Modular reactor for synthesis

Abstract

The invention relates to a continuous method for producing a prepolymer in a reactor having an elongated hollow body, in which at least two reactants are continuously introduced at one end of a reaction zone of the hollow body, the at least two reactants are polymerized with each other in the reaction zone, and the prepolymer is discharged at the other end of the reaction zone; the elongated hollow body has at least a first partial region and a second partial region in the reaction zone; the inner diameter of the hollow body in the second partial region is at least 10% greater than the inner diameter of the hollow body in the first partial region, and the length of the second partial region is greater than or equal to the length of the first partial region. The invention also relates to a reactor for use in such a process.

Description

Technical Field

[0001] The present invention relates to a continuous process for producing polyurethane prepolymers. Background Art

[0002] Prepolymers are reactive oligomers or short-chain polymers used to produce long-chain polymers. They are precursors that, unlike the final product, remain soluble or easily meltable. Prepolymers allow for the production of block copolymers or forming processes before curing through crosslinking or step polymerization to a more solid state. Similarly, prepolymers can also be finished polymers with a low molar mass. Low-molecular-weight finished prepolymers are often used as stabilizers or adjuvants.

[0003] Different conditions for producing prepolymers enable a wide range of mechanical properties to be achieved. This ranges from soft, elastic foams and fibers to solid moldings with high impact strength. This means the range of applications is already very large and is constantly expanding.

[0004] For example, WO 2007 / 037824 A2 discloses a process for the continuous production of prepolymers.

[0005] EP 1391472 A1 describes a method for the continuous production of thermoplastically processable polyurethanes, in which at least two different polyols and a chain extender are used in combination with an isocyanate. The polyurethane can be produced stepwise (prepolymer dosing method) or by reacting all components simultaneously in one step (one-shot dosing method). A continuously operating extruder is used, as also described in WO 2007 / 101807 A1 or WO 2021 / 122303 A1. The goal here is to directly produce the finished molded article. Extruders are associated with high temperatures of approximately 150°C to 300°C. Such high temperatures are not conducive to precise adjustment of the properties of the prepolymer.

[0006] Polyurethanes are products formed during the polyaddition polymerization of primarily (poly)isocyanates with (poly)alcohols. The connecting unit is the carbamate group. Carbamate groups can also link sequences of other functional groups (polyesters, polyethers, or others). In addition to carbamate groups, the polymerization of polyurethanes can also (in particular) form urea, imide, amide, or isocyanurate groups, depending on the reactants.

[0007] US Pat. No. 7,795,359 describes the continuous production of various prepolymers in a spiral microreactor with a micromixer. Ultrasonic treatment is used to avoid high molecular weight polymers. The spiral shape results in a loss of high pressure and limits reaction control, such as setting a specific product composition or viscosity.

[0008] EP 1 669 385 A1 describes a continuous process for the synthesis of acid-terminated isocyanates.

[0009] US 5471037 A describes a process for producing polymers in a tubular reactor, wherein a static mixer is used upstream of the reaction zone of the tubular reactor.

[0010] EP 2287228 A2 describes the production of silylated prepolymers. For the synthesis, a tubular reactor with an internal static mixer is described. Several reactors can be connected in series, with the catalyst or silylating agent being fed between the reactors. A length / diameter ratio of 10:1 to 50:1 is mentioned as the reactor dimensions. The reaction temperature is between 80°C and 200°C. The examples provide no information on the exact dimensions of the reactors, nor on characteristic product properties, such as molar mass and molar mass distribution.

[0011] JP 2019-202477A describes a method for coating a laminate with an adhesive.

[0012] To better control product quality, WO 2021 / 122284 A1 uses a loop reactor. Here, a portion of the stream is fed back into the reactor. Simultaneously, the product is continuously discharged. This allows for at least partial influence on product quality. However, the ability to influence overall product quality is limited.

[0013] Previous reactor systems exhibited the following disadvantages: variability in product properties and poor adjustability, unwanted side reactions leading to gel formation, and reactor blockages that necessitated repeated experiments. Summary of the Invention

[0014] The present invention aims to improve process control, homogeneous product properties (reproducible adjustment of the desired product molar mass and molar mass distribution), and the problem of by-products leading to reactor maintenance costs. Furthermore, the present invention aims to provide a scalable process for producing prepolymers, in particular polyurethane prepolymers, which enables high yields, low to no by-products and degradation products, and efficient conversion.

[0015] The present invention relates to a continuous method for producing a prepolymer in a reactor having an elongated hollow body, wherein at least two reactants are continuously introduced at one end of a reaction zone of the hollow body, polymerize with one another in the reaction zone, and the prepolymer is discharged at the other end of the reaction zone; the elongated hollow body comprises at least a first subregion and a second subregion in the reaction zone; the inner diameter of the hollow body in the second subregion is at least 10% greater than the inner diameter of the hollow body in the first subregion. Preferably, the length of the second subregion is greater than or equal to the length of the first subregion.

[0016] Preferably, in all embodiments of the present invention, the prepolymer is a polyurethane prepolymer. One of the reactants contains at least one alcohol group, and one of the reactants contains at least one isocyanate group. Therefore, the present invention particularly relates to a continuous method for producing a polyurethane prepolymer in a reactor having an elongated hollow body, wherein at least two reactants are continuously introduced at one end of a reaction zone of the hollow body, polymerized in the reaction zone, and the prepolymer is discharged at the other end of the reaction zone; one of the reactants contains at least one alcohol group, and one of the reactants contains at least one isocyanate group; the elongated hollow body comprises at least a first subregion and a second subregion in the reaction zone; the inner diameter of the hollow body in the second subregion is at least 10% greater than the inner diameter of the hollow body in the first subregion. Preferably, the length of the second subregion is greater than or equal to the length of the first subregion.

[0017] The present invention further relates to a continuous process for producing a polyurethane prepolymer in a reactor having an elongated hollow body, wherein at least two reactants are continuously introduced at one end of a reaction zone of the hollow body, polymerized in the reaction zone, and the prepolymer is discharged at the other end of the reaction zone; one of the reactants contains at least one alcohol group and at least one of the reactants contains one isocyanate group;

[0018] The reactor is operated at a temperature (T), residence time (t) and optional molar excess (c) of the reactants such that a target average molecular weight of the prepolymer of 5000 Da to 80000 Da is obtained according to the following formula:

[0019]

[0020] in

[0021] M k (T, t, c) is the target average molecular weight of the prepolymer,

[0022] A(T) is 0.00039Da,

[0023] K(T) is 0.05733K -1 ,

[0024] A(t) is 1354Da min -1 ,

[0025] A(c) is 534Da mole- 1 ,

[0026] T is the temperature in K,

[0027] t is the residence time in minutes,

[0028] c is the molar excess of the reactants in mol %.

[0029] The present invention further relates to a reactor suitable for carrying out the method according to the invention, wherein the reactor comprises an elongated hollow body with an inlet at one end and an outlet at the other end; the elongated hollow body comprises at least a first subregion and a second subregion; the inner diameter of the hollow body in the first subregion is <2.2 mm, and the inner diameter of the hollow body in the second subregion is ≥2.2 mm; the inner diameter of the hollow body in the second subregion is at least 10% greater than the inner diameter of the hollow body in the first subregion; the first subregion and the second subregion independently of one another each have a length of ≥1 m. Preferably, the length of the second subregion is greater than or equal to the length of the first subregion.

[0030] All of these aspects of the present invention can be combined with one another. For example, the description of the method according to the present invention can be applied to the reactor according to the present invention. The reactor can be used in the method according to the present invention. Therefore, the following detailed description relates to both the method and the reactor, even if only one of these two aspects is explicitly mentioned. DETAILED DESCRIPTION

[0031] The present invention relates to a continuous process for producing prepolymers in a reactor having an elongated hollow body. The reactor is also referred to as a microreactor because the elongated hollow body is typically a thin tubular body or hose, i.e., a hollow body whose length is many times greater than its width / diameter, for example, with a length to width (or diameter) ratio of 50:1 to 20,000:1, in particular 100:1 to 10,000:1, or 200:1 to 5,000:1, and particularly preferably 400:1 to 2,000:1. This ratio should be present in particular in the reaction zone of the hollow body. In the case of partial regions with staggered width / diameter, the width / diameter of each partial region is used as a fraction of the length of the partial region relative to the total length of the hollow body or reaction zone, or as an average value of the width / diameter. Particularly efficient reactions can occur in these thin hollow bodies.

[0032] The tubular body may have different cross-sections, such as circular, elastic, rectangular, square, and mixtures thereof.

[0033] The tubular body is essentially circular, cylindrical, or prismatic, i.e., within a subregion with a given width / diameter, this width / diameter should remain constant. Mixing elements may be unused, for example due to the constriction of the tubular body, for example, over less than 5%, preferably less than 1%, of the length of the hollow body or reaction zone, or may be completely unused. Alternatively, the hollow body may be curved, for example, to accommodate the reactor in a compact manner.

[0034] For simplicity, the term "inner diameter" is used herein to refer to the internal width or diameter of a hollow body, meaning the average dimension of the cross-section of the hollow body, wherein the shape can be different, such as, as mentioned above, circular, oval, rectangular, square, and mixtures thereof. This means that when referring to a diameter (which also refers to a description of width) below, it is not limited to a circular cross-sectional shape unless this is explicitly mentioned. The present invention includes cross-sectional dimensions having a cross-sectional area that is the same as the cross-sectional area of ​​a specified diameter (e.g., inner diameter) of a circular cross-section.

[0035] In the process according to the invention, at least two reactants are introduced continuously at one end of the reaction zone of the hollow body, polymerized in the reaction zone to form a prepolymer, and the prepolymer is discharged at the other end of the reaction zone.

