Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-02-06
2003-04-29
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S348500, C526S348600
Reexamination Certificate
active
06555642
ABSTRACT:
The invention relates to a process for the manufacture of a solid catalytic component for the polymerization or copolymerization of olefins, resulting in a polymer or copolymer with broadened molecular mass distribution.
Some plastics conversion processes require the development of thermoplastic resins with broadened molecular mass distribution, including a high mass component and a low mass component at the same time. The high mass component gives the material consistency during its conversion. In blow-extrusion this component prevents the resin from flowing too rapidly, and this allows the resin to be better laid flat on the walls of the mould during the blowing to form a hollow body.
In addition, this high mass component gives the final material better mechanical properties like impact strength, stress cracking resistance and tensile strength.
The low mass component acts as a lubricant, and this makes the conversion of the resin easier.
A polymer or copolymer has a broadened molecular mass distribution if it has, at the same time, a high Mw/Mn, a high Mz/Mw and a high Mz, Mw denoting its weight-average molecular mass, Mn denoting its number-average molecular mass, and Mz denoting its z-average molecular mass. The ratio Mw/Mn is more representative of the broadening towards the low masses, whereas Mz/Mw and Mz are more representative of the broadening towards the high masses.
The production of catalysts producing such resins, and with high output efficiencies, is particularly difficult. A set of reactors in cascade is generally used, these having different polymerization conditions and each producing a specific population of molecular masses. Polymers or copolymers which have a broader molecular mass distribution overall are generally obtained by this means. However, while the catalyst itself produces a narrow distribution in a single reactor, the polymer or copolymer obtained by a set of reactors in cascade will exhibit as many narrow distributions as reactors (bimodal, trimodal distribution, and so on), the said distributions exhibiting a small degree of overlap between them. Such a composition runs the risk of giving rise to demixing phenomena during the conversion. In addition, it is with difficulty that such a molecular mass distribution also has, at the same time, a low proportion of high molecular masses and a low proportion of low molecular masses.
It is desired, furthermore, that thermoplastic resins should contain as few catalyst residues as possible. A low catalyst residue content gives the resin better heat stability and makes it necessary to employ smaller quantities of antioxidants. For example, in the case of Ziegler catalysts based on MgCl
2
/TiCl
4
, attempts are made to ensure that the titanium content in the final resin is as low as possible, because this expresses a low content of catalyst residues, that is to say not only a low content of titanium, but also of magnesium and chlorine.
The process according to the invention involves a solid support. This support gives the particles of catalytic component their shape. Thus, if it is desired that the catalytic component should have a substantially spherical shape, a support which has a substantially spherical shape can be chosen.
The catalytic component according to the invention does impart its shape to the growing polymer or copolymer: a good morphological replication exists between the final polymer or copolymer and the catalytic component and therefore also the solid support employed. This good morphological replication ensues from the absence of bursting of the particles as they grow, and this is additionally reflected in a small ratio of fine particles in the final polymer or copolymer. The presence of fine particles is not desired because when they are being conveyed, for example during a gas-phase polymerization, they become more easily charged electrically and tend to agglomerate on the walls. Thus, if it is desired to obtain a polymer or copolymer exhibiting good pourability, it is desirable that the polymer or copolymer particles should be substantially spherical, and this is obtained more easily by starting with the catalytic component according to the invention, by virtue of the good morphological replication during the polymerization or copolymerization and provided that a substantially spherical support has been chosen for the production of the said catalytic component.
The catalytic component according to the invention produces, with a high output efficiency, a polymer or copolymer exhibiting a high Mw/Mn, a high Mz/Mw and a high Mz, as well as a low transition metal content, generally lower than 6 ppm.
One characteristic of the solid support according to the invention is that it is easily dehydrated in comparison with the solid supports as employed in the prior art: within the scope of the present invention the solid support has at its surface at least 5 hydroxyl groups per square nanometer (OH
m
2
).
Documents EP 32,308, EP 529,978 and EP 296,021 describe the use of highly dehydrated silica in the context of the preparation of a solid catalytic component.
For EP 127,530 the silica was dehydrated at more than 600° C. under nitrogen purging, and this provides a high dehydration of its surface.
Document EP 239,475 describes the preparation of a catalytic component on a MgCl
2
support (free from hydroxyl groups) by reaction of an organic chlorine compound, in the presence of an electron-donor and of a mixture of an alkylmagnesium and of an organic aluminium compound, the organic chlorine compound, used in combination with an electron-donor, being reacted in the preliminary mixture of alkylmagnesium compound, of aluminoxane and/or of aluminosiloxane, and optionally of electron-donor. This document recommends, in particular, carrying out two successive chlorination treatments.
The process according to the invention includes a first stage including bringing into contact
a) a solid support including at its surface at least 5 hydroxyl groups per square nanometer (OH
m
2
) and
b) an organic magnesium derivative, and optionally, preferably,
c) an aluminoxane,
to obtain a first solid, and then a second stage including bringing the first solid and a chlorinating agent into contact to obtain a second solid and then, in a later stage, impregnation of the second solid with a transition metal derivative.
The solid support includes at its surface preferably 6 to 19 hydroxyl groups per square nanometer. The solid support is preferably a porous metal oxide. The metal oxide may be silica, alumina, magnesia or a mixture of at least two of these oxides. The metal oxide support preferably includes pores of diameter ranging from 7.5 to 30 nm (75 to 300 Å). At least 10 k of its total pore volume preferably consists of pores of diameter ranging from 7.5 to 30 nm (75 to 300 Å). The porous metal oxide support preferably has a porosity ranging from 1 to 4 cm
3
/g. The solid support preferably has a surface area ranging from 100 to 600 m
2
/g.
There are many means which make it possible to attain the recommended content of hydroxyl groups per unit area.
These means can depend on the chemical nature of the support. These means also make it possible to free the surface from water, which is desired. A simple means making it possible to attain the desired surface quality before bringing into contact with the organic magnesium derivative consists in heating the support under purging with an inert gas such as nitrogen or argon. To speed up the dehydration it is possible to heat the solid support under vacuum. Investigation of the conditions for obtaining the content of hydroxyl groups per unit area is within the ability of a person skilled in the art using routine tests. When the support is made of silica the desired surface quality is generally obtained by heating between 70 and 200° C. and preferably between 80 and 180° C. under nitrogen purging at atmospheric pressure for 2 to 4 hours.
The support's hydroxyl group content per unit area can be determined according to known techniques such as, for example
Brun Claude
Lacombe Jean-Loup
Malinge Jean
Elf Atochem S.A.
Rabago R.
Smith , Gambrell & Russell, LLP
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