CN114213638A - Method for improving polylactic acid molecular weight based on in-situ drying dehydration - Google Patents
Method for improving polylactic acid molecular weight based on in-situ drying dehydration Download PDFInfo
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Abstract
The invention relates to the field of polylactic acid synthesis, and aims to provide a method for improving the molecular weight of polylactic acid based on in-situ drying and dewatering. The method comprises the following steps: adding lactide, a catalyst, an initiator and desiccant powder into a polymerization kettle, and mechanically stirring and uniformly mixing; the drying agent is anhydrous calcium salt, sodium salt or aluminum oxide; under the condition of 50-200 Pa, raising the temperature of the polymerization kettle to 40-80 ℃, and keeping for 0.5-2 h; introducing protective gas into the polymerization kettle, and keeping mechanical stirring; raising the temperature to 170-210 ℃, and reacting for 0.5-4 h; and discharging from the bottom of the kettle and granulating to obtain the high molecular weight polylactic acid. The invention applies a trace amount of anhydrous desiccant to the polymerization reaction process of polylactic acid, and can effectively improve the molecular weight of the polylactic acid. The anhydrous desiccant has the advantages of little usage amount and low chemical activity, and can not obviously influence the properties of the polylactic acid product. The invention adopts a mechanical stirring method for mixing, has simple process, low technical cost and no pollution, and can realize large-scale industrial production.
Description
Technical Field
The invention relates to the field of polylactic acid synthesis, in particular to a method for improving the molecular weight of polylactic acid based on in-situ drying and dewatering.
Background
Global annual plastic production is over 3.5 million tons producing over 1 million tons of white waste. Because the raw material of the traditional plastic product, namely the high molecular resin, has extremely strong stability, the degradation can be carried out for hundreds of years under the natural environment state, not only a large amount of land resources are occupied, but also the water body and the air are seriously polluted. The polylactic acid is biodegradable plastic with highest neutral cost ratio in the prior synthetic resin, has excellent mechanical property, can replace part of general plastic to be used in the fields of agriculture, packaging materials, clothes and the like, and can be completely degraded into water and carbon dioxide to reduce white pollution. In addition, the polylactic acid has a carbon capture property due to the characteristics of a biomass source, and can greatly reduce the carbon emission of plastics by performing a self-closed loop system of 'planting carbon fixation, fermentation carbon discharge, production carbon discharge, decomposition carbon discharge'.
At present, the preparation of high molecular weight polylactic acid mainly adopts a two-step method, namely, lactic acid is firstly dehydrated and condensed to prepare polylactic acid oligomer; then depolymerizing and cyclizing to prepare lactide, purifying the lactide, and then opening the ring to polymerize to prepare the high molecular weight polylactic acid. However, in the process of preparing polylactic acid by ring-opening lactide, the presence of a trace amount of water causes ring-opening polymerization of lactide, resulting in a decrease in molecular weight, a broadening of molecular weight distribution, and deterioration of heat resistance of polylactic acid, which is not favorable for quality control in the industrial production process of polylactic acid. Therefore, the control and removal of trace water are crucial in the process of preparing high molecular weight polylactic acid by ring-opening polymerization of lactide.
Disclosure of Invention
The invention aims to solve the technical problem of overcoming the defects in the prior art and provides a method for improving the molecular weight of polylactic acid based on in-situ drying and dewatering.
In order to solve the technical problem, the solution of the invention is as follows:
the method for improving the molecular weight of the polylactic acid based on in-situ drying and water removal comprises the following steps:
(1) adding lactide, a catalyst, an initiator and desiccant powder into a polymerization kettle, and mechanically stirring and uniformly mixing; the drying agent is anhydrous calcium salt, sodium salt or aluminum oxide, and the mass of the drying agent accounts for 0.01-0.1% of that of the lactide;
(2) under the condition of 50-200 Pa, raising the temperature of the polymerization kettle to 40-80 ℃, and keeping for 0.5-2 h;
(3) filling inert gas as protective gas into the polymerization kettle, and keeping mechanical stirring; raising the temperature to 170-210 ℃, and reacting for 0.5-4 h; and discharging from the bottom of the kettle and granulating to obtain the high molecular weight polylactic acid.
In a preferred embodiment of the present invention, the drying agent is one of anhydrous calcium sulfate, anhydrous calcium chloride, anhydrous magnesium sulfate, anhydrous sodium sulfate, and anhydrous alumina.
In a preferred embodiment of the present invention, the average particle size of the desiccant powder is 0.01 to 100 μm.
