Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-08-14
2002-03-05
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S316000, C526S340000, C526S346000, C526S347000, C526S152000, C526S124200, C526S125100, C526S177000, C526S187000
Reexamination Certificate
active
06353056
ABSTRACT:
The present invention relates to a process for the preparation of block copolymers from vinylaromatic monomers and dienes.
Anionic polymerizations typically proceed very rapidly, so that they are difficult to control on an industrial scale owing to the considerable amount of heat generated. Lowering the polymerization temperature results in an excessive increase in viscosity, in particular with a concentrated solution. Reducing the initiator concentration increases the molecular weight of the polymer formed. Controlling the reaction by appropriate dilution of the monomers results in a higher solvent requirement and lower space-time yields.
It has therefore been proposed to include in the anionic polymerization initiators various additives to influence the polymerization rate.
The effect of Lewis acids and Lewis bases on the rate of the anionic polymerization of styrene was described in Welch, Journal of the American Chemical Society, 82 (1960), 6000-6005. For instance, it has been found that small amounts of Lewis bases such as ethers and amines accelerate the n-butyllithium-initiated polymerization of styrene at 30° C. in benzene, whereas Lewis acids such as zinc and aluminum alkyls reduce the polymerization rate or, when used in superstoichiometric amounts, stop the polymerization completely.
In Macromolecules, 19 (1966), 299-304, Hsieh and Wang investigate the complexation of dibutylmagnesium with the alkyllithium initiator or the living polymer chain, respectively, in the presence or absence of tetrahydrofuran and discover that dibutylmagnesium reduces the polymerization rate of styrene and butadiene without affecting the stereochemistry. U.S. Pat. No. 3,716,495 discloses initiator compositions for the polymerization of conjugated dienes and vinylaromatics where a more efficient use of the lithium alkyl as initiator is achieved by the addition of a metal alkyl of a metal of group 2
a
, 2
b
or 3
a
of the Periodic Table of the Elements, such as diethylzinc and polar compounds such as ethers or amines. Owing to the required large amounts of solvent, relatively low temperatures and long reaction times in the region of several hours, the space-time yields are correspondingly low.
W097/33923 describes initiator compositions which are useful for the anionic polymerization of vinyl monomers, comprise alkali metal and magnesium compounds bearing hydrocarbon radicals and have a molar [Mg]/[alkali metal] ratio of at least 4.
Earlier, Patent application PCT/EP97/04497, unpublished at the priority date of the present invention, describes continuous processes for the anionic polymerization or copolymerization of styrene or diene monomers using alkali metal alkyl as polymerization initiator in the presence of an at least bivalent element as a retarder.
PCT/EP97/04498, which was also unpublished at the priority date of the present invention, describes processes for the anionic polymerization of dienes and/or vinylaromatic monomers in a vinylaromatic monomer or monomer mixture in the presence of a metal alkyl or aryl of an at least bivalent element without added Lewis bases.
Various initiator mixtures which may comprise alkali metals, alkaline earth metals, aluminum, zinc or rare earth metals are known, for example, from EP-A 0 234 512 for the polymerization of conjugated dienes with a high degree of 1,4-trans-linking. German Offenlegungsschrift 26 28 380 teaches, for example, the use of alkaline earth aluminates as cocatalyst in conjunction with an organolithium initiator for the preparation of polymers or copolymers of conjugated dienes having a high trans-1,4-linkage content and low 1,2-linkage or 3,4-linkage content. This is said to lead to an increase in polymerization rate.
It is an object of the present invention to provide a process for the preparation of block copolymers from vinylaromatic monomers and dienes which does not have the abovementioned disadvantages and which can be conducted in a controlled manner, in particular at high monomer concentrations.
We have found that this object is achieved by a process for the preparation of block copolymers from vinylaromatic monomers and dienes in which the monomers are polymerized in the presence of at least one alkali metal organyl or alkali metal alkoxide and at least one magnesium, aluminum or zinc organyl.
