Production of modified polypropylenes

A modified polypropylene having improved impact resistance is obtained by producing, in the presence of a stereoregular polymerization catalyst and in three steps, two types of polypropylene blocks formed stepwise at different temperatures and then poly(ethylene or ethylene/propylene) block, the polymerization temperatures employed and the quantities of polymers produced in each step being in specific ranges.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a process for producing modified polypropylenes 
containing propylene-ethylene copolymer blocks. 
As a method for improving the impact resistance of polypropylenes while 
maintaining their desirable properties, a method for 
block-copolymerization wherein polymer blocks comprising an ethylene unit 
are introduced into the polypropylene has been known. The block copolymer 
can be produced by polymerizing propylene and ethylene stepwise in the 
presence of a stereoregular polymerization catalyst. The conventional 
method for this purpose comprises producing polypropylene and then 
copolymerizing ethylene or an ethylene-propylene mixture with the 
resulting polypropylene. If desired, polyethylene- or 
poly(ethylene/propylene)-block is additionally formed. By this 
conventional method, a modified polypropylene having some impact 
resistance is obtained. This impact resistance, however, cannot be said to 
be satisfactory high. 
SUMMARY OF THE INVENTION 
It is an object of this invention to produce a modified polypropylene 
having excellent impact resistance wherein the above mentioned problems 
have been solved. This object has been achieved by producing two types of 
polypropylene blocks formed stepwise at different temperatures and 
poly(ethylene or propylene/ethylene) blocks in three steps. 
Thus, the process for producing a modified polypropylene in accordance with 
the present invention is characterized by the combination of the following 
steps 1, 2, and 3 which are carried out in the presence of a stereoregular 
polymerization catalyst. Quantities given in percent (%) in this 
disclosure are by weight. 
Step 1 
Propylene is polymerized at a temperature of not higer than 60.degree. C., 
to produce 0.5 to 30% of a crystalline propylene polymer on the basis of 
the total polymerization product obtained in Steps 1 through 3. 
Step 2 
Propylene is further polymerized at a temperature which is at least 
5.degree. C. higher than that of Step 1, to produce 60 to 95% of a 
crystalline propylene polymer on the basis of the total polymerization 
product, the quantity of the crystalline propylene polymer being the total 
quantity through Steps 1 and 2. 
Step 3 
Ethylene or an ethylene-propylene mixture is polymerized to produce 5 to 
40% of an ethylene polymer on the basis of the total polymerization 
product, the ethylene content in the ethylene polymer being 100 to 20%. 
One of the features of the process of the present invention is that two 
types of polypropylene blocks are produced stepwise at different 
temperatures, and the former step of the two steps is carried out at a low 
temperature of not higher than 60.degree. C. More particularly, by 
producing a crystalline propylene polymer in the first step, the resulting 
block copolymer can be provided with excellent properties such as high 
rigidity, high softening point and the like which are characteristic of 
polypropylenes. Thus, polymerization is initiated in the former step by 
contacting propylene with a stereoregular polymerization catalyst at a 
temperature of lower than 60.degree. C. and a relatively small amount of 
polypropylene is produced in the former low temperature step, whereby the 
impact resistance of the finally-produced modified polypropylene can be 
markedly improved. (Reference is made to Comparative Examples 1 and 2 set 
forth hereinafter.) 
It is also required in the present invention that the ethylene content in 
the ethylene polymer block be in the range of 100 to 20%. The impact 
resistance of the resulting modified polypropylene is greatly improved 
when the ethylene content is not less than 20%. (Reference is made to 
Comparative Example 4.) 
DETAILED DESCRIPTION OF THE INVENTION 
The process of the present invention is carried out essentially as in the 
conventional stereoregular polymerization of propylene or the like and the 
block copolymerization of propylene and ethylene, except that 
consideration is given to the condition of the polymerization temperatures 
to be employed and the quantity of each block to be produced in each 
polymerization step. 
1. Stereoregular Polymerization 
A catalyst generally employed in the stereoregular polymerization of 
propylene, ethylene, etc. can be used as the catalyst for the present 
invention. 
Most representative is a complex catalyst comprising a transition metal 
halide component and an organo-aluminum compound component. 
As the transition metal halide, titanium halides are preferably used and 
titanium trichloride and titanium tetrachloride are especially preferred. 