[0036] The elongated hollow body should comprise at least a first partial region and a second partial region in the reaction zone, wherein the inner diameter of the hollow body in the second partial region is preferably at least 10% greater than the inner diameter of the hollow body in the first partial region, and the length of the second partial region is greater than or equal to the length of the first partial region. Therefore, in the case of a larger diameter in the second partial region, even if the second partial region has the same length as the first partial region, the volume of the reaction zone in the second partial region increases and is 21% greater than the volume of the first partial region (e.g., D1=1 / D2=1.1>d 2 =1.21).

[0037] Particularly preferably, the volume (internal volume) of the second partial region is greater than the volume of the first partial region, preferably the volume of the second partial region is at least 5%, preferably at least 10%, greater than the volume of the first partial region. The increasing volume from one partial region to the next can create particularly stable production conditions, in particular in the case of prepolymers.

[0038] The two reactants are usually mixed in the reactor at the beginning of the reaction zone so that they can only react with each other there. In other cases, they can be mixed beforehand, i.e., if they do not react immediately after mixing, for example, when the reaction conditions are only created in the reaction zone (e.g., by requiring a higher temperature and / or the presence of a catalyst).

[0039] In a particularly preferred embodiment, the prepolymer is a polyurethane prepolymer. For the production of polyurethane, at least one of the reactants preferably contains at least one alcohol group, preferably two or more alcohol groups, and at least one of the reactants contains at least one isocyanate group, preferably two or more isocyanate groups. Preferably, a reactant having two alcohol groups and a reactant having two isocyanate groups are used. Additional reactants having three or more alcohol groups and / or three or more isocyanate groups may be added as crosslinking agents, the amount of the additional reactants preferably being less than that of the reactant having two alcohol groups or two isocyanate groups.

[0040] The present invention further relates to a reactor suitable for carrying out the method according to the present invention. A preferred reactor according to the present invention comprises an elongated hollow body with an inlet at one end and an outlet at the other end. The hollow body has staggered inner diameters, i.e., at least two subregions with different inner diameters. The elongated hollow body comprises at least a first subregion and a second subregion, wherein the inner diameter of the hollow body in the first subregion is preferably < (less than) 2.2 mm, and the inner diameter of the hollow body in the second subregion is ≥ (greater than or equal to) 2.2 mm; the inner diameter of the hollow body in the second subregion is at least 10% larger than the inner diameter of the hollow body in the first subregion. Furthermore, the first subregion and the second subregion preferably each independently have a length of ≥ (greater than or equal to) 1 m. The length of the second subregion is greater than or equal to the length of the first subregion. The reactor can be used with or without the preferred features of the method according to the present invention. These specified diameters and lengths of the subregions enable particularly preferred prepolymer production, reducing side reactions and offering the advantage of reduced reactor clogging, thereby benefiting from increased reusability without the need for intermediate flushing.

[0041] Preferably, the inner diameter in the second subregion is at least 20%, preferably at least 30%, particularly preferably at least 40%, and even more preferably at least 50% greater than the inner diameter in the first subregion. The increased inner diameter of the second subregion compared to the first subregion is associated with the above-mentioned particularly significant advantages.

[0042] Preferably, the second partial region is longer than the first partial region. Particularly preferably, the second partial region has a length that is at least 10% greater than the length of the first partial region. Preferably, the partial region is at least 20% longer than the first partial region, particularly preferably at least 40%, or at least 60%, or even at least 80%.

[0043] In principle, the aforementioned subregions describe longitudinal regions of the elongated hollow body having the aforementioned relative dimensions relative to one another. These subregions can, in principle, be located at any desired position within the hollow body. In this case, the first subregion is located in front of the second subregion, so that the inner diameter increases from the inlet to the outlet. The first subregion is preferably located at the entrance to the reaction zone. Alternatively, or in combination therewith, the second subregion is located at the outlet from the reaction zone.

[0044] Depending on the specific requirements of the first and second partial regions, the inner diameter can have these two types of inner diameter classifications. In a further embodiment, the inner diameter has at least three types of diameter classifications over the length of the reaction zone. The first and second partial regions mentioned herein form regions within these at least three classifications. In this case, the first and / or second partial regions may have one or more subregions to form further diameter classifications. The entire partial region and the subregions together meet the described relative or absolute dimensions (e.g., the inner diameter is larger or smaller than the other partial regions described). Alternatively, or in combination therewith, additional partial regions may be provided that have dimensions different from the currently specified dimensions. For example, in addition to the above, there may be an intermediate partial region (or "central partial region") between the first and second partial regions that differ in size from the other partial regions, particularly the first and second partial regions. However, the inner diameter should always increase from inlet to outlet, i.e., the inner diameter of the intermediate partial region should not be smaller than the preceding partial region (in the inlet direction), and the inner diameter should not be larger than the following partial region (in the outlet direction). This intermediate subregion (also referred to as the central subregion) can be disposed between the first subregion and the second subregion, wherein the inner diameter of the central subregion is larger than the inner diameter of the first subregion and smaller than the inner diameter of the second subregion. Preferably, the central subregion has a length of at least 30 cm. The inner diameter of the central subregion can be at least 5%, preferably at least 10%, larger than the inner diameter of the first subregion; and the inner diameter of the second subregion can be at least 5%, preferably at least 10% larger than the inner diameter of the central subregion.

[0045] In a preferred embodiment, the second partial region comprises subregions having at least two different inner diameters, wherein the inner diameter of the subregion closer to the first partial region (in the inlet direction) is smaller than the inner diameter of the subregion farther away from the first partial region (in the outlet direction). Preferably, each subregion has a length of at least 30 cm.

[0046] In a preferred embodiment, the first partial region comprises subregions having at least two different inner diameters, wherein the inner diameter of the subregion closer to the second partial region (in the outlet direction) is larger than the inner diameter of the subregion farther away from the second partial region (in the inlet direction). Preferably, each subregion has a length of at least 30 cm.

[0047] Intermediate inner diameters can be further graded.

[0048] Preferably, the reaction zone has a length of at least 50 cm, preferably at least 1 m. Similarly, the hollow body preferably has an internal diameter of <2.2 mm, preferably <2.0 mm, in the first partial region, and / or the hollow body has an internal diameter of ≥2.2 mm, preferably ≥2.6 mm in the second partial region. For example, the internal diameter in the first partial region may be 1.4 mm to 2.1 mm, and the internal diameter in the second partial region may be 2.2 mm to 18 mm. The partial regions meet the specific diameter requirements over their entire length. Of course, the relative requirement of a diameter that is at least 10% larger must still be met. That is, if the internal diameter in the first partial region is 2.1 mm, the internal diameter in the second partial region is at least 2.31 mm.

[0049] Preferably, the reaction zone has a volume of at least 25 ml, preferably at least 100 ml, and particularly preferably at least 500 ml. Alternatively, or in combination therewith, the reaction zone preferably has a volume of at most 5 liters, preferably at most 3 liters, and particularly preferably at most 2 liters. For example, the volume of the reaction zone may be from 25 ml to 2 liters. The volume of the reaction zone is considered to be the volume of the region in the hollow body where polymerization conditions are applied or purification is possible, for example, the volume of the region from the inlet to the outlet. At the inlet, the reactants are typically combined. At the outlet, the prepolymer and any unreacted reactants are discharged from the reactor.

[0050] The residence time in the reactor can be determined or regulated by volume and throughput (or flow). The residence time of the polymerized reactant that is polymerized into prepolymer in the reaction zone is preferably at least 2min, preferably at least 3min or at least 4min, for example 2min to 15min, preferably 3min to 12min, particularly preferably 4min to 10min. During these times, for example, by selecting suitable temperature, reactant concentration and optional catalyst, it is possible to achieve good polymerization into prepolymer. Preferably, according to the present invention, catalyst is not added to the reactant fluid. Similarly, specific catalyst is preferably not used on the wall of the hollow body. Specific catalyst is prepared specifically for polymerization. According to the present invention, the hollow body is not particularly intended to accelerate the metal body of polymerization. However, polymerization may occur on its surface.

[0051] Preferably, the reactants are introduced into the reaction zone in the form of a solution. The total concentration of the reactants is preferably 20% to 60% (mass %). "Total" means the concentration of the various reactants added. After polymerization, in the case of complete polymerization, the reactant concentration also corresponds to the concentration of the prepolymer (in mass %). In the case of incomplete polymerization, the concentration of the prepolymer after the outlet is lower than the total concentration of the reactants at the inlet. The polymerization can be easily adjusted in the reactor according to the present invention at a specified mass %. This concentration is also well matched to the above-mentioned residence time. In a particularly preferred embodiment, the total concentration of the reactants is 24% to 56%, particularly preferably 30% to 50% (total mass %).

[0052] Preferably, a reactant is introduced into the reaction zone in excess relative to another reactant. Particularly preferably, it is introduced in an excess of at least 3% (mol %), preferably 5% (mol %), particularly preferably at least 10% (mol %) or even at least 20% (mol %). Preferably, the excess of a reactant relative to another reactant (which has other functional groups, such as NCO when the excess reactant has an OH functional group) is between 2% and 30%, preferably between 5% and 22% (mol %). The molar excess can produce a target molar mass distribution, particularly a maximum molar mass, in the obtained prepolymer. This is generally desirable so that the prepolymer remains soluble. In the production of polyurethane prepolymers, the reactant with one or more (especially two) alcohol groups is preferably in excess.

