WO1994006833A1

WO1994006833A1 - Process for polymerizing alpha-olefin

Info

Publication number: WO1994006833A1
Application number: PCT/US1993/008622
Authority: WO
Inventors: Stanley Edward Wilson; David Merrill Rebhan
Original assignee: Shell Oil Company
Priority date: 1992-09-14
Filing date: 1993-09-14
Publication date: 1994-03-31
Also published as: AU4859193A

Abstract

A process for polymerizing one or more α-olefins of up to 10 carbon atoms which comprises contacting the one or more α-olefin under polymerization conditions with a catalyst system comprising: (a) a titanium halide-containing magnesium, titanium, halide and polycarboxylic acid containing a 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 halohydrocarbon and a polycarboxylic acid ester electron donor, (b) an organo-aluminum cocatalyst component, and (c) an organosilane selectivity control agent represented by general formula (I), wherein R?1 and R2¿ are, independently, alkyl groups containing from 1 to 12 carbon atoms; aryl groups containing from 1 to 12 carbon atoms, alkaryl groups containing from 1 to 12 carbon atoms, aralkyl groups containing from 1 to 12 carbon atoms, hydrocarbyloxy groups containing 1 to 12 carbon atoms or halogen; and R?3 and R4¿ are hydrocarbyloxy groups containing from 2 to 12 carbon atoms. The process affords high catalyst productivity and produces polymer products having improved polymer properties such as broad molecular weight distribution, and high stiffness while retaining low oligomer content.

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 for producing α-olefin polymers having improved proper-ties, using a novel high activity stereoregular polymerization catalyst system. Background Art The use of a solid, transition-metal based, olefin polymerization catalyst system including a magnesium-containing, titanium halide-based catalyst component to produce a polymer of an α-olefin such as ethylene, propylene, and butene-1, is well known in the art. Such polymerization catalyst systems are typically obtained by the combination of a titanium 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 partially or totally complexed with the organoaluminum compound, as "selectivity control agent" (SCA) . It is also known to incorporate electron donor compounds into the procatalyst. 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 may be the same or different 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, lower hydrogen demand as well as the 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 C - C alkyl-t- butoxydi ethoxysilanes. Other aliphatic silanes are described in Hoppin et al, U.S. Patent 4,829,038.

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 broad molecular weight distribution. Further, it is desired to produce polymers or copolymers that exhibit a reduction in the amount of volatiles, e.g., smoke and/or oil, liberated during subsequent processing, e.g. extrusion.

Disclosure of the Invention

The invention relates to a process for the production of polymers or copolymers 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, and a halohydrocarbon, (b) an organoaluminum cocatalyst component, and (c) an organosilane selectivity control agent having the general formula:

wherein R¹ and R² are, independently, alkyl containing 1 to 12 carbon atoms, aryl containing 1 to 12 carbon atoms, alkaryl containing 1 to 12 carbon atoms, aralkyl containing 1 to 12 carbon atoms, hydrocarbyloxy containing 1 to 12 carbon atoms or halogens; and R³ and R⁴ are hydrocarbyloxy containing from 2 to 12 carbon atoms. It is preferred that R¹ and R² are alkyl groups or alkoxy groups and R³ and R⁴ are alkoxy groups. It is further preferred that R¹ and R² are, independently, alkyl or alkoxy, and R³ and R⁴ are ethoxy groups. It is further preferred that R¹, R², R³ and R⁴ are ethoxy groups. The preferred selectivity control agents are tetraethoxysilane and isobutyltriethoxysilane. Best Mode for Carrying Out 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 or aryloxide group 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, contain from 1 to 10 carbon atoms. Alkoxide containing fy?m 1 to 8 carbon atoms is 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 preferably present as bromine, fluorine, iodine or chlorine, with chlorine being more preferred.

Suitable magnesium compounds are magnesium chloride, ethoxy magnesium bromide, isobutoxy magnesium chloride, phenoxy magnesium iodide, cumyloxy magnesium bromide, magnesium diethoxide, magnesium isopropoxide, magnesium ethyl carbonate and naphthoxy magnesium chloride. The preferred magnesium compound is magnesium diethoxide. Halogenation of the magnesium compound with the halo-genated tetravalent titanium compound is effected by using an excess of the titanium compound. At least 2 moles of the titanium compound should ordinarily be 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 can be 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 120°C. Usually the reaction is allowed to proceed over a period of 0.1 to 6 hours, preferably from about 0.5 to about 3.5 hours. The halogenated product is a solid material which can be isolated from the liquid reaction medium by filtration, decantation or a suitable method.

