Catalyst system for improved stereoselectivity and broader molecular weight distribution in polymerization of olefins.

IS 2 164 114 T3

DESCRIPTION

Catalytic systems for improved stereoselectivity and broader molecular weight distribution in olefin polymerization.

Technical field

The present invention provides a catalyst system for olefin polymerization that includes the combination of a conventional supported Ziegler-Natta catalyst with a mixture of different electron donor compounds, an electron donor of the formula:

OR2

R₁ —Yes - R₄

OR3 where R 1 and R₄ are both an alkyl or cycloalkyl group containing a secondary or tertiary carbon atom attached to the silicon atom, with R 1 and R being₄ equal; R₂ and R₃ are alkyl or aryl groups, where R₂ and R₃ the same or different; and the other has the formula

OR'2

I

R'i - Yes - R '₄I OR3 where R '₁ is an alkyl or cycloalkyl group containing a primary, secondary or tertiary carbon atom attached to the silicon atom, R '₂ and R '₃ are an alkyl or aryl group, where R '₂ and R '₃ the same or different; and R '₄ is an alkyl group with a primary carbon attached to the silicon atom, where R '₁and R '₄ the same or different.

Description of the previous art

Catalytic systems for olefin polymerization are well known in the art. Typically these systems include a Ziegler-Natta type polymerization catalyst; a cocatalyst, usually an organoaluminum compound; and an electron donor compound, usually an organosilicon compound. Examples of these catalyst systems are shown in the following US patents: 4,107,413; 4,294,721; 4,439,540; 4,115,319; 4,220,554; 4,460,701 and 4,562,172. These are just a few of the achievements of issued patents relating to catalysts and catalytic systems primarily intended for the polymerization of propylene and ethylene.

A Ziegler-Natta type polymerization catalyst is basically a complex derived from a halide of a transition metal, for example titanium, chromium or vanadium with a metal hydride and / or a metal alkyl which is typically an organoaluminum compound. The catalyst is usually constituted by titanium halide supported on a magnesium compound complexed with an alkylaluminum.

EP-A-452916 describes a process for producing polyolefins having a high stereoregularity with the use of a catalyst comprising a solid catalyst component consisting of, as essential components, a magnesium compound, halogenated titanium and an electron donor compound; an organoaluminum compound; and tetraalkoxysilane having a specific structure.

The development of these polymerization catalysts has occurred in a similar way in generations of catalysts. The catalyst described in the patents referenced above are considered to be third generation catalysts. With each new generation of catalysts, the properties of the catalysts have been improved. In particular, the efficiency of the catalysts, expressed in kilograms of polymeric product per gram of catalyst in two hours, has increased from the range of 1-3 to the range of 10-12 and more. Catalysts have been developed that not only have higher efficiencies but also retain their activity for a longer period of time, thus being able to produce more polymeric product during the life of the catalyst. Any increase in catalyst efficiency and life leads to lower costs due to lower catalyst consumption, and also lowers capital expenditures in building and running a plant as the size of reactors is reduced for plant capacities.

ES 2 164 114 T3 and the reactor residence time is reduced. Higher efficiency also leads to a cleaner polymer product thereby avoiding the need to wash or treat the product to remove ash residue from the catalyst.

In addition to the improved catalysts, the improved activation methods have also led to increases in catalytic efficiency. A more recent discovery includes a process for the pre-polymerization of the catalyst just before introducing the catalyst into the reaction zone. This procedure is described in US Patent No.^or 4.767.735.

In addition to the development of new catalysts and new reaction procedures, a discovery of an appropriate co-catalyst or electron donor to go with the new generation of catalyst in forming a total catalyst system would be of great benefit to the art of polymerization, especially if it leads to improved stereoselectivity of the polymeric product. In such a total catalyst system a co-catalyst activates the catalyst and provides for the initiation of a polymer chain. The cocatalyst that works well with newer generation catalysts is an organoaluminum compound, more typically triethylaluminum (TEAI) or another trialkylaluminum. Examples of other useful organoaluminum compounds include an alkyl aluminum dihalide, a trialkoxyaluminum, a dialkylaluminum halide, and a triisobutylaluminum.

