DE2050824C - Process to accelerate the sulfur vulcanization of poly urethanes - Google Patents

Description

The sulfur vulcanizable ones. unsaturated polyurethanes, such as those used, for. As described in French patents 1484 729 and 1486 448, are generally more difficult to vulcanize than the saturated or unsaturated polyurethanes that are vulcanized with peroxides. In addition to organic accelerators 1 of the mercaptobenzothiazole type, metallic accelerators, in particular complexes of zinc halides and mercaptobenzothiazole sulfides, are used to activate and accelerate vulcanization with sulfur. However, these metallic accelerators have the disadvantage that, when used in an amount sufficient for a relatively rapid vulcanization of not more than, for example, 30 minutes at a temperature of about 150 to 160 C, the properties of the vulcanizates are adversely affected by their aging resistance, in particular in the Warmth, diminish.

The inventive method for accelerating the sulfur vulcanization of unsaturated Polyurethanes are characterized by the fact that an N-alkenyl compound with an accelerator or more alkenyl radicals located on a nitrogen atom in such an amount that 2 to 4 nitrogen atoms meet a polyurethane molecule. a) the vulcanization or b) the reaction mixture for the polyurethane is added, wherein in case b) a N-alkenyl compounds with one or two isocyanate-reactive groups are used will. do

According to a preferred embodiment of the invention one uses a connection with two or even three alkenyl radicals located on the same nitrogen atom, these radicals being the same or different could be.

The invention, on the other hand, can be carried out in two different ways.

According to a first embodiment, the N-alkenyl compound is used as one of the components of the vulcanization mixture, and it is brought with the other components, namely polyurethane, Soot, sulfur etc .. together during the preparation of the mixture.

According to a second type of implementation, one fixes the compound N-alkenyl in the polyurethane molecule itself. For this purpose one chooses an N-alkenyl compound with one or two opposite Isocyanate-reactive groups, in particular with one or two alcohol and / or amine groups During the production of the polyurethane through the reaction of a dihydroxylated polymer - for Example of a polyester - with diisocyanate, the N-alkenyl compound is then either ai.i chain end or built into the interior of the polyurethane chain, ie after whether they have one or two opposite isocyanates !, has reactive groups.

Of course you could do both of them above-described Verfahrc-'sformen combi kidney by having an N-alkenyl compound in the polyurethane molecule or one of the polyurethane building components and an N-Alkeny! · connection to the polyurethane rubber mixture to be vulcanized admits

The amount of N-alkenyl compound to be used is such that there are 2 to 4 atoms of nitrogen per polyurethane molecule. If the N-alkenyl compound is only a single ethylenic Has a double bond, it is preferably limited to a maximum of 2 nitrogen atoms per polyurethane molecule corresponding amount. If it has two double bonds, you can get more accelerators use, preferably not exceeding 4 nitrogen atoms per polyurethane molecule. In fact, the acceleration effect increases with the proportion of nitrogen atoms. runs pretty much though quickly flat. The properties of the vulcanizates are improved even when the proportion of nitrogen atoms is increased at first only imperceptibly, then more quickly worse. The preferred proportion of nitrogen atoms is the acceleration effect is pronounced without any noticeable deterioration in the properties or such a mistake determines which could not be compensated by adjusting the proportions of the various constituents forming the vulcanization mixture accordingly.

As examples of usable N-alkenyl compounds are mentioned:

a) as compounds with three alkenyl radicals: triallylamine, N - diallyl vinylamine. N - diisobutenylmethallylamine. N - dimethallylallylamine or N-divinylamino-1-pentene-4;

b) as compounds with two alkenyl resrene: diallylamine. Diallylb <, nzylamine. Diallylethanolamine, N - diallylamino -1 - propanediol-2,3, N - vinyl-N - ethylamino - 1 - butene - 3, N - N '- dimethyl-N - N' - divinylethylenediamine, N - dibutenyl-2-ethanolamine, N-N'-AIIyl-ethylenediamine or N-dimethallylaniline;

c) as compounds with a single alkenyl radical: N -allylmethylaniline, N -allyl -N-benzylaniline. N - allyl - N - methylethanolamine. N - Allyl diethanoiamine, vinylamine, methallylamine. Ethylamino-1-butene-3. Amino-1-pentene-4, N-vinyldiethanolamine, N-butynyl-2-dibutylamine or N-vinyl-N-methylaniline.