The halogenated tetravalent titanium 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 compounds has up to two alkoxy or aryloxy groups. Examples of suitably 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 con-ducted in the presence of a halohydrocarbon and an electron donor. If desired, an inert hydrocarbon diluent or solvent may also be present, although this is not necessary.

The halohydrocarbon employed is an aromatic or aliphatic, including cyclic and alicyclic compounds. Preferably the halohydrocarbon contains 1 or 2 halogen atoms, although more halogens may be present if desired. It is preferred that each halogen is chlorine, bromine or fluorine, particularly chlorine. Suitable aromatic halohydrocarbons include 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 contain from 1 to 12 carbon atoms. Preferably such halohydrocarbons contain from 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, dichloro- butane, chloropentane, trichlorofluorooctane, tetrachloro- isooctane, dibromodifluorodecane. The preferred aliphatic halohydrocarbons are carbon tetrachloride and trichloro¬ ethane. Aromatic halohydrocarbons are preferred, particularly those containing from 6 to 12 carbon atoms, and especially those containing from 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, phosphineε, phosphites, stibines, arsines, phosphoramides and alcoholateε. Aromatic poly-carboxylic acid esters are frequently incorporated into electron donors. Illustrative of such electron donors are methyl benzoate, ethyl benzoate, diethyl phthalate, diisoamyl phthalate, ethyl p- ethoxybenzoate, methyl p-ethoxybenzoate, diisobutyl phthalate, dimethyl napthalenedicarboxylate, diisobutyl maleate, diisopropyl terephthalate, and diisoamyl phthalate. Diisobutyl phthalate is the preferred aromatic carboxylic acid ester. 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. Pre-ferably, 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. As in the initial halogenation, at least 2 moles of the titanium compound should ordinarily be 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. The reaction conditions employed to treat the solid halogenated product with the titanium compound are the same as those employed during the initial halogenation of the magnesium compound.

Optionally, the solid halogenated product is treated at least once with one or more acid chlorides after washing the solid halogenated product at least once with additional amounts of 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 t e, liquid reaction medium, washed t 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 washing are isopentane, isooctane, hexane, heptane and cyclohexane.

The final washed product has a titanium content of from 0.5 percent by weight to 6.0 percent by weight, preferably from 2.0 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, preferably between 0.02:1 and 0.1:1.

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

The organoaluminum cocatalyst is employed in sufficient quantity to provide from 1 mole to about 150 moles of aluminum per mole of titanium in the procatalyst. It is preferred that the cocatalyst is present in sufficient quantities to provide from 10 moles to about 100 moles of aluminum per mole of titanium in the procatalyst.

The o: anosilr.ne selectivity control agents in the catalyst system contain at least one silicon-oxygen- carbon linkage. Suitable organosilane compounds includes compounds having the following general formula: R' R³

^s ^y^ ^V \_R4 wherein R¹ and R² are, independently, alkyl groups containing from 1 to 12 carbon atoms, aryl groups containing from 1 to 12 carbon atoms, alkaryl groups containing from 1 to 12 carbon atoms, aralkyl groups containing from 1 to 12 carbon atoms, hydrocarbyloxy groups containing 1 to 12 carbon atoms or halogen; and R³ and R⁴ are hydrocarbyloxy groups containing from 2 to 12 carbon atoms. It is preferred that R¹ and R² are, independently, groups containing from 1 to 12 carbon atoms, alkyl or alkoxy groups containing from 1 to 12 carbon atoms, and R³ and R⁴ are alkoxy groups containing from 2 to 12 carbon atoms, and R³ and R⁴ are ethoxy groups. It is further preferred that R¹, R², R³ and R⁴ are ethoxy groups. Examples of suitable organosilane selectivity control agents include tetraethoxysilane, isobutyltriethoxysilane, diethyldi- ethoxysilane, phenyltriethoxysilane, benzyltriethoxyεilane, methyltriethoxysilane, diphenyldiethoxysilane, ethyltri- ethoxysilane, diisobutyldiethoxysilane and mixtures thereof. The preferred organosilane selectivity control agents are tetraethoxysilane and isobutyltriethoxysilane, with tetraethoxysilane being more preferred. 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 2 to about 60. Molar ratios from about 8 to about 45 are preferred, with molar ratios from about 10 to about 35 being more preferred.

