Process for producing propylene-ethylene block copolymers

A process for producing a propylene-ethylene block copolymer by subjecting propylene and ethylene to three-step polymerization using a stereoregular polymerization catalyst, which comprises in the first step polymerizing propylene alone or a propylene/ethylene mixture so that the average ethylene/propylene reaction ratio is 6/94 or less, thereby polymerizing 60 to 95% by weight of the total polymerization amount, in the second step polymerizing a propylene/ethylene mixture so that the average ethylene/propylene reaction ratio is 25/75 to 67/33, thereby polymerizing 1 to 20% by weight of the total polymerization amount, and in the third step polymerizing a propylene/ethylene mixture so that the average ethylene/propylene reaction ratio is 76/24 to 89/11, thereby polymerizing 4 to 35% by weight of the total polymerization amount, wherein in the second and third steps, ethylene alone is supplied thereby gradually decreasing the amount of propylene in the polymerization system from the first step to the succeeding steps.

The present invention relates to a process for producing propylene-ethylene 
block copolymers improved in properties, particularly, such as impact 
resistance, stiffness, transparency and impact blushing. Crystalline 
polyolefins have been produced on a commercial basis since a stereoregular 
catalyst was invented by Ziegler and Natta. Particularly, crystalline 
polypropylene has been used as a general-purpose resin having excellent 
stiffness and heat resistance. 
Crystalline polypropylene, however, has the drawback that it is brittle at 
low temperatures, so that it is not suitable for usages requiring impact 
resistance at low temperature. Many improvements have already been 
proposed as a result of extensive studies to overcome this drawback. Of 
these improvements, those disclosed in Japanese Patent Publication Nos. 
14834/1963, 1836/1964 and 15535/1964 are particularly useful from the 
industrial point of view. They are a process including the block 
copolymerization of propylene and other olefins, particularly, ethylene. 
But, block copolymers produced by these well-known methods also have 
drawbacks. For example, they are inferior to the crystalline polypropylene 
in the stiffness and transparency of molded or fabricated products. 
Further, when the block copolymers are deformed by impact or bending, 
blushing appears at the deformed portion (referred to as "impact blushing" 
hereinafter), which leads to a remarkable reduction in commercial value. 
In order to improve such drawbacks, there have been proposed many processes 
in which the block copolymerization is carried out in three steps. 
Specifically, Japanese Patent Publication No. 20621/1969 discloses an 
improvement in transparency, Japanese Patent Publication No. 24593/1974 
an improvement in impact blushing and Japanese Patent Publication 
(unexamined) No. 25781/1973 an improvement in impact resistance. 
In general, however, these properties, impact resistance, stiffness, 
transparency and impact blushing are in competition with one another, so 
that satisfactory, well-balanced polymers can not be obtained by these 
well-known processes. 
The inventors extensively studied to overcome these difficulties, and found 
a process for obtaining polymers which are markedly well balanced in the 
physical and optical properties. 
An object of the present invention is to provide a novel process for 
producing propylene-ethylene block copolymers which comprises carrying out 
polymerization in three steps using a stereoregular polymerization 
catalyst. 
Another object of the present invention is to provide propylene-ethylene 
block copolymers markedly well-balanced in impact resistance, stiffness, 
transparency and impact blushing. 
Other objects and advantages of the present invention will be apparant from 
the following descriptions. 
According to the present invention, there is provided a polymerization 
process for producing propylene-ethylene block copolymers, by subjecting 
propylene and ethylene to a three-step polymerization using a 
stereoregular polymerization catalyst, characterized in that the 
first-step polymerization is carried out by polymerizing propylene alone 
or a propylene/ethylene mixture so that the average ethylene/propylene 
reaction ratio {the molar ratio of ethylene to propylene which are taken 
into the copolymer (referred to as "ethylene/propylene reaction ratio" 
hereinafter)} is 6/94 or less, preferably 4.5/95.5 or less, thereby 
polymerizing 60 to 95% by weight, preferably 65 to 93% by weight, of the 
total polymerization amount, the second-step polymerization is carried out 
by polymerizing a propylene/ethylene mixture so that the average 
ethylene/propylene reaction ratio is 25/75 to 67/33, preferably 30/70 to 
60/40, thereby polymerizing 1 to 20% by weight, preferably 2 to 18% by 
weight, of the total polymerization amount, and the third-step 
polymerization is carried out by polymerizing an ethylene/propylene 
mixture so that the average ethylene/propylene reaction ratio is 76/24 to 
89/11, thereby polymerizing 4 to 35% by weight, preferably 6 to 30% by 
weight, of the total polymerization amount, wherein, in the second and 
third steps, ethylene alone is supplied thereby gradually decreasing the 
amount of propylene in the polymerization system from the first step to 
the succeeding steps. 
