FI95475B - Process for preparing a impact-resistant vinyl aromatic resin directly from butadiene - Google Patents

Abstract

Process for the manufacture of impact-resistant vinylaromatic resin by radical polymerisation in an inert solvent medium of a vinylaromatic monomer in the presence of a polybutadiene, characterised in that butadiene is polymerised anionically in a solvent which is inert towards butadiene and the vinylaromatic monomer and then, after destruction of the anionic catalyst, the radical polymerisation is initiated after addition of vinylaromatic monomer to the mixture.

Description

95475

The invention relates to a process for the preparation of an impact-resistant vinyl aromatic resin from a vinyl aromatic monomer by radical polymerization in the presence of an inert solvent in the presence of polybutadiene. Such a polymerization process is particularly suitable for the preparation of impact-resistant vinylaromatic resins such as impact-resistant styrene.

The mechanical strength of these styrene resins, the best known of which is probably impact-resistant polystyrene, i.e. Acrylonitrile Butadiene Styrene 15 (ABS), is based on the addition of polybutadiene to a polymerization mixture consisting of a polynomial monomer or a mixture thereof with another ethylene.

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The preformed polybutadiene is dissolved in the vinyl aromatic monomer by conventional methods, optionally in combination with a third solvent prior to polymerization. Polybutadiene is obtained, using various known methods, from butadiene by polymerization in an inert solvent environment in the presence of an anionic polymerization catalyst. Such a process using a lithium compound as a catalyst is described in U.S. Patent 3,317,918. In these processes, polybutadiene, after decomposition of the catalyst, is collected in as little viscous form as possible after removal of catalyst residues, solvent and unreacted monomer. Such a treatment involves a step during which a feature characteristic of polybutadiene, crosslinking, occurs, which causes problems in the production of impact-resistant styrene resin.

When it is desired to use polybutadiene in the preparation of impact-resistant vinyl aromatic resins, prior to polymerization as a pulp or mass / suspension, it is necessary to silence the vinyl aromatic monomer solution to obtain the desired final properties of the styrene polymer. The preparation of a solution of polybutadiene and vinyl aromatic monomer requires extensive equipment and it takes a considerable time to dissolve the elastomer 5 in the monomer. The crosslinked polybutadiene is poorly soluble, the resulting solution must be filtered beforehand before polymerizing the vinyl aromatic monomer to avoid clogging of the equipment.

10 In addition, butadiene, which has lost ethylene bonds during crosslinking, is not so easy to graft into vinylaromatic chains. Its compatibility with polyvinylaromatic monomers is impaired, which in turn reduces the mechanical properties of the final impact-resistant resin; visible signs of inferiority are e.g. fish eyes.

For these reasons, methods have been sought for the production of polybutadiene which would not require such cumbersome steps.

For example, in EP patent application 0 050 231, butadiene is partially anionically polymerized, in the presence of a vinyl aromatic monomer, with the lithium compound as a catalyst. The process yields a vinyl aromatic Buta-diene copolymer which, after being blended with a vinyl aromatic monomer, can be immediately polymerized. In this way, the preparation of polybutadiene and the impact-resistant polymer can be significantly simplified, since, on the one hand, the solvent removal step and the drying of the polybutadiene and, on the other hand, the comminution and dissolution of the polybutadiene in the vinyl aromatic monomer are not required. However, the method has two significant drawbacks. First, not pure polybutadiene 35 is formed but a vinyl aromatic butadiene copolymer. Second, there is a risk that when the anionic catalyst is contacted with the vinyl aromatic monomer, the reaction may fall out of control and reach the reactor flash limits.

40 il. - »UI Carbon lii #» 1 3 95475

As is apparent from said patent application EP-O 059 231, in order to prevent rapid uncontrolled polymerization of the vinyl aromatic monomer, it is essential to operate below 50 ° C and to partially polymerize the butadiene, in which case the unreacted butadiene still has to be removed at the end of the reaction.

In the present invention, these disadvantages are eliminated by the anionic polymerization of butadiene in a solvent inert to butadiene and a vinyl aromatic monomer of 20 to 50% by weight relative to the total amount of butadiene used in the reaction at 20 to 130 ° C in a polybutadiene anionic solvent. after destruction, the polymerization is continued after the addition of vinyl aromatic monomer and radical initiator at 90-170 ° C to the solvent solution. Ethylbenzene is a suitable solvent, although it is also possible to use toluene, benzene or cyclohexane.

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After the butadiene is polymerized and the catalyst is destroyed, the polymerization is carried out by adding a vinyl aromatic monomer to the mixture. No purification step or removal operation of a third substance, solvent or monomer is required, although unreacted butadiene may be removed, for example by vacuum distillation, if desired.

