Propylene homopolymer

Abstract

A propylene homopolymer optionally containing up to 1.0 wt% of ethylene derived units characterized in that: - two melting points are present -the higher melting point ranges from 155°C to 170°C; - the fraction soluble in xylene at 25°C is comprised between 6.0 wt% and 2.0wt%; -the isotactic pentads mmmm % ranges from 96.5 mol% to 90.0 mol%. - the intrinsic viscosity (IV) measured in tetrahydronaphthalene at 135 °C ranging from 5.5 to 12.0 dl / g - the melt strength is higher than 0.70 N.

Description

PROPYLENE HOMOPOLYMERFIELD OF THE INVENTION

[0001] The present disclosure relates to polypropylene homopolymer having high molecular weight and high melt strength.BACKGROUND OF THE INVENTION

[0002] Propylene homopolymer is widely used in the processing fields of injection, extrusion, tape casting and biaxial stretching due to the tailoring structure thereof However, the common polypropylene molecular chain is of linear structure, which is unlike amorphous polymers, such as polystyrene PS with a region having property similar to the rubber elasticity in a wide temperature range. Thus, polypropylene cannot be thermoformed in a wide temperature range. Meanwhile, the softening point of polypropylene is close to its melt point. When the temperature is higher than the melt point, the melt strength and melt viscosity of polypropylene will decrease rapidly, thus causing the following problems including uneven wall thickness of the products during thermoforming, edges curling and shrinkage that would easily appear during extrusion, coating and rolling, and foam collapse during extrusion foaming etc. Therefore, the use of polypropylene in the fields of thermoforming, foaming and blow molding is limited. As a result, development of polypropylene with high melt strength is always an interest issue. Therefore there is the need to develop a propylene homopolymer to be used in blend for increasing the melt strength of more conventional propylene polymer.SUMMARY OF THE INVENTION

[0003] The present disclosure is directed to a propylene homopolymer optionally containing up to 1.0 wt% of ethylene derived units characterized in that:- two melting points are present in the DSC thermogram, measured according to ISO 11357-3, with heating and cooling rate of 20°C / min;-the higher melting point, measured according to ISO 11357-3, with heating and cooling rate of 20°C / min, ranges from 155°C to 170°C;- the fraction soluble in xylene at 25°C , measured according to ISO 16 152 - 2005 is comprised between 6.0 wt% and 2.0wt%;-the isotactic pentads mmmm %, measured with C13NMR as reported in the examples section ranges from 96.5 mol% to 90.0 mol%;- the intrinsic viscosity (IV) measured in tetrahydronaphthalene at 135 °C ranges from 5.5 to 12.0 dl / g;- the melt strength measured according to ISO 16790-2005, at 250°C and applying an acceleration equal to 6 mm / s2is higher than 0.070 N.DETAILED DESCRIPTION OF THE INVENTION

[0004] The present disclosure is directed to a propylene homopolymer optionally containing up to 1.0 wt% of ethylene, preferably up to 0.6 wt% of ethylene derived units characterized in that:- two melting points are present in the DSC thermogram measured according to ISO 11357- 3, with heating and cooling rate of 20°C / min; preferably the lower melting point ranges from 135°C to 150°C;-the higher melting point, measured according to ISO 11357-3, with heating and cooling rate of 20°C / min, ranges from 155°C to 170°C; preferably from 157°C to 168°C;- the fraction soluble in xylene at 25°C measured according to ISO 16 152 - 2005, is comprised between 6.0 wt% and 2.0wt%; preferably comprised between 5.0 wt% and 2.5wt%; more preferably comprised between 4.0 wt% and 2.8wt%;-the isotactic pentads, mmmm %, measured with C13NMR as reported in the examples section ranges from 96.5 mol% to 90.0 mol%, .preferably from 96.0 mol% to 93.0 mol%; more preferably from 95.5 mol% to 93.5 mol%;- the intrinsic viscosity (IV) measured in tetrahydronaphthalene at 135 °C ranges from5.5dl / g to 12.0 dl / g; preferably from 7.0 dl / g to 11.0 dl / g; more preferably from 8.0 dl / g to 10.0 dl / g;- the melt strength measured according to ISO 16790-2005 at 250°C and applying an acceleration equal to 6 mm / s2, is higher than 0.070 N; preferably higher than 0.080 N; more preferably higher than 0.090 N.

[0005] Preferably the propylene homopolymer of the present disclosure is not nucleated.

