the solvent under reduced pressure, wash with ethanol for 3 Second, remove solvent, vacuum drying obtains porphyrin aluminum PorphyrinAl (OOCCCl ₃ ) catalyst, structural formula is as follows:

Add 39mg (0.035mmol) of the above-mentioned PorphyrinAl (OOCCCl ₃ ) catalyst, 20mg (0.035mmol) of co-catalyst PPNCl, 0.504g (3.5mmol) of lactide, 2mL of epoxycyclohexane, and 18mL of dichloromethane into a glass bottle (PorphyrinAl (OOCCCl ₃ ) catalyst: cocatalyst: lactide = 1:1:100 (molar ratio)), stirred at room temperature 25°C for 4h, added 10mL of hydrochloric acid methanol (the mass percent concentration of HCl was 1%) to terminate, and depressurized Solvent was removed. The polymer was washed with a large amount of methanol and dried under vacuum to obtain PLA, a white aliphatic polyester. The polymerization yield is greater than 90%, the number-average molecular weight of polylactic acid is 7,500, the molecular weight distribution is 1.2, and the product Pm=0.85 (see Example 1 for the calculation method of Pm, and the distribution of [mmm] is similar to that in Figure 1, and the figure is omitted).

Example 6

Preparation of the main catalyst: Dissolve 7.7g benzaldehyde (72.6mmol) and 4.2g pyrrole (62.6mmol) in 180mL propionic acid solvent under nitrogen atmosphere, reflux reaction for 24h, after the reflux reaction, concentrate the solution to half of the original volume , and then add an equal volume of methanol, mix and stand at 0°C for 24 hours, filter with suction, dry in vacuum, and column purify to obtain tetraphenylporphyrin TPPH ₂ . Dissolve 1 g of tetraphenylporphyrin (1.6 mmol) in 20 mL of dichloromethane solvent, add 1.2 mL of a 2M trimethylaluminum hexane solution (2.4 mmol), stir at room temperature for 24 h, remove the solvent under reduced pressure, and Wash 3 times with pentane, remove the solvent, add 20 mL of dichloromethane, add 0.11 g of ethanol, reflux for 24 hours, remove the solvent, wash with ethanol for 3 times, and dry in vacuo to obtain the PorphyrinAl (OEt) catalyst, the structural formula of which is as follows:

Add 23.9mg (0.035mmol) of the above-mentioned PorphyrinAl (OEt) catalyst, 10mg (0.0175mmol) of cocatalyst PPNCl, 0.504g (3.5mmol) of lactide, 15mL of propylene oxide, and 5mL of toluene into a glass bottle respectively (PorphyrinAl (OEt) catalyst : cocatalyst: lactide=1:0.5:100 (molar ratio)), room temperature 25 ℃ stirring reaction 2h, add 20mL hydrochloric acid methanol (the mass percent concentration of HCl is 1%) termination, remove solvent under reduced pressure. The polymer was washed with a large amount of methanol and dried under vacuum to obtain PLA, a white aliphatic polyester. The polymerization yield is greater than 90%, the number-average molecular weight of polylactic acid is 8,500, the molecular weight distribution is 1.1, and the product Pm=0.8 (see Example 1 for the calculation method of Pm, and the distribution of [mmm] is similar to that in Figure 1, and the figure is omitted).

Example 7

Prepare the main catalyst: Dissolve 2g of 3,5-dimethyl salicylaldehyde (13.3mmol) in 50mL of ethanol, add dropwise 0.44mL of 1,2-ethylenediamine (6.65mmol), add 2-3 drops of formic acid, and react at room temperature for 24h , settled at 0°C for 24 hours, filtered, then washed with water for 3 times, ethanol for 3 times, and vacuum-dried to prepare 3,5-dimethyl salicyloyl ethylenediamine (Salen ligand). Take 1g of 3,5-dimethyl The ethylenediamine ligand (3mmol) of salicyloyl ethylenediamine was dissolved in 30mL of dichloromethane solvent, 0.57g of anhydrous chromous chloride (4.5mmol) was added, and the reaction was stirred at room temperature under a nitrogen atmosphere for 24h, and 1.03g2,4 , 6-trinitrophenol (4.5mmol), ventilated air, stirred at room temperature for 24 hours, removed the solvent, added 100mL water to wash, filtered, washed 3 times with water, washed 3 times with ethanol, and dried in vacuo to obtain SalenCr(OC ₆ H ₂ (NO ₂ ) ₃ ) catalyst, the structural formula is as follows:

