CH686438A5 - Stabilising vinyl monomers against uncontrolled polymerisation - Google Patents

Abstract

Vinyl monomers (I) are stabilised against uncontrolled polymerisation during prodn., transport and storage by using, as polymerisation inhibitor, a fullerene, the reaction prod. of a fullerene with a dienophile, or a mixt. of fullerenes and/or reaction prods. of fullerenes with dienophiles, nucleophiles or halogens. Also claimed is a process for coating metal surfaces, by evaporating a 60-70C fullerene or fullerene prod. etc. as above (II) and depositing the vapour on a metal surface, esp. the inside of containers and tubes. Also claimed is a tank or tube system in which the inside, which is intended to come into contact with reactive materials, esp. (I), is coated with fullerene etc. as above.

Description

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description

The present invention relates to a polymerization inhibitor, a method for stabilizing vinyl monomers against uncontrolled polymerization during production, transportation and storage by adding a polymerization inhibitor. The invention further relates to measures for preventing the growth of polymers on surfaces, in particular those which come into contact with vinyl compounds. Finally, the invention also relates to a special method for coating surfaces.

Vinylic monomers are used worldwide for the production of polymers, preferably by radical polymerization, for a large number of applications. Examples include only thermoplastic materials, dispersions for paints and coatings, detergent additives and baby diapers.

Since vinyl monomers tend to spontaneously and uncontrolled polymerization, which can lead to an explosive reaction, safety precautions must be taken to avoid uncontrolled polymerization reactions during the production, storage and transport of vinyl monomers.

Not only explosive polymerization reactions are to be avoided, but also undesirable polymerization reactions, such as those involved in the purification of vinyl monomers, e.g. can occur by working up by distillation.

Finally, premature polymerization is also undesirable in systems which contain vinyl monomers; pressure plates are only mentioned here as examples.

The stabilization of vinyl monomers against the above-mentioned reactions and effects by adding so-called polymerization inhibitors is known per se; known polymerization inhibitors are kerobite and phenothiazine, to name just two examples. However, the stabilizing effect of the known polymerization inhibitors is not always sufficient.

The object of the present invention was to provide a process for stabilizing vinyl monomers by means of which vinyl monomers can be reliably protected against premature polymerization.

This object is achieved according to the invention with a polymerization inhibitor which is a fullerene C60-70. Contains reaction products of a fullerene C60-70 with a dienophile, or a mixture of fullerenes C60-70 and / or reaction products of fullerenes C60-70 with dienophiles, nucleophiles or halogens.

Another object of the invention is the use of one or more of the above-mentioned polymerization inhibitors for coating in particular metallic surfaces, and in a method for coating in particular metallic surfaces by vapor deposition of one or more of the above-mentioned polymerization inhibitors on the surface in question, such as these subjects are defined in the claims.

Finally, the subject of the invention is a vessel or tube arrangement as defined in the claims.

Fullerene C60-70 as such and processes for its production are known per se and e.g. by Krätschmer et al. in Nature, Vol. 347, p. 357 (1990) or by Huffmann and Krätschmer in WO 92/04279.

In principle, all compounds which have a vinyl double bond of the general formula in the molecule are to be mentioned as vinyl monomers

CH2 = CH-R

have, where R can be halogen or an organic radical.

Examples include only styrene, acrylic acid and methacrylic acid and their esters, vinyl esters of alkane carboxylic acids such as vinyl acetate, vinyl propionate etc., vinyl halides such as vinyl chloride and vinyl bromide, and vinyl acetic acid nitrile as the technically most important ones, which relate to polystyrene, polyvinyl acetate or polyvinyl chloride or general poly (metb) acrylates are implemented. In addition, N-vinylformamide and N-vinylpyrrolidone are technically widespread products.

According to the method according to the invention, the fullerene C60-70 or its reaction products with dienophiles, nucleophiles or halogens (hereinafter referred to as fullerene inhibitor) is added to the monomer to be stabilized before uncontrolled polymerization occurs. This can take place during the production of the monomer itself or immediately before storage or transport.

In addition to fullerenes themselves, mixtures of various fullerenes and / or reaction products of fullerenes with dienophiles, as are also used in Diels-Alder reactions, or reaction products with nucleophiles or halogens can be used.

Corresponding compounds are known per se to the person skilled in the art, maleic anhydride being only an example as dienophile, thiols and amines, e.g. Morpholine and 1,4-phenylenediamine and bromine or chlorine is mentioned as halogen, bromine being preferred.

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The reaction of fullerene with these compounds is generally carried out in a molar ratio of 1: 1 to 1:50, preferably 1: 1.5 to 1:10 and can be carried out in solution (for example in benzene) or in bulk. The temperatures used here are generally in the range from 20 ° C. to 200 ° C. and the reaction times in the range from 0.2 to 100 hours, preferably 2 to 30 hours.

In general, a sufficient stabilizing effect is achieved with additions of 0.1 to 5000 ppm, based on the vinyl monomer; the amount of addition required in individual cases depends, of course, on the monomers to be stabilized.