The high activity stereoregular polymerization cata-lyst 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 can be introduced into the polymerization reactor separately or, if desired, two or all of the components may be 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 as 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. Typical poly-merization 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 may be 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 recycled, 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 semi-continuous process with constant or intermittent addition of the catalyst components and/or α-olefin to the polymerization reactor. Preferably the process is a continuous process. 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, and the rate of addition of feed component and molecular hydrogen is broadly within the skill of the art. In addition to hydrogen, other chain transfer agents may be employed to regulate the molecular weight of the polymers.

The present invention is useful in the polymerization of α-olefins of up to 10 carbon atoms, including mixtures thereof. It is preferred that α-olefins of 3 carbon atoms to 8 carbon atoms, such as propylene, butene-l and pentene-1 and hexane-1, are polymerized, if copolymerization, α-olefins of 2 carbon atoms to 8 carbon atoms. The polymers produced according to this invention are predominantly isotactic. Polymer yields are high relative to the amount of catalyst employed. It is desirable that the process of the invention produce polymer or copolymer including random or impact copolymer, having a relatively high stiffness (as indicated by high Flexural Modulus) while maintaining an oligomers content (determined by the weight fraction of C₂ι oligomer) of less than 200 ppm. An oligomers content of less than 150 ppm is more desirable, with an oligomers content of less than 130 ppm being most preferred. The Flexural Modulus of the homopolymers or copolymers, including both random and impact copolymers, produced according to this invention, is greater than 180,000 psi. The Flexural Modulus is often greater than 200,000 psi and may be greater than 230,000 psi being most desirable.

Other features, advantages and embodiments of the invention disclosed herein will be readily apparent to those exercising ordinary skill after reading the foregoing dis-closure. 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 the Comparative Example. The following terms are used throughout the Illustrative Embodiments and Comparative Example:

DEDES (Diethyldiethoxysilane)

ETES (Ethyltriethoxysilane)

DPDES (Diphenyldiethoxysilane) TEOS (Tetraethoxysilane)

PEEB (Ethyl p-ethoxybenzoate)

DPDES (Diphenyldiethoxysilane)

VTES (Vinyltriethoxysilane)

MCHDES (Methylcyclohexyldiethoxysilane) MTES (Methyltriethoxysilane)

IBTES (Isobutyltriethoxysilane)

NPTMS (n-propyltrimethoxysilane)

DIBDES (diisobutyldiethoxysilane) 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 (0.66 ml, 2.50 mmol), the mixture was heated in an oil bath and stirred at 110°C for 60 minutes. The mixture was filtered hot and slurried in 55 ml of a 50/50 (vol/vol) mixture of TiCl₄/chlorobenzene. 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 slurried again in a fresh 50/50 mixture of TiCl₄/chlorobenzene. After stirring at 110°C for 30 minutes, the mixture was filtered and the reaction vessel was 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 (DEDES, TEOS, ETES, DPDES, MTES, MCHDES, and DIBDES) and others that are not within the scope of the invention (NPTMS and DIBDMS) . Propylene (2700cc) and molecular hydrogen were introduced into a 1 gallon autoclave. The temperature of the propylene was raised to 62°C. An organosilane selectivity control agent, triethylaluminum, and the procatalyst slurry 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 (0.56 mmoles) and the amount of the procatalyst slurry (sufficient quantity of procatalyst to provide 0.008 mmoles of titanium to the autoclave) remained constant. The autoclave was then heated to about 67°C 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,,,) and the number average molecular weight (M , 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^ "Melt Flow" is determined according to ASTM D-1238-73, condition L. The results of a series of polymerizations are shown in TABLE I.

TABLE I

² mmoles of hydrogen added tc the liquid phase reactor system

To further illustrate the advantages obtained using the catalyst system of the invention, viscosity ratio values were taken for polymers having a melt flow of about 3 dg/min. "Viscosity Ratio" 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 values are shown in TABLE II.

