WO1997038031A1

WO1997038031A1 - Continuous method for the production of thermoplastic moulding materials

Info

Publication number: WO1997038031A1
Application number: PCT/EP1997/001669
Authority: WO
Inventors: Hermann Gausepohl; Wolfgang Fischer; Wolfgang Loth
Original assignee: Basf Aktiengesellschaft
Priority date: 1996-04-11
Filing date: 1997-04-03
Publication date: 1997-10-16
Also published as: JPH11507984A; DE19614293A1; MX9710011A; TW339349B; EP0832141A1

Abstract

Described is a method for the production in two stages of, in particular, impact modified styrene and styrene-acrylonitrile polymer moulding materials in solution. In a first reaction zone in which at least the last section in the direction of flow consists of a reactor, in particular a tubular reactor without back-mixing, a styrene-butadiene block copolymer is produced by anionic polymerization, the active chain ends optionally being coupled and/or stripped off. Immediately afterwards, the copolymer is fed to a second reaction zone where a styrene homopolymer or copolymer is produced by radical polymerization or copolymerization, respectively.

Description

Continuous process for the production of thermoplastic molding compounds

description

The invention relates to an essentially two-stage process for the production of tough modified, thermoplastic molding compositions, in particular impact modified styrene homopolymers and copolymers in solution. In addition to impact-resistant polystyrene, the invention relates in particular to the production of styrene-acrylonitrile polymers. For the purposes of the invention, “styrene” is also to be understood below to mean its technical equivalents, vinyltoluene, tert-butylstyrene, p-methylstyrene, ethylstyrene or α-methylstyrene. Likewise, the term “butadiene” is also intended for isoprene, dimethylbutadiene, pentadiene -1.3 or hexadiene-1.3.

Impact-resistant polystyrene is usually produced thermally or with radical-forming initiators in a series of reactors (a so-called cascade). Polybutadiene in styrene and i.a. dissolved in a solvent such as ethylbenzene and the solution fed to a cascade from at least two reaction zones. Many process variants have been described and are also practiced technically; typical processes are described, for example, in US Pat. Nos. 2,727,884 or 3,903,202.

All processes carried out industrially in solution or in bulk have the disadvantage that the rubber - e.g. Polybutadiene - previously produced in-house {i.a. commercially available rubbers are used) and are initially in solid form. This rubber must be comminuted in a cumbersome manner, dissolved and the solution filtered before it can be used for the polymerization.

Attempts have therefore been made several times to find processes in which the rubber is produced in a process directly upstream of the polymerization and - in the solution in which it is obtained - is immediately further processed. So in the

GB-A-1 013 205 proposed a process in which the rubber is first polymerized in cyclohexane. This solvent is exchanged for styrene and then polymerized in the usual way. The disadvantage of this process is that an additional solvent is used which has to be removed before the subsequent radical polymerization. EP-A-334 715 therefore proposes a method which is to avoid this disadvantage. First of all, polybutadiene is produced in ethylbenzene, the common auxiliary solvent for styrofoamisation. After the active chains have been broken off, part of the solution is then diluted with preheated styrene and prepolymerized to a solids content of 30%. The polymerization is finally brought to an end in further reactors.

The disadvantage of this process is that it cannot be operated fully continuously, since the rubber solution to be prepared in a continuously operated Ruhr kettle always contains monomeric butadiene due to the wide range of residence times. Since butadiene would cause crosslinking of the entire polymer mass in the subsequent radical polymerization (even small amounts of free butadiene lead to so-called specks), it must either be removed in a separate step or the monomer feed must be interrupted after a certain time and polymerize the rubber solution to completion before starting radical polymerization of styrene in the rubber solution. Both preclude a fully continuous process.

The process according to EP-A-334 715 is also disadvantageous because, owing to the high viscosity of the dissolved polybutadiene, only dilute rubber solutions can be used, ie a large amount of solvent is required. This leads to high expenditure of energy and apparatus for the removal and cleaning of the solvent. If, as proposed, ethylbenzene is used as the solvent, its regulating action also leads to polymers with a molecular weight which is too low and thus to inferior products.

