Note: Descriptions are shown in the official language in which they were submitted.
3~4~ .
1.
This invention relates to particular polymers of
ethylene having a linear structure (-that is substantially
devoid of legthy brancing oils having a density lower than
0.9450 g/cm . More particularly, the invention relates to
copolymers of ethylene with at least another alpha-olefin
having densities comprised in the range from 0.9150 and
0.9450 g/cm3 and also relates to the methods for preparing
such polymers.
It is already known (for example, Brit. Patent N
1 131 528 and US Patent N 4 067 882), that it is possible
to obtain linear polyethylene having a low or a medium
density by low pressure polymerization processes, during
progress of which ethylene is copolymerized with another
: alpha-olefin, butene-l or octene-l preferably, in the presence
: of Ziegler type catalysts or, at any rate, in the presence of
; catalytic systems of the kind conventionally employed for
the preparation of poly-alpha-olefines.
; Such linear low-density copolymers differ from the
conventional low-density polyethylene (as obtained with
:~ 20 radicalic high-pressure procedures) not only for their linear
: structure rather than branched off, but, above all, for the
considerable improvement of a few properties such as the
modulus and the elongation-at break as illustrated by the
Table reported hereunder:
Density Melt Flexural Elonga- Tensile
Flow Modulus tion at Strength
Index break
g/cm g/10 min MPa % MPa
, = , _
Linear LDPE 0.9213 2.0 278 617 14.9
30 Conventional 0.9230 2.0 214 545 10.0
LDPE
LDPE = Low Density Polyethylene
I
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2.
The linear low density polyethylene has a higher
mechanical resistance than the conventional low density poly-
ethylene and this property, for example in the processing
runs for obtaining films, may make it possible to save up to
30% of the product and appreciable advantages are achieved
in injection moulding and in the manufacture of filaments and
cables by virtue of the improved mechanical properties at the
low temperatures, such as shock resistance and the properties
of the copolymers are a function of the distribution of the
comonomer in the polymeric chain.
The present invention, in particular, provides
ethylene copolymers with at least one other alpha olefin
comonomer having, as a function of the quantity of comonomer
which is present, densities comprised in the range from
0.9150 g/cm3 to 0.9450 g/cm3, a melting point comprised
between 115C and 130C, an X-ray crystallinity variable
between 39% and 55%, a Melt Flow Index according to the
ASTM D-1238 method comprised between 0.1 and 50 g/10 min.,
and a contents of comonomer variable from 1% to 7% molar.
In accordance with the present invention the other
alpha olefin may be selected from the group consisting of
butene-l, hexene~l and octene-l.
The present invention, in anothex aspect, provides
a process for preparing copolymers of ethylene as defined
above characterized in contacting ethylene with at least one
other alpha olefin in the presence of a catalytic system
comprising an organic metallic compound of aluminium and a
composition selected from the product of the reaction of
metallic vapours with a titanium compound and a halogen donor
or the product obtained from the preceding reaction previously
modified by an organic metallic compound of aluminium or an
alcohol.
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2a .
In accordance with the present invention, it is
pos-- /
/
/
.
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sible to prepare polymers having a differential distribution
of the comonomer by using catalytic systems of the high-
-yield class which are already known for the preparation of
high-density and medium-density polyethylene as disclosed
in the Canadian Patent N1.118.748 granted on February 23,
1982, Canadian Patent Nl.108.110 granted on September 1,
1981, Canadian Pat. Appln. N407.655 filed on July 20,
1982 and Canadian Patent Appln. N368.250-1 filed on January
9, 1981, by modifying the production process or introducing
variations in the process itself.
The catalytic systems in question comprise
constituents which are basically composed of an organic
metallic compound of alumlnium and a second compound which
may be the product of the reaction of metallic vapours with
a compound of titanium and a halogen donor or such compound
as modified by a subsequent reaction with an organic me-
tallic compound of aluminium or with an alcohol.
In the first case, the catalyst can be represented
by a formula such as TiX3.m'MXn, wherein X is a halogen, M
a metal selected from among Mg, Al, Ti, V, Mn, Cr, Mo, Ca, Zn,
n is the valency of M an m' is equal to or higher than l:n.
