RU2467029C1 - Method of obtaining biodegradable polyesters - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: claimed invention relates to method of obtaining biodegradable complex polyesters based on hydroxycarboxylic acids, used as polymers of household purpose. Method lies in direct polycondensation of one or several hydroxycarboxylic acids or their mixture with aliphatic dicarboxylic acids and dioles or diamines at higher temperature and normal pressure in presence of titanium tetrabutoxide. Removal of waste products of polycondensation is carried out at 180-200°C applying as exsiccant zeolites, which are introduced directly into reaction medium.

EFFECT: method makes it possible to obtain biodegradable polyesters based on hydroxycarboxylic acids with high molecular weight at relatively low temperatures of synthesis and normal pressure.

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Description

The invention relates to a method for producing biodegradable polyesters based on renewable plant materials from one or more hydroxycarboxylic acids or a mixture of these acids with aliphatic dicarboxylic acids and diols or diamines. These polymers can be used as polymers for domestic use.

Hydroxycarboxylic acid biodegradable polyesters are typically prepared by catalytic polymerization of cyclic dimers of these acids, for example, lactide or glycolide. The method of direct polycondensation of hydroxycarboxylic acids to produce high molecular weight polyesters is associated with the difficulty of removing water from the reaction medium, as well as with depolymerization processes leading to the formation of low molecular weight hydroxyacid oligomers. Various methods are proposed for increasing the molecular weight of low molecular weight polycondensation products of hydroxycarboxylic acids: the use of various peroxides or diisocyanates as crosslinking agents or chain extenders (EP 2184307); azeotropic distillation of water and other by-products with a solvent; solid state polycondensation using vacuum and special design reactors (JP 6298914), extruder reactors (JP 8143649); use of high vacuum and temperatures (JP 10204156); or various combinations of these methods.

A method of increasing the molecular weight of low molecular weight hydroxyacid based polyesters is widely presented in the patent literature, for example EP 2184307, CN 1927911, RU 2008139288, and consists in adding peroxides or diisocyanates to low molecular weight oligomers. The disadvantage of this method is the potential toxicity of the compounds used for crosslinking and lengthening polymer chains.

US Pat. No. 5,310,865 describes a method for producing polyhydroxyacids using azeotropic distillation of by-products with a solvent under reduced pressure (30-12 mm Hg) and temperatures of 130-170 ° C with circulation of the solvent through zeolites to effectively remove water. According to this patent, polyhydroxy acids with characteristic viscosities of more than 0.4 dl / g and molecular weights of more than 50,000 Da can be obtained.

Significant disadvantages of this method are the use of high-boiling solvents, including aromatic compounds - acetophenone, anisole, thioanisole, methoxytoluene, the removal of which from polyester requires additional purification by reprecipitation from large volumes of solvent, followed by continuous drying of the polyester in vacuo (5 mmHg); significant loss of polymer during its forced cleaning; large quantities (up to two masses of reagents used) of irrevocably used zeolites; the use of vacuum (40-13 mm Hg) with azeotropic removal of water; a large total duration (more than 55 hours) of polycondensation to obtain a polymer with a high molecular weight.

A known method of producing polylactic acid using an extruder reactor of a special design (JP 8143649, C08G 63/78), which uses a vacuum of 0.1-100 mm Hg and a temperature of 90-130 ° C to remove water and low molecular weight products. According to this patent, the resulting polyesters have a weight average molecular weight of 30,000-100,000 Da. The main disadvantages of this method are the low polycondensation reaction rates due to low reaction temperatures and the use of high vacuum at certain stages of the synthesis, as well as the need for reactors of a special design.

The preparation of polyhydroxyacids with a weight average molecular weight of 50,000-300,000 Da in the method of JP 10204156, C08G 63/06 is based on polycondensation at temperatures up to 250 ° C and high vacuum in the presence of aluminum silicate and alkali metal compounds. The disadvantage of this method is the high vacuum and high temperatures, leading to darkening of the polymer and the formation of large quantities of by-products due to thermal degradation of the polymer.

The invention solves the problem of developing a method for producing biodegradable polyesters with a high molecular weight based on hydroxycarboxylic acids by direct polycondensation without the use of vacuum, solvents, special design reactors, at relatively low synthesis temperatures and suitable for use as polymer materials for domestic use.

The problem is solved by the method of producing biodegradable polyesters based on hydroxycarboxylic acids by direct polycondensation of one or more hydroxycarboxylic acids or a mixture of these acids with aliphatic dicarboxylic acids and diols or diamines using or without using a chain extender at elevated temperature in the presence of one titanium tetrabutoxide catalyst, the method is carried out at normal pressure, the removal of by-products of polycondensation is carried out by a stream of inert gas at a rate a temperature of 180-200 ° C, a desiccant - zeolites are introduced directly into the reaction medium.

