DE102024121056A1 - Process for the production of highly linear and controlled branched polybutylene succinate - Google Patents

Abstract

The present invention relates to a process for producing highly linear and controlled branched polybutylene succinate, a highly linear polybutylene succinate and the use of multifunctional comonomers for adjusting the degree of branching in polybutylene succinate.

Description

Technical field

The present invention relates to a process for producing highly linear and controlled branched polybutylene succinate, a highly linear polybutylene succinate and the use of multifunctional comonomers to adjust the degree of branching in polybutylene succinate.

Technical background

Polybutylene succinate (PBS) is an aliphatic polyester and is classified as a synthetic polymer (colloquially known as a plastic). Starting from its monomers succinic acid (succinate) and 1,4-butanediol, polymer chains with ester bonds along the main chain are formed through polycondensation. Polyesters are produced by polymerization or polycondensation. Both processes involve linking monomeric building blocks to form polymer chains of varying lengths. These macromolecules can be linear, branched, or circular.

PBS is produced by polycondensation. The degree of polymerization, and thus the chain lengths, can be variably adjusted. Depending on the average chain length, a polymer with different molecular weights is obtained. The most widespread synthesis methods are two-step processes in which succinic acid is first esterified with 1,4-butanediol to form oligomers, and these oligomer-esters are then converted into high-molecular-weight polymers by catalyzed transesterification.

However, during the production of PBS, side reactions typically occur that affect the chain structure of the PBS. If the polycondensation phase is carried out in process engineering setups, autoclaves, or reactors with stirring systems, in which the increasingly viscous polymer melt is necessarily mixed and exposed to influences favorable to branching reactions, branching reactions are induced that lead to the loss of the linear chain structure and the accumulation of molar mass (autobranching).

The branching reactions occur uncontrollably, thus precluding the production of well-defined chain structures. Controlling the degree of branching through the defined addition of multifunctional monomers or comonomers becomes impossible, as these branches overlap with the process-induced branching.

The occurrence of branching reactions can be demonstrated via rheological measurements. The altered flow behavior of branched compared to linear polymers is visible both in the extent of the observed shear thinning and in the van Gurp-Palmen plot, which plots the phase angle against the complex modulus. Commercial PBS types exhibit the typical flow behavior that differs from that of linear polymers.

The observed behavior is caused by thermally generated terminal double bonds, which in turn induced branching reactions following a radical mechanism. These terminal double bonds, or their reaction products in the polymer, can be detected by ^1H NMR and are present in commercially available PBS types.

The chain structure and the resulting rheological properties, or flow behavior, of the polymer melts play a crucial role in almost all processing methods for thermoplastics. For certain processing methods, such as injection molding of thin-walled parts or the production of fibers by melt spinning, the avoidance of uncontrolled branching is essential.

A method that prevents process-induced branching-generating side reactions would therefore be advantageous. Furthermore, it would be advantageous to be able to selectively generate branches to the desired extent for the processing method, instead of uncontrolled branching reactions. A method that can meet both requirements by adding only one monomer or comonomer during synthesis would be particularly preferred.

A suitable method has now been found for producing linear PBS polymers that exhibit no detectable double bonds and the resulting branching. Such a highly linear polybutylene succinate has new industrial significance. Furthermore, the inventive method can be used to achieve this by adding a suitable net, multifunctional comonomers to produce a controlled branched PBS.

Summary of the invention

1. a) Vorlegen eines Gemisches umfassend Bernsteinsäure und 1,4-Butandiol, wobei das Stoffmengenverhältnis von Bernsteinsäure zu 1,4-Butandiol im Bereich von 1,0:1,5 bis 1,0:2,5, bevorzugt von 1,0:1,7 bis 1,0:2,0 liegt,
2. b) Aufheizen des Gemisches auf eine Temperatur im Bereich von 160 bis 235 °C, bevorzugt 180 bis 230 °C, wobei während dem Aufheizen
   • i) Bestandteile des Reaktionsgemisches, welche bei den vorliegenden Temperaturen gasförmig sind, wie Wasser und Tetrahydrofuran, aus dem Reaktionsgemisch entfernt werden, und
   • ii) ein Katalysator zu dem Reaktionsgemisch zugegeben wird, wobei der Katalysator ein Metall butoxid umfasst, wobei das Metall des Metall butoxids bevorzugt ausgewählt ist aus der Gruppe bestehend aus Ti, Zr, und Hf,
3. c) Verringern des Drucks auf einen Absolutdruck von weniger als 200 mbar, bevorzugt in einem Bereich von 1 bis 180 mbar und Einstellen der Temperatur in einen Bereich von 220 °C bis 240 °C, wobei während dessen
   • i) ein Katalysator zu dem Reaktionsgemisch zugegeben wird, wobei der Katalysator ein Metall butoxide umfasst, wobei das Metall des Metall butoxids bevorzugt ausgewählt ist aus der Gruppe bestehend aus Ti, Zr, und Hf, und
   • ii) Bestandteile des Reaktionsgemisches, welche bei den vorliegenden Temperaturen und Absolutdrücken gasförmig sind, aus dem Reaktionsgemisch entfernt werden,
4. d) Einstellen des Absolutdrucks auf einen Druck von weniger als 10 mbar, bevorzugt von weniger als 5 mbar, besonders bevorzugt in einem Bereich von 0,1 bis 4 mbar, während die Temperatur im Bereich von 220 °C bis 240 °C gehalten wird,
5. e) Halten des Absolutdrucks auf einem Druck von weniger als 10 mbar, bevorzugt von weniger als 5 mbar, besonders bevorzugt in einem Bereich von 0,1 bis 4 mbar und der Temperatur im Bereich von 220 °C bis 240 °C für einen Zeitraum von mehr als 1 h, bevorzugt in einem Bereich von 2 bis 15 h, besonders bevorzugt von 3 bis 13 h; und
6. f) Abkühlen des Reaktionsprodukts.

In one aspect, the invention relates to a process for the production of polybutylene succinate (PBS), characterized in that the process comprises the steps in the following order:

1. a) Providing a mixture comprising succinic acid and 1,4-butanediol, wherein the molar ratio of succinic acid to 1,4-butanediol is in the range of 1.0:1.5 to 1.0:2.5, preferably from 1.0:1.7 to 1.0:2.0,
2. b) Heating the mixture to a temperature in the range of 160 to 235 °C, preferably 180 to 230 °C, wherein during heating
   • i) Components of the reaction mixture which are gaseous at the temperatures present, such as water and tetrahydrofuran, are removed from the reaction mixture, and
   • ii) a catalyst is added to the reaction mixture, wherein the catalyst comprises a metal butoxide, the metal of the metal butoxide being preferably selected from the group consisting of Ti, Zr, and Hf,
3. c) Reducing the pressure to an absolute pressure of less than 200 mbar, preferably in a range of 1 to 180 mbar, and adjusting the temperature to a range of 220 °C to 240 °C, while during this process
   • i) a catalyst is added to the reaction mixture, wherein the catalyst comprises a metal butoxide, wherein the metal of the metal butoxide is preferably selected from the group consisting of Ti, Zr, and Hf, and
   • ii) Components of the reaction mixture which are gaseous at the present temperatures and absolute pressures are removed from the reaction mixture,
4. d) Adjusting the absolute pressure to a pressure of less than 10 mbar, preferably less than 5 mbar, particularly preferably in a range of 0.1 to 4 mbar, while maintaining the temperature in the range of 220 °C to 240 °C,
5. e) Maintaining the absolute pressure at less than 10 mbar, preferably less than 5 mbar, particularly preferably in a range of 0.1 to 4 mbar, and the temperature in the range of 220 °C to 240 °C for a period of more than 1 h, preferably in a range of 2 to 15 h, particularly preferably from 3 to 13 h; and
6. f) Cooling of the reaction product.

