Method for the continuous synthesis of polyoxazolines using a spiral tube reactor

Abstract

A process for the continuous synthesis of polyoxazolines comprising the step of passing at least one oxazoline monomer through a helical tube reactor under the influence of heat, wherein the helical tube reactor has a spirally wound tube with an inner tube diameter and a diameter of the spiral winding, characterized in that: • the inner tube diameter is between 4.5 mm and 34 mm, and • the lambda ratio, as the ratio of the inner tube diameter to the diameter of the spiral winding, is in the range of 0.11-0.17, and • the spirally wound tube is a stainless steel tube.

Description

The invention relates to a process for the continuous polymerization of oxazolines to polyoxazolines (hereinafter the poly(2-oxazoline)s are meant). These are also called poly(N-acetylenimine)s and consist of polymerized 2-oxazoline monomer units. It is known that oxazolines, in particular 2-substituted 2-oxazolines, can be polymerized to polyoxazolines in a cationically ring-opening, living polymerization. Syntheses in a batch process, also for example in the microwave, are possible and widely used. However, it is disadvantageous that the products differ slightly from batch to batch (also called batch-to-batch variation). Furthermore, batch sizes in the batch process are limited.Helical tube reactors (also called: coiled flow reactor) have likewise been known for some time. On an industrial scale, regardless of the mechanism of polymerization, there is a great interest in further increasing the throughput of the polymerization methods. In addition, for example for medical use, the polyoxazolines should have a dispersibility of <1.5, better <1.3.WO 2014 / 191171 A1 describes a continuous process for the production of polyoxazolines in a tubular flow reactor which contains a static mixer in the form of a "metal grid". Various advantages over the known batch processes are mentioned. Nevertheless, the only example mentioned gives only one polymer having a 4850 g / mol molar mass (corresponds to 30 repeat units, with 33 repeat units set) and a high dispersibility of 1.6. The dispersibility of this polymer would not be sufficient for medical use. WO 2017 / 182610 A1 describes a process for preparing polymers from cyclic imino ethers, polyoxazolines, in a tubular reactor wound up, for example, where the linear flow rate is at least 120 cm / min. It is disadvantageous that in the tubular flow reactor without a mixing device, the polymer is not homogeneous despite comparatively very high flow rates. The dispersibility is good at 1.10-1.20. The reactors used have only small internal diameters of 0.75 to 2.4 mm. It is disclosed that as tube diameters in the present system increase, dispersibility increases independent of other parameters. As explained in the present case under comparative example 4 and calculated in table 3 / line 2, a maximum lambda value of 0.06 results-even a maximum of 0.027 for PTFE as pipe material (table 3 / line 26). The lambda ratio is the ratio of the tube inner diameter to the diameter of the turns of the helical tube.EP 2 719 452 A1 describes in other contexts such as crystallizations, emulsion polymerizations or heterogeneous catalysis a helical tube reactor having a very low lambda ratio of 0.03-0.1.CN212942950U describes a bundle of spiral reaction tubes in connection with ring opening polymerization.CN1390240A describes the use of spiral reaction tubes in connection with the production of polyether polyols.Reis et al. (2020) describe helical tube reactors for the synthesis of block-like copolymers by means of modular construction.Accordingly, continuous tube reactors are suitable for producing polyoxazolines with low dispersibility, since homogeneous products are produced in the so-called steady state without interruption of production and, unlike in numerous examples from research, no batch-to-batch differences can occur.In order to achieve very low dispersibility, it is known that slight mixing in the direction of flow is necessary. In the case of a helical tube reactor through which flow takes place, however, laminar flow is often present. This laminar flow leads to a mixing in the flow direction due to the different flow speeds at the wall and the middle of the tube.However, tubular reactors through which turbulent flow takes place are also used. However, these have hitherto been of very small diameters in the range <1 mm. Tubular reactors with such small diameters are not suitable for allowing a high product throughput, i.e. they are not upscaleable. When the diameter is increased, it is to be expected that the turbulent flow will convert into a laminar flow. As is known, tubular reactors with diameters of ≥1 mm are only still capable of effecting a laminar