WO1999036451A1

WO1999036451A1 - Method for producing statistical styrene-butadiene-copolymers

Info

Publication number: WO1999036451A1
Application number: PCT/EP1999/000137
Authority: WO
Inventors: Klaus-Dieter Hungenberg; Wolfgang Loth; Konrad Knoll; Lutz Janko; Friedhelm Bandermann
Original assignee: Basf Aktiengesellschaft
Priority date: 1998-01-15
Filing date: 1999-01-12
Publication date: 1999-07-22
Also published as: AU2616699A; DE19801101A1

Abstract

The invention relates to a method for producing statistical copolymers from anionically polymerisable monomers S and B by means of anionic polymerisation with a polymerisation initiator I, by: a) producing a mixture containing the monomers S and B in the initial concentrations [S]0 and [B]0, the concentration [B]0 of the monomer B in the mixture being calculated according to a certain equation; b) initialising the copolymerisation by bringing the mixture obtained in a) into contact with the polymerisation initiator I or a growing polymer chain PBI or PSI; c) adding the remaining quantity of the monomer B at a charging speed of rz during the copolymerisation, said charging speed of rz in relation to time t being obtained by iterative solution of a differential equation system.

Description

Process for the preparation of statistical styrene-butadiene copolymers

description

The invention relates to a process for the preparation of statistical copolymers from anionically polymerizable monomers S and B by anionic polymerization with a polymerization initiator I, and to the copolymers obtainable thereby.

The anionic polymerization of vinyl aromatic monomers such as styrene and dienes such as butadiene generally gives block copolymers. This is due to the different relative polymerization rates of the monomers used.

However, statistical copolymers or block copolymers with random copolymer blocks composed of vinylaromatic monomers and dienes are frequently desired on account of their properties, such as glass transition temperature and mechanical behavior, which differ from the block copolymers.

By adding polar solvents such as ethers, it is possible to influence the copolymerization parameters and polymerization rates in such a way that copolymers with a statistical distribution of the comonomer units along the polymer chain can be obtained. However, the amount of polar solvents required for this usually leads to copolymers with a significantly higher vinyl content.

Various processes with different dosages of the monomers have therefore been proposed, in which the statistical monomer incorporation is effected via the respective concentration ratios during the reaction. GB-A 903 331 describes a process for the preparation of statistical styrene-butadiene copolymers with a low vinyl content, in which the comonomers are added to the polymerization solution so slowly that under the respective polymerization conditions the comonomers are completely converted during the addition. However, the space-time yield is low with this method.

According to the process according to DE-A 21 17 995, the comonomers are metered in at a constant rate, the preselected monomer ratio of the feed being different from the monomer ratio of the initial charge. In this way it should be possible to keep the concentration of each monomer constant during the reaction.

GB-A 994 726 teaches a process in which the total amount of the vinyl aromatic monomer and the proportion of diene monomer necessary for the desired copolymer composition are introduced. The faster polymerizing butadiene is metered in so that the initially selected monomer ratio is kept constant during the polymerization. The method requires continuous or at least regular sampling and analysis to determine the respective styrene concentration.

The object of the present invention was to provide a simple and economical process for the preparation of random copolymers from monomers S and B. In particular, the process should be suitable for the production of statistical styrene-butadiene copolymers with a low vinyl content and it should be possible to dispense with complex process analysis.

Accordingly, a process for the preparation of statistical copolymers from anionically polymerizable monomers S and B by anionic polymerization using a polymerization initiator I was found, where

a) produces a mixture containing the monomers S and B in the initial concentrations [S] o and [Bio, the concentration [BJo of the monomer B in the mixture being calculated according to equation 1:

with s desired proportion of the monomers S in the copolymer in

Mole percent, b desired proportion of the monomers B in the copolymer in

Mole percent, k _BB reaction rate constant of the addition of a

Monomers B to the growing polymer chain PBI with a

Monomers B as the last added monomer, kg _s reaction rate constant of the addition of a

Monomers S to the growing polymer chain PSI with a monomer S as the last attached monomer, k≤ _B reaction rate constant of the addition of a monomer B to the growing polymer chain PSI with a monomer S as the last added monomer, k _B s reaction rate constant of the addition of a monomer S to the growing polymer chain PBI with a