The fullerene inhibitor is preferably used in amounts of 2 to 200 ppm.

In the following examples, the stabilizing effect of various polymerization inhibitors was determined by the so-called isoperibolic calorimetry method, which is known in principle to the person skilled in the art.

The vinyl monomer of interest is placed in a calorimeter together with the other recipe components (initiators, solvents and possibly auxiliary substances) and the inhibitor (kerobite, phenothiazine or fullerene C60-70) and heated to a certain temperature.

As the initiator decays, the radicals formed attempt to start the polymerization.

When the polymerization begins, the heat of reaction released heats up the batch.

The amount and, if the amount used is known, the effectiveness of the polymerization inhibitors can be determined from the time between heating the batch and the start of the polymerization (= inhibition time).

According to the preferred method according to the invention, fullerene products are vapor-deposited on, in particular, metallic surfaces. If these are introduced into the corresponding plants, this represents a measure with which vinyl monomers in chemical plants and storage containers are reliably protected against premature polymerization.

Thermal evaporation of the fullerenes is particularly suitable for producing the layers according to the invention. The starting material, which is in solid form, is preferably introduced into an evaporator boat and applied to the metal surface to be coated in a pressure range between 10 ~ 6 bar and 10 mbar and a temperature range between 200 ° C. and 500 ° C. The thickness of the applied layer is in particular in the range between 1 nm and 100 μm It is possible according to the invention to subject the metal surface to a pretreatment in order to improve the adhesiveness of the applied layer The pretreatment can consist of a wet chemical treatment, a plasma treatment, a UV treatment, an ion bombardment treatment or a combination thereof Methods exist: The temperature of the substrate during treatment can be maintained between room temperature and 400 ° C.

example 1

Acrylic acid was mixed in an amount of 10 g with four times the amount of the inert solvent toluene, in which 2,2'-azobis-2,4-valeronitrile and the respective inhibitor were dissolved as radical formers, and transferred to a plastic calorimeter reaction vessel and the batch heated to 60 ° C.

The radical starter was activated by the temperature increase and formed radicals that started the acrylic acid polymerization.

This released heat of polymerization, which heated the reaction vessel.

The temperature change over time is plotted in FIG. 1 for a test without the addition of an inhibitor, a test with the addition of the inhibitor phenothiazine used hitherto and a test with the addition of C60-70 fullerene. The longer inhibition time shows the significantly higher effectiveness of the C6o fullerene at the same mass concentration. While one molecule of phenothiazine is able to trap 0.25 radicals, one molecule of C6o fullerene can trap 3.5 radicals.

Example 2

With the method described in Example 1, 1 part of 2-hydroxyethyl acrylate, mixed with 0.5 mol% (based on the monomer) of the radical generator 2,2'-azobis-2,4-valeronitrile, with 4 parts of a toluene solution of inhibitor to be examined and polymerized.

2 shows the measured temperature profiles with the common inhibitor phenothiazine and with C6o-7o fulllerene compared to a test without the addition of an inhibitor. While the addition of phenothiazine showed almost no inhibitory effect, C60-70 fullerene is very effective as an inhibitor: From the measured duration of inhibition, it can be calculated that one molecule of C60-70 captured about 5.3 radicals.

Example 3

The polymerization of five very reactive monomers was investigated in the presence of the inhibitors phenothiazine (PTZ, thiodiphenylamine, C12H9NS) and kerobite used to date, and in the presence of C60-70 using the method described in Example 1. The results of the investigation are summarized in the table (including the results of Examples 1 and 2).

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Table 1

Effectiveness of inhibitors with fast monomers

Inhibition time1)

Effectiveness2)

Monomer

PTZ

Kerobite

C60-70

PTZ

Kerobite

060-70

Acrylic acid3)

16

0

53

0.25

0

3.5

Hydroxyethyl acrylate3>

6

0

145

0.06

0

5.3

N-vinylformamide4)

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116

0.29

0.7

6.8

N-vinylpyrrolidone5)

0

0

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0

0

2.5

n-butyl acrylate6)

6

6

95

0.11

0.12

4.1

1) Time interval between heating the batch and the start of polymerization in s

2) Number of radicals trapped per inhibitor molecule used (radical yield factor of initiator decay f = 0.5)

3) 20% in toluene with 0.5 mol% V-65, 50 ppm inhibitor / monomer and 60 ° C

4) 25% in toluene with 0.2 mol% V-65, 50 ppm inhibitor / monomer and 60 ° C

5) 70% in toluene with 0.5 mol% V-65, 50 ppm inhibitor / monomer and 70 ° C

6) 50% in toluene with 1.0 mol% V-65, 50 ppm inhibitor / monomer and 60 ° C (V-65 = 2,2'-azobis-2,4-valeronitrile)

Table 1 shows that C60-70 is a more effective inhibitor for all monomers than the previously used inhibitors phenothiazine or kerobite BPD.