[0053] Preferably, the temperature in the reaction zone is from 20° C. to 80° C., preferably from 30° C. to 70° C. or from 35° C. to 60° C., particularly preferably from 40° C. to 55° C., or any range between these values. The reactor may include a heating device for heating the hollow body. At these temperatures, the polymerization can be well controlled without causing excessively rapid polymerization leading to high molar masses or with little or no undesirable side reactions.

[0054] In the production of prepolymers, preferably polyurethane prepolymers, the reactor is preferably operated at a temperature (T), residence time (t) and optional molar excess (c) of the reactants such that a target average molecular weight of the prepolymer of 5000 Da to 80000 Da is obtained according to the following formula:

[0055]

[0056] Among them, M k (T, t, c) is the target average molecular weight of the prepolymer, A(T) is 0.00039 Da, K(T) is 0.05733 K -1 , A(t) is 1354Da min -1 , A(c) is 534Da mol-1 , T is the temperature in K,

[0057] T is the residence time in minutes, and c is the molar excess of the reactants in mol%. The temperature (T), residence time (t), and molar excess can be easily adjusted and matched to satisfy the above formula. For example, the temperature (T), residence time (t), and molar excess can be within the above ranges. This allows the molar mass of the product to be well predicted (with fuzzy deviations) and well set.

[0058] All of the above-mentioned parameters and structural features of the reactor are preferably used for the production of polyurethane prepolymers.

[0059] The reactants for polyurethane production are primarily (poly)isocyanates and (poly)alcohols (e.g., polyesters, polyethers, and polycarbonate polyols). Isocyanates may have one or more isocyanate (NCO) functional groups. (Poly)alcohols may have one or more alcohol (OH, hydroxyl) groups. The hydrogens of the alcohol groups suitable for polymerization with the isocyanate groups may be Zerewitinoff-active hydrogens.

[0060] In addition, reactants such as isocyanates or alcohols may have special molecular building blocks, such as ethanolamine, carboxylic acid, olefins, organic sulfones or chlorosulfones. Typically, polymers with a low degree of polymerization have been used so that the polymer is soluble and preferably has a low viscosity in solution. For example, a polymeric reactant at a certain concentration (mass %) in DMAC as a solvent may have a Brookfield viscosity of no more than 200 mPas, preferably 1 to 150 mPas, at 25°C. Such polymeric reactants may also be used at other concentrations or in other solvents.

[0061] A catalyst can optionally be used for the polymerization in the reactor according to the invention. Catalysts are, for example, organic Lewis bases, Lewis acids, phosphates or (organic) metal salts / oxides. It is also possible not to use such catalysts or to use conventional catalysts.

[0062] As reactants, NCO functionalized reactants are combined with OH functionalized reactants. The reactants can be NCO or OH functionalized one or more times. Typical but non-limiting examples are NCO terminated reactants such as methylene diphenyl isocyanate (MDI), hexamethylene diisocyanate (HDI), toluene-2,4-diisocyanate (TDI), p-toluenesulfonyl isocyanate (TSI) and isomers thereof. Typical but non-limiting examples are OH terminated reactants such as methyldiethanolamine (MDEA), diethanolamine (DEA), tert-butyldiethanolamine (TBDEA), diols (e.g., ethylene glycol), alkyl alcohols (e.g., C 2-10 alcohols, such as ethanol) and polyols.

[0063] Preferably, the isocyanate reactant is an organic diisocyanate. Suitable organic diisocyanates include, for example, aliphatic diisocyanates, alicyclic diisocyanates, heterocyclic diisocyanates, and aromatic diisocyanates. Aliphatic diisocyanates include, for example, branched or unbranched C2-C 18 Alkyl diisocyanates, for example hexamethylene diisocyanate. Cycloaliphatic diisocyanates are, for example, isophorone diisocyanate, 1,4-cyclohexane diisocyanate, 1-methyl-2,4- and 2,6-cyclohexane diisocyanate and the corresponding isomer mixtures, 4,4′-, 2,4′- and 2,2′-dicyclohexylmethane diisocyanate and the corresponding isomer mixtures. Examples of aromatic diisocyanates include 4,4-methylenebis(phenylisocyanate), 2,4-toluene diisocyanate, a mixture of 2,4- and 2,6-toluene diisocyanates, 4,4'-diphenylmethane diisocyanate, a mixture of 2,4'-diphenylmethane diisocyanate and 2,2'-diphenylmethane diisocyanate, a mixture of 2,4'-diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate, urethane-modified liquid 4,4'-diphenylmethane diisocyanate and / or 2,4'-diphenylmethane diisocyanate, 4,4'-diisocyanatodiphenyl-ethan-(1,2) and 1,5-naphthylene diisocyanate. 4,4-Methylenebis(phenylisocyanate) ("MDI") is preferred.

[0064] Preferably, the alcohol reactant is an organic diol. Preferred diols are methyldiethanolamine ("MDEA") and tert-butyldiethanolamine ("TBDEA").

[0065] The polyurethane prepolymer is preferably prepared in an isothermally controlled reactor. In all embodiments of the present invention, and in this embodiment, the elongated hollow body is preferably a tubular body for the synthesis of the polyurethane prepolymer. The process flow of the synthesis can be carried out as follows.

[0066] The reactants are placed in a suitable container. Depending on the state of aggregation and product quality, a solvent is used for the reactants. Preferably, only liquid components are used or the reactants are introduced into the reactor in liquid form. If necessary, the reactants may also be preheated. The temperature of the reactants is preferably between 0°C and 80°C or 10°C and 70°C, preferably between 20°C and 60°C, or a combination of these ranges.

[0067] The storage and / or handling of the reactants upstream of the reaction zone is preferably carried out under inert conditions, preferably including anhydrous conditions. Under inert conditions, the stored contents of the reactants are flushed with an inert gas and the reactants are superimposed with an inert gas. In addition, storage is carried out with or without a stabilizer. For example, toluene-2,4-diisocyanate (TSI) or similar components can be used as a stabilizer.

[0068] The reactant(s) are preferably used in dissolved form. The isocyanate and / or alcohol are particularly preferably used in dissolved form.

[0069] As a solvent, a known aprotic polar substance such as DMAc, tetrahydrofuran (THF), dimethyl sulfoxide (DMSO) or dimethylformamide (DMF) can be used.

[0070] Two or more reactants can be transported to the reactor and brought together by means of pumps such as diaphragm pumps, piston pumps, or gear pumps. The choice of pump to be used is ultimately a matter of proportionality or viscosity of the respective reactants. Preferably, no mixing element is used in the merging process. Preferably, the reactants are supplied only via branch lines.

[0071] In a preferred embodiment, the flow profile in the hollow body (especially in the reaction zone) is laminar. Laminar flow can be adjusted by selecting flow rate, viscosity (which in turn depends on the solvent, reactant concentration and temperature).

[0072] The structure of the elongated hollow body is preferably composed of one or more tubular elements arranged in rows. The tubular element can have an inner diameter of 0.5mm to 20mm, preferably 1mm to 12mm. As mentioned above, different inner diameters are adopted in some areas. The purpose is to increase the diameter as the reaction progresses to reduce the influence of thermal effects while minimizing the pressure loss generated. As the reaction progresses and the concentration of the prepolymer product increases, the viscosity increases. According to the present invention, this viscosity can be compensated by staggered inner diameters. The length of the partial area (e.g., tubular element) is preferably 0.1m to 7m, preferably 0.3m to 5.8m, for example 0.8m to 3m. The elongated hollow body can have a cross-sectional length of 0.1m to 7m, preferably 0.3m to 5.8m.

[0073] The elongated hollow body (particularly a tubular body) may have one or more bends, particularly J-shaped bends. For example, on or in a plate, the hollow body is primarily straight (for example, >70% of its length, preferably <80%), but may have bends so as to accommodate the entire length in a compact form. In general, the shape produced by the entire hollow body may be a tortuous shape, for example, in the case of a plurality of J-bend tubular bodies. Preferably, no mixer, in particular no static mixer, is used in the elongated hollow body or the reaction zone. The mixer may, for example, be a baffle plate with another straight hollow body. In the reaction zone, a laminar flow is preferably set (by appropriate structural measures without a mixer (which may cause turbulence), and / or by an appropriate flow rate at a given viscosity).

[0074] Preferably, the first and second subregions independently of one another each have a length of ≥ 1 m, and the length of the second subregion is greater than or equal to the length of the first subregion, as already described above. The length of the elongated hollow body or reaction zone can be up to 120 m or longer, for example up to 240 m or longer. Preferably, the hollow body or reaction zone has a length of at least 2 m, at least 3 m, at least 5 m, at least 8 m, at least 10 m, at least 15 m, particularly preferably (especially for industrial applications) at least 20 m, or even at least 25 m.

[0075] Examples of staggering according to the invention in a hollow body or reaction zone have the following dimensions: These are examples of the invention and further alternatives are possible within the general concept according to the invention.

[0076] 1. The first area: the inner diameter is 1.5mm to 2.15mm, and the length is 1m to 50m; the second area: the inner diameter is 2.3mm to 6mm, and the length is 1m to 50m.

[0077] 2. The first part area: the inner diameter is 1.5mm to 2.15mm, and the length is 1m to 50m; the central part area: the inner diameter is 2.2mm to 2.8mm, and the length is 1m to 50m; the second part area: the inner diameter is 2.9mm to 7mm, and the length is 1m to 50m.

[0078] 3. The first area: inner diameter is 1.5mm to 2.0mm, and length is 1m to 50m; the second area: inner diameter is 2.1mm to 11mm, and length is 1m to 50m.

[0079] 4. The first part area: the inner diameter is 1.5mm to 2.0mm, and the length is 1m to 50m; the central part area: the inner diameter is 1.8mm to 2.8mm, and the length is 1m to 50m; the second part area: the inner diameter is 2.9mm to 11mm, and the length is 1m to 50m.