In a preferred embodiment of the present invention, the catalyst is one of a tin-based catalyst, a titanium-based catalyst, and a zinc-based catalyst, and the mass of the catalyst is 0.01 to 1% of the mass of the lactide.
In a preferred embodiment of the present invention, the catalyst is one of stannous octoate, stannous chloride, tetraisopropyl titanate, and zinc oxide.
In a preferable embodiment of the present invention, the initiator is an alcohol, and the mass of the initiator is 0.01 to 1% of the mass of the lactide.
In a preferred embodiment of the present invention, the initiator is one of lauryl alcohol, benzyl alcohol, ethylene glycol, glycerol, and pentaerythritol.
As a preferred embodiment of the present invention, the inert gas is nitrogen or argon.
Description of the inventive principles:
desiccants may be used to remove traces of water, as is well known to those skilled in the art. Therefore, desiccants are often used to keep the reagents dry and free from moisture effects. However, in order to prevent the desiccant from contaminating the reagent, it is necessary to isolate the desiccant from the reagent to be preserved. The common using methods are as follows: the spacing method, such as a glass dryer commonly used in laboratories, places a drying agent in the lower space and a reagent in the upper space; individually packaged methods such as individual small-pack commercial desiccants common in food or pharmaceutical packaging. Based on the above teachings of extended use, it has become a technical thought that it is not possible to contact or mix a desiccant with the product being dried.
The innovation of the invention is that the invention breaks through the inertial thinking way of technicians in the field and provides a brand-new use way of the drying agent. According to the invention, the drying agent is mixed with the reactant before the polymerization reaction is started, so that the drying agent is used for removing trace water in the key monomer lactide of polylactic acid, and the efficiency of removing the trace water is improved. Then ring-opening polymerization is carried out to finally obtain the high molecular weight polylactic acid. In addition, the invention ensures that the polymerization reaction of the polylactic acid is not influenced by the participation of the drying agent and can also keep the physicochemical properties (such as heat resistance and the like) of the high molecular weight polylactic acid by controlling the selection of the type, the average particle size and the dosage of the drying agent.
In the present invention, the use of a trace amount of anhydrous drying agent can effectively remove trace amount of water generated during the neutralization of lactide, thereby forming crystalline hydrate with the drying agent. The partially absorbed water can not be removed at the reaction temperature, so that the ring-opening polymerization of the lactide initiated by trace amount of water can be effectively prevented; thereby ensuring that only a specific initiator initiates the ring-opening polymerization of lactide, effectively improving the molecular weight of polylactic acid and further improving the heat resistance of the polylactic acid; the quality control in the industrial production process of the polylactic acid is facilitated, and the performance difference of the polylactic acid caused by the existence of trace water in different batches is reduced.
Compared with the prior art, the invention has the beneficial effects that:
1. the invention applies a trace amount of anhydrous desiccant to the polymerization reaction process of polylactic acid, and can effectively improve the molecular weight of the polylactic acid.
2. The anhydrous desiccant provided by the invention is very small in usage amount and low in chemical activity, and cannot obviously influence the properties of polylactic acid products.
3. The invention adopts the commercialized anhydrous desiccant as the accelerant for improving the molecular weight of the polylactic acid, can adopt a mechanical stirring method for mixing, has simple process, low technical cost and no pollution, and can realize large-scale industrial production.
Detailed Description
The present invention is described in further detail below with reference to specific embodiments, but the scope of the invention as claimed is not limited to the scope expressed by the examples.
The raw materials used in the present invention are illustrated below: lactide was purchased from praac (Purac) in the netherlands; stannous octoate, stannous chloride, tetraisopropyl titanate, zinc oxide, lauryl alcohol, benzyl alcohol, ethylene glycol, glycerol, pentaerythritol, calcium sulfate, calcium chloride, magnesium sulfate, sodium sulfate, and aluminum oxide are all available from Sigma-Aldrich. The material and type of the polymerizer are not particularly limited, and may be purchased and used directly by a known method; the method for granulating the polylactic acid is not particularly limited, and a known method such as underwater granulation can be used.
In the invention, other auxiliary agents such as an antioxidant, an anti-hydrolysis agent, a nucleating agent and the like can be added according to actual needs in the polymerization process, but the invention is not particularly limited and can be directly purchased and used by adopting a known method.
The following examples are presented to enable those skilled in the art to more fully understand the present invention and are not intended to limit the invention in any way.
