Modular reactor for synthesis

Abstract

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

Description

[0001]Modular reactor for synthesis The present invention relates to a continuous process for the production of polyurethane prepolymers. Background of the invention Prepolymers are reactive oligomers or short-chain polymers that are used to produce long-chain polymers. They are precursors that, in contrast to the final product, are still soluble or easily meltable. Prepolymers allow the production of block copolymers or shaping before consolidation through crosslinking or progressive polymerization leads to a more solid state. Accordingly, a prepolymer can also be a finished polymer with a low molecular weight. Finished prepolymers with low molecular weights are often used as stabilizers or auxiliaries. Different conditions during the production of the prepolymers enable a broad spectrum of mechanical properties.These range from soft, elastic foams and fibers to rigid molded parts with high impact resistance. This demonstrates the already very broad range of applications, which is continuously evolving. A process for the continuous production of prepolymers is disclosed, for example, in WO 2007 / 037824 A2. EP 1391472 A1 describes a process for the continuous production of thermoplastically processable polyurethanes, in which at least two different polyols and chain extenders are used in combination with an isocyanate. Polyurethanes can be produced stepwise (prepolymer dosing process) or by the simultaneous reaction of all components in a single step (one-shot dosing process). A continuously operated extruder is used, as also described in WO 2007 / 101807 A1 or WO 2021 / 122303 A1. The goal here is to produce the finished molded part directly.Extruding involves high temperatures of around 150-300°C. Such high temperatures are detrimental to precisely tuning the properties of prepolymers. Polyurethanes are products formed by polyaddition, usually from (poly)isocyanates with (poly)alcohols. The connecting unit here is the urethane group. The urethane group can also link sequences of other functional groups (polyester, polyether, or others). During the polymerization of polyurethanes, in addition to the urethane group, urea, imide, amide, or isocyanurate groups can also be formed (specifically), depending on the starting material. US 7,795,359 describes the continuous production of various prepolymers in a spiral microreactor with a micromixer. To avoid high-molecular-weight polymers, ultrasonic treatment is used.The spiral shape leads to a high pressure drop and limits reaction control, such as adjusting a specific product composition or viscosity. EP 1669385 A1 describes a continuous process for the synthesis of an acid-functional blocked isocyanate. US 5471037 A describes a process for producing polymers in a tubular reactor, wherein a static mixer is used upstream of a reaction zone of the tubular reactor. EP 2287228 A2 describes the production of a silylated prepolymer. A tubular reactor with an internal static mixer is described for the synthesis. Several reactors can be connected in series, with catalysts or silylating reagents being fed between the reactors. A length / diameter ratio of 10:1 to 50:1 is mentioned as the reactor dimension. The reaction temperature is between 80 and 200 °C.The examples also do not provide any information about the exact reactor sizes, nor about characteristic product properties such as molar mass and molar mass distribution. JP 2019-202477 A describes a process for coating a laminate with an adhesive. To better control product quality, WO 2021 / 122284 A1 uses circular reactors. A partial stream is returned to the reactor. At the same time, product is continuously withdrawn. This makes it possible to at least partially influence product quality. However, the potential for influencing overall product quality is limited. Previous reactor systems exhibit disadvantages such as varying and poorly adjustable product properties and harmful side reactions that lead to gel formation and possibly reactor blockage after repeated experiments.Summary of the Invention It is an object of the present invention to improve process control, uniform product properties (reproducible adjustment of the desired product molecular weight and molecular weight distribution), and problems with byproducts that lead to reactor maintenance costs. It is also an object of the present invention to provide a scalable process for producing prepolymers, particularly polyurethane prepolymers, that enables high yield, low to no byproducts and degradation products, and efficient conversion.The invention relates to 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 with one another in the reaction zone, and prepolymer is discharged at another end of the reaction zone, wherein the elongated hollow body in the reaction zone has at least a first and a second sub-region, wherein the hollow body in the second sub-region has an internal diameter that is at least 10% larger than the internal diameter of the hollow body in the first sub-region. Preferably, the second sub-region has a length that is greater than or equal to the length of the first sub-region. Preferably, in all embodiments of the invention, the prepolymer is a polyurethane prepolymer.One of the reactants has at least one alcohol group and one of the reactants has at least one isocyanate group. In particular, the invention therefore relates to a continuous process for producing a polyurethane prepolymer in a reactor with 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 prepolymer is discharged at another end of the reaction zone, wherein one of the reactants has at least one alcohol group and one of the reactants has at least one isocyanate group, wherein the elongated hollow body in the reaction zone has at least a first and a second partial region, wherein the hollow body in the second partial region has an inner diameter that is at least 10% larger than the inner diameter of the hollow body in the first partial region.Preferably, the second sub-region has a length that is greater than or equal to the length of the first sub-region. Furthermore, the invention relates to a continuous process for producing a polyurethane prepolymer in a reactor with 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 prepolymer is carried out at another end of the reaction zone, wherein one of the reactants has at least one alcohol group and at least one of the reactants has an isocyanate group, wherein the reactor is operated at a temperature (T), a residence time (t), and an optional molar excess of a reactant (c), so that a targeted average molecular weight of the prepolymer of 5000 Da to 80,000 Da according to the formula. where ^ ^(^, ^, ^) 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 1354 Da min -1 , A(c) is 534 Da mol -1, T is the temperature in K, t is the residence time in min, c is the molar excess of a reactant in mol%, is obtained. Furthermore, the invention relates to a reactor suitable for carrying out a process according to the invention, wherein the reactor has an elongated hollow body with an inlet at one end and an outlet at another end of the hollow body, wherein the elongated hollow body has at least a first and a second partial region, wherein the hollow body in the first partial region has an inner diameter of <2.2 mm and the hollow body in the second partial region has an inner diameter of ≥2.2 mm, wherein the hollow body in the second partial region has an inner diameter which is at least 10% larger than the inner diameter of the hollow body in the first partial region, the first and second partial regions each have a length of ≥ 1 m, independently of one another.Preferably, the second sub-region has a length that is greater than or equal to the length of the first sub-region. All of these aspects of the invention can be combined with one another; for example, descriptions of the process according to the invention can represent suitability of the reactor according to the invention. The reactor can be used in the process according to the invention. Therefore, the following detailed description relates to both the process and the reactor, even if only one of the two aspects is explicitly referred to. Detailed description of the invention The invention relates to a continuous process for producing a prepolymer in a reactor with an elongated hollow body. The reactor is also referred to as a microreactor because the elongated hollow body is usually thin tubes or hoses, i.e. hollow bodies with a length many times greater than its width / diameter, e.g.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, especially preferably 400:1 to 2,000:1. This ratio should be present in particular in a reactor zone of the hollow body. In the case of staggered widths / diameters in sub-regions, the width / diameter of the respective sub-region is used as an aliquot of the length of the sub-region to the total length of the hollow body or reactor zone, or the average of the width / diameter. Particularly effective reactions are possible in these thin hollow bodies. The tubes can have different cross-sections, e.g. round, eleatic rectangular, square, and mixtures thereof. The tubes are essentially round, cylindrical, or prismatic, i.e. in a sub-region with a given width / diameter, this width / diameter should remain constant. Mixing elements, e.g. due to pipe crushing, are avoided, e.g.are present on less than 5% of the length, preferably less than 1% of the length of the hollow body or reactor zone, or are avoided entirely. The hollow body can, however, be curved, for example, to accommodate the reactor compactly. For the sake of simplicity, the term "inner diameter" is used herein for the inner width or diameter of the hollow body, meaning the average dimension in the cross-section of the hollow body, whereby the shape can be different, as mentioned above round, elliptical, rectangular, square and mixtures thereof. This means that when a diameter is mentioned below, this also means a description of the width, without restriction to a circular cross-sectional shape, unless this is explicitly stated.According to the invention, cross-sectional sizes are included which have the same cross-sectional area as the cross-sectional area for a specified diameter, such as an inner diameter, with a circular cross-section. In processes according to the invention, 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 to prepolymer in the reaction zone, and prepolymer is discharged at another end of the reaction zone. The elongated hollow body should have at least a first and a second partial region in the reaction zone, wherein the hollow body in the second partial region preferably has an inner diameter that is at least 10% larger than the inner diameter of the hollow body in the first partial region and the second partial region has a length that is greater than or equal to the length of the first partial region.This results in the volume of the reaction zone in the second sub-area increasing with a larger diameter, even if the second sub-area is the same length as the first sub-area, and having a volume 21 percent larger than the volume of the first sub-area (e.g., D1 = 1 / D2 = 1.1 > d² = 1.21). Particularly preferably, the second sub-area has a volume (internal volume) that is larger than the volume of the first sub-area, preferably with the second sub-area having a volume that is at least 5%, preferably at least 10%, larger than the volume of the first sub-area. An increasing volume from one sub-area to the next leads to particularly stable production conditions, especially for the prepolymers. The two reactants are usually mixed at the beginning of the reaction zone in the reactor