The process of the present invention will be illustrated in detail 
hereinafter. 
The propylene-ethylene block copolymerization of the present invention can 
be carried out in substantially the same manner as in the conventional 
polymerization for producing isotactic polypropylene using a stereoregular 
polymerization catalyst, except that said block copolymerization is 
divided into many steps and that attention needs to be given to the 
ethylene/propylene reaction ratios and polymerization amounts in the 
second and third steps. 
Consequently, as the stereoregular polymerization catalyst used in the 
present invention, there are used the well-known catalysts consisting 
essentially of titanium trichloride, an organo-aluminum compound and 
optionally a stereoregularity-improving agent. 
Herein, the titanium trichloride may include its composition. 
As examples of the titanium trichloride there may be given, for example, 
titanium trichloride produced by the reduction of titanium tetrachloride 
with a metal or organo-metallic compound, or, further, the activation of 
the reduction product; products obtained by the pulverization of the 
foregoing substances; titanium trichloride obtained by the method 
disclosed in British Patent No. 1391067; and titanium trichloride obtained 
by the methods disclosed in U.S. Pat. No. 4,165,298. 
The organo-aluminum compound includes for example dimethylaluminum 
chloride, diethylaluminum chloride, diisobutylaluminum chloride, 
diethylaluminum bromide and triethylaluminum. Of these compounds, 
diethylaluminum chloride is particularly preferred. 
The stereoregularity-improving agent used as a third component of the 
catalyst includes for example the well-known compounds such as amines, 
ethers, esters, sulfur, halogen, benzene, azulene derivatives, organic or 
inorganic nitrogen compounds and organic or inorganic phosphorus 
compounds. 
The polymerization of the present invention may be carried out in either of 
inert hydrocarbon or liquid propylene monomer in the substantial absence 
of an inert hydrocarbon. Further, it may be carried out in a gaseous 
phase. The polymerization temperature is not particularly limited, but 
generally, it is within a range of 20.degree. to 90.degree. C., preferably 
40.degree. to 80.degree. C. The polymerization is carried out in the 
presence of the foregoing catalyst. 
At the first step of the polymerization, propylene alone is polymerized, 
or a propylene/ethylene mixture is polymerized so that the average 
ethylene/propylene reaction ratio is 6/94 or less, preferably 4.5/95.5 or 
less. In the case of the polymerization of propylene, polymers having the 
physical properties markedly well balanced can be obtained by carrying out 
the subsequent polymerization of the present invention. When improvements 
in transparency, impact blushing and impact strength are desired at a 
little sacrifice of stiffness if necessary, a small amount of ethylene is 
added. 
In the copolymerization, propylene and a small amount of ethylene may be 
polymerized at the same time in a mixed state, or propylene alone may be 
first polymerized followed by copolymerization of a mixture of propylene 
and a small amount of ethylene. In either case, almost the same effect can 
be obtained. 
When the ethylene/propylene reaction ratio exceeds the scope of the present 
invention, stiffness is extremely lowered. 
In this polymerization step, preferably the well-known molecular 
weight-regulating agent such as hydrogen is added in order to regulate the 
melt processability of the polymer. 
The second step of the polymerization follows the first step. In this step, 
copolymerization is carried out by polymerizing a propylene/ethylene 
mixture so that the average ethylene/propylene reaction ratio is 25/75 to 
67/33, preferably 30/70 to 60/40. The reaction ratio below 25/75 is not 
desirable because impact strength particularly at lowered temperatures 
characteristic of propylene-ethylene block copolymers becomes poor. The 
reaction ratio above 67/33 is not also desirable because impact strength 
becomes poor. 
In the second step, ethylene alone is supplied to the polymerization 
system. Propylene is not supplied, and, if necessary, a part of propylene 
in the reactor after the first polymerization step may be removed from the 
reactor prior to the second step polymerization thereby adjusting 
propylene/ethylene ratio in the second polymerization system to a desired 
value. Particularly, in the second step, the molar ratio of total amount 
of ethylene supplied and present in the system to propylene present in the 
system is in the range of from 10/90 to 60/40, preferably from 15/85 to 
50/50. 
In this step, a molecular weight-regulating agent is not particularly 
necessary. 
The third step of the polymerization follows the second step. In this step, 
copolymerization is carried out by polymerizing ethylene/propylene mixture 
so that the average ethylene/propylene reaction ratio is 76/24 to 89/11. 
The reaction ratio below 76/24 is not desirable because stiffness, impact 
blushing and transparency becomes poor. 
