Propylene polymer with high melt strength and preparation method thereof

Abstract

The invention belongs to the technical field of polypropylene products, and particularly relates to a propylene polymer with high melt strength and a preparation method thereof, the method comprises the following steps: (i) in the presence of a polymerization catalyst and hydrogen, propylene or propylene and one or more comonomers are subjected to a first-stage (co) polymerization reaction for 0.1-10 hours to prepare a material flow containing a polymer-I component; (ii) after the first-stage reaction is finished, introducing a hydrogenation catalyst and one or more optional comonomers into the system, and continuing the (co) polymerization reaction for 0.01-3 hours; stopping the reaction to obtain the propylene polymer containing the ultra-high molecular weight polypropylene component; wherein the molar ratio of the hydrogenation catalyst to the total hydrogen in the system is 1 / 10000 to 1 / 100. The polypropylene resin with high melt strength is prepared by the method, and the tensile strength, the impact strength and the processability of the polypropylene resin are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of propylene polymerization, and in particular relates to a propylene polymer with high melt strength and a preparation method thereof. Background Art

[0002] Polypropylene has a linear, semi-crystalline molecular chain structure, and its molecular weight is relatively small (100,000 to 300,000 or 400,000). Its softening point is very close to its melting point. After exceeding the melting point, the melt strength drops rapidly, resulting in uneven container wall thickness during thermoforming, edge curling and shrinkage during extrusion coating and calendering, and cell collapse during extrusion foaming. In order to improve this shortcoming of the use of polypropylene materials, the method of introducing high molecular weight components or long chain branches is usually adopted. At present, the methods for improving the melt strength of polypropylene mainly include irradiation, chemical cross-linking modification, reactive extrusion and direct polymerization.

[0003] Among them, the method of preparing high melt strength polypropylene by direct polymerization includes preparing wide molecular weight distribution polypropylene with high molecular weight components through multiple reactors in series, or obtaining long-chain branched polypropylene by in-situ polymerization with a metallocene catalyst, thereby improving the melt strength of the final polypropylene.

[0004] The advantage of using the direct polymerization method to prepare high melt strength polypropylene is that high melt strength polypropylene resin is produced directly from the reactor, which has the advantages of uniform product quality, relatively economical production process, and suitability for industrial production.

[0005] For example, patent documents US 6875826B1 and US 7365136B2 both disclose a method for preparing a propylene homopolymer or copolymer that can be used for foaming and thermoforming. In a series of loop-gas phase polymerization reactors, the same Ziegler-Natta or metallocene catalyst and the same external electron donor (dicyclopentyldimethoxysilane or cyclohexylmethyldimethoxysilane) are selected to prepare a wide distribution polypropylene by changing the amount of hydrogen in different reactors. Usually, no hydrogen is added in the first reactor to produce a high molecular weight component with MFR<0.1g / 10min, and the weight proportion is 5-50wt%; an appropriate amount of hydrogen is added in the second reactor to produce medium and low molecular weight components with MFR>0.5g / 10min, and the weight proportion is 50-95wt%; the obtained polypropylene has the characteristics of high melt strength. Although the patent believes that it is possible to try to set the load ratio of the two reactors to 5:95 to 95:5, due to the difficulty of such a design in actual operation, the proportion of high molecular weight components in the embodiment is controlled to be not less than 20wt%.

[0006] Patent document CA1241196A discloses that in the first stage of polymerization, propylene is polymerized in the absence of hydrogen to prepare a high molecular weight polypropylene with an intrinsic viscosity [η] of 8 to 13 dl / g, and the high molecular weight polypropylene accounts for 15 to 50 wt% of the total amount of the final polypropylene resin composition; then, in the second stage, two or more polymerization reactors are used to polymerize propylene to prepare a low molecular weight polypropylene with an intrinsic viscosity [η] of less than 8 dl / g, and the melt flow rate (MFR) of the final polypropylene resin composition is 0.01 to 5 g / 10 min, and the load ratio of the two reactors is 85:15 to 50:50. The obtained polypropylene composition has high melt strength and can be used for blow molding, vacuum molding, calendaring molding, foaming or extrusion molding, etc.