so that they can only react with each other here. In other cases, they can be mixed beforehand, e.g.if they do not react immediately after mixing, e.g. if the conditions for a reaction are only created in the reaction zone, e.g. by a required, higher temperature and / or the presence of a catalyst. In particularly preferred cases, the prepolymer is a polyurethane prepolymer. To produce polyurethane, preferably at least one of the reactants has at least one alcohol group, preferably two or more, and at least one of the reactants has at least one isocyanate group, preferably two or more. Preference is given to using one reactant with two alcohol groups and one reactant with two isocyanate groups. Additional reactants with three or more alcohol groups and / or three or more isocyanate groups can be added as crosslinkers, preferably in smaller amounts than the reactants with two alcohol groups or two isocyanate groups.The invention further relates to a reactor suitable for carrying out a process according to the invention. A preferred reactor according to the invention has an elongated hollow body with an inlet at one end and an outlet at another end of the hollow body. The hollow body has a staggered inner diameter, i.e. at least two partial regions with different inner diameters. The elongated hollow body has at least a first and a second partial region, wherein the hollow body in the first partial region preferably has an inner diameter of < (less than) 2.2 mm and the hollow body in the second partial region has an inner diameter of ≥ (greater than or equal to) 2.2 mm, wherein the hollow body in the second partial region has an inner diameter that is at least 10% larger than the inner diameter of the hollow body in the first partial region.Furthermore, the first and second subregions preferably each have a length of ≥ (greater than or equal to) 1 m, independently of one another. The second subregion has a length that is greater than or equal to the length of the first subregion. The reactor can be used with or without the preferred features for the process according to the invention. These specified diameters and lengths of the subregions enable a particularly preferred implementation of the production of prepolymers, with reduced side reactions and the advantage of less blockage of the reactor, which thus benefits from greater reusability without intermediate flushing. Preferably, the internal diameter in the second subregion is at least 20%, preferably at least 30%, especially preferably at least 40%, particularly preferably at least 50%, larger than the internal diameter of the first subregion.Such an enlargement of the inner diameter in the second sub-region compared to the first sub-region is associated with particularly pronounced advantages, as described above. Preferably, the second sub-region is longer than the first sub-region. Particularly preferably, the second sub-region has a length that is at least 10% greater than the length of the first sub-region. Preferably, the sub-region is at least 20%, especially preferably at least 40%, or at least 60% or even at least 80% longer than the first sub-region. In principle, the aforementioned sub-regions describe length regions in the elongated hollow body which have the aforementioned relative dimensions to one another. These sub-regions can in principle be positioned anywhere in the hollow body. The first sub-region is positioned in front of the second sub-region, so that the inner diameter widens in the direction from the inlet to the outlet.The first sub-region is preferably at the inlet to the reaction zone. Alternatively, or in combination with this, the second sub-region is at the outlet from the reaction zone. According to the information on the first and second sub-regions, the inner diameter can have these two inner diameter graduations. In further embodiments, the inner diameter has at least 3 diameter graduations over the length of the reaction zone. The said first and second sub-regions form regions in these at least 3 graduations. The first and / or second sub-region can have one or more sub-regions to form further diameter graduations. The entire sub-region, including the sub-region, fulfills the said relative or absolute dimensions (e.g., inner diameter larger or smaller than in the said other sub-region).Alternatively, or in combination with this, a further sub-area can be provided which has dimensions other than those specified so far. For example, an intermediate sub-area (or "middle sub-area") between the first and second sub-areas, which has size differences other than those mentioned compared to the others, in particular the first and second sub-areas. However, the inner diameter should always increase from the inlet to the outlet, i.e. an intermediate sub-area should not have a smaller inner diameter than a previous sub-area (towards the inlet) and should not have a larger inner diameter than a subsequent sub-area (towards the outlet).Such an intermediate section, also called a middle section, can be provided between the first and second sections, the middle section having an inner diameter that is larger than the inner diameter of the first section and smaller than the inner diameter of the second section. The middle section preferably has a length of at least 30 cm. The inner diameter of the middle section can be at least 5%, preferably at least 10%, larger than the inner diameter of the first section; the inner diameter of the second section can be at least 5%, preferably at least 10%, larger than the inner diameter of the middle section.In preferred embodiments, the second sub-region has sub-regions with at least two different inner diameters, wherein a sub-region closer to the first sub-region (towards the inlet) has a smaller inner diameter than a sub-region further from the first sub-region (towards the outlet). Each of the sub-regions preferably has a length of at least 30 cm. In preferred embodiments, the first sub-region has sub-regions with at least two different inner diameters, wherein a sub-region closer to the second sub-region (towards the outlet) has a larger inner diameter than a sub-region further from the second sub-region (towards the inlet). Each of the sub-regions preferably has a length of at least 30 cm. Further staggering with intermediate inner diameters is possible.The reaction zone preferably has a length of at least 50 cm, preferably of at least 1 m. Likewise preferably, the hollow body in the first partial region has an inner diameter of <2.2 mm, preferably <2.0 mm, and / or the hollow body in the second partial region has an inner diameter of ≥2.2 mm, preferably ≥2.6 mm. For example, the inner diameter in the first partial region can be 1.4 mm to 2.1 mm and the inner diameter in the second partial region can be 2.2 mm to 18 mm. The partial regions meet the specified diameters over their entire length. Of course, the relative requirement of a diameter that is at least 10% larger is still met. This means that with an inner diameter of 2.1 mm in the first partial region, the inner diameter in the second partial region is at least 2.31 mm. The reaction zone preferably has a volume of at least 25 ml, preferably of at least 100 ml, particularly preferably of at least 500 ml.Alternatively, or in combination therewith, the reaction zone preferably has a volume of a maximum of 5 l, preferably a maximum of 3 l, particularly preferably a maximum of 2 l. For example, the volume of the reaction zone can be 25 ml to 2 l. The volume of the reaction zone is considered to be the volume of the zone of the hollow body in which the conditions for polymerization prevail or can be adjusted, e.g., from the inlet to the outlet. The reactants are usually brought together at the inlet. Prepolymer and any unreacted reactants are discharged from the reactor at the outlet. The residence time in the reactor can be determined or adjusted by volume and throughput (or flow rate). The residence time of the reactants polymerizing to form prepolymer and polymerized in the reaction zone is preferably at least 2 min, preferably at least 3 min or at least 4 min, e.g.,2 min to 15 min, preferably 3 min to 12 min, particularly preferably 4 min to 10 min. Good polymerization to prepolymer can be achieved within these times, e.g. by selecting a suitable temperature, reactant concentrations, and optionally a catalyst. Preferably, according to the invention, no catalyst is added to reactant fluids. Likewise, no specific catalyst is used on the hollow body wall. A specific catalyst is specially prepared for polymerization. According to the invention, the hollow body is a metal body which is not specifically intended to accelerate polymerization. Nevertheless, it may occasionally occur that polymerization takes place on its surface. Preferably, the reactants are introduced into the reaction zone in a solution. The concentration of the reactants together is preferably 20% to 60% (mass %). “Together” means that the concentrations of the individual reactants are added together.The reactant concentration after polymerization then also corresponds to the concentration of the prepolymer (in mass %) in the case of complete polymerization. In the case of incomplete polymerization, the prepolymer is present in a lower concentration after the outlet than the reactants combined at the inlet. With the stated mass % the polymerization can be easily adjusted in the reactor according to the invention. This concentration also corresponds well to the above-mentioned residence times. In particularly preferred embodiments the combined concentration of the reactants is 24% to 56%, especially preferably 30% to 50% (all mass %). Preferably one of the reactants is introduced into the reaction zone in an excess over another of the reactants. In particular 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 %).The excess of one reactant over another reactant (with other functionalities, e.g. NCO with the excess reactant having OH functionalities) is preferably between 2-30%, more preferably between 5-22% (mol%). A molar excess can lead to a targeted molar mass distribution and in particular a maximum molar mass in the produced prepolymer. This is often desired so that the prepolymer remains soluble. When producing polyurethane prepolymer, the reactant preferably has an excess of one or more (especially two) alcohol groups. The temperature in the reaction zone is preferably 20°C to 80°C, preferably 30°C to 70°C or 35°C to 60°C, especially preferably 40°C to 55°C, or any desired ranges between these values. The reactor can have a heating means for heating the hollow body.At these temperatures, the polymerization can be well controlled without leading to excessively rapid polymerizations leading to high molecular weights, or with little or no unwanted side reactions. When producing a prepolymer, preferably a polyurethane prepolymer, the reactor is preferably operated at a temperature (T), a residence time (t), and an optional molar excess of a reactant (c) such that a targeted average molecular weight of the prepolymer of 5000 Da to 80000 Da is achieved, according to the formula. where ^ ^ ( ^, ^, ^ ) 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 1354 Da min -1 , A(c) is 534 Da mol -1, T is the temperature in K, t is the residence time in min, c is the molar excess of a reactant in mol%. Temperature (T), residence time (t), and molar excess can be easily adjusted and coordinated to fulfill the above formula. Temperature (T), residence time (t), and molar excess can, for example, lie within the ranges mentioned above. This allows the molar mass of the product to be accurately predicted (with uncertainty deviations) and easily adjusted. All of the above-mentioned parameters and structural features