Add 21mg (0.035mmol) of the above-mentioned SalenCr (OC ₆ H ₂ (NO ₂ ) ₃ ) catalyst, 20mg (0.035mmol) of the promoter PPNCl, 10mL of ethylene oxide, 0.504g (3.5mmol) of lactide, and 10mL of the solvent THF into the glass In the bottle (SalenCr(OC ₆ H ₂ (NO ₂ ) ₃ ) catalyst: cocatalyst: lactide = 1:1:100 (molar ratio)), stirred at room temperature 25°C for 2 h, added 10 mL of methanol hydrochloride (the mass of HCl The percent concentration is 1%), and the solvent is removed under reduced pressure. The polymer was washed with a large amount of methanol and dried under vacuum to obtain PLA, a white aliphatic polyester. The polymerization yield is greater than 90%, the number-average molecular weight of polylactic acid is 5,500, the molecular weight distribution is 1.3, and the product Pm=0.8 (see Example 1 for the calculation method of Pm, and the distribution of [mmm] is similar to that in Figure 1, and the figure is omitted).

Example 8

Prepare the main catalyst: Dissolve 2g of 3-tert-butyl-5-chloromethyl salicylaldehyde (8.8mmol) in 50mL of ethanol, add dropwise 0.38mL of 1,2-propylenediamine (4.4mmol), add 2-3 drops of formic acid , react at room temperature for 24 hours, settle at 0°C for 24 hours, filter, then wash with water for 3 times and ethanol for 3 times, and dry in vacuum to prepare 3-tert-butyl-5-chloromethyl salicylic propylenediamide (Salen ligand) , take 1g of 3-tert-butyl-5-chloromethyl salicylic propylene glycol ligand (2mmol) and dissolve it in 30mL of dichloromethane solvent, add 0.375g of anhydrous chromous chloride (3mmol), first in a nitrogen atmosphere Stir at room temperature for 24 hours, add 0.3 mL of trifluoroacetic acid (3 mmol), ventilate with air, stir at room temperature for 24 hours, remove the solvent, add 100 mL of water to wash, filter, wash with water 3 times, ethanol 3 times, and vacuum dry to obtain SalenCr (OOCCF ₃ ) catalyst, the structural formula is as follows:

Add 23 mg (0.035 mmol) of the above-mentioned SalenCr (OOCCF ₃ ) catalyst, 40 mg (0.07 mmol) of bis-(triphenylphosphoryl) ammonium chloride PPNCl, 10 mL of ethylene oxide, and 0.504 g (3.5 mmol) of lactide, respectively In a glass bottle (SalenCr(OOCCF ₃ ) catalyst: co-catalyst: lactide = 1:2:100 (molar ratio)), stirred at room temperature 0°C for 4 hours, added 10 mL of hydrochloric acid methanol (the mass percent concentration of HCl was 1% ) terminated, and the solvent was removed under reduced pressure. The polymer was washed with a large amount of methanol and dried under vacuum to obtain PLA, a white aliphatic polyester. The polymerization yield is greater than 90%, the number-average molecular weight of polylactic acid is 5,500, the molecular weight distribution is 1.3, and the product Pm=0.8 (see Example 1 for the calculation method of Pm, and the distribution of [mmm] is similar to that in Figure 1, and the figure is omitted).