Furthermore, the invention relates to a polybutylene succinate (PBS), characterized in that the values of the complex viscosity η* of the PBS in the frequency range from 0.05 to 10 rad/s are determined by dynamic frequency sweeps over a frequency range of 0.5-500 rad/s at 130 °C with an elongation of 0.5%. DIN 53019-4 , less than 30%, preferably less than 20%, and most preferably less than 16% of the average value of the complex viscosity ${\overline{\eta }}_{\mathrm{0,05}-}^{*}$ in this frequency range.

In another aspect, the invention relates to the use of multifunctional comonomers as described herein in an amount of 0.01 to 5.0 mol%, preferably 0.02 to 1.0 mol%, based on the sum of the amounts of succinic acid, 1,4-butanediol and the multifunctional comonomer, in the process as described herein for adjusting the degree of branching in the polybutylene succinate (PBS) obtained.

Description of the characters

• 1 Figure 1 shows a graphical evaluation of the dynamic frequency sweeps performed over a frequency range of 0.5 to 500 rad/s at 130 °C with a strain of 0.5% for the PBS product obtained in inventive example 1 and the commercially available PBS product FZ91PM from Mitsubishi.
• 2 shows a Van Gurp Palmen plot in which the phase angle is plotted against the complex modulus G*, for the PBS product obtained in inventive example 1 and the commercially available PBS product FZ91PM from Mitsubishi.
• 3 shows a Van Gurp palm plot for inventive examples 1 to 5 and the commercially available PBS product FZ91PM from Mitsubishi.
• 4 shows a Van Gurp palm plot for the PBS products of inventive examples 1, 2, 6 and 7.

Detailed description of the invention

1. Procedure

The present invention relates to a process for the production of highly linear and controlled branched polybutylene succinate.

Reactor designs suitable for the inventive process are known to those skilled in the art. Exemplary reactor designs are given below as examples of the inventive process. The experimental section is described. Methods for adjusting pressures, temperatures and rotational speeds, as well as for removing gaseous components under the given conditions, are known to those skilled in the art.

The steps of the inventive process are described in more detail below.

Mixture in step a)

In step a) of the inventive process, a mixture comprising succinic acid and 1,4-butanediol is presented.

To ensure that as few free carbonic acid groups as possible remain in the reaction mixture after esterification, the molar ratio of succinic acid to 1,4-butanediol is in the range of 1.0:1.5 to 1.0:2.5, preferably from 1.0:1.7 to 1.0:2.0.

Succinic acid and 1,4-butanediol are the main monomers of polybutylene succinate.

Accordingly, it is preferred that the mixture in step a) consists of more than 85 wt.%, preferably more than 92 wt.%, of succinic acid and 1,4-butanediol.

The present inventive process essentially prevents the uncontrolled branching reactions that typically occur in the production of PBS.

However, if a branched PBS is to be obtained, the mixture can include, in addition to the succinic acid and the 1,4-butanediol, a multifunctional comonomer which can be incorporated into the polymer chain and leads to branching due to its multifunctionality.

A multifunctional comonomer within the meaning of this disclosure is a comonomer which has ≥ 3 functional groups, wherein the functional groups are selected from the group consisting of hydroxyl, carboxyl and combinations thereof.

Preferred comonomers are polyhydric aliphatic alcohols, polyhydric aromatic alcohols, polyhydric aliphatic carboxylic acids, polyhydric aromatic carboxylic acids, and combinations thereof. Even more preferred are the multifunctional comonomers polyhydric aliphatic alcohols, polyhydric aromatic carboxylic acids, and combinations thereof.

Particularly preferred is the multifunctional comonomer selected from the group consisting of 1,2,3,4-tetrahydroxybutane, 1,3,5-tricarboxybenzene, and combinations thereof.

Depending on the desired degree of branching, a larger or smaller amount of multifunctional comonomer can be used in the mixture.

Preferably, the amount of multifunctional comonomer in the mixture is in the range of 0.01 to 5.0 mol%, more preferably 0.02 to 1.0 mol%, based on the sum of the amounts of succinic acid, 1,4-butanediol and the multifunctional comonomer.

Another advantage of the inventive process is that a PBS compound can be produced directly. Compounds are plastics to which additional fillers, reinforcing agents, or other additives have been added.

Normally, compounds are produced from the finished polymer and the corresponding fillers, reinforcing agents, or other additives, e.g., by extrusion. In the inventive process, however, fillers, reinforcing agents, or other additives can already be present in the monomer mixture in step a).

Typical additives are known to experts and commercially available. Furthermore, typical additives are described, for example, in "Plastic Additives Handbook", 6th edition 2009 by Hans Zweifel (pages 1141 to 1190).

Examples of suitable additives are titanium dioxide (filler), Irganox1010 and Irgafos 168.

In the embodiment of the inventive process in which a PBS compound is to be obtained, the mixture preferably comprises less than 15 wt.%, particularly preferably less than 8 wt.%, as in the range of 0.1 wt.% to 7.9 wt.%, additives.

To prevent side reactions with atmospheric oxygen, it is advantageous to allow the esterification to take place under an inert atmosphere.

Accordingly, it is preferred that the air atmosphere present in the reactor is replaced with a nitrogen atmosphere before the mixture is heated in step b).

Methods for establishing a nitrogen atmosphere are known to those skilled in the art.

Step b)

In step b) of the inventive process, the reaction mixture is brought to an elevated temperature in the range of 160 to 235 °C, preferably 180 to 230 °C.

The temperature increase leads to esterification of the dicarboxylic acids with 1,4-butanediol, releasing water. In addition to water of reaction, tetrahydrofuran can also be formed as a byproduct.

These components of the reaction mixture, which are gaseous at certain temperatures during the heating phase, are removed from the reaction mixture.

Methods for removing gaseous components from reaction mixtures are known to those skilled in the art. For example, a distillation column can be used for this purpose.

Furthermore, a catalyst is added to the reaction mixture during heating in step b).

The catalyst comprises a metal butoxide. Preferably, the metal of the metal butoxide is selected from the group consisting of Ti, Zr, and Hf.

In a preferred embodiment of the inventive method, the catalyst is zirconium(IV) butoxide.

The catalyst can be dissolved in a solvent. 1-Butanol is the preferred solvent.

The amount of catalyst added is preferably in the range of 0.01 to 5.0 mmol/mol (succinic acid), more preferably 0.1 to 1.0 mmol/mol (succinic acid).

Furthermore, it is preferred that the catalyst is added only after the water produced during esterification has been substantially removed from the reaction mixture.

The duration of the heating phase in step b) can range from 1 to 10 hours, preferably from 2 to 5 hours.

The catalyst is preferably added shortly before the final temperature is reached. This ensures that the water produced during esterification has been substantially removed from the reaction mixture. Depending on the duration of the heating phase, it is preferred that the catalyst be added between 1 minute and 1 hour before the final temperature is reached.

In step b) esterification of succinic acid with 1,4-butanediol occurs, forming oligomers that are typically composed of one succinic acid and two 1,4-butanediol subunits, or two succinic acid and three 1,4-butanediol subunits.

