WO1994011409A1

WO1994011409A1 - Process for polymerizing alpha-olefin

Info

Publication number: WO1994011409A1
Application number: PCT/US1993/010653
Authority: WO
Inventors: David Bell Morse
Original assignee: Shell Oil Company
Priority date: 1992-11-06
Filing date: 1993-11-05
Publication date: 1994-05-26
Also published as: CN1092431A; KR950704372A; AU5458394A; BR9307390A; CA2148596A1; EP0667875A1; MX9306919A

Abstract

A process for polymerizing one or more α-olefins of up to 20 carbon atoms which comprises contacting the one or more α-olefins under polymerization conditions with a catalyst system comprising: (a) a titanium halide-containing, magnesium-containing pro-catalyst component wherein the component is obtained by contacting a magnesium compound of the formula MgR'R', wherein R' and R' are, independently, alkoxide group, aryloxide group or halogen, with a halogenated tetravalent titanium compound in the presence of a polycarboxylic acid ester electron donor with or without a halohydrocarbon, (b) an organo-aluminium cocatalyst component, and (c) an organosilane selectivity control agent represented by general formula (i), wherein R1 is alkyl group of 13 to 30 carbon atoms, alkaryl group of 16 to 36 carbon atoms or aralkyl group of 16 to 36 carbon atoms; R?2 and R3¿ are, independently, methyl or alkyl group of 13 to 30 carbon atoms or hydrocarbyloxy group of 1 to 6 carbon atoms; and R4 is a hydrocarbyloxy group of 1 to 6 carbon atoms. The process affords high catalyst productivity and produces polymer products that have broad molecular weight distribution while retaining low oligomer content properties.

Description

DESCRIPTION

PROCESS FOR POLYMERIZING ALPHA-OLEFIN

Technical Field

This invention relates to a process for producing α- olefin polymers. More particularly, the invention relates to a process that utilizes a novel high activity stereoregular polymerization catalyst system to produce α-olefin polymers having improved polymer properties.

Background Art

The use of a solid, transition-metal based, olefin polymerization catalyst system including a titanium-containing, magnesium halide-based catalyst component to produce a polymer of an α-olefin such as ethylene, propylene, and butene-l, is well known in the art. Such polymerization catalyst systems are typically obtained by the combination of a magnesium halide-based catalyst component, an organoaluminum compound and one or more electron donors. For convenience of reference, the solid titanium-containing catalyst component is referred to herein as "procatalyst", the organoaluminum compound, as "cocatalyst", and an electron donor compound, which is typically used separately, or used partially or totally complexed with the organoaluminum compound, as "selectivity control agent" (SCA). It is also known to incorporate electron donor compounds into the pro-catalyst. The electron donor which is incorporated with the titanium-containing compounds serves a different purpose than the electron donor referred to as the selectivity control agent. The compounds which are used as the electron donor are the same as or different from compounds which are used as the selectivity control agent. The above-described stereoregular high activity catalysts are broadly conventional and are described in numerous patents and other references including Nestlerode et al, U. S. Patent 4,728,705, which is incorporated herein by reference.

Although a broad range of compounds are known generally as selectivity control agents, a particular catalyst component may have a specific compound or groups of compounds with which it is specially compatible. For any given procatalyst and/or cocatalyst, discovery of an appropriate type of selectivity control agent can lead to significant increases in catalyst efficiency, hydrogen utilization efficiency as well as an improvement in polymer product properties.

Many classes of selectivity control agents have been disclosed for possible use in polymerization catalysts. One class of such selectivity control agents is the class of organo-silanes. For example, Hoppin et al, U.S. Patent 4,990,478, describe branched C₃ - C₁₀ alkyl-t- butoxydimethoxysilanes. Other aliphatic silanes are described in Hoppin et al, U.S. Patent 4,829,038. Kioka et al, U.S. Patent 5,028,671, describe a catalyst system which incorporates various alkylalkoxysilanes, such as di-n- octadecyldimethoxysilane and di-n-octadecyldiethoxysilane as selectivity control agents.

