Method for preparing high molecular weight poly-L-lactic acid

Abstract

A method for preparing high molecular weight poly(L-lactic acid) with high performance, including: a) providing a biogenic guanidine (BG) as a catalyst, and a nontoxic acid salt of an essential metal trace element as an activator (Act), and adding the catalyst, the activator, and L-lactide monomer to a polymerization reactor; b) evacuating under vacuum and charging the polymerization reactor with nitrogen for three consecutive times to remove air, and allowing the L-lactide monomer to undergo bulk polymerization under vacuum. The bulk polymerization includes a first reaction stage and a second reaction stage, which are separately carried out at different temperatures, pressures, and reaction times.

Claims

1. A method for preparing poly(L-lactic acid), comprising: a) providing a biogenic guanidine (BG) as a catalyst and an acid salt of a trace metal as an activator (Act), and adding the catalyst, the activator, and L-lactide monomer (LLA) to a polymerization reactor; b) evacuating and purging the polymerization reactor with nitrogen three times to remove air, evacuating the polymerization reactor and conducting bulk polymerization of the L-lactide monomer under vacuum; wherein: the trace metal is selected from a group consisting of potassium (K), iron (Fe), zinc (Zn), and calcium (Ca); the bulk polymerization comprises a first reaction stage and a second reaction stage; in the first reaction stage, a reaction temperature is between 125 and 140° C., a reaction pressure is between 0.4 and 0.6 torr, a reaction time is between 16 and 24 hours, and a resulting product is a medium molecular weight poly-L-lactic acid (m-PLLA) having a weight average molecular weight (Mw) of between 4.0×10.sup.4 and 5.0×10.sup.4; in the second reaction stage, a reaction temperature is between 140 and 160° C., a reaction pressure is between 0.1 and 0.3 torr, a reaction time is between 25 and 60 hours, and a final product is a high molecular weight poly-L-lactic acid (h-PLLA) having a weight average molecular weight of between 4.0×10.sup.5 and 5.5×10.sup.5; the first reaction stage of the bulk polymerization is represented by equation I: ##STR00003## the second reaction stage of bulk polymerization is represented by equation II: ##STR00004##

2. The method of claim 1, wherein the final product has a white color and has the following performance index: a polydispersity index (PDI) is less than or equal to 1.70, a melting point (Tm) is greater than or equal to 185° C., and a crystallinity (Xc) is greater than or equal to 80.2%.

3. The method of claim 2, wherein the final product has the following performance index: Mw=5.5×10.sup.5, PDI=1.50, Tm=188° C., and Xc=82.9%.

4. The method of claim 1, wherein the catalyst is an organic guanidine derivative selected from a group consisting of arginine, glycocyamine, creatine, creatinine, and phosphocreatine; and the catalyst and the activator constitute a two-component catalyst system, and a dosage of the two-component catalyst system accounts for between 0.001 and 0.05 wt. % of that of the L-lactide monomer.

5. The method of claim 4, wherein the acid salt is a carbonate, acetate, lactate, or glycolate.

6. The method of claim 5, wherein the acid salt is K.sub.2CO.sub.3, FeCO.sub.3, (CH.sub.3CH(OH)COO).sub.2Zn, CaCO.sub.3, (CH.sub.3CH(OH)COO).sub.2Ca, CH.sub.3COOK, (HOCH.sub.2COO).sub.2Zn, or (CH.sub.3COO).sub.2Ca.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

(1) For further illustrating the invention, experiments detailing a method for preparing poly(L-lactic acid) are described below. It should be noted that the following examples are intended to describe and not to limit the invention.

(2) LLA monomer, a catalyst and an activator are added to a polymerization reactor. The dosage of the two-component catalyst system accounts for between 0.001 and 0.05 wt. % of that of the LLA monomer. The polymerization reactor is vacuumized and charged with nitrogen for three consecutive times for air removal, and then is allowed for bulk polymerization, which comprises a first reaction stage and a second reaction stage. In the first reaction stage, a reaction temperature is between 125 and 140° C., a reaction pressure is between 0.4 and 0.6 torr, a reaction time is between 16 and 24 hours, and a resulting product is medium molecular weight poly-L-lactic acid (m-PLLA) having a weight average molecular weight (Mw) of between 4.0×10.sup.4 and 5.0×10.sup.4. Thereafter, the second reaction stage is followed, where a reaction temperature is between 140 and 160° C., a reaction pressure is between 0.1 and 0.3 torr, a reaction time is between 25 and 60 hours, and a final product is a high molecular weight poly-L-lactic acid (h-PLLA) having a weight average molecular weight of between 4.0×10.sup.5 and 5.5×10.sup.5.

