Highly functionalised polyurethanes

The invention relates to highly functional, dendritic polyurethanes, their production and monomers for the production of such polyurethanes.

Highly functionalized molecules, so-called dendrimers or arborols, and highly branched polymers, also known as hyperbranched polymers, have recently found increasing interest in chemistry and pharmacy.

Dendrimers are three-dimensional, highly ordered, highly branched oligomeric and polymeric compounds that, starting from small molecules, result from a constantly repeating reaction sequence. This creates ever higher branches, at the end of which there are functional groups, which in turn are the starting point for further branches.

A description of dendrimers can be found in DA Tomalia, AM Naylor, WA Goddard III, Angew. Chem., 1990, 102, 119-157.

A highly branched polyurethane is described in R. Spindler, JMJ Fréchet, J. Chem Soc. Perkin Trans. I, 1993, 913.

The monomer used there has the structural formula<chemistry id="chem0001" num="0001"><img file="EP0836626B1_D0001.tif" /></chemistry>

An isocyanate-terminated, highly branched polyurethane can be produced from this monomer by a polyaddition reaction.

The production of the monomer is problematic here. A connection with the following structure serves as the starting product:<chemistry id="chem0002" num="0002"><img file="EP0836626B1_D0002.tif" /></chemistry>

First the hydroxyl group is blocked with tert-butyldiphenylsilyl chloride, and the nitro groups are converted into isocyanate groups by hydrogenation and subsequent phosgenation, which groups are blocked with phenol. The blocking agents are removed to carry out the polyaddition reaction. Due to the need to remove the phenol and the use of the very expensive tert-butyldiphenylsilyl chloride, the preparation of the highly branched polyurethanes described is uneconomical.

A. Kumar and S. Ramachrishnan, J. Chem. Soc., Chem. Commun. 1993, 1453, describe highly branched polyurethanes which are produced from monomers of the following structure:<chemistry id="chem0003" num="0003"><img file="EP0836626B1_D0003.tif" /></chemistry>

The acid azide eliminates nitrogen when heated, and rearrangement creates the isocyanate, which reacts further to form a hydroxyl-terminated polyurethane.

Here too, the starting monomer is difficult to prepare, because acid azides decompose easily and under sometimes violent reactions, and the urethane group consisting of isocyanate and phenolic hydroxyl group is not thermally stable.

The object of the invention was to provide dendrimeric polyurethanes which can be reproducibly produced from easily accessible monomers by simple process steps.

The object of producing dendrimeric polyurethanes was achieved by reacting monomers with an NCO group and with n with NCO reactive groups or with an NCO reactive group and n NCO groups, with NCO reactive groups in particular mercapto, but preferably amino or Hydroxyl groups are and n is in the range from 2 to 5, in particular 2 to 4 and particularly preferably is 2 to 3.

The difference between highly branched and dendrimeric polyurethanes is that, starting from an initiator core, dendrimeric polyurethanes are shell-shaped in defined reaction stages (generations) and have a defined molecular weight, whereas highly branched polyurethanes are randomly structured and have a molecular weight distribution.

These structural differences are illustrated in the following schematic representations:<ul id="ul0001" list-style="none" compact="compact"><li>Highly branched polyurethane from AB₂Monomers:<chemistry id="chem0004" num="0004"><img file="EP0836626B1_D0004.tif" /></chemistry></li><li>Polyurethane dendrimer from initiator core I and AB₂Monomers:<chemistry id="chem0005" num="0005"><img file="EP0836626B1_D0005.tif" /></chemistry></li></ul>

In this case, A and B can be a hydroxyl or isocyanate group, BA can be a urethane group and I can be the initiator core. Depending on the functionality, several of the dendrimer branches shown can also be attached to the initiator core I.

To prepare the compounds according to the invention, it is first necessary to use monomers of the AB type_n to produce, where A and B each represent an isocyanate group and an H-functional group reactive therewith and n is a natural number ≧ 2, in particular equal to 2 or 3.

As an example, the production of an AB should first₂Monomers based on 2,4-tolylene diisocyanate (TDI) and trimethylolpropane are described.

First, one of the TDI's NCO groups is capped in a manner known per se. This can be done for example by uretdionization, reaction with an oxime, a phenol or another suitable blocking agent. Due to the different reactivity of the two NCO groups, the NCO group located in the 4-position is preferably blocked in the case of 2,4-TDI.

