WO1996004320A1

WO1996004320A1 - Catalyst system containing a solid titanium component for the stereoregulation of polyolefins

Info

Publication number: WO1996004320A1
Application number: PCT/US1995/009670
Authority: WO
Inventors: Nemesio Delgado Miro; James Carlton Randall; George Byron Georgellis
Original assignee: Exxon Chemical Patents, Inc.
Priority date: 1994-08-03
Filing date: 1995-08-01
Publication date: 1996-02-15

Abstract

The present invention provides a catalyst system that exhibits unprecedented control of stereoregularity and generates an olefin polymer product having low to moderate crystallinity. The catalyst system includes (a) a solid titanium catalyst component, (b) a mixture comprised of diethylaluminum chloride and another organoaluminum compound as co-catalyst, and (c) an alkylsilane electron donor. When employed in the polymerization of propylene, the system exhibits control over the polymer stereoregularity and generation of undesirable atactic polymers resulting in the preparation of a novel polypropylene polymer of low to moderate crystallinity.

Description

CATALYST SYSTEM CONTAINING A SOLID TITANIUM COMPONENT FOR THE STEREOREGULATION OF POLYOLEFINS

FIELD OF THE INVENTION

The present invention relates to a catalyst system and an olefin

polymeization that results in an olefin polymer composition demonstrating moderate to low crystallinity and relatively low amounts of by-product amorphous polymer. The low proportion of amorphous polymers in the instant polyolefins enables continuous reactor preparation of such resins without the accompanying production difficulties generally associated with polyolefin compositions of moderate to low crystallinity.

BACKGROUND OF THE INVENTION

Catalyst systems for the polymerization of olefins are well known in the art. Typically, these systems include a Ziegler-Natta type polymerization catalyst component; a co-catalyst, usually an organoaluminum compound; and an electron donor compound. Examples of such catalyst systems are shown in U. S. Patent Numbers: 5,066,738 (Ewen); 4,990,479 (Ishimaru); 4,990,477

(Kioka); and 4,970,186 (Terano) the entire disclosures of which U. S. patents are hereby incorporated by reference for purposes of US patent practice. These are a few of many issued patents and other prior art relating to Ziegler-Natta catalyst and catalyst systems designed primarily for the polymerization of olefins.

Ziegler-Natta type polymerization catalyst components are basically a complex derived from a halide of a transition mmeetal, f example, titanium, chromium, or vanadium with a metal hydride and/or a metal alkyl that is typically an organoalumium compound. The catalyst is usually comprised of a titanium halide composition supported on a magnesium compound complexed with an alkylaluminum compound. There have been generations of these catalysts as well as new polymerization processes developed in the prior art.

One of the newer generations of these catalyst components is disclosed in the U. S. Patent number 4,970,180, cited above, and in U. S. Patent numbers: 4,847,227; 4,839,321; 4,829,037; 4,816,433 and 4,686,200, all of which are owned by the TOHO Titanium Company of Tokyo, Japan and the entire disclosures of which are hereby incorporated by reference for purposes of US patent practice.

In addition to the improvement or development of new Ziegler-Natta catalyst components and polymerization processes, the discovery of more appropriate co-catalysts and/or electron donors to accompany these new generations of titanium-supported catalyst systems have resulted in improved quality control of the polyolefin polymer product. The co-catalysts that work well with the newer generations of solid titanium-supported catalysts are organoaluminum compounds, most typically the alkylaluminum series such as triethylaluminum ("TEAT), diethyl-aluminum chloride ("DEAC") and trisobutylaluminum. Examples of other useful organoaluminum compounds include alkylaluminum dihahdes and trialkoxyaluminum compounds. Mixtures of these prior art organoaluminum co-catalysts are disclosed in the prior art as in U. S. Patents 4,678,768 (Fujita et al.); 4,716,206 (Fujita et al.); and

4,634,687 (Fujita et al.), all of which teach co-catalyst mixtures of DEAC and TEAl for use in magnesium supported ΗCI₄ catalyst component systems.

It is known that the levels of stereoregularity achieved by classical Ziegler-Natta catalyst recipes containing titanium chlorides and various co- catalysts can be controlled by the choice and level of the type of electron donor. An electron donor compound is generally used along with catalyst components in olefin polymerization reactions to increase the stereoregularity of the polymer while concurrently decreasing the production of atactic or amorphous polymers thereby ensuring higher crystallinity of the polyolefin product. Various types of external donors, used in polypropylene catalyst recipes to control the level of stereoregularity, include alkyl, alkoxy (or even chlorine) substituted silane compounds (U. S. Patent 5,206,198), benzoic acid esters (U. S. Patents