[0007] Patent documents CN102134291A, CN102884093A, CN102816269A and CN105623077A all disclose a method of using two reactors in series, using a traditional Ziegler-Natta catalyst, asymmetric addition of external electron donors and asymmetric hydrogen regulation technology, and directly polymerizing in the reactor to obtain a wide distribution and high melt strength propylene homopolymer or propylene-ethylene copolymer; first, a dicyclopentyldimethoxysilane (D-donor) type hydrogen-insensitive, high isotactic external electron donor is added to the first reactor to prepare a high molecular weight propylene homopolymer or copolymer under hydrogen-free or low hydrogen conditions; then, a tetraethoxysilane (TEOS) type hydrogen-sensitive external electron donor is added to the second reactor to prepare a low molecular weight propylene homopolymer or copolymer under high hydrogen concentration, and finally a propylene homopolymer, random copolymer or impact copolymer product with a melt index of 2.0 to 3.0 g / 10 min and a melt strength of 0.8 to 1.0 N is obtained. In this method, the load ratio of the two reactors is 30:70 to 70:30.

[0008] However, both asymmetric hydrogenation and the method of adding an external electron donor have great limitations. When an external electron donor with a lower hydrogen adjustment sensitivity is used in the catalyst system, although the molecular weight of the polymer can be higher when producing a higher molecular weight component, when producing a lower molecular weight component, due to its insensitivity to hydrogen adjustment, an extremely high hydrogen content is required to meet the actual requirements. When an external electron donor with a higher hydrogen adjustment sensitivity is used in the catalyst system, although the amount of hydrogen used is less when producing a lower molecular weight component, when producing a higher molecular weight component, its molecular weight cannot be large enough, thereby affecting the melt strength of the final product. As a result, it has to rely on a complex process, that is, matching external electron donors with different hydrogen adjustment sensitivities and hydrogen concentrations in different reactors to achieve the purpose of preparing high melt strength polypropylene.

[0009] The above-mentioned methods for producing high melt strength polypropylene by direct polymerization in various reactors all have various problems. If the external electron donor is not changed but only hydrogen is adjusted asymmetrically, the amount of hydrogen used is too large, the adjustment range is limited, the reactor is operated at the edge, the operation risk is high, the molecular weight distribution of the obtained polypropylene is not wide enough, and the processing performance is poor; if the external electron donor and hydrogen are adjusted asymmetrically at the same time, the amount of external electron donor is large, the operation of the two reactors is complicated, the load adjustment is difficult, the proportion of high molecular weight components is higher than 30wt%, the distribution width is not enough, and the product processing performance is poor.

[0010] In the improved method of the prior art, the content of the high molecular weight component generated is relatively high, generally above 15 wt %. However, if the content of the high molecular weight polymer component is too high, the processability of the obtained polypropylene material will be affected.

[0011] In view of this, continuing to explore the process and method of preparing high melt strength polypropylene by direct polymerization has become a topic worthy of research. Summary of the invention

[0012] In view of some problems existing in the prior art for preparing polypropylene, the object of the present invention is to provide a propylene polymer with high melt strength and a preparation method thereof; a propylene polymer containing an ultra-high molecular weight polypropylene (UHMWPP) component is directly prepared in a single reactor by using a hydrogenation catalyst, and the propylene polymer has high melt strength and improved tensile strength, impact strength and processing properties.

[0013] In order to achieve the above object, the present invention provides the following technical solutions:

[0014] In a first aspect, there is provided a method for preparing a propylene polymer having a high melt strength, using two or more stages of polymerization reactions arranged in sequence in a single reactor; the method comprising the steps of:

[0015] (i) in the presence of a polymerization catalyst and hydrogen, propylene or propylene and one or more comonomers are subjected to a first stage (co)polymerization reaction in a reactor for 0.1 to 10 hours (e.g., 0.5 h, 1 h, 2 h, 4 h, 5 h, 8 h, 9 h) to prepare a feed stream containing a polymer-I component;

[0016] (ii) after the first stage reaction, a hydrogenation catalyst and one or more optional comonomers are introduced into the reaction system, and the (co)polymerization reaction is continued for 0.01-3 hours (e.g., 0.02 hours, 0.05 hours, 0.1 hours, 0.2 hours, 0.5 hours, 1.0 hours, 1.5 hours, 2.0 hours, 2.5 hours); that is, during the second stage polymerization reaction, an ultra-high molecular weight polypropylene (UHMWPP) component is generated in the reaction system;

[0017] Then, the reaction is stopped to obtain the propylene polymer containing an ultra-high molecular weight polypropylene (UHMWPP) component;

[0018] The molar ratio of the hydrogenation catalyst to the total amount of hydrogen in the system is 1 / 10000 to 1 / 100, for example, the molar ratio is 1 / 10000, 1 / 8000, 1 / 6000, 1 / 5000, 1 / 4000, 1 / 2000, 1 / 1000, 1 / 500, 1 / 200, 1 / 150, preferably 1 / 10000 to 1 / 1000.

[0019] According to the preparation method provided by the present invention, in some embodiments, the molecular weight MW of the ultra-high molecular weight polypropylene (UHMWPP) component is ≥10,000,000, for example, 1,000,000,000≥molecular weight MW≥10,000,000.

