CN101538359B - Method for preparing high molecular weight branched polylactic acid by molten polymerization - Google Patents

Abstract

The invention relates to a method for preparing high-molecular-weight branched polylactic acid by melt polymerization. The method uses polyolefin containing multiple epoxy groups or fatty acid containing epoxy groups to copolymerize with lactic acid to obtain high-molecular-weight branched polylactic acid. The preparation process of the polylactic acid is simple, the reaction period is short, the side reaction is low, the yield is high, the cost is low, the quality of the obtained polylactic acid is good, and the polylactic acid can be used in many fields as an environment-friendly general plastic.

Description

A method for preparing high molecular weight branched polylactic acid by melt polymerization

technical field

The invention belongs to the technical field of polymer materials, and in particular relates to a method for preparing high-molecular-weight branched polylactic acid by melt polymerization.

Background technique

Plastic has gradually developed into a material widely used in various fields, however, due to the non-degradability of plastic, it poses a serious threat to the ecosystem of the world. In addition, plastics are mainly derived from petroleum non-renewable resources, and the extensive use of plastics will inevitably cause serious energy and human survival crises. Therefore, under the circumstances that the supply of global oil resources is becoming increasingly tense, and the environmental protection problems caused by synthetic plastics that use oil as raw materials are becoming more and more prominent, there has been an upsurge in the study of biodegradable plastics worldwide. Among many biodegradable polymers, polylactic acid has suddenly emerged, and has won people's attention and favor for its excellent mechanical properties and wide application fields. Polylactic acid is the most typical biodegradable plastic in the aliphatic family. It can be completely decomposed into water and carbon dioxide under the action of microorganisms in nature, so it has no harm to the environment and overcomes the biggest drawback of chemical plastics. In addition, polylactic acid is derived from renewable resources (such as starch, cellulose, etc.), so it can reduce the consumption of non-renewable resources, thereby alleviating the crisis of human resources.

There are two ways to synthesize polylactic acid. One is to obtain it through ring-opening polymerization of lactide (lactic acid cyclic dimer). The polylactic acid synthesized by this method has high molecular weight, small dispersion coefficient and excellent physical properties, but The preparation process of lactide is complex and requires high purity during polymerization, so that the production cost remains high. Therefore, polylactic acid synthesized by this method cannot be widely used as ordinary plastics. Polylactic acid can also be prepared by the direct polycondensation method of lactic acid, but due to the following balance in the direct polycondensation process of lactic acid:

Therefore, the molecular weight of polylactic acid obtained by direct polymerization is low,

In order to increase the molecular weight of the direct polymerization product of lactic acid, the following approaches are mainly adopted at present: as mentioned in the patent CN1563138, the low molecular weight lactic acid polycondensation product is first synthesized, and then chain extension such as polybasic acid, polyalcohol, polyisocyanate, etc. is applied. However, due to the direct The condensation polymer formed by condensation polymerization has complex components, including small molecular oligomers, lactic acid and lactide monomers, etc. During the chain extension process, the chain extender will first react with small molecular products. Chain dosage. In patent CN1616515, high-molecular-weight polylactic acid is prepared by melting polycondensation-solid-state polymerization. This method is only suitable for L-type lactic acid, and because the prepolymer needs to be crystallized-pulverized-solid-phase polymerization process in the process, it does not Conducive to continuous large-scale production requirements, and the reaction cycle is longer. In the patent US5310865, the azeotropic dehydration solution of an organic solvent is used to polymerize polylactic acid. Due to the use of a large amount of organic solvent, the difficulty of the production process and the production cost are increased. The key to the direct polymerization method is to effectively eliminate the water generated in the reaction and reduce the side reaction of polymer cracking to generate lactide during high temperature and high vacuum polymerization.

Contents of the invention

The purpose of the present invention is to provide a method for preparing high-molecular-weight branched polylactic acid by melt polymerization, which overcomes the defects of low molecular weight and poor quality when synthesizing polylactic acid by the existing melt method.

The preparation method of the high molecular weight branched polylactic acid that the present invention proposes, concrete method comprises the following steps:

1. Raw material lactic acid dehydration:

At a temperature of 70-100°C and a vacuum of 5-30KPa, mechanically stir to remove the moisture in the lactic acid; the lactic acid is D, L-lactic acid or L-lactic acid;

2. Prepolymerization

Add 0.1-3.0wt% of branching agent to the dehydrated lactic acid according to the mass percentage, after mixing, raise the temperature to 140-160°C and polymerize for 4-5h under the pressure of 5-10Kp to obtain a lactic acid molecule with a degree of polymerization of about 8 lactic acid molecules. Prepolymer;

3. Add catalyst, melt polymerization

Add 0.3-1.0wt% catalyst to the prepolymer, polymerize at 160-180°C, 5-10Kpa, pressure and vacuum for 10-20 hours, and directly obtain polylactic acid with a weight-average molecular weight of 150,000-200,000 ; or further add 0.1-3.0wt% branching agent by weight of the prepolymer, continue to react for 1-5 hours, and perform chain extension to obtain high-molecular-weight polylactic acid;

The catalyst is one of stannous octoate, stannous chloride, p-toluenesulfonic acid, antimony trioxide, butyl titanate, lanthanum-titanium composite catalyst or a mixture thereof;

Said branching agent is fatty acid containing epoxy group, low molecular weight polyolefin containing epoxy group, including BASF's ADR-4368, ADR-4370, epoxidized soybean oil and the like.