Step c)

After the reaction mixture from step a) has been brought to a temperature in the range of 160 to 235 °C, preferably 180 to 230 °C, in step b), the pressure is reduced in step c) to an absolute pressure of less than 200 mbar, preferably in a range of 1 to 180 mbar.

At the same time, the temperature is set to a range of 220 °C to 240 °C.

If the temperature has already been increased to a range of 220°C to 235°C in step b), no further temperature adjustment is needed in step c) and the temperature can simply be maintained.

The reduced pressure and temperatures in the range of 220 °C to 240 °C are required to produce longer-chain polybutylene succinates from the oligomers formed in step b) by transesterification.

To accelerate the transesterification, a catalyst can be added, and the reaction equilibrium can be shifted towards the desired product by removing a reaction product.

Therefore, in step c), a catalyst is again added to the reaction mixture. The catalyst is preferably the same catalyst as in step b), wherein the catalyst comprises a metal butoxide, the metal of the metal butoxide being preferably selected from the group consisting of Ti, Zr, and Hf.

In a preferred embodiment of the inventive method, the catalyst is zirconium(IV) butoxide.

The catalyst can be dissolved in a solvent. 1-Butanol is the preferred solvent.

The amount of catalyst added is preferably in the range of 0.01 to 5.0 mmol/mol(succinic acid), more preferably 0.1 to 1.0 mmol/mol(succinic acid).

However, since a catalyst was already added in step b), it is preferred that the catalyst be added in step c) only after a certain time. Similar to step b), the catalyst is preferably added shortly before the final pressure is reached. Depending on the duration of the pressure reduction phase, it is preferred that the catalyst be added between 1 minute and 1 hour before the final pressure is reached.

The time required to reach the final pressure and temperature in step c) can range from 0.5 to 5 hours.

Furthermore, in step c) of the inventive process, the components of the reaction mixture which are gaseous at the present temperatures and absolute pressures are removed from the reaction mixture.

While the gaseous components in step b) are mostly water and THF, in step c) they are predominantly 1,4-butanediol. Other components present are tetrahydrofuran and 1-butanol.

By removing 1,4-butanediol from the reaction mixture, the reaction equilibrium shifts towards longer-chain polybutylene succinates, since the ratio of succinic acid to 1,4-butanediol subunits is greater in these.

Step d)

In step d) the absolute pressure is set to a pressure of less than 10 mbar, preferably less than 5 mbar, particularly preferably in a range of 0.1 to 4 mbar, while the temperature is kept in the range of 220 °C to 240 °C.

If the pressure has already been reduced to a range of 1 to 10 mbar in step c), no further pressure adjustment is required in step d) and the pressure is simply maintained.

Step e)

After an absolute pressure of less than 10 mbar, preferably less than 5 mbar, particularly preferably in the range of 0.1 to 4 mbar, is reached in step d), this pressure is maintained in step e) for a period of more than 1 hour, preferably in the range of 2 to 15 hours, particularly preferably in the range of 3 to 13 hours. The temperature is maintained in the range of 220 °C to 240 °C.

During step e), further components of the reaction mixture, which are gaseous at the present temperatures and absolute pressures, can be removed from the reaction mixture.

During step e), the viscosity of the reaction mixture increases significantly due to the formation of longer-chain polybutylene succinates.

It can therefore be advantageous to indirectly measure the viscosity of the reaction mixture during the process, for example by using an agitator with torque or power measurement. An increase in the torque or power required by the agitator indicates an increase in viscosity. Once a high torque or power value is reached, the rotational speed can then be continuously reduced, among other things to protect the agitator from overload.

Step f)

After step e), the polymerization is complete and the resulting PBS must be cooled. Methods for cooling are known to those skilled in the art.

The polymerization product can, for example, be transferred to a water bath using nitrogen overpressure. The resulting PBS strand can then be granulated and dried at low absolute pressures (e.g., 10 mbar) and elevated temperatures (e.g., 40 °C).

2. Product

The inventive process described herein can prevent uncontrolled branching during the production of PBS.

Accordingly, the invention relates not only to the method but also to a highly linear PBS.

The inventive polybutylene succinate (PBS) is characterized in that the values of the complex viscosity η* in the frequency range from 0.05 to 10 rad/s, determined by dynamic frequency sweeps over a frequency range of 0.5-500 rad/s at 130 °C with an elongation of 0.5 % according to DIN 53019-4 , less than 30%, preferably less than 20%, and most preferably less than 16% of the average value of the complex viscosity ${\overline{\eta }}_{\mathrm{0,05}-10}^{*}$ in this frequency range.

The essentially constant complex viscosity η* as the frequency changes is a characteristic of highly linear polymers, since non-Newtonian properties only appear in linear polymers at high frequencies. Non-Newtonian properties are manifested by a significant change in the complex viscosity with changing frequency.

Furthermore, the inventive polybutylene succinate (PBS) preferably has a melt flow rate MFR ₂ (190 °C; 2.16 kg) measured according to ISO 1133 in the range of 1 to 50 g/10 min, more preferably from 10 to 30 g/10 min.

The intrinsic viscosity iV, determined by dynamic-mechanical analysis according to DIN EN ISO 1628-1:2021-06 , is preferably in a range of 1.1 to 1.6 dL/g.

3. Use

As already described, the inventive process can prevent uncontrolled branching during the production of PBS.

However, by using a multifunctional comonomer in the mixture in step a) of the inventive process, branching sites can be incorporated into the polymer chains of the PBS, thereby enabling the obtaining of a controlled branched PBS.

Depending on the amount of multifunctional comonomer, the degree of branching can therefore be adjusted and thus the properties of the resulting PBS can be controlled.

Accordingly, the invention relates to the use of multifunctional comonomers in an amount of 0.01 to 5.0 mol%, preferably 0.02 to 1.0 mol%, based on the sum of the amounts of succinic acid, 1,4-butanediol and the multifunctional comonomer, in the inventive process as described herein for adjusting the degree of branching in the polybutylene succinate (PBS) obtained.

The preferred multifunctional comonomers correspond to the preferred embodiments already described in step a).

4. Experimental section

Measurement methods:

Determination of intrinsic viscosity iV:

The intrinsic viscosity was determined according to the method described in the WO 2013/087547 A1 described method:

First, the flow time t of a solution of the sample in the solvent chloroform at a concentration c of 1.0 g/dL is determined using an Ubbelohde-type viscometer (capillary 0c according to DIN 51562) at a temperature of 20 °C. From this, the relative solution viscosity η _{_rel} is calculated as the ratio of the flow time t₀ to the flow time t_₀ of the pure solvent in the identical viscometer, also at 20 °C. $${\eta }_{rel}=\frac{t}{t_0}$$

From the relative solution viscosity η _rel , the intrinsic viscosity η _intr (iV) can be calculated according to the Solomon-Ciuta formula: $${\eta }_{intr}=\frac{1}{c}\sqrt{2\ast \left({\eta }_{rel}-1-ln{\eta }_{rel}\right)}$$ where the concentration c of the solution is to be specified as 1.0 g/dL.

Determination of melt flow rate MFR ₂ :

The melting flux rate (MFR ₂ ) was determined according to ISO 1133 at a temperature of 190 °C and a load of 2.16 kg and is given in g/10 min.

Rheological measurements:

Dynamic viscoelastic spectra were determined using an ARES rheometer (TA Instruments). A parallel plate-to-plate geometry with a plate radius of 25 mm, separated by a 650 µm gap, was used. The samples were loaded into the rheometer and equilibrated for 5 min at 130 °C. Strain sweep experiments were then performed with strains from 0.01% to 100% at 10 rad/s and 130 °C to determine the linear viscoelastic region. Subsequently, dynamic frequency sweeps were performed over a frequency range of 0.5–500 rad/s at 130 °C with a strain of 0.5% to determine the complex viscosity η* in this frequency range.