4,463,102; 4,716,206; 4,678,768; and 4,246,136), aromatic esters containing nitrogen atoms (U. S. Patents 4,716,206 and 4,634,687), alkyl substituted piperidines (U. S. Patent 4,634,687), and aliphatic amines (U. S. Patent 4,634,687). Discovery of an appropriate type of electron donor can lead to significant increases in catalyst efficiency as well as improved control of the stereoregularity of the desired polymer product and, if desired, control of other properties of the polymer polyolefin product such as molecular weight distribution ("MWD") and melt flow. Likewise, discovery of a specific group of electron donors in combination with a solid titanium-supported

component/co-catalyst system could result in control of the percentage heptane insolubles (% HI) of a desired polyolefin polymer product by maintaining control over the formation of undesirable by-product amorphous atactic polymer. The success of the various donors is generally established by determining the percent of heptane insolubles, "% HI" (U. S. Patent numbers 4,246,136; 4,335,015; 4,634,687; 4,678,768; 4,716,206; and 4,463,102). The % HI is also often used as an index of the isotacticity of a crystalline polypropylene. Throughout this specification, the level of polypropylene isotacticity shall be defined by the average undisturbed stercoregular run lengths of meso diads in the crystalline fraction of the subject polyolefin polymers composition. The % HI shall be used to indicate the level of the crystalline fraction of a polypropylene composition.

Specified % HI levels are generally important in processing of polypropylene polymer compositions as the atactic polymer contained therein will act as a processing aid. This is particularly true for processes that make polypropylene films. A particular example is oriented polypropylene films made by a process called the tenter frame. An example where low levels of atactic polypropylene are desirable are in molding applications which require good heat resistance as reflected by a higher heat distortion temperature ("HDT").

Reducing atactic polypropylene levels in the polypropylene composition will lead to an increase in the heat distortion temperature of the resulting molded articles. It is clearly advantageous to have a polypropylene composition that is both easily processable yet can also be designed to contain relatively low levels of atactic polypropylene so as to increase the heat distortion characteristics of manufactured articles. The present invention involves the discovery of a certain catalyst system that can be used to control the stereoregularity of polyolefin polymers and thereby achieve polymer compositions of moderate to low crystallinity which contain relatively low levels of amorphous or atactic polymer. It has been surprisingly found that a (1) a particular organoaluminum co-catalyst mixture and (2) a specific group of silane compounds serving as electron donors in combination with a TiCl₄ supported catalyst component results in a catalyst system which can generate a polyolefin composition having a low to moderate crystallinity and an unexpectedly lower amount of by-product heptane soluble amorphous polymer than ordinarily generated in the preparation of olefin polymer compositions of comparable crystallinity. The instant catalyst system enables the practice of a polymerization process exhibiting an improved control of the stereoregularity of the polymer product than otherwise provided with catalyst systems of the prior art.

SUMMARY OF THE INVENTION The present invention provides a catalyst system for the polymerization of olefins which system includes a combination of a solid titanium component with a specific composition comprised of an organoaluminum co-catalyst mixture and an organosilane electron donor compound, resulting in unexpected and significant control of the properties of the polymer product generated therewith. The catalyst component is a solid titanium component which contains magnesium, titanium, halogen, and an internal electron donor as essential elements. The organoaluminum co-catalyst mixture is comprised of diethyl aluminum chloride ("DEAC") in an amount of 3 to 75 mole percent and at least one other organoaluminum compound such as triethylaluminum, in an amount of 97 to 25 mole percent. The external electron donor is an

organosilane compound such as methylcyclohexyl dimethoxysilane ("MCMS"), or dicyclopentyldimethoxysilane ("DCPMS"). The present catalyst system is used in polymerization processes to generate a novel polyolefin polymer composition of moderate to low (relatively low) crystallinity having lower than expected atactic (amorphous) polymer formation as reflected in lower heptane solubles in the polymer than comparable prior art polyolefin compositions.

The invention also provides for a process for the polymerization of olefins. The process comprises: (a) providing a catalyst system comprised of (i) a solid titanium catalyst component comprising magnesium, titanium, halogen, and an internal electron donor; (ii) a co-catalyst comprised of a mixture of diethylaluminum chloride in an amount of 3 to 75 mole percent and at least one other organoaluminum compound, such as triethylaluminum, in an amount of 97 to 25 mole percent; and (iii) an external organosilane electron donor such as MCMS or DCPMS; (b) introducing the catalyst system into a polymerization reaction zone containing additional amounts of (i) the organoaluminum co-catalyst mixture, (ii) the external organosilane electron donor, and (iii) olefin monomer wherein polymerization of the monomer takes place. The process may include the optional step of prepolymerizing the catalyst system by contacting a small amount of olefin monomer with the catalyst system prior to entry into the reaction zone. The instant polymerization process further includes the steps of (c) maintaining the mole percent of DEAC in the reaction zone between about 3 to 75 mole percent of the total amount of organoaluminum co-catalyst employed, and (d) withdrawing from the reaction zone a polyolefin composition containing heptane soluble polymer in an amount of 2 to 10 weight percent of total polyolefin polymer. It is further preferable that the Al/Si mole ratio in the reaction zone be maintained within the range of from 5 to 1000.