Monomers B as the last added monomer,

b) the copolymerization is initiated by bringing the mixture of a) into contact with the polymerization initiator I or a growing polymer chain PBI or PSI,

c) during copolymerization and the remaining amount of the monomer B with the feed rate r ₂ added, with the feed rate r ₂ at the time t by iteratively solving the differential equations (2) to (6)

-dB / dt = -r _z - [B] _z + ∞. psi • B + ^ • PBI • B (2)

V V

-dS / dt kßS PBI S + kss PSI (3) V

-dPBI / dt = - • PBI • S -— • PSI • B (4)

V V

-dPSI / dt = - • PSI • B - ^ 2§ • PBI • S (5)

V V

-dV / dt = -r ₂ - M _B -dB / dt (6)

With

V volume of the polymerization mixture at the respective time and

[B] _z concentration of the monomer B in the feed ρ _s , Q _B density of the monomer S and B ρ _p density of the copolymer

M _s , Mτ molar mass of the monomers S and B S, B Quantity of the monomers S and B

on condition (7)

b d [S] d [B] / dt = s dt (7)

results.

The term statistical copolymers is understood to mean copolymers or copolymer blocks in which the comonomers are incorporated into the polymer in largely statistical order in accordance with their relative mole percent.

The method can be applied to all anionically polymerizable monomers, preferably those with a vinyl group, such as vinyl aromatics, dienes, acrylates, methacrylates, acrylonitrile, methacrylonitrile, acrylamides and methacrylamides.

The process is particularly suitable for the copolymerization of monomers S and B, which tend to form homopolymers or homopolymer blocks in the mixture, i.e. where one of the monomers in the mixture reacted much more slowly. Monomer S is the monomer that reacts more slowly in the mixture.

Vinylaromatic monomers are preferably used as monomers S and dienes as monomers B.

Styrene and its derivatives substituted in the α-position or on the aromatic ring with 1 to 4 carbon atoms, for example α-methylstyrene, p-methylstyrene, ethylstyrene, tert-butylstyrene, vinyltoluene, can be used as vinylaromatic monomers. Styrene will be used particularly preferably.

In principle, all dienes are suitable as dienes, but preference is given to those with conjugated double bonds such as 1,3-butadiene, isoprene, 2,3-dimethylbutadiene, 1,3-pentadiene, 1,3-hexadienes, phenylbutadiene, piperylene or mixtures thereof. 1,3-Butadiene is particularly preferably used.

All customary initiators which can trigger the anionic polymerization can be used as the polymerization initiator I. As a rule, organometallic compounds are suitable for this, preferably alkali metal alkyls or aryls. Purpose-

-c:?: cr / .e: sc e άer. 1 ; -. ": τ" .crrεr.: scr.e Vercir-c r-cer- en ores such as ethyl, propyl, isopropyl, n-butyl, sec-butyl, ter.-butyl, Phenyl, diphenylhexyl, hexamethylenedi, butadienyl, isoprenyl or. Butyllithium, polystyryllithium PSLi or 1, 1-diphenylhexyllithium is preferably used, which is readily obtainable from the reaction of 1, 1-diphenylethylene with n- or sec-butyllithium 5. The amount of initiator required results from the desired molecular weight and is generally in the range from 0.002 to 5 mol percent, based on the amount of monomer to be polymerized.

Suitable solvents are solvents which are inert to the polymerization initiator. It is expedient to use aliphatic, cycloaliphatic or aromatic hydrocarbons with 4 to 12 carbon atoms such as pentane, hexane, heptane, cyclohexane, methylcyclohexane, iso-octane, benzene, alkylbenzenes such as toluene, xylene, ethylbenzene or decalin or suitable mixtures. 15

The initial concentration [S_o of the monomer S in the initial charge is generally 2 to 40, preferably 5 to 25 percent by weight. The initial concentration [B] ₀ of monomer B results from the desired copolymer composition and the reaction rate constants according to equation (1).

Monomer B is preferably added solvent-free in the feed. However, it can also be added in a suitable solvent. The same solvent is preferably used in which the polymerization is carried out. This allows z. B. achieve better dosing accuracy.

