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PROPYLENE POLYMERS INCORPORATING
This application is a divisional application of U.S. Ser. No. 09/020,306, filed Feb. 6, 1998, now U.S. Pat. No. 6,197,910, which was based on Provisional Application Ser. No. 60/069,189, filed Dec. 10, 1997.
FIELD OF THE INVENTION
The present invention relates to propylene polymers incorporating macromers and a method for the preparation of branched polypropylene utilizing chiral, stereorigid transition metal catalyst compounds.
BACKGROUND OF THE INVENTION
Polypropylene and related polymers are known to have low melt strength. This is a significant deficiency in key application areas such as thermoforming and blow molding. Polyethylene on the other hand is used extensively in blown film applications requiring good melt strength. The limitations in the melt strength of polypropylenes show up as excess sag in sheet extrusion, rapid thinning of walls in parts thermoformed in the melt phase, low draw-down ratios in extrusion coating, poor bubble formation in extrusion foam materials, and relative weakness in large-part blow molding. Thus, it would be highly desirable to produce polypropylene and related polymers having enhanced melt strength as well as commercially valuable processability.
Increasing the melt strength of polymers such as polypropylene has been an industrial goal for well over ten years, however, success has been limited. The desirable properties that have made low density polyethylene commercially successful are attributed in large part to high melt strength and excellent processability. Both of these properties are attributed to the presence of long chain branching which is thought to occur under high pressure polymerization conditions.
There has been some success in increasing the melt strength of polypropylene. For example, EP 190 889 A2 discloses high energy irradiation of polypropylene to create what is believed to be polypropylene having substantial free-end long branches of propylene units. EP 384 431 discloses the use of peroxide decomposition of polypropylene in the substantial absence of oxygen to obtain a similar product.
Other attempts to improve the melt properties of polypropylene include U.S. Pat. No. 5,541,236, which introduces long chain branching by bridging two PP backbones to form H-type polymers, and U.S. Pat. No. 5,514,761, which uses dienes incorporated in the backbones to achieve a similar effect. However, it is difficult to avoid cross-linking and gel formation in such processes.
Thus, there is still a need for propylene polymers having improved melt strength and good processability.
SUMMARY OF THE INVENTION
The present invention meets that need by providing a polyolefin composition consisting essentially of isotactic polypropylene and, optionally, one or more comonomers, wherein the total comonomer content of the polyolefin composition is from 0 to 20 mole percent, and further, wherein the weight average branching index g' for the lower molecular weight region of the polyolefin composition is less than 0.93. Additionally, a process is provided for producing a polyolefin composition comprising:
a) contacting, in solution, at a temperature from about 90° C. to about 120° C, propylene monomers with a catalyst composition comprising a first chiral, stereorigid transition metal catalyst compound capable of
5 producing isotactic polypropylene;
b) copolymerizing the product of a) with propylene and, optionally, one or more copolymerizable monomers, in a polymerization reactor under suitable polypropylene polymerization conditions using a second chiral, stere
1° origid transition metal catalyst capable of producing isotactic polypropylene; and
c) recovering a branched olefin polymer.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graphic illustration of the relationship between the weight average branching index g' and the molecular weight for the polymer product produced in Example 2.
FIG. 2 is a graphic illustration of the relationship between 20 the weight average branching index g' and the molecular weight for the polymer product produced in Example 3.
FIG. 3 is a graphic illustration of the relationship between the weight average branching index g' and the molecular weight for the polymer product produced in Comparative 25 Example 4.
FIG. 4 is a graphic illustration of the complex viscosity vs. shear rate curve for the polymer products produced in Example 3 and Comparative Example 4.