Although many methods are known for producing highly stereoregular α-olefin polymers, it is still desired to improve the activity of the catalyst and produce polymers or copolymers that exhibit improved properties such as high melt flow and broad molecular weight distribution. Further, it is desired to produce polymers or copolymers that exhibit a reduction in the amount of volatiles.

Disclosure of the Invention

The invention relates to an improved process for the production of homopolymers or copolymers of α-olefins that have improved polymer properties.

More particularly, the present invention is a process for the production of polymers using a high activity olefin polymerization catalyst system which comprises (a) a titanium halide-containing procatalyst component obtained by halogenating a magnesium compound of the formula MgR'R", wherein R' and R" are alkoxide groups containing from 1 to 10 carbon atoms with a halogenated tetravalent titanium compound in the presence of a polycarboxylic acid ester electron donor, with or without a halohydrocarbon, (b) an organoaluminum cocatalyst component, and (c) an organosilane selectivity control agent having the general formula:

wherein R¹ is linear alkyl group of 13 to 30 carbon atoms, alkaryl group of 16 to 36 carbon atoms or aralkyl group of 16 to 36 carbon atoms; R² and R³ are, independently, methyl or alkyl groups of 13 to 30 carbon atoms, or hydrocarboxyloxy group of 1 to 6 carbon atoms; and R⁴ is hydrocarbyloxy group of 1 to 6 carbon atoms.

Description of the Invention

Although a variety of chemical compounds are useful for the production of the procatalyst, a typical procatalyst of the invention is prepared by halogenating a magnesium compound of the formula MgR'R", wherein R' is an alkoxide, aryloxide group or hydrocarbyl carbonate and R" is an alkoxide, hydrocarbyl carbonate, aryloxide group or halogen, with a halogenated tetravalent titanium compound in the presence of a halohydrocarbon and an electron donor.

The magnesium compound employed in the preparation of the solid catalyst component contains alkoxide, aryloxide, hydrocarbyl carbonate or halogen. The alkoxide, when present, contains from 1 to 10 carbon atoms. Alkoxides containing from 1 to 8 carbon atoms are preferable, with alkoxides of 2 to 4 carbon atoms being more preferable. The aryloxide, when present, contains from 6 to 10 carbon atoms, with 6 to 8 carbon atoms being preferred. The hydrocarbyl carbonate, when present, contains 1 to 10 carbon atoms. When halogen is present, it is present as bromine, fluorine, iodine or chlorine, with chlorine being preferred.

Suitable magnesium compounds are magnesium chloride, magnesium bromide, magnesium fluoride, ethoxy magnesium bromide, isobutoxy magnesium chloride, phenoxy magnesium iodide, cumyloxy magnesium bromide, magnesium diethoxide, magnesium isopropoxide, magnesium ethyl carbonate, ethoxy magnesium, magnesium stearate, magnesium laurate, and naphthoxy magnesium chloride. Especially preferred as the magnesium compounds are magnesium dialkoxides. Preferred magnesium compound is magnesium diethoxide.

Halogenation of the magnesium compound with the halogenated tetravalent titanium compound is effected by using an excess of the titanium compound. At least 2 moles of the titanium compound are used per mole of the magnesium compound. Preferably from 4 moles to 100 moles of the titanium compound are used per mole of the magnesium compound, and most preferably from 4 moles to 20 moles of the titanium compound are used per mole of the magnesium compound.

Halogenation of the magnesium compound with the halogenated tetravalent titanium compound is effected by contacting the compounds at an elevated temperature in the range from about 60°C to about 150°C, preferably from about 70°C to about 120ºC. Usually the reaction is allowed to proceed over a period of 0.1 to 6 hours, preferably from about 0.6 to about 3.5 hours. The halogenated product is a solid material which is isolated from the liquid reaction medium by a suitable separation method, such as conventional filtration.

