Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-09-26
2003-06-10
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S240000
Reexamination Certificate
active
06576710
ABSTRACT:
The invention relates to a process for the preparation of &agr;-olefin polymers, especially polypropene, having a controlled stereoregularity, comprising the successive steps of: (i) producing a first polymerization product by contacting under polymerization conditions an &agr;-olefin monomer with a polymerization catalyst system comprising a transition metal compound, a first organometal compound and a stereoregulating external electron donor, to give a first polymerization reaction mixture; (ii) producing a second polymerization product by contacting an &agr;-olefin monomer with at least the first polymerization reaction mixture.
The word “comprising” means that the subsequently listed subject matter must be included, but that further subject matter may also be included. It is open. See Grubb, P. W., Patents in Chemistry and Biotechnology, Clarendon Press, Oxford, 1986, p. 220.
The first and second polymerization products may have the same or different melt flow rate (MFR) values. The MFR values disclosed here are measured according to the standard ISO 1133 at 230° C. using a 2.16 kg load.
By &agr;-olefin monomer is in this connection meant an &agr;-olefin which is capable of polymerization by the insertion (Ziegler-Natta) mechanism. An &agr;-olefin is a compound having the structure CH
2
═CHR, wherein R is a linear or cyclic alkyl group. Typical &agr;-olefin monomers of the invention are propene (R=—CH
3
), butene-1 (R=—CH
2
CH
3
), 4-methylpentene-1 (R=CH
2
CH(CH
3
)
2
), hexene-1 (R=—(CH
2
)
3
CH
3
) and octene-1 (R=—(CH
2
)
5
CH
3
). By an &agr;-olefin polymer is meant an &agr;-olefin homopolymer or copolymer. As monomers to be copolymerized can, in addition to &agr;-olefin monomers of the above mentioned type, also be used ethene. By transition metal compound is in this connection meant a transition metal compound which is capable of contributing to the polymerization ability of said polymerization catalyst system. The transition metal compound is the basis of the Ziegler-Natta system's so called “catalyst” or “procatalyst”. By first organometal compound is in this connection meant an organometal compound which is capable of contributing to the polymerization ability of said polymerization catalyst system. The organometal compound is also called the “cocatalyst” of the Ziegler-Natta system.
The presence of a stereoregulating electron donor in an &agr;-olefin polymerization catalyst produces a stereospecific polymer. Such a polymer usually has high isotacticity, i.e. a high portion of &agr;-olefin mers in the macromolecular chain having the same configuration with respect to a common direction along the chain. With propene polymers, the isotactic index I.I., measured as the percentage of a polypropene sample which is insoluble in boiling n-hexane, or the xylene soluble fraction XS thereof, is a measure of the isotacticity of the polymer. Isotactic macromolecules are associated and crystallized whereby their solubility is lower. Thus, the lower the XS of an &agr;-olefin polymer, the higher is its isotacticity. The isotacticity may also be measured by Fourier Transform Infrared Spectroscopy (FTIR).
The preparation of highly stereoregular polymers of C
3
-C
10
-&agr;-olefins, such as propene, in many phases or steps, is known e.g. from JP Patent Application 91048, EP Patent Specification 339 804 and FI Patent Application 961722.
According to the examples of the last mentioned document, propylene is in a first step polymerized in the presence of an MgCl
2
/TiCl
4
/Et
3
Al/D (D=stereoregulating external electron donor, Et=ethyl) type catalyst system and no or little hydrogen as molar mass limiting termination agent into a stereoregular propylene polymer having a low MFR, and in a second step polymerized in the presence of the same catalyst system and a large amount of hydrogen termination agent into a stereoregular propylene polymer having a high MFR. The result is a stereoregular propene polymer product having a broad molar mass distribution in the form of a low MFR (high molar mass) fraction and a high MFR (low molar mass) fraction.
It is assumed that the overall high stereoregularity and the presence of a polymer fraction of low MFR gives good strength and rigidity as well as low creep to the polymer product. The presence of a polymer fraction of high MFR, on the other hand, gives good melt processability and flexibility to the polymer product.
In multi-phase or -stage processes of the above mentioned type for the preparation of &agr;-olefin polymers, the isotacticities tend to vary between the phases or stages of the process, due to different conditions and donor concentrations, and control of the isotacticity is sometimes difficult. For example, if the average XS of the product in the preceding step is 3-3.5%, in the subsequent step it might have decreased to only 2-2.5%. In practice, this means that the polymer fraction produced in the subsequent step or steps has an XS of below 1.5%. In some applications such as in film and fibre products the isotacticity of the propene polymer needs to be controlled to give an XS value of about 3.5-4%. In order to reach such XS values for the final product in an uncontrolled propene polymerization process, the XS in the first reactor should be more than 5%, because the second reactor is producing an XS of only 2-3%. However, this kind of isotacticity and crystallinity difference between the materials of the first and second steps results in homogeneity problems which can be detrimental for the film and fibre products.
The above mentioned problems and findings relating to the multi-stage production of &agr;-olefin polymer products have now been dealt with principally in the following way.
As was previously mentioned, the present invention relates to a process for the polymerization of an &agr;-olefin polymer having controlled stereoregularity. In the process, a first and a second polymerization product are produced by contacting an &agr;-olefin with a high activity polymerization catalyst system comprising a first organometal compound in two steps (i) and (ii).
Now, it has been realized that the above mentioned problem can be solved, if in the process, the second polymerization product is produced in the presence of a stereoregularity controlling agent in step (ii). The stereoregularity controlling agent is selected from a second organometal compound which contains, on an atom basis, more halogen per metal than the first organometal compound, or 0.01-1.2% of an olefin which is not said used &agr;-olefin monomer(s), calculated on the total molar amount of the olefin and the &agr;-olefin monomer(s).
It has also been found that in view of the quality of some end products, more important than the level of XS of the polymer obtained from the reactor system is that the XS values are essentially on the same level in every phase or stage of the process. Especially very good quality fibres and films, but also different molding applications are achieved with polymers, which are produced in multi-phase or -stage process where isotacticities, i.e. XS values, are controlled to essentially the same level in every phase or stage.
According to a preferred embodiment of the present invention, controlling the stereoregularity means especially controlling the stereoregularity to essentially the same level in every phase or stage of the process, i.e. the isotacticities or XS values are balanced in every phase or stage of the process.
The improvements obtained by using a more halogenated organometal compound and/or small amounts of olefins when producing the second polymer fraction are verified by the examples.
The polymer products prepared according to the process of the invention may be unimodal polymers or bimodal polymers with narrow or more or less broad molecular mass distribution. MFR values can vary in wide ranges from 0.03 to 2000 g/10 min. Unimodal polymers, i.e. polymers having the same MFR values in every phase are especially suitable e.g. for fibre applications.
The &agr;-olefin monom
Garoff Thomas
Huovinen Päivi
Leskinen Pauli
Birch & Stewart Kolasch & Birch, LLP
Borealis Technology Oy
Nutter Nathan M.
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