In the polymerization reaction, an electron donor compound is used to reduce the atactic form of the polymer, thus giving control and increasing the production of isotectic polymers. While a wide range of compounds are generally known as electron donors, a particular catalyst may have a specific compound or groups of compounds with which it is especially compatible. The discovery of an appropriate type of electron donor that provides significant increases in control of the isotactic index of the desired polymeric product and other properties of the product would be highly advantageous.

The present invention comprises such a discovery. It has been surprisingly discovered that a combination of two specific groups of silane compounds that serve as electron donors in combination with a conventional type of supported Ziegler-Natta catalyst results in significant increases in stereoselectivity over that of this particular type of catalyst using one of these electron donors alone.

Summary of the invention

The present invention provides a catalytic system for olefin polymerization wherein the system includes the combination of a particular type of catalyst with a mixture of a combination of two specific groups of electron donor compounds that results in significant increases in the stereoselectivity of the catalyst. and improved control of polymeric product properties. The catalyst is a conventional supported Ziegler-Natta catalyst.

In this catalytic system an electron donor is chosen from a silane compound of the following formula

OR2

R₁ —Yes - R₄Or R3 where R 1 and R₄ are both an alkyl or cycloalkyl group with 3 to 5 carbon atoms containing a secondary carbon atom attached to the silicon atom or an alkyl group of at least 4 carbon atoms containing a tertiary carbon atom attached to the silicon atom , having R₄ and R₄ an image of identical symmetry and they are the same; R₂ and R₃ are aryl groups, where R₂ and R₃ the same or different;

and the other electron donor is chosen from a silane compound of the following formula:

OR'2

I

R'i - Yes - R '₄

I

OR'3

ES 2 164 114 T3 where R '_i is an alkyl or cycloalkyl group containing at least one primary, secondary or tertiary carbon atom attached to the silicon atom, R '₂ and R '₃ are an alkyl or aryl group, being

R '₂ and R '₃ the same or different; and R '₄ is an alkyl group with a primary carbon attached to the silicon atom, where R '_i and R '₄ the same or different.

In a preferred embodiment, R _i and R₄ are both a secondary alkyl or cycloalkyl group with 3 to 5 carbon atoms or a tertiary alkyl group of at least 4 carbon atoms, having R _i and R₄an image of identical symmetry and they are the same; R₂ and R₃ they are methyl, ethyl, propyl or butyl groups and are the same; preferred electron donors are diisopropyldimethoxysilane (DIDS); di-t-butyldimethoxysilane (DTDS) or dicyclopentyldimethoxysilane (CPDS); R '_i is a cyclohexyl or t-butyl group, R '₂ and R '₃ are methyl, ethyl or propyl groups, and R '₄ is a group containing 1-6 carbon atoms; preferred electron donors are cyclohexylmethyldimethoxysilane (CMDS), di-n-propyldimethoxysilane (DPDS), d-nbutyldimethoxysilane (DBDS) or butylmethyldimethoxysilane (BMDS); the most preferred electron donor is CMDS.

In addition, the system may contain an organoaluminum compound that acts as a cocatalyst. The most preferred organo-aluminum cocatalyst is described by the formula AlR3 where R * is an alkyl of 1 to 8 carbon atoms and R * can be the same or different. The most preferred cocatalyst is a trialkylaluminum, such as triethylaluminum (TEA1).

The invention also provides a catalyst system as described above, wherein the system is capable of polymerizing an olefinic monomer with a xylene soluble of less than about 5.0% by weight. The particular catalyst systems included in the invention may show somewhat lower xylene solubles. The catalyst system can be further characterized as having an isotactic capacity such that the system produces a polymeric product wherein the xylene soluble atactic form can be kept within the range of 1.7-5.1% by weight of the product, while the Si / Ti molar ratio is around 2.