30 DETAILED DESCRIPTION OF THE
The polyolefin compositions of this invention are comprised of branched polymers wherein both the polymer
35 backbone and polymeric sidechains are derived from propylene polymerized under coordination or insertion conditions with activated transition metal organometallic catalyst compounds. The sidechains are stereospecific (either isotactic or syndiotactic) polypropylene which exhibit crystalline,
40 semi-crystalline or glassy properties suitable for hard phase domains in accordance with the art understood meaning of those terms, and are attached to a polymeric backbone that is also crystalline. The backbone is composed of stereospecific polypropylene and, optionally, one or more comono
45 mers. Preferably, the backbone and the sidechains are isotactic polypropylene. These compositions are useful as thermoforming resins and exhibit improved processability over current polypropylene compositions. The Macromer Sidechains
50 The sidechains are polypropylene macromers, which can be prepared under solution polymerization conditions with metallocene catalysts suitable for preparing either of isotactic or syndiotactic polypropylene. A preferred reaction process for propylene macromers having high levels of terminal
55 vinyl unsaturation is described in co-pending U.S. application Ser. No. 60/067,783 filed Dec. 10, 1997. Typically used catalysts are stereorigid, chiral or asymmetric, bridged metallocenes. See, for example, U.S. Pat. Nos. 4,892,851, 5,017,714, 5,132,281, 5,132,381, 5,155,080, 5,296,434,
60 5,278,264, 5,304,614, 5,510,502, WO-A-(PCT/US92/ 10066) WO-A-93/19103, EP-A2-0 577 581, EP-A1-0 578 838, and academic literature "The Influence of Aromatic Substituents on the Polymerization Behavior of Bridged Zirconocene Catalysts", Spaleck, W., et al, Organometallics
65 1994, 13, 954-963, and "ansa-Zirconocene Polymerization Catalysts with Annelated Ring Ligands-Effects on Catalytic Activity and Polymer Chain Lengths", Brinzinger, H., et al,
Organometallics 1994, 13, 964-970, and documents referred to therein.
Preferably, the stereorigid transition metal catalyst compound is selected from the group consisting of bridged bis(indenyl) zirconocenes or hafnocenes or azulenyl ligand 5 equivalents thereof. In a preferred embodiment, the transition metal catalyst compound is a dimethylsilyl-bridged bis(indenyl) zirconocene or hafnocene. More preferably, the transition metal catalyst compound is dimefhylsilyl bis(2mefhyl-4-phenylindenyl) zirconium or hafnium dichloride or dimethyl. In another preferred embodiment, the transition metal catalyst is a dimethylsilyl-bridged bis(indenyl) hafnocene such as dimefhylsilyl bis(indenyl)hafnium dimethyl or dichloride. The method for preparing propylenebased macromers having a high percentage of vinyl terminal bonds involves: 15
a) contacting, in solution at a temperature from about 90° C. to about 120° C, propylene, optionally a minor amount of copolymerizable monomer, with a catalyst composition containing the stereorigid, activated transition metal catalyst compound; and 20
b) recovering isotactic or syndiotactic polypropylene chains having number average molecular weights of about 2,000 to about 50,000 Daltons.
Preferably, the solution comprises a hydrocarbon solvent such as toluene. Also, the propylene monomers are prefer- 25 ably contacted at a temperature from 95° C. to 115° C. More preferably, a temperature from 100° C. to 110° C. is used. Most preferably, the propylene monomers are contacted at a temperature from 105° C. to 110° C. The pressures of the reaction generally can vary from atmospheric to 345 MPa, 30 preferably to 182 MPa. The reactions can be run batchwise or continuously. Conditions for suitable slurry-type reactions will also be suitable and are similar to solution conditions, the polymerization typically being run in liquid propylene under pressures suitable to such. 35
Additionally the invention branched polyolefin composition can be prepared directly from the selected olefins concurrently in the presence of a mixed catalyst system comprising at least one first transition metal olefin polymerization catalyst capable of preparing propylene copolymers 40 having greater than 50% chain end-group unsaturation and at least one second transition metal olefin polymerization catalyst capable of incorporating the propylene homopolymer or copolymer sidechains into said branched olefin copolymer. This in situ method can be practiced by any 45 method that permits both preparation of isotactic polypropylene macromers having crystalline, semi-crystalline or glassy properties and copolymerization of the macromers with polypropylene and other comonomers such that a branched copolymer is prepared. Gas phase, slurry and 50 solution processes can be used under conditions of temperature and pressure known to be useful in such processes.