It can be seen from the technical scheme disclosed above that the process for preparing polylactic acid in the present invention is simple, the reaction cycle is short, the side reaction is low, the yield is high, the cost is low, and the quality of the obtained polylactic acid is good. As an environmentally friendly general plastic Can be applied in many fields.

Detailed ways

Example 1

Take by weighing 100g L-lactic acid (lactic acid content is greater than 85%) in the three-neck bottle of 250ml, remove the moisture in lactic acid under 15KPa, 80 ℃ of temperature, then add 0.25wt% ADR-4370 (German BASF company product), stir and mix After uniformity, the temperature was raised to 140°C, and the decondensation water was continued for 5 hours to obtain a prepolymer with an average degree of polymerization of about 8 lactic acid molecules. Then add 0.5wt% stannous octoate, raise the temperature to 180° C., and react for 20 hours under vacuum conditions with a pressure of 5 KPa to obtain 50 g of polylactic acid with a weight average molecular weight of 63,280.

Example 2

Weigh 100g D, L-lactic acid (the content of lactic acid is greater than 85%) in a 250ml three-necked bottle, remove the moisture in the lactic acid at 15KPa and 80°C, then add 0.5wt% ADR-4370 and mix well, and raise the temperature to At 140°C, continue to decondense the water for 5 hours to obtain a prepolymer with an average degree of polymerization of about 8 lactic acid molecules. Add 0.4wt% stannous chloride and p-toluenesulfonic acid in equal amount, raise the temperature to 180°C, and react for 20h under vacuum conditions with a pressure of 5KPa to obtain 56g of polylactic acid with a weight average molecular weight of 113,500.

Example 3

Weigh 100g of L-lactic acid (the content of lactic acid is greater than 85%) in a 250ml three-neck bottle, remove the moisture in the lactic acid at 15KPa and 80°C, then add 0.75wt% ADR-4370 and mix well, and raise the temperature to 140 °C, continue to decondense the water for 4-5 hours to obtain a prepolymer with an average degree of polymerization of about 8 lactic acid molecules. Add 0.5wt% stannous octoate, raise the temperature to 180° C., and react for 15 hours under vacuum conditions with a pressure of 5 KPa to obtain 55 g of polylactic acid with a weight average molecular weight of 179,700.

Example 4

Weigh 100g of D, L-lactic acid (the content of lactic acid is greater than 85%) in a 250ml three-necked bottle, remove the moisture in the lactic acid at 15KPa and 80°C, then add 1.0wt% ADR-4368 and stir to mix evenly. At 140°C, continue to decondense water for 4 hours to obtain a prepolymer with an average degree of polymerization of about 8 lactic acid molecules. Add 0.4wt% stannous chloride and p-toluenesulfonic acid of equal substance, raise the temperature to 180°C, and react for 15h under vacuum conditions with a pressure of 5KPa to obtain 52g of polylactic acid with a weight average molecular weight of 165,300.

Example 5

Weigh 100g of L-lactic acid (the lactic acid content is greater than 85%) in a 250ml three-necked bottle, remove the moisture in the lactic acid at 15KPa and 80°C, then add 1.0wt% epoxidized soybean oil, and raise the temperature to 140°C , Continue to decondense the water for 5 hours to obtain a prepolymer with an average degree of polymerization of about 8 lactic acid molecules. Add 0.5wt% stannous octoate, raise the temperature to 180° C., and react for 20 hours under vacuum conditions with a pressure of 5 KPa to obtain 57 g of polylactic acid with a weight average molecular weight of 145,800.

Example 6

Take by weighing 100g D, L-lactic acid (lactic acid content is greater than 85%) in the three-neck bottle of 250ml, remove the moisture in the lactic acid under 15KPa, 80 ℃ of temperature, add 1.0wt% epoxidized soybean oil then, temperature rises to At 140°C, continue to decondense water for 4 hours to obtain a prepolymer with an average degree of polymerization of about 8 lactic acid molecules. Add 0.4wt% stannous chloride and p-toluenesulfonic acid in equivalent amount, raise the temperature to 180°C, and react for 20h under vacuum conditions with a pressure of 5KPa to obtain 53g of polylactic acid with a weight average molecular weight of 152,300.