The invention also provides a process for the polymerization of olefins. The procedure includes:

(a) selecting a conventional Ziegler-Natta catalyst component; and (b) contacting the catalyst component with an organoaluminum compound; preferably a trialkylaluminum;

(c) contact said catalyst component with a mixture of at least two electron donors, simultaneously with or after step (b), one described by the formula:

OR2

R₁ —Yes - R₄

OR3 where R _i and R₄ are both an alkyl or cycloalkyl group containing a secondary or tertiary carbon atom attached to the silicon atom, where R₁ and R₄ equal; R₂ and R₃ are alkyl or aryl groups, where R₂ and R₃ the same or different;

and the other described by the faormula:

OR'2

R '_i —Yes - R '₄

OR'3 where R '_i is an alkyl or cycloalkyl group containing at least one primary, secondary or tertiary carbon atom attached to the silicon atom, R '₂ and R₃ are an alkyl or aryl group, where R '₂ and R '₃the same or different; and R '₄ is an alkyl group with a primary carbon attached to the silicon atom, where R'i and R '₄ the same or different;

ES 2 164 114 T3 (d) pre-polymerizing said catalyst by contacting a small amount of monomer with said catalyst;

(e) introducing said catalyst into a polymerization reaction zone containing said organoaluminum compound, said electron donors, and said monomer; and (f) extracting the polymer product from the polymerization reaction zone.

In a preferred embodiment the process comprises extracting a polymeric product where the xylene solubles are within the range of less than about 5.0% by weight; while the Si / Ti ratio in the reaction zone is within the range of 0.5-10.

Brief description of the drawings

A more complete appreciation of the invention and many of the advantages derived therefrom will be readily understood with reference to the detailed description that follows when considered in connection with the accompanying drawings, wherein:

Figure 1 is a graph of the effect of mixed silyl ethyl donor systems on xylene solubles.

Figure 2 is a graph of the effect of silyl ethyl donor systems on polydispersity.

Detailed description of the invention

The present invention relates to the combination of a particular group of compounds as electron donors with a particular type of catalyst for use in the polymerization of olefins, particularly propylene. This combination results in a catalytic system that has better control of the xylene solubles of the polymeric product than with this type of catalyst with other conventional electron donors. These and other beneficial advantages will be apparent from the following detailed description of the invention and the accompanying examples.

Electron donors are typically used in two ways in the formation of a Ziegler-Natta catalyst and a catalyst system. First, an internal electron donor can be used in the catalyst formation reaction when the transitional metal halide is reacted with the metal or metal alkyl hydride. Examples of internal electron donors include: amines, amides, ethers, asters, aromatic asters, ketones, nitriles, phosphines, stibines, arsines, phosphoramides, thioethers, thioasters, aldehydes, alcoholates, and salts of organic acids. The second use of an electron donor in a catalytic system is an external electron donor and stereoregulator in the polymerization reaction. The same compound can be used in both cases, although they are typically different. A common external electron donor is an organic silicon compound, for example, cyclohexylmethyl dimethoxysilane (CMDS). A description of the two types of electron donors is provided in US Patent 4,535,068.

Because the present invention refers particularly to external electron donors the term "electron donor" as used herein refers to the external donor. The external electron donor acts as a stereoselectivity control agent (SCA) to control the amount of atactic form of polymer produced. The production of isotactic polymers can also be increased. Organic silicon compounds are known in the art for use as electron donors. Examples of electron donors that are organic silicon compounds are described in US patents mims. 4,218,339; 4,395,360; 4,328,122; 4,473,660 and 4,927,797. As indicated a particular catalyst can produce better results when it pairs with a particular group of electron donors. Examples of this pairing of catalyst and electron donors is described in US patents mims. 4,562,173; 4,547,552; and 4,927,797.

The combination of two particular groups of electron donors has been found to significantly improve the catalytic properties of a particular olefin polymerization catalyst, ie, conventional supported Ziegler-Natta catalysts. Any of the conventional supported Ziegler-Natta catalysts can be used in the present invention. The catalyst component of a conventional supported Ziegler-Natta catalyst preferably contains a transition metal compound of the general formula MR + where M is the metal, R⁺ is a halogen or a hydrocarboxyl and x is the valence of the metal. Preferably M is a group IVB, VB or VIB metal, more preferably a group IVB, and most preferably titanium. Preferably R⁺ it is chlorine, bromine, an al5

ES 2 164 114 T3 coxyl or phenoxy, more preferably chlorine or ethoxy and more preferably chlorine. Illustrative examples of the catalyst components of the transition metal compound are TiCl₄, TiBr₄, Ti (OC₂H₅)₃Cl,

Ti (OC₃H₇)₂Cl₂, TiOC6Hi₃)₂Cl₂, Ti (OC₂H5)₂Br₂ and Ti (OC₄₂H₂₅) Cl₃. Mixtures of the transition metal compounds can be used.