The halogenated tetravalent compound employed to halogenate the magnesium compound contains at least two halogen atoms, and preferably contains four halogen atoms. The halogen atoms are chlorine atoms, bromine atoms, iodine atoms or fluorine atoms. The halogenated tetravalent titanium compound has up to two alkoxy or aryloxy groups. Examples of suitable halogenated tetravalent titanium compounds include diethoxytitanium dibromide, isopropoxytitanium triiodide, dihexoxytitanium dichloride, phenoxytitanium trichloride, titanium tetrachloride and titanium tetrabromide. The preferred halogenated tetravalent titanium compound is titanium tetrachloride.

Halogenation of the magnesium compound with the halogenated tetravalent titanium compound, as noted, is conducted in the presence of a halohydrocarbon and an electron donor with or without a halohydrocarbon. If desired, an inert hydrocarbon diluent or solvent may also be present. Suitable halohydrocarbons include aromatic or aliphatic, including cyclic and alicyclic compounds. Preferably the halohydrocarbon contains 1 or 2 halogen atoms, although more may be present if desired. It is preferred that the halogen is, independently, chlorine, bromine or fluorine. Exemplary of suitable aromatic halohydrocarbons are chlorobenzene, bromobenzene, dichlorobenzene, dichlorodibromobenzene, o-chlorotoluene, chlorotoluene, dichlorotoluene, chloronaphthalene. Chlorobenzene, o- chlorotoluene and dichlorobenzene are the preferred halohydrocarbons, with chlorobenzene and o-chlorotoluene being more preferred.

The aliphatic halohydrocarbons which can be employed suitably of 1 to 12 carbon atoms. Preferably such halohydrocarbons of 1 to 9 carbon atoms and at least 2 halogen atoms. Most preferably the halogen is present as chlorine. Suitable aliphatic halohydrocarbons include dibromomethane, trichloromethane, 1,2-dichloroethane, trichloroethane, dichlorofluoroethane, hexachloroethane, trichloropropane, chlorobutane, dichlorobutane, chloropentane, trichlorofluorooctane, tetrachloroisooctane, dibromodi-fluorodecane. The preferred aliphatic halohydrocarbons are carbon tetrachloride and trichloroethane.

Aromatic halohydrocarbons are preferred, particularly those of 6 to 12 carbon atoms, and especially those of 6 to 10 carbon atoms.

Typical electron donors that are incorporated within the procatalyst include esters, particularly aromatic esters, ethers, particularly aromatic ethers, ketones, phenols, amines, amides, imines, nitriles, phosphines, phosphites, stibines, arsines, phosphoramides and alcoholates. Esters of polycarboxylic acids are the preferred electron donors. Particularly preferred are alkyl esters of aromatic polycarboxylic acid. Illustrative of suitable esters of polycarboxylic acid electron donors are diethyl phthalate, diisoamyl phthalate, ethyl p-ethoxybenzoate, methyl p- ethoxybenzoate, diisobutyl phthalate, dimethyl napthalenedicarboxylate, diisobutyl maleate, diisopropyl terephthalate, and diisoamyl phthalate. Diisobutyl phthalate and ethyl-p-ethoxybenzoate are the preferred alkyl ester of an aromatic carboxylic acid.

After the solid halogenated product has been separated from the liquid reaction medium, it is treated one or more times with additional halogenated tetravalent titanium compound. Preferably, the halogenated product is treated multiple times with separate portions of the halogenated tetravalent titanium compound. Better results are obtained if the halogenated product is treated twice with separate portions of the halogenated tetravalent titanium compound. If desired, the solid halogenated product is treated one or more times with a mixture of halogenated tetravalent titanium compound and a halohydrocarbon. As in the initial halogenation, at least 2 moles of the titanium compound are employed per mole of the magnesium compound, and preferably from 4 moles to 100 moles of the titanium compound are employed per mole of the magnesium compound. Most preferably from 4 moles to 20 moles of the titanium compound per mole of the magnesium compound.