Example 1

(3) 200.0 g of LLA, 2.0 mg of arginine, and 2.0 mg of K.sub.2CO.sub.3 were added to a polymerization reactor. The polymerization reactor was vacuumized and charged with nitrogen for three consecutive times for air removal, and then was allowed for bulk polymerization, which comprised a first reaction stage and a second reaction stage. In the first reaction stage, a reaction temperature was 125° C., a reaction pressure was 0.4 torr, a reaction time was 16 hours, and a resulting product was medium molecular weight poly-L-lactic acid (m-PLLA) having a weight average molecular weight (Mw) of 5.0×10.sup.4. Thereafter, the second reaction stage was followed, where a reaction temperature was 140° C., a reaction pressure was 0.1 torr, a reaction time was 40 hours, and a final product was a high molecular weight poly-L-lactic acid (h-PLLA) having a weight average molecular weight of 5.5×10.sup.5. The final product has the following performance index: Mw=5.5×10.sup.5, PDI=1.50, Tm=188.1° C., Xc=82.9%, and snowy white in color.

Example 2

(4) 200.0 g of LLA, 2.0 mg of arginine, and 2.0 mg of K.sub.2CO.sub.3 were added to a polymerization reactor. The polymerization reactor was vacuumized and charged with nitrogen for three consecutive times for air removal, and then was allowed for bulk polymerization, which comprised a first reaction stage and a second reaction stage. In the first reaction stage, a reaction temperature was 125° C., a reaction pressure was 0.4 torr, a reaction time was 16 hours, and a resulting product was medium molecular weight poly-L-lactic acid (m-PLLA) having a weight average molecular weight (Mw) of 5.0×10.sup.4. Thereafter, the second reaction stage was followed, where a reaction temperature was 140° C., a reaction pressure was 0.1 torr, a reaction time was 39 hours, and a final product was a high molecular weight poly-L-lactic acid (h-PLLA) having a weight average molecular weight of 5.4×10.sup.5. The final product has the following performance index: Mw=5.4×10.sup.5, PDI=1.51, Tm=187.9° C., Xc=82.5%, and snowy white in color.

Example 3

(5) 200.0 g of LLA, 2.0 mg of arginine, and 2.0 mg of K.sub.2CO.sub.3 were added to a polymerization reactor. The polymerization reactor was vacuumized and charged with nitrogen for three consecutive times for air removal, and then was allowed for bulk polymerization, which comprised a first reaction stage and a second reaction stage. In the first reaction stage, a reaction temperature was 125° C., a reaction pressure was 0.4 torr, a reaction time was 16 hours, and a resulting product was medium molecular weight poly-L-lactic acid (m-PLLA) having a weight average molecular weight (Mw) of 5.0×10.sup.4. Thereafter, the second reaction stage was followed, where a reaction temperature was 140° C., a reaction pressure was 0.1 torr, a reaction time was 38 hours, and a final product was a high molecular weight poly-L-lactic acid (h-PLLA) having a weight average molecular weight of 5.3×10.sup.5. The final product has the following performance index: Mw=5.3×10.sup.5, PDI=1.53, Tm=187.8° C., Xc=82.4%, and snowy white in color.

Example 4

(6) 200.0 g of LLA, 2.0 mg of arginine, and 2.0 mg of K.sub.2CO.sub.3 were added to a polymerization reactor. The polymerization reactor was vacuumized and charged with nitrogen for three consecutive times for air removal, and then was allowed for bulk polymerization, which comprised a first reaction stage and a second reaction stage. In the first reaction stage, a reaction temperature was 125° C., a reaction pressure was 0.4 torr, a reaction time was 16 hours, and a resulting product was medium molecular weight poly-L-lactic acid (m-PLLA) having a weight average molecular weight (Mw) of 5.0×10.sup.4. Thereafter, the second reaction stage was followed, where a reaction temperature was 140° C., a reaction pressure was 0.1 torr, a reaction time was 37 hours, and a final product was a high molecular weight poly-L-lactic acid (h-PLLA) having a weight average molecular weight of 5.2×10.sup.5. The final product has the following performance index: Mw=5.2×10.sup.5, PDI=1.53, Tm=187.8° C., Xc=82.3%, and snowy white in color.