Example 1: preparation of PLLA1 samples
Firstly, lactide, stannous octoate 0.1% of the mass of the lactide, lauryl alcohol 0.1% of the mass of the lactide and anhydrous sodium sulfate 0.01% of the mass of the lactide are added into a polymerization kettle and are mechanically stirred and mixed, the average particle size of anhydrous sodium sulfate powder is 0.01 micron, the temperature of the polymerization kettle is raised to 60 ℃ under 50Pa, and the polymerization kettle is kept for 2 hours; and secondly, filling nitrogen into the polymerization kettle, keeping mechanical stirring, raising the temperature to 170 ℃, reacting for 2 hours, discharging materials from the bottom of the kettle, and granulating to obtain a high molecular weight polylactic acid PLLA1 sample.
Example 2: preparation of PLLA2 samples
Firstly, lactide, stannous octoate 0.1% of the mass of the lactide, lauryl alcohol 0.1% of the mass of the lactide and anhydrous sodium sulfate 0.05% of the mass of the lactide are added into a polymerization kettle and are mechanically stirred and mixed, the average particle size of anhydrous sodium sulfate powder is 0.01 micron, the temperature of the polymerization kettle is raised to 60 ℃ under 50Pa, and the polymerization kettle is kept for 2 hours; and secondly, filling nitrogen into the polymerization kettle, keeping mechanical stirring, raising the temperature to 170 ℃, reacting for 2 hours, discharging materials from the bottom of the kettle, and granulating to obtain a high molecular weight polylactic acid PLLA1 sample.
Example 3: preparation of PLLA3 samples
Firstly, lactide, stannous octoate 0.1% of the mass of the lactide, lauryl alcohol 0.1% of the mass of the lactide and anhydrous sodium sulfate 0.1% of the mass of the lactide are added into a polymerization kettle and are mechanically stirred and mixed, the average particle size of anhydrous sodium sulfate powder is 0.01 micron, the temperature of the polymerization kettle is raised to 60 ℃ under 50Pa, and the polymerization kettle is kept for 2 hours; and secondly, filling nitrogen into the polymerization kettle, keeping mechanical stirring, raising the temperature to 170 ℃, reacting for 2 hours, discharging materials from the bottom of the kettle, and granulating to obtain a high molecular weight polylactic acid PLLA3 sample.
Example 4: preparation of PLLA4 samples
Firstly, lactide, stannous octoate 0.1% of the mass of the lactide, lauryl alcohol 0.1% of the mass of the lactide and anhydrous sodium sulfate 0.1% of the mass of the lactide are added into a polymerization kettle and are mechanically stirred and mixed, the average particle size of anhydrous sodium sulfate powder is 1.0 micron, the temperature of the polymerization kettle is raised to 60 ℃ under 50Pa, and the polymerization kettle is kept for 2 hours; and secondly, filling nitrogen into the polymerization kettle, keeping mechanical stirring, raising the temperature to 170 ℃, reacting for 2 hours, discharging materials from the bottom of the kettle, and granulating to obtain a high molecular weight polylactic acid PLLA4 sample.
Example 5: preparation of PLLA5 samples
Firstly, lactide, stannous octoate 0.1% of the mass of the lactide, lauryl alcohol 0.1% of the mass of the lactide and anhydrous sodium sulfate 0.1% of the mass of the lactide are added into a polymerization kettle and mechanically stirred and mixed, wherein the average particle size of anhydrous sodium sulfate powder is 100 microns, the temperature of the polymerization kettle is raised to 60 ℃ under 50Pa, and the polymerization kettle is kept for 2 hours; and secondly, filling nitrogen into the polymerization kettle, keeping mechanical stirring, raising the temperature to 170 ℃, reacting for 2 hours, discharging materials from the bottom of the kettle, and granulating to obtain a high molecular weight polylactic acid PLLA5 sample.
Example 6: preparation of PLLA6 samples
Firstly, lactide, stannous octoate 0.1% of the mass of the lactide, lauryl alcohol 0.1% of the mass of the lactide and anhydrous sodium sulfate 0.1% of the mass of the lactide are added into a polymerization kettle and are mechanically stirred and mixed, the average particle size of anhydrous sodium sulfate powder is 0.1 micron, the temperature of the polymerization kettle is raised to 60 ℃ under 50Pa, and the polymerization kettle is kept for 2 hours; secondly, filling argon into the polymerization kettle, keeping mechanical stirring, raising the temperature to 170 ℃, reacting for 2 hours, discharging materials from the bottom of the kettle, and granulating to obtain a high molecular weight polylactic acid PLLA6 sample.