flow.Furthermore, in the case of tubular reactors through which turbulent flow takes place, the residence times in the reactor are frequently too short to achieve complete reaction of the reactants, and so hitherto laminar, and consequently also slower, tubular reactors through which flow has been used in the living polymerization.In summary, with known methods, when the tube inner diameters are expanded to obtain high flow rates (i.e. mass transfer per time), the mixing in the flow direction and consequently the dispersibility of the polymer obtained becomes greater.EP 0 944 431 B1 describes an apparatus for continuously carrying out chemical reactions, in particular a curved tubular flow reactor having a substantially circular or ellipsoidal cross section, characterized in that it has a plurality of curvatures with alternating direction of curvature, wherein a change in the direction of curvature takes place at the latest when the distance of the center of gravity of the tube cross-sectional surface traversed from the beginning of a curvature is 200 times the tube diameter, wherein a curvature can comprise up to three revolutions about the axis of curvature.DE 101 25 583 A1 describes a process for preparing homopolymers and copolymers of isobutene by continuous cationic polymerization of isobutene or mixtures of isobutene with ethylenically unsaturated comonomers in the presence of an initiator system, characterized in that the polymerization is carried out in a tubular continuous reactor which has a plurality of curvatures with alternating directions of curvature.It is accordingly an object of the invention to develop a novel process with which polyoxazolines can be prepared industrially and continuously, the conversion per time (throughput) being to be as high as possible. However, the process should at the same time permit good and controllable properties with respect to the polyoxazoline obtained. The polymer should be homogeneous and have a low dispersibility in the range <1.5, better <1.3. The helical tube reactor used is intended to bring about good mixing of the mixtures flowing through it orthogonally to the direction of flow, thus counteracting the mixing in the direction of flow through the laminar regime and being resistant in the case of aggressive media.The object is achieved with the features of the independent patent claims. Preferred embodiments are described by the dependent claims.The invention relates to a process for the continuous synthesis of polyoxazolines, in particular poly(2-oxazolines)n, comprising the steppassing at least one oxazoline monomer (in a reaction mixture) through a helical tube reactor under the action of heat, comprising a helically wound tube having an inner tube diameter and a helical winding diameter (of the tube), characterized in that,• the tube inner diameter (of the spirally wound tube) at 4.5 mm to 34 mm, and• the ratio of the lambda as the ratio of the inner diameter of the tube to the diameter of the helical winding is in the range of 0.11-0.17, and• the spirally wound tube is a stainless steel tube.The spiral winding of the tube forms so-called coils of the helical tube reactor. According to the invention, the shaped coil (formed by the wound tube) has a constant diameter over the substantial part of the length of the coil. This is called a helical tube reactor. This constant diameter of the spiral corresponds to the diameter of the spirally wound tube according to the invention. This means that the helical tube reactor does not form a conical shape but a cylindrical shape, wherein it is nevertheless encompassed that the diameter also changes stepwise-within the scope of the value defined according to the inventionThe "lambda ratio" is the ratio of the tube inner diameter to the helical coil diameter.In order to achieve the corresponding lambda ratio at the predetermined tube inner diameter, the diameter of the spiral windings could be in the range of 35 mm to 305 mm in a meaningful manner.The invention further provides the use of a helical tube reactor in a process for the continuous synthesis of polyoxazolines (from a reaction mixture comprising at least one oxazoline monomer), wherein said reactor comprises: a spirally wound tube having an inner diameter of the tube and a diameter of the spiral winding (of the spirally wound tube), characterized in that,• the inner diameter of the tube is from 4.5 mm to 34 mm, and• the lambda ratio as the ratio of the inner diameter of the tube to the diameter of the helical winding is in the range of 0.11-0.17, and• the spirally wound tube is a stainless steel tube;In particular, the use in the process according to the invention is also used.In use, at least one oxazoline monomer (in a reaction mixture) is passed through the helical tube reactor under the action of