Van Gurp Palm Plot

The Van Gurp-Palmen plots are generated as follows and as described in the cited publications. In one publication, Van Gurp and Palmen propose an approach for verifying the time-temperature superposition principle (TTS) ( Van Gurp M, Palmen J, 1998, Time temperature superposition for polymeric blends, Rheol Bull 67:5-8 The phase angle δ of the measured rheological data is plotted against the corresponding absolute value of the complex shear modulus |G*|. Such isothermal frequency curves merge into a common line when the TTS is satisfied. In addition to this information, the Van Gurp-Palmen plot contains further information, e.g., about the polydispersity and long-chain branching (LCB) of the polymers ( Rheol Acta (2001) 40: 322-328, Springer-Verlag 2001, Stefan Trinkle, Christian Friedrich ).

Manufacturing process

Inventive Example 1 (linear PBS):

In a 15,500 mL stainless steel stirred tank reactor equipped with an anchor stirrer, oil heating, a distillation column, a condenser, a condensate collection tank, a vacuum port, and a stirrer with torque measurement, succinic acid (4,457 g, 37.7 mol) and 1,4-butanediol (5,950 g, 66.0 mol) were weighed and homogenized for 30 minutes at a speed of 60 revolutions per minute. The mixture was then evacuated via the reactor's vacuum port to a pressure of 1 mbar, and the vacuum was maintained for 5 minutes. The reactor was then flooded with pure nitrogen ( _N₂ ) and adjusted to a gauge pressure of 50 mbar. The evacuation procedure was subsequently repeated four more times.

The reactor contents were then heated to 224 °C over 3 hours using the oil heater. After 1 hour and 20 minutes, the resulting water of reaction was drawn off via the distillation column. Two hours and 30 minutes after the start of heating, 7.5 g of zirconium(IV) butoxide solution (80 wt% in 1-butanol) was added to the reaction mass. After 3 hours of heating, a total of 1,588 g of condensate was collected at the column head. The condensate consisted of a mixture with water and tetrahydrofuran (THF) as the main components.

After the first heating period, the reactor contents were heated to 230 °C over two hours, while the reactor pressure was simultaneously reduced to 6 mbar absolute pressure. One hour and 30 minutes after the start of the second temperature increase, 11.9 g of the same zirconium(IV) butoxide catalyst solution were added to the reaction mass. During this two-hour heating period, 1,681 g of condensate were drawn off under vacuum. The condensate consisted predominantly of 1,4-butanediol. Other components included THF and 1-butanol.

The reactor pressure was then reduced to 1.0 mbar for a further 30 minutes while maintaining a temperature of 230 °C. Subsequently, the reactor pressure and temperature were held constant for another 5 hours. Three and a half hours before the end of the reaction, the torque began to increase, starting from an idle torque of 0.2 Newton meters. One and a half hours before the end of the experiment, the torque reached 27.5 Newton meters. From this point on, the torque was held constant, and the stirrer speed was reduced until it reached its minimum of 13 revolutions per minute 40 minutes before the end of the experiment. The torque then increased to 30.0 Newton meters at a constant speed of 13 revolutions per minute. By this time, another 307 g of condensate had been obtained. Again, the condensate consisted almost entirely of 1,4-butanediol. The reactor contents were emptied into a water bath through a 6 mm nozzle using a stationary stirrer and nitrogen overpressure of 3.42 bar over a period of 56 minutes. The resulting strand was granulated and dried overnight in a vacuum drying oven at 10 mbar and 40 °C. The resulting product has an intrinsic viscosity of 1.25 dL/g, as measured according to the formula in WO 2013/087547 AI described method. The melt flow rate MFR ₂ (190 °C; 2.16 kg), measured according to ISO 1133, was 18 g/10 min.

Analysis of inventive example 1

The PBS obtained from inventive example 1 exhibits a behavior typical for a linear polymer in the rheometer. Dynamic frequency sweeps over a frequency range of 0.5–500 rad/s at 130 °C with a strain of 0.5% were performed to determine the changes in the complex viscosity η* in this frequency range. The values obtained are shown in 1 graphically represented. As a comparative example, the commercial PBS product FZ91PM from Mitsubishi was analyzed. The PBS obtained in inventive example 1 had the values shown in Table 1 for the complex viscosity η* in the frequency range from 0.05 to 10 rad/s. Table 1: Complex viscosity of the obtained PBS at frequencies in the range of 0.05 to 10 rad/s. frequency complex viscosity [rad/s] η* [Pa s] 500 596,559 397,164 752,811 315,479 869,028 250,594 994,763 199,054 1129.27 158,114 1258.37 125,594 1404.64 99,7631 1556.67 79,2447 1699.15 62,9463 1859.37 50 1998.48 39,7164 2199.28 31,5479 2270.01 25,0594 2478.87 19,9054 2594.09 15,8114 2713.16 12,5594 2837.88 9,97631 2939.78 7.92446 3027.92 6,29462 3131.32 5 3204.39 3,97164 3285.99 3,15479 3331.41 2.50593 3407.32 1.99053 3455.4 1.58114 3458.54 1.25594 3472.81 0.99763 3517.35 0.79245 3494.2 0.62946 3590.85 0.5 3554.43 0.39716 3486.29 0.31548 3408.19 0.25059 3356.66 0.19905 3345.75 0.15811 3358.24 0.12559 3059.07 0.09976 3259.1 0.07924 3120.61 0.06295 3637.87 0.05 3064.06

1 Table 1 clearly shows that the obtained PBS exhibits an almost constant complex viscosity η* in the frequency range from 0.05 to 10 rad/s, indicating high linearity of the polymer chain. In contrast, the commercial PBS product FZ91PM shows a significant reduction in the complex viscosity η* from ~11,500 to ~5,000 Pa s in this frequency range, suggesting the non-Newtonian behavior of branched polymers. Furthermore, the Van Gurp-Palmen plot in 2 Inventive Example 1 exhibits a concave phase angle over the complex modulus G*, which is typical for linear polymers. FZ91PM, on the other hand, shows a linear phase angle, which is typical for branched polymers.

Inventive example 2 (controlled branched PBS):

