Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-05-12
2001-08-07
Pezzuto, Helen L. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S173000, C526S177000, C526S179000, C526S180000, C526S181000, C526S185000, C526S187000, C526S189000, C526S193000, C526S209000, C526S217000
Reexamination Certificate
active
06271324
ABSTRACT:
The present invention relates to a process for the preparation of homopolymers, copolymers or block copolymers by anionic polymerization of acrylates and/or methacrylates in the presence of an initiator composition containing
A) an organic alkali metal compound,
B) an organic aluminum compound and
C) an additive which forms a complex with the alkali metal cation and is selected from the group consisting of open-chain ethers having at least two ether oxygen atoms, macrocyclic ethers and cryptands or from the group consisting of quaternary cations of the general formula I
where
A is N, P, As or Sb and
R
a
, R
b
, R
c
and R
d
,
independently of one another, are each unsubstituted or substituted alkyl, cycloalkyl, aralkyl or aryl, where two neighboring radicals, together with the heteroatom A, may form a 5- or 6-membered heterocyclic structure which may contain one or two further heteroatoms selected from nitrogen, oxygen and sulfur atoms.
The present invention furthermore relates to the initiator composition and a process for the preparation of the initiator composition and the use thereof.
The anionic and coordinate polymerization of (meth)acrylates is difficult owing to the secondary reactions associated with the carbonyl group, such as transfer and chain termination reactions, particularly with regard to the regulation of molecular weight, molecular weight distribution and stereoregularity. Various possibilities for the controlled polymerization of (meth)acrylates were reviewed in J.M.S.—Rev. Makromol. Chem. Phys. C34(2) (1994), 243-324, with their advantages and disadvantages.
For example, EP-B-0 274 318 describes the anionic polymerization of acrylate monomers with an alkali metal alkyl or alkaline earth metal alkyl as an initiator in the presence of macrocyclic complexing agents. The process is carried out in tetrahydrofuran at −78° C. Furthermore, LiCl and lithium alcoholates were also used as complexing additives. However, a narrow molecular weight distribution is obtained only at low temperatures, resulting in long polymerization times and technically complicated and expensive apparatuses. Moreover, when tetrahydrofuran is used as a solvent, further safety precautions must be taken owing to peroxide formation.
Macromolecules 25 (1992), 4457-4463, describes the polymerization of methyl methacrylate in toluene with diphenylmethylsodium as an initiator in the presence of macrocyclic crown ethers. The polymethyl methacrylate obtained has only low syndiotacticity.
EP-A-0 434 316 discloses the polymerization of methacrylates by means of alkali metal alkyls in the presence of organic aluminum compounds having bulky radicals. However, the reaction times are still in the region of several hours, even at relatively high temperatures.
A widespread problem in the anionic polymerization of acrylates in the presence of alkyllithium and alkylaluminum compounds is gel formation. This presumably arises because a plurality of molecules (monomers or polymer chains already formed) form coordinate bonds with the central metal. As a result of this phenomenon, on the one hand the reaction mixture is difficult to handle and on the other hand the molecular weight distribution of the polyalkyl acrylates is broad and frequently complete monomer conversion is not achieved.
Metal-free initiation of resonance-free carbanions by ammonium salts is disclosed in EP-A-0 306 714. However, tetraalkylammonium salts tend to undergo Hoffmann elimination in the presence of strong bases, for example uncomplexed carbanions, which leads to chain termination.
It is an object of the present invention to provide a novel initiator composition which permits good control of the polymerization reaction. In particular, it was intended to provide a process which leads to products having a narrow molecular weight distribution even at relatively high temperatures. Furthermore, it was intended to achieve very highly quantitative conversions and to prepare block copolymers. Moreover, the reaction rate should be suitable for industrial purposes. It is a further object of the present invention to provide a process which is substantially insensitive to the impurities present in monomers and solvents of industrial quality. Furthermore, it was intended to provide a process in which gel formation is avoided.
We have found that these objects are achieved by a process for the preparation of homopolymers, copolymers or block copolymers by anionic polymerization of acrylates and/or methacrylates in the presence of an initiator composition containing
A) an organic alkali metal compound,
B) an organic aluminum compound and
C) an additive which forms a complex with the alkali metal cation and is selected from the group consisting of open-chain ethers having at least two ether oxygen atoms, macrocyclic ethers and cryptands, or from the group consisting of quaternary cations of the general formula I
where
A is N, P, As or Sb and
R
a
, R
b
, R
c
and R
d
,
independently of one another, are each unsubstituted or substituted alkyl, cycloalkyl, aralkyl or aryl, where two neighboring radicals, together with the heteroatom A, may form a 5- or 6-membered heterocyclic structure which may contain one or two further heteroatoms selected from nitrogen, oxygen and sulfur atoms.
Suitable polyalkyl (meth)acrylates are both homopolymers and copolymers or block copolymers. For example, copolymers can be prepared from mixtures of different alkyl acrylates or different alkyl methacrylates or mixtures of alkyl acrylates with alkyl methacrylates. Block copolymers can be obtained, for example, from different alkyl acrylates or different alkyl methacrylates or from alkyl acrylates and alkyl methacrylates. In the novel process, both two-block copolymers and multi-block copolymers can be prepared. The composition by weight of the blocks may vary within wide limits.
The suitable alkyl methacrylates include those having 1 to 20, preferably 1 to 10, in particular 1 to 6, carbon atoms in the ester radical. The ester radical may be either linear or branched. The ester radical may also be a cycloalkyl radical. It is preferably linear. The alkyl methacrylates can also be substituted by one or more halogen atoms. Examples are methyl methacrylate, ethyl methacrylate, 2,2,2-trifluoroethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, n-octyl methacrylate, n-decyl methacrylate and dihydrodicyclopentadienyl methacrylate. Methyl methacrylate is particularly preferably used.
Among the alkyl acrylates, C
1
-C
20
-alkyl acrylates are preferred. C
1
-C
10
-alkyl acrylates are particularly preferred, in particular C
1
-C
8
-alkyl acrylates. The alkyl radicals may be either linear or branched or may form a ring. For example, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, n-pentyl acrylate, isopentyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, n-octyl acrylate, n-decyl acrylate or dihydrodicyclopentadienyl acrylate may be used.
Preferred block copolymers are those which are composed of methyl methacrylate and n-butyl acrylate blocks, tert-butyl acrylate blocks or tert-butyl methacrylate or 2-ethylhexyl acrylate blocks, in particular of methyl methacrylate and tert-butyl methacrylate.
According to the invention, the initiator composition contains an organic alkali metal compound or a mixture of different organic alkali metal compounds of this type. A preferred alkali metal is lithium, sodium or potassium. The choice of the alkali metal influences, inter alia, the reaction rate of the polymerization reaction, so that the choice of the metal depends on the monomers to be reacted and on the desired reaction rate. In general, organolithium compounds are preferred.
Alkyl- or alkylaryl-alkali metal compounds are preferably used. Their alkyl radical has, as a
Jungling Stephan
Mehler Christof
Muller Axel
Schlaad Helmut
Schmitt Bardo
BASF - Aktiengesellschaft
Keil & Weinkauf
Pezzuto Helen L.
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