Optionally, the solid halogenated product is treated at least once with one or more acid chlorides during the additional treatments with the halogenated tetravalent titanium compound. Suitable acid chlorides include benzoyl chloride and phthaloyl chloride. The preferred acid chloride is phthaloyl chloride.

After the solid halogenated product has been treated one or more times with additional halogenated tetravalent titanium compound, it is separated from the liquid reaction medium, washed at least once with an inert hydrocarbon of up to 10 carbon atoms to remove unreacted titanium compounds, and dried. Exemplary of the inert hydrocarbons that are suitable for the invention are isopentane, isooctane, hexane, heptane and cyclohexane.

Preferred final washed products have a titanium content of from 0.5 percent by weight to 6.0 percent by weight. A more preferred final wash product has from 1.5 percent by weight to 4.0 percent by weight. The atomic ratio of titanium to magnesium in the final product is between 0.01:1 and 0.2:1. A preferred final product has an atomic ratio of titanium to magnesium from about 0.02:1 to 0.15:1.

The cocatalyst is an organoaluminum compound which is typically an alkylaluminum compound. Suitable alkylaluminum compounds include trialkylaluminum compounds, such as triethylaluminum or triisobutylaluminum; dialkylaluminum halides such as diethylaluminum chloride and dipropylaluminum chloride; and dialkylaluminum alkoxides such as diethylaluminum ethoxide. Trialkylaluminum compounds are preferred, with triethylaluminum being the preferred trialkylaluminum compound.

The organosilane selectivity control agents in the catalyst system contain at least one silicon-oxygen-carbon linkage. Suitable organosilane compounds include compounds having the following general formula: 4

wherein R¹ is a linear alkyl group of 13 to 30 carbon atoms, alkaryl group of 16 to 36 carbon atoms or aralkyl group of 16 to 36 carbon atoms. It is preferred that R¹ is alkyl group of 16 to 30 carbon atoms, alkaryl group of 19 to 30 carbon atoms or aralkyl group of 19 to 30 carbon atoms. It is further preferred that R¹ is alkyl group of 18 to 28 carbon atoms. R² and R³ are, independently, methyl or alkyl group of 13 to 30 carbon atoms, or hydrocarbyloxy groups of 1 to 6 carbon atoms. It is preferred that R² and R³ are, independently, methyl or alkyl group of 16 to 30 carbon atoms or alkoxy group of 1 to 4 carbon atoms. It is further preferred that R² is methyl or alkyl group of 18 to 28 carbon atoms or alkoxy group of 1 to 4 carbon atoms and R³ is alkoxy group of 1 to 4 carbon atoms. It is preferred that R⁴ is alkoxy group of 1 to 4 carbon atoms. R⁴ is hydrocarbyloxy group of 1 to 6 carbon atoms. It is further preferred that R², R³ and R⁴ are ethoxy or methoxy groups. Examples of suitable organosilane selectivity control agents include n-octadecyltriethoxysilane, n-triacontyl- triethoxysilane, methyl-n-octadecyldimethoxysilane, methyl-n- octadecyldiethoxysilane, n-octadecyltrimethoxysilane, n- triacontyltrimethoxysilane and mixtures thereof. The preferred organosilane selectivity control agents are n-octadecyltriethoxysilane, n-methyloctadecyldimethoxysilane and n- octadecyltrimethoxysilane. The invention also contemplates the use of mixtures of two or more selectivity control agents. The selectivity control agent is provided in a quantity such that the molar ratio of the selectivity control agent to the titanium present in the procatalyst is from about 0.5 to about 80. Molar ratios from about 2 to about 60 are preferred, with molar ratios from about 5 to about 40 being more preferred.

The high activity stereoregular polymerization catalyst is utilized to effect polymerization by contacting at least one α-olefin under polymerization conditions. In accordance with the invention, the procatalyst component, organoaluminum cocatalyst, and selectivity control agent are introduced into the polymerization reactor separately or, if desired, two or all of the components are partially or completely mixed with each other before they are introduced into the reactor.