Temperature and pressure are not critical for the implementation of the process. As a rule, polymerization is carried out at a pressure in the range from 1 to 30 20 bar and a temperature from 20 ° C. to 130 ° C., preferably 60 ° C. to 100 ° C.

If in the process of the invention as a polymerization initiator is not a viable polymer PSI, e.g. B. Polystyryl 35 lithium is used directly, arise for the first

Iteration step of the growing polymer chains PSI according to equation (13) or PBI according to equation (14):

Initiator ₍₀ )

40 PSI (0) k _SB _ initiator (Q) (13) K _BS S ₍ o)

PBI (O) = initiator ₍₀ ) - PSI ₍₀ ) (14)

45 The solution of the differential equations (2) to (6) with the condition (7) are known to the person skilled in the art. For the approximate solution of the equation system (2) to (7), for example, the following procedure has proven suitable, for which programs are also available on common personal computers:

For time increments Δt which are small compared to the total feed time of the monomer B, the feed rate r _z = 0 can approximately be used to solve the differential equations (2) to (6). The result is the amount of the monomers S _{t + Δt} and B _{t + Δt} and the growing polymer chains PSI _{t + Λt} and PBl _{t + Λ} as well as the instantaneous volume V _{t + Δt of} the polymerization mixture at the time t + Δt. During this time increment .DELTA.t, the polymerization solution becomes depleted in the more rapidly polymerizing monomer B, so that the ratio of the monomers B to monomers S at time t + .DELTA.t no longer corresponds to the initial ratio [B_o / -S] o according to equation (1). The amount of monomer B _z in moles which is necessary to restore the initial ratio [B] o / [S] o according to equation (1) is now calculated according to equation (15)

B _z = S _t + Δt * B ₀ / S ₀ - Bt + Δt d5)

The feed rate r _z can be calculated from this amount of monomer B ₂ in mol and the concentration [B] ₂ in the feed in order to set the target ratio -B_o / [S] o again before the next time increment Δt.

This process is repeated iteratively as often as the intended amount of monomer B from the feed corresponds. In this way, a step-like function of the inlet speed r ₂ over time is obtained. The time increments Δt can be chosen to be constant or variable. The values of the inlet speeds obtained at different times can also be smoothed according to known mathematical methods and approximated by continuous functions, for example the form r ₂ = b * m ^fc . In this way, simple functions for controlling the inflow can be selected.

Towards the end of the feed of the monomers B, the feed rate r _z decreases. It has therefore proven to be advantageous to add the remaining amount in the feed at once or at a constant feed rate after polymerization of 90%, preferably 95%, in particular 98% of the total amount of monomer B to be polymerized. This can increase the polymerization time can be abbreviated without significantly influencing the polymer composition.

In order to achieve an ideal statistical incorporation of the comonomers into the polymer, the feed rate r ₂ determined by one of the methods described above is adhered to as precisely as possible, but the metering accuracy is limited, particularly in the case of technical apparatus. As a rule, however, copolymers with the desired properties are obtained if the deviation from higher or lower feed rates on each side is less than 10%, preferably less than 5%, in particular less than 2% of the feed rate r ₂ determined at the respective time.

The reaction rate constants k _BB , k _{SS /} k _SB and k _B s are determined experimentally with their temperature dependence for the respective polymerization system, that is to say for the respective combination of monomers, solvents and optionally additives such as Lewis bases.

For the system styrene, 1,3-butadiene and cyclohexane, for example, the temperature-dependent reaction rate constants result from equations (8) to (11):

11170 k _BB = 1,2-10 ^ exρ - mol -ι _s -l (8)

7074 k _ss = 2.2.108exp (- ——- I mol- ^l s- ⁱ (9)

k _SB = 2, l-10 ¹² exp (- - ^ -) ol- ⁱ s- ¹ (10)

k _BS = 1.3-10 ¹² exp (- —— j mol- ⁱ s- * (11)

After inserting the molar masses and densities for styrene, butadiene and the density of the random styrene / butadiene copolymer in equation (6), equation (6a) results:

-dV / dt = -r ₂ - 0.020 dS / dt - 0.029 dB / dt (6a). The feed rate r _z can be approximated by a

Exponential equation of formula (12)

r _z = Vges * ci * exp (-c ₂ * t) (12;

With

Vges total volume from supply and inflow cι, c ₂ approximation parameters t time from the start of the inflow of monomer B.

describe.