heat.Statements relating to the method apply equally to the use and vice versa. "At least one oxazoline monomer" does not mean at least one single molecule in the sense of the invention, but is to be understood in the sense of "monomers of at least one chemical structure", i.e. explicitly many individual molecules are meant. A monomer of one chemical structure would be, for example, 2-methyl-2-oxazoline, one of another chemical structure would be, for example, styrene or 2-ethyl-2-oxazoline.It is also explicitly included that the entire tube of helical tube reactor does not have to be wound spirally. However, by "spirally wound tube" is meant the part which is spirally wound, it also being possible for straight intermediate sections to be provided.In this context, it is also included that there may be further pipes (also having a configuration according to the invention).Linearly extending starting, end or intermediate regions are also possible, for example. In these regions, a laminar flow can then also be present. These ranges do not serve the major part of the polymerization, but in some cases merely a post-reaction, a reaction of the last small amounts of monomer or a cooling of the reaction mixture. In such a helical tube reactor according to the invention, however, at least 80% of the stainless steel tube sections are wound spirally.Equally, it is explicitly included that only a part of the tube is heatable or that not all tubes are heatable in the case of a plurality of tubes. In general, the heating ensures that the polymerization can take place at these points.There is an important relationship between the relatively large inside tube diameters of the invention and the homogeneous mixing which is necessary. This is because it was possible to observe a stabilization of the flow regime by a secondary flow (orthogonal to the primary flow). This secondary flow most likely stabilizes the laminar primary flow (primary flow in the tube flow direction), so that higher flow speeds are possible with nevertheless good mixing during the flow through the helical tube reactor. The mixing in the direction of flow, which leads to an increase in the dispersibility, is thus minimized. The residence time would nevertheless appear to be large enough to allow complete oxazoline polymerization. This is because if the residence time during the flow at the heat points is too short, the polymerization is incomplete.For example, in the case that a block copolymer is to be produced, it could happen that the reaction mixture still contains first monomer, so that after addition of the second monomer, the block comprising the second monomer building blocks is contaminated with first monomer building blocks, since these have not yet been consumed. If, on the other hand, the residence time is too long, side reactions take place to an increased extent, such as, for example, chain transfer by proton abstraction and subsequent initiation of new polymer chains by the species formed.The mixing in the direction of flow, which leads to an increase in dispersibility, is minimized by the invention.The invention allows to obtain in 5 minutes as much polyoxazoline as would be possible with conventional batch syntheses only in 1 week. These are 1g-30g syntheses.With the invention it is possible for the first time to achieve polyoxazolines in a high (mass) throughput, namely from 6 mmol / min to 480 mmol / min, with simultaneously good dispersibility in the range 1.23-1.3 (as demonstrated in the three exemplary embodiments, here 41 mmol / min). Good dispersibility is apparently due to sufficiently good intermixing during passage through the helical tube reactor. In the prior art, on the other hand, when the tube inner diameters are widened to achieve high flow rates (i.e., molar conversion per time), the intermixing becomes insufficient and the dispersibility of the obtained polymer becomes large.In order to achieve high flow rates in the case of the tube inner diameter according to the invention, high pressures are often necessary. The material stainless steel allows the necessary pressure stability, but changes the thus possible minimum diameters of a spiral winding, which in turn leads to the flow conditions changing and thus also the thorough mixing and consequently the dispersibility of the polymer.The combination according to the invention of stainless steel with the stated tube inner diameters and the very large lambda ratio, which in turn specifies a small diameter of the spiral winding, is a surprisingly favorable spiral tube reactor configuration for the polymerization of oxazolines.Stabilization of the primary laminar flow by a secondary swirling flow (orthogonal to the primary flow) in the spirally wound tube is a possible reason for the surprising results. In any case, the