Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F10/00—Homopolymers and copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond
  • C08F10/04—Monomers containing three or four carbon atoms
  • C08F10/06—Propene

Definitions

• This invention relates to novel, high flexural moduli polymeric materials, i.e., in situ polymerized polypropylene homopolymers, formed by a single stage polymerization process conducted in the presence of a blend of electron donor materials.
• novel polypropylene homopolymers can be further used to make high impact polypropylene copolymers.
• the present inventors have discovered that by using a blend of a first donor material and a second electron donor material each having different hydrogen responses and stereoregulating properties, an olefin polymer exhibiting an unusually good balances of impact resistance, flexural strength and processability can be provided.
• BACKGROUND OF THE INVENTION The physical properties of homopolymers of propylene formed by typical
• Ziegler-Natta polymerization are highly dependent on the stereoregularity of the polymer itself.
• Highly stereoregular polymers are generally crystalline, provide desirable high flexural moduli and are formed with a suitable choice of electron donor.
• These highly crystalline polymers also display high melting points, but innately exhibit low melt flow rates (MFR) that render them generally unsuitable for applications that require high processing rates, such as in injection molding, oriented films and thermobond fibers.
• MFR melt flow rates
• conventional polypropylene homopolymer and copolymer products formed from highly crystalline polypropylenes lack sufficient impact resistance for many intended uses.
• the addition of various electron donor materials to Ziegler-Natta catalysts has been known to influence the degree of stereoregularity in polypropylene homopolymers and copolymers.
• a single base catalyst e.g., a magnesium chloride supported base Ziegler-Natta catalyst
• any number of electron donor materials each of which, or combinations of which, will lead to a specific level of stereoregularity and MFR.
• One of the properties of electron donors is that the polypropylene MFR, at the same reactor hydrogen level, decreases with increasing polypropylene stereoregularity caused by the donor. Additional hydrogen is required to reach desirable MFRs when highly stereoregulating donors are employed.
• Use of the term copolymer herein, is intended to mean those polymeric materials often known as impact copolymers. Impact copolymers typically include homopolymer polypropylene (homo PP) and an ethylene-propylene copolymer component. All references to the term copolymer are intended to include only impact copolymers (ICP) and not statistical or random copolymers. The production of such ICP's is discussed in Polypropylene Handbook, pg. 92, Hansen Publishers.
• MFR polypropylene has been required for larger scale injection molding processes producing items such as automotive or appliance parts.
• Such MFR's are typically in the range of from 30- 100 dg/min. for copolymers, and 75- 180 dg/min. for homopolymers.
• Crystallinity of polypropylene is defined by the catalyst system. To compare the ability of catalyst systems to produce higher crystallinity polypropylene, crystallinity of the polypropylene at fixed MFR can be used, because crystallinity of polypropylene increases with MFR of the polypropylene. Crystallinity is usually evaluated with heat of fusion (defined herein by ( H TM ) or alternatively heat of melting) from DSC (Differential Scanning Calorimeter) measurements.
• H TM heat of melting
• MWD molecular weight distribution
• Novel in situ polymerized materials e.g., polypropylene
• novel in situ polymerized materials with substantial degrees of crystallinity and high MFRs can be produced in a single stage polymerization conducted in the presence of certain supported Ziegler-Natta catalysts and a blend of two electron donors including about 2.5 to less than 50 mol.% dicyclopentyldimethoxysilane (DCPMS) and greater than 50 mol.% propyltriethoxysilane (PTES) based on total moles % of electron donor.
• DCPMS dicyclopentyldimethoxysilane
• PTES propyltriethoxysilane
• high MFRs were exhibited only by lesser stereoregular polymers having a higher amorphous content than desireable.
• the method includes the subjection of an ⁇ -olefin (e.g., propylene, 1-butene, 1- pentene, 1-hexene, and the like) to a single stage polymerization in the presence of a supported Ziegler-Natta catalyst and a blend of two electron donors including about 2.5 to less than 50 mol.% dicyclopentyldimethoxysilane (DCPMS) and greater than 50 mol.% propyltriethoxysilane (PTES) based on the total moles of the electron donor.