The particular type of polymerization process utilized is not critical to the operation of the present invention and the polymerization processes now regarded as conventional are suitable in the process of the invention. The polymerization is conducted under polymerization conditions as a liquid phase or a gas-phase process employing a fluidized catalyst bed.

The polymerization conducted in the liquid phase employs as reaction diluent an added inert liquid diluent or alternatively a liquid diluent which comprises the olefin, such as propylene or 1-butene, undergoing polymerization. If a copolymer is prepared wherein ethylene is one of the monomers, ethylene is introduced by conventional means to a diluent. Typical polymerization conditions include a reaction temperature from about 25°C to about 125°C, with temperatures from about 35°C to about 90°C being preferred, and a pressure sufficient to maintain the reaction mixture in a liquid phase. Such pressures are from about 150 psi to about 1200 psi, with pressures from about 250 psi to about 900 psi are preferred. The liquid phase reaction is operated in a batchwise manner or as a continuous or semi-continuous process. Subsequent to reaction, the polymer product is recovered by conventional procedures. The precise controls of the polymerization conditions and reaction parameters of the liquid phase process are within the skill of the art.

As an alternate embodiment of the invention, the polymerization is conducted in a gas phase process in the presence of a fluidized catalyst bed. One such gas phase process polymerization process is described in Goeke et al, U.S. Patent 4,379,759, incorporated herein by reference. The gas phase process typically involves charging to reactor an amount of preformed polymer particles, gaseous monomer and separately charge a lesser amount of each catalyst component. Gaseous monomer, such as propylene, is passed through the bed of solid particles at a high rate under conditions of temperature and pressure sufficient to initiate and maintain polymerization. Unreacted olefin is separated and recovered and polymerized olefin particles are separated at a rate substantially equivalent to its production. The process is conducted in a batchwise manner or a continuous or semicontinuous process with constant or intermittent addition of the catalyst components and/or α-olefin to the polymerization reactor. Typical polymerization temperatures for a gas phase process are from about 30°C to about 120°C and typical pressures are up to about 1000 psi, with pressures from about 100 to about 500 psi being preferred.

In both the liquid phase and the gas-phase polymerization processes, molecular hydrogen is added to the reaction mixture as a chain transfer agent to regulate the molecular weight of the polymeric product. Hydrogen is typically employed for this purpose in a manner well known to persons skilled in the art. The precise control of reaction conditions, the rate of addition of feed component and molecular hydrogen is broadly within the skill of the art.

The present invention is useful in the polymerization of α-olefins of up to 20 carbon atoms, such as propylene, dodecane, including mixtures thereof. It is preferred that α- olefins of 3 carbon atoms to 8 carbon atoms, such as propylene, butene-1 and pentene-1 and hexane-1, are polymerized.

The polymers produced according to this invention are predominantly isotactic. Polymer yields are high relative to the amount of catalyst employed. The process of the invention produce homopolymers and copolymers including both random and impact copolymers having a relatively high stiffness while having a broad molecular weight distribution and maintaining an oligomers content (determined by the weight fraction of C₂₁ oligomer) of less than 300 ppm if a homopolymer and less than 600 ppm if a copolymer. The preferred homopolymers of the invention have an oligomers content of less than 150 ppm is preferred. More preferred homopolymers have oligomers content of less than 80 ppm. A reduction in oligomers content is indicative of a reduction in volatiles, e.g. smoke and/or oil, liberated during subsequent processing, e.g. extrusion.

Other features, advantages and embodiments of the invention disclosed herein will be readily apparent to those exercising ordinary skill after reading the foregoing disclosure. In this regard, while specific embodiments of the invention have been described in detail, variations and modifications of these embodiments can be effected without departing from the spirit and scope of the invention as described and claimed.

