WO2005118663A1 - Transparent mixtures of styrene-butadiene block copolymers and polystyrene - Google Patents

Abstract

The invention relates to a method for producing mixtures of block copolymers S1-B-S2 and styrene polymers, comprising the steps: a) production of a lithium-terminated block copolymer solution S1-B-Li by sequential anionic polymerisation, b) stabilisation of the solution from step a) by the addition of a magnesium or aluminium organyl, c) addition of vinyl aromatic monomers and an anionic polymerisation initiator, d) addition of a chain termination or chain coupling agent and isolation of the mixture. In the formula, S1 represents a block of vinyl aromatic monomers with a mean molecular weight Mn ranging between 8,000 and 40,000 g/mol, S2 represents a block of vinyl aromatic monomers with a mean molecular weight Mn ranging between 50,000 and 250,000 g/mol and B represents a block, optionally consisting of several sub-blocks, of dienes and/or dienes and vinyl aromatic monomers. The invention also relates to mixtures that are obtained according to said method.

Description

Transparent blends of styrene-butadiene block copolymers and polystyrene

description

The invention relates to a process for the preparation of mixtures of block copolymers S BS ₂ and styrene polymers, comprising the steps:

a) preparing a lithium-terminated block copolymer solution S B-Li by sequential anionic polymerization, b) stabilizing the solution from stage a) by adding a magnesium or aluminum organyl, c) adding vinylaromatic monomers and an anionic polymerization initiator, d) adding a chain terminator - or coupling agent and isolation of the mixture, wherein Si for a block of vinyl aromatic monomers and a number average molecular weight M _n in the range from 8,000-40,000 g / mol, S ₂ for a block of vinyl aromatic monomers and a number average molecular weight M _n in the range from 50,000 to 250,000 g / mol and B stands for a block of dienes and / or dienes and vinylaromatic monomers, optionally composed of several subblocks, mixtures obtainable by this process.

Blend from styrene polymers with styrene-butadiene block copolymers are usually produced by melting and mixing the starting polymers in extruders in order to adapt the mechanical or processing-relevant properties to the requirements of the respective application.

EP-A 0710681 describes a process in which a blend of a styrene-butadiene block copolymer with polystyrene is described by double initiation and simultaneous polymerization of the second stryol block and the polystyrene. However, the molecular weights of the mixtures are very low.

The production of impact-resistant polystyrene by anionic polymerization of styrene in the presence of styrene-butadiene block copolymers is known, for example, from US Pat. No. 6,506,846, DE-A 10206 213 and the unpublished DE-A 102 502 80. These processes occur during the Polymerization to a phase inversion and the styrene-butadiene block copolymers are in the form of rubber inclusions in a polystyrene matrix. As a rule, these products are not transparent.

The object of the present invention was to design styrene polymer mixtures with high rigidity, toughness and high transparency as well as an inexpensive process to make their production available. The mixtures should also have a low turbidity.

Accordingly, the process described above and the mixtures obtainable thereafter have been found.

It is essential for the process according to the invention that the styrene-butadiene block copolymer S BS _{2 formed} and the styrene polymer are sufficiently compatible so that no phase separation occurs.

The proportion of diene is preferably less than 50% by weight, preferably in the range from 15 to 35% by weight, particularly preferably in the range from 18 to 30% by weight, based on the block copolymer S BS ₂ . It is determined by the diene content of the block copolymer solution SrB-Li formed in step a) and the amount of the vinyl aromatic monomer added in step c) and the molar ratio of anionic polymerization initiator in step c) and SrB-Li.

The molecular weights of the blocks of the block copolymer S BS ₂ and the styrene polymer can be controlled by the amount of the polymerization initiators used and the particular amount of the monomers added.

The block S _{1 is formed} in step a) by sequential anionic polymerization, the molar ratio of vinylaromatic monomers and lithium organyl as the anionic polymerization initiator being selected such that the block Si has a number-average molecular weight M _n in the range from 8,000 to 40,000 g / mol, preferably in the range from 10,000 to 30,000 g / mol.