of the reactor are preferably used in polyurethane prepolymer production. The reactants for polyurethane production are mainly (poly)isocyanates and (poly)alcohols (e.g. polyester, polyether, polycarbonate polyols). The isocyanates can have one or more isocyanate (NCO) functionalities. (poly)alcohols have one or more alcohol (OH, hydroxy) groups.The hydrogen of the alcohol group that is suitable for polymerization with the isocyanate group can be a Zerewitinoff-active hydrogen. In addition, the reactants, e.g. the isocyanate or the alcohol, can have special molecular building blocks such as ethanolamines, carboxylic acids, alkenes, organosulfones or chlorosulfones. Frequently, polymers thereof with a low degree of polymerization are also used, so that the polymers are soluble and preferably have a low viscosity in solution. For example, polymeric reactants at a concentration (mass %) in DMAc as solvent can have a Brookfield viscosity of not more than 200 mPas, preferably from 1 mPas to 150 mPas, at 25 °C. Such polymeric reactants can also be used in other concentrations or other solvents. Catalysts for polymerization can optionally be used in the reactor according to the invention.Catalysts include, for example, organic Lewis bases, Lewis acids, phosphates, or (organic) metal salts / oxides. Such catalysts, or catalysts in general, can also be avoided. NCO-functionalized reactants are combined with OH-functionalized reactants. The reactants can be mono- or polyfunctionalized with NCO or OH. Typical, but not limited to, examples are NCO-terminated reactants such as methylenediphenyl isocyanate (MDI), hexamethylene diisocyanate (HDI), toluene-2,4-diisocyanate (TDI), p-toluenesulfonyl isocyanate (TSI), and their isomers. Typical, but not limited to, examples are OH-terminated reactants such as methyldiethanolamine (MDEA), diethanolamine (DEA), tert-butyldiethanolamine (TBDEA), glycols such as ethylene glycol, alkyl alcohol (e.g., C). 2-10Alcohol, e.g., EtOH) and polyols. The (or an) isocyanate starting material is preferably an organic diisocyanate. Suitable organic diisocyanates include, for example, aliphatic, cycloaliphatic, heterocyclic, and aromatic diisocyanates. Aliphatic diisocyanates are, for example, branched or unbranched C2-C 18-Alkyl diisocyanate, such as hexamethylene diisocyanate. Cycloaliphatic diisocyanates include 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. Aromatic diisocyanates include, for example, 4,4-methylenebis(phenyl isocyanate), 2,4-tolylene diisocyanate, mixtures of 2,4- and 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, and 2,2'-diphenylmethane diisocyanate, mixtures of 2,4'-diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate, urethane-modified liquid 4,4'-diphenylmethane diisocyanates and / or 2,4'-diphenylmethane diisocyanates, 4,4'-diisocyanatodiphenylethane-(1,2) and 1,5-naphthylene diisocyanate. 4,4-methylenebis(phenyl isocyanate) ("MDI") is preferred. Preferably, the (or an) alcohol reactant is an organic diol.Preferred diols are methyldiethanolamine (“MDEA”) and tert-butyldiethanolamine (“TBDEA”). The production of a polyurethane prepolymer preferably takes place in an isothermal reactor. In all embodiments of the invention, and also in this one for polyurethane prepolymer synthesis, the elongated hollow body is preferably a tube. The synthesis can proceed as follows: The reactants are initially introduced into suitable containers. Depending on the state of aggregation and product quality, solvents are used with the reactants. Preferably, only liquid components are used or the reactants are introduced into the reactor in liquid form. If necessary, the reactants can also be preheated. The temperature of the reactants is preferably between 0-80°C or 10-70°C, more preferably 20-60°C, or combinations of these ranges.Storage and / or treatment of the reactants upstream of the reaction zone preferably takes place under inert conditions, which are preferably (among other things) anhydrous conditions. For inert conditions, the storage containers for the reactants are purged with inert gas and the reactants are blanketed with inert gas. In addition, storage takes place with or without a stabilizer. Toluene-2,4-diisocyanate (TSI) or similar components can be used as a stabilizer. One or more of the reactants is preferably used in dissolved form. Particular preference is given to using the isocyanate and / or the alcohol in dissolved form. Known aprotic polar substances, for example DMAc, tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), or dimethylformamide (DMF), can be used as solvents. Two or more reactants can be transported and combined in the reactor using pumps, e.g. diaphragm, piston, or gear pumps.The decision as to which pumps are used is ultimately purely a question of the scaling factor or the viscosity of the respective reactant. Mixing elements are preferably not used during the combination process. Reactants are preferably only fed in via a branch. In preferred embodiments, the flow profile in the hollow body, particularly in the reaction zone, is laminar. Laminar flow can be adjusted by selecting the flow velocity and viscosity (again dependent on the solvent, reactant concentration, and temperature). The structure of the elongated hollow body preferably consists of one or more tubular elements arranged in a row. The tubular elements can have an internal diameter of 0.5 mm to 20 mm, preferably 1 mm to 12 mm. As already described above, different internal diameters are used in the sub-regions.The aim is to increase the diameter as the reaction progresses in order to reduce the effect of heat of reaction and at the same time create a minimum of pressure loss. As the reaction progresses and the prepolymer product concentration increases, the viscosity increases. This viscosity can be compensated for by the inventive staggering of the inner diameter. The length of a sub-region, e.g. a pipe element, is preferably 0.1 m to 7 m, more preferably 0.3 m to 5.8 m, e.g. 0.8 m to 3 m. The elongated hollow bodies can have a cross-sectional length of 0.1 m to 7 m, preferably 0.3 m to 5.8 m. The elongated hollow body, in particular pipes, can have one or more bends, in particular J-type shapes. The hollow body is largely straight (e.g. in > 70%, preferably < 80%, of its length), but may have bends to accommodate the entire length in a compact form, e.g. on or in plates.In total, the resulting shape of the entire hollow body, e.g. in the case of several J-type bent pipes, can be a meander shape. Preferably, no mixers, in particular no static mixers, are used in the elongated hollow body or in the reaction zone. Mixers can, for example, be baffles in an otherwise straight hollow body. A laminar flow in the reaction zone is preferably established (with appropriate structural measures without mixers which can cause turbulence, and / or with an appropriate flow velocity for a given viscosity). Preferably, the first and second sub-regions each have a length of ≥ 1 m, independently of one another, and the second sub-region has a length which is greater than or equal to the length of the first sub-region, as already explained above. The length of the elongated hollow body or the reaction zone can be up to 120 or more, e.g. up to 240 m or more. Preferably, the hollow body orthe 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. Examples of the gradation according to the invention into hollow bodies or reaction zones have the following dimensions. These are examples of the present invention and further alternatives are possible within the overall concept according to the invention. 1. first sub-area: inner diameter 1.5 mm to 2.15 mm, length 1 m to 50 m; second sub-area: inner diameter 2.3 mm to 6 mm, length 1 m to 50 m. 2. first sub-area: inner diameter 1.5 mm to 2.15 mm, length 1 m to 50 m; middle sub-area: inner diameter 2.2 mm to 2.8 mm, length 1 m to 50 m; Second sub-range: inner diameter 2.9 mm to 7 mm, length 1 m to 50 m. 3.first sub-range: inner diameter 1.5 mm to 2.0 mm, length 1 m to 50 m; second sub-range: inner diameter 2.1 mm to 11 mm, length 1 m to 50 m. 4. first sub-range: inner diameter 1.5 mm to 2.0 mm, length 1 m to 50 m; middle sub-range: inner diameter 1.8 mm to 2.8 mm, length 1 m to 50 m; second sub-range: inner diameter 2.9 mm to 11 mm, length 1 m to 50 m. 5. first sub-range: inner diameter 1.5 mm to 2.19 mm, length 1 m to 50 m; first middle sub-range: inner diameter 2.2 mm to 2.5 mm, length 1 m to 50 m; second middle sub-range: inner diameter 2.51 mm to 3.5 mm, length 1 m to 50 m; Second sub-range: inner diameter 3.6 mm to 14 mm, length 1 m to 50 m. Preferred examples of such gradations are given in the examples in the Rector setups 4-6, which can also be used for applications other than those shown in the examples.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 sub-region thereof, e.g., in the first, second, and / or third sub-region. For example, the length-to-width ratio (or to the diameter instead of the width) can be 50 or more, preferably 75 or more, more preferably 100 or more, in particular 125 or more, 150 or more, especially preferably 200 or more, or 300 or more, especially preferably 400 or more, or 500 or more, in the hollow body, in particular in the reaction zone, or a sub-region thereof, e.g., in the first, second, and / or third sub-region. This ratio of length to width (or diameter instead of width) can be 50:1 to 20000:1, in particular 75:1 to 15000:1, or 100:1 to 10000:1, or 200:1 to 5000:1, especially preferably 400:1 to 2000:1, in the hollow body, in particular in the reaction zone, or a part of it, e.g.in the first, second, and / or third sub-area. This ratio should be present, in particular, in a reactor zone of the hollow body. With staggered widths / diameters in sub-areas, the width / diameter of the respective sub-area can be used as an aliquot of the length of the sub-area to the total length of the hollow body or reactor zone, or the average of the width / diameter. Particularly effective reactions are possible in hollow bodies with this length-to-width (or diameter) ratio. The materials used for the hollow body or the reactor in general are 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, or similar), metals such as stainless steels (1.4301, 1.4404, 1.4571, 1.4539, 1.4547 or similar) or nickel-based alloys (2.4602, 2.4819, 2.4858 or similar) and comparable. The pipe dimensions are preferably selected so that a surface-to-volume ratio of 350 m² / m³ to 6000 m² / m³, preferably 1000 m² / m³ to 3000 m² / m³ is achieved. This applies to the elongated hollow body as a whole, and preferably also to each sub-area individually. Furthermore, the reactor-specific surface loading is in the range of 2 l / hm² to 140 l / hm², preferably 4 l / hm² to 40 l / hm². The reactor-specific surface loading is a value for the throughput (flow rate in l / h) per surface area in the elongated hollow body or in the reaction zone. Preferably, the reactor-specific volumetric load is in the range from 300 l / hm³ to 23000 l / hm³, preferably from 700 l / hm³ to 5000 l / hm³.The reactor-specific surface area is a parameter for the throughput (flow rate in l / h) per volume in the elongated hollow body or in the reaction zone. The hydrodynamic residence time in the process is preferably between 0.5 and 20 minutes, more preferably between 2 and 15 minutes. The residence time can be adjusted by the throughput (flow rate) for a given reactor. It indicates the average residence time of the reactants and the products polymerized from them together in the reaction zone. If a higher conversion is desired, the internal diameter in the elongated hollow body and, if necessary, the length of the hollow body or its subsections are increased. Thus, the pipe diameter