Up until the present invention, it has been assumed in the polymerization of propylene, that there is a consistently proportionate relationship between the amount of atactic amorphous polypropylene in the catalyst generated polyolefin composition and the level of stereoregularity in the crystalline portion of that composition (see prior art patents cited above). In other words, the higher the stereoregularity in terms of unperturbed stereoregular sequences in the crystalline (heptane insoluble) segment, the lower the amount of amorphous or atactic polymer formation, and vice versa. The development of the present invention goes beyond that assumption through the discovery of a

polypropylene synthesis that leads to a composition that has a crystalline (heptane insoluble) portion of moderate to low crystallinity, but without a corresponding proportionate increase in the formation of atactic polypropylene. This unexpected reduction in atactic polypropylene formation in the instant polypropylene compositions of relatively low, or moderate to low, crystallinity is measured by a generally lower heptane soluble portion than otherwise measured in comparable prior art polypropylenes of moderate to low

crystallinity.

The above described unexpected results of the present invention are due to the instant catalyst system recipes that can be designed to yield

polypropylene compositions having crystalline polypropylene portions of low stereoregularity accompanied by lower than expected amorphous polymer formation as measured by differentials in the heptane soluble portions of the respective polypropylene compositions. By use of the present catalyst system in the polymerization of propylene, it has been found that the stereoregularity of the polymer chains can be controlled and manipulated to the extent of achieving a polyolefin composition having relatively higher portions of low or moderately crystalline polymers and a lower than expected amount of amorphous polypropylene than demonstrated by polypropylenes of comparable similar crystallinity in the prior art

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a characteristic diagram illustrating the correlation between heats of fusion and corresponding average meso run lengths of the crystalline portions of the series of polypropylene compositions.

Figure 2 is the plot of Figure 1 further illustrating the crystallinity region of interest for the polypropylene compositions of the present invention.

Figure 3 is a characteristic diagram illustrating and highlighting the correlation between the heats of fusion, as a measure of crystallinity, and corresponding heptane insoluble contents of polypropylene compositions of the prior art and the present invention.

Figure 4 is an expanded view of the highlighted compositions of the present invention shown in Figure 3.

Figure 5 is a characteristic diagram illustrating and highlighting the correlation between the average meso run lengths, as an indicator of crystallinity, versus percentage of heptane insolubles in polypropylene compositions of the prior art and of the present invention.

Figure 6 is an expanded view of the highlighted compositions of the present invention shown in Figure 5.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to an olefin polymerization catalyst system which is the combination of (i) a solid titanium-supported Ziegler-Natta catalyst component; (ii) a particular mixture of organoaluminum compounds as co-catalysts; and (iii) an external organosilane electron donor for use in the polymerization of propylene. This catalyst system is based on the discovery that the use of certain co-catalyst mixtures in combination with silane donors are factors controlling the isotacticity of polypropylene compositions as measured by the heptane insoluble portions of same.

As used herein isotacticity and isotactic level refers to the average run length of unperturbed stereoregular so-called "meso diad sequences". This is the length of the meso diad sequences that are terminated by some type of "stereo-defect" in the recurring stereoregular sequence. Theoretically predicted stereo-defects that disrupt continuous meso diad sequences are shown as follows: ("1" is used to designate one type of stereochemical configuration, and "0" is used to designate the other, and only second, type of stereochemical configuration. A meso diad sequence can be either "00" or "11". A racemic diad can either be "01 " or "10".).

The above stereo-defects can terminate runs of like configurational (meso) diad sequences. It is to be appreciated that each type of stereo-defect begins with the sequence, mmmr, and ends with the sequence, rmmm. The frequency of these stereo-defects will determine the run lengths of the meso diad sequences. An average meso run length per 10,000 repeat units can be determined from carbon 13 NMR methyl pentad data from a heptane insoluble polypropylene fraction and the following relationship:

"Average Meso run length" = 2/[mmmr] where [mmmr], determined from carbon 13 NMR analysis, is equal to mmmr plus rmmm. The technique for generating NMR methyl pentad data to describe crystallinity is given in U. S. Patent number 4,522,994, the entire disclosure of which is incorporated by reference herein for purposes of US patent practice.

Another more traditional method for evaluating polypropylene crystallinity is the percent heptane insolubles (% HI). Atactic polypropylenes are produced concurrently by the catalysts and polymerization processes that produce these polypropylene compositions. Atactic polypropylene has no stereoregularity and, consequendy, it is amorphous and has no melting point Atactic polypropylene, in contrast to crystalline polypropylene, is soluble in most aromatic solvents (including heptane) at room temperature and can be extracted from crystalline polypropylenes with aliphatic hydrocarbon solvents near their boihng point. Historically, there has been a systematic relationship between % HI and polypropylene crystallinity. Consequendy, % HI has often been used in literature and patents as a method to establish the level of polypropylene crystallinity. Values for % HI generally range from percentages in the mid 80s to the upper 90s with the higher % HI levels usually indicating higher levels of crystallinity in the heptane insoluble portion of the polymer composition.