[0080] 5. The first part area: the inner diameter is 1.5mm to 2.19mm, and the length is 1m to 50m; the first central part area: the inner diameter is 2.2mm to 2.5mm, and the length is 1m to 50m; the second central part area: the inner diameter is 2.51mm to 3.5mm, and the length is 1m to 50m; the second part area: the inner diameter is 3.6mm to 14mm, and the length is 1m to 50m.

[0081] Preferred examples of such staging are given in the examples of reactor arrangements 4 to 6, which can also be used for applications other than those shown in the examples.

[0082] Preferably, the length of the hollow body is greater than the width / diameter of the hollow body, in particular in the reaction zone or a partial region thereof, for example in the first partial region, the second partial region, and / or the third partial region. For example, in the hollow body, in particular in the reaction zone or a partial region thereof, for example in the first partial region, the second partial region, and / or the third partial region, the ratio of length to width (or to diameter instead of width) can be 50 or more, preferably 75 or more, more preferably 100 or more, in particular 125 or more, 150 or more, particularly preferably 200 or more, or 300 or more, particularly preferably 400 or more, or 500 or more. In the hollow body, in particular in the reaction zone or its sub-regions, for example in the first, second and / or third sub-regions, the ratio of length to width (or to diameter instead of width) can be 50:1 to 20,000:1, in particular 75:1 to 15,000:1, or 100:1 to 10,000:1, or 200:1 to 5,000:1, particularly preferably 400:1 to 2,000:1. This ratio should be present in particular in the reaction zone of the hollow body. In the case of staggered widths / diameters in the sub-regions, the width / diameter of each sub-region can be used as a fraction of the length of the sub-region relative to the total length of the hollow body or reaction zone, or as an average value of the width / diameter. Reactions can be particularly efficient in hollow bodies with such a length to width (or diameter) ratio.

[0083] Plastics (e.g. polytetrafluoroethylene - PTFE, polypropylene - PP, polyethylene - PE, polyvinyl chloride - PVC, polyvinylidene fluoride - PVDF, polychlorotrifluoroethylene - PCTFE, ethylenechlorotrifluoroethylene - ECTFE, perfluoroalkoxyalkane - PFA, perfluoroethylenepropylene - FEP, polyoxymethylene - POM, etc.), metals such as stainless steel (1.4301, 1.4404, 1.4571, 1.4539, 1.4547, etc.) or nickel-based alloys (2.4602, 2.4819, 2.4858, etc.) are usually used as materials for the hollow body or reactor.

[0084] The tubular body dimensions are preferably selected so as to achieve a 350 m 2 / m 3 Up to 6000m 2 / m 3 , preferably 1000m 2 / m 3 Up to 3000m 2 / m 3 This applies to the entire elongated hollow body and preferably also to each partial region individually.

[0085] In addition, the specific surface loading of the reactor is 2 l / hm 2 Up to 140 l / hm 2 , preferably 4 l / hm 2 Up to 40 l / hm 2 The specific surface loading of the reactor is the variable of the throughput (flow rate in l / h) per unit surface of the elongated hollow body or reaction zone.

[0086] The specific volume loading of the reactor is preferably 300 l / hm2. 3 Up to 23000l / hm2 3 , preferably 700 l / hm 3 Up to 5000l / hm2 3 The specific volume loading of the reactor is the variable of the throughput (flow rate in l / h) per unit volume in the elongated hollow body or reaction zone.

[0087] In the process, the hydrodynamic residence time is preferably between 0.5 and 20 minutes, preferably between 2 and 15 minutes. The residence time can be adjusted by the throughput (flow rate) of a given reactor. It represents the average residence time of the reactants and the products polymerized therefrom in the reaction zone.

[0088] If greater conversion is desired, the inner diameter of the elongated hollow body can be increased, and the length of the hollow body or its subsections can be increased. Thus, the tubular body diameter can be adjusted to increase conversion. A defined proportion of the heat of reaction can be compensated by a suitable combination of reaction enthalpy and the diameter and length of the subsections or tubular elements. Ideal reaction conditions are achieved through a combination of maximum conversion with minimal pressure loss, residence time, and temperature control.

[0089] The elongated hollow body is housed in a heating medium or heat exchanger. The heat exchanger can be composed of a single plate containing the hollow body, which is embedded in or surrounded by the heat exchanger. These plates can be arranged individually or in stacks of 2 to 50. Depending on the application, multiple stacks can also be connected to each other. Preferably, the hollow body is introduced into the plate, embedded, for example, in a groove-shaped recess in the plate, or placed on it, preferably placed in 1 to 30 plates. Such a structure is described in WO 2010 / 055034 A1 (incorporated herein by reference).

[0090] The plate and the tubular body can be made of a variety of materials, such as plastics (e.g., polytetrafluoroethylene (PTFE), polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), ethylenechlorotrifluoroethylene (ECTFE), perfluoroalkoxyalkane (PFA), perfluoroethylenepropylene (FEP), polyoxymethylene (POM), etc.), metals such as stainless steel (1.4301, 1.4404, 1.4571, 1.4539, 1.4547, etc.), nickel-based alloys (2.4602, 2.4819, 2.4858, etc.), etc. Preferably, the plate is made of fiber-reinforced (especially glass-fiber-reinforced) plastic, aluminum, or stainless steel. In these plates, the heating medium flows around the tubular body in a channel.

[0091] Depending on the configuration, one or more plates can be divided into separate temperature zones. Each temperature zone is maintained at the desired temperature by upstream temperature control.

[0092] The reaction temperature can be from 10°C to 80°C, preferably from 20°C to 60°C, preferably at least 25°C, particularly preferably at least 40°C.

[0093] The reactors or reaction parameters are designed so that they can be individually adapted to the specific prepolymer synthesis. For this purpose, tubular elements (together forming subregions of the reaction zone) are connected together differently, their temperatures (zones) are adjusted and the residence time (throughput) is varied.

[0094] The process conditions are preferably selected so that a conversion of 80% to 100%, preferably 95% to 100%, based on the NCO reactant (total mass %) is achieved at the end (outlet) of the reaction zone. For this purpose, the reaction size (especially the length), temperature and concentration, especially the excess alcohol reactant, are selected.

[0095] After the outlet, the product can be collected or harvested in a collection vessel. In the collection vessel, there are usually no polymerization conditions, for example, a relatively low temperature such as room temperature (e.g., 22° C.). It is also possible to prevent any polymerization by quenching. For this purpose, a monovalent reactant, preferably a monovalent alcohol, can be present in the collection vessel.

[0096] A particular feature of the reactor according to the invention is also that the reactor unit can be precisely matched to any reaction product (reaction enthalpy, molar mass, etc.).

[0097] Preferably, the product quality is monitored online, for example, by infrared spectroscopy, refractive index, viscosity, density, titration and / or light (laser) diffraction measurement. After leaving the reactor (at the outlet) and / or for the product in the collecting container, the conversion rate and product quality can be directly determined. For this purpose, the product can be analyzed inline / online by infrared (IR), viscosity, density, ultraviolet and visible light (UV-Vis), refractive index and titration. Online results (such as IR measurements) can be used directly to adjust process conditions, such as reactant flow. In particular, NCO conversion can be tracked by infrared spectroscopy.

[0098] The product container (as well as the reactant container) is preferably flushed / overpressurized with an inert gas and is anhydrous to prevent changes in product quality. The temperature of the product during storage or in the collection container is preferably controlled between -20°C and 50°C.

[0099] According to the present invention, the product prepolymer can be post-treated after the reaction zone. If necessary for polymerization, post-treatment can be performed in the product prepolymer collection vessel or in the hollow reactor, for example, at different temperatures or without a catalyst. Post-treatment can include temperature adjustment, inertization, end group modification, or a combination thereof. End group modification can include, for example, reaction with a monohydric alcohol to obtain an aliphatic-terminated polymer; reaction with a polyhydric alcohol to obtain a hydroxyl-terminated polymer; reaction with water to obtain amine end groups; reaction with a carboxylic acid to obtain amide end groups; or a combination thereof.

[0100] By using reactor according to the present invention and reaction parameters, side reaction can be avoided, and the reusability of reactor can be improved.Especially, side reaction product may be undesirable biuret, allophanate or higher urea formation thing, and they have negative properties for required prepolymer (especially in the case of polyurethane prepolymer).This may cause too high molar mass and crosslinking.Likely cause formation of the very high slightly soluble gel of viscosity.Gel may make reactor unable to use.

[0101] Depending on the requirements, post-processing is carried out in the reaction zone or in a collection vessel. Product quality can be stabilized by adding additives. Depending on the degree of conversion, reactive end groups may still be present. Additives are used to adjust the desired end group reactivity. A distinction can be made between NCO, amine, amide, hydroxyl, and aliphatic end groups.

[0102] To achieve NCO-terminated polymers, the degree of conversion is controlled accordingly and storage / filling is carried out under inert and anhydrous conditions.

[0103] Amine terminated polymers are achieved by adding precisely controlled amounts of water to the reaction zone or collection vessel and by rapid conversion.

[0104] Amide terminated polymers are achieved by adding precisely controlled amounts of carboxylic acid in the reaction zone or by rapid conversion in the collection vessel.

[0105] Hydroxyl terminated polymers are achieved by adding a polyol to the reaction zone or collection vessel.

[0106] Aliphatic terminated polymers are achieved by adding monohydric alcohols to the reaction zone or collection vessel.