Table II

SCA Viscosit Ratio

TEOS DPDES

NPTMS¹ DIBDES MTES MCHDES

^or comparison

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

(a) Preparation of Procatalyst Component The procatalyst was prepared as directed in

Illustrative Embodiment I, section (a) , except the filtered product (solid halogenated product) was not treated with phthaloyl chloride.

(b) Gas-Phase Polymerization of Propylene The polymerization activity of the various catalyst systems was determined by gas-phase polymerization as described and illustrated in U.S. Patent 4,983,562, incorporated herein by reference. In each polymerization, the procatalyst component was fed into a gas-phase reactor as a 30 percent by weight dispersion in mineral oil. Simultaneously and continuously, triethylaluminum cocatalyst, as a 5 percent by weight solution in isopentane and the indicated selectivity control agent (various catalysts were produced using several organosilanes as the selectivity control agent, some of which are within the scope of the invention and others are used to prepare comparison catalysts), as a 0.5 to 5 percent by weight solution in isopentane, were introduced into the reactor. Sufficient hydrogen was introduced to regulate the molecular weight of the polymer produced. A small amount of nitrogen was also present. The partial pressure of propylene was from about 330 psi to about 380 psi. The polymerization temperature was 65°C and the residence time was 2 hours. The polypropylene product was recoverec by conventional means. The results of a series of polymerizations are shown in TABLE III.

²Ratio of mmoles of hydrogen to mmoles of propylene in gas phase reactor system

ILLUSTRATIVE EMBODIMENT III

Injection Molding of Polypropylene Product

Some of the polypropylene products, produced according to Illustrative Embodiment II, were recovered by conventional means. Each recovered product was mixed and pelletized with the following additives package: 1000 ppm of Irganox® 1010 hindered phenolic primary antioxidant, 1000 ppm of Irgrfos® 168 phosphite secondary antioxidant and 500 ppm of Calcium Stearate as an acid acceptor. The pelletized polymer products were injection molded in an Arburg Injection Molder. The "melt temperature" (°C) is obtained from a differential scanning calorimetry curve for each polymer product produced. A higher melt temperature correlates to higher isotacticity of the polymer product. The "Flexural Modulus" (1% secant at 0.05 inches/min) of the molded polymer products was determined according to ASTM D790A [ISO 178]. The "Oligomers Content" was determined by the overnight extraction of a polypropylene sample in a chloroform solution containing hexadecane (n- Cι₆) as an internal standard. An aliquot of the extract is shaken in methanol and filtered to remove trace amounts of atactic material. The filtered liquid is then injected onto a capillary column which uses a flame ionization gas chromatograph. Relative amounts of the extracted components are calculated based on the weight of polymer extracted using the internal standard quantitation against the C₂, oligomer groups. The oligomers content is an indicator of the amount of volatiles, e.g. smoke and/or oil that will be liberated by the polymer during extrusion. For instance, a lower oligomers content for a polymer product translates into lower smoke generation during further processing (e.g. extrusion) of the polymer product for film and textile applications. The results of the various analyzes of polymer products are shown in Table IV. 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 30 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.

The resulting polypropylene product was mixed, pelletized and injection molded as described in Illustrative Embodiment III. The results are furnished in TABLE IV.

TABLE IV

'For comparison

Comparative catalyst system

Claims

1. A process for polymerizing one or more α- olefins of up to 10 carbon atoms which comprises contacting the one or more α-olefins under polymerization conditions with a catalyst system comprising:

(a) a titanium 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 containing from 1 to 10 carbon atoms, with a halogenated tetravalent titanium compound, in the presence of a halohydrocarbon and a polycarboxylic acid ester electron donor; (b) an organoaluminum cocatalyst component; and

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

wherein R¹ and R² are, independently, alkyl groups containing from 1 to 12 carbon atoms, aryl groups containing from 1 to 12 carbon atoms, alkaryl groups containing from 1 to 12 carbon atoms, aralkyl groups containing from 1 to 12 carbon atoms, hydrocarbyloxy groups containing 1 to 12 carbon atoms; and R³ and R⁴ are hydrocarbyloxy groups containing from 2 to 12 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 1 to about 70.

3. The process of claim 2 wherein R¹ and R² are, independently, alkyl groups or alkoxy group containing from 1 to 12 carbon atoms containing from 1 to 12 carbon atoms and R³ and R⁴ are alkoxy groups containing from 2 to 12 carbon atoms.