The reaction ratio above 89/11 is not also desirable becuae impact strength 
particularly at room temperature becomes poor depending upon the 
polymerization conditions at the second step. In this step, preferably, 
the well-known molecular weight-regulating agent such as hydrogen is added 
to regulate the melt processability of the copolymer. 
In the third step, ethylene alone is supplied to the polymerization system. 
Propylene is not supplied and, if necessary, a part of propylene may be 
removed from the reactor in the same manner as in the second step. 
Particularly, in this step, the molar ratio of ethylene to propylene 
present in the system is preferably in the range of from 25/75 to 60/40. 
The three-step polymerization of the present invention may be carried out 
in a continuous way using three or more vessels, or in a batchwise way 
using one or more vessels, or in combination of the both. 
Further, the three-step polymerization may be repeated several times. 
The block copolymer described above can be obtained with a variety of 
embodiments. Particularly, when each step is finished, the unreacted 
propylene required in the succeeding step is reserved, and the propylene 
existing in the system is gradually reduced with progress of the step. 
This method is preferable to obtain the desired ethylene/propylene reaction 
ratio in each step economically. Consequently, in the second and third 
steps, a method comprising supplying ethylene alone and copolymerizing 
ethylene and propylene is preferably used. Particularly, when the present 
invention is carried out in an inert solvent, it is possible to reduce to 
extremely large extent the amount of propylene to be purged. 
A preferable embodiment of the present invention performed by a batch 
process is shown below. 
In the first step, propylene is polymerized alone or under the addition of 
small amount of ethylene, by supplying the monomer(s) at a relatively high 
pressure during the early stage of the step. After a certain duration, the 
feeding of propylene is ceased while continuing the polymerization whereby 
a requisite amount of propylene necessary in the following second and 
third steps is secured. In other words, the amount of propylene monomer in 
the polymerization system is decreased by continuing the polymerization so 
as to reach the desired amount of propylene monomer. It is permissible, if 
necessary, to purge the excess amount of monomer(s) at the end of the 
first step. 
After the first step is over, the second step of the polymerization is 
allowed to start by supplying ethylene monomer to the system. The amount 
of ethylene to be supplied should be determined taking into account of the 
amount of monomers remaining in the system and of the ethylene/propylene 
reaction ratio determined by the polymerization conditions, so as to 
obtain the desired copolymer. In practice, the polymerization is performed 
in such a manner, that the ethylene/propylene reaction ratio lies in the 
specified range in the present invention, and preferably, so as to 
maintain a constant reaction ratio over the entire course of the step, 
under the regulation of the amount of ethylene to be fed in accordance 
with the decrement of the remaining amount of propylene so as to decrease 
the pressure of the reaction system gradually. 
When a monomer mixture of ethylene and propylene is supplied at relatively 
higher pressure in the second step of the polymerization, the degree of 
saturation (super-saturation) of propylene in the reaction mixture in the 
third step after purging off of unreacted monomers varies depending on the 
size of the reaction vessel, condition of the slurry in the reaction 
vessel, condition of agitation and so on, so that unchanged steady 
polymerization cannot be expected. On the contrary, by performing the 
second step as defined by the present invention, a constant and unchanged 
polymerization in the third step is warranted always in an easier manner, 
since a condition close to saturation of propylene is achieved regardless 
of the polymerization condition. 
In the third step, the polymerization is carried out while supplying 
ethylene, so as to attain an average ethylene/propylene reaction ratio 
lying within the range prescribed according to the present invention. 
In the following, the present invention is further explained by 
exemplifying a continuous form of the process also in a preferable 
embodiment. 
For carrying out the process according to the present invention in a 
continuous manner, three or more reaction vessels are used in serial 
connection. Here, the first step of the polymerization is performed by 
employing one or more reaction vessels. The first step can be effected in 
a similar manner as in the batch-wise process, for example, by a propylene 
polymerization, followed by purging off of the unreacted monomer(s), or 
polymerization through two or more vessels connected in series wherein the 
feeding of propylene is excluded in the final vessel to attain the 
requisite decrease of the propylene monomer content at the end of the 
step, which can be followed, if necessary, by the purging off of excess 
monomer(s). 
The second step of the polymerization is conducted in one or more reaction 
vessels by supplying ethylene to effect the ethylene/propylene 
copolymerization under the consumption of propylene monomer unreacted and 
retained in the system. Here, it is permitted to conduct the 
polymerization, as in the batchwise operation, in two or more reaction 
vessels to realize the sequential pressure decrease, with occasional 
employment of further purging off of unreacted propylene monomer in case 
propylene monomer is reserved excessively. 