There is no limitation on the number of transition metal compounds as long as at least one transition metal compound is present. A particular Ziegler-Natta catalyst that can be used in the present invention is described in US patents ni'uiis. 4,927,797; 4,816,433 and 4,839,321. In these patents the Ziegler-Natta type catalyst component is described as comprising a solid catalyst component obtained (i) by suspending a magnesium dialkoxy in an aromotic hydrocarbon that is liquid at normal temperatures, (ii) by contacting the magnesium dialkoxy with a halide titanium and additionally (iii) contacting the resulting composition a second time with the titanium halide, and contacting the magnesium dialkoxy with a diiester of an aromotic dicarboxylic acid at some point during the treatment with the titanium halide in (ii).

The support must be an inert solid that is chemically unreactive with any of the components of the conventional Ziegler-Natta catalyst. The support is preferably a magnesium compound. Examples of the magnesium compounds to be used to provide a source of support for the catalyst component are magnesium halides, dialkoxymagnesiums, alkoxymagnesium halides, magnesium oxyhalides, dialkylmagnesiums, magnesium oxide, magnesium hydroxide, and magnesium carboxylates.

Internal electron donor compounds suitable for the preparation of conventional Ziegler-Natta catalyst components include others, ketones, lactones, electron donor compounds with N, P and / or S otoms and specific classes of esters. Particularly suitable are the esters of phthalic acid, such as diisobutyl, dioctyl, diphenyl and benzylbutylphthalate; maloonic acid esters, such as diisobutyl and diethylmalonate; alkyl and arylpivalates; alkyl, cycloalkyl, and arylmaleates; alkyl and aryl carbonates such as diisobutyl, ethylphenyl, and diphenylcarbonate; succonic acid osesters, such as mono and diethyl succinate. These phthalic acid osters are the preferred donors.

When a particular combination of electron donors is used, the above-described catalyst generally exhibits the same efficiency or an increase over previously known catalysts, such as those described in US Patent No.^or 4,929,797. This improved efficacy has been found to be accompanied by better operational control of polymer product properties such as improved stereoselectivity.

The two groups of electron donors included in the present invention are the orgaonic silicon compounds described by the above-mentioned formulas.

Preferred electron donors of one group are diisopropyldimethoxysilane (DIDS), di-t-butyldimethoxysilane (DTDS) and dicyclopentyldimethoxysilane (CPDS) and the preferred electron donors of the other group are di-n-propyldimethoxysilane (DPDS), di-n-butyldimethoxysilane (DBDS) ), butylmethyldimethoxysilane (BMDS) and cyclohexylmethyldimethoxysilane (CMDS), with CMDS being the most preferred.

The combination of DIDS, DTDS or CPDS and CMDS with conventional supported Ziegler-Natta catalyst provides totally unexpected results that surpass previously known catalyst systems. The most significant unexpected result obtained from the combination of the above-described catalyst and DIDS, DTDS or CPDS with CMDS is the notable increase in the stereoselectivity of the catalytic system measured by a decrease in the weight percent of xylene soluble material and the increase in the molecular weight distribution (MWD) which is the ratio of the weight average molecular weight (M_w) versus number average molecular weight (M_n) [MWD = M_w/ M_n]. This relationship is also known as polydispersity. The catalyst system including a conventional commercially supported Ziegler-Natta catalyst, at least two organosilicon electron donors at a molar ratio of 1: 3 to 3: 1 and an organo-aluminum cocatalyst, has been shown to obtain xylene solubles of less than about 5.0% by weight. This catafitic system at a molar ratio of the two electron donors from 1: 3 to 1: 1 has also been shown to produce a polyomer having polydispersity greater than 9. This result is considered effective for Si / Ti molar ratios within the range from 0.5 to 10. The preferred Si / Ti ratio is in the range of 2 to 10. The most preferred Si / Ti molar ratio is in the range of 2 to 4.