The heart of the present invention resides in the use of critical amounts of diethylaluminum chloride in the catalyst system to achieve a polyolefin polymer having desirable meso diad (or recurring stereoregular sequences) resulting in relatively lower crystallinity in the polyolefin without an increase in the concurrent formation of undesirable atactic (amorphous) polyolefin. This catalyst system enables the preparation of a more processable polyolefin composition because of the relatively lower % heptane insolubles which produces a polymer composition with an unexpected lower content of undesirable amorphous polymer. This latter feature reduces the "stickiness" associated with atactic portions of the polyolefin and the likelihood of "fouling" in polymerization reaction systems, particularly in bulk or continuous processes. In particular, the instant catalyst system generates a novel polypropylene composition having adequately and consistently distributed perturbations in the polymers thereof resulting in a composition of relatively low crystallinity, and low amounts of amorphous (atactic) polypropylene, as measured by a relatively higher heptane insolubility (% HI) than would ordinarily be expected from prior art polyolefins of comparably lower crystallinity. In other words, the instant polypropylene compositions and those of the prior art having crystalline portions thereof at the same isotactic level have different heptane solubilities. Accordingly, the catalyst system provides a polymerization process exhibiting better control of undesirable amorphous (atactic) polymer, an unexpected result over prior art processes employing other combinations of co-catalysts and electron donors. These and other beneficial advantages will become more 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 component and a catalyst system. First, an internal electron donor may be used as a stereoregulator in the formation reaction of the catalyst as the transition metal halide is reacted with the metal hydride or metal alkyl. The second use for an electron donor in a catalyst system is as an external electron donor. It may exchange with the internal donor and change the direction of stereoregulation of the catalyst system. The same compound may be used in both instances, although typically they are different. Organic silicon compounds, for example, dicyclopentyldimethoxysilane ("DCPMS"), are common external electron donors. Examples of electron donors that are organic silicon compounds are disclosed in U. S. Patent numbers 4,218,339; 4,395,360; 4,328,122; and 4,473,660, the entire disclosures of these patents being hereby incorporated by reference for purposes of US patent practice. As the present invention relates particularly to external electron donors, the term "electron donor" as used herein, generally refers to the external donor unless otherwise stipulated. It has been discovered that the particular co-catalyst and electron donor recipe of the present invention does significandy enhance the catalytic properties of a solid titanium Ziegler-Natta catalyst component. The preferred catalyst component demonstrating the most promising results in the present invention is a new generation Ziegler-type titanium catalyst component for the polymerization of olefins. This prefeιτed catalyst comprises a solid catalyst component obtained by (1) suspending a dialkoxy magnesium in an aromatic hydrocarbon that is liquid at normal temperatures, (ii) contacting the dialkoxy magnesium with a titanium halide and further, (iii) contacting the resulting composition a second time with the titanium halide, and contacting the dialkoxy magnesium with a diester of an aromatic dicarboxylic acid at some point during the treatment with the titanium halide in (ii). A full description of these newer generation catalyst components and their preparation are disclosed in the previously cited U. S. Patents owned by the Toho Titanium Company of Japan.

The present invention employs any magnesium-supported titanium- based catalyst components, such as the new generation Toho THC, or the more conventional Ziegler-Natta components such as Mitsui TK-220, Himont FT4S, and HMC-101. Each can be combined with a mixture of organoaluminum co- catalysts, containing DEAC and a selected amount of an organosilane donor, such as MCMS or DCPMS to yield the catalyst system of this invention. The only constituent concentrations within the instant catalyst system that are allowed to vary are (1) the ratio of DEAC to the other organoaluminum components in the co-catalyst mixture and (a) the amount of the organosilane external donor. It is the ratio of DEAC to the other organoaluminum components that establishes the low crystalline stereoregularity of the instant polypropylene compositions without the traditionally expected decreases in % HI. As the relative amount of DEAC increases, the frequencies of stereo- defects increase in the crystalline component and consequently, the average meso run lengths become shorter. Structurally similar crystalline

polypropylenes can be made with the use of conventional ΗCI₄ supported catalyst system employing TEAl as the sole co-catalyst, but with considerably higher levels of atactic polymer. By controlling the basic catalyst system recipe within the parameters of the present invention (such as the new generation Toho component catalyst with a specified amount of DEAC/TEAl co-catalyst and organosilane donor), it is possible to generate novel stereoregular polypropylenes of low crystallinity characterized by average meso run lengths of less than 200 and lower than expected amounts of heptane solubles. For any other prior art catalyst recipe and choice of donor, polypropylene polymers of low crystallinity can be prepared only with unacceptable amounts of atactic polypropylene as reflected in relatively low heptane insolubles (% HI). While the ratios of (a) the catalyst component (b) the organoaluminum co-catalyst and (c) the silane electron donor components of the instant catalyst system are generally not critical one to the other, (1) the relative amounts of DEAC to other organoaluminum co-catalysts and (2) the presence of organosilane external donor are important to the practice of this invention. Accordingly, the ratio of DEAC to the other organoaluminum compounds in the co-catalyst mixture must be in an amount of from 3 to 75 mole percent, and the organosilane electron donor is used in an amount of at least 0.1 part per million (ppm) of total propylene in the reaction mixture.