[0006] Preferably the homopolymer of the present disclosure shows a value of melt strength lower than 0.30 N.

[0007] Preferably the homopolymer of the present disclosure shows a polydispersity index, PI, measured according to ISO 6721-10, comprised between 4.5 and 7.5; more preferably between 5.0 and 7.2; more preferably from 5.5 to 6.5.

[0008] Preferably the homopolymer of the present disclosure shows a tensile modulus ranging from 2100 MPa to 1100 MPa; preferably from 1800MPa, to 1200 Mpa.

[0009] Preferably the homopolymer of the present disclosure shows a charpy impact test at 23°C ranging from 4.0 kJ / m2 to 11.0 kJ / m2; preferably from 5.5 kJ / m2 to 9.0 kJ / m2.

[0010] If present, the ethylene derived units are measured with 13C-NMR as reported in examples section

[0011] The polypropylene homopolymer of the present disclosure is characterized by having an high melt strength and an high molecular weight. For this reason the homopolymer of the present disclosure can be used in blend with other polymers having a lower melt strength in order to increase the latter so that the resulting blend can be used for the production of foam products, biaxial stretching films, thermoforming products and blow molded products.

[0012] The propylene homopolymers disclosed herein can be prepared by a process comprising polymerizing propylene optionally with ethylene, in the presence of Ziegler-Natta catalysts. An essential component of said catalysts is a solid catalyst component comprising a titanium compound having at least one titanium-halogen bond, and an electron-donor compound, both supported on a magnesium halide in active form. Another essential component (co-catalyst) is an organoaluminium compound, such as an aluminium alkyl compound. An external donor is optionally added.

[0013] Catalysts having the above mentioned characteristics are well known in the patent literature; particularly advantageous are the catalysts described in US patent 4,399,054 and European patent 45977. Other examples can be found in US patent 4,472,524.

[0014] The solid catalyst components used in said catalysts comprise, as electron-donors (internal donors), compounds selected from the group consisting of ethers, ketones, lactones, compounds containing N, P and / or S atoms, and esters of mono- and dicarboxylic acids.

[0015] Particularly suitable electron- donor compounds are esters of phtalic acid and 1,3- diethers of formula:

[0016] wherein RI and RII are the same or different and are Cl -Cl 8 alkyl, C3-C18 cycloalkyl or C7-C18 aryl radicals; RIII and RIV are the same or different and are C1-C4 alkyl radicals; or are the 1,3-diethers in which the carbon atom in position 2 belongs to a cyclic or polycyclic structure made up of 5, 6, or 7 carbon atoms, or of 5-n or 6-n' carbon atoms, and respectively n nitrogen atoms and n' heteroatoms selected from the group consisting of N, O, S and Si, where n is 1 or 2 and n' is 1, 2, or 3, said structure containing two or three unsaturations (cyclopolyenic structure), and optionally being condensed with other cyclic structures, or substituted with one or more substituents selected from the group consisting of linear or branched alkyl radicals; cycloalkyl, aryl, aralkyl, alkaryl radicals and halogens, or being condensed with other cyclic structures and substituted with one or more of the above mentioned substituents that can also be bonded to the condensed cyclic structures; one or more of the above mentioned alkyl, cycloalkyl, aryl, aralkyl, or alkaryl radicals and the condensed cyclic structures optionally containing one or more heteroatom(s) as substitutes for carbon or hydrogen atoms, or both.

[0017] Ethers of this type are described in published European patent applications 361493 and 728769.

[0018] Representative examples of said diethers are 2-methyl-2-isopropyl-l,3- dimethoxypropane, 2,2-diisobutyl-l,3-dimethoxypropane, 2-isopropyl-2-cyclopentyl-l,3- dimethoxypropane, 2-isopropyl-2-isoamyl- 1,3 -dimethoxypropane, 9,9-bis (methoxymethyl) fluorene.

[0019] Other suitable electron-donor compounds are phthalic acid esters, such as diisobutyl, dioctyl, diphenyl and benzylbutyl phthalate.

[0020] The preparation of the above mentioned catalyst component is carried out according to various methods.

[0021] For example, a MgC12»nROH adduct (in particular in the form of spheroidal particles) wherein n is generally from 1 to 3 and ROH is ethanol, butanol or isobutanol, is reacted with an excess of TiC14 containing the electron-donor compound. The reaction temperature is generally from 80 to 120° C. The solid is then isolated and reacted once more with TiC14, in the presence orabsence of the electron-donor compound, after which it is separated and washed with aliquots of a hydrocarbon until all chlorine ions have disappeared.