[0020] In some embodiments, in the propylene polymer, the content of the ultra-high molecular weight polypropylene (UHMWPP) component is 0.025wt%-10wt% (e.g., 0.035wt%, 0.04wt%, 0.05wt%, 0.08wt%, 0.1wt%, 0.2wt%, 0.4wt%, 0.5wt%, 1.0wt%, 1.5wt%, 5wt%, 8wt%), preferably 0.03wt%-2wt%.

[0021] According to the preparation method provided by the present invention, in the polymerization reaction, propylene monomer can be polymerized, or propylene monomer and one or more comonomers can be copolymerized. In some embodiments, the comonomer can be ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-nonene, 1-decene, or a mixture of any two or more of these comonomers.

[0022] In the present invention, the polymerization catalyst used in propylene (co)polymerization includes but is not limited to Ziegler-Natta type catalysts, and such catalysts may generally include:

[0023] (a) an active solid catalyst component, preferably a titanium-containing solid catalyst active component; (b) an organoaluminum compound as a co-catalyst component; and optionally, (c) an external electron donor component.

[0024] The ratio of the active solid catalyst component to the organoaluminum compound can be 1:5 to 1:400 (e.g., 1:10, 1:50, 1:120, 1:200, 1:300), preferably 1:25 to 1:100, calculated by Ti / Al molar ratio.

[0025] The optional active solid catalyst component (active main catalyst component) includes commercially available SUG catalyst, SAL catalyst, or other catalysts containing both titanium chloride and magnesium chloride, etc.

[0026] The organoaluminum compound as the co-catalyst component is preferably an alkylaluminum compound, more preferably a trialkylaluminum, such as triethylaluminum, triisobutylaluminum, tri-n-butylaluminum, methylaluminoxane (MAO), modified methylaluminoxane (MMAO), and the like.

[0027] The compound used as the external electron donor component can be various electron donating compounds, including but not limited to alkoxy-substituted silane compounds; for example, its general formula is SiR n (OR') 4-n , where:

[0028] 0≤n≤2,

[0029] R and R' are the same or different, and are independently selected from an alkyl group, a cycloalkyl group, an aryl group, a haloalkyl group, a nitrogen-containing group, etc. R can also be a halogen or a hydrogen atom; specifically, they may include but are not limited to tetramethoxysilane, tetraethoxysilane (TEOS), dimethyldimethoxysilane, dimethyldiethoxysilane, methyl tert-butyldimethoxysilane, methylisopropyldimethoxysilane, diphenoxydimethoxysilane, vinyltrimethoxysilane, methylcyclohexyldimethoxysilane, ethylcyclohexyldimethoxysilane, di-n-propyldimethoxysilane, diisopropyldimethoxysilane, di-n-butyldimethoxysilane, diisobutyldimethoxysilane, alkane, di-tert-butyldimethoxysilane, dicyclopentyldimethoxysilane (D-donor), cyclopentyltrimethoxysilane, isopropyltrimethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, ethyltriethoxysilane, diethylaminotriethoxysilane, cyclohexylpyrrolidinedimethoxysilane, bis(pyrrolidine)-dimethoxysilane, bis(perhydroisoquinoline)dimethoxysilane, 2-ethylpiperidinyl-2-tert-butyldimethoxysilane, (1,1,1-trifluoro-2-propyl)-2-ethylpiperidinyldimethoxysilane and (1,1,1-trifluoro-2-propyl)-methyldimethoxysilane, etc. Preferred are dicyclopentyldimethoxysilane (D-donor), methylcyclohexyldimethoxysilane, diisopropyldimethoxysilane, diisobutyldimethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, tetraethoxysilane (TEOS), and diethylaminotriethoxysilane.

[0030] The amount of the external electron donor component in the polymerization catalyst can be selected according to conventional methods in the art and will not be described in detail here.

[0031] In some embodiments, the hydrogenation catalyst is a mixture of a metal organic compound and an alkyl aluminum compound.

[0032] In some embodiments, the metal organic compound has a structural formula of R(R')-MX(X'), wherein:

[0033] R, R' are each independently an unsubstituted or substituted cyclopentadienyl, indenyl, or fluorenyl group, wherein the substituent is preferably selected from methyl, ethyl, propyl, butyl, or cycloalkyl group;

[0034] M is a transition metal element, preferably one or more selected from Fe, Ti, Zr, Cr and Mn;

[0035] X, X' are each independently a halogen atom, an alkyl group or an alkoxy group;

[0036] In the mixture, the molar ratio of aluminum in the alkyl aluminum compound to the metal organic compound is in the range of 5.5-10.0:1, for example, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9.5:1, preferably 5.5-8.0:1.