[0107] Cleaning the reactor is also important. The polymerization of reactive components occurs throughout the entire process flow in the reaction zone. Polymerization is not limited to the combination of different reactants. Due to their high reactivity, reactants can also react or polymerize with themselves. In addition, laminar flow exists throughout the entire process flow. Therefore, reactive components can always be present in the flow up to the outlet or collection container. This can lead to the side reactions mentioned above (polyurea, allophan, biuret, gel formation and crosslinking). This can disrupt production and, in the worst case, irreversibly block the reactor. Therefore, in order to be able to operate the process flow continuously, regular flushing and defined startup / shutdown procedures are advantageous. The flushing procedure can vary depending on the process flow step.

[0108] Depending on the product requirements, flushing can be combined with post-treatment (stabilization step). This prevents the production of inferior products. Post-treatment can be performed near the end of the reaction zone, after the reaction zone in the reactor, or in a collection vessel. Stabilizers can be monohydric or polyhydric alcohols.

[0109] In the case of product changes or during medium-length downtimes (<7 days), it is preferred to first flush at least four reactor volumes with solvent. Suitable solvents have been described above, preferably DMAc. This is followed by a flush with a solvent / stabilizer mixture (preferably a mixture of 2:1 to 1:1) over four to ten reactor volumes. The exact volume is determined by online measurement (IR). Flushing is complete when no reactants or prepolymers, in particular no NCO reactants, are detected in at least two reactor volumes. If downtime is imminent, all line inputs and outputs are sealed and closed.

[0110] For downtimes of more than 7 days or when disassembling system parts, a larger-scale procedure is recommended. Preferably, the flushing step is performed as for medium-length downtimes. This is followed by a flush with an anhydrous stabilizer of 4 to 8 reactor volumes. Diols and alcohols are particularly suitable for this purpose, but are not limited thereto. The resulting insoluble components (oligomers, insoluble functionalized monomers) are removed by a further solvent flush of approximately 4 reactor volumes. In the case of longer downtimes of >30 days or disassembly, a flush sequence of approximately 4 reactor volumes with 96% ethanol, 50% ethanol / water, and water is also performed.

[0111] In laboratory analysis, the macromolecular properties of the prepolymer and its purity can be investigated. These properties depend on the reactants, their ratio, and the polymer chain length. The chain length is determined by size exclusion chromatography (SEC) (e.g., using THF or DMSO, 35° C., butylated hydroxytoluene (BHT) mobile phase marker 30.6 ml ret. Vol., RI detector, polystyrene (PS) standards, PSSSDV column, 0.8 ml / min). The average molecular weight (Mw) of the prepolymer is preferably in the range of 4000 Da to 80,000 Da, preferably 7000 Da to 50,000 Da, and particularly preferably 8000 Da to 25,000 Da. The polydispersity Mw / Mn is preferably less than 4, preferably less than 2. The above parameters can be set to achieve these ranges.

[0112] The chain length of the prepolymer directly affects the viscosity of the product. Therefore, product quality can also be determined by viscosity. This can be measured using a rheometer (Anton Paar MCR102, CC27 measuring instrument, cylindrical, 25°C). At 25°C, the preferred viscosity range is between 20 mPa*s and 30,000 mPa*s, preferably between 90 mPa*s and 7,000 mPa*s, and particularly preferably between 120 mPa*s and 5,000 mPa*s.

[0113] Preferably, the process according to the invention, in particular the process for preparing a polyurethane prepolymer, is operated such that for a given target molar mass M [Da] and a given prepolymer concentration [m %] in the product, a target viscosity is obtained in the range of 20 mPa*s to 30 000 mPa*s or another viscosity range as described above according to the formula

[0114]

[0115] Where μ(M, c) is the target viscosity, M is the target molecular weight [Da], c(PUR) is the prepolymer concentration in the product [m%], A(PUR) is 0.8319 mPa s, and K(PUR) is 0.1561 m% -1 , A(M) is 73 mPa s, K(M) is 0.0000829 Da -1 , A(η) is 0.00502. The target molar mass M [Da] and target prepolymer concentration are as described above, for example, a target molar mass Mw of 4,000 to 80,000 Da or 20% to 60% (mass %) or the preferred values ​​listed above. Preferably, the polymer content of the product, determined gravimetrically (vacuum drying oven Binder VDL 23 at 180°C for 3 hours), is 10% to 60%, preferably 30% to 50% (mass %).

[0116] The specific density of the polymer product, measured with a hydrometer (Carl-Roth, measuring range 0.75 to 1 and 1 to 1.1), is preferably from 0.8 to 1.2, preferably from 0.9 to 1.1.

[0117] The polymer content of the product, determined gravimetrically (vacuum drying oven Binder VDL 23 at 180° C., 3 hours), is preferably from 10% to 60%, preferably from 30% to 50% (total mass %).

[0118] The water content (Karl Fischer, Metrohm 907 Titrando) in the prepolymer is preferably less than <4000 ppm, preferably <2500 ppm (ppm by mass).

[0119] In particular, the sum of the metal contents of iron and copper (optical emission spectroscopy using inductively coupled plasma: ICP-OES, Thermo Scientific iCAP 7400, in H 2 SO 4 ) is preferably <10 ppm, preferably <4 ppm.

[0120] The product color (yellowness) is a measure that allows conclusions to be drawn about the quality and aging of the prepolymer product. Visually, the color is preferably colorless to slightly yellow. The HAZEN color value of the product (according to the Pt / Co scale and / or according to DIN ISO 6271) (UV-Vis, Thermo Scientific Evolution 350) is preferably <100, preferably <50.

[0121] Depending on the requirements, the residual NCO content is high (according to DIN EN ISO 14896, Metrohm 907 Titrando). If NCO blocking is not desired, the residual NCO content should be <0.1%, preferably <0.05% (total mass %).

[0122] The process according to the invention is freely scalable and preferably produces prepolymers at conversions of 0.13 kg / h to 1536.8 kg / h or multiples thereof.

[0123] Polyurethane prepolymers are widely used in building materials, packaging materials, vehicles, electrical equipment, insulation materials, household appliances, clothing, chemical additives, and more. The prepolymers according to the present invention can be used in these areas. For example, they can be used to achieve simpler and more intensive dyeing of fibers and end products. In these applications, the prepolymers can be used, for example, as color stabilizers to prolong the color stability of products.

[0124] The prepolymers according to the present invention can be used as spinning additives in (synthetic) fiber production. This improves fiber production with regard to process technology and fiber stability. The addition of prepolymers generally increases the resistance of plastics or fibers to degradation mechanisms caused by UV rays, light, oxidation, and heat. The prepolymers can be used as color stabilizers for polyurethane (PU) polymers (more strongly polymerized PU, e.g., PU that is no longer soluble in the aforementioned solvents (e.g., DMAc)). In particular, the prepolymers can be used to improve the spinning of PU fibers. Generally, prepolymers can be used as PU stabilizers.

[0125] The prepolymer can also be used as a reactant for further polymerization, for example as a chain extender. The prepolymer is combined with other monomers and chain extenders (e.g., polyols, polyglycols (ethylene glycol), polyacrylates, polyethers, polyesters, etc.). Any polymer such as polyurethane, polyurea, or other functionalized polymers can be extended. This can also be done in combination with other chain extenders such as polyols, polyglycols, polyacrylates, polyethers, or polyesters.

[0126] In specific embodiments, the present invention is defined by the following numbered embodiments and aspects, all of which can, of course, be further combined by any parameter, embodiment or aspect described herein.

[0127] 1. A continuous process for producing a prepolymer in a reactor having an elongated hollow body, wherein at least two reactants are continuously introduced at one end of a reaction zone of the hollow body, the at least two reactants are polymerized in the reaction zone, and the prepolymer is discharged at the other end of the reaction zone,

[0128] The elongated hollow body comprises at least a first partial region and a second partial region in the reaction zone, the inner diameter of the hollow body in the second partial region being at least 10% larger than the inner diameter of the hollow body in the first partial region.

[0129] 2. The method according to 1, wherein the volume of the second partial region is greater than the volume of the first partial region, preferably the volume of the second partial region is at least 5%, preferably at least 10% greater than the volume of the first partial region.

[0130] 3. The method according to 1 or 2, wherein the prepolymer is a polyurethane prepolymer, one of the reactants contains at least one alcohol group, and one of the reactants contains at least one isocyanate group.

[0131] 4. The method according to 1 to 3, wherein the inner diameter in the second partial region is at least 20%, preferably at least 30%, particularly preferably at least 40%, and especially preferably at least 50% larger than the inner diameter in the first partial region.

[0132] 5. The method according to 1 to 4, wherein the length of the second partial region is greater than or equal to the length of the first partial region.

[0133] 6. The method according to 5, wherein the second partial region has a length that is at least 10% greater than a length of the first partial region.

[0134] 7. The method according to 1 to 6, wherein the first partial region is located at the inlet into the reaction zone and / or the second partial region is located at the outlet of the reaction zone.

[0135] 8. The method according to 1 to 7, wherein the inner diameter has at least 3 diameter grades over the length of the reaction zone.

[0136] 9. The method according to 8, wherein a central partial region is provided between the first partial region and the second partial region, and an inner diameter of the central partial region is larger than an inner diameter of the first partial region and smaller than an inner diameter of the second partial region.

[0137] 10. The method according to 8 or 9, wherein the second partial region includes subregions having at least two different inner diameters, wherein the inner diameter of a subregion closer to the first partial region is smaller than that of a subregion farther from the first partial region.

[0138] 11. The method according to items 1 to 10, wherein the reaction zone has a length of at least 50 cm, preferably at least 1 m; and / or the hollow body has an inner diameter of <2.2 mm in the first partial region and / or the hollow body has an inner diameter of ≥2.2 mm in the second partial region.

