Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Plural component system comprising a - group i to iv metal...
Patent
1994-08-10
1997-11-11
Caldarola, Glenn A.
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Plural component system comprising a - group i to iv metal...
502119, 502150, 502152, 502154, 502158, 526127, 526128, 585502, 585506, 585507, 585530, 585532, B01J 3100, C08F 444, C08F 402, C07C 202
Patent
active
056863713
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/GB92/01645 filed on Sep. 9, 1992.
This invention relates to the polymerisation of one or more conjugated dienes. In particular, it relates to a process for the polymerisation of one or more conjugated dienes carried out using a rare earth based catalyst to give a polymer containing high contents of cis isomer, for example 93% or more, preferably 97% or more.
Several catalyst systems are known to cause the polymerisation of one or more conjugated dienes to give a polymer containing high contents of cis isomer. For many years such systems were based on a transition metal compound such as a titanium, cobalt or nickel compound. More recently, catalyst systems have been devised based on a compound of a so-called rare earth (lanthanide) element, i.e. an element having an atomic number of 57 (lanthanum) to 71 (lutetium), which give diene polymers with a very high cis content. The development of rare earth based polymerisation catalysts is reviewed, for example, in Bruzzone, M. "Elastomers and Rubber Elasticity", Ch. 2., A.C.S. Symposium Series No. 193, 1982 and Gargani L. et al "Rare Earth Catalysts for High Cis Polybutadiene" Paper I-14 Proceedings Int. Rubber Conf. Paris 1982. For reasons of activity, compounds of cerium, lanthanum, praseodymium, neodymium or gadolinium are preferred. A particularly preferred catalyst is formed from (a) a rare earth salt (e.g. a neodymium salt), preferably hydrocarbon soluble, (b) an organo aluminium cocatalyst and (c) a source of halogen.
Although rare earth based catalysts give the desired very high cis polydienes, one problem with such catalysts is the difficulty of controlling the molecular weight (Mw and Mn) and/or the molecular weight distribution (Mw/Mn) of the diene polymer product, particularly in a continuous polymerisation system.
The molecular weight and molecular weight distribution of diene polymers are important characteristics since they affect the processing characteristics of the diene polymer, such as the processability and carbon black incorporation time, the physical properties of the cured polymer and also the solution viscosity of the raw polymer in styrene, which is of great importance in the production of high impact polystyrene. Broad molecular weight distribution is characteristic of the majority of olefinic and diene polymers prepared with Ziegler type catalysts. Typical values range from about 3 to more than 10 and seem to be largely independent of the transition metal/rare earth compound used in the catalyst. In rare earth based catalysts, some control can be exercised over polymer molecular weight by, for example, varying the aluminium to rare earth ratio in the catalyst, and/or controlling the catalyst level and/or the degree of conversion. However, as with most Ziegler type catalysts, molecular weight distribution is generally much more difficult to control.
The difficulty in controlling the molecular weight of diene polymers prepared with rare earth type catalysts is referred to in U.S. Pat. No. 4,663,405 (Goodyear Tire/EniChem Polimeri) which describes and claims the use of vinyl halides as molecular weight regulators for polymerisations which are catalysed with lanthanide and actinide catalyst systems. However vinyl halides also affect molecular weight distribution, in many cases broadening it (see Tables III, IV and VI of this U.S. patent), whereas a narrow molecular weight distribution is desirable for many applications.
We have now found a method of preparing a rare earth catalyst which, when used in the polymerisation of conjugated dienes, offers the possibility of producing a diene polymer of narrower molecular weight distribution and/or smaller high molecular weight fractions.
According to the present invention a process for the polymerisation of one or more conjugated dienes by means of a catalyst comprising a rare earth salt, an organo aluminium cocatalyst and a source of halogen is characterised in that the catalyst is formed by bringing together in liquid hydrocarbon medium in the presence of a small
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L. Gargani, et al., "Rare Earth Catalysts for High Cis Polybutadiene", Proceedings Int. Rubber Conference, Paper 1-14, Jun. 1982, pp. 1-4.
"Elastomers and Rubber Elasticity", Synthetic Aspects of Crystallizable Elastomers, Bruzzone, Ch. 2., A.C.S. Symposium Series No. 193, 1982. no month available.
"Rare Earth Catalysts for High Cis Polybutadiene", Paper 1-14, Proceedings Int. Rubber Conf., Paris 1982. no month available.
Chemical Abstracts, vol. 109, No. 4, 1988 Abstract No. 24077A. no month available.
Ansell Peter John
Williams Hugh David
Caldarola Glenn A.
Enichem Elastomers Ltd.
Pasterczyk J.
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