[0022] In the solid catalyst component the titanium compound, expressed as Ti, is generally present in an amount from 0.5 to 10% by weight. The quantity of electron-donor compound which remains fixed on the solid catalyst component generally is 5 to 20% by moles with respect to the magnesium dihalide.

[0023] The titanium compounds, which can be used for the preparation of the solid catalyst component, are the halides and the halogen alcoholates of titanium. Titanium tetrachloride is the preferred compound.

[0024] The reactions described above result in the formation of a magnesium halide in active form. Other reactions are known in the literature, which cause the formation of magnesium halide in active form starting from magnesium compounds other than halides, such as magnesium carboxylates.

[0025] The Al-alkyl compounds used as co-catalysts comprise the Al-trialkyls, such as Al- triethyl, Al-triisobutyl, Al-tri-n-butyl, and linear or cyclic Al-alkyl compounds containing two or more Al atoms bonded to each other by way of O or N atoms, or SO4 or SO3 groups.

[0026] The Al-alkyl compound is generally used in such a quantity that the Al / Ti ratio be from 1 to 1000.

[0027] The electron-donor compounds that can be used as external donors include aromatic acid esters such as alkyl benzoates, and in particular silicon compounds containing at least one Si- OR bond, where R is a hydrocarbon radical.

[0028] Examples of silicon compounds are (tert-butyl)2Si(OCH3)2, (cyclohexyl)(methyl)Si (OCH3)2, (cyclopentyl)2Si(OCH3)2 and (phenyl)2Si(OCH3)2 and (1,1,2- trimethylpropyl)Si(OCH3)3.

[0029] 1,3 -diethers having the formulae described above can also be used advantageously. If the internal donor is one of these diethers, the external donors can be omitted.

[0030] In particular, even if many other combinations of the previously said catalyst components may allow to obtain compositions according to the present invention, the component A) are preferably prepared by using catalysts containing a phthalate as internal donor and (cyclopentyl)2Si(OCH3)2 as outside donor, or the said 1,3-diethers as internal donors.

[0031] The polymerization is generally carried out at temperatures of from 20 to 120°C, preferably of from 40 to 80°C. When the polymerization is carried out in gas-phase, the operating pressure is generally between 0.5 and 5 MPa, preferably between 1 and 4 MPa. In bulk polymerization, the operating pressure is generally between 1 and 8 MPa, preferably between 1.5 and 5 MPa. Hydrogen is typically used as a molecular weight regulator. The polymerization can be in gas phase or in slurry or in solution. In one or more reactors. Preferably the polymerization is carried put in two slurry reactors operating in series.

[0032] The propylene homopolymer optionally containing up to 1.0 wt% of ethylene derived units of the present disclosure can be used for obtaining fibers, film, molded articles and foamed articles.

[0033] The following examples are given in order to illustrate, but not limit the present disclosure.EXAMPLESCHARACTERIZATIONSXylene-insoluble and soluble fraction at 25°C

[0034] Xylene Solubles fraction has been measured according to ISO 16 152 - 2005; with solution volume of 250 ml, precipitation at 25°C for 20 minutes, 10 of which with the solution in agitation (magnetic stirrer), and drying at 70°.Melt Flow Rate (MFR)

[0035] Measured according to ISO 1133 at 230°C with a load of 21.6 kg, unless otherwise specified.Polydispersity (PI)

[0036] Some grams of molten homopolymer are submitted to a dynamic test in rate sweep with a parallel plate rheometer, at temperature of 200°C, according to the ISO 6721-10. G’ (storage modulus) and G” (loss modulus) are measured as function of frequency. From the rate sweep data, PI is defined by PI=105 / Gc, wherein Gc is the crossover modulus as value of modulus at G’ = G”.Melting temperature via Differential Scanning Calorimetry (DSC)

[0037] The melting points of the polymers (Tm) were measured by differential scanning calorimetry (DSC) on a Perkin Elmer DSC-1 calorimeter, previously calibrated against indiummelting points, and according to ISO 11357-1, 2009 and 11357-3, 2011, at 20°C / min. The weight of the samples in every DSC crucible was kept at 6.0 ± 0.5 mg.In order to obtain the melting point, the weighted sample was sealed into aluminium pans and heated to 200°C at 20°C / minute. The sample was kept at 200°C for 2 minutes to allow a complete melting of all the crystallites, then cooled to 5°C at 20°C / minute. After standing 2 minutes at 5°C, the sample was heated for the second run time to 200°C at 20°C / min. In this second heating run, the peak temperature (Tp,m) was taken as the melting temperature.13C NMR of homopolymer and propylene / ethylene copolymers

[0038] 13C NMR spectra were acquired on a Bruker AV-600 spectrometer equipped with cryoprobe, operating at 160.91 MHz in the Fourier transform mode at 120°C.