[0037] In some embodiments, the metal organic compound is selected from one or more of bis(cyclopentadienyl)titanium dichloride, bis(cyclopentadienyl)titanium dibromide, bis(cyclopentadienyl)methoxytitanium chloride, bis(cyclopentadienyl)ethoxytitanium chloride, bis(cyclopentadienyl)phenoxytitanium chloride, bis(cyclopentadienyl)dimethyltitanium, bis(cyclopentadienyl)diethyltitanium, diindenyltitanium dichloride, diindenyltitanium dibromide, diindenyldimethyltitanium, diindenyldiethyltitanium, bis(cyclopentadienyl)zirconium dichloride, bis(cyclopentadienyl)zirconium dibromide, bis(cyclopentadienyl)dimethylzirconium and bis(cyclopentadienyl)diethylzirconium, preferably selected from one or two of bis(cyclopentadienyl)titanium dichloride and bis(cyclopentadienyl)diethyltitanium, more preferably Cp2TiCl2.

[0038] In some embodiments, the alkylaluminum compound is selected from one or more of trimethylaluminum, triethylaluminum, tributylaluminum, triisobutylaluminum, trihexylaluminum, trioctylaluminum, tridecylaluminum, dimethylaluminum monochloride, diethylaluminum monochloride, dibutylaluminum monochloride, diisobutylaluminum monochloride, methylaluminoxane (MAO) and modified methylaluminoxane (MMAO), preferably selected from triethylaluminum and / or methylaluminoxane.

[0039] In some embodiments, the hydrogenation catalyst is a mixture of Cp2TiCl2 and an alkyl aluminum compound; wherein the molar ratio of aluminum in the alkyl aluminum compound to Cp2TiCl2 is in the range of 5.5-10.0:1, for example, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9.5:1, preferably 5.5-8.0:1.

[0040] According to the preparation method provided by the present invention, in some embodiments, in step (i), the polymerization reaction time of the first stage reaction is 0.2-4 hours (for example, 0.5 hours, 1 hour, 1.5 hours, 2.5 hours, 3 hours, 3.5 hours), preferably 0.3-2 hours.

[0041] In some embodiments, in step (i), the polymerization temperature of the first stage reaction is 40-250°C (eg, 45°C, 60°C, 80°C, 100°C, 150°C, 180°C, 220°C), preferably 50-200°C.

[0042] In some embodiments, the polymerization reaction time of step (ii) is 0.2-2 hours (eg, 0.25 hours, 0.4 hours, 0.5 hours, 1.0 hours, 1.5 hours, 1.8 hours), preferably 0.3-2 hours.

[0043] In some embodiments, the polymerization reaction temperature of step (ii) is 0-250°C (eg, 10°C, 30°C, 50°C, 80°C, 100°C, 150°C, 180°C, 220°C), preferably 20-200°C.

[0044] In a second aspect, a propylene polymer prepared by the preparation method as described above is provided, wherein the melt strength of the propylene polymer is greater than or equal to 2.0 cN, such as 4.0 cN, 5.0 cN, 6.0 cN, 8.0 cN, 15.0 cN.

[0045] According to the propylene polymer provided by the present invention, in some embodiments, the melt flow rate MFR of the propylene polymer is 0.1g / 10min~100g / 10min (for example, 0.4g / 10min, 0.5g / 10min, 0.8g / 10min, 1.0g / 10min, 2g / 10min, 4g / 10min, 5g / 10min, 10g / 10min, 60g / 10min, 80g / 10min), preferably 0.2g / 10min~50g / 10min, more preferably 0.3g / 10min~40g / 10min.

[0046] In some embodiments, the ratio of the number average molecular weight Mn of the ultrahigh molecular weight polypropylene (UHMWPP) component to the peak molecular weight Mp of the propylene polymer is Mn / Mp≥10, for example, 12, 15, 20, 40, 50, 60, 80, 100, preferably ≥30.

[0047] The present invention can, for example, use a Ziegler-Natta catalyst to divide the polymerization reaction into two stages in a single reactor. In the first stage, propylene polymerization is carried out under normal hydrogen concentration to generate a propylene polymer-I component with a lower molecular weight; then a small amount of hydrogenation catalyst is added to the single reactor to remove the residual hydrogen in the reactor, and in the second stage, the polymerization reaction continues in the single reactor under nearly hydrogen-free conditions, so that a certain amount of ultra-high molecular weight polypropylene component (UHMWPP) can be generated in the system, and finally a propylene polymer product containing an ultra-high molecular weight polypropylene component (UHMWPP) is obtained. The method of the present invention is applicable to propylene gas phase polymerization, slurry polymerization or solution polymerization processes.