Examples of the titanium trichloride to be used in the catalyst are a 
reduction product of titanium tetrachloride reduced by a conventional 
method, the above mentioned reduction product which has been activated by 
a ballmill treatment or/and a washing treatment with a solvent (washing 
with an inert solvent or/and a polar compound-containing inert solvent), 
and a modified titanium compound mixture prepared by co-milling titanium 
trichloride or a titanium trichloride eutectic crystal mixture (such as 
TiCl.sub.3. 1/3AlCl.sub.3) with any of electron donors such as amines, 
ethers, esters, derivatives of sulfur or halogen, organic or inorganic 
nitrogen- or phosphorus-compounds, etc. 
Representative compounds which can be used as electron donors are ethers 
and esters. Among these, a C.sub.1 -C.sub.12 alkyl ester selected from 
.alpha., .beta. unsaturated aliphatic carboxylates and aromatic 
monocarboxylates is suitable. More specifically, ethyl benzoate, ethyl 
paratoluate, ethyl paraanisate, and the like are preferable. 
An electron donor of this character is used in a quantity, in general, of 
0.001 to 2 mols, preferably 0.01 to 1 mol with respect to 1 mol of the 
transition metal halide compound. 
The titanium trichloride, titanium tetrachloride, and other titanium 
halides can also be employed in a form wherein they are supported on 
magnesium halides such as magnesium chloride. 
As the organo-aluminum compound to be combined with such a transition-metal 
catalyst component, a compound represented by the formula AlR.sub.n 
X.sub.3-n is suitable. In this formula: R is an alkyl group with two to 
six carbon atoms; X is a halogen, especially chlorine; and n is a number 
defined as n.ltoreq.n.ltoreq.3. Examples of such a compound are 
dimethylaluminum chloride, diethylaluminum chloride, ethylaluminum 
sesquichloride, ethylaluminum dichloride, triethylaluminum, and mixtures 
thereof. 
The molar ratio of these two components is generally in the range of 1 mol 
of the transition metal compound to 1 to 300 mols, preferably from about 1 
to about 100 mols of the organo-aluminum compound. 
Furthermore, an electron donor can be added to the catalyst system when 
necessary. 
Representative compounds which can be used as electron donors are ethers 
and esters. Among these, a C.sub.1 -C.sub.12 alkyl ester selected from 
.alpha., .beta. unsaturated aliphatic carboxylates and aromatic 
monocarboxylates is suitable. More specifically, ethyl benzoate, ethyl 
paratoluate, ethyl paraanisate, and the like are preferable. 
An electron donor of this character is used in a quantity, in general, of 
0.01 to 10 mols, preferably 0.1 to 0.7 mol with respect to 1 mol of the 
o-rganoaluminum compound. 
2. Formation of Crystalline Propylene Polymer Blocks (Steps 1 and 2) 
In the Step 1 of the present invention, the polymerization of propylene is 
initiated at a temperature of not higher than 60.degree. C., preferably at 
50.degree. C. to room temperature and most preferably at 40.degree. to 
20.degree. C. The polymerization is continued until the polymerized 
quantity reaches 0.5 to 30%, preferably 1 to 10% of the total 
polymerization product obtained in Steps 1 through 3. The temperature in 
Step 1 may not be required to be always constant through Step 1 provided 
that it is not higher than 60.degree. C. The lower limit is about 
0.degree. C. When the temperature at which the polymerization of propylene 
is initiated is above 60.degree. C., a polymerization product having a 
quality balance which is markedly excellent in both rigidity and impact 
resistance cannot be obtained. 
In the subsequent second stage (Step 2), the polymerization of propylene is 
carried out at a temperature of at least 5.degree. C. and preferably at 
least 10.degree. C. higher than that of Step 1. The polymerization 
temperature itself in the Step 2 is not especially restricted provided 
that the above-mentioned difference in the temperature exists, but is 
generally preferred to be a temperature above 50.degree. C. and especially 
above 65.degree. C. The polymerization temperature set at a relatively 
higher level is industrially preferred from the viewpoint of the catalytic 
efficiency and the heat-removal efficiency of the polymerization reactors. 
The upper limit of the polymerization temperature in Step 2 is generally 
about 90.degree. C. The temperature in Step 2 may not be required to be 
always kept constant through Step 2. 
The polymerized quantity in Step 2 should be controlled to be 60 to 95% and 
preferably 75 to 93% of the total polymer quantity produced through Steps 
1 and 2 on the basis of the total polymerization product obtained in Steps 
1 through 3. 
If the content of the crystalline propylene polymer blocks produced through 
these two steps is less than 60% of the total polymerization product, the 
resulting modified polypropylene will fail to fully exhibit the excellent 
properties of polypropylene, especially those such as high rigidity and 
high softening point. 
