Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-08-21
2002-06-04
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...
C526S183000, C526S346000, C502S152000, C502S155000, C502S156000, C556S001000, C556S007000, C556S009000, C556S011000, C556S013000, C556S019000, C260S66500B
Reexamination Certificate
active
06399727
ABSTRACT:
The invention relates to a polymerization initiator comprising an alkaline ear th metal compound chosen from the group
a) of heteroleptic alkaline earth metal compound s of the formula I
L—M—R (I)
or
b) of cationic alkaline earth metal complexes of the formula II
[D→M—R]
+
X
−
(II),
where
M: is Ca, Sr or Ba,
L: is a polymerization-inactive ligand,
R: is a polymerization-active ligand,
D: is a donor ligand, and
X: is a non-coordinating anion.
The invention further relates to processes for the preparation of the polymerization initiators and processes for anionic polymerization in the presence of the polymerization initiator.
Styrene can be polymerized either free-radically, anionically, cationically or in the presence of metallocene catalysts. Free-radical polymerization initiated thermally or by means of peroxides produces atactic polystyrene.
The preparation of syndiotactic polystyrene in the presence of metallocene catalyst system is known and is described, for example, in detail in EP-A-0 535 582. Because of its crystallinity, syndiotactic polystyrene has a very high melting point of about 270° C., high rigidity and tensile strength, dimensional stability, a low dielectric constant and high chemical resistance. The profile of mechanical properties is retained even at temperatures above the glass transition temperature.
Isotactic polystyrene, obtainable by means of catalysts comprising titanium tetrachloride and alkylaluminum chlorides, has been described by G. Natta et al. in Journal of the American Chemical Society 77 (1955), page 1708. Isotactic polystyrene is crystalline and has a melting point of 240° C. Because of the very slow rate of crystallization, it is unsuitable for industrial applications, e.g. for injection molding.
Anionic and cationic polymerization, like free-radical polymerization, usually also leads to atactic polystyrene. Anionic polymerization has living character and therefore several advantages over free-radical polymerization or polymerization catalyzed by metallocenes. Thus, for example, it is possible to control simply the molecular weight via the ratio of initiator to monomers and the formation of block copolymers. The polymers prepared by the anionic process have a narrow molecular weight distribution and low residual monomer contents.
The anionic polymerization of styrene and butadiene is usually initiated by organolithium polymerization initiators. The anionic polymerization initiation by organobarium compounds is known, for example, from U.S. Pat. Nos. 3,965,080, 4,012,336. The unpublished DE-A 197 54 504 describes an improved process for the preparation of bisorganoalkaline earth metal compounds.
Russian Chemical Reviews, Vol. 50, 1981, p. 601-614 gives an overview of the synthesis methods and the use of organoalkaline earth metals in the anionic polymerization of unsaturated monomers. Some of the known syntheses for organoalkaline earth metals are complex or produce the desired compounds in low yields or contaminated with byproducts.
B. Nakhmanovich et al., Journal of Makromol. Science Chem. A9(4), pages 575 to 596 (1975) describe the random copolymerization of styrene and butadiene with a high cis 1,4-content of the butadiene units.
The stereoselective polymerization of styrene using anionic polymerization initiators has hitherto not been described.
The heteroleptic alkaline earth metal compounds known from Tesh et al. Journal of the American Chemical Society 116 (1994), page 2409 to 2417, and Burkey et al. Organometallics 13 (1994), page 2773 to 2786 are not polymerization-active.
It is an object of the present invention to provide an anionic polymerization initiator which is also stereoselective with regard to the polymerization of styrene. The polymerization initiator was to combine the advantages of anionic and of metallocene-catalyzed styrene polymerization.
It is a further object of the invention to provide a simple and favorable process for the preparation of the polymerization initiators.
