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
2002-02-26
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...
C526S178000, C526S186000, C526S187000, C526S189000, C526S195000, C526S196000, C526S346000, C525S272000
Reexamination Certificate
active
06350834
ABSTRACT:
The present invention relates to a process for the homopolymerization of vinylaromatic monomers or the copolymerization of vinylaromatic monomers and dienes in the presence of at least one alkali metal organyl or alkali metal alkoxide and at least one aluminum or boron organyl and to an initiator composition for carrying out the process.
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 has been 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.
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 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. PCT/EP97/04497, which was 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-translinking. 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 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.
It is an object of the present invention to provide a process for the homopolymerization of vinylaromatic monomers or the copolymerization of vinylaromatic monomers and dienes which does not have the abovementioned disadvantages, and, in particular, to provide an initiator composition for the process which makes it possible to adjust the polymerization rate within wide temperature and concentration ranges.
We have found that this object is achieved by a process for the homopolymerization of vinylaromatic monomers or the copolymerization of vinylaromatic monomers and dienes in the presence of at least one alkali metal compound and at least one compound of an element of group 3a of the Periodic Table of the Elements, the compounds containing, based on the sum of molar equivalents of alkali metal and elements of group 3a in each case,
a) from 0.1 to 3.9 molar equivalents of oxygen, sulfur, nitrogen or phosphorus and
b) from 0.1 to 3.9 molar equivalents of an organyl ligand.
It is immaterial whether the alkali metal compound or a compound of an element of group 3a or both contain oxygen, sulfur, nitrogen or phosphorus or an organyl ligand. It is therefore also possible to use mixtures of compounds having only organyl ligands and compounds having only some or no organyl ligands and contain the corresponding hetero atoms. The ranges given for the hetero atoms or organyl ligands apply to the sum of molar equivalents of all alkali metals and elements of group 3a, irrespectively of the ratio of alkali metal to element of group 3a selected in each case.
For the purposes of the invention organyl ligands are ligands which are attached to the alkali metal or element of group 3a of the Periodic Table of the Elements via a more or less polar direct bond between metal and carbon.
The hetero atoms preferably stem from alkoxide, thiolate, amide, imide or phosphide ligands attached to the alkali metal or the element of group 3a of the Periodic Table of the Elements. However, it is also possible for the hetero atoms to be present as bridges between the elements, as in aluminoxanes or boroxanes.
The alkali metal compound used is preferably an alkali metal organyl, alkali metal alkoxide, alkali metal thiolate or alkali metal amide, and the compound of an element of group 3a of the Periodic Table of the Elements used is preferably an aluminum or boron 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 or 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 0.0001-5 mol percent, based on the total amount of monomers.
Alkali metal alkoxides which may be used, alone or in admixture, 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, 3,7-dimethyl-3-octoxide, phenoxide, 2,4-di-tert-butylphenoxide, 2,6-di-tert-butylphenoxide, 3,5-di-tert-butylphenoxide, 2,4-di-tert-butyl-4-methylphenoxide and trimethylsilanoate. Preference is given to using the methoxides, ethoxides, tert-butyl-substituted phenoxides or branched alkyl alkoxides, in particular lithium tert-butoxide, amyl alkoxide or 3,7-dimethyl-3-octoxide.
Alkali metal thiolates which may be used, alone or in admixture, are aliphatic, aromatic or araliphatic thiolates of lithium, sodium or potassium. Examples are lithium, sodium or potassium methyl sulfide, ethyl sulfide, butyl sulfide, hexyl sulfide, decyl sulfide, dodecyl sulfide, stearyl sulfide, thiophenoxide, tolyl sulfide, cyclohexyl sulfide or dilithium 1,2-dimercaptoethane. Preference is given to aliphatic thiolates having from 8 to 18 carbon atoms in the alkyl chain.
Alkali metal amides which may be used, alone or in admixture, are lithium, sodium or potassium salts of ammonia or primary or secondary amines having aliphatic, aromatic or araliphatic substituents. Examples of suitable amides are lithiumamide, N-lithiummethylamide, N-lithiumethylamide, N-lithiumpropylamide, N-lithiumbutylamide, N-lithiumamylamide, N-lithiumphenylamide or the corresponding sodium or potassium salts; N-lithiumdim
Deffieux Alain
Desbois Philippe
Fischer Wolfgang
Fontanille Michel
Gausepohl Hermann
BASF - Aktiengesellschaft
Keil & Weinkauf
Teskin Fred
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