DE2130070C3 - Process for the photopolymerization of acrylic, methacrylic compounds or styrene in the presence of azo compounds - Google Patents

Description

R '

RN = NC- _(CH2) ^ X
R '

used, where
η = 1 or 2 and at
η = 2

R '
R = -C-CH ₂ -X

η
R.
R '

R '

Alkyl groups with 1 to 8 carbon atoms,

these two groups can also form a ring, and

-OH, -OCOR ", -NH ₂ or NH-CO · R" mean, where R "means an alkyl, cycloalkyl, aryl or aralkyl radical, and at

Aryl radical,

Alkyl groups with 1 to 8 carbon atoms,

these two groups can also form a ring, and

X = -COOR, -CN,

- C

NH

or

NH-R '

NH-R '

and light with a wavelength of 200 to 500 nm is irradiated with such an intensity that the polymerization takes place in a temperature range between room temperature and 100 ^° C.

2. The method according to claim 1, characterized in that 2,2'-azo-bis-isobutyl alcohol and 2,2'-azo-bis-isobutyl acetate or phenyl-azo-isobutyronitrile can be used as initiators.

3. The method according to claim 1 and 2, characterized in that acrylic and methacrylic compounds can only be polymerized until a partial conversion and the polymerization is then terminated will.

4. The method according to claim 1 and 2, characterized in that acrylic and methacrylic compounds polymerized into blocks from 30 to 300 mm thick.

It is known to take the polymerization of unsaturated compounds in the presence of photoinitiators exposure to light. As initiators of the type in question comes such. B. Oster and Nan-Loh-Yang in Chemical Review, Vol. 1968, pp.

125 - 151 have carried out a wide range of chemical compounds, such as organic carbonyl compounds, Peroxides, organic sulfur compounds, azo compounds, halogen-containing compounds, Metal carbonyls and inorganic oxides or salts and certain dyes in question. In the case of the The present invention forming processes are certain azo compounds as Photoinitiators used. Therefore, the relevant state of the art is discussed:

The best known, used in photopolymerization Azo compound is such. B. in GB-PS 6 22 374, claim 9, is indicated, 2,2'-azo-di-isobutyronitrile Other azo compounds, such as azomethane and diazomethane, are in GB-PS 6 04 902 for the same purpose described. In the journal of Polymer Science 24, (1957), p. 300 is about the use of Azoxystyrene and azoxybenzene have been reported as initiators in the polymerization of acrylonitrile. With the so far Azo compounds commonly used as photoinitiators are superimposed on "pure" photopolymerization and one radical polymerization, in which the radicals formed by the thermal decomposition of the initiators Trigger chain waxing. To control the course of the polymerization, i. H. an uncontrolled, The exothermic process of polymerization must prevent an explosive course of the reaction if necessary at comparatively low temperatures, d. H. under constant cooling and thus under acceptance a long implementation period.

From US-PS 33 06 888 azo compounds are known, which are only at high temperatures, for. B. in Decompose range of 150 and 300 '. These azo compounds become unsaturated to carry out bulk, solution, emulsion or suspension polymerization

Ή) ter compounds such as ethylene, isobutylene. Acrylic and Methacrylic compounds, vinyl and vinylidene compounds have been proposed. Because of the thermal stability the azo bodies mentioned must undergo polymerization at high temperatures, d. H. usually under Pressure, within the temperature range already mentioned for thermal decomposition from 150 to 300 °.

In the process according to FR-PS 15 86 468 are Azo compounds with groups capable of reacting with hydroxyl groups, undecomposed to polymers Compounds bound and in the presence of radically polymerizable monomers by UV light or heat decomposes, thereby forming polymers with a block or graft structure. the

Azo compounds used in h5 are thermally labile, see above that the light-induced polymerization as a result of the self-heating of the system in a thermal initiated polymerization passes through alone

Switching off the light source cannot be canceled.

According to DE-AS 1105 170 vinyl chloride is polymerized with UV light in the presence of azo compounds or other polymerization initiators at temperatures between -5 and 20 ^° C. At these low temperatures, the polymerization proceeds only at a slow rate.

The aim of the invention described below was to carry out a "pure" photopolymerization the monomers mentioned in claim 1 while avoiding an additional exposure thermally formed radicals taking place. The weaker requirement was that Polymerization in a temperature range between room temperature and 100 ° and thus with a perform technically usable speed. In view of this requirement was the use such initiators excluded the temperatures occurring during the exothermic polymerization disintegrate with formation of radicals.

Against the use of the described for example in US-PS 33 06 888, only at high temperatures decaying azo compounds spoke the expert prediction that the described, unusually thermostable azo compounds are also stable to the action of short-term light, d. H. do not form any radicals and thus are unable to initiate the polymerization. The applicant of the Therefore, for good reasons, the mentioned property right has to use high polymerization temperatures and with it the acceptance of the measure indispensable for almost all monomers, the polymerization to be carried out in pressure vessels is mandatory, but "pure" photopolymerization is not suggested.

It has now been found that the azo compounds characterized in more detail in claim 1, whose half-life at 100 ^c C is over 10 hours, are highly effective photoinitiators so that they can be used as initiators in a process for the photopolymerization of acrylic, methacrylic compounds or styrene according to the invention be used.

Of the azo bodies represented by a formula, there are 2,2'-azo-bis-isobutyl alcohol and 2,2'-azo-bis-isobutyl acetate or phenyl-azo-isobutyronitrile mentioned as compounds to be used particularly advantageously.