The third step of the polymerization is effected under the supply of 
ethylene in one or more reaction vessels. 
While it is possible to carry out the polymerization according to the 
present invention either in a medium of the liquefied monomers under the 
substantial exclusion of any inert solvent or in gaseous phase, it is 
preferable for an economical production of the copolymer, to conduct the 
polymerization in such a manner, that the first step is effected either in 
the liquefied monomer or in gaseous phase and the following second and 
third steps are conducted in gas phase. Here, it is recommended to pursue 
the procedure to realize the gradient decrease of propylene monomer 
content through the first, second and third steps. 
While it is preferable to perform the process in the form of embodiment in 
which ethylene only is supplied in the second and third steps, it is 
permissible to incorporate an addition of propylene monomer. Through the 
course of second and third steps, when propylene becomes wanting. 
The present invention will be illustrated more specifically with reference 
to the following examples and comparative examples which are not however 
to be interpreted as limiting the invention thereto. 
The results of the examples are shown in Tables 1 to 6. The values of 
physical properties in the tables were those measured by the following 
testing methods. 
Melt index: ASTM D 1238-57T 
Brittle temperature: ASTM D 746 
Stiffness: ASTM D 747-58T 
Haze: ASTM D 1003 
Test sample: Sheet (1 mm thick) molded by pressing. 
Izod impact strength: ASTM D 256 
Test temperature: 20.degree. C., -20.degree. C. 
Impact blushing: Injection-molded sheet (1 mm thick) is placed at 
20.degree. C. on a Du Pont impact tester; the hemi-spherical tip (radius 
6.3 mm) of the dart is contacted with the sheet; impact is given to the 
top of the dart with the 20 cm or 50 cm natural fall of a weight (1 kg); 
and the area of the blushed portion is measured. 
Intrinsic viscosity (referred to as [.eta.] for brevity): [.eta.] is 
measured at 135.degree. C. in tetralin.

These values were measured using test samples prepared as follows: The 
polymer particles obtained by the examples were mixed with the well-known 
additives such as an antioxidant, formed into pellets through an extruder 
and then pressed or injection-molded. 
EXAMPLE 1 
An autoclave having a capacity of 360 l and equipped with a stirrer, which 
had been evacuated preliminarily, was pressurized with propylene to a 
pressure of 1 Kg/cm.sup.2 gauge and then evacuated to -600 mm Hg gauge. 
This procedure was repeated three times. 
Then, 100 l of heptane, 28 g of titanium trichloride (a product of the firm 
Toho-Titanium with trade name of TAC 132) and 320 g of diethylaluminum 
chloride were charged therein. 
In the first step of the polymerization, propylene monomer was supplied at 
a polymerization temperature of 70.degree. C. in the presence of hydrogen 
until a pressure reached 14 Kg/cm.sup.2 gauge. At this occasion, the 
supply of propylene was stopped and the polymerization was continued to 
consume the propylene monomer in the system until the pressure in the 
system decreased to 6 Kg/cm.sup.2 gauge. 
Thereafter, the remaining unreacted monomer was purged off until the 
pressure reached to 2.5 kg/cm.sup.2 gauge and then, the temperature was 
adjusted at 65.degree. C. 
In the second step, the polymerization was further advanced in such a 
manner, that the autoclave was charged with ethylene at a polymerization 
temperature of 60.degree. C. to increase the pressure, and then, the 
polymerization was caused to proceed by adjusting the feeding of ethylene 
so as to maintain a constant ethylene/propylene reaction ratio until the 
polymerization pressure reached to 1.8 Kg/cm.sup.2 gauge. 
Then, 60 l of heptane were added thereto and the temperature was adjusted 
at 52.degree. C. 
The third step of the polymerization was conducted in such a manner, that 
the pressure was elevated once to 2 Kg/cm.sup.2 gauge by charging ethylene 
in the system and then the polymerization was caused to proceed at 
52.degree. C. in the presence of hydrogen while supplying ethylene. 
The resulting polymerization mixture in the form of slurry was subjected to 
the decomposition of catalyst by the addition of butanol. After it was 
filtered and dried, a white powdery polymer product was obtained. 
The [.eta.]-values estimated by the samples taken after the end of each 
step and the ethylene/propylene reaction ratios for the second and third 
steps as well as the percent polymerization in each step, both calculated 
from the materials balance, are recited in Table I. The material 
properties of the polymer obtained are summarized in Table II. 
Besides, it has been confirmed from another estimation of 
ethylene/propylene reaction ratio by a known method using infrared 
absorption spectra, that this value is nearly concordant with that 
obtained from the calculation of materials balance. 