These two steps can be carried out according to any polymerization process 
which can be applied to the stereoregular polymerization of propylene such 
as slurry-in-solvent polymerization, non-solvent liquid phase 
polymerization, and gas-phase polymerization. Slurry-in-solvent 
polymerization, however, is typically employed. The polymerization 
pressure is generally at 1 to about 50 Kg/cm.sup.2 (absolute pressure 
(abs.)), and particularly in slurry-in-solvent polymerization is usually 
about 1 to about 12 Kg/cm.sup.2. abs. 
Step 2 is normally carried out by addition-polymerizing propylene 
additional to the "active" polypropylene obtained in Step 1, wherein a 
further catalyst is not generally supplemented. If desired, however, the 
catalyst can also be added upon starting Step 2 or in the course of Steps 
1 and 2. 
These two steps can be carried out either in a single polymerization 
reactor or in reactors respectively for the two steps connected in series. 
In this connection, provided that the excellent contribution which the 
crystalline propylene polymer makes to the properties of the modified 
polypropylene of the present invention is not impaired, the propylene 
monomer used in Steps 1 and 2 may contain a small amount of a 
copolymerizable manner such as ethylene, isobutylene, or 1-butene. The 
monomer may also contain hydrogen or the like as a molecular weight 
modifier. 
3. Formation of Ethylene Polymer Block (Step 3) 
The process in Step 3 is carried out essentially in the same way as in the 
process of the Step 2 (and the Step 1), except that the monomer to be 
polymerized is ethylene or a mixture of ethylene and propylene. 
The ethylene content contained in the block formed in Step 3 is 100 to 20% 
and preferably 90 to 30%. When the ethylene content is less than 100%, the 
balance is propylene, or may be propylene and a small amount of a 
copolymerizable monomer such as isobutylene and 1-butene provided that the 
presence of such a copolymerizable monomer does not unduly impair the 
properties of the resulting modified polypropylene. 
The polymerized quantity in Step 3 is 5 to 40% and preferably 7 to 25% of 
the total polymerization product obtained in Steps 1 through 3. A 
sufficient impact resistance cannot be obtained when the polymerized 
quantity in Step 3 is less than 5%, and the excellent properties which 
polypropylene possesses cannot be exhibited when the polymerized quantity 
is more than 40%. 
Step 3 is generally carried out at a temperature of not higher than 
100.degree. C., preferably in the range of 20.degree. to 80.degree. C., 
and under pressure of about 1 to 50 Kg/cm.sup.2 abs., preferably under a 
pressure of atmospheric pressure to 30 Kg/cm.sup.2 abs. Step 3 is carried 
out substantially in the same way as in Step 2 (and Step 1) with respect 
to the polymerization processes, polymerization reactors, use of the 
catalyst with or without further addition thereof, and so forth.

4. Examples of Experiments 
EXAMPLE 1 
A polymerization reactor of 100-liter capacity was charged with 40 g of 
titanium trichloride and 80 g of diethylaluminum monochloride together 
with 45 liters of heptane. 
(Step 1) 
As the first step of the polymerization, the polymerization temperature was 
raised to 40.degree. C., and propylene was supplied to raise the pressure 
to 1 Kg/cm.sup.2 G. Polymerization of propylene was continued until the 
polymerized quantity reached 1 Kg. 
(Step 2) 
As the second step of the polymerization, the polymerization temperature 
was then raised to 75.degree. C., and propylene was supplied at a rate of 
5 Kg/hr. The polymerization of propylene was continued at a temperature of 
75.degree. C. until the polymerized quantity reached 19 Kg. 
(Step 3) 
In the subsequent third step of polymerization, unreacted propylene was 
purged until its pressure reached 0.5 Kg/cm.sup.2 (gauge pressure (G)). 
Ethylene was then supplied at a rate of 2 Kg/hr, and copolymerization was 
carried out at 75.degree. C. until the quantity of polymerized ethylene 
reached 2.6 Kg, the quantity of propylene copolymerized simultaneously 
being 0.4 Kg. 
To the resulting polymer slurry was added 3 liters of butanol to terminate 
the polymerization. The mixture was subjected to a catalyst-decomposition 
operation for 1 hour. The product was then subjected to centrifuging, 
washing with water, and drying to obtain a white powdery copolymer. 
The properties of the copolymer thus obtained are shown in Table 1. 