Such a formulation is obtained by a process which provides
for the vaporization under vacuum of at least one of the
metals enumerated above and the reaction of the vapours
thus obtained with the titanium compound in the presence
of a compound capable of delivering halogen atoms. As
outlined above, such a composition can be used as such or
it can be modified by reacting it with an organic metallic
compound of aluminium, whereby a formulation is obtained
which is of the type TiX3.mM'Yn.qM 'Y'p.cAlY 3_sR 5 wherein
X is a halogen, M' and M" are metals different from one
; another and selected from among those enumerated above,
Y, Y' and Y", equal or different from each other are halo-
gens and, in their turn, can be equal to or different from
~Z~:I 399~9
-- 4 --
X, _ and can be 0 or different from 0 but cannot be zero
simultaneously, c is always other than zero, n and are
; the valencies of M' and Ml',respectively, s can take any
value between 0 and 3, R' is a hydrocarbon radical, preferably
having a number of carbon atoms lower than or equal to 10.
As an alternative, the catalyst can be the product of the
reaction between a titanium compound, selected from among
the halides and the alcoholates, vapours of an electrically
positive metal having reducing properties condensed at a low
temperature, an organic halogen compound or an inorganic
halogen compound and an alcohol.
As a co-catalyst, at any rate, a derivative of
aluminium having the formula Al R"p,X3_p,is always employed,
wherein R" is a hydrocarbon radical, X is a halogen and p'
is a number variable from 1 to 3. In addition to the com-
positions aforementioned, the catalyst system can be ob-
tained starting from (a) the product of the reaction bet-
ween a compound of titanium selected from among the ha-
lides and the alcoholates, vapours of magnesium condensed
at low temperatures, an organic or an inorganic halogen
compound and an alcohol, (b) an aluminium trialkyl and an
aluminium halide corresponding to the formula AlR'''SX3 s
wherein X is C1 or Br, and s is comprised between 0 and 2.
The adoption of the catalytic compositions
outlined above permits to obtain low-density polyethylene,
and more particularly linear low density polyethylene by
having the polymerization of ethylene taking place in the
presence of at least another alpha olefin having a number
of carbon atoms from 3 to 10. It has been observed that
the alpha olefins, particularly butene-l improves the
efficiency of the catalytic systems employed.
Quite particular advantages have been achieved
by using butene-l, hexene 1 and octene-l: the final
crystalline copolymers have a comonomer contents ranging
,, .
~Z~ 4~
-- 5 --
from 1% molar to 7% molar, a melting point comprised between
115C and 130C, a crystallinity (X-ray) variable from 39%
and 55% as a function of the amount of comonomer which is
present, and a Melt Flow Index (according to the ASTM D-1238
method) comprised between 0.1 and 50 grams per 10 minutes
(g/10 min.), the density being always below 0.9450 g/cm3
and preferably comprised between 0.9150 and 0.9450 g/cm3.
The distribution of the comonomer in the polymeric
chain is differentiated as a function of the process adopted
for its preparation and this fact is evidenced by the
different contents of substances which can be extracted by
boiling heptane if the density is the same and the Melt Flow
Index is the same.
The polymerization can be carried out, indifferently,
in suspension, in solution, and in the gaseous phase, and,
; whenever necessary, the reaction medium can be composed of
linear or branched C4-C10 hydrocarbons, cyclic hydrocarbons,
halogenated hydrocarbons, or a C4-cut from reforming, con-
sistently with the procedure to be adopted.
; 20 obviously, also the procedures vary consistently
with the method which is adopted: thus the polymerization
in the gaseous phase is carried out by feeding the cataly-
tic system aforementioned into a gaseous mixture consisting
of ethylene, one alpha-olefin, preferably propylene or
butene-l, and hydrogen as a molecular weight adjuster in
variable proportions consistently with the product to be
obtained, at a temperature which can be selected between
10C and 100C, preferably between 60C and 90C under a
pressure comprised between 5 and 50 bar, preferably from
10 to 30 bar. The products thus obtained are characterized
by a density comprised between 0.9150 and 0.9450 g/cm3 and
by a content of substances extractable by boiling heptane
which range, for products having the same Melt Flow Index,
from 65% to 5.9%.
,
3~
The suspension polymerization is carried out in
aliphatic C4-C10 hydrocarbonaceous solvents, straight line
or bxanched, preferably butane or isobutane, or halogen-sub-
stituted hydrocarbons, using as the comonomer alpha olefins
of the C3-C10 range, those from C3 to C6 being preferred,
and any of the catalytic system described hereinabove.