[0048] The preparation method of the present invention does not need to use a system composed of multiple reactors and complex reaction condition control, does not need to use complex matching of different external electron donors, does not need to use a large amount of hydrogen, and does not need to use a large amount of hydrogenation catalyst. It can cleverly overcome the technical barriers of the prior art in a single reactor. After the polymerization reaction in a single reactor is completed, the hydrogenation catalyst is directly used in the reactor to continue polymerization, so that a polypropylene resin with high melt strength characteristics can be prepared, and its tensile strength, impact strength and processing performance are improved. When the melt strength is increased to a certain extent, the obtained propylene polymer will show strain hardening phenomenon during the extension rheology.

[0049] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0050] The present invention performs polymerization in stages in a single reactor, and adds a suitable amount of hydrogenation catalyst after the first stage, so that the polymerization reaction can continue in the reactor under nearly hydrogen-free conditions in the second stage to generate an ultra-high molecular weight polypropylene (UHMWPP) component; at the same time, by adjusting the residence time of the second stage material in the reactor (i.e., the polymerization reaction time), the generation amount of the ultra-high molecular weight polypropylene component can be flexibly regulated, and its content range can be controlled to be 0.025-10wt%; and by adjusting the amount of hydrogenation catalyst, the molecular weight of the ultra-high molecular weight polypropylene component can be regulated to reach a molecular weight Mw of 10,000,000 or above. Thus, a series of high melt strength polypropylenes containing ultra-high molecular weight polypropylene components and having different compositions can be prepared.

[0051] The present invention can control the content of high molecular weight components in the product within a relatively low range, and has substantially no effect or little effect on the processing fluidity of the product while improving the melt strength; that is, the melt strength of the obtained polypropylene resin is significantly improved, and at the same time, its tensile strength, impact strength and processing performance are significantly improved, and can be extended to application fields such as injection molding, extrusion foaming, coating, thermoforming and the like.

[0052] Since the amount of hydrogenation catalyst and the amount of alkyl aluminum therein are controlled within a suitable range, the effect of alkyl aluminum as a chain transfer agent on the molecular weight of the ultra-high molecular weight component can be reduced, and the catalyst residue in the product can also be reduced. DETAILED DESCRIPTION

[0053] In order to understand the technical features and content of the present invention in detail, the preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described in the embodiments, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. For those who do not specify specific conditions in the embodiments, they are carried out according to normal conditions or the conditions recommended by the manufacturer.

[0054] <Source of raw materials>

[0055] In the following examples and comparative examples, the catalyst A used was prepared according to Example 5 in patent application CN101054424A, and the Ti content in the catalyst A was 3.0 wt%.

[0056] In the following examples and comparative examples, the preparation steps of the titanocene hydrogenation catalyst used are as follows: under a nitrogen atmosphere, titanocene dichloride and triethylaluminum (triethylaluminum is present in the form of a 1.0 mol / L n-hexane solution) are mixed at different molar ratios (for example, the molar ratio of the two is 1:2.5, 1:4, 1:6, 1:8, 1:10, etc.) at room temperature for at least 24 hours to prepare multiple groups of mixed solutions, that is, to obtain titanocene hydrogenation catalysts; then, 1.0 ml of each mixed solution is taken, 33 ml of n-hexane is added to dilute it, and then used.

[0057] In each embodiment and comparative example, the relevant data of the obtained polymer product are obtained according to the following test methods:

[0058] (1) Melt flow rate (MFR): The sample to be tested was tested according to ASTM D1238;

[0059] (2) Xylene soluble content XS, wt%: The samples were tested using a fully automatic xylene soluble content tester (CRYSTEX QC) from Polymer Char Company;

[0060] (3) Molecular weight and its distribution: The samples were tested using a high temperature gel permeation chromatograph (GPC-IR6) from Polymer Char.

[0061] (4) Melt strength: The samples were tested using a RH7-2 capillary rheometer + balance from Malvern Instruments;

[0062] (5) Mechanical properties

[0063] Tensile strength: Test the sample in accordance with GB / T 1040.2-2006;

[0064] Bending strength: Test the sample in accordance with GB / T 9341-2008;

[0065] Impact test: Test the sample in accordance with GB / T 1843-2008;

[0066] (6) Extensional rheology: The samples were tested using a TA HR-2 rheometer at 180 °C and an extension rate of 0.05 s. -1 , 0.1s -1 , 0.5s -1 , 1.0s -1 .