IS 2 164 114 T3

The catalyst system is capable of controlling the formation of atactic, or xylene-soluble, polymer at relatively low levels. When a conventional supported Ziegler-Natta catalyst described herein is bonded with an electron donor, such as DIDS, DTDS, CPDS, or CMDS alone, the system exhibits a relatively high level of xylene solubles (2.0 to 6.0% in weigh). The present catalyst system using electron donors such as DIDS, DTDS or CPDS in combination with CMDS exhibits a decrease in weight% of xylene solubles from 1.7 to 5.1% by weight.

The catalyst system is also capable of controlling the molecular weight distribution of the polymer at relatively high levels. When a conventional supported Ziegler-Natta catalyst described herein is bonded with an electron donor such as DIDS, DTDS, or CPDS alone, the system exhibits a relatively low level of polydispersity (8 to 9). The present catalyst system using electron donors such as DIDS, DTDS or CPDS in combination with CMDS exhibits an increase in polydispersity up to above 9.

The present invention also provides a process for the polymerization of olefins that uses the catalyst and the electron donor described by the previous formulas, consisting essentially of:

a) selecting a conventional Ziegler-Natta catalyst component;

b) contacting the catalyst with an organo-aluminum compound;

c) contacting the catalyst with a mixture of at least two electron donors simultaneously with or after contact with the organoaluminum, the electron donors being composed of silane as described by means of the above formulations;

d) introducing the catalyst into a polymerization reaction zone containing the organoaluminum compound, the electron donor and the monoimer; Y

e) extracting the polymeric product from the reactor.

While the catalyst system can be used in almost any commercially known polymerization process, the preferred process of the present invention includes a prepolymerization of the catalyst by contacting a small amount of monomer with the catalyst after the cocatalyst has been contacted with the electron donor. In US patents niiiiiis. 4,767,735 and 4,927,797 describe a pre-polymerization process.

Seguín has been disclosed in these patents, a carrier current for the catalyst is provided, the catalyst is contacted with the cocatalyst or organo-aluminum compound, the catalyst is contacted with the electron donor, and the contacting the catalytic stream with a relatively small amount of the total amount of the monimer to be polymerized, the catalyst stream passes through a tubular reactor, and the pre-polymerized catalyst and catalytic stream are introduced into the polymerization reaction zone. The electron donor can be contacted with the catalyst simultaneously with the cocatalyst. A polynic product can then be removed from the reactor.

The present invention also provides a process for controlling the molecular weight distribution of polypropylene produced with a polymerization process using a conventional ziegler-Natta catalyst. The molecular weight distribution (MWD) is the ratio of the weight average molecular weight (M_w) vs. number average molecular weight (M_n): MWD - M_w/ M_n. This relationship is also known as polydispersity.

The examples and comparative examples that follow illustrate the present invention and its various advantages in greater detail. The results are summarized in Tables 1-5. The catalyst used was prepared with the materials and processes as described in US Pat. 4,927,797; 4,816,433 and 4,839,321.

Example 1

Before a polymerization test, all traces of humidity and air were expelled from the reactor by heating to a temperature above 100^or C for a minimum of 30 minutes under a constant dry nitrogen purge. After this heating, the reactor was cooled to room temperature (25^orC) under nitrogen. The reactor was stabilized at room temperature and then 16 mmol of hydrogen and 1.0 l of propylene were added. The reactor was shaken at 1000 rpm and raised

ES 2 164 114 T3 temperature up to 70^orC. 1.0 mmol of TEAl and 0.0075 mmol of DTDS and 0.0025 mmol of CMDS, that is a total amount of 0.01 mmol of electron donor were added to a 40 cc tubular reaction vessel. Ten milligrams of standard commercially supported Ziegler-Natta catalyst found in a mineral oil slurry was added to the 40 cc reaction cylinder. The TEAl and donor were left in pre-contact for approximately five minutes and the catalyst was allowed to precontact the mixture of TEAl and donor for approximately two minutes. The tubular reaction vessel was then attached to a reactor inlet point and filled with room temperature liquid propylene, which was allowed to polymerize for five seconds to effect catalyst prepolymerization. The contents of the vessel were then flushed into the reactor with 0.2 L of propylene at room temperature. The total amount of liquid propylene present in the reactor was around 1.2 L. The temperature of the reactor was then raised to 70^or C. The polymerization reaction was allowed to proceed for one hour at 70^orC, at which point it ended up expelling excess propylene and cooling the reactor to room temperature. The reactor was then opened to collect the polymer product which was dried and analyzed.

