DE2118685C3 - Process for polymerizing unsaturated compounds in a thick layer - Google Patents

Description

It is known that in free radical polymerization the start is inhibited by the oxygen dissolved in the monomer, in such a way that the through the decay of an initiator or radicals created by the irradiation of short-wave light with the Oxygen react and the polymerization only takes place after the oxygen in the system has been consumed begins. This inhibition naturally has an effect with small radical concentrations as well as in systems with high oxygen concentration, e.g. B. when polymerizing thin layers with access to air, particularly annoying. - The skilled person is still the difficulty of polymer blocks of z. B. 10 to 20 cm thick in optically perfect quality

ίο make known. The polymerization of such Blocks of z. B. Polymethyl methacrylate requires polymerization times of a few weeks, with bubbles often not forming until the end of the polymerization create an unusable block.

Before describing the process of the present invention, reference should also be made to that of the polymer specialist common use of phosphines pointed out: For example, in the German patent application V 6712 IV b / 39c, announced on 11.

10. 56, a process for the polymerization of vinyl compounds described, after which one monomers (Meth) acrylic esters, acrylonitrile or certain other unsaturated compounds in the presence of tertiary Phosphines polymerized with exclusion of water

/ 5 rized. So this procedure is a polymerization proceeding according to the anionic ion chain mechanism. - According to the DE-AS 1 264 067 is the photopolymerization of acrylic esters carried out with the use of triphenylphosphine as a photoinitiator. - In “Pure and applied Chemistry ", 1967, Ind. Vol. 11-15, pp. 587 to 600, P. Weiss has the photoinduced polymerization of polymethacrylic acid methyl ester in the presence of triphenylphosphine and investigated found that the phosphine was converted into triphenylphosphine oxide transforms.

The presented prior art does not convey any teaching for the simple and safe production of thick Polymer blocks.

It has been found that ethylenically unsaturated compounds rapidly and completely in thick layers and can be polymerized with the formation of optically perfect structures if the polymerization is carried out as indicated in the claims.

Insofar as temperatures above the boiling point of the monomers are reached during the polymerization, it may be necessary to work under pressure. - Type and amount of free radical thermal initiator are chosen so that this is completely consumed when the desired partial conversion is achieved is. In the case of the combination of known individual measures according to the invention, it proceeds like the above Comparative experiments prove the polymerization in a surprisingly short time while avoiding the the production of thick-layer structures is known to have the risk of blistering. The initially surprising one The effect can of course be explained in retrospect: the one dissolved in the monomers and the start of polymerization Inhibitory oxygen is bound by the reducing phosphine. Under the influence the radicals set free from the added initiator sets in the polymerization, after consumption of the initiator to come to a standstill at the specified conversion in the range from 50 to 90%. During the temperature increase of the material to be polymerized which occurs in the first polymerization phase, the pho-

The initiator does not yet undergo thermal decomposition, but it does stimulate the polymerization in the second polymerization stage and leaves this to practically complete, avoiding harmful high temperatures Sales expire. The clear separation of the two in the process according to the invention Polymerization phases suggests the explanation that that which forms in a conventional polymerization polymeric monomer peroxide is prevented or decomposed by the phosphine from the formation. if If this effect were not to occur, the polymerization would inevitably take place at higher temperatures from Z. B. over 120 ° - under the action of the peroxide just mentioned - out of control so that the two polymerization stages merged into one another.

On the basis of the explanation given, the obvious conclusion that it is simply the addition of a reducing agent to the monomer need to harmless the polymerization-inhibiting oxygen to make does not lead to success. As is well known, shorten those familiar to the polymerisation expert Redox systems, consisting of z. B. a tertiary amine and a peroxide, the inhibition period not. Also the replacement of one phosphkin with another Reducing agents, e.g. B. by hydrazine or hydroxylamine, does not lead to the same effect as such substances with the formation of undesirable side reactions in the radical polymerization mechanism intervention.