As used herein, "isotactic polypropylene" is defined as having at least 70% isotactic pentads according to analysis by 13C-NMR. "Highly isotactic polypropylene" is defined 55 as having at least 90% isotactic pentads according to analysis by 13C-NMR. "Syndiotactic polypropylene" is defined as polypropylene having at least 70% syndiotactic pentads according to analysis by 13C-NMR. Preferably, the macromers of the present invention are highly isotactic polypro- 60 pylene.
The polypropylene macromers can have narrow or broad molecular weight distribution (Mw/Mn), for example, from 1.5 to 5, typically 1.7 to 3. Optionally, mixtures of sidechains with different molecular weights may be used. 65
The number-average molecular weight (M„) of the polypropylene macromers of the present invention typically
ranges from greater than or equal to 2,000 Daltons to less than about 50,000 Daltons, preferably less than 40,000 Daltons, more preferably less than 30,000 Daltons, most preferably less than or equal to 20,000 Daltons. Preferably, the M„ of the polypropylene macromers of the present invention is greater than or equal to 5,000 Daltons, more preferably greater than or equal to 7,500 Daltons, most preferably greater than or equal to 10,000 Daltons. The number of sidechains is related to the M,, of the sidechains such that the total weight fraction of the polymeric backbone segments between and outside the incorporated sidechains is greater than 0.40, preferably greater than 0.5-0.6. Weight here is determined by gel permeation chromatography (GPC) and differential refractive index (DRI) measurements Preferably, the macromers of the present invention are made using solution-phase conditions. Preferred solvents for solution phase reactions are selected on the basis of polymer solubility, volatility and safety/health considerations. Nonpolar alkanes or aromatics are preferred. More preferably, the solvent is aromatic. Most preferably, the solvent is toluene.
The Polyolefin Backbone
The polyolefin backbone of the present invention is composed of propylene monomers and, optionally, one or more comonomers. In one embodiment of the present invention, no comonomers are present in the polyolefin backbone, resulting in a polymer having an isotactic polypropylene backbone and stereospecific polypropylene sidechains. Preferably, the sidechains are isotactic polypropylene.
In another embodiment of the present invention, one or more comonomers are present in the backbone. Comonomers which are useful in the present invention include ethylene, C4-C20 a-olefins, and lower carbon number (C3-C8) alkyl substituted analogs of the cyclic and styrenic olefins. Other copolymerizable monomers include geminally disubstituted olefins such as isobutylene, C5-C25 cyclic olefins such as cyclopentene, norbornene and alkylsubstituted norbornenes, and styrenic monomers such as styrene and alkyl substituted styrenes. Comonomers are selected for use based on the desired properties of the polymer product and the metallocene employed will be selected for its ability to incorporate the desired amount of olefins.
When comonomers are used, they preferably comprise from 3 to 20 mole percent of the branched polyolefin composition. More preferably, the comonomers comprise from 5 to 17 mole percent of the branched polyolefin composition.
In another embodiment of the present invention, the backbone of the present invention contains syndiotactic polypropylene and, optionally, one or more comonomers. Essentially all of the backbone can be syndiotactic, resulting in a polymer having a syndiotactic polypropylene backbone and stereospecific polypropylene sidechains. Alternatively, the backbone can be a combination of syndiotactic and isotactic polypropylene with, optionally, one or more comonomers.
An unusual feature of the branched polyolefin of the present invention is the presence of a significant amount of branching in the lower molecular weight range of the polymer. This branching results in improved melt strength, as well as other unique physical properties. In this case, the amount of branching is determined using the weight average branching index g' of the branched polyolefin. The weight average branching index g' is defined as g -[IVJ^/flVJ^J^^. It is well known in the art that as the g' value decreases,
branching increases. See B. H. Zimm and W. H. Stockmayer, J. Chem. Phys. 17, 1301 (1949).
Preferably, the weight average branching index g' for the lower molecular weight region of the branched polyolefin of the present invention is less than 0.93. More preferably, the weight average branching index g' for the lower molecular weight region of the branched polyolefin of the present invention is less than 0.90. Most preferably, the weight average branching index g' for the lower molecular weight 10 region of the branched polyolefin of the present invention is less than 0.88.