In a 15,500 mL stainless steel stirred tank reactor equipped with an anchor stirrer, oil heating, a distillation column, a condenser, a condensate collection tank, a vacuum port, and a stirrer with torque measurement, 4,457 g of succinic acid (4,457 g, 37.74 mol), 1,4-butanediol (5,950 g, 66.04 mol), and meso-1,2,3,4-tetrahydroxybutane (40 g, 0.33 mol) were weighed out and homogenized for 30 minutes at a speed of 60 revolutions per minute. The mixture was then evacuated via the reactor's vacuum port to a pressure of 1 mbar, and the vacuum was maintained for 5 minutes. The reactor was then flooded with pure nitrogen and adjusted to a gauge pressure of 50 mbar. The evacuation procedure was subsequently repeated four more times. The reactor contents were then heated to 224 °C over 3 hours using the oil heater. After 1 hour and 20 minutes, the resulting water of reaction was drawn off via the distillation column. Two hours and 30 minutes after the start of heating, 5.2 g of zirconium(IV) butoxide solution (80 wt.% in 1-butanol) were added to the reaction mass. After 3 hours of heating, a total of 1.675 g of condensate was collected at the column head. The condensate consists mainly of water and tetrahydrofuran. After the heating period ended, the reactor contents were heated to 230 °C over 2 hours, while the pressure in the reactor was simultaneously reduced to 6 mbar. The reactor pressure was reduced. One hour and 30 minutes after the start of the second temperature increase, 12.7 g of the same zirconium(IV) butoxide catalyst solution were added to the reaction mass. During this two-hour heating period, 1,078 g of condensate were removed under vacuum. The condensate consists predominantly of 1,4-butanediol; other components include tetrahydrofuran and 1-butanol. Subsequently, the reactor pressure was evacuated to an absolute pressure of 1.0 mbar over a further 30 minutes while the temperature was maintained at 230 °C. The reactor pressure and temperature were then held constant for a further 5.5 hours. Three hours before the end of the reaction, the torque began to increase, starting from its no-load torque of 0.2 newton meters. One hour before the end of the experiment, the torque reached a value of 32.0 newton meters. From this point onward, the torque was kept constant and the agitator speed was reduced until it reached its minimum of 13 revolutions per minute 20 minutes before the end of the experiment. Subsequently, the torque increased to 60.0 newton meters while maintaining a constant speed of 13 revolutions per minute. Up to this point, a further 66 g of condensate had been obtained. Again, the condensate consisted almost entirely of 1,4-butanediol. The reactor contents were emptied into a water bath through a 6 mm nozzle using a stationary agitator and nitrogen overpressure of 4.42 bar over a period of 113 minutes. The resulting strand was granulated and dried overnight in a vacuum drying oven at 10 mbar and 40 °C. The resulting product has an intrinsic viscosity of 1.10 dL/g, as measured according to the formula in [reference missing]. WO 2013/087547 The method described in AI was used. The melt flow rate MFR ₂ (190 °C; 2.16 kg) was 18 g/10 min. The polymer showed a typical behavior for a branched polymer in the rheometer.

Inventive example 3 (controlled branched PBS):

In a 15,500 mL stainless steel stirred tank reactor equipped with an anchor stirrer, oil heating, a distillation column, a condenser, a condensate collection tank, a vacuum port, and a stirrer with torque measurement, succinic acid (4,461 g, 37.77 mol), 1,4-butanediol (6,631 g, 73.60 mol), and meso-1,2,3,4-tetrahydroxybutane (10 g, 0.08 mol) were weighed out and homogenized for 30 minutes at a speed of 60 revolutions per minute. The mixture was then evacuated via the reactor's vacuum port to a pressure of 1 mbar, and the vacuum was maintained for 5 minutes. The reactor was then flooded with pure nitrogen and adjusted to a gauge pressure of 50 mbar. The evacuation procedure was subsequently repeated four more times. The reactor contents were then heated to 220 °C via the oil heater within 2 hours and 20 minutes. After 1 hour and 20 minutes, the resulting water of reaction was drawn off via the distillation column. Two hours after the start of heating, 9.8 g of zirconium(IV) butoxide solution (80 wt.% in 1-butanol) were added to the reaction mass. After 2 hours and 20 minutes of heating, a total of 1.657 g of condensate was collected at the column head. The condensate consists of a mixture whose main components are water and tetrahydrofuran. After the end of the heating period, the reactor contents were increased to 230 °C within 1 hour, while the pressure in the reactor was simultaneously reduced to 130 mbar absolute pressure. Two hours after the start of the second temperature increase, 9.6 g of the same zirconium(IV) butoxide catalyst solution were added to the reaction mass. During this 2-hour heating period, 1,662 g of condensate were removed under vacuum. The condensate consists predominantly of 1,4-butanediol; other components include tetrahydrofuran and 1-butanol. The reactor pressure was then evacuated to an absolute pressure of 1.0 mbar over a further 30 minutes while maintaining a temperature of 230 °C. Subsequently, the reactor pressure and temperature were held constant for another 11 hours. Five hours before the end of the reaction, the torque began to increase, starting from its no-load torque of 0.2 Newton meters. Two hours before the end of the experiment, the torque reached a value of 30.0 Newton meters. From this point on, the torque was held constant, and the stirrer speed was reduced until it reached its minimum of 20 revolutions per minute 50 minutes before the end of the experiment. The torque then increased to a value of 39.6 Newton meters at a constant speed of 20 revolutions per minute. Up to this point, a further 736 g of condensate were obtained. Again, the condensate consists almost entirely of 1,4-butanediol. The reactor contents were emptied into a water bath through a 6 mm nozzle using a stationary stirrer and nitrogen overpressure of 4.02 bar over a period of 59 minutes. The resulting strand was granulated and dried overnight in a vacuum drying oven at 10 mbar and 40 °C. The resulting product has an intrinsic viscosity η _{_intr} of 1.41 dL/g, as measured according to the formula in [reference missing]. WO 2013/087547 The method described above was used. The melt flow rate MFR ₂ (190 °C; 2.16 kg) was 14.8 g/10. The polymer showed a typical behavior for a branched polymer in the rheometer.

Inventive example 4 (controlled branched PBS):

In a 15,500 mL stainless steel stirred tank reactor equipped with an anchor stirrer, oil heating, a distillation column, a condenser, a condensate collection tank, a vacuum port, and a stirrer with torque measurement, succinic acid (4,461 g, 37.77 mol), 1,4-butanediol (6,639 g, 73.68 mol), and meso-1,2,3,4-tetrahydroxybutane (5 g, 0.04 mol) were weighed out and homogenized for 30 minutes at a speed of 60 revolutions per minute. The mixture was then evacuated via the reactor's vacuum port to a pressure of 1 mbar, and the vacuum was maintained for 5 minutes. The reactor was then flooded with pure nitrogen and adjusted to a gauge pressure of 50 mbar. The evacuation procedure was subsequently repeated four more times. The reactor contents were then heated to 221 °C via the oil heater within 2 hours and 40 minutes. After 1 hour and 20 minutes, the resulting water of reaction was drawn off via the distillation column. Two hours and 20 minutes after the start of heating, 9.9 g of zirconium(IV) butoxide solution (80 wt.% in 1-butanol) were added to the reaction mass. After 2 hours and 40 minutes of heating, a total of 1,735 g of condensate was collected at the column head. The condensate consists of a mixture whose main components are water and tetrahydrofuran. After the end of the heating period, the reactor contents were increased to 230 °C within 1 hour, while the pressure in the reactor was simultaneously reduced to 40 mbar absolute pressure. Fifty minutes after the start of the second temperature increase, 9.8 g of the same zirconium(IV) butoxide catalyst solution were added to the reaction mass. During this 2-hour heating period, 1,231 g of condensate were drawn off under vacuum. The condensate consists predominantly of 1,4-butanediol; other components include tetrahydrofuran and 1-butanol. The reactor pressure was then evacuated to an absolute pressure of 1.0 mbar over a further 30 minutes while maintaining a temperature of 230 °C. Subsequently, the reactor pressure and temperature were held constant for another 10 hours. Six hours before the end of the reaction, the torque began to increase, starting from its no-load torque of 0.2 Newton meters. Two hours and 30 minutes before the end of the experiment, the torque reached a value of 30.0 Newton meters. From this point on, the torque was held constant, and the stirrer speed was reduced until it reached its minimum of 20 revolutions per minute 30 minutes before the end of the experiment. The torque then increased to 39.1 newton meters at a constant speed of 20 revolutions per minute. Up to this point, a further 939 g of condensate were obtained. Again, the condensate consisted almost entirely of 1,4-butanediol. The reactor contents were emptied into a water bath through a 6 mm nozzle over a period of 55 minutes using a stationary stirrer and nitrogen overpressure of 3.81 bar. The resulting strand was granulated and dried overnight in a vacuum drying oven at 10 mbar and 40 °C. The resulting product has an intrinsic viscosity η _{_intr} of 1.32 dL/g, as measured according to the formula in [reference missing]. WO 2013/087547 The method described in AI was used. The melt flow rate MFR ₂ (190 °C; 2.16 kg) was 12.2 g/10 min. The polymer exhibits a typical behavior for a branched polymer in the rheometer.