EP-A-059 231 describes a process in which a styrene-butadiene block copolymer is anionically pre-formed and the free-radical polymerization of styrene is carried out in the presence of this block copolymer. The styrene-butadiene copolymer is first polymerized up to a conversion of at most 30%. The excess butadiene is then distilled off, since the presence of butadiene, as in the aforementioned case, would bring about crosslinking in the radical polymerization. Again, the necessary removal of the butadiene practically does not allow the process to be carried out continuously.

It was therefore an object of the invention to find a continuous process for the radical polymerization or copolymerization of styrene, the rubber, the radical polymer merization upstream, manufactured by anionic polymerization and immediately processed further.

This is achieved according to the invention in that a styrene-butadiene block copolymer ("block rubber") is polymerized anionically in a reaction zone which at least in its - in the working direction - last section from a reactor with plug flow, i.e. consists of a tubular reactor, the reaction product from this zone - possibly after chain termination (quenching) or coupling - is mixed with styrene or, in the case of the production of copolymers - with styrene and the selected comonomer and the mixture in a known manner radically polymerized.

Immediate subject matter of the invention is a process for the production of the production of toughened styrene polymers, in particular toughened styrene homo- and styrene-acrylonitrile copolymers in solution in two stages, with a styrene-butadiene block copolymer in a first reaction zone by anionic copolymerization of butadiene and styrene is produced and fed directly to a second reaction zone in which the desired styrene homopolymer or copolymer is prepared by radical polymerization or copolymerization.

This process is designed according to the invention in such a way that a first reaction zone is provided which, at least in its - in the working direction - last section from a reactor with plug flow, i.e. a tubular reactor.

This ensures that the block rubber formed in the first reaction zone is practically free of butadiene monomer. In general, a residual content of less than 1000 ppm of butadiene is achieved, which is sufficient for the crosslinking to be avoided.

The process according to the invention is also expediently designed such that the target product obtained after the second reaction zone, i.e. an impact-modified styrene homo- or copolymer is fed to a degassing device operated under reduced pressure and the vapors obtained are condensed, preferably purified by distillation, dried and fed back to the first reaction zone.

If the target product is impact-resistant polystyrene, the vapors can be recycled without time-consuming separation of solvent and residual styrene if the monomer in the second zone is reacted to such an extent that the ratio of monomer to solvent in the Vapors are less than or equal to the monomer / solvent ratio in the approach for the production of the rubber. In this case, a simple distillation is sufficient to remove, for example, oligomeric components and stopping agents. The last traces of impurities are removed by cleaning the distillate with a drying agent such as aluminum oxide or molecular sieve.

If the target product is an impact resistant styrene copolymer, e.g. with acrylonitrile, the comonomer will first be separated off and the vapors will then be returned to the first reaction zone. This is usually easy to do because of the favorable spacing of the boiling points.

According to the preferred mode of operation of the invention, the

Conversion of styrene or styrene and selected comonomer in the last reaction zone is carried out to such an extent that no more styrene is recycled with the solvent than is used for the (anionic) production of a styrene-butadiene block copolymer. In practice, a conversion of styrene of about 90 to 95% must be achieved. Otherwise, it would have to be continuously thinned and the amount of solvent circulating continuously increased.

As a further feature of the method of operation preferred according to the invention, this means that the amount of solvent circulated in the process is kept essentially constant.

An advantage of the process is that it is possible to produce impact-modified polystyrene molding compositions continuously in solution in a single polymerization section with only monomeric feedstocks. Another advantage is the use of styrene-butadiene block rubber as an impact modifier, which results in a reduced proportion of butadiene polymer and thus high stability and resistance of the process product to e.g. Weather and light (yellowing).

In the following, the process is described on the basis of the production of impact-resistant polystyrene (see FIG. 1).