can be adjusted with increasing conversion. Depending on the reaction enthalpy and a suitable combination of the diameter and length of a subsection or pipe element, a defined proportion of the reaction heat can be compensated.Ideal reaction conditions result from a combination of maximum conversion with minimal pressure drop, residence time, and temperature control. The elongated hollow body is housed in a heating medium or a heat exchanger. The heat exchanger can consist of individual plates in which the hollow body is housed, embedded in, or surrounded by the heat exchanger. The plates can be provided individually or stacked in numbers from 2 to 50. Depending on the configuration, several stacks can also be connected to one another. Preferably, the hollow bodies are introduced into plates, embedded, e.g., embedded in groove-shaped recesses in plates, or placed on top, preferably in 1 to 30 plates. Such a structure is described in WO 2010 / 055034 A1 (incorporated herein by reference).The plates and tubes can be made of a variety of materials, such as plastics (polytetrafluoroethylene - PTFE, polypropylene - PP, polyethylene - PE, polyvinyl chloride - PVC, polyvinylidene fluoride - PVDF, polychlorotrifluoroethylene - PCTFE, ethylenechlorotrifluoroethylene - ECTFE, perfluoroalkoxyalkane - PFA, perfluoroethylenepropylene - FEP, polyoxymethylene - POM, or similar), metals such as stainless steels (1.4301, 1.4404, 1.4571, 1.4539, 1.4547 or similar), nickel-based alloys (2.4602, 2.4819, 2.4858 or similar), and similar. The plates are preferably made of fiber-reinforced, especially glass-fiber-reinforced) plastic, aluminum, or stainless steel. In these plates, the heating medium flows around the pipes in channels. Depending on the design, one or more plates can be divided into individual temperature zones. Each temperature zone is maintained at the desired temperature by an upstream temperature control system.The reaction temperature can be 10-80 °C, preferably 20-60 °C, preferably at least 25 °C, particularly preferably at least 40 °C. The reactor and the reaction parameters are designed so that they can be individually adapted to the specific prepolymer synthesis. For this purpose, pipe elements (sub-areas that together make up the reaction zone) are connected differently, the temperature (zones) are adapted, and the residence time (throughput) is varied. The process conditions described above are preferably selected so that at the end of the reaction zone (at the outlet), a conversion based on the NCO reactant of 80-100%, preferably 95-100% (all mass %) is achieved. For this purpose, the reaction dimensions (especially length), temperature, and concentrations, especially an excess of alcohol reactant, are adjusted. After the outlet, the product can be trapped or collected in a collecting container.Typically, no polymerization conditions are present in the collection vessel, e.g., a lower temperature such as room temperature (e.g., 22°C). It is also possible to prevent any polymerization by quenching. For this purpose, a monohydric reactant, preferably a monohydric alcohol, can be present in the collection vessel. A special feature of the reactor according to the invention is that the reactor unit can be precisely tailored to each reaction product (reaction enthalpy, molar mass, etc.). Preferably, the product quality is monitored online, e.g., using infrared spectroscopy, refractive index, viscosity, density, titration, and / or light (laser) diffraction measurement. The conversion and product quality can be determined directly after leaving the reactor (at the outlet) and / or on the product in the collection vessel.For this purpose, the product can be analyzed inline / online using infrared (IR), viscosity, density, ultraviolet and visible light (UV-Vis), refractive index, and titration analysis. The online results, such as the IR measurement, can be used directly to adjust the process conditions, such as reactant flow rates. In particular, the NCO conversion can be monitored using infrared spectroscopy. Preferably, the product container (like the reactant containers) is purged / covered with inert gas and is water-free to prevent any change in product quality. The product is preferably kept at a temperature between -20 °C and 50 °C during storage or in the collection container. According to the invention, post-treatment of the product prepolymer can be carried out after the reaction zone. This can take place in a collection container for the product prepolymer or even in the reactor in a hollow body, e.g.at a different temperature or without a catalyst, if this is necessary for the polymerization. The post-treatment can be a temperature adjustment, inerting, end-group modification, or a combination thereof. End-group modifications include, for example, obtaining an aliphatically terminated polymer, e.g., by reaction with a monohydric alcohol; obtaining a hydroxy-terminated polymer, e.g., by reaction with a polyhydric alcohol; obtaining amine end groups, e.g., by reaction with water; obtaining amide end groups, e.g., by reaction with a carboxylic acid; or combinations thereof. By using the reactor according to the invention and the reaction parameters, side reactions can be avoided and a higher reusability of the reactor can be achieved. Side reaction products can primarily be a possibly undesirable biuret, allophanate, or high-grade urea formation, which can have negative properties on the desired prepolymer, especiallyin the case of polyurethane prepolymer. This can lead to excessively high molecular weight and crosslinking. This results in the formation of a poorly soluble gel with very high viscosity. Gel can render the reactor unusable. Depending on requirements, further treatment takes place in a reaction zone or in the collection vessel. Product quality can be maintained 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 primarily be made between NCO, amine, amide, hydroxyl, and aliphatic terminated polymers. To achieve NCO-terminated polymers, the degree of conversion is controlled accordingly, and storage / filling is inert and water-free. Amine-terminated polymers are produced by adding precisely controlled amounts of water and rapid conversion in the reaction zone or collection vessel.Amide-terminated polymers are achieved by adding precisely controlled amounts of carboxylic acids in the reaction zone or by rapid conversion in the collection vessel. Hydroxy-terminated polymers are achieved by adding polyhydric polyols in the reaction zone or in the collection vessel. Aliphatic-terminated polymers are achieved by adding monohydric alcohols in the reaction zone or in the collection vessel. Reactor cleaning is also essential. The polymerization of the reactive components takes place throughout the entire process stream in the reaction zone. Polymerization is not limited to the combination of different reactants. Due to their high activity, the reactants can also react or polymerize with themselves. In addition, the flow is laminar throughout the entire process. As a result, reactive components are always present in the stream up to the outlet or collection vessel.This can lead to the side reactions mentioned above (polyurea, allophane, biuret, gel formation, and crosslinking). This disrupts production and, in the worst case, irreversibly blocks the reactor. Regular rinsing and a defined start-up / shutdown procedure are therefore advantageous for continuous process operation. The rinsing procedure can vary depending on the process step. Depending on product requirements, rinsing can be combined with post-treatment (fixation step). No inferior products are formed. Post-treatment can take place towards the end of the reaction zone, after the reaction zone in the reactor, or in the collection vessel. The fixative can be a mono- or polyhydric alcohol. During product changeovers or up to medium downtimes (< 7 days), it is preferable to first rinse the reactor with a solvent using at least 4 volumes. Suitable solvents have been described above, preferably DMAc.This is followed by rinsing 4-10 reactor volumes with a solvent / fixing agent mixture, preferably a 2:1 to 1:1 mixture. The exact amount of volume is determined by online measurement (IR). Rinsing is complete when no reactant or prepolymer, especially no NCO reactant, is detected for at least 2 reactor volumes. If a shutdown is pending, the inlets and outlets of all lines are sealed hermetically. For downtimes of 7 days or more, or when system components are disassembled, a more extensive procedure is recommended. The rinsing steps are preferably carried out as for a medium shutdown. This is followed by rinsing 4-8 reactor volumes with anhydrous fixative. Glycols and alcohols are particularly suitable for this purpose, but are not limited to these. The insoluble components that precipitate (oligomers, insoluble refunctionalized monomers) are removed with a further solvent rinse of about 4 reactor volumes.For longer downtimes (> 30 days) or disassembly, a purge sequence is performed with approximately four reactor volumes each containing 96% ethanol, 50% ethanol / water, and water. The macromolecular properties of the prepolymer and its purity can be analyzed in the laboratory. These properties are determined from the reactants, their ratio, and the polymer chain length. The chain length is determined using size exclusion chromatography (SEC) (e.g., with THF or DMSO, 35 °C, butylhydroxytoluene (BHT) flow marker 30.6 ml ret. vol., RI detector, polystyrene (PS) standards, PSS SDV column, 0.8 ml / min). The average molecular weight (Mw) of the prepolymer is preferably in the range from 4,000 Da to 80,000 Da, preferably 7,000 Da to 50,000 Da, particularly preferably 8,000 Da to 25,000 Da. The polydispersity Mw / Mn is preferably less than 4, preferably less than 2. The above-mentioned parameters can be adjusted to achieve these ranges.The chain length of the prepolymer directly influences the viscosity of the product. Therefore, product quality can also be determined via viscosity. A rheometer can be used for this purpose (Anton Paar MCR102, CC27 measuring instrument, in cylinder, 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, particularly preferably 120 mPa*s and 5,000 mPa*s, at 25 °C. The process according to the invention, in particular for producing a polyurethane prepolymer, is preferably operated such that, for a given target molecular weight M [Da] and a given prepolymer concentration in the product [m%], a target viscosity of 20 mPa*s to 30,000 mPa*s, or another viscosity range as stated above, according to the formula. where µ(M,c) is the target viscosity, M is the target molar mass [Da], c(PUR) is the prepolymer concentration in the product [m%], A(PUR) 0.8319 mPa s, K(PUR) 0.1561 m% -1, A(M) 73 mPa s, K(M) 0.0000829 Da -1, A(η) 0.00502. The target molar mass M [Da] and the targeted prepolymer concentration are as stated above, e.g. a target molar mass Mw of 4000 Da to 80000 Da or 20%-60% (mass %) or the preferred values ​​stated above. The gravimetrically determined polymer content in the product (vacuum drying oven Binder VDL 23, at 180 °C, 3h) is preferably 10-60, preferably 30-50% (mass %). The specific density of the polymer product measured with the hydrometer (Carl-Roth, measuring ranges 0.75-1 and 1-1.1) is preferably 0.8-1.2, more preferably 0.9-1.1. The polymer content in the product, determined gravimetrically (Binder VDL 23 vacuum drying oven, at 180 °C, 3 h), is preferably 10%-60%, more preferably 30%-50% (all mass %). The water content in the prepolymer (Karl Fischer, Metrohm 907 Titrando) is preferably <4000 ppm, preferably <2500 ppm (mass ppm).The metal content, especially of iron and copper (inductively coupled plasma optical emission spectrometry - ICP-OES, Thermo Scientific iCAP 7400, in H2SO4) sum parameter is preferably < 10 ppm, preferably < 4 ppm. The product color (yellowing) is a parameter that can be used to determine the quality and age of the prepolymer product. Visually, the color is preferably colorless to slightly yellowish. The Hazen color number (according to the Pt / Co scale and / or DIN ISO 6271) (UV-Vis, Thermo Scientific Evolution 350) of the product is preferably < 100, preferably < 50. Depending on requirements, the residual NCO content is important (according to DIN EN ISO 14896, Metrohm 907 Titrando). If no NCO termination is desired, the residual NCO content should be <0.1%, preferably <0.05% (all mass %). The process according to the invention is freely scalable; prepolymer is preferably produced at a conversion of 0.13 kg / h to 1536.8 kg / h or a multiple thereof.Polyurethane prepolymers are widely used in building materials, packaging, automotive, electrical equipment, insulation, household appliances, clothing, chemical additives, and much more. The prepolymers according to the invention can be used in these areas. Examples of applications include the use for simpler and more intensive dyeing of fibers and end products. Prepolymers can be used as color stabilizers to extend the color stability of products, e.g., in these areas of application. The prepolymer according to the invention can be used as a spinning additive in (synthetic) fiber production. This improves fiber production processes and the stability of the fibers. In general, the addition of the prepolymers increases the resistance of plastics or fibers to degradation mechanisms via UV, light, oxidation, and heat. The prepolymer can be used as a color stabilizer for polyurethane (PU) polymers (more highly polymerized PU, e.g.,no longer soluble in the above solvents, such as DMAc, soluble PU). In particular, the prepolymer can be used to improve PU fiber spinning. In general, prepolymer can be used as a PU stabilizer. The prepolymers can also be used as a starting material for further polymerizations, e.g., as chain extenders. In this process, the prepolymers are combined with other monomers and chain extenders (such as polyalcohols, polyglycols (EtGlycol), polyacrylates, polyethers, polyesters, and the like). Any polymers can be extended, such as PU, polyurea, or other functionalized polymers. This can also be done in combination with other chain extenders, such as polyalcohols, polyglycols, polyacrylates, polyethers, or polyesters.In particular embodiments, the invention is defined by the following numbered embodiments and aspects, all of which can of course be further combined by any of the parameters, embodiments, or aspects described herein. 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 prepolymer is discharged at another end of the reaction zone, wherein the elongated hollow body in the reaction zone has at least a first and a second subregion, wherein the hollow body in the second subregion has an inner diameter that is at least 10% larger than the inner diameter of the hollow body in the first subregion. 2.Process according to 1, wherein the second subregion has a volume that is greater than the volume of the first subregion, preferably wherein the second subregion has a volume that is at least 5%, preferably at least 10%, greater than the volume of the first subregion. 3. Process according to 1 or 2, wherein the prepolymer is a polyurethane prepolymer and one of the reactants has at least one alcohol group and one of the reactants has at least one isocyanate group. 4. Process according to 1 to 3, wherein in the second subregion the inner diameter is at least 20%, preferably at least 30%, especially preferably at least 40%, particularly preferably at least 50% greater than the inner diameter of the first subregion. 5. Process according to 1 to 4, wherein the second subregion has a length that is greater than or equal to the length of the first subregion. 6.The process according to claim 5, wherein the second sub-region has a length that is at least 10% greater than the length of the first sub-region. 7. The process according to claims 1 to 6, wherein the first sub-region is at the inlet to the reaction zone and / or the second sub-region is at the outlet of the reaction zone. 8. The process according to claims 1 to 7, wherein the inner diameter has at least three diameter graduations over the length of the reaction zone. 9. The process according to claim 8, wherein a middle sub-region is provided between the first and second sub-regions, the middle sub-region having an inner diameter that is greater than the inner diameter of the first sub-region and smaller than the inner diameter of the second sub-region. 10.Process according to 8 or 9, wherein the second sub-region has sub-regions with at least two different inner diameters, wherein a sub-region closer to the first sub-region has a smaller inner diameter than a sub-region further from the first sub-region. 11. Process according to 1 to 10, wherein the reaction zone has a length of at least 50 cm, preferably of at least 1 m; and / or the hollow body in the first sub-region has an inner diameter of <2.2 mm and / or the hollow body in the second sub-region has an inner diameter of ≥2.2 mm. 12. Process according to 1 to 11, wherein the reaction zone has a volume of at least 25 ml, preferably of at least 100 ml, particularly preferably of at least 500 ml; and / or wherein the reaction zone has a volume of at most 5 l, preferably of at most 3 l, particularly preferably of at most 2 l. 13.The process according to 1 to 12, wherein the residence time of the reactants polymerizing and polymerizing to form prepolymer in the reaction zone is at least 2 minutes, preferably 3 minutes to 15 minutes, particularly preferably 4 minutes to 10 minutes. 14. The process according to 1 to 13, wherein the reactants are introduced into the reaction zone in a solution and the concentration of the reactants together is 20% to 60% (mass %). 15. The process according to 1 to 14, wherein one of the reactants is introduced into the reaction zone in an excess over another of the reactants, preferably with an excess of at least 3% (mol %), preferably 5% (mol %), particularly preferably at least 10% (mol %). 16.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 of a reactant (c) such that a targeted average molecular weight of the prepolymer of 5000 Da to 80000 Da according to the formula. where ^ ^ (^, ^, ^) 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 1354 Da min -1 , A(c) is 534 Da mol -1, T is the temperature in K, t is the residence time in min, c is the molar excess of a reactant in mol%. 17. Process according to 1 to 16, wherein the elongated hollow body, preferably in the reaction zone, has a length-to-width ratio of 100:1 to 20,000:1. 18. Process according to 1 to 17, wherein in a partial region its width or diameter remains essentially constant, wherein optional tube pinches are limited to less than 5% of the length of the hollow body or the reactor zone. 19. Process according to 1 to 18, wherein no mixer is used in the reaction zone. 20. Reactor suitable for carrying out a process according to 1 to 19, wherein the reactor has an elongated hollow body with an inlet at one end and an outlet at another end of the hollow body, wherein the elongated hollow body has at least a first and a second partial region, wherein the hollow body in the first partial region has an inner diameter of <2,2 mm and the hollow body in the second sub-region has an inner diameter of ≥2.2 mm, wherein the hollow body in the second sub-region has an inner diameter that is at least 10% larger than the inner diameter of the hollow body in the first sub-region. 21. Reactor according to 20, wherein the first and second sub-regions each independently have a length of ≥1 m. 22. Reactor according to 20 or 21, wherein the second sub-region has a length that is greater than or equal to the length of the first sub-region. 23. Reactor according to 20, 21, or 22, wherein the second sub-region has a volume that is greater than the volume of the first sub-region, preferably wherein the second sub-region has a volume that is at least 5%, preferably at least 10%, larger than the volume of the first sub-region. 24. A continuous process for producing a prepolymer in a reactor with 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 prepolymer is discharged at another end of the reaction zone, wherein the elongated hollow body in the reaction zone has at least a first and a second sub-region, wherein the hollow body in the second sub-region has an inner diameter that is at least 10% larger than the inner diameter of the hollow body in the first sub-region and the second sub-region has a volume that is larger than the volume of the first sub-region,and wherein preferably the reaction zone of the elongated hollow body has a length-to-width ratio of 75:1 or more; preferably combined with one of 1 to 23. The present invention is further illustrated by the following specific embodiments of the examples. Examples Example 1: Preparation of the reactant solutions and temperature control Preparation of the isocyanate solution (reactant 1): Reactant 1 is prepared by mixing 4,4-methylenebis(phenylisocyanate) (MDI) (Sigma-Aldrich, 98%) with N,N-dimethylacetamide (DMAc) (Sigma-Aldrich, ≥99.8%). The MDI content is 10-70%, depending on the targeted polyurethane content in the product (see Table 1, column [B]). Depending on the pretreatment (see Table 1, column [I]), 1% of p-toluenesulfonyl isocyanate (TSI) (Sigma-Aldrich, 96%) is added to reactant 1. A 5% molecular sieve (Carl-Roth, 4A,Bead form) was added. Preparation of the diol solution (educt 2): Educt 2 is prepared from N-methyldiethanolamine (MDEA) (Sigma-Aldrich, ≥99%) in DMAc. The concentration is 30-100% depending on the PUR content in the product (see Table 1, column [B]). 5% (Carl-Roth, 4A, bead form) is added to the solution as a drying agent. For post-treatment, solutions of the fixatives ethanol (EtOH) (Carl Roth, 99.5%, extra pure), ethylene glycol (Carl Roth, 99%, for synthesis), and MDEA were prepared in DMAc. The fixative concentration was 30% in each case. 5% (Carl-Roth, 4A, bead form) was added to the solutions as a drying agent. The solutions were prepared in a glove bag under a nitrogen atmosphere. The nitrogen used (Linde, 99.8%) was additionally dried over a drying column with glass wool and Sicapent (Merck, phosphorus pentoxide,with indicator) to reduce the humidity of the gas. After preparation, the solutions were sealed with a septum and discharged. The reactants were integrated into the process stream under argon (Linde, 99.996) blanketing. Throughout the entire process, the reactant and product containers were blanketed with slight argon overpressure (0.14-0.2 bar overpressure). All containers were equipped with septums to allow the addition of fixatives or additives (see Table 1, columns [H] and [I]). The temperature was controlled with a water bath thermostat (Huber CC-205B). The thermostat is equipped with a cooling coil.which also allows temperatures below room temperature. The cooling medium is supplied externally from the building services system. Process control was performed online using a Fourier transform infrared spectrometer (FTIR) device (Bruker Alpha II). This was used to determine the residual isocyanate content. Between each experiment, the reactor system was rinsed with a fixative solution of ethanol (EtOH) with DMAc until no isocyanate was detectable in the FTIR after two reactor residence times. Example 2: Experimental Series, Continuous Reactor 1. The experimental series comprises experiments 1-9 from Table 1, column [A]. The solution preparation is carried out analogously to Example 1. A reactor