Example 7: preparation of PLL7 sample
Firstly, lactide, stannous octoate accounting for 0.1 percent of the mass of the lactide, lauryl alcohol accounting for 0.1 percent of the mass of the lactide and anhydrous calcium sulfate accounting for 0.1 percent of the mass of the lactide are added into a polymerization kettle to be mechanically stirred and mixed, the average particle size of the anhydrous calcium sulfate powder is 0.1 micron, the temperature of the polymerization kettle is raised to 60 ℃ under 50Pa, and the polymerization kettle is kept for 2 hours; secondly, filling argon into the polymerization kettle, keeping mechanical stirring, raising the temperature to 170 ℃, reacting for 2 hours, discharging materials from the bottom of the kettle, and granulating to obtain a high molecular weight polylactic acid PLLA7 sample.
Example 8: preparation of PLLA8 samples
Firstly, lactide, stannous octoate 0.1 percent of the mass of the lactide, lauryl alcohol 0.1 percent of the mass of the lactide and anhydrous magnesium sulfate 0.1 percent of the mass of the lactide are added into a polymerization kettle to be mechanically stirred and mixed, the average particle size of anhydrous magnesium sulfate powder is 0.1 micron, the temperature of the polymerization kettle is raised to 60 ℃ under 50Pa, and the polymerization kettle is kept for 2 hours; secondly, filling argon into the polymerization kettle, keeping mechanical stirring, raising the temperature to 170 ℃, reacting for 2 hours, discharging materials from the bottom of the kettle, and granulating to obtain a high molecular weight polylactic acid PLLA8 sample.
Example 9: preparation of PLLA9 samples
Firstly, lactide, tetraisopropyl titanate 0.1% of the mass of the lactide, ethylene glycol 0.1% of the mass of the lactide and anhydrous magnesium sulfate 0.1% of the mass of the lactide are added into a polymerization kettle and mechanically stirred and mixed, the average particle diameter of anhydrous magnesium sulfate powder is 0.1 micron, the temperature of the polymerization kettle is raised to 60 ℃ under 50Pa, and the polymerization kettle is kept for 2 hours; secondly, filling argon into the polymerization kettle, keeping mechanical stirring, raising the temperature to 170 ℃, reacting for 2 hours, discharging materials from the bottom of the kettle, and granulating to obtain a high molecular weight polylactic acid PLLA9 sample.
Example 10: preparation of PLLA10 samples
Firstly, lactide, zinc oxide accounting for 0.1 percent of the mass of the lactide, glycerol accounting for 0.1 percent of the mass of the lactide and anhydrous magnesium sulfate accounting for 0.1 percent of the mass of the lactide are added into a polymerization kettle to be mechanically stirred and mixed, the average particle size of magnesium sulfate powder is 0.1 micron, the temperature of the polymerization kettle is raised to 60 ℃ under 50Pa, and the mixture is kept for 2 hours; secondly, filling argon into the polymerization kettle, keeping mechanical stirring, raising the temperature to 170 ℃, reacting for 2 hours, discharging materials from the bottom of the kettle, and granulating to obtain a high molecular weight polylactic acid PLLA10 sample.
Example 11: preparation of PLLA11 samples
Firstly, lactide, stannous chloride accounting for 0.01 percent of the mass of the lactide, pentaerythritol accounting for 0.01 percent of the mass of the lactide and anhydrous calcium chloride accounting for 0.05 percent of the mass of the lactide are added into a polymerization kettle to be mechanically stirred and mixed, the average particle size of anhydrous calcium chloride powder is 1 micron, the temperature of the polymerization kettle is raised to 40 ℃ under 100Pa, and the polymerization kettle is kept for 0.5 hour; and secondly, filling nitrogen into the polymerization kettle, keeping mechanical stirring, raising the temperature to 190 ℃, reacting for 0.5h, discharging materials from the bottom of the kettle, and granulating to obtain a high molecular weight polylactic acid PLLA11 sample.
Example 12: preparation of PLLA12 samples
Firstly, lactide, stannous chloride accounting for 1 percent of the mass of the lactide, benzyl alcohol accounting for 1 percent of the mass of the lactide and anhydrous aluminum oxide accounting for 0.05 percent of the mass of the lactide are added into a polymerization kettle to be mechanically stirred and mixed, the average particle size of the anhydrous aluminum oxide powder is 100 microns, the temperature of the polymerization kettle is raised to 80 ℃ under 200Pa, and the temperature is kept for 1.0 hour; and secondly, filling nitrogen into the polymerization kettle, keeping mechanical stirring, raising the temperature to 210 ℃, reacting for 4.0h, discharging materials from the bottom of the kettle, and granulating to obtain a high molecular weight polylactic acid PLLA12 sample.
