CN118027257A

CN118027257A - Olefin polymerization catalyst, application thereof and preparation method of polypropylene

Info

Publication number: CN118027257A
Application number: CN202410060805.9A
Authority: CN
Inventors: 张建新; 郭天瑞; 田宇
Original assignee: Wanhua Chemical Group Co Ltd
Current assignee: Wanhua Chemical Group Co Ltd
Priority date: 2024-01-16
Filing date: 2024-01-16
Publication date: 2024-05-14

Abstract

The invention provides an olefin polymerization catalyst and application thereof, and a preparation method of polypropylene, wherein the olefin polymerization catalyst comprises a nano carrier and a combination of titanium halide, alkyl magnesium mercaptide and an internal electron donor which are loaded on the nano carrier; the alkyl magnesium mercaptide has a structure shown in a formula I. Through the design and the compounding of the catalyst components, the olefin polymerization catalyst has both the catalytic activity and the function of the transparent nucleating agent, is used for preparing polypropylene, can enable polypropylene products to realize finer and uniform crystallization, greatly improves the transparency of the polypropylene, improves the mechanical properties, enables the processing of the transparent polypropylene to be free from adding the transparent nucleating agent, reduces the production cost, and can be widely applied to all polypropylene products such as homopolymerization, random and impact resistance.

Description

Olefin polymerization catalyst, application thereof and preparation method of polypropylene

Technical Field

The invention belongs to the technical field of olefin polymerization, and particularly relates to an olefin polymerization catalyst and application thereof, and a preparation method of polypropylene.

Background

Polypropylene is a polymer with excellent performance, low cost and wide application, and is one of three general plastics. Polypropylene belongs to an incompletely crystallized resin, is generally in a semitransparent state, and in recent years, the conventional semitransparent polypropylene has been difficult to meet the demands of people, and the market demands of transparent polypropylene are gradually increasing. Transparent polypropylene refers to polypropylene with higher transparency, and the domestic market mainly comprises: sheets, plastic cups, microwave cookers, and other small amounts of injection molded articles (e.g., commodity, thin-walled containers, disposable syringes, various blow molded bottles, etc.) and film articles (e.g., composite packaging for high-end food, heat shrink wrap films, etc.), and the like. The application of the transparent polypropylene covers a plurality of fields such as food vessels, medical appliances, infant products, high transparent packaging materials and the like, and has high application value.

At present, the main method for producing transparent polypropylene in the industry is to add transparent nucleating agents, wherein the commercially available transparent nucleating agents comprise aryl phosphates, sorbitol, carboxylic acid metal salts, rosin, branched amides and the like, and polypropylene production enterprises usually select one or more transparent nucleating agents for compounding. For example, CN103030886a discloses a transparent polypropylene, which is prepared from the following raw materials: 100 parts of polypropylene, 0.1-0.4 part of nucleating agent, 0.1-0.2 part of antioxidant, 0.05-0.2 part of acid absorber, 0.05-0.1 part of lubricant and 0.05-0.15 part of dispersing agent; the nucleating agent is compounded by phosphate and sorbitol transparencies, and the weight ratio of the phosphate to the sorbitol transparencies is 0.1-100, so that the transparency of polypropylene is obviously improved. CN105585774a discloses a homo-polymeric transparent polypropylene composition, which is prepared from homo-polymeric polypropylene resin, a transparent nucleating agent, a hindered phenol antioxidant, a phosphite antioxidant and an acid neutralizer, wherein the transparent nucleating agent is sorbitol transparent nucleating agent or organic carboxylate transparent nucleating agent. CN114524974a discloses a nucleating agent composition for transparent polypropylene, which comprises the following components by weight, based on 100 parts by weight of polypropylene: 0.001-0.2 part of main antioxidant, 0.001-0.2 part of auxiliary antioxidant, 0.01-0.3 part of acid scavenger, 0.15-0.5 part of sorbitol acetal nucleating agent, 0.05-0.5 part of transparent modifier and 0.03-0.2 part of antistatic agent; the nucleating agent is 1,3:2, 4-di (3, 4-dimethylbenzylidene) -D-sorbitol, and the transparent modifier can be at least one of lithium stearate, lithium dodecahydroxystearate, lithium laurate and lithium oleate.