as described in WO 2010 / 055034 A1 was used. In short, the reactor is a flow reactor.The reaction takes place in one or more tubes. The reactants are fed into one end of the tube system, and the product is obtained at the other end. The reactor is operated continuously. The tubes can be arranged in one or more plates. For the first series of experiments, the reactor with a volume of 17.5 ml was used (see Table 1, column [F]). Piston pumps (Knauer Azure, P4.1S, and P2.1S) were used to pump the media. The media were fed into the reactor together via a T-connector. The product [B] was produced at a temperature [C] and a flow [D]. The parameters [H], [I], [M], [N], [O], and [P] were varied (Tables 1 and 2). The product exhibited a polyurethane content [B] and the associated properties [J],[K] and [L] according to Table 2. The dimensions of the piping system in Setup 1 are shown in the following table; the tubes are described in order from top to bottom. The total volume in the reactor is given below. Table: Reactor Setup 1 Inner diameter (D) Length (L) / m Length (L) / Inner / mm diameter (D) 1.00 2.22 2200 1.50 1.11 740 2.00 0.56 280 2.16 0.56 259 2.32 0.56 241 2.98 0.56 188 4.00 0.3 75 17.5 ml volume Experiments with Setup 1 showed that this setup was not ideally suited. The residence time in the small diameters (< 2.2 mm) is too long compared to the medium and large diameters (>= 2.2 mm). This made it difficult to control the molecular weight. Experiments 1-9 show that the molecular weight varied between 243,017 Da and 8,913 Da despite relatively narrow temperature windows. In addition, two phase mixtures were observed in the final product during the experiments. The two-phase mixtures show,that side reactions are occurring. The dominant side reactions are crosslinking and polyurea, allophane, and biuret synthesis (see literature [3]), which lead to gel formation. Precisely these side reactions and polyurea formation can also be seen in the examples of US 7795359 B2. The data on molecular weight, polydispersity, and viscosity in Table 2 reflect only the properties of the liquid phase. The gel phase was not analyzed because it was not soluble for GPC analysis and because the viscosity was outside the measuring range. The proportion of gel formation increased with each experiment, so the setup was expanded and reactor setup 2 was developed. Example 3: Test series continuous reactor 2 The test series includes experiments 10-12 from Table 1.Column [A]. Here, reactor setup 1 was expanded by one reactor zone to increase conversion. Switching back from large to small diameters improves mixing. This leads to fewer side reactions because the residence time distribution is reduced. This results in slight changes to the process parameters. Otherwise the procedure was analogous to Example 2. Table: Reactor Setup 2 Inner diameter Length / m Length (L) / Inner diameter / mm (D) 1,00 2,22 2200 1,50 1,11 740 2,00 0,56 280 2,16 0,56 259 2,32 0,56 241 2,98 0,56 188 4,00 0,3 75 1,00 3,08 308 1,50 1,67 1113 2,00 1,11 555 26,3 ml volume. Gel formation could not be controlled. The jump back to small diameters and the frequent change in diameter (10) led to many poorly flushed dead zones (laminar flow). The positive effect of increased mixing was thus overcompensated by the increase in dead zones (negative effect). Here, too, it was not possible to separate the production of a (particularly preferred) prepolymer (see side reactions in Example 3; molecular weight) and gel formation. As a result, the tubes of Setup 2 were completely blocked by gel formation after Experiment 12. The setup was taken out of service. The next step was the development of a simpler setup. Example 4: Continuous Reactor 3 Test Series. The test series includes Experiment 13 from Table 1, column [A]. Here, the extent to which the setup could be scaled down to only one reactor plate was tested.which results in a smaller reactor volume (Table 1, column [F]). In addition, the efficiency of the post-treatment and cleaning was investigated. In addition, the setup serves as a preliminary test for a more robust setup in order to eliminate the problems (gel formation) from the first two setups. The procedure was analogous to Example 2. Table: Reactor Setup 3 Inner diameter Length / m Length (L) / Inner diameter / mm (D) 1.00 0.5 500 2.98 0.3 101 2.5 ml Volume The results with this setup show good control of the setup. Very low molecular weights could be deliberately produced. Gel formation was not observed. However, the setup is not designed for high conversion rates. Therefore, Setup 4 was developed. Example 5: Test series for continuous reactor 4 The test series includes tests 14-22 from Table 1, column [A]. From the findings of examples 2-4, reactor setup 4 with two plates was created,which results in a larger reactor volume (Table 1, column [F]). Here, in combination with temperatures [C], higher product contents [B] were achieved. This example showed the highest yield with good product properties and their controllability. The procedure was analogous to Example 2. Table: Reactor Setup 4 Inner Diameter Length / m Length (L) / Inner Diameter / mm (D) 2.16 1.97 912 2.32 2.22 957 2.98 1.67 560 28.2 ml Volume The setup consisting of a small diameter (< 2.2) with a larger proportion of medium and large diameters (>= 2.2) proved advantageous in the synthesis. With this reactor system, it was possible for the first time to produce a broad product range (different molecular weights) without observing gel formation. The conversion could be controlled so well that the product quality remained stable even without quenching. Gel formation also did not occur subsequently,as was recognized in later experiments. The setup was subsequently used again for the later experiments 28-29. Example 6: Continuous Reactor 5 Test Series The test series includes experiment 23 from Table 1, column [A]. Based on Example 5, the reactor was multiplied by a factor of 4 (8 plates) to increase the throughput. The product properties remained the same as shown in Table 2. The procedure was analogous to Example 2. Table: Reactor Setup 5 Inner diameter / Length / m Length (L) / Inner diameter mm (D) 2.16 7.85 3634 2.32 8.88 3828 2.98 6.66 2235 112.8 ml Volume In this setup, the reactor was scaled up for one experiment,to get closer to industrial production. The geometric ratio was maintained, and only the reactor volume and throughput were increased. The product properties from Experiment 23 remained consistently good, with no side reactions or gel formation. Example 7: Continuous Reactor 6 Test Series. The test series includes Experiment 24 from Table 1, column [A]. Based on Example 5, the reactor was multiplied by a factor of 28 (4 reactors with 28 plates each) to increase the throughput. The product properties remained the same as shown in Table 2. Here, the pipe diameters were optimized for efficiency. To enable the higher throughputs, the pump system was changed. Piston diaphragm pumps (Prominent Hydro H2PA,HP2AE040050SST0000R0000 and HP2AA040050SST000000000) with pulsation dampers (Prominent PZ000008). The remaining procedure was analogous to Example 2. Even at even higher sales, the quality and controllability of product properties remained unchanged. Table: Reactor Setup 6 Inner diameter Length / m Length (L) / Inner diameter / mm (D) 1.50 12.21 8140 2.16 11.10 5139 2.32 23.31 10047 2.98 17.76 5960 4.00 5.55 1388 6.00 4.44 740 10.88 3.33 306 789.6 ml Volume For an industrial reactor, a scale-up from Setup 5 to Setup 6 was tested. The geometric composition in the table above was selected based on the findings from previous setups. The comparison of Setups 1 to 4 shows that the medium and large diameters (>= 2.2 mm) should make up the larger proportion of the geometric composition of the tubes in order to be able to preferentially control the product properties. Setup 2 also shows,that a change back to smaller diameters as well as the number of diameter changes of 10 has a negative impact on product quality. Setup 4 shows that two diameter changes work well. In order to meet the criteria and achieve the highest possible production volume, a maximum of 6 diameter changes was set for Setup 6. In particular, a distinction can be made between medium and larger diameters in this setup. Small diameters d1 are < 2.2 mm, medium diameters d2 >= 2.2 mm and < 4 mm, and large diameters d3 are >= 4 mm. The product properties of the setup remain good with high turnover. Production increases are planned as a multiplication of this setup. Example 8: Test series for continuous reactor 7 The test series includes test 25 from Table 1, column [A]. To test the process-related limits, a reactor with a small inner diameter (0.5-0.75 mm) with higher temperatures (60 °C) and short residence times (0.26 min). The procedure was analogous to Example 2. This example confirms the broad application range of the process. Table: Reactor Setup 7 Inner diameter / Length / m Length (L) / Inner diameter mm (D) 0.50 0.5 1000 0.75 0.56 747 0.34 ml Volume Experiment 25 shows a product still within the broad range of polymer properties. The preferred molecular weights or NCO residues are no longer achieved. The conversions are also very limited and gel formation also occurs as a by-product. Example 9: Test series continuous reactor 8 The test series includes experiments 26-27 from Table 1, column [A]. In order to test the process-related limits, a reactor with a large inner diameter (10-12 mm) with varying residence times (1.17 - 21,14 min). The procedure was analogous to Example 2. This example confirms the broad application range of the process. Table: Reactor Setup 8 Inner diameter Length / m Length (L) / Inner diameter / mm (D) 10.88 0.3 27.6 27.9 ml Volume Similar to Setup 7, this setup has only limited applications. The reaction process is not taken into account. This results in poor heat dissipation, especially at the beginning. This creates a temperature gradient along the flow profile. This leads to local overheating. These locally elevated temperatures lead to uncontrolled side reactions with gel formation. Experiments 26-27 showed strong gel formation. There is also an increase in the polydispersity (PDI) to 4.68 and 3.04, respectively. The increase in PDI shows,that the setup deviates from the ideal residence time distribution. Furthermore, the setup was blocked by gel after the two tests and could no longer be used. Setup 4, with a similar volume (28.2 ml), is therefore clearly preferred. Example 10: Continuous Reactor 4 Test Series The test series includes tests 28-29 from Table 1, column [A]. To test the process-related and chemical limits, the reactor from Example 5 was tested with different test parameters. The procedure is analogous to Example 2 with the following deviations. Tert-butyldiethanolamine (TBDEA) was used as the hydroxy-terminated reactant. Since the viscosity of the solution is higher at room temperature with TBDEA, the reactant was preheated (40-80 °C). This example confirms the broad application range of the process. Reactor Setup 4 was used again for this example. It has proven to be very suitable,to produce consistent product quality. Reactor setups 4, 5, and 6 provide the best configurations for optimal control of polymer properties. Table 1: Test parameters for polyurethane (PUR) prepolymer synthesis, part 1. [A] [B] [C] [D] [E] [F] [G] [H] [I] Treatment c(PUR) T - Flow c - Volu- NCO Post- Pretreatment PUR Tempe- rate Over- amount Residues Treatment No. Content temperature ml / min reac- after pro- / K reactant / reactant / 2 / ml reactant / m% mol% mol% 1 8 298.15 6.45 5 17.5 10 no DMAc 17 293.15 6.45 5 17.5 15 no DMAc 35 293.15 6.67 5 17.5 20 no DMAc, TSI 35 323.15 6.67 5 17.5 10 no DMAc, TSI 35 293.15 2.23 5 17.5 5 no DMAc, TSI 