Comparative example 1: preparation of PLLA01 samples
Firstly, lactide, stannous octoate which accounts for 0.1 percent of the mass of the lactide and lauryl alcohol which accounts for 0.1 percent of the mass of the lactide are added into a polymerization kettle to be mechanically stirred and mixed, the temperature of the polymerization kettle is raised to 60 ℃ under 50Pa, and the polymerization kettle is kept for 2 hours; and secondly, filling nitrogen into the polymerization kettle, keeping mechanical stirring, raising the temperature to 170 ℃, reacting for 2 hours, discharging materials from the bottom of the kettle, and granulating to obtain a high molecular weight polylactic acid PLLA01 sample.
Testing of molecular weight:
the Gel Permeation Chromatography (GPC) test was carried out at 30 ℃ with tetrahydrofuran as the mobile phase and at a flow rate of 1.0mL/min, using polystyrene as the calibration standard. MnIs the number average molecular weight, MwIs the weight average molecular weight.
Testing of heat resistance:
and testing by using a thermogravimetric analyzer (TGA), wherein the testing temperature is 50-600 ℃, and the heating rate is 10 ℃/min.
TABLE 1 molecular weight (M) of polylactic acid prepared in comparative example 1 and examples 1 to 12nAnd Mw) Molecular weight distribution (PDI) and thermal degradation temperature
| Mn(kg/mol) | Mw(kg/mol) | PDI | Thermal degradation temperature (. degree.C.) | |
| Comparative example 1 | 96 | 203 | 2.11 | 264.2 |
| Example 1 | 120 | 208 | 1.73 | 271.3 |
| Example 2 | 139 | 211 | 1.52 | 275.8 |
| Example 3 | 137 | 208 | 1.52 | 275.4 |
| Example 4 | 121 | 208 | 1.72 | 271.6 |
| Example 5 | 102 | 200 | 1.96 | 265.3 |
| Example 6 | 137 | 205 | 1.50 | 275.1 |
| Example 7 | 131 | 202 | 1.54 | 274.3 |
| Example 8 | 134 | 210 | 1.57 | 274.8 |
| Example 9 | 63 | 103 | 1.64 | 246.1 |
| Example 10 | 34 | 63 | 1.85 | 225.3 |
| Example 11 | 48 | 83 | 1.73 | 231.4 |
| Example 12 | 2.8 | 4.6 | 1.64 | 193.8 |
Table 1 shows the statistics of the molecular weights (M) of the polylactic acids prepared in comparative example 1 and examples 1 to 12nAnd Mw) And molecular weight distribution (PDI). Comparing the molecular weight and the molecular weight distribution of comparative example 1 and examples 1 to 3, it can be seen that the addition of the desiccant anhydrous sodium sulfate powder can significantly increase the molecular weight of the polylactic acid and decrease the molecular weight distribution. For example, the number average molecular weight of example 2 is about 4 ten thousand higher than that of comparative example 1, and the increase is more than 40%, and the molecular weight distribution is reduced from 2.11 of comparative example 1 to 1.52 of example 2, and the reduction is nearly 30%. As can be seen from comparative example 1 and examples 1 and 2, when the content of the desiccant anhydrous sodium sulfate powder was increased from 0 to 0.05%, the molecular weight of polylactic acid was significantly increased, indicating that the addition of the desiccant facilitates the removal of trace amounts of water in the polymerization kettle and in the lactide monomer; when the content of the anhydrous sodium sulfate powder is more than 0.05%, the molecular weight of the polylactic acid is basically kept unchanged, indicating that the molecular weight of the polylactic acid cannot be further increased by adding excessive drying agent. Therefore, the best experimental effect can be achieved when the addition amount of the drying agent is 0.05% of the mass of the lactide monomer. Comparative examples 3 to 5 show that the average particle size of the desiccant powder also has a certain influence on the molecular weight of the final polylactic acid: when the average particle diameter of the desiccant powder is smaller, the specific surface area is larger, more water molecules can be effectively absorbed, and the molecular weight of the polylactic acid is increased. It is clear from comparative examples 6 to 8 that the types of the drying agents, such as sodium sulfate, calcium sulfate, magnesium sulfate, etc., do not greatly affect the final molecular weight and molecular weight distribution of the polylactic acid when a sufficient amount of the drying agent is added. Comparing comparative example 1 with examples 1 to 12, it can be seen that the higher the molecular weight of the polylactic acid, the better the heat resistance, and the higher the thermal degradation temperature, which indicates that the addition of the drying agent does not have an obvious effect on the heat resistance of the polylactic acid. Further comparing comparative example 1 with example 5, the polylactic acid prepared by the two methods has similar molecular weight (96 and 102kg/mol, respectively) and the heat resistant temperature of the two methods is basically the same (264 and 265 deg.C, respectively), which also shows that the addition of drying does not have obvious influence on the heat resistant performance of the polylactic acid.
