Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-01-04
2004-02-17
Choi, Ling-Siu (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S158000, C526S142000, C526S124100, C526S124300
Reexamination Certificate
active
06693161
ABSTRACT:
The present invention relates to a process for the preparation of random copolymers of propylene with ethylene or other &agr;-olefins. The invention moreover relates to random propylene copolymers which have excellent properties in terms of low content of xylene-solubles. In particular, the present invention relates to a process for the preparation of random propylene copolymers, carried out in the presence of a catalytic system comprising: (A) a solid component comprising a Ti compound supported on MgCl
2
and an electron-donor compound, (B) an alkylaluminium compound and (C) an external electron-donor compound selected from the group of 1,3-diethers.
Copolymers containing from 85 to 99% by weight of propylene and from 1 to 15% by weight of ethylene and/or another &agr;-olefin, in which the comonomer is randomly distributed in the polypropylene chain, are generally known as random propylene copolymers. Compared with propylene homopolymers, the said copolymers have a molecular structure which is disturbed by the presence of the comonomer, leading to a substantially inferior degree of crystallinity therein. As a result, random copolymers have a sealing temperature and a modulus of elasticity which are lower than those of propylene homopolymers. These characteristics make the said copolymers particularly useful in the preparation of films or articles in which improved impact resistance and low sealing initiation temperatures (S.I.T.) are required. However, the introduction of the comonomer into the polypropylene chain leads to a significant increase in the fraction of polymer which is soluble in xylene at 25° C., the said soluble polymer being mainly composed of low molecular weight chains and containing percentages of comonomer which are higher than the average content of comonomer calculated on the basis of the total polymer. The amount of soluble fraction generally increases as the content of comonomer in the copolymer increases and, beyond defined limits, precludes the use of the copolymers in certain sectors, for example in the preparation of films for wrapping food, unless recourse is made to a costly stage of elimination of the soluble fraction. The presence of relevant amounts of the said fractions therefore decreases the flowability of the polymer granules, thereby making operations such as discharging and transferring the polymer difficult and giving rise to problems of management of the polymerization plant. Moreover, the presence of the said soluble fractions in significant amounts leads over time to phenomena of deterioration of the optical properties owing to migration of these fractions to the surface (blooming).
It is therefore necessary to have available a catalyst which has a tendency to produce low levels of soluble fractions and which, at the same time, is capable of distributing the comonomer satisfactorily in the polypropylene chain so as to obtain the desired effect (lowering of the modulus and/or lowering of the sealing initiation temperature) with low contents of comonomer. Moreover, the said catalyst must possess an activity such that it produces a copolymer which has very low levels of catalytic residues (Ti<15 ppm), so as to make a further removal stage unnecessary. It is known from European patent EP-B-318,049 that stereorigid and chiral zirconocenes used as catalysts in the polymerization of olefins are capable of giving, in high yields, random propylene copolymers having a low content of xylene-solubles. However, the said copolymers have a very narrow molecular weight distribution which makes them difficult to process using standard techniques and process apparatus.
European patent application EP-A-341,724 describes a process for the preparation of random propylene copolymers carried out in the gas phase, in the presence of a catalytic system consisting of: a solid catalytic component (i) consisting of magnesium, titanium, halogen and an electron-donor compound belonging to the group of polycarboxylic acid esters; an alkylaluminium (ii); an external electron-donor compound (iii) having at least one Si—O—C bond. The amount of xylene-solubles in the copolymers is, however, still high (19% by weight of solubles with 6.7% by weight of ethylene).
It has now surprisingly been found a process which is capable of providing, in high yields, random propylene copolymers having a particularly low content of xylene-soluble fractions. It is therefore an object of the present invention a process for the preparation of propylene copolymers containing up to 15% by weight of ethylene and/or of an &agr;-olefin CH
2
═CHR
1
, where R
1
is a hydrocarbon radical having from 2 to 10 carbon atoms, the said process being carried out in the presence of a catalyst comprising:
(A) a solid component comprising a Ti compound containing at least one Ti-halogen bond supported on magnesium chloride in active form and an electron-donor compound;
(B) an alkyl-Al compound; and
(C) an electron-donor compound selected from the group of 1,3-diethers of formula (I):
in which R, R
I
, R
II
, R
III
, R
IV
and R
V
, which are identical or different, are hydrogen or linear or branched alkyl radicals, cycloalkyl radicals, aryl radicals, alkylaryl radicals or arylalkyl radicals having 1-18 carbon atoms, with the proviso that R and R
I
cannot simultaneously be hydrogen; R
VI
and Ru
VII
, which are identical or different, are linear or branched alkyl radicals, cycloalkyl radicals, aryl radicals, alkylaryl radicals or arylalkyl radicals having 1-18 carbon atoms; at least two of the said radicals from R to R
VII
can be linked together to form one or more cyclic structures.
The &agr;-olefin CH
2
═CHR
1
is preferably butene or hexene. The magnesium chloride in active form present in the solid component (A) is widely known in the art and is characterized by an X-ray spectrum in which the most intense diffraction line appearing in the spectrum of the non-activated chloride shows a decreased intensity and in said spectrum a halo appears the maximum intensity of which is shifted towards lower angles with respect to those of the most intense line. The preferred Ti compounds are TiCl
4
and TiCl
3
; however, Ti haloalkoxides of formula Ti(OR)
n-y
X
y
, where n is the valency of the titanium and y is a number between 1 and n, can also 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 maleic 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 solid component (A) can conveniently be prepared by reaction between a titanium compound of formula Ti(OR)
n-m
X
m
, where n is the valency of the titanium and m is a number between 1 and n, and a MgCl
2
·pROH adduct, where p is a number from 0.1 to 4 and R is a hydrocarbon radical having 1-18 carbon atoms. The adduct can conveniently be prepared in spherical form by mixing the alcohol and the magnesium chloride, under stirring conditions, in an inert hydrocarbon which is immiscible with the adduct and operating at the melting point of the adduct (100-130° C.). The emulsion thus obtained is then cooled rapidly, causing the adduct to solidify in the form of spherical particles. Examples of the preparation of adducts in spherical form are described in U.S. Pat. No. 4,399,054. The so obtained adduct generally contains from 2 to 4 moles of alcohol per mole of MgCl
2
. The adduct can be directly reacted with the titanium compound or can be previously subjected to a thermal controlled dealcoholation (between 80 and 130° C.) so as to reduce the alcohol content to less than 2 mol, preferably between 0.1 and 1.5 mol.
The reaction between the adduct and the titanium compound (preferably TiCl
4
) can be carried out by suspending the MgCl
2
-alcohol adduct in cold (generally 0° C.) TiCl
4
; the mixture
Collina Gianni
Morini Giampiero
Bryan Cave LLP
Bsell North America Inc.
Choi Ling-Siu
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