According to the invention, there is a reaction zone 1 (ie a reactor) which, for example, consists of a tube section, which is advantageously without a stirrer. To mix and produce sufficient wall contact of the reaction mixture, the pipe section is equipped, for example, with a static mixing element. For example, a suitably equipped simple pipe reactor or a tube bundle heat exchanger. Suitable static mixers are known and are described, for example, in Chem. Eng. Commun. , Vol 36 pp. 251-267 or Chem. Eng. Technol. 13 (1990), pp. 214-220. For example, the currently available mixers of type SMX or SMXL (Gebr. Sulzer, Wmterthur,

Switzerland), so-called Kenics mixers (Chemmeer Ltd. West Meadows, Great Britain) or SMR reactors (Sulzer) can be used.

Of course, a reaction vessel 1 or a tower reactor with a downstream tube zone can also be used as reaction zone 1, this also expediently also provided with a static mixing element, with conventional tower reactors already having properties which achieve an approximate plug flow. It is only essential that the reaction mixture is subjected to a plug flow under polymerization conditions before it leaves reaction zone 1 until the residual diene content, e.g. is below 1000, preferably below 500 and particularly preferably below 100 ppm. This is achieved by a tubular reactor with static mixers.

The reaction in zone 1 can be carried out isothermally, adiabatically or partially adiabatically.

The absolutely dry solvent and the required amount of stabilizer-free, dried monomer (styrene) and a suitable initiator solution (e.g. see-butyllithium) are metered in continuously in the desired ratio at the entrance to reaction zone 1. Pure butadiene is metered in downstream (lb). A styrene-butadiene block copolymer is obtained. The living chain ends are broken off with a protic solvent or coupled with a suitable coupling agent (lc). Since the monomers fed to the second reaction stage are polymerized by free radicals, they do not have to be cleaned particularly strictly; the stabilizers and traces of water present in the monomers which are fed to the second reaction stage are therefore often sufficient to terminate the living chain ends of the first reaction stage. Coupling can give three-block or star block copolymers with correspondingly favorable properties. The rubber solution obtained at the end of reaction zone 1 is fed to reaction zone 2, in which polymerization is carried out in a conventional manner by free radicals.

When the first reaction zone is operated isothermally, temperatures in the range from 50 to 150 ° C. or preferably from 70 to 120 ° C. are expediently selected. However, it is also possible to remove the heat of reaction only to such an extent that a final temperature is reached as is desired for the subsequent radical polymerization. In this case you get along the reaction zone a temperature profile starting at approximately room temperature and an exit temperature of up to 180 ° C, but preferably up to 130 ° C.

To produce block rubber, further monomers can be fed along reaction zone 1. Depending on the feed sequence, linear styrene-butadiene block copolymers of the type (S-B) n, S-B-S, B-S-B are obtained in this way, or the corresponding star block copolymers are also obtained by coupling with conventional coupling agents. For this purpose, reaction zone 1 is expediently divided into a number of segments in order to be able to freely select the temperature control in each segment.

Initiator can also be replenished downstream. This method is e.g. advantageous if you want to obtain rubbers with a broad or bimodal molecular weight distribution or if you want to influence the block lengths.

To terminate the living chain ends, these are either coupled, giving star polymers, or immediately treated with proton-active substances.

The concentration of the (finished) rubber solution can be varied within wide limits. However, it is limited by the viscosity of the solution and by economic factors. A final concentration of 5-60% by weight is preferred, but preferably 20 to 45% by weight.

The rubber solution prepared in reaction zone 1 is fed to a second reaction zone with the addition of monomers and, if appropriate, radical initiators and conventional auxiliaries. This second reaction zone generally consists of at least two stirrers, for example two stirrers or two stirred tower reactors, or combinations of these units. Such devices are e.g. in U.S. Patents 3,396,311 and 3,868,434 or DE-A-1,769,118 and 1,770,392.

The polymer solution finally obtained is freed of volatile constituents (residual monomers, solvents and possibly oligomers) in so-called degassing devices at temperatures of 190-320 ° C. For example, custom-built extruders or evaporators operated under reduced pressure (so-called flash evaporators) are customary. Description of the input materials

Suitable solvents for the production of the rubbers and the thermoplastic molding composition are aliphatic, cycloaliphatic, aromatic hydrocarbons with 4 to 12 carbon atoms or mixtures thereof. Suitable are e.g. Pentane, hexane, heptane, octane, cyclohexane, methylcylohexane, benzene, alkylbenzenes such as toluene, xylene or ethylbenzene. It is essential that these solvents are free of proton-active substances. They should therefore be distilled before use and dried over aluminum oxide or molecular sieve.