The polymerization is carried out at a temperature
which can be selected between 20C and 90C, preferably
between 50C and 80C under a pressure comprised between
1 and 60 bar, preferably between 13 and 30 bar. The poly-
merization can be carried out as a single-step run or in a
plural stage run with serially arranged reactors and by
feeding the gaseous phase with different composition.
The finishing of the product can be carried out
lS either by evaporation of the solvent in the case of low-
boiling solvents, or by centrifugation and drying of the
powder, or by stripping.
The products which are obtained from a single-
step process and having a density comprised between 0.9150
and 0.9450 g/cm3 have a fraction of substances extractable
by boiling heptane comprised between 43% and 3%, whereas
the samples obtained from a two-step process have a fraction
of extractable subtances comprised between 50~ and 3.5%.
For the polymerization process in solution, it is
necessary to work with solvents the critical temperature of
which is above the temperature of polymerization, the latter
being selected within the range 130C - 250C; particularly
advantageous have proven to be the cyclic hydrocarbons such
as cyclohexane and methylcyclohexane and mixture of normal
and isohydrocarbons the boiling point of which is comprised
between 120C and 180C, inasmuch as they have a fair
dissolving power towards the copolymers to be produced, the
best results being obtained by maintaining the concentration
of the polymer in the reaction mixture not above 40~ by
I: s
~lzl~39~9
7 --
weight relative to the solvent.
The adjustment of the molecular weight of the
copolymers as produced is carried out in a conventional way
by using hydrogen in an amount comprised between 0.003 and
0.5 mol per mol of ethylene.
The polymerization can be carried out by intro-
ducing in the reaction environment ethylene, hydrogen, an
alpha-olefin (C3-C10l preferably C6-C10, straight line of
branched) and any or the catalytic systems described above,
while maintaining the reaction mixture stirred so as to
encourage the dissipation of the polymerization heat and
to achieve an improved homogeneousness of the system. The
stay times of the polymeric solution may vary consistently
with the polymerization conditions Erom 1 minute to 24 hours,
the preferred range being between 5 minutes and 4 hours,
the polymerization pressures are comparatively low and are
comprised between 5 and 100 bar.
The copolymers are recovered by removing the un- -
reacted monomers and the solvent from the polymerization
mixture and by deactivating the catalytic system with
appropriate reagents.
The products thus obtained, having a density
comprised between 0.9150 and 0.9450 g/cm3 have a fraction
of substances extractable by boiling heptane comprised
between 56% and 5%.
In order to give an evidence of the differentiation
of the products which can be obtained with the different
procedures,Table 1 reports data as to the substances which
can be extracted by nC7 (normal heptane) at the boiling
point temperature, as well as a few technological proper-
ties of the films obtained correspondingly.
f '
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T A B L E _l
Example Process reaction Density Polymer. Melt Extracta- Ccmonomer
No. Medium Temper. Flow ble nC7 contents
Index at 98C
g/cm3 C g/lOmin % % by wt
2 l-step
isobutane 0.9210 122 1.2 33.8 6.8
slurry
2-step
isobutane 0.9204 122 1.1 39 7.0
slurry
6 l-step
nor.hexane 0.9213 122.5 0.9 50.1 6.2
slurry
9 gaseous
--------- 0.9198 121.5 1.3 58 6.9
phase
solution cyclohe~neO.9210 124 1.0 44 6.0
The foregoing and other modes of operation will
become still more conspicuous from the scrutiny of the
following examples, to which a mere function of illustration
is to be attributed, without however construing them as
being limitations whatsoever to the scope of the present
invention.
EXAMPLE 1
Preparation of the catalyst
A rotary evaporator is used, in the flask of which,
centrally a tungsten filament is arranged, which is spiralled
and connected to a source of electricity Beneath the flask
a cooling bath is horizontally arranged.
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g
The apparatus is connected, via a 3-way cock to the
vacuum and the nitrogen-feed lines.
Around the tungsten resistor, which is appropriately
protected, a magnesium wire of 1 gram is coiled and the
500-ml flask is charged under a nitrogen blanket with 250 mls
of anhydrous and de-aerated heptane, 15 mls of l-chlorohexane,
corresponding to 105 millimols (mM) and 0.23 ml of TiC14
corresponding to 2.1 mM. The flask is cooled to -70C, a
vacuum of 10 2 Torr is produced and the tungsten spiral is
heated so as to vaporize the metal coiled thereon. On
; completion of the vaporization step nitrogen is fed into
the apparatus and the flask is restored to room temperature
while keeping the mixture stirred, whereafter the flask is
heated during 1 hour to 80C (Catalyst A).