The free NCO group can be reacted with a compound containing at least 3 H-functional groups, for example trimethylolpropane, glycerol or an alkanolamine, such as diethanolamine.

After the capping agent has been split off, a molecule with 2 hydroxyl groups and an NCO group is formed which can be converted into dendrimeric polyurethanes.

In an analogous manner, that is to say by capping a part of the isocyanate groups and reacting the other part with compounds containing at least 3 H-functional groups, in principle all aliphatic and aromatic di- or polyisocyanates can be converted to monomers with an NCO and at least 2 H-functional groups be implemented. Particularly suitable isocyanates are 2,4-tolylene diisocyanate (2,4-TDI), 2,6-tolylene diisocyanate (2,6-TDI), 2,4'-diphenylmethane diisocyanate (2,4'-MDI), 4,4'- Diphenylmethane diisocyanate (4,4'-MDI), 1,5-naphthylene diisocyanate (NDI), 1,4-phenylene diisocyanate, 1,3-tetramethylxylylene diisocyanate (TMXDI), hydrogenated MDI (HMDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate 1,6 ( HDI), 2-isocyanatopropylcyclohexyl isocyanate (IPCI), 2-butyl-2-ethyl-pentaethylene diisocyanate (BEPDI), lysine diisocyanate (LDI), 1,12-dodecyl diisocyanate, cyclohexyl-1,3- or 1,4-diisocyanate, 2-methylpentamethylene diisocyanate (MPDI).

Conversely, it is also possible to AB_nTo produce monomers by capping at least one of the H-functional groups in a compound containing at least 2 H-functional groups and reacting the free H-functional groups with isocyanate groups.

In the case of polyfunctional alcohols, the capping can take place, for example, by acetal or ketal formation. For example, two hydroxyl groups of trimethylolpropane or glycerol can be capped by reaction with acetone and the free hydroxyl group can be reacted with an isocyanate group.

If a triol capped in this way with 2,4-tolylene diisocyanate (TDI), in which the NCO group in the 4-position is blocked, for example by uretdionization or by reaction with an oxime, for example acetone oxime, is obtained with higher Selectivity of a monomer with two hydroxyl groups and one blocked NCO group. The reaction should be shown schematically using trimethylolpropane (TMP), acetone, 2,4-TDI and acetone oxime:<chemistry id="chem0006" num="0006"><img file="EP0836626B1_D0006.tif" /></chemistry><chemistry id="chem0007" num="0007"><img file="EP0836626B1_D0007.tif" /></chemistry><chemistry id="chem0008" num="0008"><img file="EP0836626B1_D0008.tif" /></chemistry><chemistry id="chem0009" num="0009"><img file="EP0836626B1_D0009.tif" /></chemistry>

In the first step, the protected triol (1) is produced from TMP and acetone, ie 2 hydroxyl groups are blocked. In the second step, whereby "first and second step" should not be interpreted as a chronological sequence, an NCO group of 2,4-TDI is blocked with acetone oxime, and the monoisocyanate (2) is formed.

These two starting compounds are converted into a compound with 2 blocked hydroxyl groups and one blocked isocyanate group (3).

The hydroxyl groups can be made accessible again by hydrolysis (4); a monomer is formed which, after the isocyanate group has been released, can be converted into highly branched or dendrimeric polyurethanes.

As an alternative to a blocked trimethylolpropane, blocked glycerol, N-hydroxyalkyl-oxazolidine or dialkanolamine can also be used. In the case of dialkanolamines, the NH group reacts preferentially, so that the OH groups cannot be capped.

The reactions are highly selective.

An isomerically built monomer can be obtained by reacting acetone-capped TMP with 2,4-TDI.

The reaction follows the following equation:<chemistry id="chem0010" num="0010"><img file="EP0836626B1_D0010.tif" /></chemistry>

Due to the higher reactivity of the 4-position NCO groups, this reaction is also very selective.

The free NCO group in compound (5) should also be blocked after the reaction, for example with oxime, in order to enable hydrolysis of the dioxane ring without the monomers reacting with one another. After hydrolysis of the dioxane ring, an AB isomeric to (4) is obtained₂-Monomer.

The monomers capped in this way are stable in storage at room temperature for weeks.

To produce the dendrimeric polyurethanes according to the invention, the functional groups of the monomers are activated in order to enable the reaction.

A distinction must be made between the convergent and the divergent method in the production of the dendrimeric polyurethanes according to the invention.

With the divergent method, starting from an initiator core, the monomers are deposited around it for generations.