Although the transparency of polypropylene is improved to a certain extent by adopting a method of adding the transparent nucleating agent in the industry, the method has the advantages of high production cost, single product performance, limitation on improvement of the transparency of polypropylene and difficulty in meeting the requirements of high-performance transparent polypropylene materials. Therefore, the preparation strategy of transparent polypropylene with low development cost and wide application range is a problem to be solved in the field.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide an olefin polymerization catalyst and application thereof, and a preparation method of polypropylene, wherein the olefin polymerization catalyst has both catalytic activity and the function of a transparent nucleating agent through the design and compounding of catalyst components, is used for preparing polypropylene, can enable polypropylene products to realize finer and uniform crystallization, greatly improve the transparency of the polypropylene, improve the mechanical properties, enable the processing of the transparent polypropylene to be free from adding the transparent nucleating agent, reduce the production cost, and can be widely applied to all polypropylene products such as homopolymerization, random, impact resistance and the like.

To achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the present invention provides an olefin polymerization catalyst comprising a nanocarrier and a combination of titanium halide, magnesium alkyl mercaptide, and an internal electron donor supported on the nanocarrier;

the alkyl magnesium mercaptide has a structure shown in a formula I:

In the formula I, R is selected from any one of C1-C3 linear or branched alkyl, such as C1, C2 and C3 linear or branched alkyl including methyl, ethyl, n-propyl and isopropyl.

In formula I, m represents the number of substituents R, selected from integers from 0 to 4, for example, 0, 1,2,3 or 4; when m is more than or equal to 2, a plurality of R are the same or different groups.

In formula I, n represents the number of methylene groups, is selected from integers of 6-12, and can be, for example, 6, 7, 8, 9, 10, 11 or 12.

Compared with the traditional magnesium chloride, the olefin polymerization catalyst provided by the invention is more beneficial to greatly improving the transparency and the mechanical strength by adopting the nano carrier; meanwhile, alkyl magnesium mercaptide with a molecular structure shown in a formula I is introduced, and through design and compounding of components, the olefin polymerization catalyst has excellent catalytic activity, and meanwhile, the alkyl magnesium mercaptide and the nano carrier can be fully fused with polypropylene and uniformly dispersed in the preparation process of the polypropylene, so that the effect of a transparent nucleating agent is exerted, the spherulitic size of the polypropylene is thinned, the crystallization is more perfect, the crystallization defect is reduced, the more tiny and uniform crystallization is realized, the haze of a prepared polypropylene product is reduced, the transparency is greatly improved, and the polypropylene product has more excellent shock resistance. The olefin polymerization catalyst is used for preparing polypropylene, a transparent nucleating agent is not required to be introduced in the processing procedures of mixing granulation and the like, the production cost required by the transparent nucleating agent is obviously reduced, and the catalyst can be widely applied to all polypropylene products such as homopolymerization, random and impact resistance.

The following is a preferred technical scheme of the present invention, but not a limitation of the technical scheme provided by the present invention, and the following preferred technical scheme can better achieve and achieve the objects and advantages of the present invention.

Preferably, R is methyl.

Preferably, m is selected from integers from 1 to 3, more preferably 2.

Preferably, the alkyl magnesium mercaptide is selected from any one or a combination of at least two of the following compounds:

Preferably, the alkyl magnesium mercaptide is prepared by a method comprising the following steps:

(S1) carrying out condensation reaction on alkyl dithiol with a structure shown in a formula II and benzaldehyde compounds with a structure shown in a formula III to obtain an intermediate with a structure shown in a formula IV, wherein the reaction formula is as follows:

wherein R, m and n have the same defined ranges as in formula I;

(S2) reacting an alkaline aqueous solution comprising the intermediate with magnesium to obtain the magnesium alkyl mercaptide of the structure shown in formula I.

Preferably, the condensation reaction of step (S1) is carried out in the presence of a solvent.

Preferably, the solvent comprises a combination of a hydrophilic organic solvent and a hydrophobic organic solvent.

Preferably, the hydrophilic organic solvent comprises any one or a combination of at least two of acetonitrile, N-dimethylformamide, N-dimethylacetamide, acetone, butanone and tetrahydrofuran.

Preferably, the hydrophobic organic solvent comprises any one or a combination of at least two of benzene, carbon tetrachloride, diethyl ether, alkane solvents (e.g. gasoline).

Preferably, the mass ratio of the hydrophilic organic solvent to the hydrophobic organic solvent is (2-4): 1, for example, 2.2:1, 2.5:1, 2.8:1, 3:1, 3.2:1, 3.5:1, or 3.8:1, etc.