Block B is formed on block Si in the same stage a) by sequential addition of dienes and / or vinylaromatic monomers, optionally in the presence of randomizers such as tetrahydrofuran or potassium salts. Block B generally has a number average molecular weight M _n in the range from 20,000 to 200,000 g / mol, preferably in the range from 50,000 to 150,000 g / mol. Block B can be constructed from diene blocks or copolymer blocks B / S from dienes and vinylaromatic monomers. The copolymer blocks B / S can have a statistical structure or have a gradient. Block B can also be composed of several sub-blocks B of dienes, sub-blocks S of vinyl aromatic monomers or sub blocks B / S of dienes and vinyl aromatic monomers. A block B which is composed of 2 to 0, preferably 3 to 5, copolymer blocks B / S is particularly preferred. The glass transition temperature Tg is preferably in the range from -90 to + 10 ° C., preferably in the range from -60 to -10 ° C. The presence of randomizers favors the statistical distribution of the diene units and vinyl aromatic units in the soft blocks. Suitable randomizers are donor solvents, such as ethers, for example tetrahydrofuran, or tertiary amines, or soluble potassium salts.

For an ideal statistical distribution of the monomer units, in the case of tetrahydrofuran, amounts of generally more than 0.25 percent by volume, based on the solvent, are used as randomizers. At low concentrations, "tapered" blocks are obtained with a gradient in the composition of the comonomers. At the higher amounts of tetrahydrofuran given, the relative proportion of the 1,2-linkages of the diene units simultaneously increases to about 30 to 35%.

By contrast, when using potassium salts as a randomizer, the 1,2-vinyl content in the soft blocks increases only insignificantly. The block copolymers obtained are therefore less susceptible to crosslinking and have a lower glass transition temperature with the same butadiene content.

The potassium salt is generally used in molar deficiency with respect to the anionic polymerization initiator. A molar ratio of anionic polymerization initiator to potassium salt is preferably selected in the range from 10: 1 to 100: 1, particularly preferably in the range from 30: 1 to 70: 1. The potassium salt used should generally be soluble in the reaction medium. Suitable potassium salts are, for example, potassium alcoholates, in particular a potassium alcoholate of a tertiary alcohol with at least 5 carbon atoms. Potassium 2,2-dimethyl-1-propanolate, potassium 2-methyl-2-butanolate (potassium tert-amylate, KTA), potassium 2,3-dimethyl-3-pentanolate, potassium 2- methyl hexanolate, potassium 3,7-dimethyl 3-octanolate (potassium tetrahydrolinalolate) or potassium 3-ethyl 3-pentanolate. The potassium alcoholates are accessible, for example, by reacting elemental potassium, potassium / sodium alloy or potassium alkylates and the corresponding alcohols in an inert solvent.

Block S ₂ and the styrene polymer are formed simultaneously in step c). Their molecular weight and quantitative ratio result from the amount of vinyl aromatic monomers and the molar ratio of anionic polymerization initiator to SrB-Li. The number average molecular weight M _{n of} the block S ₂ is in the range from 50,000 to 250,000 g / mol, preferably in the range from 100,000 to 200,000. The styrene polymer preferably has a molecular weight M _n in the range from 15,000 to 250,000 g / mol, particularly preferably in the range from 40,000 to 150,000 g / mol.

The mixture preferably contains 20 to 90% by weight, particularly preferably 30 to

60% by weight of the block copolymer S BS ₂ and 10 to 80% by weight, preferably 40 to 70% by weight of the styrene polymer. As a result of chain termination, chain transfers or reinitiations, it is possible that the mixture still contains proportions of block copolymers of the structure S _r B in amounts of 0 to 20% by weight. The proportion of SB can be controlled by adding demolition agents after stage a).

The mixture particularly preferably contains 30 to 50% by weight of the block copolymer, SrB-S _2l 40 to 60% by weight of styrene polymer and 5 to 15% by weight of block copolymer S B.

Stages a) and b) are preferably carried out batchwise in a stirred tank K1 and steps c) and d) continuously in a reactor cascade comprising a stirred tank K2 and a tubular reactor R.

Here, the block copolymer solution S B-Li obtained from stages a) and b) can be fed continuously via a buffer tank P into a reactor cascade consisting of a stirred tank K2 for carrying out stage c) and a tubular reactor R.

