Polybutene-1 (co)polymers and process for their preparation

Details Polybutene-1 (co)polymers and process for their preparation Polybutene-1 (co)polymers and process for their preparation

1999-03-04

2001-10-23

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...

C526S065000, C526S124900, C526S125300, C526S348300, C526S348400, C526S348500, C526S901000, C526S902000, C526S904000

Reexamination Certificate

active

06306996

ABSTRACT:

The present invention relates to polybutene-1 (co)polymers and to a process for their preparation. The invention further relates to the articles obtained from the polybutene-1 (co)polymers of the invention. In particular the present invention relates to polybutene-1 (co)polymers characterized by high cristallinity and broad molecular weight distribution. Polybutene-1 (co)polymers are well known in the art. In view of their good properties in terms of pressure resistance, creep resistance, and impact strength they are mainly used in the manufacture of pipes to be used in the metal pipe replacement. Despite their good properties, the performances of polybutene-1 articles, and in particular pipes, sometimes resulted to be not completely satisfactory in terms of general mechanical performances and of pressure resistance in particular. Therefore, it would be desirable to improve the properties of said polybutene-1 (co)polymers, and in particular the mechanical properties, so as to have articles (in particular pipes) in which the pressure resistance (also called Burst Stress Resistance) is highly improved. The polybutene-1 (co)polymers are generally prepared by polymerizing butene-1 in the presence of TiCl
3
based catalysts components together with diethylaluminum chloride (DEAC) as cocatalyst. In some cases diethyl aluminum iodide (DEAI) is also used in mixtures with DEAC. The polymers obtained, however, generally do not show satisfactory mechanical properties. Furthermore, in view of the low yields obtainable with the TiCl
3
based catalysts, the polybutenes prepared with these catalysts have a high content of catalyst residues (generally more than 300 ppm of Ti) which lowers the properties of the polymers making it necessary a deashing step.
Polybutene-1 (co)polymers can also be obtained by polymerizing the monomers in the presence of a stereospecific catalyst comprising (A) a solid component comprising a Ti compound and an electron-donor compound supported on MgCl
2
; (B) an alkylaluminum compound and, optionally, (C) an external electron-donor compound.
A process of this type is disclosed in EP-A-17296. This process allows the preparation of polybutene-1 polymers having an intrinsic viscosity [&eegr;] of from 1.5 to 4, as measured in decalin at 135° C., an isotacticity value of at least 95% and a Molecular Weight Distribution (MWD), expressed in terms of Mw/Mn, of not more than 6. However, the mechanical properties shown by the polymers disclosed in said application are not completely satisfactory.
Accordingly, there is still a need of polybutene-1 copolymers having excellent mechanical properties and being capable of giving pipes with high burst stress resistance. It has now surprisingly been found that polybutene-1 (co)polymers characterized by very high cristallinity and broad molecular weight distribution meet the above requirements.
It is therefore an object of the present invention to provide polybutene-1 homopolymers, or copolymers containing up to 20% by weight of &agr;-olefins having from 2 to 10 carbon atoms other than butene- 1, characterized by the following properties:
(i) an isotactic index (mmmm %), measured by NMR analysis according to the method specified below, of higher than 93;
(ii) a Molecular Weight Distribution (MWD) in terms of Mw/Mn, measured by GPC analysis according to the method specified below, of higher than 6; and
(iii) a content of catalytic residues expressed in terms of Ti ppm of lower than 50.
Preferably, the (co)polymers of the present invention have an isotactic index higher than 94 and more preferably higher than 95. Moreover, polybutene-1 (co)polymers having a MWD higher than 7 and more preferably higher than 9 are highly preferred since it has been observed that the (co)polymers coupling very high cristallinity and very broad MWD have better mechanical properties. As explained above, also copolymers of butene-1 containing up to 20% by weight of &agr;-olefins, provided that they fulfill the above conditions, are within the scope of the present invention. Among the &agr;-olefins different from butene particularly preferred are those selected from the group consisting of ethylene, propylene and hexene-1. The copolymers of the present invention preferably contain from 2 to 15% by weight of such olefins and more preferably from 5 to 10% by weight.
While there is no particular limitation as to the molecular weight of the polymers, it is preferred that the (co)polymers have a Mw such that the Melt Index “E” is comprised in the range of from 100 to 0.01, more preferably from 10 to 0.1. In particular, when the polymers are used in the extrusion devices for the manufacture of pipes, polymers having a Melt Index in the range of from 1 to 0.1 and particularly from 0.3 to 0.5 are preferred.
The polymers of the present invention can be prepared by polymerization of the monomers in the presence of a stereospecific catalyst comprising (A) a solid component comprising a Ti compound and an internal electron-donor compound supported on MgCl
2
; (B) an alkylaluminum compound and, optionally, (C) an external electron-donor compound.
Magnesium dichloride in active form is preferably used as a support. It is widely known from the patent literature that magnesium dichloride in active form is particularly suited as a support for Ziegler-Natta catalysts. In particular, U.S. Pat. No. 4,298,718 and U.S. Pat. No. 4,495,338 were the first to describe the use of these compounds in Ziegler-Natta catalysis. It is known from these patents that the magnesium dihalides in active form used as support or co-support in components of catalysts for the polymerization of olefins are characterized by X-ray spectra in which the most intense diffraction line that appears in the spectrum of the non-active halide is diminished in intensity and is replaced by a halo whose maximum intensity is displaced towards lower angles relative to that of the more intense line.
The preferred titanium compounds used in the catalyst component of the present invention are TiCl
4
and TiCl
3
; furthermore, also Ti-haloalcoholates of formula Ti(OR)
n−y
X
y
, where n is the valence of titanium and y is a number between 1 and n, can be used.
The internal electron-donor compound may be selected from esters, ethers, amines and ketones. It is preferably selected from alkyl, cycloalkyl or aryl esters of monocarboxylic acids, for example benzoic acid, or polycarboxylic acids, for example phthalic or malonic acid, the said alkyl, cycloalkyl or aryl groups having from 1 to 18 carbon atoms. Examples of the said electron-donor compounds are methyl benzoate, ethyl benzoate and diisobutyl phthalate.
The preparation of the solid catalyst component can be carried out according to several methods.
According to one of these methods, the magnesium dichloride in an anhydrous state and the internal electron donor compound are milled together under conditions in which activation of the magnesium dichloride occurs. The so obtained product can be treated one or more times with an excess of TiCl
4
at a temperature between 80 and 135° C. This treatment is followed by washings with hydrocarbon solvents until chloride ions disappeared. According to a further method, the product obtained by co-milling the magnesium chloride in an anhydrous state, the titanium compound and the internal electron donor compound is treated with halogenated hydrocarbons such as 1,2-dichloroethane, chlorobenzene, dichloromethane etc. The treatment is carried out for a time between 1 and 4 hours and at temperature of from 40° C. to the boiling point of the halogenated hydrocarbon. The product obtained is then generally washed with inert hydrocarbon solvents such as hexane.
According to another method, magnesium dichloride is preactivated according to well known methods and then treated with an excess of TiCl
4
at a temperature of about 80 to 135° C. which contains, in solution, an internal electron donor compound. The treatment with TiCl
4
is repeated and the solid is washed with hexane in order to eliminate any non-reacted TiCl
4
.

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