The anionic polymerization is usually used with mono-, bi- and multifunctional organometallic compounds. For reasons of price worthiness and manageability, organolithium compounds are primarily used. Ethyllithium, propyllithium, isopropyllithium, n- or see-butyllithium, t-butyllithium, phenyllithium, hexyldiphenyllithium, hexamethylenedilithium and butadienyllithium or isoprenyldilithium may be mentioned as examples. The dosage depends on the desired molecular weight, but is generally in the range of 0.002-5 mol%, based on the monomers. Suitable diene monomers for the production of the rubber are, in addition to butadiene, in principle all dienes which are used for the production of rubber and for themselves or together with vinylaromatic

Compounds are anionically polymerizable. Examples of dienes are butadiene, isoprene, dimethylbutadiene, 1,3-pentadiene or 1,3-hexadiene and styrene, vinyltoluene, t-butylstyrene, p-methylstyrene, ethylstyrene or α-methylstyrene for vinylaromatic compounds.

Linear or star block copolymers with a sharp or smeared transition of type (SB) _n , SBS, BSB or (SB) mX, (BS) _m X, (SBS) mX are used as block rubbers. (BOD) mX with n = 1-6 and m = 2-10, where X represents the remainder of a multifunctional coupling agent and S is a block of styrene or - generally speaking - a vinylaromatic monomer and B is a block of one Alkadiene means. The molecular weight of the blocks should be in the range from 1000 to 500,000 and preferably in the range from 20,000 to 300,000. Block lengths and sequence length distribution of block copolymers can be influenced in the usual way by selecting the ratio of initiator and monomer and, if appropriate, by dividing the addition of the initiator over several metering points along reaction zone 1. In the case of the block rubbers, the total styrene content is 3 to 85, preferably 10 to 60, and particularly preferably 10 to 45% by weight. The 1,2-vinyl content (short chain branches) of the Diene blocks, based on the total content of olefinic double bonds, should be less than 30%.

Preferred block copolymers are composed of styrene or α-methylstyrene and butadiene or isoprene. Both block S and block B can represent a statistical sequence of an alkadiene and a vinyl aromatic compound. Preferred block copolymers are made up of styrene or α-methylstyrene and butadiene or isoprene. The glass transition temperatures of the diene-containing segments of the rubber produced should be below -20 ° C, preferably below -40 ° C. The statistical structure is achieved by simultaneous addition of both monomers for block S and block B and addition of small amounts of Lewis bases such as dimethyl ether, tetrahydrofuran, diethylene glycol dimethyl ether, alkali metal salts of primary, secondary and tertiary alcohols or by tertiary amines such as pyridine, tributylamine. These connections are generally used in amounts of 0.1 - 5 vol.%. Alkolates such as potassium tetrahydrolinaloate are required in an amount of 3 to 10%, based on the initiator used. Multi-functional compounds such as aldehydes, ketones, esters, anhydrides or polyfunctional epoxides can be used to couple the rubbers.

Proton-active substances or Lewis acids such as e.g. Water, alcohols, aliphatic or aromatic carboxylic acids as well as inorganic acids, e.g. Carbonic acid or boric acid.

The glass transition temperatures of the diene-containing segments should be below -20, preferably below -40 ° C, i.e. these segments should have rubber-elastic properties.

In addition to styrene, α-methylstyrene, tert-butylstyrene, vinyltoluene, p-methylstyrene or diphenylethylene are also suitable as monomers for the production of the impact-resistant thermoplastic molding compositions. These can be copolymerized in a conventional manner with aliphatic vinyl compounds such as acrylonitrile, (meth) acrylates, maleic anhydride and / or maleimide.