configuration according to the invention allows higher flow rates (in the polymerization of polyoxazolines) than would be possible in laminar flow without this geometry according to the invention. The high pressure that can occur at such high flow rates is withstood by the stainless steel. It is evident that the geometry of a spirally wound pipe and the flow behavior achievable therewith are critically dependent on the material of the pipe.The invention permits (for the synthesis of polyoxazolines) an optimum ratio between high yield per time and simultaneously suppression of secondary reactions, as might occur, for example, by excessively long residence times in the reactor under the action of heat.It is advantageously possible, using the tubular reactor according to the invention, to enable complete consumption of the oxazoline monomer present in each case in the reaction mixture in the process according to the invention. The reaction mixture is the mixture which is passed through the tubular reactor in continuous operation with the aim of preparing the polyoxazoline. At the same time, good thorough mixing is achieved, which is fundamentally necessary in order to obtain a homogeneous polymer which has a minimum dispersibility of 1.0. This means that the polymer has the same composition as possible in each molecule.The polyoxazoline polymer obtained is also homogeneous.As already indicated above, the invention advantageously allows improved mass, heat and energy transport and thus an increase in the conversion per time. A more homogeneous reaction mixture is achieved in the reactor, so that the polydispersity is <1.5, often even <1.3.Preferably, the tube is 2m to 5m long.The relatively large inner diameter allows the production of larger quantities per time, which consequently also reduces the proportion of personnel costs in the product price. The invention is industrially applicable. The continuous mode of operation permits the production of a polymer of defined and constant quality.The geometry according to the invention (thus is the above-mentioned. By tube inner diameter and the lambda ratio for the stainless steel tube) it is also possible to provide a space-saving arrangement and thus a modular construction. That is, if the helical tube reactor has a plurality of spirally wound tubes which are connected to one another in a linear and preferably separable manner, the very simple production of copolymers, in particular of block copolymers, is possible.The specific pitch of the coils has no influence on the invention.In a preferred embodiment of the invention, the tube inner diameter of the spirally wound tube is 6.35-38.1 mm, particularly preferably 8-12 mm, also 9-10 mm, in particular even 10 mm.In a likewise preferred embodiment, the lambda ratio is 0.11-0.16.It is likewise preferred if, in one embodiment of the invention, the diameter of the helical winding is 50-300 mm, even 50-120 mm, particularly preferably 70-95 mm, in particular also 72 mm.In one embodiment of the invention, the stainless steel tube (spirally wound tube) has a wall thickness of 0.9-2.2 mm, in particular also of 1-2.2 mm. This is optimal in order to achieve the inventive configuration of the helical tube reactor with this material.In a preferred embodiment, the lambda ratio is 0.13±0.01.It is also a preferred embodiment when the pressure is low.• Inner diameter of the tube at 10 mm±1 mm, and• The diameter of the spiral winding is 72 mm±7 mm.These are particularly favorable parameters for the spirally wound tube made of stainless steel for stabilizing the laminar primary flow.The wall thickness (of the spirally wound tube) in this embodiment is very particularly preferably 1 mm±0.2 mm, better 0.9-1.1 mm.In a preferred embodiment of the invention, the monomer throughput in passing the oxazoline monomer through the spiral wound tube is from 6 to 480 mmol / min. Very particularly preferably, the concentration of the oxazoline monomer at the beginning of the passage is 4 mol / L±2.5 mol / L (preferably ±1.5 mol / L; in particular even 3-5 mol / L).In this embodiment, it is particularly preferred if the flow of the oxazoline monomer is 10 ml / min when it is passed through the helical tube reactor according to the invention.In another embodiment of the invention, the concentration of the oxazoline monomer at the start of the passage is 1-10 mol / L, in particular also 3-5 mol / L.It is also a preferred embodiment of the invention if the lambda ratio is 0.13±0.01 and the pressure during the passage is 40 bar±5 bar (or also 39-41 bar).This advantageously achieves the best possible flow behavior in the stainless steel tube according to the invention (wound in a spiral shape).The temperature in the spirally wound tube during passage is, in a preferred embodiment, 130-150° C. This range