Alkali metal organyls which may be used are mono-, bi- or multifunctional alkali metal alkyls, aryls or aralkyls customarily used as anionic polymerization initiators. It is advantageous to use organolithium compounds such as ethyllithium, propyllithium, isopropyllithium, n-butyllithium, sec-butyllithium, tert-butyllithium, phenyllithium, diphenylhexyllithium, hexamethylenedilithium, butadienyllithium, isoprenyllithium, polystyryllithium or the multifunctional compounds 1,4-dilithiobutane, 1,4-dilithio-2-butene or 1,4-dilithiobenzene. The amount of alkali metal organyl required depends on the desired molecular weight, the type and amount of the other metal organyls used and the polymerization temperature and is typically in the range from 0.0001 to 5 mol percent, based on the total amount of monomers.
Alkali metal alkoxides which may be used, alone or in a mixture, are aliphatic, aromatic or araliphatic alkoxides of lithium, sodium or potassium. Examples are lithium, sodium or potassium methoxide, ethoxide, n-propoxide, isopropoxide, n-butoxide, sec-butoxide, tert-butoxide, n-pentoxide, isopentoxide, hexoxide, amyl alkoxide, phenoxide, mentholate, 2,4-di-tert-butylphenoxide, 2,6-di-tert-butylphenoxide, 3,5-di-tert-butylphenoxide, 2,4-ditert-butyl-4-methylphenoxide and trimethylsilanoate. Preference is given to using the methoxides, ethoxides, tert-butyl-substituted phenoxides or branched alkylalkoxides, in particular lithium tert-butoxide, amylate or 3,7-dimethyl-3-octoxide.
Useful magnesium organyls are those of the formula R
2
Mg, wherein the radicals R are each, independently of one another, hydrogen, halogen, C
1
-C
20
-alkyl or C
6
-C
20
-aryl. Preference is given to using ethyl, propyl, butyl, hexyl or octyl compounds which are commercially available. Particular preference is given to using (n-butyl) (s-butyl)magnesium which is soluble in hydrocarbons.
Aluminum organyls which may be used are those of the formula R
3
Al, wherein the radicals R are each, independently of one another, hydrogen, halogen, C
1
-C
20
-alkyl or C
6
-C
20
-aryl. Preferred aluminum organyls are aluminum trialkyls. Particular preference is given to using triisobutyl aluminum.
Zinc organyls which may be used are those of the formula R
2
Zn, wherein the radicals R are each, independently of one another, hydrogen, halogen, C
1
-C
20
-alkyl or C
6
-C
20
-aryl. Preferred zinc organyls are zinc dialkyls. Particular preference is given to using diethyl zinc.
The aluminum, magnesium or zinc alkyls may also be present in partially or completely hydrolyzed, alcoholized or aminolyzed form.
Particular preference is given to using sec-butyllithium together with dibutylmagnesium or triisobutyl aluminum.
The molar ratios of the metal organyls with respect to each other may vary within wide limits, but depend primarily on the desired retardation effect, the polymerization temperature, the monomer composition and concentration and the desired molecular weight.
The molar ratio of magnesium, aluminum or zinc, respectively, to alkali metal is preferably in the range from 0.1 to 100, preferably in the range from 1 to 10.
In a preferred embodiment, the polymerization is carried out in the presence of an alkali metal organyl, an aluminum organyl and a magnesium organyl. The molar ratio of magnesium to alkali metal is advantageously in the range from 0.2 to 3.8, the molar ratio of aluminum to alkali metal in the range from 0.2 to 4. The molar ratio of magnesium to aluminum is preferably in the range from 0.005 to 8.
In the process of the invention use is made primarily of alkali metal organyls, magnesium, aluminum and zinc organyls. Barium, calcium or strontium organyls are preferably only present in ineffective amounts not having a significant effect
Fischer Wolfgang
Gausepohl Hermann
Knoll Konrad
Schade Christian
Warzelhan Volker
Acquah Samuel A.
Asinovsky Olga
BASF - Aktiengesellschaft
Keil & Weinkauf
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