The examples could easily be multiplied by adding nan replaced the Mkenyl radical (s) in the above compounds by other alkenyl radicals and / ider the nature of the others on the nitrogen atom , itzenden residues changes, regardless of whether these active groups, e.g. B. the alcohol residue, wear or light and whether you keep these groups or not.

A long list would be pointless. Essential for the invention is

1. that at least 1 nitrogen atom is present,

2. that there is at least one ethylenic double bond and

3. that the nitrogen atom ο directly or via a small number of dazwischenbcfindlichen carbon atoms at the double bond äthyfcnische 1 r is bonded to the ethylenic double bonds.

Di ... ■ Ethylenic, bonded to a nitrogen atom or in the vicinity of such a double bond do indeed have the property. the rate of VuL anization of the polyurethane with sulfur increase. It appears that these ethylenic atoms are bound to nitrogen atoms Double bonds react quickly with sulfur and common organic sulfur-containing ones Bes (Meunigern and thereby form a very effective sulphurizing agent: sulfur is brought into a very active form and then acts on the other double bonds, i.e. H. on the Double bonds not bound to these nitrogen atoms and present in the polyurethane chain.

The vulcanization system to be used in the process of the invention may be appropriate to 100 parts by weight of polyurethane, except for the N-alkenyl compound, 1 to 3 parts by weight of sulfur. 1 to 3 parts by weight of mercaptobenzothir: ol or 2 to 6 parts by weight of mercaptobenzothiazole sulfide. The simultaneous use of a small amount of a metallic accelerator, e.g. B. a complex of zinc halide and mercaptobenzothiazole disulfide, optionally also combined with cadmium stearate. may prove necessary. However, these metal compounds are used in a lot of less than 1 part by weight to 100 parts by weight of elastomer.

With a vulcanization system like the one described above, a polyurethane can be used in vulcanize with sulfur within a reasonable time, usually within less than 30 minutes. So exceeds that Vulcanization time at 155 ° C is not 25 minutes: at 135 ° C it is still only 45 minutes. Of course, the term "vulcanization time" is understood to mean the time required to achieve a vulcanizate with optimum Characteristics required time: when you get vulcanization followed with the Monsanto rheometer, this corresponds to a shear or shear modulus of about 90% of the maximum value.

The invention is fully understandable on the basis of the following exemplary embodiments:

The following abbreviations are used in these various examples:

AOP = allyloxypropanediol.

DAP = diallyl propanol.

MDI = methar.diphenyl diisocyanate.

MBT = mercaptobenzothiazole.

MBTS = mercaptobenzothiazole disulfide.

MBZ = complex of zinc bromide - Mercaptc-

benzothiazole disulfd.
SCd = cadmium stearate.

Mooney plasticity: This is the Mooney plasticity ML (1 + 4) for WC.

B a i s ρ i e 1 1

^r

In this example, an N-alkylene compound fixed in the polyurethane chain is used, and the vulcanization properties of the polyurethane thus obtained are compared with those of a similar polyurethane not containing this compound.

To 10 kg of a mixed, unsaturated polyadipate from ethylene glycol. Propylene glycol and allyloxypropanediol. with a molecular weight of 2740 and a double bond to 4700 molecular weight units give:

47.7 grams of DAP.

96 g of N-diallylamino-1-propanediol-2,3. d. H. the Compound of formula

CH ₂ "CH - CH ₂
\
N-CH ₂ -CH -CH ₂

I I

CH ₂ CH -CH, OH OH

The mixture, heated to 80 ° C., is mixed with 1055 g of MDI. After holding at 90 ^° C. for 24 hours, an unsaturated polyurethane with a molecular weight of about 80,000 and a Mooney plasticity of 56 is obtained.

In the same way, another preliminary product B according to the invention is produced, which, however, by the Contains half less of the N-alkali: yl compound, based on:

10 kg of the same unsaturated mixed polyadipate,

47.7 g DAP,

47.5 g of N-diallylamino-l-propanediol-2.3,
1000 g MDI.

$ 5 A well-known preliminary product is produced in the same way C her. starting from:

10 kg of the same unsaturated mixed poly

adipate.

47.2 g of DAP.
945 grams of MDI.

B and C have molecular weights of about XOOOO like A. and the Mooncy plasticities are also similar to that of A.