Comparative Example 1 
The process of Example 1 was repeated to produce a copolymer, except that 
propylene was polymerized at a temperature of 75.degree. C. from the 
initiation of the polymerization until the quantity of polymerized 
propylene reached 20 Kg. 
The properties of the resulting copolymer are also shown in Table 1. 
TABLE 1 
______________________________________ 
Comparative 
Properties Example 1 Example 1 
______________________________________ 
MI (g/10 minutes) 
0.9 1.0 
Ethylene content (% by wt.) 
12 11 
Impact strength (Kg-cm/cm.sup.2) 
23 15 
Rigidity (Kg/cm.sup.2) 
11500 10700 
______________________________________ 
MI (melt index): ASTM D123857T method (temperature 230.degree. C., load 
2,160 g) 
Ethylene content: IR analysis 
Impact strength: Charpy impact strength test (20.degree. C.) Japanese 
Industiral Standards JIS B7722- 
Rigidity: ASTM D74750 method 
From the results, it is apparent that a modified polypropylene which was 
prepared by initiating the polymerization at a temperature higher than 
60.degree. C. has insufficient impact resistance and rigidity. 
EXAMPLE 2 
A 100-liter capacity polymerization reactor was charged with 40 g of 
titanium trichloride and 80 g of diethylaluminum monochloride together 
with 45 liters of heptane. 
(Step 1) 
The polymerization temperature was raised to 30.degree. C., and propylene 
was then supplied to raise the polymerization pressure to 1 Kg/cm.sup.2 G. 
The polymerization of propylene was continued until the quantity of 
polymerized propylene reached 0.5 Kg. 
(Step 2) 
The polymerization temperature was then raised to 75.degree. C., and 
propylene was supplied at a rate of 5 Kg/hr. Polymerization was continued 
at 75.degree. C. until the quantity of polymerized propylene reached 19.5 
Kg. 
(Step 3) 
Unreacted propylene was purged until the pressure became 0.5 Kg/cm.sup.2 G, 
and ethylene was then supplied at a rate of 2 Kg/hr. Copolymerization was 
continued at 70.degree. C. until the quantity of polymerized ethylene 
reached 2.6 Kg, the quantity of the propylene copolymerized simultaneously 
being 0.4 Kg. 
The polymer slurry thus obtained was subjected to post-treatment similarly 
as in Example 1 to obtain a white powdery copolymer. The properties of the 
resulting copolymer are shown in Table 2. 
Comparative Example 2 
Polymerization and post-treatment were carried out as in Example 2, except 
that the first step polymerization was carried out at a polymerization 
temperature of 70.degree. C. 
The properties of the resulting copolymer are shown in Table 2. This 
Comparative Example 2 is set forth to show the effect of a higher 
temperature in the polymerization Step 1. 
EXAMPLE 3 
A 100-liter capacity polymerization reactor was charged with 40 g of 
titanium trichloride and 80 g of diethylaluminum monochloride together 
with 45 liters of heptane. 
(Step 1) 
The temperature in the polymerization reactor was raised to 50.degree. C., 
and propylene was then supplied until the pressure became 2 Kg/cm.sup.2 G. 
The polymerization of propylene was continued until the polymerized 
quantity of the propylene reached 2 Kg. 
(Step 2) 
The polymerization temperature was then raised to 75.degree. C., and 
propylene was supplied at a rate of 5 Kg/hr. The polymerization was 
continued until the polymerized quantity of the propylene reached 18 Kg. 
(Step 3) 
Unreacted propylene was then purged until the pressure became 0.5 
Kg/cm.sup.2 G, and then ethylene was supplied at a rate of 2 Kg/hr. 
Copolymerization was carried out at a temperature of 70.degree. C. until 
the polymerized quantity of the ethylene reached 2.6 Kg, the quantity of 
the propylene copolymerized simultaneously being 0.4 Kg. 
The polymer slurry thus obtained was subjected to post-treatment as in 
Example 1 to obtain a white powdery copolymer. 
The properties of the resulting copolymer are shown in Table 2. 
Comparative Example 3 
Polymerization and post-treatment were carried out as in Example 3, except 
that the first step polymerization was carried out under a pressure of 1 
Kg/cm.sup.2 until the polymerized quantity of the propylene reached 70 g, 
and the polymerization in the second step was continued until the 
polymerized quantity of the propylene reached 20 Kg. 
The properties of the resulting copolymer are shown in Table 2. This 
Comparative Example 3 is set forth to show the effect when a small amount 
of the crystalline propylene polymer was produced in the first step. 