A 500-ml flask is charged with 70 g of polyethylene
powder having a controlled particle-size, drying under vacuum
-I is carried out for 30 minutes whereafter the flask is filled
with nitrogen and, still in such an inert atmosphere, the
suspension previously obtained is charged in the flask. The
solvent is driven off under vacuum with vigorous stirring
by heating the flask to 50C-60C.
On completion of the solvent evaporation, the
flask is filled with nitrogen again. The catalyst thus
obtained (catalyst B) is a free-flowing powder having a
hazelnut colour.
The analysis gives:
Ti= 0.029 milligramatom/g - Mg= 0.532 milligramatom/g
and Cl =1.12 milligramatom/g.
EXAMPLE 2
A 5-litre autoclave fitted with an anchor-shaped
stirrer is de-aerated under vacuum and charged with 1.3
litres of isobutane, the temperature is raised to 60C
whereafter there are added 120 g of butene-l, 7mM of
aluminium triisobutyl, hydrogen to a pressure of 1.55 bar,
I'
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- 10 -
ethylene to a total pressure of 13 bar and 0.5 g of the
catalyst (B) equivalent to 0.0145 milligramatom of Ti.
The temperature is maintained at 60C and
ethylene is fed by weeping the total pressure constant.
After polymerization for 2 hours, the reaction
is stopped with 20 mls of ethanol, whereafter the solvent
is evaporated off. There are obtained 310 g of polymer
corresponding to a yield of 430 ~g of polymer per g of Ti,
the polymer having the following specifications:
Density 0.9210 g/cm3
Butene contents (NMR) 6.8~ by wt
CH3/100 C (number) 1.70
Melt Flow Index (MFI)
at 2.16 kg 1.2 g/10 mins.
Melting point 122C
X-ray cristallinity 42%
Apparent density 0.33 g/cm
Ave.diameter of the powder 350 microns
Extract from boiling C7 33.8%
EXAMPLE 3
The same apparatus and procedure as in Example 2
are adopted but with different quantity of butene, that is,
80 g. There are obtained 260 g of polymer, corresponding
to a yield of 360 kg of polymer per g of titanium, the
25 polymer having the following specifications:
Density 0.9284 g/cm3
Butene contents 4.8% by wt
CH3/100 C (number) 1.1
MFI (Melt Flow Index) 0.4 g/10 min.
Apparent density 0.30 g/cm
Melting point 124.5C
EXAMPLE 4
The same apparatus and procedure as in Example 2
I
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-- 11 --
are adopted but with a quantity of butene-l equal to 140 g.
There are obtained 350 g of polymer corresponding
to a yield of 480 kg of polymer per g of Ti, the polymer
having the following specifications:
Density 0.9152 g/cm3
Butene contents 10.3% by wt
CH3/100 C 2.5
MFI (2.16 kg) 1.2 g/10 min.
Apparent density 0.25 g/cm3
Melting point 120C
Heptane extract (boiling) 52%
EXAMPLE 5
The same apparatus as in Example 2 is used, but
by varying the mode of operation as follows: there is
charged 1.3 litre of isobutene, which is brought to 60~C,
whereafter there are added 40 g of butene-l, 6 mM (millimols)
of aluminium triisobutyl, hydrogen to a pressure of 1.70 bar,
ethylene up to a pressure (total) of 14 bar and 0.5 g of
catalyst (B) of Example 1, which is equivalent to 0.0145
milligramatom of Ti. The temperature is maintained at 60C
and ethylene is introduced by keeping the total pressure
constant. After a 15-minute polymerization (about 30% of
the total polymer is produced), there are charged 140 g of
butene and polymerization is continued while the total
pressure is maintained at 14 bar by feeding ethylene again.
After a overall polymerization time of 2 hours, the polyme-
rization is halted with 19 cm3 of ethanol, whereafter the
solvent is evaporated off. There are obtained 320 g of po-
lymer, which correspond to a yield of 445 kg of polymer per
g of Ti, the polymer having the following properties:
Density 0.9204 g/cm3
Butene contents 7.0% by wt
Melt Flow Index 1.1 g/10 min.
Apparent density 0.33 g/cm3
.,, =.