Example 5

(7) 200.0 g of LLA, 2.0 mg of arginine, and 2.0 mg of K.sub.2CO.sub.3 were added to a polymerization reactor. The polymerization reactor was vacuumized and charged with nitrogen for three consecutive times for air removal, and then was allowed for bulk polymerization, which comprised a first reaction stage and a second reaction stage. In the first reaction stage, a reaction temperature was 125° C., a reaction pressure was 0.4 torr, a reaction time was 16 hours, and a resulting product was medium molecular weight poly-L-lactic acid (m-PLLA) having a weight average molecular weight (Mw) of 5.0×10.sup.4. Thereafter, the second reaction stage was followed, where a reaction temperature was 140° C., a reaction pressure was 0.1 torr, a reaction time was 36 hours, and a final product was a high molecular weight poly-L-lactic acid (h-PLLA) having a weight average molecular weight of 5.1×10.sup.5. The final product has the following performance index: Mw=5.1×10.sup.5, PDI=1.52, Tm=187.6° C., Xc=82.2%, and snowy white in color.

Example 6

(8) 100.0 g of LLA, 2.0 mg of arginine, and 2.0 mg of K.sub.2CO.sub.3 were added to a polymerization reactor. The polymerization reactor was vacuumized and charged with nitrogen for three consecutive times for air removal, and then was allowed for bulk polymerization, which comprised a first reaction stage and a second reaction stage. In the first reaction stage, a reaction temperature was 125° C., a reaction pressure was 0.4 torr, a reaction time was 16 hours, and a resulting product was medium molecular weight poly-L-lactic acid (m-PLLA) having a weight average molecular weight (Mw) of 5.0×10.sup.4. Thereafter, the second reaction stage was followed, where a reaction temperature was 140° C., a reaction pressure was 0.1 torr, a reaction time was 40 hours, and a final product was a high molecular weight poly-L-lactic acid (h-PLLA) having a weight average molecular weight of 5.0×10.sup.5. The final product has the following performance index: Mw=5.0×10.sup.5, PDI=1.54, Tm=187.4° C., Xc=82.1%, and snowy white in color.

Example 7

(9) 150.0 g of LLA, 4.5 mg of arginine, and 4.5 mg of K.sub.2CO.sub.3 were added to a polymerization reactor. The polymerization reactor was vacuumized and charged with nitrogen for three consecutive times for air removal, and then was allowed for bulk polymerization, which comprised a first reaction stage and a second reaction stage. In the first reaction stage, a reaction temperature was 125° C., a reaction pressure was 0.4 torr, a reaction time was 16 hours, and a resulting product was medium molecular weight poly-L-lactic acid (m-PLLA) having a weight average molecular weight (Mw) of 5.0×10.sup.4. Thereafter, the second reaction stage was followed, where a reaction temperature was 140° C., a reaction pressure was 0.1 torr, a reaction time was 36 hours, and a final product was a high molecular weight poly-L-lactic acid (h-PLLA) having a weight average molecular weight of 4.5×10.sup.5. The final product has the following performance index: Mw=4.5×10.sup.5, PDI=1.58, Tm=186.8° C., Xc=82.1%, and snowy white in color.

Example 8

(10) 200.0 g of LLA, 8.0 mg of arginine, and 8.0 mg of K.sub.2CO.sub.3 were added to a polymerization reactor. The polymerization reactor was vacuumized and charged with nitrogen for three consecutive times for air removal, and then was allowed for bulk polymerization, which comprised a first reaction stage and a second reaction stage. In the first reaction stage, a reaction temperature was 125° C., a reaction pressure was 0.4 torr, a reaction time was 16 hours, and a resulting product was medium molecular weight poly-L-lactic acid (m-PLLA) having a weight average molecular weight (Mw) of 5.0×10.sup.4. Thereafter, the second reaction stage was followed, where a reaction temperature was 140° C., a reaction pressure was 0.1 torr, a reaction time was 25 hours, and a final product was a high molecular weight poly-L-lactic acid (h-PLLA) having a weight average molecular weight of 4.0×10.sup.5. The final product has the following performance index: Mw=4.0×10.sup.5, PDI=1.51, Tm=185.4° C., Xc=80.5%, and snowy white in color.