The invention described herein is illustrated, but not limited by the following Illustrative Embodiments and

Comparative Example. The following terms are used throughout the Illustrative Embodiments and Comparative Example:

ODTMS (n-octadecyltrimethoxysilane)

ODTES (n-octadecyltriethoxysilane)

DNDDMS (di-n-decyldimethoxysilane)

DDTMS (n-dodecyltrimethoxysilane)

TCTMS (n-triacontyltrimethoxysilane) MNDDMS (methyl-n-decyldimethoxysilane)

MODDES (methyl-n-octadecyldiethoxysilane) PEEB (ethyl-p-ethoxybenzoate)

NPTMS (n-propyltrimethoxysilane)

DIBDES (diisobutyldiethoxysilane)

DIBDMS (diisobutyldimethoxysilane)

ILLUSTRATIVE EMBODIMENT I

(a) Preparation of Procatalyst Component

The procatalyst was prepared by adding magnesium diethoxide (2.17 g, 19 mmol) to 55 ml of a 50/50 (vol/vol) mixture of TiCl₄/chlorobenzene. After adding diisobutyl phthalate (0.74 ml, 2.75 mmol), the mixture was heated in an oil bath and stirred at 110°C for 60 minutes. The mixture was filtered hot and the solid portion was slurried in 55 ml of a 50/50 (vol/vol) mixture of TiCl₄/chlorobenzene. In the preparation of some of the procatalyst, phthaloyl chloride (0.13 ml, 0.90 mmol) was added to the slurry at room temperature. The resulting slurry was stirred at 110°C for 60 minutes, filtered, and the solvent obtained was slurried again in a fresh 50/50 mixture of TiCl₄/chlorobenzene. After stirring at 110°C for 30 minutes, the mixture was filtered and allowed to cool to room temperature. The procatalyst slurry was washed 6 times with 125 ml portions of isooctane and then dried for 120 minutes, at 25°C, under nitrogen.

(b) Polymerization of Propylene

Various catalysts were produced using several organosilanes as the selectivity control agent, some of which are within the scope of the invention (TCTMS, ODTES, ODTMS, and MODDES) and others that are not within the scope of the invention (NPTMS, DNDDMS, DIBDES, DDTMS, MNDDMS and DIBDMS). Propylene (2700cc) and molecular hydrogen were introduced into a 1 gallon autoclave. The temperature of the propylene and molecular hydrogen was raised to 67°C. An organosilane selectivity control agent, triethylaluminum, and the procatalyst slurry produced above were premixed for about 20 minutes and then the mixture was introduced into the autoclave. The amount of silane utilized in the polymerization also varied. The amount of triethylaluminum (0.70 mmoles) and. the amount of the procatalyst slurry (sufficient quantity of procatalyst to provide 0.01 mmoles of titanium) remained constant. The autoclave was then heated to about 67ºC and the polymerization was continued at 67°C for one hour. The polypropylene product was recovered from the resulting mixture by conventional methods and the weight of the product was used to calculate the reaction yield in millions of grams of polymer product per gram (MMg/g) of titanium in the procatalyst. The term "Q" was calculated as the quotient of the weight average molecular weight (M_w) and the number average molecular weight (M_n) determined by gel permeation chromatography. The term "M_z" as defined in "Encyclopedia of Polymer Science and Engineering, 2nd Edition", Vol. 10, pp. 1-19 (1987), incorporated herein by reference, is the z-average molecular weight. The term "R" was calculated as the quotient of M_z and M_w. "Melt Flow" is determined according to ASTM D-1238-73, condition L. "Viscosity Ratiof was determined by cone and plate rheometry (dynamic viscosity measurements) as a ratio of the viscosity of the product at a frequency of 0.1 Hz divided by the viscosity of the product at a frequency of 1.0 Hz. As the viscosity ratio of polymer product increases, the molecular weight distribution increases.

The results of a series of polymerizations are shown in TABLE I.

¹ Comparison

² Final melt flow of polymer product

³ Viscosity Ratio - η_0.1/η_1.0 at 200ºC

⁴ Procatalyst prepared with phthaloyl chloride.

⁵ Procatalyst prepared without phthaloyl chloride.