The three preliminary products A. B. C are used to produce mixtures, their composition by weight is given below.

Pre-product A
Pre-product B
Pre-product »C
Stearic acid ..
SAF soot ....

MBTS

MBT

MBZ

sulfur

SCd

Al

A.

100

0.3 25 3.4 1.7 0.3 1.7 0.5 sheets

100

0.3 25 4.8 2.4 0.4 2.4 0.5 100

0.3 25 3.4 1.7 0.3 1.7 0.5

B2 C. 100 __ - 100 0.3 0.3 25th 25th 3.8 3.4 1.9 1.7 0.34 0.3 1.9 1.7 0.5 0.5

The five mixtures were vulcanized at 154 ° C. and followed with the Monsanto rheometer. Mixtures A reach 90% of the final value of the shear modulus recorded by the apparatus within 19 minutes, the mixes B within; ! b 24 minutes and mixture C within JO minutes.

The vulcanizates have the following properties:

Module (at 100%

Elongation) in kg cm ² ....

ISO hardness

Hysteresis losses,%

at 20 C "

at 60 C-

Breaking strength at 20 C
in kg, cm ²

Al

21.5 69

33 26

378

A2

24.2 70

29.4 21.5

374 sheets

21.1 70

34.4 27.3

390

B2

24.7 69

33

24.7

357

20.1 68

36 28.9

383

As can be seen, the presence of an N-dialk ^ nyl compound in the polyurethane chain causes one substantial acceleration of vulcanization, with a slight improvement in properties, especially if 4 moles of N-dialkenyl compound are introduced into each polyurethane molecule (A); the The effect is still pronounced with 2 moles of N-dialkenyl compound in each polyurethane molecule (B). Man should adjust the amount of vulcanization system (sulfur and organic accelerators) so that the additional double bonds introduced by the N-dialkenyl compound are taken into account.

It s ^ i noticed that one expediently the amount on in the pole; N-alkenyl compound built into an arethane molecule or N-dialkenyl compound not increased too much.

If, for example, in the context of this example, that for the preparation of the mixed polyadipate Replace the AOP used with the same molar amount of N-diallylamino-1-propanediol-2,3 and then would produce a polyurethane in compliance with the proportions specified for C, would be obtained a polyurethane D that gives sticky Vuikanisate with poor properties.

For the purposes of this example, it is A which indicates the improved rate of vulcanization and simultaneously which offers more advantageous properties.

Example 2

This example, like the previous one, illustrates the use of an incorporated into the polyurethane molecule N-alkenyl compound. It is intended to show the influence of the amount of N-alkenyl compound used.

Starting from a mixed folyedipai of Ethylene glycol and propylene glycol with a molecular weight of 2780 are prepared as in Example 1 four different polyurethanes from the following components:

40

polyester

AOP

N-Ally! Diethanolamine

DAP

MDI

B. C. A. G G G 1000 1000 1000 25.3 21.5 29.3 4.3 8.57 0 5.1 5.1 5.1 144 144 144

1000 17.5

12.86 5.1 144

6o The polyurethane A does not contain any nitrogen compounds. The polyurethanes B, C, D contain the same in such an amount that there are on average 2, 4 or 6 nitrogen atoms per molecule.

Mixtures are then prepared based on the following composition (on a weight basis) from:

polyester

Stearic acid 0.3

SAF carbon black MBTS MBT sulfur MBZ

Vulcanization is carried out at 154 ^° C., the vulcanization being followed with a Monsanto rheometer.

90% of the maximum value of the shear modulus is reached after the following times:

Mixture A 25 minutes

Mixture B 18 minutes

Mixture C 15 minutes

Mixture D 12.5 minutes

The vulcanizates have the following properties:

Module (at 100% elongation) kg / cm ²

ISO hardness

Hysteresis losses,%

at 20 ^° C

at 60 'C

Elongation at break,%

Breaking Strength, kg / cm ²

Properties on the
Goodrich Flexometer
initial compression,%

Warming, ° C

permanent deformation, % ...

24.8
74

33.3

26th
640
379

11.6

34.5

2.6

As you can see, it is advisable to limit the amount of nitrogen compound. In the case of the present For example, elastomer B represents the better compromise, and it does not seem to be expedient be, with the N-alkenyl compound more than 2 nitrogen atoms to introduce into a polyurethane molecule. In the previous example you could use an N-dialkenyl compound advantageously 4 nitrogen atoms per polyurethane molecule use.