We have found that the first object is achieved by a polymerization initiator comprising an alkaline earth metal compound chosen from the group
a) of heteroleptic alkaline earth metal compounds of the formula I
L—M—R (I)
or
b) of cationic alkaline earth metal complexes of the formula II
[D→M-R]
+
X
−
(II),
where
M: is Ca, Sr or Ba,
L: is a polymerization-inactive ligand,
R: is a polymerization-active ligand,
D: is a donor ligand, and
X: is a non-coordinating anion.
Where appropriate, solvents coordinated to the alkaline earth metal M, such as tetrahydrofuran, or groups carrying heteroatoms in the ligand R are not shown in the formulae (I+II) for simplicity.
We have also found that the second object is achieved by a process for the preparation of the polymerization initiators and processes for anionic polymerization in the presence of the polymerization initiator.
The term heteroleptic alkaline earth metal compound is used to describe one with two different ligands on the alkaline earth metal.
A suitable polymerization initiator is also a mixture of two or more alkaline earth metal compounds of the formula I or II.
The polymerization initiators can additionally comprise alkaline earth metal compounds of the formulae III and IV:
L—M—L (III)
R—M—R (IV),
where L, M and R are as defined in claim
1
.
For the stereoselective anionic polymerization, heteroleptic alkaline earth metal compounds are necessary which have a polymerization-active radical and a second, sterically directing ligand. As a result of ligand exchange, these compounds are in Schlenk equilibrium with the respective homoleptic complexes:
L—M—L+R—M—R⇄L—M—R
The position of the Schlenk equilibrium can be determined using the following equation:
K
=
[
L
-
M
-
R
]
2
[
(
L
)
2
M
]
*
[
(
R
)
2
M
]
Complexes suitable for the stereoselective polymerization must have a Schlenk equilibrium which is predominantly on the side of the heteroleptic complexes and in which the ligand exchange proceeds slowly in relation to the polymerization.
For a stereoselective polymerization, it is advantageous for the proportion of alkaline earth metal compounds of the formula IV to be at most 10 mol %, preferably 0 to 1 mol %, based on the total of all alkaline earth metal compounds.
The polymerization-inactive ligand L generally has a lower basicity than polystyryllithium. The pKa value of the ligand is preferably below 30, in particular below 20.
Examples of suitable polymerization-inactive ligands L are cyclic or open-chain hydrocarbons having a delocalized electron system in which one or more CH fragments can be replaced by isoelectronic fragments, sterically hindered hydrocarbons bonded by heteroatoms, or clusters bonded by a halogen.
Examples of cyclic hydrocarbons having a delocalized electron system are unsubstituted or mono- or polysubstituted cyclopentadienyls, indenyls, fluorenyls, fulvalenediyls or hydropentalenyls. The substituents can be alkyls, preferably C
1
- to C
10
-alkyl, 5- to 7-membered cycloalkyl, which for its part can carry a C
1
to C
10
-alkyl as substituent, C
6
- to C
15
-aryl or arylalkyl. Other suitable substituents are groups with heteroatoms such as silanes, amines, phosphanes, arsanes, stilbanes. Preferred heteroatom-carrying groups as substituents are trialkylsilyls, in particular trimethylsilyl.
One or more CH fragments of the cyclic hydrocarbons can also be released by isoelectronic N or P or S fragments, e.g. pyrrolyl anion C
4
H
4
N
−
, phosphacyclopentadiene C
4
H
4
P
−
or arsacyclopentadiene C
4
H
4
As
−
. Suitable polymerization-inactive ligands are also anionic boron heterocycles such as diborolenyl or borinate. Preferred cyclic hydrocarbons are cyclopentadienyl, methylcyclopentadienyl, ethylcylopentadienyl, n-butylcyclopentadienyl, pentamethylcyclopentadienyl, trimethylsilylcyclopentadienyl, indenyl and fluorenyl.
Two identical or different cyclic hydrocarbons can also be bridged via a
Brintzinger Hans-Herbert
Feil Florian
Harder Sjoerd
Knoll Konrad
Weeber Armin
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