Comparative Example

(a) Preparation of Procatalyst Component

The procatalyst was prepared by adding magnesium diethoxide (50 mmol) to 150 ml of a 50/50 (vol/vol) mixture of chlorobenzene/TiCl₄. After adding ethyl benzoate (16.7 mmol), the mixture was heated in an oil bath and stirred at 110°C for approximately 60 minutes. The resulting slurry was filtered and slurried twice with 150 ml of a fresh 50/50 (vol/vol). Benzoyl chloride (0.4 ml) was added to the final slurry. After stirring at 110°C for approximately 30 minutes, the mixture was filtered. The slurry was washed six times with 150 ml portions of isopentane and then dried for 90 minutes, at 30°C, under nitrogen.

(b) Polymerization

Using the above-described procatalyst (section a), propylene was polymerized as, described in Illustrative Embodiment I, section (b), except the selectivity control agent was PEEB.

Illustrative Embodiment II

To illustrate a further advantage of the catalyst system of the invention, polymer products having a melt flow of about 3.0 dg/min were produced according to the procedures described in Illustrative Embodiment I and the Comparative Example. In particular, the polymer products were produced using 0.2 mmol of the specified selectivity control agent ("SCA") and sufficient hydrogen necessary to produce a polymer having a melt flow of about 3.0 dg/min. The values are shown in TABLE II.

TABLE II

1 0.2 mmol of each selectivity control agent was used. 2 For comparison

3 Comparative Example

4 mmol of H₂ required to make a polymer product having a melt flow of about 3 dg/min

As noted, the catalyst systems of the invention exhibit increased hydrogen utilization efficiency.

Illustrative Embodiment Ill

Viscosity ratio values were taken for the polymers having a melt flow of about 3 dg/min. The values are shown in TABLE III.

Table III

¹ For comparison

It is seen from TABLE III that the catalyst systems of the invention exhibit a higher viscosity ratio and therefore a broader molecular weight distribution than conventional catalyst systems using NPTMS as the selectivity control agent.

Claims

1. A process for polymerizing one or more α-olefins of up to 20 carbon atoms which comprises contacting the one or more α-olefins under polymerization conditions with a catalyst system comprising:

(a) a magnesium halide-containing procatalyst component containing magnesium, titanium, halide and a polycarboxylic acid ester, said procatalyst component being obtained by halogenating a magnesium compound of the formula MgR'R", wherein R' and R" are alkoxide groups of 1 to 10 carbon atoms, with a halogenated tetravalent titanium compound, in the presence of a halohydrocarbon and a polycarboxylic acid ester electron donor with or without a halohydrocarbon;

(b) an organoaluminum cocatalyst component; and

(c) an organosilane selectivity control agent having the formula:

wherein R¹ is a linear alkyl group of 13 to 30 carbon atoms, alkaryl group of 16 to 36 carbon atoms or aralkyl group of 16 to 36 carbon atoms; R² and R³ are, independently, methyl or alkyl group of 13 to 30 carbon atoms or hydrocarbyloxy group of 1 to 6 carbon atoms; and R⁴ is a hydrocarbyloxy group of 1 to 6 carbon atoms.

2. The process of claim 1, wherein said organosilane selectivity control agent is present in a quantity such that the molar ratio of the selectivity control agent to titanium present in the procatalyst component is from about 0.5 to about 80.

3. The process of claim 2 wherein R¹ is alkyl group of 16 to 30 carbon atoms, alkyaryl group of 19 to 30 carbon atoms or aralkyl group of 19 to 30 carbon atoms; R² and R³ are, independently, methyl or alkyl group of 16 to 30 carbon atoms or alkoxy group of 1 to 4 carbon atoms, and R⁴ is alkoxy group of 1 to 4 carbon atoms.

4. The process of claim 3, wherein the organosilane selectivity control agent is n-octadecyltriethoxysilane, n- octadecyltrimethoxysilane, n-triacontyltrimethoxysilane, n- triacontyltriethoxysilane, methyl-n-octadecyldimethoxysilane, methyl-n-octadecyldiethoxysilane or mixtures thereof.

