Polyolefin production

Details Polyolefin production Polyolefin production

2000-09-18

2001-07-24

Sergent, Rabon (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S170000, C526S351000

Reexamination Certificate

active

06265503

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a metallocene compound for use as a catalyst component in the production of short sequence syndiotactic/isotactic block polyolefins, catalyst systems containing the metallocene compound and their use in processes for the production of such polyolefins.
BACKGROUND OF THE INVENTION
Olefins having 3 or more carbon atoms can be polymerised to produce a polymer with an isotactic stersochemical configuration. For example, in the polymerisation of propylene to form polypropylene, the isotactic structure is typically described as having methyl groups attached to the tertiary carbon on atoms of successive monomeric units and the same side of a hypothetical plane through the main chain of the polymer. This can be described using the Fischer projection formula as follows:
Another way of describing the structure is through the use of NMR spectroscopy. Bovey's NMR nomenclature for an isotactic pentad is . . . mmmm with each “m” representing a “meso” diad or successive methyl groups an the same side in the plane.
In contrast to the isotactic structure, syndiotactic polymers are those in which the methyl groups attached to the tertiary carbon atoms of successive monomeric units in the chain lie an alternate sides of the plane of the polymer. Using the Fischer projection formula, the structure of a syndiotactic polymer is described as follows:
In NMR nomenclature, a syndiotactic pentad is described as . . . rrrr . . . in which “r” represents a “racemic” diad with successive methyl groups on alternate sides of the plane.
In contrast to isotactic and syndiotactic polymers, an atactic polymer exhibits no regular order of repeating unit. Unlike syndiotactic or isotactic polymers, an atactic polymer is not crystalline and forms essentially a waxy product.
The production of syndiotactic/isotactic block polypropylene is known from EP-A-0747406. In these known block polypryoplylenes there is a long isotactic block and few short syndiotactic blocks, A generically defined metallocene compound is disclosed as a catalyst component in the production of these block polypropylenes. The metallocene compound has a cyclopentadienyl ring which is monosubstituted, as exemplified by isopropylidene (3-trimethylsilylcyclopentadienyl-9-fluorenyl) zirconium dichloride and diphenylmethylidene(3-trimethylsilyl cyclopentadienyl-9-fluorenyl) zirconium dichloride.
The production of syndictactic/atactic block polyolefins is known from EP-A-0818475. In these known block polypropylenes there are alternating blacks of long syndiotactic and short atactic sequences. A generically defined metallocene compound is disclosed as a catalyst component in the production of these block polyolefins. The metallocene compound requires a hetero-exemplified atom ligand coordinated to the metal of the metallocene, as exemplified by 2,7-bis-tert-butyl-fluorenyl-9-dimethylsilyl-tert-butyl-amido titanium dichloride.
In EP-A-0423101 and EP-A-0742227 a metallocene compound is described which has a lack of bilateral symmetry, one example of which is isopropylidene (3-methyl cyclopentadienyl-1-fluorenyl)zirconium dichloride. This compound was used in the production of hemiisotactic polypropylene. The structure of hemiisotactic polymers may be represented in a Fischer projection as follows:
The monomeric unit of the polymer is of the following structure:
wherein R
s
is a hydrocarbyl group or nonhydrocarbyl group.
The structure of the polymer is characterised by R
s
groups attached to every other asymmetric carbon atom being on the same side of the principal polymer chain as represented in a Fischer projection and R
s
groups attached to the remaining asymmetric carbon atoms being either on the same side or the opposite side of the principal polymer chain. Since only every other one conforms to the isotactic structure, it is “hemi”. The material is a noncrystalline polymer.
SUMMARY OF THE INVENTION
The present applicants have surprisingly found that short sequence syndiotactic/isotactic block polypropylenes can be prepared which have high clarity and elastomeric properties using an —aryl—substituted metallocene compound as a catalyst component.
The present invention provides a C
1
symmetric metallocene compound of general formula R″(CpR
n
) (Cp′R′
m
) MQ
p
for use as a catalyst component in the production of short sequence syndictactic/isotactic block polyolefins, wherein Cp is a substituted cyclopentadienyl; each R is independently aryl or hydrocarbyl having 1 to 20 carbon atoms, at least position 3 of Cp is substituted with aryl, at least one other position of Cp is substituted with a non-bulky substituent, and n is an integer in the range from 2 to 4; Cp′ is substituted or unsubstituted fluorenyl; each R is independently hydrocarbonyl having 1 to 20 carbon atoms and m is O or an integer in the range 1 to 8; R″ is a structural bridge to impart stereorigidity between Cp and Cp′; M is a metal from Group IIIB, IVB, VB or VIB; Q is a hydrocarbyl radical having 1 to 20 carbon atoms or a halogen; and p is the valence of M minus 2.
The polyolefin is preferably polypropylene. By short sequence syndiotactic/isotatic block polypropylene is meant a polypropylene that comprises alternating blacks of syndiotactic and isotactic sequence. Preferably, the average sequence length of each sequence is in the range 5 to 20, more preferably 5 to 10, most preferably around 6. The relative frequency of each sequence is typically in the range 1:3 to 3:1.
Preferably the isotactic and syndiotactic sequences have approximately the same length and frequency.
In the metallocene compound, the non-bulky substituent is preferably a linear hydrocarbyl having 1 to 20 carbon atoms, isobutyl or aryl. The non-bulky substituent should not interfere with the bridge and could be situated at position 2 and/or position 5, preferably at position 5. Cp is preferably substituted at position 3 of the ring with Ph.
The metal, M, is preferably Ti, Zr or Rf and Q is preferably a halogen, usually Cl. Typically R″ is alkylidene having 1 to 20 carbon atoms, a dialkyl germanium or silicon or siloxhane, alkyl phosphine or amine, preferably a hydrocarbyl radical having at least one carbon atom to form the bridge. More preferably R″ is isopropylidene.
In a further aspect there is provided a catalyst system for use in preparing short sequence syndiotactic/isotactic block polyolefins, which comprises (a) a metallacens compound as defined above; and (b) a cocatalyst capable of activating the metallocene compound. Typically, the cocatalyst comprises an aluminium- or boron-containing cocatalyst.
Suitable aluminium-containing cocatalysts comprise an alumoxane, an alkyl aluminium and/or a Lewis acid.
The alumoxanes usable in the process of the present invention are well known and preferably comprise oligameric linear and/or cyclic alkyl alumoxanes represented by the formula:
for oligomeric, linear alumoxanes and
for oligomeric, cyclic alumoxane,
wherein n is 1-40, preferably 10-20, m is 3-40, preferably 3-20 and R is a C
1
-C
8
alkyl group and preferably methyl. Generally, in the preparation of alumoxanes from, for example, aluminium trimethyl and water, a mixture of linear and cyclic compounds is obtained.
Suitable boron-containing cocatalysts may comprise a triphenylcarbenium baroizate such as tetrakis-pentafluorophonyl-borato-triphenylcarbenium as described in EP-A-0427696, or those of the general formula [L
1
—H]+[B Ar
1
Ar
2
X
3
X
4
]— as described in EP-A-0277004 (page 6, line 30 to page 7, line 7).
The catalyst system may be employed in a solution polymerisation process, which is homogeneous, or a slurry proceima, which is heterogeneous. In a solution process, typical solvents include hydrocarbons with 4 to 7 carbon atoms such as heptane, toluene or cyclohexane. In a slurry process it is necessary to immobilise the catalyst system on an inert support, particularly a porous solid support such as talc, inorganic oxides and resinous support materials such as polyo

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