[0067] Example 1

[0068] The propylene polymerization reaction was carried out in a 5L stainless steel polymerization kettle, and the specific steps were as follows:

[0069] (i) First, the reactor was purged with purified nitrogen (water <1 ppm, oxygen <1 ppm); then, 2.2 L of liquid propylene and 0.125 mol of hydrogen were added in sequence at room temperature, and then the system was heated to 70° C.;

[0070] Before the temperature of the reactor reaches 70° C., 2.0 ml of 0.5 M triethylaluminum heptane solution, 0.4 ml of 0.5 M D-donor hexane solution and 8.1 mg of catalyst A are mixed for 5 minutes to obtain a mixture. When the temperature of the reactor reaches 70° C., the mixture is injected into the reactor through the catalyst feed pipe and the reaction timer is started to carry out the first stage polymerization reaction;

[0071] (ii) After the polymerization reaction lasted for 60 minutes, 2.55 ml (concentration of 4.9×10 -6 mol / ml) prepared titanocene hydrogenation catalyst (wherein, dichlorotitacenene and triethylaluminum are mixed in a molar ratio of 1 / 6) in hexane solution, without adding hydrogen, continue polymerization reaction at 70°C for 5 minutes, then vent the material, cool down, and stop the reaction;

[0072] After the polypropylene product obtained in the reactor was taken out, it was vacuum dried at 30° C. for 2 hours, and then the performance of the dried polypropylene product was tested. The test results are shown in Table 1.

[0073] Example 2

[0074] The method and conditions for the propylene polymerization reaction are the same as those of Example 1, except that the reaction time after adding the hexane solution of the titanocene hydrogenation catalyst in step (ii) is changed to 30 minutes.

[0075] The obtained dried polypropylene product was subjected to performance tests. The test results are shown in Table 1.

[0076] Example 3

[0077] The method and conditions for the propylene polymerization reaction are the same as those of Example 1, except that the reaction time after adding the hexane solution of the titanocene hydrogenation catalyst in step (ii) is changed to 60 minutes.

[0078] The obtained dried polypropylene product was subjected to performance tests. The test results are shown in Table 1.

[0079] Example 4

[0080] The method and conditions for the propylene polymerization reaction are the same as those of Example 1, except that the reaction time after adding the hexane solution of the titanocene hydrogenation catalyst in step (ii) is changed to 90 minutes.

[0081] The obtained dried polypropylene product was subjected to performance tests. The test results are shown in Table 1.

[0082] Comparative Example 1

[0083] The propylene polymerization reaction was carried out in a 5L stainless steel polymerization kettle, and the specific steps were as follows:

[0084] (i) First, the reactor was purged with purified nitrogen (water <1 ppm, oxygen <1 ppm); then, 2.2 L of liquid propylene and 0.125 mol of hydrogen were added in sequence at room temperature, and then the system was heated to 70° C.;

[0085] Before the temperature of the reactor reaches 70° C., 2.0 ml of 0.5 M alkylaluminum heptane solution, 0.4 ml of 0.5 M D-donor hexane solution and 8.1 mg of catalyst A are mixed for 5 minutes to obtain a mixture. When the temperature of the reactor reaches 70° C., the mixture is injected into the reactor through the catalyst feed pipe and the reaction timer is started to carry out the first stage polymerization reaction;

[0086] (ii) After the polymerization reaction lasted for 65 minutes, the materials were vented, the temperature was lowered, and the reaction was stopped;

[0087] After the polypropylene product obtained in the reactor was taken out, it was vacuum dried at 30° C. for 2 hours, and then the performance of the dried polypropylene product was tested. The test results are shown in Table 1.

[0088] Comparative Example 2

[0089] The method and conditions for the propylene polymerization reaction were the same as those of Comparative Example 1, except that the reaction time was changed to 90 minutes.

[0090] The obtained dried polypropylene product was subjected to performance tests. The test results are shown in Table 1.

[0091] Comparative Example 3

[0092] The method and conditions for the propylene polymerization reaction were the same as those of Comparative Example 1, except that the reaction time was changed to 120 minutes.

[0093] The obtained dried polypropylene product was subjected to performance tests. The test results are shown in Table 1.

[0094] Comparative Example 4

[0095] The method and conditions for the propylene polymerization reaction are the same as those of Comparative Example 1, except that no hydrogen is added to the polymerization reaction in step (i).

[0096] The obtained dried polypropylene product was subjected to performance tests. The test results are shown in Table 1.

[0097] Table 1

[0098]

[0099]

[0100] From the data in Table 1, it can be seen that after the high-efficiency hydrogenation catalyst is used in the second polymerization stage of the present invention, a certain amount of ultra-high molecular weight polypropylene component is obviously generated in the second polymerization process. However, in the second polymerization stage of Comparative Examples 1-3, no high-efficiency hydrogenation catalyst is used, and the content of ultra-high molecular weight polypropylene component is extremely low. In Comparative Example 4, no hydrogen is added in the first polymerization stage. Although a certain amount of UHMWPP is generated in the product, the UHMWPP content in the propylene polymer product is too high, which will cause the product processing performance to be very poor.