Preferred organoaluminum co-catalysts with the purview of the present invention are alkylaluminum compounds such as trimethylaluminum, triethylaluminum, tri-n-propylaluminum, tri-n-butyl-aluminum,

triisobutylaluminum, tri-n-hexylaluminum, trinormal-octylaluminum, and diisobutylaluminum hydride. The most preferred alkylaluminum compound is triethylaluminum. Methods for determining the crystallinity of polypropylene include measurements of the average meso run lengths ("MRL) and heats of fusion (Δ H) of polypropylene. The heat of fusion is essentially a measurement of the energy to melt the crystalline portion of a polypropylene composition and is a direct measurement of crystallinity. The MRL is a structural measurement of the average unperturbed lengths of the meso sequences in polypropylene chains, which have the capability to crystallize in the polymer composition.

A characterization curve of average meso run length versus heat of fusion for traditionally prepared polypropylene and those polymers generated with the catalyst system of the present invention is demonstrated in Figure 1. The heat of fusion is determined by Differential Scanning Calorimetry ("DSC") reflecting the crystallinity of the crystalline portion of the polymerized propylene. The heat of fusion is a measure of the energy required to melt the crystalline polypropylene sample and consequently is direcdy related to the level of polypropylene crystallinity. The meso run length is the polypropylene structural feature that is responsible for any observed crystallinity. Accordingly, the curve illustrates higher crystallinity (heats of fusion) for those

polypropylenes with higher meso run lengths; that is, a direct relationship between the physical measurement of crystallinity and the polymeric structural reasons for expected crystallinity. Accordingly, the observed relationship between the heats of fusion and average meso run lengths of Figure 1 allows the meso run length also to be used as an indicator of incipient crystallinity of polypropylene compositions of polypropylene prepared by prior art catalyst systems and the polypropylenes prepared by the catalyst system of the present invention. The series of polypropylenes prepared by various traditional catalyst systems demonstrated in Figure 1 vary broadly in average meso (unperturbed) run lengths and, consequendy, in the stereoregularity of the polypropylene polymers. As seen in Figure 1, the average meso run lengths, which are structural measurements, show a systematic relationship to the heats of fusion, which are direct measures of polypropylene crystallinity. The average meso run lengths vary between 5 and 500 while the heats of fusion vary between 80 and 120 J/g. This range allows the relationship between the two different ways of evaluating polypropylene crystallinity to be fully observed. The plot clearly shows that the heat of fusion does not change significantly once the average meso run length reaches values of 200 and higher. Below meso run lengths of 100, the heats of fusion respond dramatically to changes in the average meso run length. Atactic polypropylene typically has an average meso run length of around 5, whereas highly crystalline polypropylenes (heats of fusion above 105) have average meso run lengths in excess of 175 and beyond.

The crystallinity/stereoregularity plot of polypropylene compositions of Figure 1 is repeated in Figure 2 to demonstrate the relevant range of polypropylene compositions yielding low to moderate crystallinities. This is demonstrated by the bold lines defining the crystallinity regions of interest for the polypropylene composition of the present invention. Numerically, this range of crystallinity occurs between average meso run lengths of 45 and 105, and heats of fusion between 75 and 109 J/g.

The polypropylenes of the present invention have low to moderate crystallinity, and have % HI's that do not follow the traditional relationship between HI and polypropylene crystallinity. In fact, they contain far less heptane soluble polypropylenes than would be ordinarily expected from their average level of crystallinity. To establish this characteristic of the present compositions, polypropylenes were prepared by the indicated catalysts to enable the instant low to moderately crystalline polypropylene polymers to be compared to comparable, traditional polypropylenes (prepared with prior art catalyst systems). The % heptane insolubles for the series of polypropylenes were compared to both their respective heats of fusion and meso run lengths.

Tables I and II represent propylene polymerization test runs using the catalyst system of the present invention which employs a new generation catalyst component manufactured by the Toho Titanium Company of Japan and commercially designated as the SP111 series. The characteristic curves of Figures 3 - 6 represent the plotting of % HI, heats of fusion, and meso run length values of Tables 1 and 2. The magnesium-supported Ziegler-Natta type catalysts employed in the preparation of polymers for the test runs of Tables 1 and 2 are also listed along with the commercial polymer examined.

TABLE 2

The experimental data in Tables 1 and 2 were generated as follows: EXPERIMENTAL

(A) DSC (Differential Scanning Calorimetry)

A TA-200/DSC-10 instrument, purchased from TA Instruments, Inc., was used to measure me thermal properties of the polymers. The polymers were first extruded and pelletized prior to taking a 8-13 mgs samples. A prepared DSC sample was placed in the cell and the cell purged with nitrogen at room temperature for five minutes. The temperature was then raised to 230°C at a heating rate of 50°C per minute. The temperature was held for ten minutes, followed by cooling to 50°C at a cooling rate of 10°C per minute. After reaching 50°C, the sample was again heated to 200°C at the rate of 10°C per minute. The heat of melting during the second heating cycle was measured, by integrating the melting curve between baseline limits of 85 and 175°C, and used to determine relative crystallinities of the indicated polypropylenes.