Diacyl, dialkyl, diaryl peroxides, azo compounds, as well as peroxiesters, peroxidicarbonates and peroxiketals are suitable as initiators which act through radical decomposition. Dibenzoyl peroxide, 1, l-di-t-butylperoxy-3, 3, 5-trimethylcyclohexane, 1, 1-di-t-butyl-peroxycyclohexane, dicumyl peroxide and dilauryl peroxide are preferred. Molecular weight regulators such as, for example, dimeric α-methylstyrene, n- or t-dodecyl mercaptan, furthermore chain branching agents such as divinylbenzene, butanediol diacrylate, lubricants, stabilizers, mold release agents can be added as auxiliaries Polymer remain, otherwise must be removed.

Examples

The experiments on the examples described below were each carried out in the experimental setup outlined in FIG. 1. This essentially consisted of a tubular reaction zone 1 consisting of four pipe sections A, B, C and D connected in series, each with an inner diameter of 18.5 mm and a length of 2.5 m, corresponding to a free volume of 0.5 each 1), which were each equipped with a suitable SMX mixer from Sulzer. The series connection was chosen only for reasons of the random availability of the components; a single mixer with correspondingly arranged metering points can also be used.

The reaction zone 2 consisted of a stirred tank R with a volume of 5 l and two subsequent stirred tower reactors Ti and T _2, each with a content of 10 liters. All individual devices can be tempered.

Feedstocks:

The following were used to manufacture the rubber:

Freshly distilled, anhydrous styrene; distilled and alumina-dried ethylbenzene; Butadiene which had been pre-dried over molecular sieves; sec-butyllithium, 12% solution in n-hexane.

Distilled styrene, stabilized acrylonitrile and methyl methacrylate were used to produce the thermoplastic molding composition.

example 1

100 g of a 12% sec-butyllithium solution in n-hexane were mixed with 100 kg each of ethylbenzene. This solution was fed to tube section A of reaction zone 1 at a rate of 1 kg / h. In addition, the tube section A was fed 0.28 kg / h butadiene and the tube section C 0.07 kg / h styrene. The Temperatures in pipe sections A and B were 80 ° C and in pipe section C 94 ° C. The living chains were broken off by adding 15 g / h of water saturated with CO ₂ into the pipe section D. The monobutadiene content was 23 ppm, the solids content 5 26% by weight.

The rubber solution obtained was fed continuously to the Ruhrkessel R together with 2.72 kg / h of styrene and polymerized at 130 ° C. to a solids content of 23%, the phase inversion taking place, ie a coherent rubber solution resulting in a coherent polystyrene solution. The contents of the stirred tank R were fed continuously to the first reaction tower Ti and from there to the second reaction tower T ₂ . At a temperature increasing from 136 to 170 ° C., a solids content 5 of 73% was implemented, which corresponds to a styrene conversion of approx. 95%.

Example 2

Example 1 was repeated with the difference that 2 times the amount of sec-butyllithium was used and the living polymer solution in tube section D was coupled with an epoxidized linseed oil (Edenol 318 B from Henkel). This resulted in a mixture of star block copolymers with predominantly 3, 4 and 5 star branches. This solution was further polymerized as described in Example 1 with 5 2.72 kg / h styrene.

Example 3

Example 1 was repeated with the difference that 0.8 times the amount of butyllithium was used and no styrene was metered into reaction zone 1.

The butadiene content after the first reaction zone was 268 ppm.

5 Example 4

1 kg / h of a mixture of 120 g of 12% sec-butyllithium solution, 100 kg of ethylbenzene and 650 g of distilled and dried tetrahydrofuran was fed to tube section A. In the same way, the tube section A was fed 0.20 kg / h of styrene and 0.17 kg / h of butadiene. The temperature was set at 75 ° C. In the pipe section D, the living chain ends were broken off with 10 g / h of a solution of CO ₂ in water. The solution emerging from the tube section D with a solids content of

45 27% by weight was fed continuously to reaction zone 2 and polymerized with the addition of 3.0 kg / h of styrene. The solids content at the end of pipe section D was 27% and the monobutadiene content 124 ppm. The solids content after reaction zone 2 is approximately 75% by weight, ie the styrene conversion is approximately 97%. A transparent, tough polystyrene is obtained.

5 Example 5

1 kg / h of a mixture of 220 g of 12% sec-butyllithium solution with 100 kg of ethylbenzene were fed to pipe section A. Further inflows were divided up as follows: 0

Pipe section A 0.51 kg / h butadiene; Pipe section C 0.17 kg / h styrene; Pipe section D 25.0 g / h C0 ₂ saturated water.