Protective groups in the monomers must ensure that the monomers react only with the functional groups of the initiator core or the dendrimer and not with one another.

In the convergent method, the individual branches are first synthesized, which are then coupled to an initiator core.

As an example, the divergent structure of a dendrimer with TMP as the initiator core and the above-described monomer from TMP and 2,4-TDI will be shown using the structural formulas:<chemistry id="chem0011" num="0011"><img file="EP0836626B1_D0011.tif" /></chemistry><chemistry id="chem0012" num="0012"><img file="EP0836626B1_D0012.tif" /></chemistry><chemistry id="chem0013" num="0013"><img file="EP0836626B1_D0013.tif" /></chemistry>

By adding further monomers (5) to the free hydroxyl groups of the dendrimer, further generations of the dendrimer can be synthesized. Due to the regular structure of the dendrimer molecules, the amount of monomers required for the construction of each generation can be precisely calculated and used for synthesis.

To build dendrimers with a defined structure, it is advantageous to isolate and purify the reaction product after the synthesis of each generation and to use the product treated in this way for the synthesis of the next generation. The dendrimeric polyurethanes are advantageously prepared in solution, it being possible to use the solvents mentioned above.

The above-mentioned urethanization catalysts can be used to accelerate the reaction.

A convergent construction of dendrimeric polyurethanes, i.e. a synthesis of the branches, which are then attached to an initiator core, is possible in the same way.

If the above-described monomer were used, a monomer unit with two OH groups and a blocked NCO group would be used, for example molecule (4), and the monomer (5) would be grafted on in generations if the dendrimeric polyurethane were used as a starter molecule. The further monomers are added as described above. The branches thus synthesized with the blocked hydroxyl groups can be attached to an H-functional initiator core after activation of the NCO group of the starting monomer. After the activation of the terminal hydroxyl groups, a dendrimer is formed which, in its structure, corresponds completely to the dendrimers produced by the divergent process.

The production of monomers of type A (B)_n, where A, B and n have the meaning described above, as is apparent from the list of the isocyanates which can be used according to the invention, is also possible with aliphatic isocyanates. The production of such a monomer from 1,6-hexamethylene diisocyanate (HDI) and masked trimethylolpropane is to be described here by way of example. Since the reactivity of the two NCO groups of the HDI is the same, a deficit of blocked alcohol should be used to prepare the monourethane. The molar ratio of capped alcohol to the diisocyanate should be at least 1: 3, in particular at least 1: 5. The conversion to monourethane proceeds under these conditions with high selectivity and high yield. The unreacted diisocyanate can be removed from the reaction product in a simple manner, for example by distillation. The representation of such a monomer can be represented schematically as follows:<chemistry id="chem0014" num="0014"><img file="EP0836626B1_D0014.tif" /></chemistry><chemistry id="chem0015" num="0015"><img file="EP0836626B1_D0015.tif" /></chemistry>

As shown in the TDI-based monomers, this molecule can be coupled directly to an H-functional initiator core. After activation of the OH groups, a dendrimer of the 0th generation is obtained, to which the molecule (9) can in turn be attached. Furthermore, by blocking the free NCO group and then activating the hydroxyl groups, a monomer can be prepared which can be converted to dendrimeric polyurethanes in the same way as described.<chemistry id="chem0016" num="0016"><img file="EP0836626B1_D0016.tif" /></chemistry>

The dendrimeric polyurethanes can be used, for example, as highly functional crosslinkers for polyurethane lacquers and coatings or for polyurethane foams.

The invention is illustrated by the examples below.

example 1

Preparation of the acetone-capped trimethylol propane (isopropylidene-TMP, (1))

250 g (1863 mmol) of trimethylolpropane were refluxed with 750 ml of acetone, 750 ml of petroleum ether 30/75 and 0.15 g of p-toluenesulfonic acid monohydrate for 25 hours. The water was then removed via a 50 cm packed column for 21 hours. The solution was then cooled to room temperature, 0.5 g of sodium methoxide was added and the mixture was stirred at room temperature for 1 hour. The solution was then filtered, excess solvent was removed on a rotary evaporator and the residue was distilled in vacuo through a 15 cm Vigreux column.

The reaction product was a colorless liquid with a boiling point at 71 to 72 ° C (0.5 mbar). The yield was 254 g ≙ 78%.