Example 3

In this example, an N-alkenyl compound attached to the end of the polyurethane chain is used used, which carries only a single alcohol group for this purpose.

A polyurethane is produced as in the previous examples, starting from:

10 kg mixed polyadipate of ethylene glycol and propylene glycol with a molecular weight of 2780,
292 g AOP,

41.6 g of N-diallylethanolamine, i.e. H. the connection the formula

CH ₂ -CH-CH ₂

CH ₂ ^ CH-CH ₂

N -CH ₂ -CH ₂ OH

1446 g MDI.

A polyurethane designated below with A and having a molecular weight of 80,000 is obtained and a Mooney plasticity of 50.

A polyurethane B which is as similar as possible to polyurethane A is produced under identical conditions here, but which does not contain a nitrogen compound; is assumed

10 kg of the same polyester,
292 g AOP,
51 g DAP,
1440 grams of MDI.

23.1
70

32.3
24.2

670

381

12.7
37
6.5

22.2
68

30.7
24.4

710

420

12.9

67

30.4 25.6

690

417

13.8 47

The molecular weight is also 80,000, the Mooney property 60.

You make with the polyurethanes A and B using the same composition as in Example 2 produces mixtures and vulcanises them at 154 ° C.

The polyurethane A reaches 90% of the final value of the shear modulus after 18 minutes, in contrast to 28 minutes for the polyurethane B. The vulcanizates have the following properties.

Module (at 100% elongation),

kg / cm ²

ISO hardness

Hysteresis losses,%

at 20 ° C

at 60 ° C

Elongation at break%, at 20 ° C ...

Breaking Strength, kg / cm ²

Properties on the
Goodrich Flexometer
initial compression,%

Warming, c

permanent deformation, % ..

23.1 70

30.7 23.8

6'7

379

12.3 36.5

24.8 74

33.3

26 648 411

11.6

31.5

As you can see, the properties of the vulcanized materials are very similar, but the pol urethane A vulcanizes more quickly: at 134 ° C it only takes 46 minutes, compared to 18 minutes at 154 ° The acceleration of vulcanization caused by the N-diallylethanolamine is very ai shaped. This makes it possible to reduce the number of metallic accelerators of the MBZ type, <in a much smaller amount than half <the amount of sulfur can then be used, ot that this has an unfavorable influence on the properties. However, there is an optims value for the amount of MBZ. Below it is shown how the Monsanto shear modulus and the optimal vulcanization time vary when the Ml

309611.

Reduces amount and otherwise leaves all proportions of the other components unchanged.

Amount of MBZ
(Weight
to 100 parts
Elastomer) Optimal
Vulcanization time
(Minutes) Maximum value of the
Monsanto module 0.6
0.4
0.2 18 to 19
22nd
31 94
90
79

As you can see, the M BZ amount can be down to a quarter or a third of the amount of sulfur reduce the corresponding value.

Example 4

In this example one proceeds as in example 3, but uses a different one at the end of the chain fixing N-alkenyl compound.

A polyurethane-A is prepared as above, starting from

10 kg of a mixed polyadipate of ethylene glycol and propylene glycol with a molecular weight from 2730, 2.3.5 g AOP,

34 g of N-methyl-N-allylethanolamine, d. H. the connection the formula

CH ₂ = CH-CH ₂

CH ₃

N-CH ₂ -CH ₂ OH The polyurethane A produced according to the invention differs less advantageously than in the previous example from the analogous polyurethane which does not contain any N-alkenyl compounds. This is due to the fact that only a single alkenyl radical located on the nitrogen atom is used instead of two compounds containing as in Example 3, while test mixture B has two terminal unsaturated bonds.

Example 5

This example, like Examples 3 and 4, relates to the use of one at the end of the polyurethane chain seated N-alkenyl compound.

A polyurethane is prepared as above, starting from

10 kg of a mixed polyadipate of ethylene glycol and propylene glycol with a molecular weight of 2730,
293.5 g AOP,
29 g of diallylamine, ie the compound of the formula

1460 g MDI.

A polyurethane B is produced with the same polyester under identical conditions by in the above composition, the N-alkenyl compound was replaced by 51 g of DAP.