[0139] 12. The method according to 1 to 11, wherein the reaction zone has a volume of at least 25 ml, preferably at least 100 ml, particularly preferably at least 500 ml; and / or the reaction zone has a volume of at most 5 l, preferably at most 3 l, particularly preferably at most 2 l.

[0140] 13. The process according to 1 to 12, wherein the residence time of the polymerized reactants in the reaction zone to form the prepolymer is at least 2 min, preferably 3 min to 15 min, particularly preferably 4 min to 10 min.

[0141] 14. The method according to 1 to 13, wherein the reactants are introduced into the reaction zone in the form of a solution, and the concentration of the reactants is 20% to 60% (mass %) in total.

[0142] 15. The process according to 1 to 14, wherein one reactant is introduced into the reaction zone in excess relative to the other reactant, preferably in an excess of at least 3% (mol %), preferably 5% (mol %), particularly preferably at least 10% (mol %).

[0143] 16. The process according to 1 to 15, in combination with 3, for producing a polyurethane prepolymer, wherein the reactor is operated at a temperature (T), a residence time (t) and an optional molar excess (c) of the reactants such that a target average molecular weight of the prepolymer of 5000 Da to 80000 Da is obtained according to the following formula:

[0144]

[0145] in

[0146] M k (T, t, c) is the target average molecular weight of the prepolymer,

[0147] A(T) is 0.00039Da,

[0148] K(T) is 0.05733K -1 ,

[0149] A(t) is 1354Da min -1 ,

[0150] A(c) is 534Da mole- 1 ,

[0151] T is the temperature in K,

[0152] t is the residence time in minutes,

[0153] c is the molar excess of the reactants in mol %.

[0154] 17. The process according to 1 to 16, wherein the elongated hollow body has an aspect ratio of 100:1 to 20,000:1, preferably an aspect ratio of 100:1 to 20,000:1 in the reaction zone.

[0155] 18. The method according to 1 to 17, wherein the width or diameter remains essentially constant in a partial region, the optional constriction of the tubular body being limited to less than 5% of the length of the hollow body or reactor zone.

[0156] 19. The process according to 1 to 18, wherein no mixer is used in the reaction zone.

[0157] 20. A reactor suitable for implementing the methods according to 1 to 19, wherein the reactor has an elongated hollow body with an inlet at one end of the hollow body and an outlet at the other end; the elongated hollow body includes at least a first partial area and a second partial area; the inner diameter of the hollow body in the first partial area is <2.2 mm, and the inner diameter of the hollow body in the second partial area is ≥2.2 mm; the inner diameter of the hollow body in the second partial area is at least 10% larger than the inner diameter of the hollow body in the first partial area.

[0158] 21. The reactor according to 20, wherein the first sub-region and the second sub-region independently of one another each have a length of ≧1 m.

[0159] 22. The reactor according to 20 or 21, wherein the length of the second partial region is greater than or equal to the length of the first partial region.

[0160] 23. The reactor according to 20, 21 or 22, wherein the volume of the second partial region is greater than the volume of the first partial region, preferably the volume of the second partial region is at least 5%, preferably at least 10% greater than the volume of the first partial region.

[0161] 24. A continuous process for producing a prepolymer in a reactor having an elongated hollow body, wherein at least two reactants are continuously introduced at one end of a reaction zone of the hollow body, the at least two reactants are polymerized in the reaction zone, and the prepolymer is discharged at the other end of the reaction zone.

[0162] The elongated hollow body comprises at least a first partial region and a second partial region in the reaction zone; the inner diameter of the hollow body in the second partial region is at least 10% larger than the inner diameter of the hollow body in the first partial region, and the volume of the second partial region is larger than the volume of the first partial region; preferably, the reaction zone of the elongated hollow body has an aspect ratio of 75:1 or greater; preferably in combination with one of 1 to 23.

[0163] The present invention is further illustrated by the following specific examples.

[0164] Example

[0165] Example 1: Preparation and temperature control of reactant solution

[0166] Preparation of the isocyanate solution (reactant 1): Reactant 1 was prepared by mixing 4,4-methylenebis(phenylisocyanate) (MDI) (Sigma-Aldrich, 98%) with N,N-dimethylacetamide (DMAc) (Sigma-Aldrich, ≥99.8%). The MDI content ranged from 10% to 70%, depending on the target polyurethane content in the product (see column [B] of Table 1). Depending on the pretreatment (see column [I] of Table 1), reactant 1 was also added at 1% based on the total solution of p-toluenesulfonyl isocyanate (TSI) (Sigma-Aldrich, 96%). 5% molecular sieves (Carl-Roth, 4A, in bead form) were added to the solution as a drying agent.

[0167] Preparation of diol solution (reactant 2): Reactant 2 was prepared from N-methyldiethanolamine (MDEA) (Sigma-Aldrich, ≥99%) in DMAc. The concentration ranged from 30% to 100%, depending on the PUR content of the product (see column [B] of Table 1). 5% (Carl-Roth, 4A, in the form of beads) was added to the solution as a drying agent.

[0168] For post-treatment, solutions of the stabilizers ethanol (EtOH) (Carl Roth, 99.5%, ultrapure), ethylene glycol (Carl Roth, 99%, used for synthesis), and MDEA in DMAc were prepared. The stabilizer concentration was 30% in each case. As a drying agent, 5% (Carl-Roth, 4A, in the form of beads) was added to the solution.

[0169] Solutions were prepared in a glove bag under a nitrogen atmosphere. In addition, the nitrogen gas used (Linde, 99.8%) was passed through a drying column with glass wool and Sicapent (Merck, phosphorus pentoxide, with indicator) to reduce the humidity of the gas.

[0170] After preparation, the solution was sealed with a septum and then drained out. The reactants were integrated into the process stream under an overlay of argon (Linde, 99.996).

[0171] Throughout the procedure, the reactant and product vessels were overpressurized by a slight argon overpressure (0.14 to 0.2 bar overpressure). All vessels were equipped with septa to allow the addition of stabilizers or additives (see Table 1, columns [H] and [I]).

[0172] The temperature was regulated using a water bath thermostat (Huber CC-205B). The thermostat was equipped with a cooling coil, which also allowed the temperature to be lower than room temperature. The cooling medium was supplied externally from the building service system.

[0173] The process was controlled online using a Fourier transform infrared spectrometer (FTIR) instrument (Bruker Alpha II). This was used to determine the residual isocyanate content.

[0174] Between each experiment, the reactor system was flushed with stabilizer solutions of ethanol (EtOH) and DMAC until no isocyanate was detected by FTIR at both reactor residence times.

[0175] Example 2: Continuous Reactor 1 Experimental Series

[0176] The experimental series includes Experiments 1 to 9 in column [A] of Table 1. Solutions were prepared similarly to Example 1. A reactor as described in WO 2010 / 055034 A1 was used. Briefly, the reactor is a flow reactor in which the reaction occurs in one or more tubular bodies. Reactants are supplied at one end of the tubular system, and products are obtained at the other end. The reactor operates continuously. The tubular bodies can be arranged in one or more plates.

[0177] For the first series of experiments, a reactor with a volume of 17.5 ml was used (see column [F] in Table 1). A piston pump (Knauer Azure, P4.1S and P2.1S) was used to transport the medium. The medium was fed into the reactor via a T-connection. Product [B] was obtained at a flow rate [D] at a temperature [C]. The parameters [H], [I], [M], [N], [O] and [P] were varied (Tables 1 and 2). The products showed a polyurethane content [B] and the associated properties [J], [K] and [L] according to Table 2. The dimensions of the tubular system in setup 1 are shown in the table below; the tubulars are described in order from top to bottom. The total volume in the reactor is given below.

[0178]

[0179] The experiment of setting mode 1 shows that this setting mode is not very suitable. Compared with medium diameter and large diameter (>=2.2mm), the residence time in small diameter (<2.2mm) is too long. This makes it difficult to control the molar mass. Experiments 1 to 9 show that, although the temperature window is relatively narrow, the molar mass varies between 243017Da and 8913Da. In addition, a two-phase mixture is observed in the final product of the experiment. The two-phase mixture shows that side reactions have occurred. The main side reactions are cross-linking and polyurea, allophanic acid (Allophan), biuret synthesis (see document [3]), which leads to gel formation. Specifically, these side reactions and polyurea formation can also be seen in the examples of US 7795359B2.

[0180] The properties of the liquid phase are reflected in the data on molecular weight, polydispersity and viscosity in Table 2. The gel phase was not analyzed because it was insoluble for GPC analysis and the viscosity was outside the measurement range.

[0181] The rate of gel formation increased with each experiment, so this setup was expanded and Reactor Setup 2 was developed.

[0182] Example 3: Continuous Reactor 2 Experimental Series

[0183] The experimental series includes experiments 10 to 12 in column [A] of Table 1. Here, reactor configuration 1 was expanded by the reaction zone to increase conversion. Switching from a large diameter back to a small diameter improved mixing. This reduced side reactions due to a narrower residence time distribution. This resulted in slight changes in the process parameters. Otherwise, the procedure was similar to Example 2.

[0184]

[0185] As a result, gel formation cannot be controlled. The jump back to a small diameter and the frequent changes in diameter (10) lead to numerous poorly flushed dead zones (laminar flow). Thus, the positive effect of increased mixing is overcompensated by the increased dead zones (negative effect). It is also impossible to separate the production of the (particularly preferred) prepolymer (see side reaction in Example 3; molar mass) from the gel formation.

[0186] Therefore, after experiment 12, the tubular body of arrangement 2 was completely blocked by gel formation. This arrangement is ineffective. The next step is to develop a simpler arrangement.