A significant increase in the molecular weight of polymers is achieved by introducing a small (7-10 wt.% Of the mass of hydroxycarboxylic acid used) amount of desiccant — zeolites directly into the reaction medium after obtaining a low molecular weight polymer and removing the main amount of water formed. The process can be carried out at a temperature of 180-200 ° C and normal pressure.

The invention is illustrated by the following examples.

Example 1

In a 150 ml glass reactor equipped with a mechanical stirrer, an inert gas inlet and a reflux condenser, 30 g of 90% L-lactic acid and 0.081 g of titanium tetrabutoxide are introduced under nitrogen atmosphere. The reaction medium is heated to 150 ° C and kept under stirring for 1.5 hours under reflux with a small stream of nitrogen. Then the temperature is raised to 180 ° C and the water formed is distilled off by purging the reactor with nitrogen at a volume rate of 0.5 l / min for 5 hours. After that, 2.0 g of NaX zeolites are loaded into the reactor and the reaction medium is kept at 200 ° C for 12 hours. blowing the reactor with an inert gas with a volumetric flow rate of 0.5 l / min. The intrinsic viscosity of the obtained polymer is 0.45 dl / g, and the weight average molecular weight is 50,000 Da.

Example 2

The process of example 1 is repeated using a mixture of 22 g of 90% L-lactic acid and 8.3 g of 67% glycolic acid, 0.078 g of titanium tetrabutoxide is introduced as a catalyst. The resulting polymer has an intrinsic viscosity of 0.46 dl / g.

Example 3

In a 150 ml glass reactor equipped with a mechanical stirrer, an inert gas inlet and a reflux condenser, 24.2 g of 90% L-lactic acid and 2.355 g of adipic acid are introduced under nitrogen atmosphere. The reaction medium is heated to 150 ° C and kept under stirring for 1.5 hours under reflux with a small stream of nitrogen. Then, the temperature is raised to 180 ° C and the resulting water is distilled off by purging the reactor with nitrogen at a volume rate of 0.5 l / min for 5 hours. After that, 1.45 g of 2,3-butanediol and 0.09 g of titanium tetrabutoxide are loaded into the reactor and the reaction mixture is kept at 1.5 h under reflux with a small stream of nitrogen (30 ml / min). Then, the water formed during the interaction of the reagents is distilled off with a stream of nitrogen (0.5 L / min) for 5 hours. After that, 1.87 g of NaX zeolites are loaded into the reactor and the reaction medium is kept for 12 hours at a temperature of 200 ° С and a volumetric flow rate of nitrogen - 0.5 l / min.

The intrinsic viscosity of the obtained polymer was 0.45 dl / g.

Example 4

The process of Example 3 is repeated using 24.2 g of L-lactic acid, 2.355 g of adipic acid, 1.44 g of 1,4-butanediol, 0.078 g of titanium tetrabutoxide and 2.2 g of NaX zeolites.

The crude polymer has an intrinsic viscosity of 0.49 dl / g.

Example 5

The process of Example 3 is repeated using 24.2 g of L-lactic acid, 2.355 g of adipic acid, 1.86 g of 1,6-hexanediamine, 0.091 g of titanium tetrabutoxide and 2.2 g of NaX zeolites.

The intrinsic viscosity of the polymer is 0.63 dl / g.

Example 6

The process of Example 3 is repeated using 24.2 g of L-lactic acid, 1.77 g of adipic acid, 1.09 g of 2,3-butanediol and 0.08 g of titanium tetrabutoxide.

The intrinsic viscosity of the resulting polymer is 0.43 dl / g.

Example 7

The process of example 3 is repeated, and after completion of exposure at 200 ° C, 0.077 g of methylenedi-para-phenyl diisocyanate is introduced and the reaction medium is maintained for 1 hour.

The intrinsic viscosity of the polymer is 0.89 dl / g.

Examples 8-10 are given for comparison.

Example 8

The process of example 1 is repeated without the use of zeolites. The resulting polymer has an intrinsic viscosity of 0.17 dl / g.

Example 9

The process of example 3 is repeated, carrying out dehydration with zeolites at 180 ° C instead of 200 ° C.

The resulting polymer has an intrinsic viscosity of 0.37 dl / g.

Example 10

The process of comparative example 9 is repeated without the use of zeolites. The resulting polymer has an intrinsic viscosity of 0.12 dl / g.

Thus, as can be seen from the above examples, the proposed method of introducing a desiccant directly into the reaction medium allows to obtain polyesters of various compositions and high molecular weights based on hydroxyacids at relatively low synthesis temperatures and normal pressure.

Claims (1)

A method for producing biodegradable hydroxycarboxylic acid polyesters by direct polycondensation of one or more hydroxycarboxylic acids or a mixture of these acids with aliphatic dicarboxylic acids and diols or diamines with or without using a chain extender at elevated temperature in the presence of one catalyst - titanium tetrabutoxide, characterized in that the method is carried out at normal pressure, the removal of by-products of polycondensation is carried out by a stream of inert gas at t temperature 180-200 ° С, desiccant - zeolites are introduced directly into the reaction medium.