Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-08-14
2001-10-09
Teskin, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S346000, C502S153000, C502S157000
Reexamination Certificate
active
06300441
ABSTRACT:
The present invention relates to a process for the preparation of an initiator composition comprising an alkali metal organyl and an aluminum organyl and to a process for the polymerization of anionically polymerizable monomers.
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 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, Vol 82 (1960), pages 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.
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 2a, 2b or 3a of the Periodic Table of the Elements, such as diethyl zinc, and polar compounds such as ethers or amines. The manner in which the individual initiator components are added to the polymerization system is said to be uncritical.
Earlier patent application PCT/EP97/04497, unpublished at the priority date of the present invention, describes continuous processes for the anionic polymerization or copolymerization of styrene or diene monomers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.
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 the polymers or copolymers of conjugated dienes having a high trans-1,4-linkage content and low 1,2-linkage or 3,4-linkage contents. This is said to lead to an increase in polymerization rate.
The use of additives such as aluminum alkyls which have a strong retarding effect on the anionic polymerization requires exact dosage and temperature control. A slight underdosage may lead to an insufficient retardation of the reaction rate, whereas a slight overdosage may completely stop the polymerization.
Separate addition, or insufficient mixing-in, of the individual initiator components to a monomer solution may lead to poor dispersion, particularly at high monomer concentrations, and house to different local concentrations of the individual initiator components. Before a homogeneous dispersion of the initiator components can be achieved, the polymerization may already be initiated in some regions, whereas the polymerization is strongly retarded or has not yet started in others. This may lead to large local temperature increases and irreproducible molecular weight distributions.
It is an object of the present invention to provide a process for the preparation of an initiator composition comprising an alkali metal organyl and an aluminum organyl to make it possible to polymerize anionically polymerizable monomers, in particular styrene, in a reproducible manner with respect to polymerization rate and molecular weight distribution.
We have found that this object is achieved by a process for the preparation of an initiator composition comprising an alkali metal organyl and an aluminum organyl, which comprises homogeneously mixing the metal organyls, dissolved in inert hydrocarbons, and aging at a temperature in the range from 0 to 120° C. for at least 2 minutes.
The initiator composition prepared in this manner is particularly useful for the polymerization of anionically polymerizable monomers.
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.
Aluminum organyls which may 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 such as triethylaluminum, triisobutylaluminum, tri-n-butylaluminum, triisopropylaluminum or tri-n-hexylaluminum. Particular preference is given to using triisobutylaluminum. It is also possible to use aluminum organyls which are formed by partial or complete hydrolysis, alcoholysis, aminolysis or oxidation of alkyl- or arylaluminum compounds or those which carry alkoxide, thiolate, amide, imide or phosphide groups. Examples are diethylaluminum N,N-dibutylamide, diethylaluminum ethoxide, diisobutylaluminum ethoxide, diisobutyl-(2,6-di-tert-butyl-4-methyl-phenoxy)aluminum (CAS No. 56252-56-3), methylaluminoxane, isobutylated methylaluminoxane, isobutylaluminoxane, tetraisobutyldialuminoxane, or bis(diisobutyl)aluminum oxide.
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 aluminum to alkali metal is advantageously in the range from 0.2 to 4.
In the process of the invention, use is made primarily of alkali metal organyls and aluminum organyls and, if desired, magnesium organyls. Barium, calcium or strontium organyls are preferably only present in ineffective amounts not having a significant effect on the polymerization rate or copolymerization parameters. Nor should transition metals or lanthanoids, especially titanium, be present in significant amounts.
The inert hydrocarbon used may be aliphatic, cycloaliphatic or aromatic. Preference is given to using solvents in which the metal alkyls are commercially available in the form of a solution. Particular preference is given to using pentane, hexane, heptane, cyclohexane, ethylbenzene or toluene.
The initiator components are advantageously used in the solution concentrations in which they are commercially available or, for a quicker establishment of equilibrium, in a more diluted form. Preference is given to concentration where the sum of all metal organyls is in the range from 0.01 to 2 mol/1, based on the initiator composition.
The temperature depends on the concentration, the type of the metal organyls and the solvent. It is usually possible to use any temperature between the freezing point and boiling point of the mixture. It is advantageous to use a temperature in the range from 0 to 120° C., preferably in the range from 20 to 80° C.
The aging of the metal organyls is
Deffieux Alain
Desbois Philippe
Fischer Wolfgang
Fontanille Michel
Gausepohl Hermann
BASF - Aktiengesellschaft
Keil & Weinkauf
Teskin Fred
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