The catalyst efficiency was determined from the mass yield of the polymer for the known amount of catalyst used. The efficiency was reported in kilograms of polymer product per gram of catalyst per hour. The Si / Ti molar ratio was calculated from the molar amount of DIDS and CMDS used divided by the molar amount of titanium. Xylene solubles were measured by dissolving the polymer in hot xylene, cooling the solution to 0^or C and precipitating the isotoxic form. The xylene solubles were the% by weight of the polymer that was soluble in the cold xylene. In addition, the bulk density of the polymeric product was measured and calculated using standard techniques. The results are shown in Table 1.

Polymerization conditions

Reagents:

catalyst: 10 mg crude catalyst

TEA1: 1.0 mmol donor: 0.01 mol

Al / Ti: 200

Al / Si: 100

Si / Ti: 2 conditions:

temp.:70 time: 1 hour

Example 2

The procedure of Example 1 was repeated except that the amount of DIDS was 0.005 mmol and the amount of CMDS was 0.005 mmol. The total amount of electron donor remained at 0.01 mmol. The results are shown in Table 1.

Example 3

The procedure of Example a was repeated except that the amount of DIDS was 0.0075 mmol and the amount of CMDS was 0.0025 mmol. The total amount of electron donor remained at 0.01 mmol. The results are shown in Table 1.

Examples 4-6

The procedures of Examples 1-3, respectively, were repeated except that DTDS was used instead of DIDS. Results are shown in table 2.

Examples 7-9

The procedures of Examples 1-3, respectively, were repeated except that DPDS was used instead of DIDS. The results are shown in Table 3.

IS 2 164 114 T3

Comparative Example A

The procedure of Example 1 was repeated except that DIDS was used alone. The total amount of electron donor was 0.01 mol. The results are shown in Table 4.

Comparative Example B

The procedure of Example 1 was repeated except that DTDS was used alone. The total amount of electron donor was 0.01 mol. The results are shown in Table 4.

Comparative Example C

The procedure of Example 1 was repeated except that CPDS was used alone. The total amount of electron donor was 0.01 mol. The results are shown in Table 4.

Comparative Example D

The procedure of Example 1 was repeated except that CMDS was used alone. The total amount of electron donor was 0.01 mol. The results are shown in Table 4.

TABLE 1

DIDS / CMDS system

<td>Example</td><td>DIDS mmol</td><td>CMDS mmol</td><td>performance g</td><td>Soluble in xylene% by weight</td>

<td> 1</td><td> 0,0075</td><td> 0,0025</td><td> 318</td><td> 1,7</td>

<td> 2</td><td> 0,005</td><td> 0,005</td><td> 315</td><td> 2,6</td>

<td> 3</td><td> 0,0025</td><td> 0,0075</td><td> 409</td><td> 2,2</td>

TABLE 2

DTDS / CMDS system

<td>Example</td><td>DTDS mmol</td><td>CMDS mmol</td><td>performance g</td><td>Soluble in xylene% by weight</td>

<td> 4</td><td> 0,0075</td><td> 0,0025</td><td> 355</td><td> 5,1</td>

<td> 5</td><td> 0,005</td><td> 0,005</td><td> 308</td><td> 4,7</td>

<td> 6</td><td> 0,0025</td><td> 0,0075</td><td> 324</td><td> 4,3</td>

TABLE 3

CPDS / CMDS system

<td>Example</td><td>CPDS mmol</td><td>CMDS mmol</td><td>performance g</td><td>Soluble in xylene% by weight</td>