4. The process of claim 2, wherein R¹ and R² are, independently, alkoxy groups containing 1 to 12 carbon atoms or alkyl groups containing from 1 to 12 carbon atoms and R³ and R⁴ are ethoxy groups.

5. The process of claim 4 wherein R¹, R², R³ and

R⁴ are ethoxy groups.

6. The process of claim 3, wherein the organo¬ silane selectivity control agent is tetraethoxysilane, isobutyltriethoxysilane, diphenyldiethoxysilane, diethyldiethoxysilane, diisobutyldiethoxysilane or mixtures thereof.

7. The process of claim 5, organosilane selectivity control tetraethoxysilane.

8. The process of claim 7,

tetraethoxysilane is present in a quantity such that the molar ratio of tetraethoxysilane to the titanium present in the procatalyst component is from about 2 to about 60.

9. The process of claim 8, wherein the halogenated tetravalent titanium compound is titanium tetrachloride.

10. The process of claim 9, wherein the magnesium compound is magnesium ethoxide.

11. The process of claim 10, wherein the poly- carboxylic acid ester electron donor is diisobutyl phthalate.

12. The process of claim 11, wherein the α- olefins are propylene and ethylene.

13. The process of claim 12, wherein the α- olefin is propylene.

14. In a process for polymerizing at least one α-olefin of up to 10 carbon atoms which comprises contacting at least one α-olefin under polymerization conditions with a catalyst system comprising: (a) a titanium halide containing pr-ocatalyst 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 halohydrocarbon and a polycarboxylic acid ester, (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:

R¹ R³ ^si

R²"^ ^R⁴ wherein R¹ and R² are, independently, alkyl groups containing from 1 to 12 carbon atoms; aryl groups containing from 1 to 12 carbon atoms, alkaryl groups containing from 1 to 12 carbon atoms, aralkyl groups containing from 1 to 12 carbon atoms, hydrocarbyloxy groups containing 1 to 12 carbon atoms or halogen; and R³ and R⁴ are hydrocarbyloxy groups containing from 2 to 12 carbon atoms.

15. The process of claim 14 wherein R¹ and R² are alkyl groups containing from 1 to 12 carbon atoms or alkoxy groups containing from 1 to 12 carbon atoms, R³ and R⁴ are alkoxy groups.

16. The process of claim 14 wherein R¹ and R² are, independently, alkyl groups containing from 1 to 12 carbon atoms or alkoxy groups containing from 1 to 12 carbon atoms and R³ and R⁴ are ethoxy groups.

17. The process of claim 16, wherein the organo¬ silane selectivity control agent is selected from the group consisting of tetraethoxysilane, diphenyldiethoxysilane, isobutyltriethoxysilane, diisobutyldiethoxysilane and mixtures thereof.

18. An olefin polymerization catalyst system comprising: (a) a titanium halide-containing procatalyst component obtained by halogenating a magnesium compound with a halogenated tetravalent titanium compound, in the presence of polycarboxylic acid ester compound and a halogenated hydrocarbon,

(b) an organoaluminum cocatalyst component, and

(c) an organosilane selectivity control agent having the formula

wherein R¹ and R² are, independently, alkyl groups containing from 1 to 12 carbon atoms; aryl groups containing from 1 to 12 carbon atoms, alkaryl groups containing from 1 to 12 carbon atoms, aralkyl groups containing from 1 to 12 carbon atoms, hydrocarbyloxy groups containing 1 to 12 carbon atoms; hydrocarbyloxy groups containing from 1 to 12 carbon atoms or halogen; and R³ and R⁴ are hydrocarbyloxy groups containing 2 to 12 carbon atoms.

19. The olefin polymerization catalyst system according to claim 18, wherein the molar ratio of the selectivity control agent to the titanium present in the procatalyst is from about 1 to about 70.

20. The olefin polymerization catalyst system of claim 19, wherein the selectivity control agent is tetraethoxysilane.

21. The olefin polymerization catalyst system according to claim 20, wherein the molar ratio of tetra¬ ethoxysilane to the titanium present in the procatalyst is from about 2 to about 60.

22. The olefin polymerization catalyst system according to claim 21, wherein the magnesium compound is magnesium diethoxide, the polycarboxylic acid ester compound is diisobutyl phthalate, and the halohydrocarbon is chlorobenzene or o-chlorotoluene.