Example 2

Preparation of the monourethane from 2,4-TDI and acetone oxime (2)

232 g of 2,4-tolylene diisocyanate (1334 mmol) were placed in 1330 ml of dried acetone under a nitrogen atmosphere. 48.7 g of acetone oxime (667 mmol) were dissolved in 450 ml of dried acetone and added dropwise to the reaction solution at room temperature within 8 hours. The solution was left overnight and evaporated the next day on a rotary evaporator. The resulting crystalline product was recrystallized from acetone and then washed with petroleum ether. A colorless solid with a melting point of 109 to 111 ° C. was formed. The yield was 89.2 g (54%).

Example 3

Preparation of the monourethane from 2,4-TDI and isopropylidene-TMP (5)

87.8 g (504 mmol) of 2,4-tolylene diisocyanate were placed in 300 ml of petroleum ether 30/75. 44.0 g of the product from Example 1 were dissolved in 80 ml of petroleum ether 30/75 and added dropwise under a nitrogen atmosphere within 8 hours at room temperature. The solution was left overnight at room temperature and suctioned off the next day. The residue was washed twice with petroleum ether and dried in vacuo. A colorless solid with a melting point of 135 to 137 ° C. was formed. The yield was 81.2 g (92%).

Example 4

Preparation of the diurethane from 2,4-TDI, isopropylidene-TMP and acetone oxime (isomer to (3))

30.0 g of the reaction product from Example 3 were dissolved in 500 ml of dried acetone. A solution of 6.29 g of acetone oxime in 100 ml of dried acetone was added dropwise under a nitrogen atmosphere over the course of 2 hours. The solution was then stirred at room temperature for 2 hours and then evaporated in a rotary evaporator at 35 ° C. The residue was washed with petroleum ether 30/75 and then dried under vacuum. A colorless solid was formed, which dissolves when left to stand for a long time. The yield was 30.5 g (83%).

Example 5

Preparation of the diurethane from 2,4-TDI, acetone oxime and isopropylidene-TMP (3)

20 g of the reaction product from Example 2 and 14.1 g of the reaction product from Example 1 were placed together in 160 ml of dried acetone, 8 μl of di-n-butyltin dilaurate were added and the solution was stirred at 45 ° C. for 16 hours. After that, the IR spectrum no longer showed any NCO band. The solution was evaporated in a rotary evaporator at 35 ° C. and the residue was rubbed in petroleum ether 30/75. The resulting pasty mass was washed with petroleum ether 30/75 and then dried in vacuo. 26.9 g (≙ 79%) of a colorless, hygroscopic solid were formed.

Example 6

Manufacture of urethane diol (4)

15.2 g of the reaction product from Example 5 were dissolved in 190 ml of methanol and 45 ml of water and 0.04 g of oxalic acid were added to this solution. The solution was stirred for 72 hours at room temperature. The methanol was then removed from the solution in a rotary evaporator at 30 ° C. The aqueous residue was extracted with ethyl acetate, the ethyl acetate phase was dried overnight with sodium sulfate and evaporated in a rotary evaporator. A yellowish solid with a melting point of 53 to 55 ° C. was formed. The yield was 8.8 g (64%).

Example 7

Preparation of the (4) isomeric urethane diol

30.0 g of the product according to Example 4 were dissolved in 80 ml of methanol and 20 ml of water and 0.09 g of oxalic acid were added to this solution. The solution was stirred at room temperature for 24 h. The methanol was then largely removed from the solution in a rotary evaporator at 30 ° C. The aqueous residue was extracted with ethyl acetate, the ethyl acetate phase was dried overnight with sodium sulfate and evaporated in a rotary evaporator. A yellowish solid was formed with a melting point of 54 to 56 ° C. The yield was 14.6 g (54%).

Example 8

Preparation of the urethane diol from 2,4-TDI, acetone oxime and diethanolamine

6.37 g (60.6 mmol) of diethanolamine were dissolved in 100 ml of dried acetone. A solution of 15.0 g (60.6 mmol) of the reaction product from Example 2 in 120 ml of dried acetone was added dropwise over a period of 2 hours at room temperature under a nitrogen atmosphere. The solution was stirred at room temperature for 1 h and left to stand overnight. It was then filtered, the solution was evaporated at 35 ° C. in a rotary evaporator and the residue was taken up in a little dry acetone. The resulting solution was covered with a little petroleum ether 30/75 and left to stand at 3 ° C. overnight. The crystallized product was filtered off and dried in vacuo. A colorless solid resulted, the yield was 9.6 g (45%).