5 The temperatures in mixers A and B were 75 ° C and in the pipe section C 85 ° C. The mixture discharged from pipe section D was transferred to reaction zone 2 and there in the stirred tank with feeds of 2.5 kg / h styrene, 0.85 kg / h acrylonitrile and 100 g / h of a 4.5% solution of tert. Butyl perbenzoate mixed in ethylbenzene 0.

Temperatures and solids contents in reactors in zone 2 were

5 Kessei: 125 ° C 29%

Tower 1: 138 ° C 45%

Tower 2: 152 ° C 75%

The polymer solution from tower 2 was continuously discharged and degassed in an extruder.

Example 6

1.0 kg / h of a mixture of 100 g of 12% sea-butyllithium solution 5 in n-hexane with 100 kg of ethylbenzene was fed to tube section A. Other inlets were divided up as follows:

Pipe section A 0.1 kg / h styrene;

Pipe section B 0.25 kg / h butadiene;

40 pipe section C 0.05 kg / h styrene;

Pipe section D 15.0 g / h C0 ₂ saturated water.

The butadiene content after the first reaction zone was 32 ppm. The temperatures in mixers A to C were 60 ° C, 85 ° C and 45 87 ° C. As in Example 1, the solution was further polymerized together with 2.72 kg / h of styrene. Example 7

The procedure for the production of a rubber-modified styrene-MMA copolymer was as follows: The rubber solution was prepared in reaction zone 1 as in Example 6, fed to the stirred tank of reaction zone 2 and there with 1.23 kg / h of styrene, 0 , 82 kg / h MMA and 100 g / h of a 0.5% solution of 1, l-di-t-butylperoxy-3,3,5-trimethylcyclohexane (TMCH) mixed in ethyl benzene. The temperature in the boiler was 122 ° C. In the downstream towers, the mass was polymerized at 142 ° C or 151 ° C. The solids content at the outlet from the last tower was 70%.

Claims

claims

1. Process for the production of tooth-modified, thermoplastic polystyrene molding compositions, in particular impact-modified styrene and styrene-acrylonitrile polymers in solution in two stages, a rubber being produced in a first reaction zone and being used directly in a second reaction zone , m the free radical styrene and optionally other monomers are polymerized or copolymerized in the presence of the rubber, characterized in that a first reaction zone is provided in which a styrene-butadiene copolymer is prepared anionically and which is at least in its - in the working direction - The last section consists of a non-jerk mixing reactor (reactor with plug flow).

2. The method according to claim 1, characterized in that the living chain ends of the rubber obtained in the first reaction zone are broken off and / or coupled in a manner known per se.

3. The method according to claim 1, characterized in that the rubber obtained in the first reaction zone is polymerized to a residual content of the reaction mixture of butadiene of less than 1000 ppm.

4. The method according to claim 1, characterized in that the reaction zone 1 as a non-jerk-mixing reactor has at least one pipe section with a static mixer or a Ruhr kettle with a downstream pipe section with a static mixer.

5. The method according to claim 1, characterized in that the styrene homo- or copolymer obtained from the second reaction zone is fed to a degassing device and the vapors obtained are condensed, distilled and dried and fed back to the first reaction zone, the conversion being chosen so that the ratio of monomer to solvent in the vapors is less than or equal to that

The monomer / solvent ratio in the batch for the production of the rubber is and the entire processed vapors can be fed back into the first reaction zone.

6. The method according to claim 1, characterized in that the

Polymerization in the first reaction stage is carried out adiabatically or quasi-adiabatically.

7. The method according to claim 1, characterized in that a styrene-butadiene block copolymer is herge¬ or used as rubber.

8. The method according to any one of claims 1-7, characterized in that styrene, styrene and in the second reaction zone

Acrylonitrile, styrene and methyl methacrylate, styrene and maleic anhydride or styrene and maleic acid-N-phenylimide can be used.

9. Use of the molding composition obtained according to any one of claims 1-8 for the production of moldings.