Preferably, the molar ratio of the alkyl dithiol to the benzaldehyde compound is 1 (1.8-2.3), for example, 1:1.85, 1:1.9, 1:1.95, 1:2, 1:2.05, 1:2.1, 1:2.15, 1:2.2 or 1:2.25, etc.

Preferably, the temperature of the condensation reaction in step (S1) is 60 to 120 ℃, for example 65 ℃, 70 ℃, 75 ℃, 80 ℃, 85 ℃, 90 ℃, 95 ℃, 100 ℃, 105 ℃, 110 ℃ or 115 ℃, and specific point values between the above point values, which are not exhaustive list of specific point values included in the range for reasons of brevity and for reasons of simplicity, more preferably 70 to 100 ℃.

Preferably, the time of the condensation reaction in step (S1) is 6-24h, for example, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 20h, 22h or 24h, and the specific point values among the above point values are limited in length and for brevity, the present invention is not exhaustive of the specific point values included in the range.

Preferably, the mass percentage of the intermediate in the alkaline aqueous solution is 1-80%, for example, may be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 62%, 65%, 68%, 70%, 72%, 75% or 78%, and specific point values between the above point values, and the present invention is not exhaustive for the sake of brevity and conciseness.

Preferably, the alkaline substance in the alkaline aqueous solution comprises any one or a combination of at least two of sodium hydroxide, potassium hydroxide, alkaline sodium salt and alkaline potassium salt.

Preferably, the alkaline substance in the alkaline aqueous solution comprises any one or a combination of at least two of Na₃PO₄、Na₂HPO₄、NaH₂PO₄、Na₂CO₃、K₂CO₃、NaHCO₃、NaOH、KOH.

Preferably, the alkaline substance in the alkaline aqueous solution has a mass concentration of 20-60%, for example, 25%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55% or 58%, and specific point values between the above point values, which are limited in space and for the sake of brevity, the present invention is not exhaustive of the specific point values included in the range.

Preferably, the mass ratio of the alkaline aqueous solution to magnesium is 1 (3-5), and for example, can be 1:3.2, 1:3.5, 1:3.8, 1:4, 1:4.2, 1:4.5, 1:4.8, and the like.

Preferably, the temperature of the reaction in step (S2) is 70-95 ℃, for example, 72 ℃, 75 ℃, 78 ℃, 80 ℃, 82 ℃, 85 ℃, 88 ℃, 90 ℃, 92 ℃ or 94 ℃, and specific point values between the above point values, the present invention is not exhaustive of the specific point values included in the range, more preferably 80-90 ℃ for the sake of brevity and conciseness.

Preferably, the reaction time in step (S2) is 1-5h, for example, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h or 4.5h, and the specific point values between the above point values, are limited in space and for the sake of brevity, the present invention is not exhaustive list of specific point values included in the range, and further preferably 2-4h.

Preferably, the nano-carrier comprises any one or a combination of at least two of nano-silica, nano-titania, nano-alumina and nano-calcium oxide, and further preferably nano-silica.

Preferably, the particle size of the nano-carrier is 10-500nm, for example, 20nm、30nm、40nm、50nm、60nm、70nm、80nm、90nm、100nm、120nm、150nm、180nm、200nm、220nm、250nm、280nm、300nm、350nm、400nm or 450nm, and the specific point values between the above point values are limited to a spread and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the range, and more preferably 50-200nm.

Preferably, the titanium halide comprises titanium tetrachloride and/or titanium trichloride, more preferably titanium tetrachloride.

Preferably, the mass ratio of the titanium halide to the nano-carrier is 1 (4-8), and for example, the mass ratio can be 1:4.2, 1:4.5, 1:4.8, 1:5, 1:5.2, 1:5.5, 1:5.8, 1:6, 1:6.2, 1:6.5, 1:6.8, 1:7, 1:7.2, 1:7.5 or 1:7.8, etc.

Preferably, the mass ratio of the alkyl magnesium mercaptide to the nano-carrier is (2-4): 1, for example, 2.1:1, 2.2:1, 2.3:1, 2.5:1, 2.6:1, 2.8:1, 2.9:1, 3:1, 3.2:1, 3.5:1 or 3.8:1, etc.