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In more detail, the preparation process polymerizes butadiene in a sufficient amount of an inert solvent so that the final polybutadiene is clearly liquid, using an anionic catalyst as the polymerization initiator, which should preferably be lithium-based. The amount of ethylbenzene used, as generally stated above, is usually 20 to 50% by weight of the total weight of butadiene. The polymerization temperature of butadiene can vary widely, cf. above, but preferably in the range of 55-130 ° C. In view of the sensitivity of the reaction, it is possible to control the polymerization temperature automatically by adding butadiene 40 to the mixture with a continuous feed. In this way, the polymerization can be carried out in the shortest possible time with the greatest possible energy savings.

The polymerization takes place in a reactor equipped with conventional heating, cooling, stirring and refluxing equipment.

The most preferred lithium catalysts are known. They are listed in particular in U.S. Patent 3,317,918, the most common of which is n-butyllithium (n-BuLi).

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Upon completion of the polymerization of butadiene, the inactivation of the catalyst is accomplished by the addition of a proton donor compound. Examples which may be mentioned are water, methanol, ethanol, propanol, acetic acid and propionic acid. The compound is added to the reaction mixture, optionally dissolved in an inert solvent, in amounts sufficient to eliminate the active sites.

The resulting polybutadiene solution in the solvent can be stored as is. However, after disposal of the catalyst, it is recommended to continue the production of the impact-resistant polymer by adding a vinylaromatic monomer and possible free radical generators to the polybutadiene mixture.

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The polybutadiene obtained using the process of the invention corresponds in every way to the butadiene prepared by the previous processes and generally has a molecular weight of 50,000 to 70,000.

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More specifically, in the process for preparing the impact-resistant polymer according to the invention, a vinyl aromatic monomer is introduced into a reactor in which the polybutadiene is dissolved in a solvent and the anionic catalyst is decomposed.

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It is preferred that the polybutadiene solution is not cooled. The radical polymerization can be initiated in a known manner, using conventional free radical initiators, such as peroxide, azo or azo and peroxide compounds.

40 The generation of free radicals can also be achieved by controlling the temperature of 5,95475. Preferably, the radical polymerization takes place at 110-170 ° C when heat is used as an initiator. During at least part of the initial polymerization step and at least until the phase change step, i.e. when 18-35% of the dry extract is formed in the reactor 5, it is recommended to stir the contents of the reactor. An apparatus suitable for such polymerization is described in U.S. Patent 3,243,481. Once the degree of polymerization of the monomer used is reached, the polymer is separated from the solvent and unpolymerized vinylaromatic monomer by heat treatment at 180-250 ° C to remove any volatile compounds in a vacuum evaporator vessel.

The vinyl aromatic monomer used in the process corresponds to the known formula: R.

c = ch2 V-- R3 wherein R1 is hydrogen or methyl, R2, R3 and R4 are selected from the group consisting of hydrogen and alkyl groups having up to 10 carbon atoms, with the proviso that the carbon of R2, R3 and R4 -: ·. The total number of 30 atoms does not exceed 10. The best known such vinyl aromatic monomers include styrene, vinyltoluene, alpha-methylstyrene, para-t-butylstyrene, 3,4-dimethylstyrene, 2-ethylhexylstyrene, n-decylstyrene and n-butylstyrene.

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By vinyl aromatic monomer is also meant mixtures in which, in addition to the vinyl aromatic monomer, there is at least one other polymerizable monomer containing an ethylene function. Of such monomers, vinyl-40 aromatic monomers are most often combined. acrylonitrile, methacrylonitrile, ethacrylonitrile and mixtures thereof, and methyl, ethyl, butyl and 2-ethylhexyl acrylates.

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It is entirely possible to add additives commonly used in conjunction with vinyl aromatic polymers at any stage of the vinyl aromatic monomer polymerization. Of these, mention may be made in particular of antioxidants or plasticizers, such as mineral oils.

The aim of the invention is to obtain, by a simplified method, products with a better degree of gelation and grafting.

Example 1 a) After a purge of nitrogen purification and several washes with n-BuLi solution, 600 g of molecular sieve using 600 g of molecular sieve and 3.5 ml of dried ethyl benzene (EA) and 3.5 ml of 1 .6 M n-BuLi as a solution in hexane. The polymerization is started by starting a continuous feed of butadiene.

The temperature in the reactor rises rapidly from 20 ° C to 80 ° C and is kept constant at 80 ° C by continuous feed of butadiene. After 1.5 hours, after 870 g of butadiene have been added, the polymerization is stopped by adding ethanol.