[0101] Compared with the comparative example, each embodiment can control the content of the generated UHMWPP component within a suitable range by adding a hydrogenation catalyst in the second polymerization stage and adjusting the polymerization time of the second polymerization stage; the melt strength of the obtained polypropylene product can be increased by more than 10 times, the tensile strength is increased by about 20%, the bending strength is increased by about 10%, and the impact strength can be increased by about 125%; and the polypropylene product obtained in each embodiment contains an appropriate content of UHMWPP component. When the melt strength is high enough, the polypropylene product has a more obvious strain hardening phenomenon and is suitable for the preparation of foamed products.

[0102] Example 5

[0103] The method and conditions for the propylene polymerization reaction are the same as those of Example 1, except that the molar ratio of the alkyl aluminum to the titanocene in the hydrogenation catalyst is 8.

[0104] The obtained dried polypropylene product was subjected to performance tests. The test results are shown in Table 2.

[0105] Embodiment 6:

[0106] The method and conditions for the propylene polymerization reaction were the same as those of Example 1, except that the molar ratio of the alkyl aluminum to the titanocene in the hydrogenation catalyst was 10.

[0107] The obtained dried polypropylene product was subjected to performance tests. The test results are shown in Table 2.

[0108] Embodiment 7:

[0109] The method and conditions for the propylene polymerization reaction were similar to those of Example 1, except that the amount of hydrogenation catalyst was adjusted, and the molar ratio (mol / mol) of hydrogenation catalyst / total hydrogen was 1:5000.

[0110] The obtained dried polypropylene product was subjected to performance tests. The test results are shown in Table 2.

[0111] Comparative Example 5:

[0112] The method and conditions for the propylene polymerization reaction refer to those of Example 1, except that the molar ratio of alkyl aluminum to titanocene in the hydrogenation catalyst is 1.5. This hydrogenation catalyst is no longer suitable for the present polymerization reaction system.

[0113] The obtained dried polypropylene product was subjected to performance tests. The test results are shown in Table 2.

[0114] Comparative Example 6:

[0115] The method and conditions for the propylene polymerization reaction are the same as those of Example 1, except that the molar ratio of the alkyl aluminum to the titanocene in the hydrogenation catalyst is 4.

[0116] The obtained dried polypropylene product was subjected to performance tests. The test results are shown in Table 2.

[0117] Table 2

[0118]

[0119] It can be seen from the data in Table 2 that when the molar ratio of alkyl aluminum to titanocene in the added hydrogenation catalyst is 8 or 10, the alkyl aluminum is slightly excessive, and the melt index of the product increases slightly, but it does not cause adverse effects and can be used to play the role of hydrogenation catalyst; when the molar ratio of alkyl aluminum to titanocene is less than or equal to 4, the alkyl aluminum solution cannot completely dissolve titanocene, and at this time, titanocene cannot effectively play the hydrogenation effect of the hydrogenation catalyst; when the molar ratio of alkyl aluminum to titanocene is 1.5, the hydrogenation catalyst mixed solution has obvious precipitation and is not suitable for achieving the effect of the present invention.

[0120] When the molar ratio of hydrogenation catalyst to total hydrogen (mol / mol) is 1 / 5000, the hydrogenation effect is better than that when the molar ratio of hydrogenation catalyst to total hydrogen (mol / mol) is 1 / 10000, and the obtained polymer product has a lower melt index.

[0121] The propylene polymers obtained in each example contain a relatively low content (e.g., 0.03-1 wt%) of UHMWPP component, and the average molecular weight Mn (logMW ≥ 7) of the generated UHMWPP is much higher than the peak molecular weight Mp of the obtained product; the ratio of Mn (logMW ≥ 7) / Mp is higher than 10, or even higher than 30 (see Tables 1 & 2).

[0122] Therefore, the method of the present invention can introduce an appropriate amount of ultra-high molecular weight components into the propylene polymer product, thereby improving the mechanical properties of the polypropylene product, such as the melt strength, while maintaining good processing performance.

[0123] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the spirit of the present invention.