Preferably, the internal electron donor includes any one or a combination of at least two of aliphatic carboxylic acid esters, aromatic carboxylic acid esters, phosphoric acid esters, glycol esters, aliphatic diethers, aromatic ethers.

Preferably, the internal electron donor comprises any one or a combination of at least two of diisobutyl phthalate, di-n-butyl phthalate and diethyl 2-methyl-2-isopropyl malonate.

Preferably, the mass ratio of the internal electron donor to the nano-carrier is 1 (1-3), for example, 1:1.1, 1:1.2, 1:1.4, 1:1.5, 1:1.6, 1:1.8, 1:2, 1:2.2, 1:2.4, 1:2.5, 1:2.6, 1:2.8 or 1:2.9, etc.

In a second aspect, the present invention provides a process for preparing an olefin polymerization catalyst as described in the first aspect, the process comprising:

and (3) reacting the nano carrier, titanium halide, alkyl magnesium mercaptide and an internal electron donor to obtain the olefin polymerization catalyst.

Preferably, the preparation method comprises the following steps:

Mixing nano carrier, alkyl magnesium mercaptan, 20-80% (e.g. 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% etc.) of titanium halide and solvent, performing first-stage reaction, adding internal electron donor to make second-stage reaction, adding residual titanium halide to make third-stage reaction so as to obtain the invented olefine polymerization catalyst.

Preferably, the solvent comprises an alcoholic solvent.

Preferably, the alcohol solvent comprises any one or a combination of at least two of methanol, ethanol, n-propanol and isopropanol, and further preferably ethanol.

Preferably, the solvent is used in an amount of 3-30mL, for example, 4mL, 5mL, 6mL, 7mL, 8mL, 9mL, 10mL, 12mL, 15mL, 18mL, 20mL, 22mL, 25mL or 28mL, and specific point values between the above point values, based on the mass of the nanocarrier of 1g, are not exhaustive, and the specific point values included in the range are not exhaustive for the sake of brevity.

Preferably, the temperature of the first stage reaction is 2 to 15 ℃, and may be, for example, 3 ℃,4 ℃,5 ℃,6 ℃,7 ℃, 8 ℃,9 ℃,10 ℃,11 ℃, 12 ℃, 13 ℃ or 14 ℃, and specific point values between the above point values, and the present invention is not exhaustive of the specific point values included in the range, more preferably 5 to 10 ℃ for the sake of brevity and conciseness.

Preferably, the time of the first reaction is 0.2 to 2 hours, for example, may be 0.3 hours, 0.4 hours, 0.5 hours, 0.6 hours, 0.7 hours, 0.8 hours, 0.9 hours, 1 hour, 1.2 hours, 1.5 hours or 1.8 hours, and specific point values between the above point values, and the present invention is not exhaustive of the specific point values included in the range, and further preferably 0.5 to 1 hour, for the sake of brevity.

Preferably, the internal electron donor is added at a temperature of 20-50 ℃, for example, 22 ℃, 25 ℃, 28 ℃, 30 ℃, 32 ℃, 35 ℃, 38 ℃, 40 ℃, 42 ℃, 45 ℃ or 48 ℃, and specific point values between the above point values, which are limited in space and for the sake of brevity, the present invention is not exhaustive of the specific point values included in the range.

Preferably, the rate of temperature increase from the temperature of the first stage reaction to the addition temperature of the internal electron donor is 2 to 8 c/h, and may be, for example, 2.5 c/h, 3 c/h, 3.5 c/h, 4 c/h, 4.5 c/h, 5 c/h, 5.5 c/h, 6 c/h, 6.5 c/h, 7 c/h or 7.5 c/h, and specific point values between the above point values, are limited in length and for brevity, and the present invention is not exhaustive of the specific point values included in the range.

Preferably, the temperature of the second stage reaction is 120-180 ℃, and may be, for example, 125 ℃, 130 ℃, 135 ℃, 140 ℃, 145 ℃, 150 ℃, 155 ℃, 160 ℃, 165 ℃, 170 ℃ or 175 ℃ and specific point values between the above point values, which are limited in space and for the sake of brevity, the present invention is not exhaustive of the specific point values included in the range.