Inventive example 5 (controlled branched PBS):

In a 15,500 mL stainless steel stirred tank reactor equipped with an anchor stirrer, oil heating, a distillation column, a condenser, a condensate collection tank, a vacuum port, and a stirrer with torque measurement, succinic acid (4,444 g, 37.63 mol), 1,4-butanediol (6,631 g, 73.60 mol), and 1,3,5-tricarboxybenzene (13.9 g, 0.07 mol) were weighed out and homogenized for 30 minutes at a speed of 60 revolutions per minute. The mixture was then evacuated via the reactor's vacuum port to a pressure of 1 mbar, and the vacuum was maintained for 5 minutes. The reactor was then flooded with pure nitrogen and adjusted to a gauge pressure of 50 mbar. The evacuation procedure was subsequently repeated four more times. The reactor contents were then heated to 223 °C via the oil heater within 3 hours and 10 minutes. After 1 hour and 20 minutes, the resulting water of reaction was drawn off via the distillation column. 2 hours and 30 minutes after the start of heating, 9.8 g of zirconium(IV) butoxide solution (80 wt.% in 1-butanol) were added to the reaction mass. After 3 hours and 10 minutes of heating, a total of 2.036 g of condensate was collected at the column head. The condensate consists of a mixture whose main components are water and tetrahydrofuran. After the heating period ended, the reactor contents were raised to a temperature of 230 °C within 50 minutes, while simultaneously the pressure in the reactor was reduced to 140 mbar absolute pressure. Two hours after the start of the second temperature increase, 9.6 g of the same zirconium(IV) butoxide catalyst solution were added to the reaction mass. Up to the point of catalyst addition, 1,481 g of condensate were withdrawn under vacuum. The condensate consists predominantly of 1,4-butanediol. Other components present are... Tetrahydrofuran and 1-butanol. The reactor pressure was then evacuated to an absolute pressure of 1.0 mbar over a further 30 minutes while the temperature was maintained at 230 °C. Subsequently, the reactor pressure and temperature were held constant for another 8.5 hours. Six hours before the end of the reaction, the torque began to increase, starting from its no-load torque of 0.2 Newton meters. Two hours and thirty minutes before the end of the experiment, the torque reached a value of 30.0 Newton meters. From this point on, the torque was held constant, and the stirrer speed was reduced until it reached its minimum of 20 revolutions per minute 20 minutes before the end of the experiment. Subsequently, the torque increased to a value of 44.6 Newton meters at a constant speed of 20 revolutions per minute. Up to this point, another 519 g of condensate had been obtained. Again, the condensate consists almost entirely of 1,4-butanediol. The reactor contents were emptied into a water bath through a 6 mm nozzle using a stationary stirrer and nitrogen overpressure of 3.99 bar over a period of 61 minutes. The resulting strand was granulated and dried overnight in a vacuum drying oven at 10 mbar and 40 °C. The resulting product has an intrinsic viscosity η _{_intr} of 1.31 dL/g, as measured according to the formula in WO 2013/087547 The method described in AI was used. The melt flow rate MFR ₂ (190 °C; 2.16 kg) was 13.3 g/10 min. The polymer exhibits a typical behavior for a branched polymer in the rheometer.

Analysis of inventive examples 2 to 5

Inventive Example 2 shows that the inventive process can be used to obtain a branched PBS by introducing polar groups into the main chain using a multifunctional comonomer (0.31 mol% meso-1,2,3,4-tetrahydroxybutane). Inventive Examples 3 and 4 further demonstrate that the degree of branching can be effectively controlled by varying the amount of comonomer added (0.07 mol% and 0.04 mol%). A conventional branching process using a multifunctional acid such as 1,3,5-tricarboxybenzene (inventive Example 5) yielded comparable results and underscores the excellent controllability of the branching degrees. The rheological measurement results are presented in 3 graphically represented. From 3 It is evident that the degree of branching is easily controllable and can be adjusted within a wide range. The addition of multifunctional comonomers allows for branching levels exceeding those of commercially available products.

Inventive example 6 (linear PBS, scale-up):

In a 200-liter stainless steel stirred tank reactor equipped with a double-helix stirrer, oil heating, a distillation column, a condenser, a condensate collection tank, a vacuum port, and a stirrer with power measurement, succinic acid (48,007 g, 406.49 mol) and 1,4-butanediol (71,440 g, 792.90 mol) were weighed and homogenized for 30 minutes at a speed of 75 revolutions per minute. The mixture was then evacuated via the reactor's vacuum port to a pressure of 1 mbar, and the vacuum was maintained for 5 minutes. The reactor was then flooded with pure nitrogen and adjusted to a gauge pressure of 50 mbar. The evacuation procedure was then repeated four more times. Finally, the reactor contents were heated to a temperature of 219 °C via the oil heating system over a period of 3 hours and 50 minutes. After 1 hour and 10 minutes, the water of reaction produced was drawn off via the distillation column. Three hours and 30 minutes after the start of heating, 102 g of zirconium(IV) butoxide solution (80 wt% in 1-butanol) were added to the reaction mass. After 3 hours and 50 minutes of heating, a total of 21,160 g of condensate was collected at the column head. The condensate consisted of a mixture whose main components were water and tetrahydrofuran. After the end of the heating period, the reactor contents were raised to a temperature of 230 °C within 3 hours, while simultaneously the pressure in the reactor was reduced to 8 mbar absolute pressure. Three hours after the start of the second temperature increase, 130 g of the same zirconium(IV) butoxide catalyst solution were added to the reaction mass. Up to the point of catalyst addition, 22,920 g of condensate had been drawn off under vacuum. The condensate consists predominantly of 1,4-butanediol. Other components include tetrahydrofuran and 1-butanol. The reactor pressure was then evacuated to an absolute pressure of 1.0 mbar over a further hour while the temperature was maintained at 230 °C. Subsequently, the reactor pressure and temperature were held constant for a further 5 hours and 40 minutes. Three hours before the end of the reaction, the power consumption began to increase, starting from its idle power of 0.79 kilowatts. One hour before the end of the experiment, the power consumption reached 1.99 kilowatts. From this point on, the power consumption was kept constant, and the stirrer speed was reduced until it reached its minimum of 10 revolutions per minute 10 minutes before the end of the experiment. The power consumption then increased to 3.36 kilowatts at a constant speed of 10 revolutions per minute. At this point, a further 5,880 g of condensate were obtained. Again, the condensate consisted almost entirely of 1,4-butanediol. The reactor contents were emptied into a water bath through a 13.6 mm nozzle using a stationary stirrer and nitrogen overpressure of 1.21 bar over a period of 54 minutes. The resulting strands were granulated and dried overnight in a vacuum drying oven at 10 mbar and 40 °C. The resulting product has an intrinsic viscosity η _{_intr} of 1.51 dL/g, as measured according to the formula in [reference missing]. WO 2013/087547 The method described in AI was used. The melt flow rate MFR ₂ (190 °C; 2.16 kg) was 15.2 g/10 min. The polymer showed a typical behavior for a linear polymer in the rheometer.