25 * A portion of the resulting polybutadiene is taken to determine the molecular weight and fine structure, the results of which are given in Table I below.

30 (b) To 213 g of the polybutadiene solution prepared in accordance with (a), 100 g of heated styrene and 36 g of mineral oil (type Primol) hydrogenated to more than 95% are added without cooling. When the mixture is homogeneous by stirring, a clear, viscous solution is obtained. The temperature of the stirred reaction mixture rises from 80 ° C to 110 ° C.

When the reactor has a dry extract of 30%, the reaction mixture is transferred to a vessel equipped with a viscous mass * | is homogenized and wherein the polymerization is obtained: au i an h uin 7 95475 completed by controlling the temperature as follows: 2.5 hours at 175 ° C and 0.5 hours at 240 ° C under vacuum.

c) 96 g of industrially produced and dried polybutadiene-5 (low cis), the molecular properties of which are shown in Table I, are comparable to those of Example 1 (a), are treated in the same way as in Example 1 (b). To make the conditions as uniform as possible, 55 g of ethylbenzene are added. Poly-10 butadiene dissolves very slowly in a mixture of styrene and ethylbenzene and a clear solution is obtained only after about 14 hours. Finally, the properties of the obtained impact-resistant polymer are not particularly good.

15 Example 2

Proceed as in Example 1 (b) and treat 640 g of high cis polybutadiene, the properties of which can be seen in Table I, prepared industrially and stored in its polymerization solvent: 85% by weight of toluene.

Dissolution is immediate; the results of the analysis of the impact-resistant polymer tested under the conditions of Example 1 (b) are shown in Table II.

(B) 96 g of the same polybutadiene after high - temperature drying in an industrial evaporator is treated in the same way as in 1 (c). Dissolution takes a long time, about 15 hours. The quality of the resulting impact-resistant polymer is poor.

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Table I

Molecular weights and fine structure of the various polybutadienes of the examples 5 Polybu- Mn Mw I cis trans vinyl tadien 1.4 (%) 1.4 (%) (%)

Example 198,000 446,000 2.3 51.0 39.0 9.0 la) 10 Example 182,000 434,000 2.4 50.7 39.1 10.2 le)

Example 103,000 368,000 3.6 94.0 4.0 2.0 2a)

Example 77,000 362,000 4.7 94.0 3.0 3.0 15 2b)

Mn = Molecular Weight Mw = Molecular Weight I = Polymolecularity Mw 20 Mn

The vinyl percentage corresponds to 1.2% of the vinyl isomer obtained by adding 1.2 butadiene monomer to the polybutadiene chain.

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Table II

Degree of gelation and grafting percentage of polystyrene obtained in the examples 30

Impact resistant Gelling degree Grafted; ·, knee brace _ (_% _) _ knee brace (% \

Example Ib) 0 11.6

Example le) 0.2 8.4 35 Example 2a) 0.03 9.6

Example 2b) 0.11 6.8 [mu] m i mi n i i n 9 95475

When determining the degree of gelation, the impact-resistant polystyrene is dissolved in toluene. The solution is precipitated with homopolymerized polystyrene and polystyrene grafted onto polybutadiene with methanol. The degree of gelation is obtained by filtering the product dissolved in toluene as a 5 to 10 micron filter and collecting the microgel as a suspension.

In the solvent extraction, a mixture of cyclohexane and acetone (20/80), the precipitated product is separated from the homopolymer polystyrene grafted onto polybutadiene.

Claims (2)

A process for the preparation of a vinylaromatic resin based on a radical polymerization of a vinylaromatic monomer and an inert solution, which can be converted into anhydrous polymer, 25 to 50% by weight of the compound in the case of total reactions in the reaction day, at a temperature of 20 to 130 ° C: in the case of polybutadiene solubilizers and after which the reaction on the anionic catalyst boils at the temperature of the temperature 90-170 ° C after the addition of 30 parts of vinylaromatic monomer and radical initiator. A process for preparing an impact-resistant vinyl aromatic resin from a vinyl aromatic monomer by radical lipolymerization in the presence of an inert solvent in the presence of polybu-5-thadiene, characterized in that butadiene is anionically polymerized in a solvent at 20-130 ° C to a polybutadiene-10 ene solvent solution, and after destroying the anionic catalyst, the polymerization is continued after adding vinyl aromatic monomer and radical initiator to the solvent solution at a temperature of 90-170 ° C. Process according to Claim 1, characterized in that the solvent is ethylbenzene. 2. A patent according to claim 1, which comprises the use of ethylbenzene. 35 si i sa i, anti l i i m i