The approximate parameters ci and c ₂ depend on the temperature T and concentration of the polymerization solution as well as the desired molecular weight M _n and the desired molar ratio s / b of the monomers S and B of the copolymer. For example, they can be adapted to experimental data using standard regression methods.

For the production of statistical styrene-butadiene copolymers in cyclohexane as solvent, the parameters ci and c ₂ from Table 1 can be used, for example. They apply to the temperature range 313 K to 393 K and 30 to 70 percent by weight with a molecular weight of 25000 to 100000 g / mol and a styrene content of 30 to 70 percent by weight based on the copolymer.

r- belle 1

u>

Block copolymers which contain a random copolymer block S / B can also be produced by the process according to the invention. This can be achieved by the known methods such as sequential anionic polymerization or by multifunctional initiators or with a coupling agent.

For example, three-block copolymers SS / BS with a random copolymer block S / B and two blocks of essentially vinyl aromatic monomers S can be produced by sequential anionic polymerization. To this end, a polymer block PSI composed of vinylaromatic monomers S is first polymerized and a statistical copolymer block S / B is closed by the process according to the invention by adding a partial amount of the monomer B in accordance with equation (1) and adding further monomer B at the addition rate r determined as described above _e.g. The second block S is then polymerized onto the copolymer block S / B by adding further vinylaromatic monomer S.

After the molecular weight has been built up, the “living” polymer ends can, if appropriate, be reacted with customary chain terminating or coupling agents in amounts which usually depend on the amount of initiator used.

Suitable chain terminators are proton-active substances or Lewis acids such as water, alcohols, aliphatic and aromatic carboxylic acids and inorganic acids such as carbonic acid or boric acid.

To couple the block copolymers, bifunctional or multifunctional compounds, for example halides of aliphatic hydrocarbons, such as dibromomethane, bischloromethylbenzene or silicon tetrachloride, dialkylsilicon dichloride, alkylsilicon trichloride or tin tetrachloride, polyfunctional aldehydes such as terephthalic acid or epoxides, ester, epoxide, ester, or epoxide, ester, epidonaldehyde, and epoxides are used. Carboxylic esters such as ethyl acetate are preferably used as coupling agents if no Lewis bases such as tetrahydrofuran are present. In the presence of bases, diepoxides such as 1,4-butanediol diglycidyl ether or epoxidized vegetable oils such as epoxidized linseed oil or soybean oil are preferably used.

As an additive influencing the polymerization parameters (Randomizer), for example Lewis bases, such as polar, aprotic ös r-csr.itrel ocer o ler-water, cff soluble Meelsilize can be used. Examples of Lewis bases which can be Diethylene glycol dimethyl ether, tetrahydrofuran, or tertiary

Amines such as pyridine and tributylamine can be used. Preferred among the hydrocarbon-soluble metal salts

Alkali or alkaline earth metal salts of primary, secondary and tertiary alcohols, particularly preferably the potassium salts, such as potassium tetrahydrolinaloolate.

With the addition of a randomizer, the statistical installation of the monomer can be ensured even in the event of deviations from the ideal inlet speed r _z . The absolute rate of polymerization can also be increased in this way, thus enabling higher space-time yields.

If a low vinyl content is important, however, no randomizer is added or the concentration is kept so low that the vinyl content does not increase significantly. The ideal concentration depends on the choice of the randomizer. When using tetrahydrofuran as a randomizer, a hydrocarbon such as cyclohexane as a solvent and a lithium organyl compound as an initiator, the ideal concentration is usually below 0.3% by volume, preferably below 0.1% by volume, particularly preferably below 0.03% by volume. .

When using potassium tetrahydrolinaloolate as a randomizer, a hydrocarbon such as cyclohexane as a solvent and a lithium organyl as an initiator, a lithium / potassium ratio of at least 25/1, preferably at least 40/1 and particularly preferably at least 60/1 is advantageously selected.

The method according to the invention allows statistical

To produce copolymers S / B from monomers S, such as styrene and monomers B, such as butadiene, in a simple and reproducible manner without complex process analysis. The process can be quickly transferred to other process conditions such as temperature or to other copolymer compositions without time-consuming preliminary tests.