[0039] The peak of the Spp carbon (nomenclature according to “Monomer Sequence Distribution in Ethylene-Propylene Rubber Measured by 13C NMR. 3. Use of Reaction Probability Mode ” C. J. Carman, R. A. Harrington and C. E. Wilkes, Macromolecules, 1977, 10, 536) was used as internal reference at 29.9 ppm. The samples were dissolved in 1,1,2,2-tetrachloroethane- d2 at 120°C with a 8 % wt / v concentration. Each spectrum was acquired with a 90° pulse, 15 seconds of delay between pulses and CPD to remove 1H-13C coupling. 512 transients were stored in 32K data points using a spectral window of 9000 Hz.

[0040] The assignments of the spectra, the evaluation of triad distribution and the composition were made according to Kakugo (“Carbon- 13 NMR determination of monomer sequence distribution in ethylene-propylene copolymers prepared with 5-titanium trichloridediethylaluminum chloride” M. Kakugo, Y. Naito, K. Mizunuma and T. Miyatake, Macromolecules, 1982, 15, 1150) using the following equations:PPP = 100 Tpp / S PPE = 100 Tpg / S EPE = 100 T55 / SPEP = 100 Spp / S PEE= 100 Sp5 / S EEE = 100 (0.25 S5+0.5 S55) / SS = Tpp + Tpg + T55 + Spp + Sps + 0.25 Syg + 0.5 S55The molar percentage of ethylene content was evaluated using the following equation:E% mol = 100 * [PEP+PEE+EEE]The weight percentage of ethylene content was evaluated using the following equation:100 * E% mol * MWEE% wt. =E% mol * MWE + P% mol * MWp where P% mol is the molar percentage of propylene content, while MWE and MWp are the molecular weights of ethylene and propylene, respectively.

[0041] The product of reactivity ratio rm was calculated according to Carman (C.J. Carman,R.A. Harrington and C.E. Wilkes, Macromolecules, 1977; 10, 536) as:The tacticity of Propylene sequences was calculated as mm content from the ratio of the PPP mmTpp (28.90-29.65 ppm) and the whole Tpp (29.80-28.37 ppm).Intrinsic viscosity

[0042] The sample is dissolved by tetrahydronaphthalene at 135 °C and then it is poured into the capillary viscometer. The viscometer tube (Ubbelohde type) is surrounded by a cylindrical glass jacket; this setup allows temperature control with a circulating thermostated liquid. The downward passage of the meniscus is timed by a photoelectric device. The passage of the meniscus in front of the upper lamp starts the counter which has a quartz crystal oscillator. The meniscus stops the counter as it passes the lower lamp and the efflux time is registered: this is converted into a value of intrinsic viscosity through Huggins' equation, provided that the flow time of the pure solvent is known at the same experimental conditions (same viscometer and same temperature). One single polymer solution is used to determine IV],Melt strengthThe melt strength is measured according to ISO 16790-2005, by Haul-off Melt Strength Meter produced by Geottfert WerkstoffPruefmaschinen, Germany. This system measures the extensional properties of polymer melts by drawing a vertical melt strand at a constant pull-off speed or with a linear or exponentially accelerating velocity. The HAUL-OFF system measures the force needed to elongate the strand, and calculates elongation stress, draw ratio and apparent elongation rate and viscosity. Polymer is melt and plasticized through a capillary rheometer, then is extruded from a hole die with a 1 mm of diameter, 30 mm of length and 180° inlet angle. The test is performed at 250°C. The distance from the capillary outlet to the center of the transducer pulley is 150 mm. Themonofilament is stretched at each temperature test applying an acceleration equal to 6 mm / s2and, passing through an angular transducer, its tension is measured. The draw ratio (dimensionless value) and force (cN) values are recorded as the final result in addition to the entire curve. The value of the melt strength is the maximum force value of the curve.Charpy impact test

[0043] Charpy impact test is measured according to ISO 179-leA, e ISO 1873-2, on compression sampleTensile Modulus