Example 9

Production of a 0th generation dendrimer from 2,4-TDI and isopropylidene-TMP (6)

20.0 g of the monourethane (5) from Example 3 were dissolved in 100 ml of dried acetone at 40 ° C., 2.57 g of trimethylolpropane and 5 μl of di-n-butyltin dilaurate were added. The solution was refluxed for 6 hours under a nitrogen atmosphere. Thereafter, there was no longer any NCO band in the IR spectrum of the solution.

The solution was filtered before cooling and then evaporated in a rotary evaporator at 45 ° C. The yellowish oil obtained was left overnight at room temperature. Then it was highly viscous and crystallized when rubbed in petroleum ether 30/75. The solid was washed with petroleum ether 30/75 and dried in vacuo. 15.6 g of a colorless solid resulted.

Example 10

Production of the 0th generation dendrimer from 2,4-TDI and TMP by activation of the OH group (7)

12th g of the product (6) from Example 9 were dissolved in 80 ml of methanol and 20 ml of water and 2 ml of 0.1 molar hydrochloric acid were added to this solution. This solution was left to stand at room temperature for 72 h, neutralized with sodium carbonate, filtered and then the methanol was removed in a rotary evaporator at 30 ° C. The aqueous residue was extracted with ethyl acetate, the ethyl acetate phase was dried over sodium sulfate and evaporated to dryness in a rotary evaporator at 30 ° C. 5.4 g of a yellowish solid resulted.

Example 11

Production of the 1st generation dendrimer from 2,4-TDI and TMP (8)

4.00 g of the reaction product (7) from Example 9 and 7.90 g of the reaction product from Example 3 were dissolved together in 50 ml of dried acetone, 2.5 .mu.l of di-n-butyltin dilaurate were added and under a nitrogen atmosphere for 4 hours at 50 ° C stirred. Thereafter, there was no longer any NCO band in the IR spectrum of the solution.

The solution was evaporated at 35 ° C. in a rotary evaporator, the residue was taken up in 80 ml of methanol, 5 ml of water and 1 ml of 1M hydrochloric acid were added and the solution was left to stand at room temperature overnight. An excess of sodium carbonate was then added, the solution was filtered and the methanol was removed in a rotary evaporator at 30 ° C. The aqueous residue was extracted with ethyl acetate, the ethyl acetate phase was dried over sodium sulfate and rotated to dryness in a rotary evaporator at 30 ° C. The reaction product was a yellowish solid. The yield was 5.8 g.

Example 12

Production of the 2nd generation dendrimer from 2,4-TDI and TMP

4.00 g of the reaction product from Example 11 and 5.75 g of the reaction product from Example 3 were dissolved in 70 ml of acetone, 3.5 .mu.l of di-n-butyltin dilaurate were added and the mixture was stirred at 50.degree. C. for 3 hours under a nitrogen atmosphere. Thereafter, there was no longer any NCO band in the IR spectrum of the solution. The solution was evaporated to dryness at 35 ° C. in a rotary evaporator.

2.00 g of the residue were dissolved in 80 ml of methanol and 5 ml of water and 1 ml of 1 M hydrochloric acid were added. This solution was stirred for 24 hours at room temperature. An excess of sodium carbonate was then added, the mixture was filtered and the methanol was removed in a rotary evaporator at 30 ° C.

The aqueous residue was extracted with ethyl acetate, the ethyl acetate phase was dried over sodium sulfate and evaporated to dryness in a rotary evaporator at 30 ° C. The reaction product was a yellowish solid. The yield was 0.6 g.

Example 13

Preparation of a monourethane from HDI and isopropylidene TMP (9)

1680 g (10 mol) of HDI and 0.84 g of dibutyltin dilaurate were heated to 50 ° C. with nitrogen blanketing and stirring. At this temperature, 348 g of the reaction product from Example 1 were added dropwise with stirring over the course of 30 minutes. After the addition had ended, the reaction mixture was left at this temperature for a further 30 minutes. The reaction mixture was then freed from the monomeric HDI by distillation on a thin-film evaporator at 165 ° C. and 2.5 mbar.

The reaction product had the following characteristics:<ul id="ul0002" list-style="none" compact="compact"><li>Purity: 88.6% (area% according to GPC)</li><li>NCO content: 12.3% by weight</li><li>Viscosity at 25 ° C: 1200 mPa · s</li><li>Residual monomer content: &lt;0.2% by weight.</li></ul>

Example 14

Production of a monourethane from HDI and isopropylidene glycerin

The procedure was as in Example 13, except that 264 g (2 mol) of isopropylidene glycerol (from Fluka AG) were added instead of the reaction product from Example 1.