Preferably, the temperature is raised to the temperature of the second stage reaction at a rate of from 0.5 to 3 ℃/min, for example at 0.6 ℃/min, 0.7 ℃/min, 0.8 ℃/min, 0.9 ℃/min, 1 ℃/min, 1.2 ℃/min, 1.5 ℃/min, 1.8 ℃/min, 2 ℃/min, 2.2 ℃/min, 2.5 ℃/min or 2.8 ℃/min, and specific point values between the foregoing point values, are limited in space and for brevity, the invention is not exhaustive of the specific point values included in the range.

Preferably, the temperature rise time to the temperature of the second stage reaction is 1 to 2 hours, for example, may be 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours or 1.9 hours, and specific point values among the above point values, which are limited in space and for brevity, the present invention is not exhaustive.

Preferably, the second stage reaction is carried out for a period of time ranging from 0.5 to 4 hours, for example, from 0.6 hours, 0.8 hours, 1 hour, 1.2 hours, 1.5 hours, 1.8 hours, 2 hours, 2.2 hours, 2.5 hours, 2.8 hours, 3 hours, 3.2 hours, 3.5 hours or 3.8 hours, and specific point values between the above point values, are limited in length and for brevity, the present invention is not exhaustive of the specific point values included in the range, and further preferably from 1 to 3 hours.

Preferably, the second stage reaction and the third stage reaction further comprise the steps of settling and removing the supernatant.

Preferably, the sedimentation temperature is 60-80 ℃, and may be 62 ℃, 65 ℃, 68 ℃, 70 ℃, 72 ℃, 75 ℃ or 78 ℃, for example, and specific point values between the above point values, although the invention is not exhaustive of the specific point values included in the range for reasons of space and for reasons of simplicity.

Preferably, the settling time is 0.5-3h, for example, 0.6h, 0.8h, 1h, 1.2h, 1.5h, 1.8h, 2h, 2.2h, 2.5h or 2.8h, and specific point values between the above point values, are limited in space and for brevity, the present invention is not exhaustive of the specific point values included in the range;

Preferably, the temperature of the third reaction stage is 120-180deg.C, which may be, for example, 125deg.C, 130deg.C, 135 deg.C, 140 deg.C, 145 deg.C, 150deg.C, 155 deg.C, 160 deg.C, 165 deg.C, 170 deg.C or 175 deg.C, and specific values between the above values, which are limited in space and for brevity, the present invention is not exhaustive;

Preferably, the time of the third reaction is 0.5 to 4 hours, for example, may be 0.6 hours, 0.8 hours, 1 hour, 1.2 hours, 1.5 hours, 1.8 hours, 2 hours, 2.2 hours, 2.5 hours, 2.8 hours, 3 hours, 3.2 hours, 3.5 hours or 3.8 hours, and specific point values between the above point values, are limited in length and for the sake of brevity, the present invention is not exhaustive to list specific point values included in the range, and further preferably 1 to 3 hours.

Preferably, the third stage reaction further comprises washing and drying steps after completion.

Preferably, the washed detergent comprises an alkane solvent, further preferably hexane.

In a third aspect, the present invention provides a Ziegler-Natta catalyst comprising a combination of an olefin polymerization catalyst as described in the first aspect, an organoaluminum and an external electron donor.

Preferably, the organoaluminum comprises an alkylaluminum and/or alkylaluminum chloride, further preferably any one or a combination of at least two of trimethylaluminum, triethylaluminum, triisobutylaluminum, diethylaluminum chloride, diisobutylaluminum chloride.

Preferably, the molar ratio of Al in the organoaluminum to Ti in the olefin polymerization catalyst is (400-500): 1, and may be, for example, 410:1, 420:1, 430:1, 440:1, 450:1, 460:1, 470:1, 480:1, 490:1, or the like.

Preferably, the external electron donor includes a silane-based external electron donor, and more preferably any one or a combination of at least two of diisopropyl dimethoxy silane, dimethyl dimethoxy silane, dibutyl dimethoxy silane, diphenyl dimethoxy silane.

Preferably, the mass ratio of the external electron donor to the alkyl magnesium mercaptide is (1-4): 1, for example, 1.2:1, 1.5:1, 1.8:1, 2:1, 2.2:1, 2.5:1, 2.8:1, 3:1, 3.2:1, 3.5:1, or 3.8:1, etc.

Preferably, the mass ratio of the external electron donor to the organic aluminum is 1 (3-7), for example, 1:3.2, 1:3.5, 1:3.8, 1:4, 1:4.2, 1:4.5, 1:4.8, 1:5, 1:5.2, 1:5.5, 1:5.8, 1:6, 1:6.2, 1:6.5 or 1:6.8, etc.