(B) Polymerization Process in a Batch Reactor

An amount of silane donor (in a 0.01 M solution in hexane as parts per million donor by weight relative to the total amount of propylene employed) was charged by syringe into a 2 liter autoclave polymerization reactor that had been thoroughly cleaned, dried, and purged with nitrogen. A specified total amount of aluminum alkyl (as parts per million by weight at the desired molar mixture of DEAC and TEA1) was then added to the reactor. A desired amount of hydrogen was introduced into the reactor, as measured by the psi drop from a 300 cc vessel. Next, 1000 ml of propylene was added to the reactor. These procedures were followed by introducing the required amount of catalyst (at 15 to 20 weight percent solids in a mineral oil slurry) by pushing the catalyst into the reactor with 250 cc of propylene. The reactor temperature was raised form room temperature to 70°C and the reaction was allowed to continue for one hour. After the polymerization period, the excess propylene was vented out of the reactor and the remaining polymer was collected and dried in a vacuum oven. The polymer was pelletized with the addition of 500 ppm BHT and samples were taken for % HI, MFR, DSC (ΔH) and NMR measurements. (C) Polymerization Process in a Continuous Pilot Plant Reactor

Continuous polymerizations were carried out using a series of two autoclave reactors which are capable of producing 90 pounds of polymer per hour. The conditions were similar to those of (B), with the exception that the catalyst, silane donor, and mixed DEAC/TEAl reagents were added continuously, and polymerizations were conducted for 4 to 4.5 hours. The subsequent polymers were pelletized prior to taking samples and making the required measurements.

(D) Characterization

Turning to Figures 3 and 4, two views of a plot of % HI versus heat of fusion can be found for both the compositions of the invention and traditional polypropylenes over a broad range of crystallinity. The "window" area, described as "10" in Figure 3, represents that area of low to moderate crystallinity, which characterize the instant polypropylene compositions. This area is equivalent to the defined area of crystallinity demonstrated in Figure 2. Figure 3, which gives a complete view of the relationship between % heptane insolubles and heats of fusion as an index of crystallinity, contains data points generated from

compositions ranging from atactic polypropylene with no low crystallinity to highly crystalline polypropylenes. It is clear in Figure 3 that the % heptane insolubles and heats of fusion demonstrate a proportionally linear relationship with curvature developing only at the higher values for the heats of fusion (Δ H) and % HI. Also shown in Figure 3 is a calculated line, described as "11", which defines the boundary between polypropylenes generated by the traditional catalyst systems and those polypropylenes generated by the instant catalyst system.

Figure 4 is an expanded view of the window area 10 in Figure 3 demonstrating two calculated lines, 11 and 12. Upper calculated line 11 corresponds to the same calculated line 11 shown in Figure 3. The position of the lower line 12 in Figure 4 was determined after a linear regression analysis over the ΔH, HI relationship for the series of polypropylenes, described as "traditional" i.e., prepared from traditional catalyst systems of the prior art. The algebraic equation for line 12 is as follows:

% HI Limit = 0.477(ΔH) + 44.6 (1)

Note that the "traditional polypropylenes" have relatively low % heptane insolubles compared to diose defined as "new generation" and "invention polypropylenes". To define the relationship observed with the "new generation" catalyst recipe of the present invention, the second and higher line 11 is shown in Figure 4. It is the same line shown in Figure 3. The algebraic equation for line 11 was also determined through linear regression analysis and is given by:

% HI Limit = 0.545 (ΔH) + 40.50 (2)

This line provides a boundary between those regions defining the polypropylenes prepared with prior art catalyst systems and those polypropylene compositions prepared with the instant catalyst system. Note that the invention polypropylenes have the highest observed % HI in the ΔH range from 85 to 100 J/g. Any catalyst generated polypropylene composition having atactic polymer content and crystallinity values that give a point above line 11 falls within the purview of the instant invention, which is directed toward low to moderately crystalline polypropylenes having relatively high Hi's. Note from Tables 1 and 2 that traditional polypropylene of run # 12 and invention polypropylene of run # 7 have similar heats of fusion, that is, 92.6 and 92.5 J/g, respectively. The % HI for # 12 is 90.2, which places the composition below the line, and the % HI for composition # 7 is 93.8, which places it above the line. Six of the eight polypropylenes prepared with the instant catalyst system place above the indicated line. The other two, which incidentally place just below line 11, fall outside the defined region of compositions characterized in the present invention (their heats of fusion arc close to 109 J/g).

It should also be noted tiiat % HI versus ΔH relationship is treated as linear, when actually it is nonlinear. This means that the linear relationship is further from the actual relationship at heats of fusion values greater than 100 J/g and below 90 J/g. The deviations of the traditional relationship from the straight line, defined by Equation 2, can easily be seen in Figure 3. Treating the % HI vs. ΔH invention boundary as linear, as opposed to nonlinear, in the regions outiined by the window 10 in Figures 3, which is amplified as Figure 4, is a more conservative approach for characterizing the instant compositions than using a nonlinear relationship between HI and ΔH because the "ends" of the line are further from the actual relationship man the "center" of the line. This restricts the region defining the instant compositions even more man was empirically obtained when plotting actual values of HI and ΔH.