Inventive example 7 (controlled branched PBS, scale-up):

In a 200-liter stainless steel stirred tank reactor equipped with a double-helix stirrer, oil heating, a distillation column, a condenser, a condensate collection tank, a vacuum port, and a stirrer with power measurement, succinic acid (42.501 g, 359.87 mol), 1,4-butanediol (56.759 g, 629.96 mol), and meso-1,2,3,4-tetrahydroxybutane (381 g, 3.12 mol) were weighed and homogenized for 30 minutes at a rotational speed of 75 revolutions per minute. The mixture was then evacuated via the reactor's vacuum port to a pressure of 1 mbar, and the vacuum was maintained for 5 minutes. The reactor was then flooded with pure nitrogen and adjusted to an overpressure of 50 mbar. The evacuation procedure was subsequently repeated four more times. The reactor contents were then heated to 220 °C via the oil heater over a period of 3 hours and 40 minutes. After 1 hour and 20 minutes, the water of reaction produced was drawn off via the distillation column. Three hours after the start of heating, 99 g of zirconium(IV) butoxide solution (80 wt% in 1-butanol) were added to the reaction mass. After 3 hours and 40 minutes of heating, a total of 21,390 g of condensate was collected at the column head. The condensate consists of a mixture whose main components are water and tetrahydrofuran. After the heating period ended, the reactor contents were raised to 230 °C over a period of 3 hours, while the pressure in the reactor was simultaneously reduced to 7 mbar absolute pressure. Two hours and 30 minutes after the start of the second temperature increase, 103 g of the same zirconium(IV) butoxide catalyst solution were added to the reaction mass. Up to the addition of the catalyst, 36,360 g of condensate were removed under vacuum. The condensate consists predominantly of 1,4-butanediol. Other components present are tetrahydrofuran and 1-butanol. The reactor pressure was then evacuated to an absolute pressure of 1.0 mbar over 1 hour and 30 minutes while maintaining a temperature of 230 °C. Subsequently, the reactor pressure and temperature were held constant for a further 9 hours and 10 minutes. Five hours before the end of the reaction, the power consumption began to increase, starting from its idle power of 0.96 kilowatts. One hour and 40 minutes before the end of the experiment, the power consumption reached 1.50 kilowatts. From this point on, the power consumption was kept constant, and the stirrer speed was reduced until it reached its minimum of 10 revolutions per minute ten minutes before the end of the experiment. Subsequently, the power consumption increased to 2.85 kilowatts at a constant speed of 10 revolutions per minute. Up to this point, a further 2,188 g of condensate were obtained. Again, the condensate consisted almost entirely of 1,4-butanediol. The reactor contents were emptied into a water bath via a 13.6 mm nozzle using a stationary stirrer and nitrogen overpressure of 1.21 bar over a period of 54 minutes. The resulting strands were granulated and dried overnight in a vacuum drying oven at 10 mbar and 40 °C. The resulting product has an intrinsic viscosity η _{_intr} of 1.28 dL/g, as measured according to the formula in [reference missing]. WO 2013/087547 The method described in AI was used. The melt flow rate MFR ₂ (190 °C; 2.16 kg) was 15.2 g/10 min. The polymer showed a typical behavior for a branched polymer in the rheometer.

Analysis of inventive examples 6 and 7

Inventive examples 6 and 7 serve to demonstrate that the inventive process can be used for the synthesis of linear or controlled branched PBS types, regardless of the scale and/or the stirring system used. 4 This shows that the PBS of inventive examples 1 and 2 from the described 15.5 liter reactor and 6 and 7 from the described 200 liter reactor have very similar rheological properties.

Comparison example 8 (uncontrolled branched PBS):

In a 15,500 mL stainless steel stirred tank reactor equipped with an anchor stirrer, oil heating, a distillation column, a condenser, a condensate collection tank, a vacuum port, and a stirrer with torque measurement, succinic acid (4,457 g, 37.7 mol) and 1,4-butanediol (3,945 g, 43.8 mol) were weighed and homogenized for 30 minutes at a speed of 60 revolutions per minute. The mixture was then evacuated via the reactor's vacuum port to a pressure of 1 mbar, and the vacuum was maintained for 5 minutes. Afterward, the reactor was... Pure nitrogen ( _N₂ ) was introduced and the pressure was set to 50 mbar. The evacuation procedure was then repeated four more times.

The reactor contents were then heated to 188 °C via the oil heater within 2 hours and 40 minutes. After 40 minutes, the resulting water of reaction was drawn off via the distillation column. Two hours and 30 minutes after the start of the initial heating, 4.8 g of zirconium(IV) butoxide solution (80 wt.% in 1-butanol) were added to the reaction mass. After 2 hours and 30 minutes of the initial heating period, a total of 1.037 g of condensate was collected at the column head. The condensate consisted of a mixture whose main components were water and THF. After the end of the initial heating period, the reactor contents were heated to 235 °C within 2 hours and 30 minutes, while simultaneously the pressure in the reactor was reduced to 69 mbar absolute pressure.

The reactor was then flooded with _nitrogen and pressurized to 1,100 mbar, while the molten material was simultaneously cooled to 130 °C within one hour. The stirrer speed was then reduced to 13 revolutions per minute. The molten material was stored under these conditions for 14 hours.

The temperature of the melt in the reactor was then increased to 235 °C over 1 hour and 30 minutes while a vacuum was simultaneously applied. At the start of the heating process, 11.9 g of the same zirconium(IV) butoxide catalyst solution was added to the reaction mass. After 2 hours and 10 minutes, a reactor pressure of 1.0 mbar absolute was reached while maintaining the temperature at 235 °C. Subsequently, the reactor pressure and temperature were held constant for a further 5 hours and 20 minutes. Four hours before the end of the reaction, the torque began to increase, starting from an idle torque of 0.2 Newton meters. Two hours before the end of the experiment, the torque reached a value of 27.5 Newton meters. From this point on, the torque was held constant, and the stirrer speed was reduced until it reached its minimum of 13 revolutions per minute 40 minutes before the end of the experiment. The torque then increased to 63.8 newton meters at a constant speed of 13 revolutions per minute. The reactor contents were emptied into a water bath through a 6 mm nozzle using a stationary stirrer and nitrogen overpressure of 4.52 bar over a period of 1 hour and 22 minutes. The resulting strand was granulated and dried overnight in a vacuum drying oven at 10 mbar and 40 °C.

The resulting product exhibited an intrinsic viscosity η _{_intr} of 1.66 dL/g, measured according to the method described in WO 2013/087547 The method described in AI was used. The melt flow rate MFR ₂ (190 °C; 2.16 kg), measured according to ISO 1133, was 5.1 g/10 min. The polymer showed strong branching.