35 293.15 2.23 5 17.5 5 EtOH DMAc, TSI quench 35 293.15 4.44 5 17.5 7 EtOH DMAc, TSI quench 35 323.15 2.23 5 17.5 5 EtOH DMAc, TSI quench after 16 h 35 303.15 4.44 5 17.5 7 EtOH DMAc, TSI quench 35 323.15 4.5 15 26.3 4 no DMAc 35 323.15 4.5 15 26.3 4 MDEA DMAc quench 35 323.15 4.5 15 26,3 4 EtOH DMAc quench 35 298,15 1,32 15 2,5 5 EtOH DMAc,rühren quench 40 303,15 3,95 22 28,2 <1 EtOH DMAc,rühren, quench TSI 40 303,15 5,98 22 28,2 2 EtOH DMAc,kühlen, quench TSI 40 303,15 3,95 22 28,2 <1 Etgly- DMAc, TSI col 40 303,15 3,95 22 28,2 <1 MDEA DMAc, TSI 40 303,15 3,95 22 28,2 <1 keine DMAc, TSI 45 313,15 3,95 22 28,2 <1 EtOH DMAc, TSI quench 50 333,15 5,98 22 28,2 <1 EtOH DMAc, TSI quench 55 353,15 5,98 22 28,2 <1 EtOH DMAc, TSI quench 60 313,15 3,95 22 28,2 <1 EtOH DMAc, TSI quench 40 303,15 15,8 22 112,8 <1 EtOH DMAc, TSI quench 24 40 303,15 110,6 22 789,6 <1 EtOH DMAc, TSI quench 25 35 333,15 1,32 30 0,34 6 EtOH DMAc, TSI quench 26 35 283,15 1,32 22 27,9 <1 EtOH DMAc, TSI quench 27 35 313,15 23,92 22 27,9 <1 EtOH DMAc, TSI quench 28 40 303,15 1,975 22 28,2 <1 EtOH DMAc, TSI, quench Vortemperie- rung 40 °C 29 35 303,15 3,95 22 28,2 <1 EtOH DMAc, TSI,quench pre-tempering 80 °C Table 2: Test parameters PUR prepolymer synthesis part 2. [B] [J] [K] [L] [M] [N] [O] [P] Reactor – Reactor – t - Hydraulic test Viscosity Surface specific specific dynamic No. M - Mw / PDI / sity / che / Vo- sche Surface Volu- mic Data - mPas lumen / area load / residence time / l / hm² l / hm³ min 1 72 073 2.83 392 1855 11.92 22114 2.71 2 63 043 2.17 776 1855 11.92 22114 2.71 3 113 269 3.85 nb 1855 12.33 22869 2.62 4 243 017 4.1 nb 1855 12.33 22869 2.62 5 205 199 1.44 nb 1855 4.12 7646 7.85 6 15 864 1.87 241 1855 4.12 7646 7.85 7 8 913 2.33 143 1855 8.20 15223 3.94 8 44 074 1.62 2462 1855 4.12 7646 7.85 9 16 141 1,35 281 1855 8,20 15223 3,94 10 44 587 1,96 2646 2105 4,88 10266 5,84 11 39 057 1,57 2208 2105 4,88 10266 5,84 12 38 569 1,74 2079 2105 4,88 10266 5,84 13 5 409 1,82 127 1752 18,08 31680 1,89 14 10 459 1,4 376 1599 5,25 8404 7,14 15 6 349 1.19 264 1599 7.96 12723 4.72 16 9 548 1.72 341 1599 5,25 8404 7.14 17 10 017 1.66 369 1599 5.25 8404 7.14 18 12 511 1.81 429 1599 5.25 8404 7.14 19 21 502 1.94 1928 1599 5.25 8404 7.14 20 89 058 2.53 nb 1599 7.96 12723 4.72 21 183 062 2.84 nb 1599 7.96 12723 4.72 22 25 053 1.65 29349 1599 5.25 8404 7.14 23 13 634 1.47 453 1599 5.25 8404 7.14 24 14 539 1.56 497 1599 5.25 8404 7.14 25 53 283 2.13 4860 6156 37.84 232941 0.26 26 19 526 4.68 384 367 7.73 2839 21.14 27 12 957 3.04 218 367 140.02 51441 1.17 28 24 247 1.83 1256 1599 2.63 4202 14.28 29 11 036 2.19 193 1599 5.25 8404 7.14 Table 3: Test parameters PUR prepolymer synthesis part 3. [B] [Q] [R] [S] [T] Specific Water content PUR Metal content HAZEN color number search density [-] [ppm] (Fe+Cu)[ppm] [ppm] No. 1 1.1 >4 000 nb 248 2 1.1 >4 000 4.7 287 3 >1.2 nbnb 347 4 >1.2 nbnb 263 5 >1.2 nbnb 211 6 1.05 3 168 3.6 184 7 1 3 864 3.1 238 8 1 nbnb 157 9 1 nbnb 189 10 1.2 nbnb 162 11 1.2 nbnb 158 12 1.2 2 841 3.2 174 13 0.95 2 593 3.0 167 14 1,1 1 849 3.9 128 15 1.05 nbnb 152 16 1.1 1 527 2.4 86 17 1.1 1 473 3.6 74 18 1.1 1 892 3.1 63 19 1.15 nbnb 42 20 >1.2 nbnb 183 21 >1.2 nbnb 163 22 >1.2 nbnb 159 23 1.1 nbnb 107 24 1.1 nbnb 73 25 >1.2 nbnb 284 26 1.1 1 275 3.4 53 27 1.05 nbnb 75 28 1.15 nbnb 118 29 1 nbnb 41 In some tests, the viscosity (> 100,000 mPa s) could not be determined (nb). This is outside the target range. This occurs when high molecular weights and high polyurethane contents coincide. In tests 1-5, high proportions of isocyanate residues were present after the reactor. Without post-treatment, the product continued to react, resulting in very high molecular weights. In addition to the high molecular weights, side reactions can also occur. This further increased the viscosity. These product properties do not meet the target.because the molar mass could not be determined directly after the reactor due to post-reactions. For this purpose, a model was developed to predict the product properties, in particular the molar mass and viscosity, as a function of the reaction parameters. The model is valid for the specified ranges of molar mass, temperature, molar ratio, and residence time. The residence time is also indirectly dependent on the process parameters such as flow, volume, surface / volume ratio, the reactor-specific surface loading, and the reactor-specific volume loading. The model was derived as follows. Various approaches were used for modeling. The influence of temperature is analogous to Arrhenius with the general, where: k(T) – reaction rate constant as a function of temperature (2nd order) [m³ mol -1 s -1 ] A(T) - pre-exponential factor temperature [-] E(A) – activation energy [J mol-1 ] R – Universal gas constant [8.314 JK −1 mole −1 ] T – Temperature [K] Following Arrhenius, the formula is simplified as follows. Two constants remain to determine the temperature dependence. where: k(T) – reaction rate constant or molar mass influence of temperature [Da] K(T) - exponential factor temperature [K -1 ] A(T) - pre-exponential factor Temperature [Da] T – Temperature [K] This results in the temperature influence. The residence time is, overall, a logarithmic function. In the range defined here, the influences are in the area of ​​the steep slope. To simplify the calculation, a linear approach for the residence time was used. This is primarily because at a residence time of 0, the maximum average molar mass of the monomers is reached. This results in the dependence of the residence time: ^ ^ = ^ ^∗ ^ where: k(t) – reaction rate constant or molar mass influence depending on the residence time [Da] A(t) - linear factor residence time [Da min -1 ] t – Residence time [min] The third major influencing factor is the molar excess of a monomer (reactant). The higher the excess, the lower the molecular weights achieved. Conversely, high molar masses are only achieved at almost identical ratios. Therefore, the maximum is given at equal amounts of monomers and the minimum at a complete excess of one monomer. The general trend is an exponential function with a negative exponent. In the production of prepolymers, lower molar masses are preferred, and therefore one monomer is usually present in excess. Depending on the product, this can be between 2-30%, preferably between 5-22%. In this range, a linear adjustment provides the appropriate accuracy. Thus, the dependence of the molar excess is: ^ ^ = ^^ ∗ ^ where: k(c) – reaction rate constant or molar mass influence depending on the excess [Da] A(c) - linear factor molar excess of a monomer [Da mol -1 ] c – molar excess of a monomer [mol%] If these three dependencies are combined, the expected molar mass can be calculated as follows: ^ ^ ( ^, ^, ^ ) = ^ ^ + ^ ^ − ^ ^ This corresponds to the following overall formula: including: ^ ^ ( ^, ^, ^ )– Molar mass as a function of temperature, residence time and concentration [Da]. 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 into this overall formula for the molar mass dependence. The next step is to determine the constants for the model. In the first step, experiments in which only one parameter from temperature T, excess c and residence time t varied were used for compensation. A linear compensation was used for temperature and excess c. An exponential compensation takes place for temperature. This results in the starting values ​​for the constants A(T), K(T), A(t) and A(c). Deviation between model and experiments was achieved by minimizing the squared errors. As a constraint, a maximum single-value deviation of the molar mass from model to experiment of ≤ 25% was tolerated.In addition, an average deviation of ≤12% was defined as a constraint. The generalized reduced gradient method (GRG) for nonlinear systems of equations was used to model the constants A(T), K(T), A(t), and A(c). To validate the constants, the starting values ​​for modeling were doubled or halved. Various other local minima were found for the constants in the solution plane. None of the results found resulted in a significant improvement in model accuracy with respect to error squares and mean deviation. After modeling and rounding the non-significant figures, the numerical values ​​for the constants are as follows: A(T) - 0.00039 Da K(T) - 0.05733 K. -1 A(t) - 1354 Da min -1 A(c) - 534 Da mol -1Viscosity is an important factor for the further use of the products and their production. Excessively high viscosity makes conveying difficult both during application and during production. Furthermore, high viscosity makes further processing or blending difficult. Too low viscosity reduces yield. Therefore, the goal is to achieve the maximum permissible viscosity for the desired product properties. Using the expected PUR content in the product and the molecular weight, the viscosity can be calculated using: there is ^ ( ^, ^ ) - Total viscosity as a function of molar mass and concentration [mPa s] ^(M) – Viscosity as a function of molar mass [mPa s] ^(c) – Viscosity as a function of PUR concentration [mPa s] A(^) – Factor dependency adjustment [-] Molar mass and polymer concentration influence viscosity exponentially. Therefore, the following model formulas were used for both factors: where A(M)– pre-exponential factor molar mass [mPa s] K(M)– exponential factor molar mass [Da -1 ] A(PUR)– pre-exponential factor PUR concentration [mPa s] K(PUR)– exponential factor PUR concentration [m% -1 ] M – Molar mass [Da] c(PUR) – PUR concentration product[m%] This corresponds to the following relationship between viscosity and polymer properties after use: The experimental data for the PUR content in the product - c(PUR) (see Table 1 - column B) and molar mass - M (see Table 2 - column J) are now inserted into this formula for the viscosity dependence. The next step is to determine the constants for the model. In the first step, experiments in which one parameter from the PUR content c(PUR) and molar mass M varied were used for compensation. For the selected experiments, for the PUR content compensation, the molar mass range of 8 - 22,000 Da was chosen. An exponential compensation is carried out in each case. This results in starting values ​​for the constants A(PUR), K(PUR), A(M), and K(M). These starting values ​​were then used for the experiments used with the same PUR content and molar mass. For the "same" molar mass, an average value was calculated from the molar masses used for the molar mass window. The viscosities calculated with this ^ ( ^, ^ )at the same molar mass ^(M) or PUR content ^(c) show a deviation from the viscosities from the experiments. The deviation is a multiplier factor. The mean of the deviation factors thus gives the starting value for the dependency adjustment factor A(η). Small deviations between model and experiments were achieved by minimizing the squared errors. As a constraint, a maximum individual value deviation of the viscosity from model to experiment of ≤20% was tolerated. In addition, an average deviation of ≤7% was defined as a constraint. The generalized reduced gradient method for non-linear systems of equations was used to model the constants A(PUR), K(PUR), A(M), K(M), and A(η). To validate the constants, the starting values ​​for the modeling were doubled or halved. Various other local minima were found for the constants in the solution plane.No results found resulted in a significant improvement in model accuracy with respect to the squared error and mean deviation. After modeling and rounding the non-significant figures, the numerical values ​​for the constants are as follows: A(PUR) - 0.8319 mPa s K(PUR) - 0.1561 m%. -1 A(M) - 73 mPa s K(M) - 0.0000829 Da -1 A(η) - 0.00502 The model and the procedure were able to predict both product properties and reaction conditions.