Example 9

Preparation of the main catalyst: Dissolve 2g of 3-tert-butyl-5-bromosalicylaldehyde (7.8mmol) in 50mL of ethanol, add 0.425g of o-phenylenediamine (3.9mmol), add 2-3 drops of formic acid, reflux for 24h, Settled at 0°C for 24 hours, filtered, then washed with water for 3 times, ethanol for 3 times, and vacuum-dried to prepare 3-tert-butyl-5-bromosalicyloyl-o-phenylenediamine (Salen ligand). Take 1g of 3-tert-butyl Base-5-bromosalicyloyl-o-phenylenediamine ligand (1.7mmol) was dissolved in 30mL of dichloromethane solvent, added 0.637g of cobaltous acetate tetrahydrate, first stirred at room temperature under nitrogen atmosphere for 24h, added 0.468g2,4 - Dinitrophenol, ventilate with air, stir at room temperature for 24 hours, remove the solvent, add 100mL water to wash, filter, wash 3 times with water, wash 3 times with ethanol, and dry in vacuo to obtain SalenCo(OC ₆ H ₃ (NO ₂ ) ₂ ) Catalyst, structural formula is as follows:

The above-mentioned SalenCo (OC ₆ H ₃ (NO ₂ ) ₂ ) catalyst 29mg (0.035mmol), co-catalyst 2,6-lutidine 7.58mg (0.07mmol), ethylene oxide 10mL, lactide 0.504g ( 3.5mmol) into glass bottles (SalenCo(OC ₆ H ₃ (NO ₂ ) ₂ ) catalyst: cocatalyst: lactide = 1:2:100 (molar ratio)), stirred at room temperature for 4 hours at 25°C, and added 10mL Methanol hydrochloride (1% concentration of HCl by mass) was terminated, and the solvent was removed under reduced pressure. The polymer was washed with a large amount of methanol and dried under vacuum to obtain PLA, a white aliphatic polyester. The polymerization yield is greater than 90%, the number average molecular weight of polylactic acid is 4,500, the molecular weight distribution is 1.3, and the product Pm=0.8 (see Example 1 for the calculation method of Pm, and the distribution of [mmm] is similar to that in Figure 1, and the figure is omitted).

Example 10

Preparation of the main catalyst: Dissolve 2g of 3,5-di-tert-butyl salicylaldehyde (8.5mmol) in 50mL of ethanol, add 0.52mL of 1,2-cyclohexanediamine (4.25mmol), add 2-3 drops of formic acid, and stir at room temperature 24h, settled at 0°C for 24h, filtered, then washed with water for 3 times and ethanol for 3 times, and dried in vacuo to prepare 3,5-di-tert-butyl salicyloylcyclohexanediamine (Salen ligand). Take 1g (1.8 mmol) 3,5-di-tert-butylsalicyloylcyclohexanediamine ligand was dissolved in 30mL of dichloromethane solvent, 0.34g of anhydrous chromous chloride (2.7mmol) was added, and the reaction was first stirred at room temperature under a nitrogen atmosphere After 24 hours, add 0.11g LiCl, ventilate with air, stir at room temperature for 24 hours, remove the solvent, add 100mL of water to wash, filter, wash with ethanol 3 times, and vacuum dry to obtain the SalenCrCl catalyst. The structural formula is as follows:

Add 22.7mg (0.036mmol) of the above-mentioned SalenCrCl catalyst, 20mg (0.036mmol) of the promoter PPNCl, 0.518g of lactide, and 10mL of propylene oxide into the glass bottle respectively (SalenCrCl catalyst: promoter: lactide=1:1:100 (molar ratio)), stirred at 25° C. for 20 min, and was terminated by adding 10 mL of methanol hydrochloride (the mass percent concentration of HCl was 1%), and the solvent was removed under reduced pressure. The polymer was washed with a large amount of methanol and dried under vacuum to obtain PLA, a white aliphatic polyester. The polymerization yield is greater than 90%, the number-average molecular weight of polylactic acid is 4,500, the molecular weight distribution is 1.2, and the product Pm=0.75 (see Example 1 for the calculation method of Pm, and the distribution of [mmm] is similar to that in Figure 1, and the figure is omitted).