Comparing examples 3 and 6, it is understood that the types of the shielding gases, i.e., nitrogen and argon, have substantially no influence on the molecular weight of the polylactic acid. As can be seen from comparative examples 8 to 10, the kind of catalyst has a certain influence on the molecular weight of polylactic acid, and stannous octoate has the best catalytic effect in the present invention. In addition, the molecular weight of the polylactic acid in examples 11 and 12 is much lower than that in comparative example 1 and examples 1 to 10, because pentaerythritol contains more hydroxyl groups and has more initiation sites, which results in the decrease of the molecular weight, while in example 12, the initiator plays a leading role in controlling the molecular weight of the polylactic acid due to the addition of more initiator, which results in the negligible effect of trace amount of water on the molecular weight of the polylactic acid.
Finally, it should be noted that the above-mentioned list is only a specific embodiment of the present invention. It is obvious that the present invention is not limited to the above embodiments, but many variations are possible. All modifications which can be derived or suggested by a person skilled in the art from the disclosure of the present invention are to be considered within the scope of the invention.
Claims (8)
1. A method for improving the molecular weight of polylactic acid based on in-situ drying dehydration is characterized by comprising the following steps:
(1) adding lactide, a catalyst, an initiator and desiccant powder into a polymerization kettle, and mechanically stirring and uniformly mixing; the drying agent is anhydrous calcium salt, sodium salt or aluminum oxide, and the mass of the drying agent accounts for 0.01-0.1% of that of the lactide;
(2) under the condition of 50-200 Pa, raising the temperature of the polymerization kettle to 40-80 ℃, and keeping for 0.5-2 h;
(3) filling inert gas as protective gas into the polymerization kettle, and keeping mechanical stirring; raising the temperature to 170-210 ℃, and reacting for 0.5-4 h; and discharging from the bottom of the kettle and granulating to obtain the high molecular weight polylactic acid.
2. The method of claim 1, wherein the desiccant is one of anhydrous calcium sulfate, anhydrous calcium chloride, anhydrous magnesium sulfate, anhydrous sodium sulfate, and anhydrous alumina.
3. The method according to claim 1, wherein the desiccant powder has an average particle size of between 0.01 and 100 microns.
4. The method according to any one of claims 1 to 3, wherein the catalyst is one of a tin-based catalyst, a titanium-based catalyst, or a zinc-based catalyst, and accounts for 0.01 to 1% by mass of the lactide.
5. The method of claim 4, wherein the catalyst is one of stannous octoate, stannous chloride, tetraisopropyl titanate, or zinc oxide.
6. The method according to any one of claims 1 to 3, wherein the initiator is an alcohol and accounts for 0.01 to 1% of the mass of the lactide.
7. The method of claim 6, wherein the initiator is one of lauryl alcohol, benzyl alcohol, ethylene glycol, glycerol, or pentaerythritol.
8. A method according to any one of claims 1 to 3, wherein the inert gas is nitrogen or argon.
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| CN1594393A (en) * | 2004-07-15 | 2005-03-16 | 合肥工业大学 | Method for preparing high molecular weight poly-L-lactic acid by melt polycondensation-solid phase polymerization |
| CN101402723A (en) * | 2008-09-15 | 2009-04-08 | 青岛生物能源与过程研究所 | Method for preparing high molecular weight poly lactic acid by direct polycondensation |
| CN101735429A (en) * | 2009-12-29 | 2010-06-16 | 江西省科院生物技术有限责任公司 | Melt polycondensation method for preparing high molecular weight polylactic acid |
| CN108285528A (en) * | 2018-03-08 | 2018-07-17 | 深圳市迈启生物材料有限公司 | A kind of preparation method of the medical polylactic acid of super high molecular weight |
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