Elastomeric copolymer of ethylene

Details Elastomeric copolymer of ethylene Elastomeric copolymer of ethylene

2000-02-07

2001-07-17

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...

C526S348000, C526S348200, C526S348400, C526S348600, C526S339000, C526S916000

Reexamination Certificate

active

06262215

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for the preparation of ethylene-based copolymers and, more particulary, it relates to a slurry process for the preparation of elastomeric copolymers of ethylene.
2. Description of the Prior Art
Among the ethylene-based elastomeric copolymers, only ethylene-propylene (EPM) and ethylene-propylene-diene (EPDM) elastomers are produced on a commercial scale, at the date of the present invention.
The industrial production of EPM and EPDM elastomers is currently carried out in the presence of Ziegler-Natta vanadium-based catalysts, by solution or slurry processes.
In the solution processes the comonomers are dissolved in a solvent, generally hexane, in which the formed polymer is soluble. In the slurry processes the reaction medium is essentially constituted by liquid olefins and the polymer is formed as a precipitate suspended in the liquid phase.
A slurry process offers a number of advantages over a solution process, namely:
no stirring viscosity problems;
very homogeneous reaction medium;
easier removal of the reaction heat;
increased reactor throughput owing to higher concentration of the polymer in the medium;
higher polymerization yields;
capability of producing very high MW polymers;
energy savings for the recovery of the polymer;
lower investment and production costs.
However, a major problem of a slurry process arises from the adhesive properties of the rubbery material. As a matter of fact, the solid particles of the polymer have a tendency to stick to one another or to the wall surface and to the agitating element of the reactor. This worsens to a large extent the diffusion of ethylene in the reaction medium and, what is more, causes intensive fouling of the reactor, thus rendering the preparation of the polymer very difficult.
In order to avoid such problems, a solvent, such as toluene or cyclohexane, can be added to the reaction medium, which acts both as antifouling agent and as vehicle of the catalyst system. The use of a low boiling diluent, such as propane, has also been proposed. As a result, however, the above indicated advantages of a slurry process are drastically decreased.
Another solution which has been proposed to render the process in bulk possible, is the addition of antistatic agents into the polymerization reactor. This solution, however, is not completely satisfactory and, moreover, has the drawback of introducing undesired compounds in the final product.
Recently, processes have been disclosed for the preparation of elastomeric ethylene-based copolymers in the presence of metallocene/alumoxane catalysts.
European patent application No. 347,128 discloses a process for producing an ethylene/&agr;-olefin elastomer in slurry polymerization, utilizing a zirconocene/alumoxane catalyst supported on a silica gel support. The examples relate to the preparation of ethylene/propylene copolymers in liquid propylene. It is said that, unless the supported catalyst is prepolymerized with ethylene or another &agr;-olefin before being used in the slurry polymerization process, the reactor fouling invariably occurs to a very large extent.
In European patent application No. 535,230, a slurry polymerization process for preparing an ethylene-based copolymer has been proposed, which prevents the occurence of fouling. This process is carried out in the presence of both a polysiloxane additive and a silica gel supported zirconocene/methylalumoxane catalyst. All of the examples relate to ethylene/propylene elastomers. In the comparative examples in which no polysiloxane additive has been used, clogging and jamming have been observed.
In International patent application PCT/EP93/01528, there is described a process for the preparation of ethylene/1-butene or ethylene/1-butene/diene elastomeric copolymers in the presence of a metallocene catalyst, wherein the reaction medium is substantially constituted of liquid 1-butene. This process is free of fouling phenomena of the reactor.