[0187] Example 4: Continuous Reactor 3 Experimental Series

[0188] The experimental series includes Experiment 13 in Table 1, column [A]. Here, the extent to which the setup could be scaled down was tested, using only one reactor plate, thereby resulting in a smaller reactor volume (Table 1, column [F]). Furthermore, the efficiency of post-treatment and cleaning was investigated. Furthermore, this setup can serve as a preliminary test for a more robust setup, eliminating the problems (gel formation) of the first and second setups. The procedure is similar to that of Example 2.

[0189]

[0190] The results of this setup show good control of the setup. Very low molar masses can be produced in a targeted manner. No gel formation was observed. However, this setup is not designed for high conversion volumes. Therefore, setup 4 was developed.

[0191] Example 5: Continuous Reactor 4 Experimental Series

[0192] The experimental series includes experiments 14 to 22 in column [A] of Table 1. Based on the results of Examples 2 to 4, a reactor configuration 4 was created using two plates, which resulted in a larger reactor volume (Table 1, column [F]). Here, in combination with the temperature [C], a higher product content [B] was achieved. This example showed the highest yield as well as good product properties and their controllability. The procedure was similar to that of Example 2.

[0193]

[0194] A configuration with a small diameter (<2.2) and a relatively large proportion of medium and large diameters (>=2.2) has proven advantageous in the synthesis. This reactor system makes it possible, for the first time, to produce a wide range of products (different molar masses) without observing gel formation. The conversion is very well controlled, and the product quality remains stable even without quenching.

[0195] As a result, no gel formation occurred, as confirmed in subsequent experiments. This device configuration was then used again in subsequent experiments 28 to 29.

[0196] Example 6: Continuous Reactor 5 Experimental Series

[0197] The experimental series includes experiment 23 in column [A] of Table 1. Based on Example 5, the reactor was multiplied by 4 (8 plates) to increase the throughput. The product properties remained the same as shown in Table 2. The procedure was similar to Example 2.

[0198]

[0199] In this setup, the reactor was scaled up for a single experiment, closer to industrial production. The geometric ratios remained unchanged; only the reactor volume and throughput were increased. The product properties of Experiment 23 were consistently good, with no side reactions or gel formation.

[0200] Example 7: Continuous Reactor 6 Experimental Series

[0201] The experimental series includes experiment 24 in column [A] of Table 1. Based on Example 5, the reactor was multiplied 28 times (4 reactors, 28 plates each) to increase the throughput. The product properties remained the same as shown in Table 2. Here, the tubular body diameter was optimized for efficiency.

[0202] To achieve higher throughput, the pump system was modified. Piston diaphragm pumps (Prominent Hydro H2PA, HP2AE040050SST0000R0000 and HP2AA040050SST000000000) with pulsation dampeners (Prominent PZ000008) were used. The remainder of the procedure was similar to Example 2. Even with the higher conversion, the quality and controllability of the product properties remained unchanged.

[0203]

[0204]

[0205] For the industrial reactor, the scale-up from setting 5 to setting 6 was tested. The geometric compositions in the above table were selected based on the results of the previous settings. The comparison of settings 1 to 4 shows that in the geometric composition of the tubular body, medium diameter and high diameter (>=2.2mm) should constitute a larger proportion so that the product properties can be controlled preferentially. Setting 2 also shows that changing back to a smaller diameter and changing the diameter 10 times have a negative effect on the product quality. Setting 4 shows that two diameter changes play a good role. In order to meet the standards and achieve the highest possible production volume, setting 6 sets a maximum of 6 diameter changes. In particular, this setting can be divided between medium diameters and larger diameters. The small diameter d1 is less than 2.2mm, the medium diameter d2 is greater than or equal to 2.2mm and less than 4mm, and the large diameter d3 is greater than or equal to 4mm.

[0206] The product characteristics of this setup are still good with high conversion. The increase in yield is the intention of doubling this setup.

[0207] Example 8: Continuous Reactor 7 Experimental Series

[0208] The experimental series includes experiment 25 in column [A] of Table 1. To test the process limits, a reactor with a small internal diameter (0.5 to 0.75 mm) was combined with a higher temperature (60° C.) and a short residence time (0.26 min).

[0209] The procedure is similar to Example 2. This example demonstrates the broad scope of the method.

[0210]

[0211] Experiment 25 shows a product that still falls within a wide range of polymer properties. The preferred molar mass or residual NCO content is no longer achieved. The conversion is also very limited, and gel is formed as a by-product.

[0212] Example 9: Continuous Reactor 8 Experimental Series

[0213] The experimental series includes experiments 26 to 27 in column [A] of Table 1. To test the limits of the process, reactors with large internal diameters (10 to 12 mm) were combined with different residence times (1.17 to 21.14 min). The procedure was similar to that of Example 2. This example demonstrates the broad scope of the process.

[0214]

[0215]

[0216] Similar to setup 7, this setup can only be used to a limited extent. The progress of the reaction is not taken into account. This leads to poor heat dissipation, especially at the beginning. This creates temperature gradients along the flow profile. This can lead to local overheating. These locally elevated temperatures lead to uncontrolled side reactions and gel formation. Experiments 26 to 27 show strong gel formation. The polydispersity (PDI) also increased to 4.68 and 3.04, respectively. The increase in PDI indicates that this setup deviates from the ideal residence time distribution. In addition, after two experiments, this setup became gel-blocked and could no longer be used.

[0217] Therefore, arrangement 4 with a similar volume (28.2 ml) is clearly preferred.

[0218] Example 10: Continuous Reactor 4 Experimental Series

[0219] The experimental series includes experiments 28 to 29 in column [A] of Table 1. In order to test the procedural and chemical limits, the reactor of Example 5 was tested with deviated experimental parameters. The procedure was similar to that of Example 2, with the following differences. The hydroxyl-terminated reactant used was tert-butyldiethanolamine (TBDEA). Due to the high viscosity of TBDEA solution at room temperature, the reactants were preheated (40° C. to 80° C.). This example demonstrates the wide range of the method.

[0220] This example again used Reactor Setup 4. This proved to be very suitable for producing consistent product quality.

[0221] Reactor setups 4, 5, and 6 provided the best configurations for the best control of polymer properties.

[0222] Table 1: Experimental parameters for the synthesis of polyurethane (PUR) prepolymers, part 1.

[0223]

[0224]

[0225]

[0226] Table 2: Experimental parameters for the synthesis of PUR prepolymers part 2.

[0227]

[0228] Table 3: Experimental parameters for the synthesis of PUR prepolymers part 3.

[0229]

[0230] In some experiments, the viscosity could not be determined (>100,000 mPa s)(na). This was outside the target range. This can occur when high molar masses and high polyurethane contents are produced simultaneously.

[0231] In Experiments 1 to 5, a high proportion of isocyanate residues remained after the reactor. Without post-treatment, the product reacted, resulting in a very high molar mass. In addition to the high molar mass, side reactions may have occurred, further increasing the viscosity. These product properties were not in line with the target, as the molar mass immediately after the reactor could not be determined due to subsequent reactions.

[0232] For this purpose, a model was developed to be able to predict product properties, particularly molecular weight and viscosity, based on reaction parameters. The model is applicable to the ranges of molar mass, temperature, molar ratio, and residence time. Residence time also indirectly depends on process parameters such as flow rate, volume, surface / volume ratio, specific surface loading of the reactor, and specific volume loading of the reactor. The model was obtained as follows.

[0233] Various methods are used to model the effect of temperature. The effect of temperature is similar to the Arrhenius equation with the following general formula:

[0234]

[0235] in:

[0236] k(T) - reaction rate constant as a function of temperature (second order) [m 3 mol -1 s -1 ]

[0237] A(T) - pre-exponential factor of temperature [-]

[0238] E(A) – activation energy [J mol -1 ]

[0239] R – Universal Gas Constant [8.314JK -1 mol -1 ]

[0240] T – temperature [K]

[0241] Based on the Arrhenius formula, the formula is simplified as follows. Two constants are retained to determine the temperature dependence.

[0242]

[0243] in:

[0244] k(T) - reaction rate constant or molar mass effect of temperature [Da]

[0245] K(T)-temperature exponential factor [K -1 ]

[0246] A(T)-pre-exponential factor of temperature [Da]

[0247] T – temperature [K]

[0248] This shows the temperature effect.

[0249] Residence time is generally a logarithmic function. Within the defined range, the effect is within the steepest slope. Therefore, to simplify the calculations, a linear approach was used for residence time. This is especially true because the maximum average molecular weight of the monomer is reached at a residence time of 0.

[0250] This results in the following residence time dependencies:

[0251] k t =A t *t

[0252] in:

[0253] k(t) - reaction rate constant or molar mass effect as a function of residence time [Da]

[0254] A(t)- linear factor of residence time [Da min -1 ]

[0255] t-residence time [min]

[0256] The third major influencing factor is the molar excess of the monomers (reactants). The higher the excess, the smaller the molar mass that can be achieved. Conversely, high molar masses can only be achieved with nearly equal ratios. Therefore, a maximum value is given for equal amounts of monomers and a minimum value for a sufficient excess of monomers. The overall trend is followed by an exponential function with a negative exponent.

[0257] In prepolymer production, lower molar masses are preferred, so the monomers are usually present in excess. Depending on the product, this can range from 2% to 30%, preferably from 5% to 22%. Within this range, corresponding accuracy is achieved through linear compensation.

[0258] The molar excess dependence is thus shown:

[0259] k c =A c *c

[0260] in:

[0261] k(c) - reaction rate constant as a function of excess or molar mass effect [Da]

[0262] A(c) - linear factor of the molar excess of the monomer [Da mol -1 ]

[0263] c – molar excess of monomer [mol %]

[0264] If these three dependencies are now combined, the expected molecular weight can be calculated according to the following formula:

[0265] M k (T,t,c)=k T +k t -k c

[0266] After interpolation, this corresponds to the following overall formula:

[0267]

[0268] in:

[0269] M k (T, t, c) – molar mass [Da] depending on temperature, residence time and concentration.