• DCPMS dicyclopentyldimethoxysilane
• PTES propyltriethoxysilane
• 1 is a graph plotting MFR at a constant hydrogen pressure versus ⁇ H m at a fixed rate, 70 MFR for conventional electron donors used individually and blends containing different ratios of propyltriethoxysilane (PTES) and dicyclopentyl dimethoxysilane (DCPMS) electron donors.
• PTES propyltriethoxysilane
• DCPMS dicyclopentyl dimethoxysilane
• Fig. 2 shows the plot of crystallinity ( ⁇ H m ) as a function of the polymer MFR for the individual donors. This was obtained by carrying out polymerizations with each donor at different levels of hydrogen to vary the MFR. The intersection of the crystallinity/MFR line with the vertical line set at 70-MFR represents the crystallinity at 70-MFR, which is the value used in Fig. 1.
• Fig. 3 is similar to Fig. 2, but using four different ratios of propyltriethoxysilane (PTES) and dicyclopentyl dimethoxysilane (DCPMS) electron donors. From the figure, the crystallinity at 70-MFR was also obtained and used in Fig. 1.
• PTES propyltriethoxysilane
• DCPMS dicyclopentyl dimethoxysilane
• the homopolymer of the single stage, in situ polymerization process of certain embodiments of the present invention simultaneously display high flexural moduli (nucleated homopolymer exhibiting flexural moduli in the range of 220 - 315 K psi, preferably 280 - 315 K psi) (with a ⁇ H ⁇ in the range of from 95-120 J/g) normally associated with highly crystalline polymers, a high melt flow rates (MFRs) normally associated with less stereoregular polymers and a relatively narrow molecular weight distribution (MWD), generally in the range of from 3-6, preferably 3.5 - 5.5.
• MFRs melt flow rates
• MWD molecular weight distribution
• novel homopolymer components are formed in a process where, for example, propylene is subjected to a single stage polymerization in the presence of a Ziegler-Natta catalyst and a blend of two electron donors including about 2.5 to less than 50 mol.% dicyclopentyldimethoxysilane (DCPMS) and greater than about 50 mol.% propyltriethoxysilane (PTES).
• a Ziegler-Natta catalysts useful in the practice of the present invention are a solid titanium supported catalyst systems described in US-A- 4990479 and US-A-5159021.
• the Ziegler-Natta catalyst can be obtained by: (1) suspending a dialkoxy magnesium compound in an aromatic hydrocarbon that is liquid at ambient temperatures; (2) contacting the dialkoxy magnesium- hydrocarbon composition with a titanium halide and with a diester of an aromatic dicarboxylic acid; and (3) contacting the resulting functionalized dialkoxy magnesium-hydrocarbon composition of step (2) with additional titanium halide.
• a particularly suitable solid catalyst component is a catalyst solid sold by TOHO Titanium Company, Ltd. under the trade name of THC-C-133. Such a catalyst is used to exemplify the invention, other titanium supported catalyst systems are contemplated. Other catalyst use mechanisms are contemplated. Including, but not limited to, batch prepolymerization, in situ prepolymerization and other such mechanisms.
• Certain supported Ziegler-Natta catalysts may be used in combination with a co-catalyst.
• the co-catalyst is preferably an organoaluminum compound that is halogen free.
• Suitable halogen free organoaluminum compounds are, in particular, branched unsubstituted alkylaluminum compounds of the formula A1R 3 , where R denotes an alkyl radical having 1 to 10 carbon atoms, such as for example, trimethylaluminum, triethylaluminum, triisobutylaluminum and tridiisobutylaluminum.
• Additional compounds that are suitable for use as a co- catalyst are readily available and amply disclosed in the prior art including US-A- 4990477, which is incorporated herein by reference for purposes of US patent practice.
• a particularly suitable organoaluminum co-catalyst is triethylaluminum (TEAL).
• Electron donors are typically used in two ways in the formation of Ziegler- Natta catalysts and catalyst systems.
• An internal electron donor may be used in the formation reaction of the catalyst as the transition metal halide is reacted with the metal hydride or metal alkyl.
• Examples of internal electron donors include amines, amides, ethers, esters, aromatic esters, ketones, nitriles, phosphines, stilbenes, arsines, phosphoramides, thioethers, thioesters, aldehydes, alcoholates, and salts of organic acids.