Claims

Patent claims:

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 prepolymer is discharged at another end of the reaction zone, wherein the elongated hollow body has at least a first and a second sub-region in the reaction zone, wherein the hollow body in the second sub-region has an inner diameter that is at least 10% larger than the inner diameter of the hollow body in the first sub-region and the second sub-region has a length that is greater than or equal to the length of the first sub-region, and wherein the reaction zone of the elongated hollow body has a length-to-width ratio of 100:1 to 20,000:

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

3. Process according to one of claims 1 or 2, wherein in the second partial region the inner diameter is at least 20%, preferably at least 30%, especially preferably at least 40%, particularly preferably at least 50% larger than the inner diameter of the first partial region.

4. Process according to one of claims 1 to 3, wherein the second partial region has a length which is at least 10% larger than the length of the first partial region.

5. Process according to one of claims 1 to 4, wherein the first partial region is at the inlet to the reaction zone and / or the second partial region is 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 3 diameter gradations over the length of the reaction zone.

7. The method according to claim 6, wherein a middle sub-region is provided between the first and second sub-regions, the middle sub-region having an inner diameter that is larger than the inner diameter of the first sub-region and smaller than the inner diameter of the second sub-region.

8. The method according to one of claims 6 or 7, wherein the second sub-region has sub-regions with at least two different inner diameters, wherein a sub-region closer to the first sub-region has a smaller inner diameter than a sub-region further from the first sub-region.

9. The method according to one of claims 1 to 8, wherein the reaction zone has a length of at least 50 cm, preferably of at least 1 m; and / or the hollow body in the first sub-region has an inner diameter of <2.2 mm and / or the hollow body in the second sub-region has an inner diameter of ≥2.2 mm.Process according to one of claims 1 to 9, wherein the reaction zone has a volume of at least 25 ml, preferably of at least 100 ml, particularly preferably of at least 500 ml; and / or wherein the reaction zone has a volume of at most 5 l, preferably of at most 3 l, particularly preferably of at most 2 l.

11. Process according to one of claims 1 to 10, wherein the residence time of the reactants to be polymerized to form the prepolymer and polymerized in the reaction zone is at least 2 min, preferably 3 min to 15 min, particularly preferably 4 min to 10 min.

12. Process according to one of claims 1 to 11, wherein the reactants are introduced into the reaction zone in a solution and the concentration of the reactants together is 20% to 60% (mass%).

13. The process according to any one of claims 1 to 12, wherein one of the reactants is introduced into the reaction zone in an excess over another of the reactants, preferably with an excess. shot of at least 3% (mol%), preferably 5% (mol%), particularly preferably at least 10% (mol%).

14. Process according to one of claims 2 to 12, in combination with claim 2, for producing a polyurethane prepolymer, wherein the reactor is operated at a temperature (T), a residence time (t), and an optional molar excess of a reactant (c) such that a targeted average molecular weight of the prepolymer of 5000 Da to 80000 Da according to the formula where ^ ^ ( ^, ^, ^ ) 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 1354 Da min -1 , A(c) is 534 Da mol -1, T is the temperature in K, t is the residence time in min, c is the molar excess of a reactant in mol%, is obtained.

15. The process according to any one of claims 2 to 14, wherein the second subregion has a volume that is greater than the volume of the first subregion, preferably wherein the second subregion has a volume that is at least 5%, preferably at least 10%, greater than the volume of the first subregion. 16.Reactor suitable for carrying out a method according to one of claims 1 to 14, wherein the reactor has an elongated hollow body with an inlet at one end and an outlet at another end of the hollow body, wherein the elongated hollow body has at least a first and a second partial region, wherein the hollow body in the first partial region has an inner diameter of <2.2 mm and the hollow body in the second partial region has an inner diameter of ≥2.2 mm, wherein the hollow body in the second partial region has an inner diameter. which is at least 10% larger than the inner diameter of the hollow body in the first sub-region, the first and second sub-regions each independently have a length of ≥ 1 m, and the second sub-region has a length that is greater than or equal to the length of the first sub-region, and wherein the reaction zone of the elongated hollow body has a length-to-width ratio of 100:1 to 20,000:

1.

17. Reactor according to claim 16, wherein the second sub-region has a volume that is greater than the volume of the first sub-region, preferably wherein the second sub-region has a volume that is at least 5%, preferably at least 10%, greater than the volume of the first sub-region.

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