The molar ratio of total ethylene supplied into the system to the existing 
propylene corresponded to 30/70 in the second step and the molar ratio of 
ethylene to propylene present in the system corresponded to 42/58 in the 
third step. This measure also applies to Comparison Examples given below. 
COMISON EXAMPLES 1, 2 and 3 
Similar to Example 1, the first step is carried out in such a manner that 
propylene was supplied at a polymerization temperature of 70.degree. C. in 
the presence of hydrogen and the polymerization was continued after the 
stoppage of supply of propylene until a pressure reached 5 Kg/cm.sup.2 
gauge. Then, the remaining unreacted monomer was purged off up to the 
pressure given below: 
______________________________________ 
Comparsion Example 
1 2 3 
______________________________________ 
Purge Pressure 2.1 2.6 1.0 
(Kg/cm.sup.2 gauge) 
______________________________________ 
In the second step, the polymerization was further advanced in such a 
manner, that the autoclave was first charged with ethylene and maintained 
at a temperature of 60.degree. C. and then, the polymerization was pursued 
in the presence of hydrogen by feeding an ethylene/propylene mixture so as 
to maintain a constant ethylene/propylene reaction ratio. 
The resulting polymerization slurry was treated in a similar manner as in 
Example 1. A white powdery polymer was obtained. 
The particulars in the polymerization and the material properties of the 
products are summarized in Tables I and II respectively. 
In Comparison Examples 1, 2 and 3, each a propylene/ethylene block 
copolymer was produced according to a conventional two-step process, 
wherein the polymerization in Comparison Example 1 was performed by 
maintaining an ethylene/propylene reaction ratio corresponding to the 
average of those in the second and third steps of Example 1 and the 
polymerizations in Comparison Examples 2 and 3 were carried out by 
maintaining ethylene/propylene reaction ratio equivalent to those in the 
second and third steps of Example 1 respectively. 
According to the conventional two-step process, it may be possible to 
obtain polymer product superior in the impact strength and brittle 
temperature which are characteristic of a block copolymer, by an adequate 
selection of the polymerization condition. However, the so obtained 
product is quite inferior in transparency and is poor in the impact 
blushing and stiffness, and thus is poor in the balance of material 
properties. 
On the contrary, according to the process of the present invention, a 
polymer product showing excellent balance in the material properties can 
be obtained without deteriorating the characteristic properties, i.e. the 
impact strength and brittle temperature. 
EXAMPLE 2 
(1) Synthesis of Catalyst 
(a) In a 200 l autoclave equipped with stirrer, 45.5 l of hexane and 11.8 l 
of TiCl.sub.4 were charged. While maintaining this solution at a 
temperature between -10.degree. and -5.degree. C., there was added 
dropwise a solution composed of 43.2 l of hexane and 13.5 l of 
diethylaluminum chloride over 3 hours under agitation. The reaction 
mixture was then kept at a temperature between -10.degree. and 0.degree. 
C. for 15 minutes. Thereafter, the temperature of the mixture was elevated 
to 65.degree. C. in two hours. After maintaining at this temperature for 
further two hours, the solid formed (referred to as reduced solid) was 
separated from the liquid phase, which was then washed 6 times with 50 l 
of hexane and thereafter separated from hexane. 
(b) The so obtained reduced solid was suspended in 92 l of hexane and 
thereto were added 19.6 l of diisoamyl ether. After this suspension was 
agitated for 1 hour at 35.degree. C., the solid (denoted hereinafter as 
ether-treated solid) was removed from the liquid phase and was washed with 
50 l of hexane 6 times, whereupon the hexane was separated. To the so 
obtained ether-treated solid, there were added 60 l of a 40 vol.-% 
solution of TiCl.sub.4 in hexane and the suspension was stirred for 2 
hours at 70.degree. C. 
The so reacted solid was separated from the liquid phase and was washed 10 
times with 50 l of hexane, whereupon it was separated from hexane to dry. 
The thus obtained solid was termed "titanium trichloride solid catalyst I". 
(2) Propylene-Ethylene Block-copolymerization 
A 250 l autoclave equipped with stirrer was evacuated, whereupon it was 
pressurized with propylene to 1 Kg/cm.sup.2 and than evacuated to -600 mm 
Hg gauge and this procedure was repeated three times. Subsequently, the 
autoclave was charged with 75 l of heptane, 8.5 g of titanium trichloride 
solid catalyst I and 128 g of diethylaluminum chloride to start the 
polymerization. 