Certain azo compounds are advantageously used as initiators, which deliver free radicals at temperatures below 100 ° C, l. B. Lzo-bis-isobutyric acid dinitrile, 2,2'-azo-bis-isobutyric acid ethyl ester, azovaleronitrile and azocyclohexanecarboxylic acid nitrile - alone or in mixtures with one another -.

The new process can also be carried out with peroxidic radical formers, but it is in In these cases, the tertiary phosphine is required first, expediently at the same time Stir, leaving the monomer to act with exclusion of air in order to remove the dissolved in the monomer To bind oxygen. Only after a long time, e.g. B. after 6 hours, the peroxidic initiator is added and carried out the partial polymerization of the first stage. The required for the second stage, A comparatively thermostable photoinitiator is added to the monomers or monomer mixture before the start added to the polymerization or at any time during the polymerization, if rapid and complete dissolution or distribution of the initiator in the polymerization Mixing is still possible.

The esters of 2,2'-azo-bis-isobutylaIkohols, z. B. its Acetic acid esters, furthermore benzoin, di-isopropyldixanthogenate and azoalkylamines have particularly proven themselves.

With the aid of the process according to the invention, although in principle all ethylenically unsaturated compounds can be polymerized, the new process has proven particularly useful in the polymerization of (meth) acrylic ester and (meth) acrylonitrile, which may be mixed with other monomers, e.g. B. methacrylic acid, vinyl acetate, styrene or can be polymerized with crosslinking comonomers, proven.

For the implementation of the new process, tertiary phosphines, e.g. B. triphenylphosphine, Tri-o-tolylphosphine, triisopropylphosphine and tributylphosphine be used.

Examples

A) Comparative experiments in which no use is made of the present invention.

1. Polymerization of methyl methacrylate with an initiator that is free below 100 ° C

to deliver radicals.

In a tube made of polyterephthalic acid glycol ester with a diameter of 16 cm and 30 cm in length, which was welded at the lower end, methyl methacrylate with 0.01 wt .-% azovaleronitrile was filled and then closed. The bag was placed in a pressure vessel filled with water, an initial pressure of 20 atmospheres prevailed in the pressurized nitrogen.

During the polymerization, the occurring temperature can be tracked. When the contents of the kettle were heated up, the temperature increased rapidly at 70 ° C Temperature of the polymerizing mono

meren observed, which rose to 185 ° C in the course of 2V _{2 hours.}
After the batch had cooled, the conversion was determined to be 90%. With the help of the viscosity number η sp / c (GV Schulz, Z. f. Elektro

chemie 1937, p. 479) the average molecular weight of the polymer obtained was determined to be 2 · 10 ⁶ .

2. Polymerization of methyl methacrylate with an initiator that is free above 100 °

Radical supplies.

In the manner described for Example 1, methyl methacrylate was obtained in one content polymerized by 0.01% by weight of 2,2'-azo-bis-isobutyl acetate. When reaching a tem

temperature of 90 ° C inside the polymerizing mixture, the temperature rose rapidly to 230 ° Can. The block obtained was soft and not free of bubbles. Sales grew too 80% determined; the polymer had a

average molecular weight of 10 ⁶ .

3. Polymerization of methyl methacrylate with a free radical that produces free radicals below 100 ° C Initiator in the presence of a phosphine.

so The experiment according to Example 1 was carried out with the

Modification repeats that the amount of initiator was doubled and the monomer Contained 0.2% by weight triphenylphosphine. After 2 hours, the temperature was inside of the polymerization bag to 140 ° C

gone up. The end product still contained 30% unreacted monomer. Of the Conversion of 70% did not increase any further even when the batch was subsequently irradiated with UV light.

4. Polymerization of methyl methacrylate with a mixture of 2 initiators, one of which one below 100 ° C and the other above 100 "C delivers free radicals.

As described in Example 1, Me

ethyl methacrylate, in which 0.01% by weight of azovaleronitrile and 0.05% by weight of 2,2'-azo-bisisobutyl acetate were dissolved, polymerized.