The descriptions of the above embodiments are only used to help understand the method and core idea of the present invention. It should be pointed out that for those skilled in the art, without departing from the principle of the present invention, some improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims (6)

1. the preparation method of stereoregular poly(lactic acid) under a mild conditions, it is characterized in that step is as follows: add in reaction vessel by composite catalyst, rac-lactide, add dissolution with solvents, gained reaction solution is in 0-25 DEG C of reaction 20min-4 hour, add hydrochloric acid methanol termination reaction after reaction terminates, products therefrom methanol wash precipitation obtains stereoregulated poly(lactic acid);

Described composite catalyst is made up of Primary Catalysts and promotor, the mol ratio of Primary Catalysts and promotor is 1:0.5-2, wherein Primary Catalysts is metal salung M (III)-salen (M=Cr, or metalloporphyrin M (III)-porphyrin (M=Al Co), Cr, Co), promotor is the one in two-(dihalotriphenylphosphoranes base) ammonia chloride, dimethyl aminopyridine, 2,6-lutidine;

The structural formula of described metal salung M (III)-salen (M=Cr, Co) is:

M=Cr or Co; R ₁=o-C ₆h ₄, 1,2-cyclohexenyl ,-CH ₂cH ₂-or-CH (CH ₃) CH ₂-; R ₂, R ₃separately be selected from the aliphatic group that hydrogen, chlorine, bromine, chlorine replacement or bromine replace; X is-Cl ,-Br, CCl ₃cOO-, CF ₃one in COO-, 2,4-DNP oxygen base, 3,5-dinitrophenol(DNP) oxygen bases, 2，4，6-trinitrophenol oxygen base;

The structural formula of described metalloporphyrin M (III)-porphyrin (M=Al, Cr, Co) is:

M=Cr or Co or Al, R ₂, R ₃, R ₄separately be selected from the aliphatic group that hydrogen, fluorine, chlorine, bromine, chlorine replacement or bromine replace; X is-Cl ,-OCH ₂cH ₃,-OCH (CH ₃) ₂,-Br, CCl ₃cOO-, CF ₃one in COO-, 2,4-DNP oxygen base, 3,5-dinitrophenol(DNP) oxygen bases, 2，4，6-trinitrophenol oxygen base;

Described solvent is epoxy compounds or the mixed solvent containing epoxy compounds, the described mixed solvent containing epoxy compounds is the mixture of epoxy compounds and tetrahydrofuran (THF), or the mixture of epoxy compounds and methylene dichloride, or the mixture of epoxy compounds and toluene, or the mixture of epoxy compounds and dioxane, account for volume ratio >=10% of mixed solvent containing epoxy compounds in the mixed solvent of epoxy compounds.

2. the preparation method of stereoregular poly(lactic acid) according to claim 1, is characterized in that described Primary Catalysts and rac-lactide mol ratio are 1:100-500.

3. the preparation method of stereoregular poly(lactic acid) according to claim 1, is characterized in that described epoxy compounds is the one in propylene oxide, oxyethane, epoxy cyclohexane.

4. the preparation method of stereoregular poly(lactic acid) according to claim 1, is characterized in that described rac-lactide is 0.01-0.1g/mL at described epoxy compounds or containing the mass body volume concentrations in the mixed solvent of epoxy compounds.

5. the preparation method of stereoregular poly(lactic acid) according to claim 1, is characterized in that transformation efficiency >=90% of described rac-lactide.

6. the stereoregular poly(lactic acid) prepared according to the arbitrary described method of claim 1-5, it is characterized in that, described stereoregular poly(lactic acid) number-average molecular weight is 2500-10000, and molecular weight distribution is 1.1-1.5, and in poly(lactic acid), isotaxy content is 70-85%.