<td> 7</td><td> 0,0075</td><td> 0,0025</td><td> 381</td><td> 3,9</td>

<td> 8</td><td> 0,005</td><td> 0,005</td><td> 322</td><td> 4,3</td>

<td> 9</td><td> 0,0025</td><td> 0,0075</td><td> 313</td><td> 3,8</td>

IS 2 164 114 T3

TABLE 4

<td>Eg comp.</td><td>DIDS mmol</td><td>DTDS mmol</td><td>CPDS mmol</td><td>CMDS mmol</td><td>Yield. g</td><td>Soluble in xylene% by weight</td>

<td>TO</td><td> 0,01</td><td> -</td><td> -</td><td> -</td><td> 401</td><td> 2,0</td>

<td>B</td><td> -</td><td> 0,01</td><td> -</td><td> -</td><td> 263</td><td> 4,5</td>

<td>C</td><td> -</td><td> -</td><td> 0,01</td><td> -</td><td> 334</td><td> 3,3</td>

<td>D</td><td> -</td><td> -</td><td> -</td><td> 0,01</td><td> 357</td><td> 6,2</td>

Example 10

The polymer of Example 1 was analyzed for polydispersity. The polydispersity molecular weight distribution (D) is given as the ratio of weight-average molecular weight to number-average (Mw / Mn). The molecular weight distribution of the polymer was characterized by gel permeation chromatography of the filtered polymer samples dissolved in trichlorobenzene at 145^orC. The results are shown in Table 5.

Example 11

The procedure of Example 10 was repeated on the polymer of Example 2. The results are reported in Table 5.

Comparative Example E

The procedure of Example 10 was repeated on the polymer of Comparative Example A. The results are reported in Table 6.

Comparative example F

The procedure of Example 1 and Example 10 was repeated on the polymer of Comparative Example A. The results are reported in Table 6.

TABLE 5

DIDS / CMDS system

<td>Example</td><td>DIDS mmol</td><td>CMDS mmol</td><td>Performance g</td><td>D (Mw / Mn)</td><td>Soluble in xylene% by weight</td>

<td> 10</td><td> 0,0075</td><td> 0,0025</td><td> 318</td><td> 10,13</td><td> 1,7</td>

<td> 11</td><td> 0,005</td><td> 0,005</td><td> 315</td><td> 9,46</td><td> 2,6</td>

TABLE 6

<td>Example</td><td>DIDS mmol</td><td>CMDS mmol</td><td>Performance g</td><td>D (Mw / Mn)</td><td>Soluble in xylene% by weight</td>

<td>AND</td><td> 0,01</td><td> -</td><td> 401</td><td> 9,13</td><td> 2,0</td>

<td>F</td><td> -</td><td> 0,01</td><td> 264</td><td> 8,33</td><td> 7,8</td>

IS 2 164 114 T3

Polymerizations were carried out using different silyl ether donors in combination with cyclohexylmethyl dimethoxysilane (CMDS); the total molar number of donors used and all other conditions were held constant. These polymerizations were carried out using the same conditions, including the total donor level, and differ only in the relative amounts of each donor used. In many cases a low donor level would be advantageous to reduce donor costs and maintain high catalytic activity; therefore low levels of donor were used (Al / Si = 100; Si / Ti = 2). Representative results are given in Tables 1, 2, 3 and 4 and Figure 1 along with: di-isopropyl dimethoxysilane (DIDS); di-tert-butyl dimethoxysilane (DTDS) or dicyclopentyldimethoxysilane (CPDS). As shown, a mixture of the two electron donors in a molar ratio of about 1: 3 to about 3: 1 from the second to the first provides lower polymer xylene solubles over CMDS alone.

A combination of silyl ether donors as catalyst modifiers has been shown to improve the polydispersity of the polymer. As shown in Tables 5 and 6 and Figure 2, a combination of cyclohexylmethyldimethoxysilane (CMDS) and di-isopropyl dimethoxysilane (DIDS) provides an increase in polydispersity over any donor used alone. Compared to CMDS only a 1: 1 mixture of CMDS and DIDS increases polydispersity by about 8 to 10. In addition, this increase is obtained while keeping the xylene solubles low.

These polymerizations were carried out using the same conditions, including the total donor level, and differ only in the relative amounts of each donor used.