• an external electron donor is also used in combination with a catalyst.
• External electron donors generally affect the level of stereoregularity and MFR in polymerization reactions.
• External electron donor materials include but are not limited to, organic silicon compounds, e.g.
• TEOS tetraethoxysilane
• MCMS methylcyclohexyldimethoxysilane
• PTES propyltriethoxysilane
• DCPMS dicyclopentydimethoxysilane
• the blend of electron donors of the present invention is a blend of external electron donors used as stereoregulators, in combination with Ziegler-Natta catalysts. Therefore, except when otherwise indicated, the term "electron donor”, as used herein, refers specifically to external electron donor materials.
• the external electron donors act to control stereoregularity, which affects the amount of isotactic versus atactic polymers produced in a given system.
• the more stereoregular isotactic polymer is more crystalline, which leads to a material with a higher flexural modulus.
• Highly crystalline, isotactic polymers also display lower MFRs, as a consequence of a reduced hydrogen response during polymerization.
• the stereoregulating capability and hydrogen response of a given electron donor are directly and inversely related.
• the DCPMS donor has a substantially lower hydrogen response than the PTES donor, but produces a significantly higher level of stereoregularity than PTES.
• DCPMS is more stereoregulating, and will, at an equal reactor hydrogen pressure, provide a higher level of crystallinity and lower MFR than the lesser stereoregulating PTES donor.
• the X-axis represents the actual MFR that is obtained when using the specified polymerization donors, with all experiments carried out at 140-mmole of hydrogen, as shown in the experimental section (B).
• the Y-axis represents the corresponding crystallinity (based on DSC heat-of-melting values, ⁇ H m ) for a polymer having an MFR of 70 for each specified donor.
• the Y- values were obtained from a separate set of experiments, where the amount of hydrogen used during the polymerization was varied at different levels, in order to obtain a plot of the MFR versus the crystallinity ( Figures 2 and 3). It is important to compare the crystallinity at a fixed MFR value because the polypropylene product applications are designed based largely on MFR specifications , because crystallinity of polypropylene increases with MFR of the polypropylene. For the individual donors, an almost linear plot is obtained, which shows a decreasing crystallinity with MFR, when going from DCPMS to MCMS, PTES, and TEOS, respectively.
• the dotted line shows that at a constant hydrogen pressure, for any given MFR, a blend of PTES and DCPMS containing 2.5 mol.% to less than 50 mol.% DCPMS and more than 50 mol.% PTES provides a higher level of crystallinity than would be expected from the average hydrogen response of such a blend, represented by the continuum of the solid line of Fig. 1. This improved degree of crystallinity relative to MFR is not realized when the blend contains less than 2.5 mol.% DCPMS or less than 50 mol.% PTES.
• the reactor temperature was raised from room temperature to 70°C, and the polymerization 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 under a vacuum oven.
• the polymer was pelletized with 500 ppm butylated hydroxy toluene (BHT) and samples were taken for MFR, MWD molecular weight distribution, and DSC measurements. Tables I, II and III show the results the polymerization used to generate Figures 1, 2, and 3.
• BHT butylated hydroxy toluene
• the catalyst system and donor blend are chosen such that a relationship between a first melt flow rate of a homopolymer formed by polymerizing an alpha-olefin monomer in the presence of a Ziegler-Natta catalyst system and a first electron donor (MFR (a)), and a second melt flow rate of a homopolymer formed by polymerizing an ⁇ -olefin monomer in the presence of the Ziegler-Natta catalyst system and a second electron donor (MFR (b)), is defined by the equation;
• the ⁇ -olefin is chosen from the group consisting of a propylene, 4-methyl-l -pentene, 1-hexene, 1-butene, 1-hexene, 1-decene, 1-dodecene, 1- nonene, and mixtures thereof.
• the comonomer may include ethylene.
• Propylene is the preferred ⁇ -olefin.
• DCPMS is the preferred electron donor corresponding to a first electron donor
• PTES is the preferred second electron donor.

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• 1999
  • 1999-05-11 CA CA002327427A patent/CA2327427C/en not_active Expired - Fee Related
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  • 1999-05-11 EP EP99922932A patent/EP1080122B1/en not_active Expired - Lifetime
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