The polymerization, which began vigorously at 70 ° C., caused the temperature to rise to 210 ° C. _{in 2V 2 hours;} a conversion of 92% was achieved. The average molecular weight of the polymer was 10 *. Subsequent irradiation of the batch with UV light did not lead to any further increase in conversion.

B) Polymerization according to the present invention

5. In the manner described in Example 1 JViethyl methacrylate, in which 0.01 % By weight of 2,2'-azovaleronitrile, 0.05% by weight of 2,2'-azo-bis-isobutyl acetate and 0.1% by weight Triphenylphosphine were dissolved, heated under pressure. When a temperature is reached from 55 ° C, the temperature in the polymerizing material rose rapidly and reached after 1 hour and 50 minutes 125 ° C. A sample was taken from the bag and the conversion was determined in it. It was 70%, d. H. the mixture contained 30% monomeric methyl methacrylate.

After cooling the contents of the bag to room temperature, which reaches after about 5 hours was, the polymer was irradiated with UV light for 1 hour (commercially available 300 watt lamp, distance 50 cm). Included

the temperature rose to 145 '' Can. The conversion determined after the polymer had cooled was 99.5%. The average molecular weight of the polymer was determined to be 2.5 × 10 ⁶ . The block obtained was visually homogeneous and free of bubbles.

6. Methyl methacrylate, in which 0.01% by weight of 2,2'-azovaleronitrile, 0.05% by weight of benzoin and 0.1% by weight of tri-n-butylphosphine were dissolved, was based on the example above polymerized manner described. In the first polymerization stage, a maximum temperature of 110 ^° C. was measured in the polymerizing mixture. The conversion determined after the batch had cooled down was 60%. During the subsequent photopolymerization, the temperature rose to 160 ° C. and the conversion was 99%. The block obtained was free of bubbles and optically homogeneous.

7. The experiment was repeated 6 mh except that a 65% methyl methacrylate and 35 wt .-% of butyl acrylate monomer was subjected existing dei polymerization. In this case, too, a practically fully polymerized, optically perfect end product was obtained.

Claims (4)

Patent claims: 1. Process for polymerizing ethylenically unsaturated compounds in a thick layer below the action of initiators producing free radicals during thermal decomposition and of light in the presence of tertiary phosphines, characterized by the combination of the following known procedural measures: Encore a) a customary tertiary phosphine in amounts of 0.01 to 5 wt .-%, based on the used Monomers, b) a customary initiator which produces free radicals at temperatures below 100.degree in amounts of 0.001 to 0.5% by weight, based on on the monomers used, c) a customary one at temperatures up to 120 ° C thermostable photoinitiator in amounts of 0.001 to 0.2 wt .-%, based on the monomers used, to the monomers or monomer mixtures to be polymerized, the polymerization, optionally under pressure, in a first stage at a temperature of 70 to 150 ° C up to a conversion of 50 to 90% by weight, based on the weight of the monomers used, is carried out and the type and amount of the initiator which forms free radicals are chosen so that it is consumed when the desired conversion is reached, then the polymerizing mixture cooled after reaching the desired conversion and the polymerization then in a second stage under the action of short-wave light is brought to an end. 2. The method according to claim 1, characterized in that one at temperatures below 100 ° C free radical generating known azo compound is used. 3. The method according to claim 1, characterized in that the monomers to be polymerized first the tertiary phosphine and after a time of at least 1 hour one at temperatures Known peroxidic compound which decomposes below 100 ° C is added and the polymerization is carried out in the manner indicated, the thermostable photoinitiator to at any point in time before the start of the polymerization or at such a point in time Besann the polymerization is added to the rapid and complete dissolution or distribution in the mixture to be polymerized is still possible. 4. Process according to claims 1 to 3, characterized in that as a thermostable Photoinitiator 2,2'-azo-bis-isobutyl alcohol or its acetic acid ester is used.