By backmixing in the continuous stage in the stirred tank K2, the molecular weight distribution of the styrene polymer and of the block S2 can be broadened. The molecular weight distribution M _w / M _n is preferably less than _1.5 for the block Si and more than 1.5 for the block S ₂ , preferably in the range from 1.8 to 2.5.

Step c) and the polymerization of the block S ₂ and the styrene polymer can be carried out in a continuously flowing reactor cascade comprising at least one remixing reactor and at least one downstream non-backmixing reactor. The continuous procedure enables a solids content of more than 50% by weight at the end of the non-backmixing reactor and thus a particularly economical process.

Continuously flowed stirred tanks (CSTR) are suitable as backmixing reactors. They ensure a sufficiently rapid mixing of the feeds with the polymerization mixture and an effective removal of the heat of reaction by evaporative cooling. The vapors formed in this way usually run back into the reactor. Some of the solvent-containing condensate can also be removed using the heat of reaction.

Tube reactors or tube bundle reactors with or without internals are particularly suitable as non-backmixing reactors (PFR). Internals can be static or movable internals. Ring disc or tower reactors can also be used. The process is preferably carried out in a reactor cascade which consists of a stirred tank and a downstream tubular reactor R. The process is preferably carried out in a reactor cascade consisting of a stirred tank K1, a buffer tank P, a stirred tank K2 and a downstream tubular reactor R.

FIG. 1 shows such a reactor cascade, which consists of a stirred tank K1, a buffer tank P, a stirred tank K2 with a boiling cooler and a downstream tubular reactor R. The monomers and an initiator solution via the inlet Z3 can be metered into the stirred tank K1 via the inlet Z1 and Z2. Via inlet Z4, aluminum organyl is mixed in via a mixer 1a in the feed line. The discharge from the stirred tank is carried out by means of a gear pump. Additional styrene and initiator are metered into the stirred tank K2 via the feed Z5 and Z6. A mixer 1b is connected downstream of the tubular reactor, via which chain terminating agent and stabilizer can be mixed in via feed Z7. The polymer solution is then freed from the solvent by flash degassing in a degassing pot (E).

The aluminum organyl with the initiator mixture is preferably aged in a stirred kettle at temperatures in the range from 40 to 100 ° C. and 15 to 250 minutes and then, if necessary after cooling to room temperature, added via feed Z4 and mixer 1a.

After exiting the reactor cascade, the polymer solution can be passed through a degasser E at temperatures in the range from 200 to 280 ° C.

Styrene and styrene derivatives, in particular styrene and α-methylstyrene or mixtures of different styrene derivatives, can be used as vinyl aromatic monomers.

Suitable dienes are 1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, 2,3-dimethyl-butadiene, isoprene, piperylene or mixtures thereof. 1,3-butadiene is preferably used.

The process according to the invention can be carried out in inert solvents, for example aliphatic, cycloaliphatic or aromatic hydrocarbons or mixtures thereof. Preferred hydrocarbons are those with 3 to 12 carbon atoms. Preferred solvents are toluene, ethylbenzene, cyclohexane or methylcyclohexane.

The customary mono-, bi- or multifunctional alkali metal alkyls, aryls or aralkyls can be used as anionic polymerization initiators. Organolithium compounds are preferred, such as ethyl, propyl, isopropyl, N-butyl, sec-butyl, tert-butyl, phenyl, diphenylhexyl, hexamethyldi, butadienyl, isoprenyl or polystyryllithium and 1,4 -Dilithiumbutan, 1, 4-Dilithium-buten-2 or 1, 4-Dilithium-benzene used. The required amount depends on the desired molecular Weight. As a rule, it is in the range from 0.001 to 5 mol%, based on the total amount of monomer.

Mixtures of aluminum organyl with an alkali metal anhydride, such as lithium hydride, sodium hydride or potassium hydride, as described, for example, in DE-A 102 18 161, are also suitable.

In alkylaromatic solvents, sub-stoichiometric amounts may also be sufficient in view of a particular molecular weight to be achieved due to transfer reactions to the solvent. Depending on the polymerization temperature, the savings can be up to 50%, based on the stoichiometric amount.