,;
~35~
Melting point 122C
Extract from boiling C7 39
EXAMPLE 6
A 5-litre autoclave equipped with an anchor-shaped
stirrer is de-aerated under vacuum and is charged with 2
litres of anhydrous and de-aerated hexane and brought to
60C, whereafter there are added 130 g of butene-l, 6mM
(millimol) of aluminium triisobutyl, hydrogen to a partial
pressure of 2.2 bar, ethylene to a total gauge pressure of
6 bar and 0.5 g of the catalyst (B) of Example 1, corre-
sponding to 0.0145 milligramatom of Ti.
The temperature is maintained at 60C and ethylene
is fed by keeping the total pressure constant. After two
hours of polymerization, the reaction is stopped with 10 cm3
of ethanol, whereafter the autoclave is allowed to cool,
the gases are vented and the polymer suspension is stripped
of the solvents.
; The dried polymer, 250 g, corresponding to a yield
of 350 ky of polymer per g of Ti is a free-flowing powder
20 and exhibits the following specifications:
Density 0.9213 g/cm
Butene-l contents 6.2% by wt
Melt Flow Index 0.9 g/10 min.
Apparent density 0.23 g/cm3
Extract from boiling C7 50.1
EXAMPLE 7
The apparatus and the procedure of Example 2 are
adopted but using anhydrous nor.butane as the reaction
medium and all the same components for the polymerization
30 in the same amounts so that the overall gauge pressure is
; 11.5 bar.
The polymer is obtained in an amount of 280 g,
corresponding to a yield of 385 kg of polymer per g of Ti,
and has the following properties:
3~9
- 13 -
Density 0.9215 g/cm3
Butene contents 6.5% by wt
C~13/100 C (number) 1.65
Melt Flow Index 0.90 g/10 min.
X-ray crystallinity 41%
Apparent density 0.34 g/cm
EXAMPLE 8
The same apparatus and procedure as in Example 6
are adopted using 300 g of anhydrous and de-aerated hexene.
10 There are obtained 240 g of a polymer having the following
specifications:
Density 0.9290 g/cm3
C~3/100 C (number) 0.90
Hexene contents 5.4% by wt
Melt Flow Index 1.1 g/10 min.
Apparent density 0.25 g/cm
EXAMPLE 9
In a test tube having a tail portion which has
been previously dried and placed in an inert atmosphere,
there are charged 2 g of catalyst (B) and 6 milligramatoms
of A1-iso-Bu3 dissolved in 15 mls hexane: stirring is effected
with a magnetic stirrer whereafter hexane is evaporated off,
with stirring, until the sample is thoroughly dry.
1 g of catalyst, equivalent to 0.013 milligramatoms
of Ti, is charged under a nitrogen blanket in a 2-litre
autoclave fitted with a stirrer, dried and maintained in
an inert atmosphere. The autoclave is evacuated to drive
the nitrogen off, is heated to 70C whereafter there are
introduced with a gas stream having the following compo-
sition: ethylene 80% by volume, butene 15%, hydrogen 5%
to a pressure of 10 bar.
; After one hour of polymerization there are obtained
100 g of powdered polymer having the following properties:
Density 0.9198 g/cm3
~3~35~9
- 14 -
Butene-l contents 6.9% by wt
MFI 1.30 g/10 mint
Melting point 121.5C
Extract from boiling C7 58%
EXAMPLE 10
A 5-litre autoclave having a stirrer is charged
with 2 litres of anydrous and de-aerated cyclohexane con-
taining 1 millimol of Al(nor. Oct)3, the temperature is
raised to 150C whereafter there are added 100 g of
octene-l, hydrogen to a pressure of 0.5 bar, ethylene to
; a total gauge pressure of 10 bar and 1.5 cm3 of catalyst
of the type (A) of Example 1 corresponding to 0.012 mil-
ligramatoms of titanium. The pressure is maintamed constant
by feeding ethylene for 30 minutes. On completion of the
polymerization, the reaction is halted, the autoclave is
allowed to cool and the gases are vented. The product thus
;~ obtained consists of 140 g of polymer, corresponding to a
yield of 230 kg of polymer per g of titanium.
The polymer thus obtained has the following
properties: -
Density 0.9210 g/cm3
Octene contents 7.2~ by wt
CH3/100 C 0.96
Melting point 122C
Melt Flow Index 1.0 g/10 min.
C7 extract (boiling) 44.5~
:
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