With regard to the molecular weight distribution of the polyolefin composition of the present invention, the following definitions apply:
Lower molecular weight region: That portion of the polymer product which has a molecular weight which is less than the number average molecular weight of the
total polymer product. Higher molecular weight region: That portion of the polymer product which has a molecular weight which is more than the number average molecular weight of the total polymer product. 25 The mass of the backbone will typically comprise at least 40 wt % of the total polymer mass, that of the backbone and the sidechains together, so the backbone typically will have a nominal weight-average molecular weight (MJ weight of ^ at least equal to or greater than about 100,000. The term nominal is used to indicate that direct measurement of M„ of the backbone is largely impossible but that characterization of the copolymer product will exhibit measurements of M^, that correlate to a close approximate weight of the 35 polymeric backbone inclusive only of the monoolefin mer derivatives and the insertion moieties of the sidebranches. Catalysts
Catalysts which are useful for producing the branched 40 polyolefin of the present invention include all catalysts which are capable of producing isotactic polypropylene and incorporating significant quantities of the isotactic polypropylene macromers of the present invention. Preferably, metallocene catalysts are used. 45
As used herein "metallocene" refers generally to compounds represented by the formula CpmMRJJX<? wherein Cp is a cyclopentadienyl ring which may be substituted, or derivative thereof which may be substituted, M is a Group 50 4, 5, or 6 transition metal, for example titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten, R is a hydrocarbyl group or hydrocarboxy group having from one to 20 carbon atoms, X is a halogen, and m=l-3, n=0-3, q=0-3, and the sum of m+n+q 55 is equal to the oxidation state of the transition metal.
Methods for making and using metallocenes are well known in the art. For example, metallocenes are detailed in U.S. Pat. Nos. 4,530,914; 4,542,199; 4,769,910; 4,808,561; 4,871,705; 4,933,403; 4,937,299; 5,017,714; 5,057,475; 60 5,120,867; 5,278,119; 5,304,614; 5,324,800; 5,350,723; and 5,391,790 each fully incorporated herein by reference.
Preferred metallocenes are those that are stereorigid and comprise a Group 4, 5, or 6 transition metal, biscyclopen- 65 tadienyl derivative, preferably bis-indenyl metallocene components having the following general structure:
M1 is a metal of Group 4, 5, or 6 of the Periodic Table, for example titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten, preferably, zirconium, hafnium and titanium, most preferably zirconium and hafnium;
R1 and R2 are identical or different, are one of a hydrogen atom, a Cj-cjq alkyl group, preferably a Ct-C3 alkyl group, a Cj-cjq alkoxy group, preferably a C1-C3 alkoxy group, a C6-C10 aryl group, preferably a C6-C8 aryl group, a C6-C10 aryloxy group, preferably a C6-C8 aryloxy group, a C2-C10 alkenyl group, preferably a C2-C4 alkenyl group, a C7-C40 arylalkyl group, preferably a C7-C10 arylalkyl group, a C7-C40 alkylaryl group, preferably a C7-C12 alkylaryl group, a C8-C40 arylalkenyl group, preferably a C8-C12 arylalkenyl group, or a halogen atom, preferably chlorine;
R3 and R4 are hydrogen atoms;
R5 and R6 are identical or different, preferably identical, are one of a hydrogen atom, halogen atom, preferably a fluorine, chlorine or bromine atom, a C1-C10 alkyl group, preferably a C1-C4 alkyl group, which may be halogenated, a C6-C10 aryl group, which may be halogenated, preferably a C6-C8 aryl group, a C2-C10 alkenyl group, preferably a C2-C4 alkenyl group, a C7-C40-arylalkyl group, preferably a C7-C10 arylalkyl group, a C7-C40 alkylaryl group, preferably a C7-C12 alkylaryl group, a C8-C40 arylalkenyl group, preferably a C8-C12 arylalkenyl group, a —NR215, —SR15, —SR15, —OR15, OSiR315 or —PR215 radical, wherein R15 is one of a halogen atom, preferably a chlorine atom, a Cj-cjq alkyl group, preferably a Ct-C3 alkyl group, or a C6-C10 aryl group, preferably a C6-C9 aryl group;