Example 9

(11) 80.0 g of LLA, 5.6 mg of glycocyamine, and 3.2 mg of FeCO.sub.3 were added to a polymerization reactor. The polymerization reactor was vacuumized and charged with nitrogen for three consecutive times for air removal, and then was allowed for bulk polymerization, which comprised a first reaction stage and a second reaction stage. In the first reaction stage, a reaction temperature was 132° C., a reaction pressure was 0.5 torr, a reaction time was 20 hours, and a resulting product was medium molecular weight poly-L-lactic acid (m-PLLA) having a weight average molecular weight (Mw) of 4.5×10.sup.4. Thereafter, the second reaction stage was followed, where a reaction temperature was 150° C., a reaction pressure was 0.2 torr, a reaction time was 45 hours, and a final product was a high molecular weight poly-L-lactic acid (h-PLLA) having a weight average molecular weight of 5.5×10.sup.5. The final product has the following performance index: Mw=5.5×10.sup.5, PDI=1.56, Tm=188.0° C., Xc=82.7%, and snowy white in color.

Example 10

(12) 80.0 g of LLA, 5.6 mg of glycocyamine, and 3.2 mg of FeCO.sub.3 were added to a polymerization reactor. The polymerization reactor was vacuumized and charged with nitrogen for three consecutive times for air removal, and then was allowed for bulk polymerization, which comprised a first reaction stage and a second reaction stage. In the first reaction stage, a reaction temperature was 132° C., a reaction pressure was 0.5 torr, a reaction time was 20 hours, and a resulting product was medium molecular weight poly-L-lactic acid (m-PLLA) having a weight average molecular weight (Mw) of 4.5×10.sup.4. Thereafter, the second reaction stage was followed, where a reaction temperature was 150° C., a reaction pressure was 0.2 torr, a reaction time was 38 hours, and a final product was a high molecular weight poly-L-lactic acid (h-PLLA) having a weight average molecular weight of 4.9×10.sup.5. The final product has the following performance index: Mw=4.9×10.sup.5, PDI=1.61, Tm=187.4° C., Xc=81.9%, and snowy white in color.

Example 11

(13) 80.0 g of LLA, 5.6 mg of glycocyamine, and 3.2 mg of FeCO.sub.3 were added to a polymerization reactor. The polymerization reactor was vacuumized and charged with nitrogen for three consecutive times for air removal, and then was allowed for bulk polymerization, which comprised a first reaction stage and a second reaction stage. In the first reaction stage, a reaction temperature was 132° C., a reaction pressure was 0.5 torr, a reaction time was 16 hours, and a resulting product was medium molecular weight poly-L-lactic acid (m-PLLA) having a weight average molecular weight (Mw) of 4.5×10.sup.4. Thereafter, the second reaction stage was followed, where a reaction temperature was 150° C., a reaction pressure was 0.2 torr, a reaction time was 32 hours, and a final product was a high molecular weight poly-L-lactic acid (h-PLLA) having a weight average molecular weight of 4.4×10.sup.5. The final product has the following performance index: Mw=4.4×10.sup.5, PDI=1.58, Tm=186.4° C., Xc=80.6%, and snowy white in color.

Example 12

(14) 80.0 g of LLA, 5.6 mg of glycocyamine, and 3.2 mg of FeCO.sub.3 were added to a polymerization reactor. The polymerization reactor was vacuumized and charged with nitrogen for three consecutive times for air removal, and then was allowed for bulk polymerization, which comprised a first reaction stage and a second reaction stage. In the first reaction stage, a reaction temperature was 132° C., a reaction pressure was 0.5 torr, a reaction time was 20 hours, and a resulting product was medium molecular weight poly-L-lactic acid (m-PLLA) having a weight average molecular weight (Mw) of 4.5×10.sup.4. Thereafter, the second reaction stage was followed, where a reaction temperature was 150° C., a reaction pressure was 0.2 torr, a reaction time was 26 hours, and a final product was a high molecular weight poly-L-lactic acid (h-PLLA) having a weight average molecular weight of 4.0×10.sup.5. The final product has the following performance index: Mw=4.0×10.sup.5, PDI=1.61, Tm=185.2° C., Xc=80.4%, and snowy white in color.