The reaction product had the following key figures:<ul id="ul0003" list-style="none" compact="compact"><li>Purity: 89% (area% according to GPC)</li><li>NCO content: 13.7% by weight</li><li>Viscosity at 25 ° C: 174 mPas</li><li>Residual monomer content: &lt;0.2% by weight</li></ul>

Example 15

Production of diurethane from HDI, isopropylidene-TMP and acetone oxime

100 g of the reaction product from Example 13 and 50 mg of dibutyltin dilaurate were introduced and, with stirring and nitrogen blanketing, the equimolar amount of acetone oxime, dissolved in dry acetone, was added dropwise at room temperature in the course of 15 minutes and, after the metering had ended, the mixture was stirred at room temperature for one hour. The acetone was then removed on a rotary evaporator and the reaction product was purified by column chromatography on silica gel using ethyl acetate as the eluent. The reaction product had a viscosity of 2140 mPas at 23 ° C.

Example 16

Production of diurethane from HDI, isopropylidene glycerin and acetone oxime

The procedure was as in Example 15, except that 100 g of reaction product from Example 17 were used instead of the reaction product from Example 13.

Example 17

Manufacture of urethane diol (10)

20 g of the reaction product from Example 15 were introduced and a mixture of 100 ml of methanol, 20 ml of water and 15 ml of 0.1 molar hydrochloric acid was added. This mixture was stirred at 30 ° C for 8 hours and left overnight. The mixture was then shaken out three times with 50 ml of ethyl acetate each time. The combined ethyl acetate extracts were washed with 20 ml of 0.1 molar sodium carbonate solution and then with 2 times 20 ml of water. After the aqueous phase had been separated off, it was dried over sodium sulfate. After removing the ethyl acetate, the NCO-capped diol was obtained. The hydrolysis was quantitative. Viscosity at 23 ° c: 1070 mPas

Example 18

Production of the urethane diol from HDI, acetone oxime and glycerin

The procedure was as in Example 17, except that 20 g of the reaction product from Example 19 were used instead of the reaction product from Example 18. Viscosity at 23 ° C: 4740 mPas

Example 19

Production of a 0th generation dendrimer from HDI and isopropylidene TMP with TMP as the initiator core

1 Mol of the reaction product from Example 13 and 50 ml of dry methyl ethyl ketone were introduced and heated to 70 ° C. With stirring and nitrogen blanketing, the solution of 0.3 mol of trimethylolpropane in 150 ml of methyl ethyl ketone was added over the course of 15 minutes and stirring was continued at 70 ° C. for 90 minutes.

The solvent was then removed on a rotary evaporator and the residue was chromatographed on silica gel using ethyl acetate as the eluent.

A dendrimer of the 0th generation with capped hydroxyl groups and the following characteristics emerged.

Viscosity 2140 mPas (50 ° C in 10% by weight butyl acetate)<ul id="ul0004" list-style="none" compact="compact"><li>Elemental analysis: C₅₇H₁₀₄O₁₈</li><li>Ber: C: 58.97; H: 8.97; N: 7.24</li><li>Found: C: 58.70; H: 9.18; N: 6.98</li></ul>

Example 20

Production of the 0th generation dendrimer from HDI and TMP by activation of the OH groups

10th 30 ml of methanol, 60 ml of water and 13 ml of 1 molar hydrochloric acid were added to g of the reaction product from Example 19 and the mixture was stirred under reflux for 8 hours. The methanol was then removed on a rotary evaporator, the residue was taken up in 100 ml of methyl ethyl ketone, washed first with 15 ml of aqueous 1 molar sodium carbonate solution and then with 20 ml of water. After the aqueous phase had been separated off, the organic phase was dried using sodium carbonate.

After removal of the solvent, a 0-generation hydroxyl-terminated dendrimer was formed.

Viscosity 7110 mPa · S (at 50 ° C in 10 wt% methanol,<ul id="ul0005" list-style="none" compact="compact"><li>Elemental analysis: C₄₈H₉₂N₆O₁₈</li><li>Ber: C: 55.37; H: 8.91; N: 8.07</li><li>Found: C: 55.30; H: 9.01; N: 7.80</li></ul>