This is vulcanized beforehand with the same ingredients as in Examples 2 and 3 in FIG same composition combined polyurethanes. Vulcanize at 154 ° C and set found using the Monsanto rheometer that 90% of the maximum value of the shear modulus after 22 minutes For for polyurethane A as opposed to 28 minutes for polyurethane B.

The vulcanizates have the following properties:

Module (at 100% elongation),

kg / cm ²

ISO hardness

Hysteresis losses,%

at 20 ^D C

at «FC

Elongation at break%, at 20 ^° C

Breaking strength at 20 ⁰ C, kg / cm ² properties on the

Goodrich Flexometer

initial compression, % ..

Warming, ⁰ C

permanent deformation, % ...

22nd 24.5 68 74 34.7 35 26.6 28 697 660 421 414 15.9 13th 15.9 13th 33.5 29 10.9 3.9

N-H

CH ₂ = CH-CH ₂

CH ₂ = CH - CH ₂
147Og MDI.

After homogenization and 48 hours of heat treatment at 90 ° C., a polyurethane with a Mooney plasticity of 75.

An analogous polyurethane B is obtained. \ ve "n one in the above composition dai diallylamine replaced by 51 g of DAP.

The two polyurethanes are used in mixtures having the same composition as in Examples 2 to 4, and the mixtures are then cured at 154 ⁰ C. The Monsanto rheometer shows that the two mixtures have reached the same vulcanization state (90% of the final module) after 22 minutes for the mixture containing the polyurethane A and after 28 minutes for the mixture containing the polyurethane B.

The vulcanizates have the following properties:

Module (at 100% elongation),

kg / cm ²

ISO hardness

Hysteresis losses,%

at 20 ° C

at 60 ⁰ C

Elongation at break%, at 20 ^° C

Breaking strength at 20 ° C, kg / cm ²
Properties on the

Goodrich Flexometer
65

initial compression, % ..

Mention, ^C C

permanent deformation, %

22.8 24.5 69 74 30.8 35 23.8 28 677 66C ' 414 4J4 13.9 i3 27.5 29 2.8 3.9

The diallylamine is found to have the opposite effect the DAP significantly accelerates vulcanization without affecting the properties Suffer. Also here depends the duration of the vulcanization on the temperature: at 134 ° C it still only takes 45 minutes, compared to 20 minutes at 154 ° C. In the case of diallylamine, one can also use the Amount of MBZ used to a quarter or a third of the amount of sulfur used reduce the corresponding value without significantly increasing the vulcanization time or the Properties were markedly deteriorated. The following shows how the Monsanto module and change the optimal vulcanization time when the M BZ amount is reduced.

MBZ amount
(Parts by weight
to 100 parts
Elastomer) Oplimalc
Vulcanization time
(Minutes) Maximum value of the
Monsanto module 0.6
0.4
0.2 22 to 24
29
44 100
97
84

Λ B. C. Module (at 100%
Elongation), kg cm ² . .
ISO hardness 20.8
68 18.8
68 17.4
67 Hysicresisvcriuste. "1
at 20 ° C 33.9
25.5
713
391 32.5
27
767
424 36.1
30.2
833
427 at 6O ⁰ C Elongation at break%,
at 20 ^° C Breaking strength
at 20 ° C, kg / cm ² ...

'5 Vulcanizates A and B have roughly identical properties. On the other hand, vulcanizate C has less good properties. The properties of the vulcanizates can be improved by modifying the vulcanization system. The maximum shear modulus indicated by the Monsanto rheometer varies depending on the content of N-diallylbenzylamine using the system MBTS = 3.1, MBT = 1.9, MBZ = 0.6 and sulfur = 1.9 as follows:

N-diallylbenzylamine ..
Monsanto module ....

0.2 95

0.5 98.5

Example 6

In this example an N-alkenyl compound completely independent of the polyurethane is used.

Starting from an unsaturated polyurethane with a molecular weight of 80,000 and with im Average of a double bond to 4500 molecular weight units, which starting from a polyester, AOP, DAP, and MDI have been obtained, prepare the following blends (on a weight basis):

Polyurethane

Stearic acid

SAF soot

MBTS

MBT

MBZ

sulfur

N-diallylbenzylamine ..

A. B. 100 . 100 0.3 0.3 25th 25th 3.4 3.4 1.7 1.7 0.6 0.6 1.7 1.7 0 0.5

100
0.3 25
3.4 1.7 0.6 1.7 1.0

Mixture B contains about 2.1 n atoms Corresponding amount of N-alkenyl compound per polyurethane molecule.