Example 13

(15) 50.0 g of LLA, 25.0 mg of phosphocreatine, and 25.0 mg of (CH.sub.3CH(OH)COO).sub.2Ca were added to a polymerization reactor. The polymerization reactor was vacuumized and charged with nitrogen for three consecutive times for air removal, and then was allowed for bulk polymerization, which comprised a first reaction stage and a second reaction stage. In the first reaction stage, a reaction temperature was 140° C., a reaction pressure was 0.6 torr, a reaction time was 24 hours, and a resulting product was medium molecular weight poly-L-lactic acid (m-PLLA) having a weight average molecular weight (Mw) of 4.0×10.sup.4. Thereafter, the second reaction stage was followed, where a reaction temperature was 160° C., a reaction pressure was 0.3 torr, a reaction time was 60 hours, and a final product was a high molecular weight poly-L-lactic acid (h-PLLA) having a weight average molecular weight of 5.5×10.sup.5. The final product has the following performance index: Mw=5.5×10.sup.5, PDI=1.60, Tm=187.9° C., Xc=82.6%, and snowy white in color.

Example 14

(16) 50.0 g of LLA, 25.0 mg of phosphocreatine, and 25.0 mg of (CH.sub.3CH(OH)COO).sub.2Ca were added to a polymerization reactor. The polymerization reactor was vacuumized and charged with nitrogen for three consecutive times for air removal, and then was allowed for bulk polymerization, which comprised a first reaction stage and a second reaction stage. In the first reaction stage, a reaction temperature was 140° C., a reaction pressure was 0.6 torr, a reaction time was 24 hours, and a resulting product was medium molecular weight poly-L-lactic acid (m-PLLA) having a weight average molecular weight (Mw) of 4.0×10.sup.4. Thereafter, the second reaction stage was followed, where a reaction temperature was 160° C., a reaction pressure was 0.3 torr, a reaction time was 55 hours, and a final product was a high molecular weight poly-L-lactic acid (h-PLLA) having a weight average molecular weight of 4.8×10.sup.5. The final product has the following performance index: Mw=4.8×10.sup.5, PDI=1.58, Tm=187.3° C., Xc=81.8%, and snowy white in color.

Example 15

(17) 50.0 g of LLA, 25.0 mg of phosphocreatine, and 25.0 mg of (CH.sub.3CH(OH)COO).sub.2Ca were added to a polymerization reactor. The polymerization reactor was vacuumized and charged with nitrogen for three consecutive times for air removal, and then was allowed for bulk polymerization, which comprised a first reaction stage and a second reaction stage. In the first reaction stage, a reaction temperature was 140° C., a reaction pressure was 0.6 torr, a reaction time was 24 hours, and a resulting product was medium molecular weight poly-L-lactic acid (m-PLLA) having a weight average molecular weight (Mw) of 4.0×10.sup.4. Thereafter, the second reaction stage was followed, where a reaction temperature was 160° C., a reaction pressure was 0.3 torr, a reaction time was 50 hours, and a final product was a high molecular weight poly-L-lactic acid (h-PLLA) having a weight average molecular weight of 4.6×10.sup.5. The final product has the following performance index: Mw=4.6×10.sup.5, PDI=1.62, Tm=186.8° C., Xc=81.5%, and snowy white in color.

Example 16

(18) 50.0 g of LLA, 25.0 mg of phosphocreatine, and 25.0 mg of (CH.sub.3CH(OH)COO).sub.2Ca were added to a polymerization reactor. The polymerization reactor was vacuumized and charged with nitrogen for three consecutive times for air removal, and then was allowed for bulk polymerization, which comprised a first reaction stage and a second reaction stage. In the first reaction stage, a reaction temperature was 140° C., a reaction pressure was 0.6 torr, a reaction time was 24 hours, and a resulting product was medium molecular weight poly-L-lactic acid (m-PLLA) having a weight average molecular weight (Mw) of 4.0×10.sup.4. Thereafter, the second reaction stage was followed, where a reaction temperature was 160° C., a reaction pressure was 0.3 torr, a reaction time was 45 hours, and a final product was a high molecular weight poly-L-lactic acid (h-PLLA) having a weight average molecular weight of 4.0×10.sup.5. The final product has the following performance index: Mw=4.0×10.sup.5, PDI=1.59, Tm=185.1° C., Xc=80.2%, and snowy white in color.

(19) While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.