is particularly favorable in order to also achieve complete polymerization of all oxazoline monomers at the high flow rates according to the invention. The temperature of the tube to be chosen is also dependent on the internal diameter, this range being more optimized for the helical tube reactor design of the invention. It is also advantageously possible for more pressure to be applied by the stainless steel, so that more heat can act (i.e. a temperature higher than 130-150° C. can be applied) without the reaction mixture already boiling depending on the solvent.It is also a preferred embodiment when the lambda ratio is 0.13 ±0.01, and when passing, the concentration of the oxazoline monomer at the beginning of the passing is 4 mol / L ±1.5 mol / L, and when passing, the monomer throughput of the oxazoline monomer is 6 to 480 mmol / min (preferably 50 mmol / min±5 mmol / min). In particular, this could be methyloxazoline.In another preferred embodiment of the invention, the passing first involves passing a first oxazoline monomer and then a second oxazoline monomer different from the first through the helical tube reactor, such that the polyoxazoline obtained is a block copolymer having at least two blocks.Another preferred embodiment for blockwise polymerization is designed such that the helical tube reactor has at least two spirally wound tubes and has a monomer feed in each case upstream of the first tube and between all tubes in the direction of flow.This block construction is easily possible with the space-saving configuration of the helical tube reactor according to the invention.It is also possible for a monomer feed to be provided between each tube.By "first tube" is meant the first heated tube in which the polymerization is to take place.At these mono-feed lines, monomers of the same or different chemical structure can be introduced into the tubular reactor. This arrangement is very suitable for the production of block copolymers, various monomers being supplied to the various monomer feeds, so that polymer blocks are formed.In a variant of this embodiment, all spirally wound tubes are of the same length, so that depending on the length of the polymer block to be produced, a different number of tubes arranged one after the other (here without monomer feed in between) is used. The length of a polymer block is thus controlled by the amount of monomer (of the same chemical structure) supplied and the number of subsequent tubes. Subsequently, at the next monomer feed, for example, a monomer of a different chemical structure can be fed, which polymerizes to the "growing polymer chain" in the subsequent pipes.It is also preferred if, during the passage according to the invention, the flow velocity is 0.1-1 cm / s, particularly preferably even 0.21 cm / s (±0.05 cm / s).In a likewise preferred embodiment of the invention, the flow is at 9-11 ml / min and the tube inner diameter is at 9-11 mm when passing through. The tube length is preferably 1m (±10%).The reaction mixture which comprises the at least one oxazoline monomer according to the invention and is passed through the tubular reactor may usefully also comprise an initiator which is capable of initiating the respective polymerization reaction. The same applies to termination reagents which are capable of stopping the polymerization or of terminating the chain growth, these preferably being used at the end of the tube in which the polymerization takes place or only thereafter.In the process according to the invention, the solvent which is expediently added to the oxazoline monomer and which therefore flows through the tubular reactor as part of the reaction mixture is preferably a non-nucleophilic solvent. It is particularly preferably a polar, non-protic solvent, in particular it is selected from acetonitrile, chlorobenzene, chloroform, 1,2-dichlorobenzene, dichloromethane, dimethylformamide, dimethyl sulphoxide and mixtures thereof, in particular a mixture of acetonitrile and chlorobenzene. It is known that other solvents such as methanol, ethanol or water can also be used in the termination, i.e. when the polymerization is discontinued at the end of the process according to the invention.In one embodiment, the oxazoline monomer is methyl oxazoline.Table 1 shows the batch sizes of three exemplary embodiments, methyloxazoline (MeOx) having the terminating reagent piperidine being used in each case.Table 2 shows the corresponding analytical results of the obtained polyoxazoline Table 3 shows, in line 14, the spirally wound tube used in Working Examples 1 to 3 as a helical tube reactor. Moreover, lines 2 and 26 show prior art tube designs and the preferred embodiments of the invention in lines 4-8, 13-20 and 22-24All embodiments can be combined with one another in any desired manner.Exemplary