The first step of the polymerization was conducted in the presence of 
hydrogen in such a manner, that the polymerization proceeded during the 
preceding period under successive feeding of propylene monomer at a 
pressure of 9 Kg/cm.sup.2 gauge at 70.degree. C. and, in the succeeding 
period, the polymerization was further advanced at 75.degree. C. without 
feeding of propylene monomer until the polymerization pressure reached 5 
Kg/cm.sup.2 gauge. Then, the unreacted monomer was discharged up to an 
internal pressure of 1.7 Kg/cm.sup.2 gauge and the temperature was 
adjusted at 60.degree. C. 
The second step was conducted at a polymerization temperature of 60.degree. 
C. while feeding ethylene so as to keep a constant ethylene propylene 
reaction ratio until the polymerization pressure fell to 0.5 Kg/cm.sup.2 
gauge. Then, 23 l of heptane were added thereto. 
The third step was carried out at a polymerization temperature of 
60.degree. C. in the presence of hydrogen by succeeding the polymerization 
by charging ethylene up to a pressure of 2 Kg/cm.sup.2 gauge. 
The resulting polymer slurry was treated quite the same as in Example 1 by 
adding 4 l of butanol, whereby a white powdery polymer was obtained. 
The particulars of the experimental condition as well as the results 
thereof are recited in Tables III and IV. 
EXAMPLES 3 and 4 
A 360 l autoclave having stirrer was charged, after it had been replaced in 
the same manner as in Example 1, with 100 l of heptane and 320 g of 
diethylaluminum chloride together with titanium trichloride to carry out 
the three-step polymerization. 
The first step was conducted in such a manner, that the polymerization 
proceeded during the preceding period under feeding propylene monomer at a 
pressure of 9 Kg/cm.sup.2 gauge at 70.degree. C. and, in the succeeding 
period, the polymerization was further advanced without feeding propylene 
monomer until a pressure reached 5 Kg/cm.sup.2 gauge. Then, the 
temperature was adjusted at 60.degree. C. and a procedure of monomer 
discharge up to predetermined pressure was employed. 
The second step was conducted at a polymerization temperature of 60.degree. 
C. by charging ethylene up to an elevated pressure and subsequent feeding 
of ethylene so as to further advance the polymerization until pressure 
reached predetermined value. 
The third step was carried out at a polymerization temperature of 
50.degree. C. by charging ethylene up to an elevated pressure and 
subsequent feeding of ethylene so as to succeed the polymerization. 
The first and the third steps of the polymerization were carried out under 
an addition of hydrogen gas. 
Then, the after-treatment same as in Example 1 was performed to obtain a 
white powdery polymer. 
The particulars of the experimental condition and the results thereof are 
summarized in Table III and in Tables IV and V respectively. 
Here, a titanium trichloride solid catalyst II employed in Example 3 had 
been prepared by the manner given below: 
Synthesis of Catalyst 
(a) In a 200 l autoclave equipped with stirrer, 52 l of hexane and 13.5 l 
of titanium tetrachloride were charged. To this solution, while 
maintaining it at a temperature between -10.degree. and -5.degree. C., a 
solution composed of 35 l of hexane and 16.5 l of diethylaluminum chloride 
was added dropwise over 4 hours under agitation. 
Then, the temperature was elevated to 105.degree. C. and agitation was 
continued further 2 hours at this temperature. After cooling by keeping 
still at room temperature, the so reacted solid was separated from the 
liquid phase, which was then washed with 50 l of hexane 6 times to leave a 
heat treated solid. 
(b) The so obtained heat treated solid was suspended in 120 l of toluene 
and thereto were added 26 l of di-n-butyl ether and 2.8 Kg of iodine, 
whereupon the mixture was agitated at 95.degree. C. for 1 hour. After the 
mixture was kept at room temperature, the solid was separated from the 
liquid phase and washed with 50 l of hexane 6 times to subject to drying. 
The so obtained solid was designated as titanium trichloride solid 
catalyst II. 
COMISON EXAMPLES 4 and 5 
The procedures of Examples 3 and 4 were followed respectively in Comparison 
Examples 4 and 5, except that the catalyst was changed, that the 
polymerization conditions in the second and third steps were altered and 
that a part of the monomers remaining unreacted at the end of the second 
step was purged off as they remained in excess of the requisite amount in 
the third step. The particulars of the experimental conditions and the 
results thereof as well as the material properties of the products are 
recited in Table III and in Tables IV and V respectively. 
Comparison Examples 4 and 5 represent the case in which the block copolymer 
was produced by a three-step polymerization other than the process 
according to the present invention. It is shown, that the copolymer 
products of these Comparison Examples are superior in the stiffness, 
transparency and impact blushing but show impact strength and brittle 
temperature lying in an extremely low level, and hence, the balance of 
material properties are poor. 