Aluminum organyls which can be used are those of the formula R ₃ AI, where the radicals R independently of one another are hydrogen, halogen, CC ₂₀ alkyl or C ₆ -C ₂₀ aryl. Preferred aluminum organyls are the aluminum trialkyls such as triethyl aluminum, tri-iso-butyl aluminum, tri-n-butyl aluminum, triisopropyl aluminum, tri-n-hexyl aluminum. Triisobutyl aluminum is particularly preferably used. Aluminum organyls which can be used are those which are formed by partial or complete hydrolysis, alcoholysis, aminolysis or oxidation of alkyl or arylaluminum compounds or the alcoholate, thiolate, amide, imide or phosphide groups wear. Examples are diethyl aluminum - (N, N-dibutyIamide), diethyl aluminum ethoxide, diisobutyl aluminum ethoxide, diisobutyl (2,6-di-tert-butyl-4-methylphenoxy) aluminum (CAS No. 56252- 56-3), methylaluminoxane, isobutylated methylaluminoxane, isobutylaluminoxane, tetraisobutyldialuminoxane or bis (diisobutyl) aluminum oxide.

The aluminum organyl compound can be used in step b) in amounts which are sufficient to stabilize the living polymer chains without leading to severe retardation of the polymerization in step c) and to the addition of further retarding metal organyls, such as magnesium or zinc -Organle completely to do without. The aluminum organyl compound and the anionic initiator I are preferably used in amounts so that the molar Al / I ratio in the range from 0.001 to 0.95 is particularly preferably in the range from 0.45 to 0.90 after step c).

After the end of the polymerization, the living polymer chains can be closed with a chain terminator. Suitable chain terminators are proton-active substances or Lewis acids, such as water, alcohols, aliphatic or aromatic carboxylic acids, and inorganic acids such as carbonic acid or boric acid. Conventional additives and processing aids can also be added to the polymer mixture in an amount of 0 to 30% by weight, based on the total weight of the molding compositions. The additives or processing aids should not impair transparency. Such additives and processing agents are, for example, lubricants and mold release agents, colorants such as dyes, flame retardants, antioxidants, light stabilizers and antistatic agents, in the amounts customary for these agents.

The polymer mixtures obtained by the process according to the invention have a morphology with polystyrene domains below 0.4 μm and very little light scattering. In addition to high rigidity (modulus of elasticity) and toughness (elongation at break), they therefore also show high transparency and low haze.

Examples:

Block copolymer solution S B-Li

The preparation of the block copolymer solution (stage a) was placed in a 1500 l stirred tank K1 styrene S1 and solvent and the polymerization of the block Si was initiated at 35 ° C. with sec-butyllithium (12% solution in cyclohexane). After complete conversion, block B is polymerized by repeated metering in of styrene (feed rate 218 kg / h) and butadiene (156 kg / h). After each addition, the batch was cooled to 50 to 60 ° C. The amounts and molecular weights used are shown in Table 1. The solution was then cooled to 80 ° C. and stabilized with triethyl aluminum (20% solution in toluene) (stage b) and stored in a buffer tank P. The solids content was around 30% by weight and the residual butadiene content was below 10 ppm.

Initiator solution (TEA / NaH) for stage (c):

895 g of toluene, 932 g of styrene and 25.34 g of a 60% sodium hydride dispersion (NaH) in white oil (from Chemmetall) were combined at 25 ° C. and with 362 g of a 20% solution of triethyl aluminum (TEA) in Toluene added. The initiator solution obtained was heated to 50 ° C. for 3 hours and then cooled.

Preparation of the Mixtures S BS ₂ / Polystyrene (PS) (Stage c)

Stage c) was carried out continuously in a reactor cascade consisting of a double-walled 50 l stirred tank K2 with a standard anchor stirrer and a subsequent tube reactor R (length 7 m, diameter 500 mm). For this purpose, 5.53 kg / h of styrene, 9.3 kg / h of the block copolymer solution S B-Li and 370 g / h of the initiator were continuously added to the stirred kettle (fill level 50%, stirrer speed 115 rpm, outside temperature 130 ° C.). TEA / NaH solution added. The polymer solution was further conveyed in a tubular reactor (length 7 m, diameter 500 mm with three heating tubes of the same length (external temp. 130/150/180 ° C.) The amounts and process parameters used are shown in Table 2.

