Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-08-15
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...
C526S128000, C526S136000, C526S142000, C526S161000, C526S340000, C526S903000
Reexamination Certificate
active
06399726
ABSTRACT:
FIELD OF THE INVENTION
The present invention concerns a method for the copolymerization of conjugated diolefins and vinyl-aromatic monomers in the presence of rare-earth catalysts and the use of the copolymers in rubber mixtures for tire applications.
BACKGROUND OF THE INVENTION
The polymerization of conjugated diolefins has been known for some time and has been described for example by W. Hoffmann, Rubber Technology Handbook, Hanser Publishers (Carl Hanser Verlag) Munich, Vienna, New York, p. 52 ff., 1989. Thus, polybutadiene, for example, is now predominantly manufactured by solution polymerization with the aid of Ziegler-Natta coordination catalysts, based on titanium, cobalt, nickel and neodymium compounds, for example, or in the presence of alkyl lithium compounds. The solvent used in each case is very much determined by the type of catalyst used. Benzene or toluene and aliphatic or cycloaliphatic hydrocarbons are preferably used.
U.S. Pat. No. 5,096,970 and EP-30 40 88 describe a method for the manufacture of polybutadiene in styrene using catalysts based on neodymium phosphonates, organic aluminum compounds such as di(isobutyl)aluminum hydride (DIBAH) and a halogen-containing Lewis acid, such as ethyl aluminum sesquichloride, whereby butadiene in styrene is reacted to a cis-1,4-polybutadiene with no further addition of inert solvents. A disadvantage of this catalyst is that styrene-butadiene copolymers cannot be formed in this case.
The use of anionic initiators for the polymerization of butadiene and styrene in hexane is known from U.S. Pat. No. 4,540,744. A disadvantage of the method described is that under conditions relevant to applicational practice control of the cis/trans ratio in the butadiene component is possible to only a limited extent, as is the achievement of elevated cis contents. High cis contents are advantageous for applications in the area of tire and synthetic resin modification, however.
A disadvantage in the use of anionic initiators lies in the fact that these initiators allow little control over the microstructure. For example, under conditions relevant to applicational practice, anionic initiators cannot be used to produce a high cis-containing SBR with a cis-1,4 content of over 50%. The addition of modifiers serves only to increase the content of 1,2 units, whereby the 1,2 content leads to a rise in the glass transition temperature of the polymer. This fact is particularly disadvantageous because this method produces SBR in which the rising styrene content in comparison with homopolymeric polybutadiene (BR) causes a further rise in the glass transition temperature. Where SBR rubber is used for impact modification of HIPS or ABS, for example, a high glass transition temperature of the rubber has a negative influence on the low-temperature impact strength of the material, however, as a consequence of which rubbers with low glass transition temperatures are preferred.
In J. Polym. Sci., Part A, Polym. Chem., 33 (1995) 2175 and 36 (1998) 241, for example, Kobayashi, et al. describes a catalyst system consisting of halogenated rare-earth acetates such as Nd(OCOCCl
3
)
3
or Gd(OCOCF
3
)
3
, with tri(isobutyl) aluminum and diethyl aluminum chloride, which permit the copolymerization of butadiene and styrene in the inert solvent hexane. The disadvantage of these catalysts is that even with a low styrene component of around 5 mol % the catalyst activity falls below 10 g polymer/mmol catalyst/h and that the 1,4-cis content of the polymer falls significantly as the styrene content rises. As a further disadvantage of this method, the microstructure of the polybutadiene segments in the SBR obtained cannot be controlled by the addition of suitable modifiers.
A method for the polymerization of conjugated diolefins with vinyl-aromatic compounds is known from patent application PCT/EP 99/04741 wherein the polymerization is performed in the presence of catalysts based on rare-earth compounds, organoaluminum compounds and optionally cyclopentadienes, whereby the aromatic vinyl compounds used serve as solvent.
The copolymers produced according to this method are used especially for the manufacture of ABS resins. The ABS resin can be manufactured in this instance by performing the copolymerization as a first step and polymerizing the styrene remaining in the reaction mixture in a second polymerization stage, using styrene as solvent. This second reaction step can be performed in the presence of conventional aliphatic or aromatic solvents.
The disadvantage of the polymerization of conjugated dienes and vinyl-aromatic monomers without inert solvents as performed by the method described in the cited patent application is that, for example, technical recovery of the copolymer obtained is difficult as the vinyl-aromatic monomers used as solvents are copolymerized to only a very small degree, which can lead to an undesirable post-polymerization of the reactive monomers during separation, e.g. by stripping.
SUMMARY OF THE INVENTION
Therefore, the object of the present invention was to provide a method for the copolymerization of conjugated diolefins and vinyl-aromatic monomers whereby copolymers are obtained in which the polymer composition in terms of the content of vinyl aromatics and diolefins and in terms of the selectivity of the polymerized diolefins, i.e. the content of double bonds in the cis position and of 1,2 units with lateral vinyl groups, for example, can be varied, whereby the glass transition temperature of the polymer is below −20° C., preferably below −55° C., measured by DSC. Moreover, the copolymers obtained should be easily recoverable from the reaction mixture.
The catalyst systems according to the present invention offer the possibility of adjusting the cis content and hence the ratio of the cis to the trans component independently of the styrene content. This possibility for variation does not exist with the known lithium alkyl-based catalyst systems used in the art under conditions relevant to applicational practice, as here the cis/trans ratios are fixed.
It is known that the compounds for tire mixtures, especially for the tread, are composed of several rubbers in order to obtain the best possible properties, such as rolling resistance, abrasion and wet skid resistance. These rubbers are generally natural rubber and synthetic rubbers such as polybutadiene, butadiene-styrene rubber or polyisoprene. One problem arising from the use of rubber mixtures lies in the fact that incompatibilities can occur between the individual rubber grades. Such incompatibilities may be evidenced by increased tire abrasion, lower tear propagation resistance and a shorter working life for the tire.
It is also known that the relation between rolling resistance and wet skid resistance can be influenced by the styrene content of the butadiene-styrene rubber, a rubber with a high styrene content offering advantages in terms of wet skid resistance, for example.
With the catalyst system according to the present invention, it is now possible to adjust styrene contents selectively in order to obtain an optimum of safety and wet skid resistance and also to ensure compatibility within the rubber mixture, manifested by low abrasion and a long working life, by setting a suitable cis/trans ratio.
The object of the present invention is further to provide copolymers of conjugated diolefins and aromatic vinyl compounds which by virtue of their high content of double bonds in the cis position and the possibilities for varying the content of lateral vinyl groups are extremely suitable for use in tire construction.
DETAILED DESCRIPTION OF THE INVENTION
Therefore, the present invention provides a method for the copolymerization of conjugated diolefins with vinyl-aromatic compounds, characterized in that the polymerization of the conjugated diolefins with the vinyl-aromatic compounds is performed in the presence of catalysts comprising:
a) at least one rare-earth metal compound,
b) at least one cyclopentadienyl compound and
c) at least one organo-aluminum compound
or comprisin
Engehausen Rüdiger
Giebeler Ellen
Schertl Peter
Trimbach Jürgen
Windisch Heike
Bayer Aktiengesellschaft
Cheung Noland J.
Gil Joseph C.
Seng Jennifer R.
Teskin Fred
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