EmbodimentsWorking Examples 1-3: High Throughput Synthesis:The initiator was weighed and dissolved in a mixture of 19 ml of dry chlorobenzene and 20 ml of dry acetonitrile. To the solution was added the calculated amount of 2-methyl-2-oxazoline (oxazoline monomer). After mixing, 50 mL of the solution was pumped into a helical tube reactor.The helical tube reactor had a tube internal diameter of 10 mm and the turns had a diameter of 72 mm.The flow rate was 10 ml / min, the reactor temperature was between 130 and 150 degrees Celsius, the pressure was 40 bar. After 30 to 35 minutes of flow, the product was collected in a bottle with a small amount of piperidine initially charged for 90 minutes. The mixture obtained was concentrated, taken up in methanol and precipitated in a 15 fold excess of diethyl ether. The procedure was repeated, the product was dissolved in water and freeze-dried.For the helical tube reactor used:The inner diameter was 10 mm. The flow is calculated according to:Radius r=5 mm=0.05 dm, cylinder volume: V=r^2*pi*h, where h corresponds to the tube length and is h=10 dm.V=0.05*0.05*3.141*10 dm^3=78.5 ml→for a length of 1 m, 78.5 ml / m results.The flow was adjusted to 10 mL / min. The calculated cylinder volume is given as:Monomer throughput is calculated as follows:m(monomer)=21 g, M(monomer)=85.1 g / mol, n(monomer)=447 mmolV (solution: chlorobenzene + acetonitrile + monomer) = 19 ml + 20 ml + 21 ml = 60 mlc(Monomer) =247 mmol / 60 ml=4 mol / L247 mmol in 60 ml of solution10 Flow rate (in 5 minutes) → 247 / 5 mmol / min = 49.4 mmol / min. A safety residue is retained in order not to draw air into the plant.The following Table 1 shows various exemplary embodiments: Table 1 shows the batch sizes of three exemplary embodiments, methyloxazoline (MeOx) having been used in each case with the piperidine terminating reagent. Table 1 shows the batch sizes of three exemplary embodiments, methyloxazoline (MeOx) having the terminating reagent piperidine being used in each case.183,25877,11150MeOx21,105024835Piperidine piperidine2,450028,84293,10266,961140MeOx21,105024836Piperidine piperidine2,450028,843115,36004,141140MeOx14,070016520Piperidine piperidine2,450028,84Table 2 shows the analytical results of the polyoxazoline obtainedTable 2 shows the analytical results of the polyoxazoline obtained135393,8353,42,51,369236353,4363,43,21,3283320303,1192,22,31,2570Mn... number average molar massPn... Degree of polymerizationÐ... Dispersibility of the polymerRegarding the helical tube reactors used:Table 3 shows in line 14 the spirally wound tube used in Working Examples 1 to 3 as a helical tube reactor. Table 3: Tube Designs. Lines 2 and 26 of the Prior Art. According to the invention, lines 4-8, 13-20 and 22-24 Table 3: Tube Designs. Lines 2 and 26 of the Prior Art. According to the invention, lines 4-8, 13-20 and 22-2411 / 161,590,0140,360,03450,87634,008,000,109537521 / 83,180,0280,710,0691,75269 / 1614,2928,580,061333333Maximum value Uni Gent(lambda not specified inOffenlegung)341 / 46,350,0350,890,184,5723 / 419,0538,100,1253 / 89,530,0350,890,3057,74715 / 1623,8147,630,16266666761 / 212,700,0350,890,4310,9221 1 / 238,1076,200,14333333375 / 815,880,0651,650,49512,5731,8145,9791,950,13674033183 / 419,050,0651,650,6215,7482,255,88111,760,1409090919125,400,0832,110,83421,18364101,60203,200,10425101 1 / 431,750,0832,111,08427,53365127,00254,000,1084111 1 / 238,100,0952,411,3133,2746152,40304,800,109166667121310,001,00836,0072,000,1111111111412,001,001036,0072,000,138888889SystemWegen1515,001,001346,0092,000,1413043481616,001,001446,0092,000,1521739131718,001,2015,655,00110,000,1418181821820,001,2017,667,00134,000,1313432841922,001,2019,667,00134,000,1462686572025,001,8021,482,00164,000,1304878052128,001,8024,4112,00224,000,1089285712230,002,0026112,00224,000,1160714292332,002,0028126,00252,000,1111111112438,002,2033,6152,00304,000,110526316252610,001,008150,00300,000,026666667Supplementary Example of TMC TubeExplanations on the calculations of the tube diameters, bending radii and lambda:Table 3 lists the respective dimensions of the spirally wound tube according to the instructions of the manufacturer Swagelok. The units indicated in the columns are to be understood as decimal values for indications in mm and inches, with the exception of the columns "outer diameter [inch]" and "bending radius [inch]". With the exceptions, the measures are given in the usual (oily) fractures.The aim was to obtain the largest possible lambda=(inner diameter) / (winding diameter). For this purpose, the inner diameter should be as large as possible, with a narrow winding or a small winding diameter. Since values are specified for each outer or inner radius on the manufacturer's side, it is easily possible to reproduce these lambda values.It is to be assumed that the respective