Claims

1. A method for preparing a propylene polymer with high melt strength, characterized in that: The method comprises the following steps: (i) in the presence of a polymerization catalyst and hydrogen, propylene or propylene and one or more comonomers are subjected to a first stage (co)polymerization reaction in a reactor for 0.1 to 10 hours to prepare a feed stream containing a polymer-I component; (ii) after the first stage reaction, introducing a hydrogenation catalyst and one or more optional comonomers into the reaction system, and continuing the (co)polymerization reaction for 0.01 to 3 hours to obtain an ultra-high molecular weight polypropylene (UHMWPP) component; Then, the reaction is stopped to obtain the propylene polymer containing an ultra-high molecular weight polypropylene (UHMWPP) component; The molar ratio of the hydrogenation catalyst to the total amount of hydrogen in the system is 1 / 10000 to 1 / 100, preferably 1 / 10000 to 1 / 1000.

2. The preparation method according to claim 1, characterized in that: The molecular weight MW of the ultra-high molecular weight polypropylene (UHMWPP) component is ≥ 10,000,000; In the propylene polymer, the content of the ultra high molecular weight polypropylene (UHMWPP) component is 0.025wt%-10wt%, preferably 0.03wt%-2wt%.

3. The preparation method according to claim 1, characterized in that: The hydrogenation catalyst is a mixture of a metal organic compound and an alkyl aluminum compound; The structural formula of the metal organic compound is R(R')-MX(X'), wherein: R, R' are each independently an unsubstituted or substituted cyclopentadienyl, indenyl, or fluorenyl group, wherein the substituent is preferably selected from methyl, ethyl, propyl, butyl, or cycloalkyl group; M is a transition metal element, preferably one or more selected from Fe, Ti, Zr, Cr and Mn; X, X' are each independently a halogen atom, an alkyl group or an alkoxy group; In the mixture, the molar ratio of aluminum in the alkyl aluminum compound to the metal organic compound is in the range of 5.5-10.0:1, preferably 5.5-8.0:

1.

4. The preparation method according to claim 3, characterized in that: The metal organic compound is selected from one or more of bis(cyclopentadienyl)titanium dichloride, bis(cyclopentadienyl)titanium dibromide, bis(cyclopentadienyl)methoxytitanium chloride, bis(cyclopentadienyl)ethoxytitanium chloride, bis(cyclopentadienyl)phenoxytitanium chloride, bis(cyclopentadienyl)dimethyltitanium, bis(cyclopentadienyl)diethyltitanium, diindenyltitanium dichloride, diindenyltitanium dibromide, diindenyldimethyltitanium, diindenyldiethyltitanium, bis(cyclopentadienyl)zirconium dichloride, bis(cyclopentadienyl)zirconium dibromide, bis(cyclopentadienyl)dimethylzirconium and bis(cyclopentadienyl)diethylzirconium, preferably one or two of bis(cyclopentadienyl)titanium dichloride and bis(cyclopentadienyl)diethyltitanium; and / or The alkyl aluminum compound is selected from one or more of trimethyl aluminum, triethyl aluminum, tributyl aluminum, triisobutyl aluminum, trihexylaluminum, trioctylaluminum, tridecylaluminum, dimethylaluminum monochloride, diethylaluminum monochloride, dibutylaluminum monochloride, diisobutylaluminum monochloride, methylaluminoxane (MAO) and modified methylaluminoxane (MMAO), preferably selected from triethylaluminum and / or methylaluminoxane.

5. The preparation method according to claim 1, characterized in that: The hydrogenation catalyst is a mixture of Cp2TiCl2 and an alkyl aluminum compound; wherein the molar ratio of aluminum in the alkyl aluminum compound to Cp2TiCl2 is in the range of 5.5-10.0:1, preferably 5.5-8.0:

1.

6. The preparation method according to claim 1, characterized in that: In step (i), the polymerization reaction time of the first stage reaction is 0.2-4 hours, preferably 0.3-2 hours; and / or The polymerization temperature of the first stage reaction is 40-250°C, preferably 50-200°C.

7. The preparation method according to claim 1, characterized in that: The polymerization reaction time of step (ii) is 0.2-2 hours, preferably 0.3-2 hours; and / or The polymerization reaction temperature of step (ii) is 0-250°C, preferably 20-200°C.

8. The propylene polymer obtained by the preparation method according to any one of claims 1 to 7, characterized in that: The melt strength of the propylene polymer is greater than or equal to 2.0 cN.

9. The propylene polymer according to claim 8, characterized in that The melt flow rate MFR of the propylene polymer is 0.1 g / 10 min to 100 g / 10 min, preferably 0.2 g / 10 min to 50 g / 10 min, and more preferably 0.3 g / 10 min to 40 g / 10 min.

10. The propylene polymer according to claim 8 or 9, characterized in that The ratio of the number average molecular weight Mn of the ultra-high molecular weight polypropylene (UHMWPP) component to the peak molecular weight Mp of the propylene polymer is Mn / Mp≥10, preferably ≥30.

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