On the contrary, the products of Examples 2, 3 and 4 representing the 
present invention are improved in impact blushing and transparency without 
deteriorating the characteristic features of a block copolymer, i.e. 
impact strength and brittle temperature, so that it is clear that they are 
well-balanced in the material properties. 
TABLE I 
__________________________________________________________________________ 
Second Step Third Step 
First Step Ethylene/ Ethylene/ 
percent propylene 
percent propylene 
percent 
polymeri- 
reaction 
polymeri- 
reaction 
polymeri- 
[.eta.] 
zation 
[.eta.] 
ratio zation 
[.eta.] 
ratio zation 
dl/g 
wt % dl/g 
mole ratio 
wt % dl/g 
mole ratio 
wt % 
__________________________________________________________________________ 
Example 1 
1.71 
76 2.08 
51/49 6 3.40 
84/16 18 
Comparison 
Example 1 
1.79 
80 2.95 
74/26 20 -- -- -- 
Comparison 
Example 2 
1.81 
82 2.96 
54/46 18 -- -- -- 
Comparison 
Example 3 
1.70 
76 3.24 
83/17 24 -- -- -- 
__________________________________________________________________________ 
TABLE II 
__________________________________________________________________________ 
Izod impact 
Melt Brittle 
Flexural 
strength Impact Blushing 
index 
temp. 
stiffness 
Haze 
20.degree. C. 
-20.degree. C. 
20 cm 
50 cm 
g/10 min. 
.degree.C. 
Kg/cm.sup.2 
% Kg . cm/cm.sup.2 
cm.sup.2 
__________________________________________________________________________ 
Example 1 
1.8 -33 9500 85 13 5.0 1.6 3.1 
Comparison 
Example 1 
2.7 -24 9600 93 6.4 3.7 2.5 4.9 
Comparison 
Example 2 
3.1 -33 8700 96 16 5.0 1.9 3.8 
Comparison 
Example 3 
2.3 -15 10600 
91 5.9 3.4 1.3 2.5 
__________________________________________________________________________ 
TABLE III 
______________________________________ 
Com- Com- 
parison 
parison 
Polymerization 
Example Example Example 
Example 
condition 3 4 4 5 
______________________________________ 
Polymerization 
Titanium Titanium Titanium 
TAC-132 
catalyst trichlo- trichlo- trichlo- 
29 g 
ride ride ride 
solid solid solid 
catalyst catalyst catalyst 
II, 10 g I, 10 g I, 10 g 
First Step 
Polymerization 
temperature(.degree.C.) 
60 60 60 60 
Polymerization 
pressure(Kg/cm.sup.2 G) 
9 9 9 9 
Decreased 
reaction 
pressure(Kg/cm.sup.2 G) 
5 5 5 5 
Purged reaction 
pressure(Kg/cm.sup.2 G) 
1.4 2.1 2.4 2.2 
Second Step 
Polymerization 
temperature(.degree.C.) 
50 50 50 50 
Final 
pressure(Kg/cm.sup.2 G) 
1.0 0.8 0 0 
Ethylene/propylene 
mole ratio I* 
26/74 24/76 3.5/96.5 
13/87 
Third Step 
Polymerization 
temperature(.degree.C.) 
50 50 50 50 
Elevated 
pressure(Kg/cm.sup.2 G) 
2.0 2.0 2.0 2.5 
Ethylene/propylene 
mole ratio II** 
40/60 45/55 53/47 65/35 
______________________________________ 
*Ethylene/propylene mole ratio I represents the molar proportion of the 
amount of ethylene supplied versus the amount of propylene existing. 
**Ethylene/propylene mole ratio II represents the molar proportion of 
ethylene versus propylene. 
TABLE IV 
__________________________________________________________________________ 
Second Step Third Step 
First Step Ethylene/ Ethylene/ 
percent propylene 
percent propylene 
percent 
polymeri- 
reaction 
polymeri- 
reaction 
polymeri- 
[.eta.] 
zation 
[.eta.] 
ratio zation 
[.eta.] 
ratio zation 
dl/g 
wt % dl/g 
mole ratio 
wt % dl/g 
mole ratio 
wt % 
__________________________________________________________________________ 
Example 3 
1.81 
78 2.17 
45/55 5 3.16 
84/16 17 
Example 4 
1.79 
75 2.15 
37/63 7 3.20 
86/14 18 
Comparison 
Example 4 
2.14 
79 2.23 
7/93 6 2.83 
92/8 15 
Comparison 
Example 5 
1.90 
80 2.08 
21/79 5 2.97 
95/5 15 
__________________________________________________________________________ 
TABLE V 
__________________________________________________________________________ 
Melt Brittle 
Flexural 
Izod impact strength 
Impact blushing 
index 
temp. 
stiffness 
Haze 
20.degree. C. 