These mixtures are vulcanized at 154 ° C. The curing times, after which 90% of the Reached the maximum value of the shear modulus, amount to 25 b ^ w. 14 or i2 minutes.

The vulcanizates have the following properties:

Example 7

This example describes two variations of Example 6, with others not in the polyurethane chain built-in N-alkenyl compounds can be used.

Starting from each of the bleached unsaturated polyester urethane with a molecular weight of 80,000 and an average of a double bond to 5000 molecular weight units are set with the Mixtures A, B, C, of Example 6, identical mixtures, with the exception that one on Instead of N-diallylbenzylamine, other N-alkenyl compounds are used in varying amounts.

The N-allyl-N-phenylbenzylamine was used in this way in proportions of 0.6 and 1.2% and the N-AHyI-N-methylbenzylamine in proportions of 0.4 and 0.8%

The table below gives the vulcanization time and the Monsanto modulus in the various Cases to:

A. B. 1.2% C. 0.8% test
sample N-AHyI-
N-phenyl-
benzylamine 12th N-AlIyI-
N-methyl-
bcnzylarain 11th 0.6% 90 0.4% 87 Vulcanization
length of time
(Minutes)
at 154 ° C .... 23 14th 13th Monsanto module 94 95 99

One puts a pronounced acceleration de vulcanization otuie to s'irke de deterioration Properties of the vulcanizates are determined if the amount of N-alkenyl compound used tx restricts

According to the German Auslegeschrift 1 155 590 can be used to form the chain ends of polyurethanes compounds of the type

Q-Y

use, in which Q is a trivalent radical, Z ₁ and Z _{2 are} alkenyl radicals and Y can be - NH ₂ (or - OH or - COOH).

The invention differs from this prior art in that

a) the German interpretation document the production of vulcanisable products that can only be vulcanized with peroxides Polyurethanes concerns,

b) at no point there from an acceleration of the vulcanization of polyurethanes in general, namely neither sulfur nor peroxide vulcanization is mentioned,

c from the German Auslegeschrift is) not apparent that if the Y R.est _-NH2 actual, fast vulcanising polyurethane obtained than when employing the -OH or -COOH. The fact is that in the method according to the German Auslegeschrift the vulcanization rate is the same for all three possible Y residues.

Regarding the convincing achieved with the invention As technical progress is made, reference is made to the examples in the description - in particular Examples 1 and 2 - which clearly show the differences in the vulcanization rate depending on whether you use N-Alkeny! compounds or do not show. Example 2 shows that mixture A takes twice as long as mixture D until 90% of the maximum value of the

ίο Shear module required.

It was also not to be expected that N-containing compounds would generally be catalytically active because of their basicity act regardless of whether the C = C group sits directly on N or is bound to N via - C -.

The question under discussion here is namely whether it was to be expected that N-alkenyl compounds can accelerate a certain type of sulfur vulcanization. The answer to this I. Question is that this effect of the N-alkenyl compound was completely surprising and new to the specialist. The basicity of the nitrogenous Compounds is not the crux of the matter because it is in contrast to the N-alkenyl compounds z. B. N-alkyl compounds sulfur vulcanization do not accelerate in any way, rather cause a deterioration in the properties of the vulcanizates. The only known effect of nitrogen-) compounds in the field of polyurethane chemistry is that tertiary amines the Reaktior catalyze hydroxylated compounds with isocyanate groups. However, this affects the manufacturing process Polyurethanes and has no relation to Vulkani-I sation of the polyurethanes, neither for peroxide] nor for sulfur vulcanization.

Claims (2)

Patent claims: 1. Process for accelerating the sulfur vulcanization of unsaturated polyurethanes. characterized in that the accelerator used is an N-alkenyl compound with one or more on one nitrogen atom sitting alkenyl radicals in such an amount that 2 to 4 nitrogen atoms per polyurethane molecule meet, a) the vulcanization or b) added to the reaction mixture for the polyurethane, with an N-alkenyl compound in case b) with one or two isocyanate-reactive groups is used. 2. The method according to claim 1, characterized in that an N-alkenyl compound with one or two alkenyl radicals and in particular AlIyI radicals CH, (H CH ₂ is used.