SUMMARY OF THE INVENTION
It has now unexpectedly been found that it is possible to prepare ethylene/propylene or ethylene/propylene/polyene elastomeric copolymers, containing small amounts of one or more alpha-olefins, by means of a slurry process, free of fouling phenomena of the reactor, wherein the reaction medium is substantially constituted of a mixture of liquid propylene and alpha-olefin, without resorting to supporting and/or prepolymerization treatments of the catalyst.
Therefore, it is an object of the present invention a process for the preparation of an elastomeric copolymer of ethylene, comprising the slurry polymerization reaction of a mixture comprising ethylene, propylene, at least 15% by weight of at least one alpha-olefin of formula (I):
CH
2
═CHR  (I)
wherein R is an alkyl radical containing from 2 to 10 carbon atoms and, optionally, small amounts of at least one polyene, in a reaction medium which essentially consists of liquid propylene and alpha-olefin together with the dissolved gaseous ethylene, in the presence of a non-prepolymerized catalyst based on a metallocene compound of a transition metal belonging to the Group IIIb, IVb, Vb, VIb and of Lanthanides of the Periodic Table of the Elements.
Another object of the present invention is an elastomeric copolymer of ethylene with propylene, at least one alpha-olefin and, optionally, with a polyene, obtainable with the process of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Catalysts suitable to be used in the process of the present invention are, for example, those comprising the product obtained by contacting:
(A) a metallocene compound of formula (II)
(C
5
R
1
5−m
)R
2
m
(C
5
R
1
5−m
) MQ
2
  (II)
 wherein
M is Ti, Zr, Hf or V; the C
5
R
1
5−m
groups, same or different, are cyclopentadienyl rings equally or differently substituted;
R
1
, same or different, are hydrogen atoms or alkyl, alkenyl, aryl, alkylaryl or arylalkyl radicals containing from 1 to 20 carbon atoms, which can also contain Si or Ge atoms, or Si(CH
3
)
3
groups, or also two or four substituted R
1
of a same cyclopentadienyl group can form one or two rings having from 4 to 6 carbon atoms;
R
2
is a group bridging the two cyclopentadienyl rings and is selected from CR
3
2
, C
2
R
3
4
. SiR
3
2
, Si
2
R
3
4
, GeR
3
2
, Ge
2
R
3
4
, R
3
2
SiCR
3
2
, NR
1
and PR
1
, wherein R
3
, same or different, are defined as R
1
or two or four substituents R
3
can form one or two rings having from 3 to 6 carbon atoms;
Q, same or different, are halogen atoms, hydrogen atoms, R
1
, OR
1
, SR
1
, NR
1
2
or PR
1
2;
m can be 0 or 1; optionally pre-reacted with an organometallic compound of aluminum of formula (III):
AlR
4
3−z
H
z
  (III)
 wherein R
4
, same or different, are alkyl, alkenyl or alkylaryl radicals containing from 1 to 10 carbon atoms, and z can be 0 or 1; and
(B) an alumoxane, optionally in admixture with an organometallic compound of aluminum of formula (III):
AlR
4
3−z
H
z
  (III)
 wherein R
4
and z are defined as above, or one or more compounds able to give a metallocene alkyl cation.
In the case in which m=0, particularly suitable cyclopentadienyl compounds are those in which the C
5
R
1
5−m
groups are cyclopentadienyl, pentamethyl-cyclopentadienyl, indenyl or 4,5,6,7-tetrahydroindenyl groups, and substituents Q are chlorine atoms, C
1
-C
7
hydrocarbyl groups, preferably methyl or hydroxyl groups.
Non limitative examples of cyclopentadienyl compounds of general formula (II), wherein m=0, are:
(Cp)
2
MCl
2
(MeCp)
2
MCl
2
(BuCp)
2
MCl
2
(Me
3
Cp)
2
MCl
2
(Me
4
Cp)
2
MCl
2
(Me
5
Cp)
2
MCl
2
(Me
5
Cp)
2
MMe
2
(Me
5
Cp)
2
M(OMe)
2
(Me
5
Cp)
2
M(OH)Cl
(Me
5
Cp)
2
M(OH)
2
(Me
5
Cp)
2
M(C
6
H
5
)
2
(Me
5
Cp)
2
M(CH
3
)Cl
(EtMe
4
Cp)
2
MCl
2
[(C
6
H
5
)Me
4
Cp]
2
MCl
2
(Et
5
Cp)
2
MCl
2
(Me
5
Cp)
2
M(C
6
H
5
)Cl
(Ind)
2
MCl
2
(Ind)
2
MMe
2
(H
4
Ind)
2
MCl
2
(H
4
Ind)
2
MMe
2
{[Si(CH
3
)
3
]Cp}
2
MCl
2
{[Si(CH
3
)

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