[0270] In the overall formula for the molar mass dependence, the experimental data for temperature T (see Table 1 - column C), excess c (see Table 1 - column E) and residence time (see Table 2 - column P) are now inserted.

[0271] The next step is to determine the constants of the model. In the first step, compensation is performed using an experiment in which only one parameter—temperature T, excess c, or residence time t—is varied. Linear compensation is used for temperature and excess c. Temperature is compensated exponentially. This yields initial values ​​for the constants A(T), K(T), A(t), and A(c).

[0272] The deviation between the model and the experiment was determined by minimizing the squared error. As a secondary condition, a maximum individual deviation of ≤25% in molar mass from the model to the experiment was tolerated. Furthermore, a secondary condition was imposed on the average deviation of ≤12%. For modeling the constants A(T), K(T), A(t), and A(c), the generalized reduced gradient (GRG) method was applied to the nonlinear system of equations.

[0273] To verify the constant, the initial values ​​for the model were doubled or halved. Various other local minima for the constant were found at the solution level. None of these results led to a significant improvement in the accuracy of the model in terms of the squared error and mean deviation.

[0274] After modeling and rounding off insignificant figures, the numerical values ​​of the constants are as follows:

[0275] A(T)-0.00039Da

[0276] K(T)-0.05733K -1

[0277] A(t)-1354Da min -1

[0278] A(c) - 534 Damol -1

[0279] Viscosity is crucial for the further use and production of a product. Excessively high viscosity makes it difficult to transport during use and production. Furthermore, further processing or mixing becomes difficult at high viscosities. On the other hand, too low a viscosity reduces yield. Therefore, the goal is to achieve the maximum permissible viscosity that achieves the desired product properties.

[0280] With the expected PUR content and molar mass in the product, the viscosity can be calculated according to the following formula:

[0281] η(M,c)=η M η c *A η

[0282] in

[0283] η(M,c) - total viscosity as a function of molecular weight and concentration [mPa s]

[0284] η(M) – viscosity as a function of molecular weight [mPa s]

[0285] η(c) – viscosity as a function of PUR concentration [mPa s]

[0286] A(η) – Dependency balance factor [-]

[0287] Molar mass and polymer concentration affect viscosity exponentially. Therefore, the following model formula is used for these two factors:

[0288]

[0289] in

[0290] A(M) - pre-exponential factor of molecular weight [mPa s]

[0291] K(M)-exponential factor of molecular weight [Da -1 ]

[0292] A(PUR) - pre-exponential factor of PUR concentration [mPa s]

[0293] K(PUR)-exponential factor of PUR concentration [m% -1 ]

[0294] M-molar mass [Da]

[0295] c(PUR) - PUR concentration of the product [m%]

[0296] After application, this corresponds to the following relationship between viscosity and polymer properties:

[0297]

[0298] In this formula for the viscosity dependence, experimental data for the PUR content c(PUR) (see Table 1, column B) and the molar mass M (see Table 2, column J) in the product are used.

[0299] The next step is to determine the constants of the model. In the first step, compensation is performed using experiments in which one parameter, the PUR content c(PUR) and the molar mass M, is varied. For the selected experiments, a molar mass range of 8 to 22,000 Da was selected for PUR content compensation.

[0300] In each case, an exponential compensation is performed. This yields initial values ​​for the constants A(PUR), K(PUR), A(M), and K(M). These initial values ​​are then used for experiments with the same PUR content and molar mass. For "identical" molar masses, an average value is formed from the molar masses used for the molar mass window. The viscosity calculated using this η(M, c) at the same molecular weight η(M) or PUR content η(c) shows deviations from the experimental viscosity. The deviation is a multiplication factor. The average value of the deviation factors thus yields an initial value for the dependency compensation factor A(η).

[0301] Minimizing the squared error between the model and the experiment allowed for a slight deviation. As a secondary condition, a maximum individual deviation of ≤20% in viscosity from the model to the experiment was tolerated. Furthermore, a secondary condition was imposed on the average deviation of ≤7%. For modeling the constants A(PUR), K(PUR), A(M), K(M), and A(η), a generalized reduced gradient method was used for the nonlinear system of equations.

[0302] To verify the constant, the initial values ​​for the model were doubled or halved. Various other local minima for the constant were found at the solution level. None of these results led to a significant improvement in the accuracy of the model in terms of the squared error and mean deviation.

[0303] After modeling and rounding off insignificant figures, the numerical values ​​of the constants are as follows:

[0304] A(PUR)-0.8319mPa s

[0305] K(PUR)-0.1561m% -1

[0306] A(M)-73mPa s

[0307] K(M)-0.0000829Da -1

[0308] A(η)-0.00502

[0309] Through this model and method, product properties and reaction conditions can be predicted.

Claims

1. A continuous process for producing a prepolymer in a reactor having an elongated hollow body, wherein continuously introducing at least two reactants at one end of a reaction zone of the hollow body, polymerizing the at least two reactants with one another in said reaction zone, and discharging a prepolymer at the other end of said reaction zone, The elongated hollow body includes at least a first partial area and a second partial area in the reaction zone; the inner diameter of the hollow body in the second partial area is at least 10% larger than the inner diameter of the hollow body in the first partial area, and the length of the second partial area is greater than or equal to the length of the first partial area; the reaction zone of the elongated hollow body has an aspect ratio of 100:1 to 20000:

1.

2. The method according to claim 1, wherein The prepolymer is a polyurethane prepolymer, one of the reactants comprises at least one alcohol group, and one of the reactants comprises at least one isocyanate group.

3. The method according to claim 1 , wherein: The inner diameter in the second partial region is at least 20%, preferably at least 30%, particularly preferably at least 40%, and especially preferably at least 50% greater than the inner diameter in the first partial region.

4. The method according to any one of claims 1 to 3, wherein The second partial region has a length that is at least 10% greater than a length of the first partial region.

5. The method according to any one of claims 1 to 4, wherein The first partial region is located at the inlet into the reaction zone and / or the second partial region is located at the outlet of the reaction zone.

6. The method according to any one of claims 1 to 5, wherein The inner diameter has at least three diameter grades over the length of the reaction zone.

7. The method according to claim 6, wherein: A central partial region is arranged between the first partial region and the second partial region, the inner diameter of which is larger than the inner diameter of the first partial region and smaller than the inner diameter of the second partial region.

8. The method according to any one of claims 6 or 7, wherein The second partial region includes subregions having at least two different inner diameters, wherein the inner diameter of a subregion closer to the first partial region is smaller than the inner diameter of a subregion farther from the first partial region.

9. The method according to any one of claims 1 to 8, wherein The reaction zone has a length of at least 50 cm, preferably at least 1 m; and / or the hollow body has an internal diameter of <2.2 mm in the first partial region and / or the hollow body has an internal diameter of ≥2.2 mm in the second partial region.

10. The method according to any one of claims 1 to 9, wherein The reaction zone has a volume of at least 25 ml, preferably at least 100 ml, particularly preferably at least 500 ml; and / or the reaction zone has a volume of at most 5 1, preferably at most 3 1, particularly preferably at most 2 1.

11. The method according to any one of claims 1 to 10, wherein The residence time of the polymerized reactants in the reaction zone to form the prepolymer is at least 2 minutes, preferably from 3 minutes to 15 minutes, particularly preferably from 4 minutes to 10 minutes.

12. The method according to any one of claims 1 to 11, wherein The reactants are introduced into the reaction zone in the form of a solution with a total reactant concentration of 20% to 60% (mass %).

13. The method according to any one of claims 1 to 12, wherein One reactant is introduced into the reaction zone in excess relative to the other reactant, preferably in an excess of at least 3 mol %, preferably 5 mol %, particularly preferably at least 10 mol %.

14. The method according to any one of claims 2 to 12, when used in combination with claim 2 for producing a polyurethane prepolymer, wherein The reactor is operated at a temperature (T), residence time (t) and optional molar excess (c) of the reactants such that a target average molecular weight of the prepolymer of 5000 Da to 80000 Da is obtained according to the following formula: in M k (T, t, c) is the target average molecular weight of the prepolymer, A(T) is 0.00039Da, K(T) is 0.05733K -1 , A(t) is 1354Da min -1 , A(c) is 534Da mole- 1 , T is the temperature in K, t is the residence time in minutes, c is the molar excess of the reactants in mol %.

15. The method according to any one of claims 2 to 14, wherein The volume of the second partial region is greater than the volume of the first partial region. Preferably, the volume of the second partial region is at least 5%, preferably at least 10%, greater than the volume of the first partial region.

16. A reactor suitable for carrying out the method according to any one of claims 1 to 14, wherein The reactor comprises an elongated hollow body with an inlet at one end and an outlet at the other end; the elongated hollow body comprises at least a first partial region and a second partial region; The inner diameter of the hollow body in the first partial region is <2.2 mm, and the inner diameter of the hollow body in the second partial region is ≥2.2 mm; The inner diameter of the hollow body in the second partial region is at least 10% larger than the inner diameter of the hollow body in the first partial region, the first partial region and the second partial region each have a length ≥1m independently of each other, and the length of the second partial region is greater than or equal to the length of the first partial region; the reaction zone of the elongated hollow body has an aspect ratio of 100:1 to 20000:

1.

17. The reactor according to claim 16, wherein The volume of the second partial region is greater than the volume of the first partial region. Preferably, the volume of the second partial region is at least 5%, preferably at least 10%, greater than the volume of the first partial region.

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