Example 7

Weigh 100g of L-lactic acid (the content of lactic acid is greater than 85%) in a 250ml three-neck bottle, remove the moisture in the lactic acid at 15KPa and 80°C, then add 0.3wt% of ADR-4370, and raise the temperature to 140°C, Continue to decondense the water for 5 hours to obtain a prepolymer with an average degree of polymerization of about 8 lactic acid molecules. Add 0.4wt% stannous chloride and p-toluenesulfonic acid of the same amount, raise the temperature to 180°C, and react for 20h under vacuum conditions with a pressure of 5KPa, and then add 0.4wt% ADR-4370 to the reaction system , and continued to react at 180° C. for 2 h under a vacuum condition of 5 KPa. 55 g of branched polylactic acid having a weight average molecular weight of 2,345,000 was obtained.

Example 8

Weigh 100g of L-lactic acid (the content of lactic acid is greater than 85%) in a 250ml three-necked bottle, remove the moisture in the lactic acid at 15KPa and 80°C, then add 1.0wt% epoxy soybean oil, and raise the temperature to 140°C , Continue to decondense the water for 5 hours to obtain a prepolymer with an average degree of polymerization of about 8 lactic acid molecules. Add 0.5wt% antimony trioxide, raise the temperature to 180°C, and react for 20h under the vacuum condition of pressure 5KPa, then add 1.0wt% epoxidized soybean oil to the reaction system, continue at 180°C, 5KPa Reaction under vacuum conditions for 3h. 56 g of branched polylactic acid having a weight average molecular weight of 2,132,000 were obtained.

Example 9

Weigh 100g of L-lactic acid (the content of lactic acid is greater than 85%) in a 250ml three-necked bottle, remove the moisture in the lactic acid at 15KPa and 80°C, then add 1.0wt% epoxidized soybean oil, and raise the temperature to 140°C °C, continue to decondense the water for 5 hours to obtain a prepolymer with an average degree of polymerization of about 8 lactic acid molecules. Add 0.4wt% tin protochloride and the p-toluenesulfonic acid of equivalent substance amount, temperature is raised to 180 ℃, under the vacuum condition of pressure 5KPa, react 20h, then add 1.0wt% epoxy resin in the reaction system Soybean oil was continued to react for 3 hours at 180° C. under a vacuum condition of 5KPa. 53 g of branched polylactic acid with a weight average molecular weight of 122.100 was obtained.

Example 10

Weigh 100g of L-lactic acid (the content of lactic acid is greater than 85%) in a 250ml three-necked bottle, remove the moisture in the lactic acid at 15KPa and 70°C, then add 0.8wt% epoxy soybean oil, and raise the temperature to 140°C , Continue to decondense the water for 4 hours to obtain a prepolymer with an average degree of polymerization of about 8 lactic acid molecules. Add 0.5wt% butyl titanate, raise the temperature to 180°C, and react for 25h under a vacuum condition of 5KPa, and then add 1.0wt% epoxy soybean oil to the reaction system, and continue to heat at 180°C, 5KPa Reaction under vacuum conditions for 5h. 54 g of branched polylactic acid having a weight average molecular weight of 1,438,000 was obtained.

Comparative experiment 1

Weigh 100g of L-lactic acid (the content of lactic acid is greater than 85%) in a 250ml three-necked bottle, remove the moisture in the lactic acid at 15KPa and 80°C, then raise the temperature to 140°C, and continue to decondense the water for 5 hours to obtain the average polymerization A prepolymer with a density of 8 lactic acid molecules. Add 0.4wt% stannous chloride and p-toluenesulfonic acid in equal amount, raise the temperature to 180°C, and react for 20h under vacuum conditions with a pressure of 5KPa to obtain 42g of polylactic acid with a weight average molecular weight of 34,500.

Through comparative experiments, it can be found that under the same experimental conditions, adding a branching agent can significantly increase the molecular weight of polylactic acid, and the yield has increased.

Claims (1)

1. the method for a preparing high molecular weight branched polylactic acid by molten polymerization is characterized in that, may further comprise the steps:

(1) material acid dehydration:

Under 70～100 ℃ of temperature, under the vacuum condition of 5～30KPa pressure, mechanical stirring is removed the moisture in the lactic acid; Described lactic acid is D, L-lactic acid or L-lactic acid;

(2) pre-polymerization

Add branching agent 0.1～3.0wt% by mass percentage in the lactic acid after the dehydration, behind the mixing, be warmed up to polymerization 4-5h under 140～160 ℃, 5～10Kp pressure, obtaining the polymerization degree is the performed polymer of 8 lactic acid molecules;

(3) add catalyzer, melt polymerization

The catalyzer that in performed polymer, adds performed polymer weight 0.3～1.0wt%, at 160～180 ℃, 5～10Kpa, polymerization 10～20h under the pressure vacuum state directly obtains weight-average molecular weight in 15～200,000 poly(lactic acid);

The branching agent that adopts in the described step (2) is the ADR-4368 of BASF AG, ADR-4370 or epoxidised soybean oil;

Described catalyzer is a kind of in stannous octoate, tin protochloride, tosic acid, antimonous oxide, the butyl (tetra) titanate or their mixture.