Examples

Production of statistical styrene-butadiene copolymers

Examples 1 to 3:

Cyclohexane, styrene and butadiene were introduced in the amounts VQ shown in Table 1. The polymerization initiator n

B yll i ri -_r '3 lι' v-irάe oei 8C ° C r regeser. The butadiene feed started at the same time. The feed rate was up to specified end time (Table 1) according to the curves from Figure 1, then the remaining amount was metered in at 0.01 ml / s. The copolymers show only one glass level and the 1,2-vinyl content is below 8% (Table 1).

Claims

claims

1. A process for the preparation of statistical copolymers from anionically polymerizable monomers S and B by anionic polymerization using a polymerization initiator I, characterized in that

a) produces a mixture containing the monomers S and B in the initial concentrations [S] o and [B] ₀ , the concentration [B] o of the monomer B in the mixture being calculated according to equation 1:

/ (sb) -k _SB -k _BS -.1 / (sb) -k _SB -k _BS \ ² bk _ss -k _BS

[B], [S], (1)

2-s-kßB-ksB y \ 2 -s-kßß-ksB s ^• k _BB ^• kgß

with s desired proportion of the monomers S in the copolymer in mole percent, b desired proportion of the monomers B in the copolymer in mole percent, k _BB reaction rate constant of the addition of a monomer B to the growing polymer chain

PBI with a monomer B as the last added monomer, k _ss reaction rate constant of the addition of a monomer S to the growing polymer chain PSI with a monomer S as the last added

Monomer, k _SB reaction rate constant of the addition of a monomer B to the growing polymer chain PSI with a monomer S as the last added monomer, k _BS reaction rate constant of the addition of a monomer S to the growing polymer chain PBI with a monomer B as the last added monomer,

Sign. c) during copolymerization and the remaining amount of the monomer B with the feed rate r _z been added, with the feed rate r _z at time t by iteratively solving the differential equations (2) to (6)

-dB / dt = -r _z - [B] _z + * __? ■ PSI • B + - ^? • PBI • B (2)

V V

-dS / dt = ksss PBI S + kss PSI (3) V V

-dPBI / dt = ^ 2-? . PBI • S -— • PSI • B (4)

V V

-dPSI / dt = ≥? • SI • B - ^ _? • PBI • S (5)

V V

V Volume of the polymerization mixture at the respective time and [B] _z concentration of the monomer B in the feed ρ _{S /} ρ _B density of the monomer S and B ρ density of the copolymer

M _S , M _B molar mass of the monomers S and B

S, B Amount of substance of the monomers S and B

on condition (7)

bd [S] d [B] / dt = - ^■ —— (7) s dt

results.

2. The method according to claim 1, characterized in that styrene is used as monomer S and butadiene as monomer B in cyclohexane as the solvent and the reaction rate constants are used, which are in accordance with equations (8) to (11)

^ • BB = 7.2-10 ¹³ exp (A-ψ ^? ) Mol- (8)

k _ss = 2.2.108exp (- - ^ -) mol- ⁱ s- * (9)

k _SB = 2, l-10 ⁱ exp (- —-—) mol ^ S ^"1 (10)

11070 k _BS = 1.3-10 ¹² exp (- ——] mol ^ s- ⁱ (11)

for the reaction temperature T.

3. The method according to claims 1 or 2, characterized in that the feed rate r _z by an exponential equation of the formula (12)

r _z = V _g e _S * ci * exp (-c ₂ * t) (12)

With

Vg _es total volume from supply and inflow cι, c ₂ approximation parameters t approximate time from the start of the inflow of monomer B.

4. A process for the production of block copolymers with a random copolymer block S / B, characterized in that the copolymer block S / B is produced by a process according to claims 1 to 3.

5. Process for the production of three-block copolymers SS / BS with a random copolymer block S / B and two blocks of essentially vinylaromatic monomers S, characterized in that a) a polymer block PSI is produced by anionic polymerization of vinyl aromatic monomers S, b) a random copolymer block S / B is polymerized by the process according to one of claims 1 to 4 c) and by adding further vinyl aromatic monomers S the second block S to the copolymer block S / B polymerized.

6. Copolymers obtainable by the process according to one of claims 1 to 5.

7. Use of the copolymers according to claim 6 for the production of fibers, films and moldings.