Figures 5 and 6 are different views of the % HI versus average meso run length relationship for both prior art and invention polypropylenes. (The procedure for producing Figures 5 and 6 is comparable to the procedure for producing Figures 4 and 5.) Figure 5 shows the full relationship from atactic polypropylene to highly crystalline polypropylenes while Figure 6 is an expansion of the outlined window area 20 in Figure 5. Analogous to the procedure employed in Figure 4, calculated line "13" line is used in Figure 5 to define the boundary between traditional polypropylenes and those of the polymers prepared with the catalyst system of the present invention. A lower calculated line, "14" is also given in the expanded view of the % HI versus meso run length relationship shown in Figure 6, analogous to the linear relationships shown in Figure 4. Line 14, which defines the "traditional" polypropylene relationship was determined by performing a linear regression analysis over the traditional prior art

polypropylenes. The algebraic equation for line 14 is given below:

% HI Limit = 0.117 (MRL) + 76.2 (3)

Note that the traditional polypropylenes give the lowest % HI at meso run lengths between 55 and 95.

The second and higher line 13, shown in Figure 6, is the relationship observed for the polypropylenes prepared with the commercial Toho catalyst recipe. The equation for this line, which was also shown in Figure 5, defines the boundary between the invention and traditional polypropylenes and is given below:

% HI Limit = 0.31 (MRL) + 67.4 (4) As observed in the relationship between ΔH and % HI, the invention catalyst recipes give polypropylenes that have higher % HTs than the traditional polypropylenes. Both equations 2 and 4 describe boundaries between similar ranges of crystallinity. The HI limits of 81.3 and 100 were used to establish the MRL range of 45 to 105 and the ΔH range of 75 to 109 J/g.

Three of the five polypropylenes within the purview of the instant invention fall in the region above the upper straight line in Figure 6. Two are close to, but below, the boundary as a consequence of the fact that the actual relationship is nonlinear and these points fall in the region where the line that defines the boundary between invention and traditional polypropylenes is furthest from the actual relationship. The presence of a traditional data point in this region is another reason to use the linear relationship as the invention and traditional polypropylenes data also begin to merge at ΔH's above 108-110 J/g and meso run lengths above 95-100. Although some invention compositions, particularly for meso run lengths over 90, will be excluded from the purview of this invention, optimum compositions in this range will still fall above the line. Most traditional compositions fall well below the line as shown by the data in Figure 6.

The polypropylenes, which fall clearly and distinctively within the purview of the present invention will be identified by the combined measurements of average meso run length and % HI. Equations 2 and 4, given above, when used in the range of crystallinity defined by average meso run lengths between 45 and 105 and corresponding heats of fusion, between 75 and 109 J/g define the moderate to low crystalline polypropylene compositions of the present invention.

Experimentally measured heats of fusion, meso run lengths and % HI are compared to the calculated % HI limits, defined by Equations (2) and (4) in the following Table 3. Negative deviations from the calculated HI limits are compositions falling within the purview of the present invention. This is indicated by eitiier Δ1 or Δ2, as given below:

Δ1 = Calculated % HI Limit (Eqn. 4) - Exp. % HI (5)

Δ2 = Calculated % HI Limit (Eqn. 2) - Exp. % HI (6)

(E) Electron Donors

The electron donors included in the present invention are organic silicon compounds such as those described above in the prior art Typical organosilane compounds used as external donors in the catalyst system of the present invention include those disclosed in U. S. Patent 4,990,479 to Ishimaru et al. the entire disclosure of which is hereby incorporated by reference for purposes of US patent practice. Preferred organosilane electron donors include

methylcyclohexyldimethoxysilane ("MCMS"), dicyclopentyldimethoxy-silane ("DCPMS"), diphenyldimethoxysilane ("DPMS"). The most preferred electron donor is methylcyclohexyldimethoxysilane ("MCMS"). The combination of MCMS and the catalyst/co-catalyst subsystem described herein yields wholly unexpected results that surpass previously known catalyst systems. The electron donors as described for use in the present invention may be limited by the stability of the compound and the ease of handling including storage, transportation, and use in the plant

(F) Prepolymerization

The present invention also provides a process for the polymerization of olefins using the catalyst system described above. Although the catalyst system may be used in almost any commercially known polymerization process, the preferred process of the present invention includes a pre-polymerization of the catalyst with a small amount of monomer as described in numerous prior art patents. For example a carrier stream for the catalyst is provided, the catalyst is contacted with the co-catalyst organoaluminum compound mixture and subsequently contacted with the electron donor. The catalyst stream is then contacted with a relatively small amount of the total amount of monomer to be polymerized, the catalyst stream passing through a tubular or stirred reactor, and the pre-polymerized catalyst and catalyst stream are introduced into the polymerization reaction zone. The electron donor may be contacted with the catalyst simultaneously with the co-catalyst mixture. A polymer product may men be withdrawn from the reactor. In using the described catalyst component with the co-catalyst mixture and electron donors described above, the catalyst system may have an efficiency of at least about 20 kg/gcat. while the Al/Si mole ratio in the reaction is within the range 5-1000. The polymer product will also be characterized by hexane solubles within the range 2-10 weight percent

Having described several specific embodiments of the present invention, it will be understood by those skilled in the art that modifications may be made without departing from the scope of the present invention.