With the achievement of technically interesting polymerization rates, at reaction temperatures of e.g. 50 to 100 ° C, it succeeds Use of the azo compounds mentioned, the polymerization in strict dependence on the Let the intensity of the irradiated light run off. When controlling the light irradiation as a function on the temperature measured in the polymerizing mass, with and without additional Cooling, a polymer which is largely uniform in terms of homogeneity can be produced. the Distribution curve of such products showing the quantity ranges of polymer fractions of different molecular weights shows a uniformity that is important for the technical behavior of the end product of the polymers obtained.

In polymerisation technology, the process of b ^ "partial polymerisation" plays an important role. B. in the production of pigmented plastic compounds, a major role. A partial polymerization taking place under the action of thermally formed radicals requires z. B. in the production of acrylic, methacrylic compounds a significant cooling and stirring effort. When carrying out highly exothermic polymerizations, the expenditure just mentioned frequently limits the amount of the monomer to be polymerized in a reactor, that is to say only to be polymerized up to a certain conversion. The implementation of the method according to the invention is because the reactor is at least partly made of a translucent material, ie. consists primarily of glass, also limited in terms of the amount of material to be replicated, but it is possible to break off the ongoing polymerization in a simple manner, ie to let the reaction "fall asleep" by switching off the irradiated light.

The method according to the invention is also used with particular advantage in those cases in which which the monomers to be polymerized according to the invention are polymerized to give thick blocks should. The production of such, e.g. B. 200 mm thick blocks of polymethyl methacrylate, requires when using the polymerization technology customary to date, times of several weeks or even months, whereby, since the temperature in the polymerizing mass is difficult to keep under control. not see During the final phase of the polymerization, bubbles are formed in the hardened body. The inventive The method can be designed in a simple manner in such a way that the intensity of the irradiated Light controlled by a temperature measurement in the polymerizing mass and in this way a "runaway" of the polymerization is reliably prevented.

Although the azo compounds characterized in claim 1 for carrying out the mass, solution, Emulsion and suspension polymerization of the monomers mentioned can generally be used, deserves its use in grafting such monomers and making thicker ones Blocks special mention.

With regard to the high thermal stability of the azo compounds to be used according to the invention It must be described as surprising that it is by no means applying an energetic UV radiation needs to run the polymerization that rather normal daylight or a artificial radiation with a wavelength range of 200 to 500 nm corresponding to this mixed light The formation of the radicals that trigger the polymerization is sufficient.

The following examples illustrate the process according to the invention.

example 1

Polymerization was carried out a 3-molar Methylmethacrylatlösung in benzene with 0.5% of 2,2'-azo-bis-isobutyl acetate at 50 ^c C under the action of light. The time-sales curve is shown in the figure below. The reaction rate obtained at 50 ° C. is similar to that obtained in thermal polymerization with the same amount of ethyl 2,2'-azo-bis-isobutyrate. No polymerization is observed without exposure to light.

Example 2

Experiment 1 is repeated, but with the difference that instead of methyl methacrylate n-bulyl acrylate is polymerized. The gross polymer

The rate of operation was measured to be 2.9% min-'. The figure also shows the time-conversion course of this polymerization.

Example 3

When experiments 1 and 2 are repeated, but using styrene as the polymerizing monomer, the gross polymerization rate is 0.1% min- '. The time sales history is in the shown below.

Example eJ 4

Meihylmethacrylat is 2,2'-azo-bis-isovaleronitrile polymerized starting with exclusion of oxygen with 0.01% and 0.005% of 2,2'-azo-bis-isobutyl under pressure adiabatically of 55 ⁰ C. The temperature rises to about HO ⁰ C. At this temperature the 2,2'-azo-bis-valeronitrile has decomposed and the polymerization is stopped. The final polymerization of the methyl methacrylate can then be carried out after cooling the sample to room temperature by exposure to light, the temperature in the polymerizing mass, which increases due to the newly generated heat of polymerization, can be regulated by metering the radiation.

Example 5

Methyl is 2,2'-azo-bis-isobutyl acetate at 30 ⁰ C. bath temperature in a layer thickness of 12 polymerized under the action of light with 0.01% cm.

At a conversion rate of 3% - hour - ¹ , the stationary internal temperature is 35 ° C to about

a conversion of 30% is achieved, after which the internal temperature rises rapidly and is kept constant at 60 ° C-70 ° C by reducing the light energy. After reaching 80-90% conversion, the light energy is increased again and performed the final polymerization at internal temperatures of 100 ^0C. The resulting block is optically empty and does not show any bubble inclusions.

Example 6

A mixture of 3 parts by weight of methyl methacrylate and 7 parts by weight of acrylonitrile is irradiated in the presence of 0.2% phenyl-azo-isobutyronitrile with light from a mercury vapor lamp at 5O ⁰ C. The mixture is polymerized at an initial rate of 0.55% ■ mir.-. ¹ No polymerization takes place without exposure to light.

Example 7

Example 1 of the application is repeated with the difference that, instead of 2,2'-azo-bis-isobutyl acetate, phenyl-azo-1-cyclohexylnitrile c = 0.02 mol · 1 'is used. The gross polymerization rate here is 0.19% · min- ¹ .

Example 8

Example 1 of the application is repeated with the difference that instead of 2,2'-azo-isobutyl acetate in each case 0.02IHoI-I- ¹ 2,2'-azo-bis-isobutylamine or 2,2'-azo-bis- isobutyl-acetamide can be used. This results in polymerization rates of 0.11 and 0.09% min- ^1, respectively.

1 sheet of drawings

Claims (1)

Patent claims: 1. Process for the photopolymerization of acrylic, Methacrylic compounds or styrene in the presence of azo compounds as initiator, thereby characterized in that azo compounds of the general formula are used as initiators