-20.degree. C. 
20 cm 
50 cm 
g/10 min. 
.degree.C. 
Kg/cm.sup.2 
% Kg . cm/cm.sup.2 
Kg . cm/cm.sup.2 
cm.sup.2 
__________________________________________________________________________ 
Example 3 
2.3 -30 9400 86 12 4.2 1.7 3.2 
Example 4 
2.0 -33 9200 84 13 4.7 1.6 3.2 
Comparison 
Example 4 
1.8 +5 11200 
80 3.3 2.3 0.5 1.2 
Comparison 
Example 5 
2.4 -4 9800 85 5.3 2.7 0.5 1.1 
__________________________________________________________________________ 
TABLE VI 
__________________________________________________________________________ 
First Step Second Step Third Step 
Ethylene/ Ethylene/ Ethylene/ 
propylene 
percent propylene 
percent propylene 
percent 
reaction 
polymeri- 
reaction 
polymeri- 
reaction 
polymeri- 
[.eta.] ratio zation 
[.eta.] 
ratio zation 
[.eta.] 
ratio zation 
dl/g mole ratio 
wt % dl/g 
mole ratio 
wt % dl/g 
mole ratio 
wt % 
__________________________________________________________________________ 
Example 
5 1.66 
0.4/99.6 
74.0 2.44 
59/41 7.1 3.96 
86/14 18.9 
__________________________________________________________________________ 
TABLE VII 
__________________________________________________________________________ 
Melt Brittle 
Flexural 
Izod impact strength 
Impact blushing 
index temp. 
stiffness 
Haze 
20.degree. C. 
-20.degree. C. 
20 cm 
50 cm 
g/10 min. 
.degree.C. 
Kg/cm.sup.2 
% Kg . cm/cm.sup.2 
Kg . cm/cm.sup.2 
cm.sup.2 
__________________________________________________________________________ 
Exam- 
ple 5 
1.9 -41 9400 86 17 5.9 1.6 3.2 
__________________________________________________________________________ 
EXAMPLE 5 
A 360 l reaction vessel (A) in a form of mixing tank was connected in 
series with a 400 l reaction vessel (B) of a form of fluidized bed to 
carry out therein a block copolymerization of propylene and ethylene. 
The first step of the polymerisation was conducted as follows: 
The reaction vessel (A) was charged, after the replacement performed as in 
Example 1, with 112 Kg of propylene and thereto were added 4.0 g of the 
titanium trichloride solid catalyst I, 224 g of diethylaluminum chloride 
and 5.2 g of methyl methacrylate, whereupon the temperature was adjusted 
at 70.degree. C. The polymerization was carried out in the presence of 
hydrogen under an addition of small amount of ethylene for 3 hours in the 
reaction medium of liquefied propylene monomer. After the polymerization, 
the polymerization slurry ws transferred into the reaction vessel (B) and 
the unreacted monomers were then purged off until a pressure reached 10 
Kg/cm.sup.2 gauge. 
The second step of the polymerization was conducted at 60.degree. C. in 
such a manner, that, after the vessel (B) was further charged with 
ethylene monomer till the pressure was elevated up to 12 Kg/cm.sup.2 
gauge, the polymerization was further advanced in gaseous phase while 
feeding ethylene. At the end of the second step, the remaining unreacted 
monomers were purged off until a pressure reached 5 Kg/cm.sup.2 gauge. 
The third step was conducted thereafter at 60.degree. C. in the presence of 
hydrogen by charging the vessel with ethylene up to an elevated pressure 
of 18 Kg/cm.sup.2 gauge. 
In the reaction vessel (B), a part of monomers was drawn out continuously 
at the top of the vessel and was returned via a heat exchanger to the 
vessel by blowing it into the bottom thereof in order to effect the 
fluidization of the polymer particles and in order to remove the heat of 
reaction. 
After the completion of the polymerization, the polymer particles were 
transferred into an after-treatment tank equipped with stirrer, in which 
they were washed with a mixture of 0.5 l of propylene oxide and 170 l of 
propylene 4 times to remove the catalyst residue. A white powdery polymer 
was obtained. 
Example 5 represents an embodiment of the process according to the present 
invention in which the polymerization is carried out in the absence of any 
inert solvent. It is seen that the product obtained in this Example shows 
also a superior balanced in material properties which is as excellent as 
that of the products obtained in Examples 1 to 4 employing an inert 
solvent.