The discharge from the tubular reactor was used for chain termination (stage d) and stabilization with 15 g / h Irganox® 1010 (Ciba-Geigy), 20 g / h Sumilizer® GS (Sumitomo) 13 g / h white oil, 400 g / h ethylhexanoic acid and 130 g / h of ethylbenzene were added via a mixer and the melt was expanded via a partial evaporator and a vacuum pot operated at 10 mbar and discharged via a screw. The removed solvent was used again in stage a) after distillation.

After a short start-up time, a constant solids content of about 48% by weight is established at the outlet of the stirred tank. The turnover at the end of the tube reactor was complete. The styrene content was less than 5 ppm and the ethylbenzene content was less than 200 ppm. The mechanical properties are summarized in Table 3.

Test Methods:

The test specimens for the mechanical tests were injection molded at a melt temperature of 220 ° C and a mold temperature of 45 ° C. The modulus of elasticity, yield stress, breaking stress, elongation at break and elongation at break were determined in a tensile test according to ISO 527 with tensile bars according to ISO 3167.

The molecular weights were determined by means of gel permeation chromatography (GPC) on polystyrene gel columns of the Mixed B type from Polymer Labs, using monodisperse polystyrene standards at room temperature and tetrahydrofuran as the eluent. The high molecular weight polystyrene content was determined by precipitating the solder at the minimum of the molar mass distribution after calibration and integration of the partial areas.

Yellowness index Yl: determined as yellowness index Yl by determining the color coordinates X, Y, Z according to DIN 5033 with standard light D 65 and 10 ° normal observer. Table 1: Preparation and properties of the block copolymer solution S B-Li

Table 2: Preparation of the mixtures S BS ₂ / PS (stage c)

Table 3: Properties of the mixtures S-B-Li / PS

Table 3 (continued)

Claims

claims

1. A process for the preparation of mixtures of block copolymers SrB-S ₂ and styrene polymers, comprising the steps a) preparing a lithium-terminated block copolymer solution S B-Li by sequential anionic polymerization, b) stabilizing the solution from step a) by adding a magnesium or aluminum organyl , c) addition of vinyl aromatic monomers and an anionic polymerization initiator, d) addition of a chain terminating or coupling agent and isolation of the mixture, wherein Si for a block of vinyl aromatic monomers and a number average molecular weight M _n in the range from 8,000-40,000 g / mol, S _{2 stands} for a block of vinyl aromatic monomers and a number-average molecular weight M _n in the range from 50,000 to 250,000 g / mol and B stands for a block of dienes and / or dienes and vinyl aromatic monomers which may be composed of several subblocks.

2. The method according to claim 1, characterized in that the proportion of diene, based on the block copolymer S BS _{2 is} less than 50 wt .-%.

3. The method according to claim 1 or 2, characterized in that the block B has a number average molecular weight M _π in the range from 20,000 to 200,000 g / mol.

4. The method according to any one of claims 1 to 3, characterized in that the block B is composed of one or more copolymer blocks B / S.

5. The method according to any one of claims 1 to 4, characterized in that the styrene polymer is polystyrene with a molecular weight M _n in the range from 15,000 to 250,000 g / mol.

6. The method according to any one of claims 1 to 5, characterized in that steps a) and b) are carried out batchwise in a stirred tank K1 and steps c) and d) continuously in a reactor cascade comprising a stirred tank K2 and a tubular reactor R. become.

7. The method according to claim 6, characterized in that the block copolymer solution obtained from steps a) and b) via a buffer tank P continuously in a reactor cascade consisting of a stirred tank K2 for performing step c) and a tubular reactor R is performed.

8. The method according to claim 6 or 7, characterized in that the molecular weight distribution M _w / M _{n is} below 1.5 for the block Si and above 1.5 for the block S ₂ .

9. Mixtures of block copolymers SrB-S ₂ and styrene polymers, obtainable by one of the processes according to claims 1 to 8.

10. Mixtures according to claim 9, containing 20 to 90 wt .-% of a styrene-butadiene block copolymer S BS ₂ and 10 to 80 wt .-% polystyrene.