Inventive Example 9 (Compound - PBS):

In a 15,500 mL stainless steel stirred tank reactor equipped with an anchor stirrer, oil heating, a distillation column, a condenser, a condensate collection tank, a vacuum port, and a stirrer with torque measurement, succinic acid (4,800 g, 40.64 mol), 1,4-butanediol (7,144 g, 79.29 mol), titanium dioxide (777 g), Irganox1010 (0.94 g, commercially available from BASF AG), and Irgafos168 (1.13 g, commercially available from BASF AG) were weighed and homogenized for 30 minutes at a rotational speed of 60 revolutions per minute. The mixture was then evacuated via the reactor's vacuum port to a pressure of 1 mbar, and the vacuum was maintained for 5 minutes. Afterward, the reactor was flooded with pure nitrogen and adjusted to an overpressure of 50 mbar. The evacuation procedure was then repeated four more times. The reactor contents were subsequently heated to 196 °C via the oil heater within 2 hours and 40 minutes. After 60 minutes, the resulting reaction water was drawn off via the distillation column. Two hours and 30 minutes after the start of heating, 9.1 g of zirconium(IV) butoxide solution (80 wt% in 1-butanol) were added to the reaction mass. After 2 hours and 30 minutes of heating, a total of 1,635 g of condensate was collected at the column head. The condensate consists of a mixture whose main components are water and tetrahydrofuran. After the heating period ended, the reactor contents were raised to a temperature of 230 °C within 2 hours and 30 minutes, while simultaneously the reactor pressure was reduced to 90 mbar absolute pressure. Ten minutes later, 4.0 g of the same zirconium(IV) butoxide catalyst solution was added to the reaction mixture. After two hours, a reactor pressure of 1.0 mbar absolute was set while the temperature was maintained at 230 °C. Subsequently, the reactor pressure and temperature were held constant for another four hours and ten minutes. Two hours and forty minutes before the end of the reaction, the torque began to increase, starting from an idle torque of 0.5 newton meters. Forty minutes before the end of the experiment, the torque reached a value of 27.5 newton meters. From this point on, the torque was held constant, and the stirrer speed was reduced until it reached 30 revolutions per minute at the end of the reaction. The torque was 27.6 newton meters. The reactor contents were emptied into a water bath through a 6 mm nozzle using a stationary stirrer and nitrogen overpressure of 3.01 bar over a period of 35 minutes. The resulting strand was granulated and dried overnight in a vacuum drying oven at 10 mbar and 40 °C. The resulting product has an intrinsic viscosity η _{_intr} of 1.23 dL/g, as measured according to the method described in [reference missing]. WO 2013/087547 The method described by AI was used. The melt flow rate MFR ₂ (190 °C; 2.16 kg) was 25 g/10 min. In rheological measurements, the PBS compound showed a behavior typical for a linear polymer.

Inventive example 9 shows that a PBS compound can be directly synthesized by the inventive method without having to rely on a subsequent compounding step.

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• WO 2013/087547 A1 [0082]
• WO 2013/087547 [0091, 0094, 0095, 0096, 0097, 0099, 0100, 0106, 0107]

Cited non-patent literature

• DIN 53019-4 [0012, 0073]
• DIN EN ISO 1628-1:2021-06 [0076]
• Van Gurp M, Palmen J, 1998, Time temperature superposition for polymeric blends, Rheol Bull 67:5-8 [0087]
• Rheol Acta (2001) 40: 322-328, Springer-Verlag 2001, Stefan Trinkle, Christian Friedrich [0087]

Claims (11)

A process for the production of polybutylene succinate (PBS), characterized in that the process comprises the steps in the following order: a) providing a mixture comprising succinic acid and 1,4-butanediol, wherein the molar ratio of succinic acid to 1,4-butanediol is in the range of 1.0:1.5 to 1.0:2.5, preferably from 1.0:1.7 to 1.0:2.0, b) heating the mixture to a temperature in the range of 160 to 235 °C, preferably 180 to 230 °C, wherein during heating i) components of the reaction mixture which are gaseous at the temperatures present, such as water and tetrahydrofuran, are removed from the reaction mixture, and ii) a catalyst is added to the reaction mixture, wherein the catalyst comprises a metal butoxide, wherein the metal of the metal butoxide is preferably selected from the group consisting of Ti, Zr, and Hf, c) reducing the The process involves: reducing the pressure to an absolute pressure of less than 200 mbar, preferably in a range of 1 to 180 mbar, and adjusting the temperature to a range of 220 °C to 240 °C, during which: i) a catalyst is added to the reaction mixture, the catalyst comprising a metal butoxide, the metal of the metal butoxide preferably being selected from the group consisting of Ti, Zr, and Hf; ii) removing components of the reaction mixture that are gaseous at the present temperatures and absolute pressures from the reaction mixture; d) adjusting the absolute pressure to a pressure of less than 10 mbar, preferably less than 5 mbar, particularly preferably in a range of 0.1 to 4 mbar, while maintaining the temperature in the range of 220 °C to 240 °C; e) maintaining the absolute pressure at a pressure of less than 10 mbar, preferably less than 5 mbar, particularly preferably in a range of 0.1 to 4 mbar and a temperature in the range of 220 °C to 240 °C for a period of more than 1 h, preferably in a range of 2 to 15 h, particularly preferably from 3 to 13 h; and f) cooling of the reaction product. The procedure according Claim 1 , characterized in that the mixture in step a) additionally comprises a multifunctional comonomer, wherein the multifunctional comonomer has ≥ 3 functional groups selected from the group consisting of hydroxyl, carboxyl and combinations thereof. The procedure according Claim 2 , characterized in that the multifunctional comonomer is selected from polyhydric aliphatic alcohols, polyhydric aromatic alcohols, polyhydric aliphatic carboxylic acids, polyhydric aromatic carboxylic acids, and combinations thereof, preferably from polyhydric aliphatic alcohols, polyhydric aromatic carboxylic acids, and combinations thereof, particularly preferably from meso-1,2,3,4-tetrahydroxybutane, 1,3,5-tricarboxybenzene, and combinations thereof. The procedure according to one of the Claims 2 or 3 , characterized in that the multifunctional comonomer is present in the mixture in step a) in an amount of 0.01 to 5.0 mol%, preferably 0.02 to 1.0 mol%, based on the sum of the amounts of succinic acid, 1,4-butanediol and the multifunctional comonomer. The method according to one of the preceding claims, characterized in that the mixture in step a) consists of more than 85 wt.%, preferably more than 92 wt.%, of succinic acid and 1,4-butanediol. The method according to one of the preceding claims, characterized in that, prior to heating in step b), the existing air atmosphere is replaced by a nitrogen atmosphere. The method according to one of the preceding claims, characterized in that the catalyst is added in step b) only after the water produced during the esterification reaction has been substantially removed from the reaction mixture. A polybutylene succinate (PBS), characterized in that the values of the complex viscosity η* of the PBS in the frequency range from 0.05 to 10 rad/s, determined by dynamic frequency sweeps over a frequency range of 0.5-500 rad/s at 130 °C with an elongation of 0.5 % according to DIN 53019-4, are less than 30%, preferably less than 20%, and most preferably less than 16% of the average value of the complex viscosity ${\overline{\eta }}_{\mathrm{0,05}-10}^{*}$ in this frequency range. The polybutylene succinate (PBS) according to claim X, characterized in that it has a melt flow rate MFR ₂ (190 °C; 2.16 kg) measured according to ISO 1133 in the range of 1 to 50 g/10 min, preferably from 10 to 30 g/10 min. The polybutylene succinate (PBS) according to claim X, characterized in that it possesses an intrinsic viscosity iV, determined by dynamic mechanical analysis according to DIN EN ISO 1628-1:2021-06, in a range of 1.1 to 1.6 dL/g. Use of multifunctional comonomers according to one of the Claims 2 or 3 in an amount of 0.01 to 5.0 mol%, preferably 0.02 to 1.0 mol%, based on the sum of the amounts of succinic acid, 1,4-butanediol and the multifunctional comonomer, in the process according to one of the Claims 1 until 7 to adjust the degree of branching in the obtained polybutylene succinate (PBS).