5. The process of claim 4, wherein the organosilane is n-octadecyltrimethoxysilane, n-octadecyltriethoxysilane, methyl-n-octadecyldiethoxysilane or methyl-n-octadecyldimethoxysilane.

6. The process of claim 5, wherein the halogenated tetravalent titanium compound is titanium tetrachloride.

7. The process of claim 6, wherein the magnesium compound is magnesium ethoxide.

8. The process of claim 7, wherein the polycarboxylic acid ester electron donor is diisobutyl phthalate.

9. The process of claim 8, wherein the α-olefins are propylene and ethylene.

10. The process of claim 9, wherein the α-olefin is propylene.

11. In a process for polymerizing at least one α- olefin of up to 20 carbon atoms which comprises contacting at least one α-olefin under polymerization conditions with a catalyst system comprising:

(a) a magnesium halide containing procatalyst obtained by halogenating magnesium compound of the formula MgR'R", wherein R' and R" are, independently, alkoxide group or aryloxide group with a halogenated tetravalent titanium compound, in the presence of a polycarboxylic acid ester with or without a halohydrocarbon,

(b) an organoaluminum cocatalyst, and

(c) an organosilane selectivity control agent,

the improvement in the process wherein the organosilane selectivity control agent has the formula:

wherein R¹ is alkyl group of 13 to 30 carbon atoms, alkaryl group of 16 to 36 carbon atoms or aralkyl group of 16 to 36 carbon atoms; R² and R³ are, independently, methyl and alkyl group of 13 to 30 carbon atoms or hydrocarbyloxy group of 1 to 6 carbon atoms; and R⁴ is hydrocarbyloxy group of 1 to 6 carbon atoms.

12. The process of claim 11 wherein R¹ is alkyl group of from 16 to 30 carbon atoms, alkaryl group of 19 to 30 carbon atoms or aralkyl group of 19 to 30 carbon atoms; and R² and R³ are, independently, methyl or alkyl group of 16 to 30 carbon atoms or alkoxy group of 1 to 4 carbon atoms.

13. The process of claim 12 wherein R³ and R⁴ are alkoxy groups of 1 to 2 carbon atoms.

14. The process of claim 13, wherein the organosilane selectivity control agent is selected from the group consisting of n-octadecyltrimethoxysilane, n-octadecyltriethoxysilane, n-triacontyltri-methoxysilane, n-triacontyltriethoxysilane, methyl-n-octadecyldimethoxysilane, methyl-n- octadecyldiethoxysilane and mixtures thereof.

15. An olefin polymerization catalyst system comprising:

(a) a magnesium halide-containing procatalyst component obtained by halogenating a magnesium compound with a halogenated tetravalent titanium compound, in the presence of polycarboxylic acid ester compound with or without a halogenated hydrocarbon,

(b) an organoaluminum cocatalyst component, and

(c) an organosilane selectivity control agent having the formula

wherein R¹ is an alkyl group of 13 to 30 carbon atoms, alkaryl group of 16 to 36 carbon atoms or aralkyl group of 16 to 36 carbon atoms; R² and R³ are, independently, methyl or alkyl group of 13 to 30 carbon atoms or hydrocarbyloxy group of 1 to 6 carbon atoms; and R⁴ is hydrocarbyloxy group of 1 to 6 carbon atoms.

16. The olefin polymerization catalyst system according to claim 15, wherein the molar ratio of the selectivity control agent to the titanium present in the procatalyst is from about 0.5 to about 80.

17. The olefin polymerization catalyst system according to claim 16, wherein the magnesium compound is magnesium alkoxide, the halogenated tetravalent titanium compound contains at least four halogen atoms and the organoaluminum cocatalyst is a trialkylaluminum compound.

18. The olefin polymerization catalyst system according to claim 17, wherein the magnesium compound is magnesium diethoxide, the polycarboxylic acid ester compound is diisobutyl phthalate, and the halohydrocarbon is chlorobenzene or o-chlorotoluene.