Example 4

The polymerization of acrylic acid in bulk was investigated in the presence of the inhibitor used hitherto and in the presence of fullerene C60-70 derivatives using the method described in Example 1.

Table 2

Efficacy of inhibitors in aclylic acid polymerization

Derivative of 1 mole fullerene C60-70 with

Inhibition time in s

Efficacy: radicals trapped per inhibitor molecule

2.5 moles of morpholine

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0.10

3-4 moles of 1,4-phenylenediamine

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0.10

8-10 moles of bromine

24th

0.10

for comparison: phenothiazine

14

0.02

As Table 2 shows, the fullerene derivatives are more effective inhibitors than the previously used phenothiazine in acrylic acid polymerization.

To demonstrate the inhibiting effect of the fullerene coating, in the next example the vinyl monomer of interest is introduced into the reaction vessel of the calorimeter together with the other formulation components (initiators, solvents, etc.) and the surface coated with the fullerene. A guide with multiple holes is inserted into the opening of the reaction vessel. A thermocouple is guided through the middle hole into the middle of the reaction mixture. A hose is led through a hole on the side to the bottom of the vessel, through which the reaction mixture is gassed with nitrogen to remove the oxygen. If sufficient nitrogen has been passed through the batch, the tube is pulled out of the batch and the gas space of the reaction vessel is gassed with protective gas.

For the polymerization, the prepared reaction vessel is immersed in the thermostat liquid so that the opening of the reaction vessel is above and the liquid level of the batch is below the liquid level of the thermostat liquid. Since the thermostat is preheated to the desired reaction temperature, the batch heats up, initiator decay begins, or at sufficiently high temperatures, the monomers themselves form radicals and the radicals formed attempt to start the polymerization.

When the polymerization begins, the heat of reaction released heats up the batch. The temperature rise is registered by the thermocouple in the reaction vessel. Since the surrounding thermostat temperature is kept constant, heat flows out of the vessel. The temperature difference increases

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long on, i.e. the temperature in the reaction vessel rises (possibly up to and above the boiling point of monomers and / or solvents), as the heat generated by the reaction is greater than the heat removal. If the heat production rate drops towards the end of the reaction, the temperature in the reaction vessel also drops.

The polymerization-preventing effect of the coated surface can be determined from the time period between heating of the batch and the start of the polymerization (= inhibition time).

Example 5

A stainless steel plate is placed in the reaction vessel of the isoperibolic calorimeter, the vessel is filled with monomers (acrylic acid or 2-hydroxyethyl acrylate) until the plate is covered with monomers and immersed in the thermostat. The thermostat is preheated to a temperature that causes thermal polymerization of the respective monomer (acrylic acid 120 ° C, 2-hydroxyethyl acrylate 140 ° C). It is determined how the start of polymerization is delayed when a stainless steel plate coated with fullerene C6o is introduced. For comparison, the time of the start of polymerization with uncoated stainless steel plate is plotted.

Table 3

Thermal polymerization delayed by a fullerene C6o coating

Monomer

Coating

Inhibition time / min.

Acrylic acid without

20th

with C6o no polymerization in 120 min.

Hydroxyethyl acrylate without

10th

with C60, 1 attempt

20th

with Cöo, 2nd attempt

20th

with C60, 3rd attempt

30th

Table 3 shows that the fullerene C6o coating either completely suppressed the thermal polymerization (acrylic acid) or started at least with a considerable delay (2-hydroxyethyl acrylate). A coating of product wetted parts in the column with fullerene C6o is therefore suitable to extend the average operating time of distillation columns for monomers.

Claims (8)

Claims 1. Polymerization inhibitor which contains a fullerene C60-70, reaction products of a fullerene C60-70 with a dienophile, or a mixture of fullerenes C60-70 and / or reaction products of fullerenes C60-70 with dienophiles, nucleophiles or halogens. 2. A method for stabilizing vinyl monomers against uncontrolled polymerization during production, transport and storage by adding one or more polymerization inhibitors according to claim 1. 3. Use of one or more polymerization inhibitors according to claim 1 to form a protective layer on a surface which, without this protective layer, would come into contact with vinyl compounds, in particular with reaction mixtures containing vinyl monomers. 4. Use according to claim 3 to form a protective layer on a metallic surface. 5. Use according to claim 3 or 4, characterized in that one or more polymerization inhibitors according to claim 1 is used as a protective layer on the inside of a polymerization reactor or its feed lines in the polymerization of vinyl monomers. 6. A method for coating metallic surfaces, characterized in that one or more polymerization inhibitors according to claim 1 evaporates and the steam generated is deposited on the metal surface to be coated. 7. The method according to claim 6, characterized in that the inside of the tubes and tubes are vaporized with the polymerization inhibitor or inhibitors. 8. Vessel or tube arrangement with an inside, which is provided for contact with reactive materials, in particular vinyl compounds, characterized in that this inside is completely or partially coated with one or more polymerization inhibitors according to claim 1. 5