[0044] Tensile Modulus is measured according to ISO 527-2, and ISO 1873-2 on compression sampleExamples 1 - Preparation of homopolymerProcedure for the preparation of the solid catalyst component

[0045] The solid catalyst used in the following examples was prepared according to the Example 10 of the International Patent Application WO 00 / 63261. Triethylaluminium (TEAL) was used as co-catalyst and dicyclopentyldimethoxysilane as external donor, with the weight ratios indicated in Table 1.Polymerization

[0046] The polymerization run is carried out in continuous mode in a series of two reactors equipped with devices to transfer the product from one reactor to the one immediately next to it. The two reactors are liquid phase loop reactors. Propylene is the main solvent, hydrogen is used as molecular weight regulator. The gas phase is continuously analyzed via gas-chromatography.At the end of the run the powder is discharged and dried under a nitrogen flow. The main polymerization conditions and the properties of the polymer are reported in Tables 1 and 2.Table 1 - Polymerization conditions

[0047] The features of the polymers of example 1 and comparative example 2 are reported on table 2Table 2Comparative example 2 is HP556E a propylene homopolymer sold by LyondellBasell.

Claims

CLAIMSWhat is claimed is: A propylene homopolymer optionally containing up to 1.0 wt% of ethylene derived units characterized in that:- two melting points are present in the DSC thermogram measured according to ISO 11357- 3, with heating and cooling rate of 20°C / min;-the higher melting point, measured according to ISO 11357-3, with heating and cooling rate of 20°C / min, ranges from 155°C to 170°C;- the fraction soluble in xylene at 25°C, measured according to ISO 16 152 - 2005, is comprised between 6.0 wt% and 2.0wt%;-the isotactic pentads mmmm % measured with C13NMR as reported in examples section of the description, ranges from 96.5 mol% to 90.0 mol%;- the intrinsic viscosity (IV) measured in tetrahydronaphthalene at 135 °C ranges from 5.5 to 12.0 dl / g;- the melt strength measured according to ISO 16790-2005, at 250°C and applying an acceleration equal to 6 mm / s2higher than 0.070 N. The propylene homopolymer according to claim 1 wherein two melting points are present in the DSC thermogram measured according to ISO 11357-3, with heating and cooling rate of 20°C / min; and the lower melting point ranges from 135°C to 150°C. The propylene homopolymer according to claims 1 or 2 wherein the higher melting point, measured according to ISO 11357-3, with heating and cooling rate of 20°C / min, ranges from 157°C to 168°C. The propylene homopolymer according to anyone of claims 1-3 wherein the fraction soluble in xylene at 25°C measured according to ISO 16 152 - 2005, is comprised between 5.0 wt% and 2.5 wt%. The propylene homopolymer according to anyone of claims 1-4 wherein the fraction soluble in xylene at 25°C measured according to ISO 16 152 -2005, is comprised between 4.0 wt% and 2.8 wt%.

6. The propylene homopolymer according to anyone of claims 1-5 wherein the isotactic pentads mmmm % measured with13C-NMR ranges from 96.0 mol% to 93.0 mol%.

7. The propylene homopolymer according to anyone of claims 1-6 wherein the isotactic pentads mmmm % measured with13C-NMR ranges from 95.5 mol% to 93.5 mol%.

8. The propylene homopolymer according to anyone of claims 1-7 wherein the intrinsic viscosity (IV) measured in tetrahydronaphthalene at 135 °C ranges from 7.0 dl / g to 11.0 dl / g.

9. The propylene homopolymer according to anyone of claims 1-8 wherein the intrinsic viscosity (IV) measured in tetrahydronaphthalene at 135 °C ranges from 8.0 dl / g to 10.0 dl / g.

10. The propylene homopolymer according to anyone of claims 1 -9 wherein the melt strength measured according to ISO 16790-2005 at 250°C and applying an acceleration equal to 6 mm / s2, is higher than 0.080 N.

11. The propylene homopolymer according to anyone of claims 1-10 wherein the melt strength measured according to ISO 16790-2005 at 250°C and applying an acceleration equal to 6 mm / s2, is higher than 0.090 N.

12. The propylene homopolymer according to anyone of claims 1-11 wherein the homopolymer shows a poly dispersity index, PI measured according to ISO 6721-10, comprised between 4.5 and 7.5.

13. The propylene homopolymer according to anyone of claims 1-12 being not nucleated.14 Fibers, film, molded articles or foamed articles comprising the propylene homopolymer of claims 1-13.

15. Foamed article comprising the propylene homopolymer of claims 1-13.

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