EXAMPLE 4 
A 100-liter capacity polymerization reactor was charged with 40 g of 
titanium trichloride and 80 g of diethylaluminum monochloride together 
with 45 liters of heptane. 
(Step 1) 
The polymerization temperature was raised to 40.degree. C., and then 
propylene was supplied to bring the pressure up to 1 Kg/cm.sup.2 G. The 
polymerization of the propylene was continued until the polymerized 
quantity of the propylene reached 1 Kg. 
(Step 2) 
The polymerization temperature was then raised to 75.degree. C., and 
propylene was supplied at a rate of 5 Kg/hr. Polymerization was continued 
at 75.degree. C. until the polymerized quantity of the propylene reached 
18 Kg. 
(Step 3) 
Unreacted propylene was purged until the pressure became 0.5 Kg/cm.sup.2 G. 
Ethylene was then supplied at a rate of 1.1 Kg/hr. At the same time, 
propylene was also supplied at a rate of 0.9 Kg/hr. Copolymerization was 
carried out at 70.degree. C. until the polymerized quantity of the 
ethylene reached 2.0 Kg, the quantity of the propylene copolymerized 
simultaneously being 1.5 Kg. 
The polymer slurry thus obtained was subjected to post-treatment as in 
Example 1, whereupon a white powdery copolymer was obtained. The 
properties of the resulting copolymer are shown in Table 2. 
EXAMPLE 5 
The process of Example 4 was repeated except that, in the third step, the 
copolymerization was carried out at 70.degree. C. by supplying ethylene at 
a rate of 1.1 Kg/hr and propylene simultaneously at a rate of 0.4 Kg/hr 
until the polymerized quantity of the ethylene reached 1.3 Kg. The 
quantity of the propylene copolymerized at this time was 0.4 Kg. 
The properties of the resulting copolymer were shown in Table 2. 
Comparative Example 4 
The process of Example 4 was repeated except that, in the third step, the 
copolymerization was carried out at 70.degree. C. by supplying ethylene at 
a rate of 0.2 Kg/hr and propylene simultaneously at a rate of 2 Kg/hr 
until the polymerized quantity of the ethylene reached 0.3 Kg. The 
quantity of the propylene copolymerized at this time was 2.9 Kg. 
The properties of the resulting copolymer are shown in Table 2. 
Comparative Example 4 is set forth to show the effect when the ethylene 
content in the polymer obtained in the third step is smaller. 
Comparative Example 5 
The process of Example 4 was repeated except that, in the third step, the 
copolymerization was carried out at 70.degree. C. by supplying ethylene at 
a rate of 0.5 Kg/hr and propylene simultaneously at a rate of 0.5 Kg/hr 
until the polymerized quantity of the ethylene reached 0.3 Kg. The 
quantity of the propylene copolymerized at this time was 0.3 Kg. 
The properties of the resulting copolymer are shown in Table 2. 
Comparative Example 5 is presented to show the effect when the amount of 
the polymer produced in the third step is smaller. 
TABLE 2 
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Step 1 Step 2 
Step 3 Properties of Product 
Polyme- Polyme- 
Polyme- Polyme- Impact 
rization tempera- 
rized quantity 
rized quantity 
##STR1## 
rized quantity 
MI (g/10 
Ethylene content 
strength (Kg-cm/ 
Rigidity 
ture (.degree.C.) 
(%) (%) (%) (%) min.) 
(wt. %) 
cm.sup.2) 
(Kg/cm.sup.2) 
__________________________________________________________________________ 
EX. 1** 
40 4.4 82.6 86.7 13.0 0.9 12 23 11500 
C. EX. 1 
75 87.0 -- 86.7 13.0 1.0 11 15 10700 
EX. 2 30 2.2 84.8 86.7 13.0 0.9 11 24 11400 
C. EX. 2 
70 2.2 84.8 86.7 13.0 1.2 11 16 11000 
EX. 3 50 8.7 78.3 86.7 13.0 1.1 11 22 11700 
C. EX. 3 
50 0.3 86.7 86.7 13.0 1.3 11 14 10900 
EX. 4 40 4.4 80.0 57.1 15.6 1.4 7 20 11000 
EX. 5 40 4.8 87.0 76.5 8.2 1.0 5 21 12500 
C. EX. 4 
40 4.5 81.1 9.3 14.4 1.5 1 5 9300 
C. EX. 5 
40 5.1 91.8 50.0 3.1 1.3 1 6 12700 
__________________________________________________________________________ 
Note: 
*E = ethylene, P = propylene 
**EX. = Example, C. EX. = Comparative Example.