Claims

We claim:

1. An olefin polymerization catalyst system comprising:

(i) a solid titanium catalyst component including magnesium,

titanium, halogen, and an internal electron donor;

(ii) a co-catalyst mixture of at least two organoaluminum halide

compounds including a first organoaluminum halide, diethylaluminum chloride in a quantity of between 3 to 75 mole percent of the total organoaluminum co-catalyst mixture and a second organoaluminum halide being one of trimethylaluminum, triethylaluminum, tri-n-propylaluminum, tri-n-butylaluminum, triisobutylaluminum, tri-n-hexylaluminum,

trinormaloctylaluminum, diisobutylaluminum hydride and mixtures thereof, preferably triethylaluninum; and

(iii) an external organosilane electron donor.

2. The catalyst system of claim 1 wherein the organosilane is selected from the group consisting of methylcyclohexyldimethoxysilane,

dicyclopentyldimethoxysilane, diphenyldimetiioxysilane, phenyl- triethoxysilane, and propyltriexthoxysdane, preferably

methylcyclohexyldimethoxysilane or dicyclopentyldimethoxysilane.

3. An olefin polymerization catalyst system comprising:

(i) a solid catalyst component prepared by (i) suspending a dialkoxy magnesium in an aromatic hydrocarbon that is liquid at normal temperatures, (ii) contacting the dialkoxy magnesium with a titanium halide and further contacting the resulting composition a second time with the titanium halide and (iii) contacting the dialkoxy magnesium with a diester of an aromatic dicarboxylic acid at some point during the treatment with the titanium halide in (ii); and (ii) a co-catalyst mixture including of at least two organoaluminum halide compounds including a first organoaluminum halide, diethylaluminum chloride, present in the mixture in a quantity of between 3 to 75 mole percent of the total organoaluminum co- catalyst and a second organoaluminum halide being one of trimethylaluminum, triethylaluminum, tri-n-propylaluminum, tri-n- butylaluminum, triisobutylaluminum, tri-n-hexylaluminum, trinormaloctylaluminun, diisobutylaluminum hydride, and mixtures thereof, preferably triethylaluminum; and

(iii) an external organosilane electron donor.

4. The olefin polymerization catalyst system of claim 3 wherein the

organosilane is selected from the group consisting of

methylcyclohexyldimethoxysilane, dicyclopentyldimethoxysilane, diphenyldimethoxysilane, phenyltriethoxysilane, and propyl- triexthoxysilane preferably methylcyclohexyldimeth oxysilane or dicyclopentyldimethoxysilane.

5. The use of the catalyst systems of claims 1 or 3 in a process for the

polymerization of olefins including:

(a) providing the catalyst system of claims 1 or 3; and

(b) introducing the catalyst system into a polymerization reaction zone containing additional amounts of the organoaluminum halide co- catalyst mixture, the organosilane electron donor, and an olefin monomer wherein polymerization of the monomer takes place to form a polyolefin.

6. The process of claim 5 further including the step of prcpolymerizing the catalyst system before introduction to the reaction zone by contacting a small amount of olefin monomer with the catalyst system.

7. The process of claim 5, further comprising the additional step of: (c) removing the polyolefin polymer from the reaction zone.

8. The process of claim 7 wherein the removed polyolefin is characterized by average meso run lengths of between 45 and 105, a heat of fusion between 81.3 and 109, and heptane insolubility values falling above either line, represented by the algebraic equations:

% HI = 0.545 (ΔH) + 40.5 or % HI = 0.31 (MRL) + 67.4.

9. The polyolefin prepared by the process of claim 5.

10. A polypropylene polymer composition characterized by having an average meso run length between 45 and 105, a heat of fusion between 81.3 and 109, and a heptane insolubility falling above either line, represented by the algebraic equations:

% HI = 0.545 (ΔH) + 40.5 or % HI = 0.31 (MRL) + 67.4.

AMENDED CLAIMS

[received by the International Bureau on 23 January 1996 (23.01 .96 ) ; Original claim 10 cancel led ; remain ing c la ims unchanged (1 page ) ]

(c) removing the polyolefin polymer from the reaction zone.

8. The process of claim 7 wherein the removed polyolefin is characterized by average meso run lengths of between 45 and 105, a heat of fusion

between 81.3 and 109, and heptane insolubility values falling above either line, represented by the algebraic equations:

% HI = 0.545 (ΔH) + 40.5 or % HI = 0.31 (MRL) + 67.4.

9. The polyolefin prepared by the process of claim 5.