bending radii for the corresponding wall thicknesses for the material stainless steel are similar for many manufacturers on the basis of the material parameters. The value lambda was calculated from the stated manufacturer specifications for the bending radii and the inner radii. The winding diameter is twice the bending radius.It can be seen that lambda values of 0.10-0.17 are achieved with a minimum bending radius. For this purpose, however, the tubes must be intentionally / intentionally brought to these bending radii.Comparative Example 4 - according to WO 2017 / 182610A1:Table 3 shows, in the second entry (line 2), the calculation of the maximum lambda value for the tubular reactor from WO2017 / 182610A1.If these bending radii (as in the application specification of the Uni Gent, i.e. WO2017 / 182610A1) are not specified, it must be assumed that the bending took place unwarranted. This is plausible since, in particular, pipes of outside diameters 1 / 16" and 1 / 8" can be wound up by hand. This results in a maximum lambda value of 0.06, which is obtained from the data of the UniGent (inner diameter and bending radii from the examples of the disclosure).Table 3 shows in line 26 a calculation of the maximum lambda value corresponding to WO2017 / 1812610A1 for PTFE as pipe material.However, since WO2017 / 182610A1a) has not given a bending radius or winding diameter as a further material PTFE with an even smaller lambda value of at most 0.026 and b), it is to be assumed that in the present disclosure pure space saving by winding was used.Cited non-patent literatureRice, M. H.; Leibfarth, F. A.; Pitet, L. M.;Polymerizations in Continuous Flow: Recent Advances in the Synthesis of Various Polymeric MaterialsACS Macro Lett. 2020, 9, 123-133.

Claims

A method for the continuous synthesis of polyoxazolines comprising the step of - passing at least one oxazoline monomer through a helical tube reactor under the action of heat, wherein the helical tube reactor comprises a helically wound tube having a tube inner diameter and a helical coil diameter, characterized in that: • the tube inner diameter is 4.5 mm to 34 mm, and • the lambda ratio as the ratio of the tube inner diameter to the helical coil diameter is in the range of 0.11-0.17, and • the helically wound tube is a stainless steel tube.The method of claim 1, wherein the lambda ratio is 0.13 ±0.01.The method of claim 2, wherein • the inner diameter of the tube is 10 mm ± 1 mm, and • the diameter of the helical coil is 72 mm ± 7 mm.Method according to claim 3, wherein • the wall thickness of the spirally wound tube is 1 mm ±0.2 mm.The method according to any one of claims 1 to 4, wherein in the passing, the monomer throughput of the oxazoline monomer is 6 to 480 mmol / min.The method of claim 5, wherein the concentration of the oxazoline monomer at the beginning of the passing is 4 mol / L ±1.5 mol / L.The method of claim 6, wherein in passing, the flow of the oxazoline monomer is 10 mL / min.The method of any one of claims 1 to 7, wherein the lambda ratio is 0.13 ± 0.01, and when passing the pressure is 40 bar ± 5 bar.The method according to any one of claims 1 to 8, wherein the lambda ratio is 0.13 ±0.01, and in the passing, the concentration of the oxazoline monomer at the beginning of the passing is 4 mol / L ±1.5 mol / L, and in the passing, the monomer flow rate of the oxazoline monomer is 6 to 480 mmol / min.The method according to any one of claims 1 to 9, wherein in the passing, first a first oxazoline monomer and then a second oxazoline monomer different from the first are passed through the helical tube reactor, so that the obtained polyoxazoline is a block copolymer having at least two blocks.The method according to any one of claims 1 to 10, wherein the helical tube reactor comprises at least two helically wound tubes and comprises a monomer feed in each case upstream of the first tube and between all tubes in the flow direction.The method according to any one of claims 1 to 11, wherein the flow velocity is 0.1 - 1 cm / s during the passing.The method according to any one of claims 1 to 6 or 8 to 12, wherein in passing the flow is 9-11 mL / min and the tube inner diameter is 9-11 mm.Use of a helical tube reactor for the continuous synthesis of polyoxazolines, the helical tube reactor comprising: a helically wound tube having an inner diameter of the tube and a diameter of the helical winding, characterized in that: • the inner diameter of the tube is 4.5 mm to 34 mm, and • the lambda ratio as the ratio of the inner diameter of the tube to the diameter of the helical winding is in the range of 0.11-0.17, and • the helically wound tube is a stainless steel tube, wherein at least one oxazoline monomer in a reaction mixture is passed through the helical tube reactor under the action of heat.