In a fourth aspect, the present invention provides the use of an olefin polymerisation catalyst as described in the first aspect, a Ziegler-Natta catalyst as described in the third aspect, in the polymerisation of olefins.

Preferably, the olefin comprises any one or a combination of at least two of ethylene, propylene, 1-butene, 1-hexene, 1-octene, further preferably ethylene and/or propylene.

In a fifth aspect, the present invention provides a method for preparing polypropylene, the method comprising: propylene and optionally ethylene in the presence of a Ziegler-Natta catalyst according to the third aspect to obtain the polypropylene.

Preferably, the polymerization reaction temperature is 0-100 ℃, for example, 10 ℃, 20 ℃, 30 ℃, 40 ℃, 45 ℃,50 ℃, 55 ℃, 60 ℃, 65 ℃,70 ℃, 75 ℃,80 ℃, 85 ℃, 90 ℃ or 95 ℃, and specific point values between the above point values, are limited in space and for the sake of brevity, the present invention is not exhaustive of the specific point values included in the range.

Preferably, the polymerization reaction is carried out at a pressure of 0.1 to 5MPa, for example, 0.2MPa, 0.5MPa, 0.8MPa, 1MPa, 1.5MPa, 2MPa, 2.5MPa, 3MPa, 3.5MPa, 4MPa or 4.5MPa, and specific point values between the above point values, limited in length and for the sake of brevity, the present invention is not exhaustive of the specific point values included in the range, and further preferably 3 to 5MPa.

Preferably, the polypropylene is a random copolymer polypropylene wherein the mass percent of ethylene-based structural units is from 1 to 5%, such as 1.5%, 2%, 2.5%, 3%, 3.5% or 4%, and specific point values between the above point values, are limited in space and for the sake of brevity, the invention is not exhaustive of the specific point values comprised in the range.

Preferably, the polypropylene obtained by the polymerization reaction is processed and granulated to obtain a transparent polypropylene product with high transparency and excellent mechanical properties.

Preferably, the method of processing granulation comprises: and (3) melting and blending polypropylene, optionally an antioxidant and optionally an acid absorber, extruding and granulating to obtain a transparent polypropylene product.

Preferably, the antioxidant is 0.05 to 0.3 parts by mass, based on 100 parts by mass of the polypropylene, and may be, for example, 0.06 parts, 0.08 parts, 0.1 parts, 0.12 parts, 0.15 parts, 0.18 parts, 0.2 parts, 0.22 parts, 0.25 parts or 0.28 parts, and specific point values between the above point values, which are limited in length and for brevity, the present invention is not exhaustive.

Preferably, the antioxidant comprises any one or a combination of at least two of antioxidant 168, antioxidant 1010, antioxidant 164 and antioxidant 1076, and further preferably antioxidant 168 and/or antioxidant 1010.

Preferably, the antioxidant 168 is present in an amount of 0.08 to 0.12 parts by weight, based on 100 parts by weight of the polypropylene, such as 0.085 parts, 0.09 parts, 0.095 parts, 0.1 parts, 0.105 parts, 0.11 or 0.115 parts, and specific point values between the above point values, are limited in scope and for brevity, the present invention is not exhaustive of the specific point values included in the range.

Preferably, the antioxidant 1010 is 0.04-0.06 parts by mass, for example, 0.042 parts, 0.045 parts, 0.048 parts, 0.05 parts, 0.052 parts, 0.055 parts or 0.058 parts, based on 100 parts by mass of the polypropylene, and specific point values between the above point values are limited in length and for brevity, and the present invention is not exhaustive of the specific point values included in the range.

Preferably, the acid absorber comprises a stearate, more preferably calcium stearate.

Preferably, the acid absorber is 0.02 to 0.08 parts by mass, for example, 0.025 parts, 0.03 parts, 0.035 parts, 0.04 parts, 0.045 parts, 0.05 parts, 0.055 parts, 0.06 parts, 0.065 parts, 0.07 parts or 0.075 parts based on 100 parts by mass of the polypropylene, and specific point values between the above point values are not exhaustive, for reasons of brevity and brevity.

Preferably, the melt blended material further comprises a transparent nucleating agent, thereby further enhancing the transparency of the polypropylene product.

Preferably, the transparent nucleating agent is 0.1 to 0.4 parts by mass, for example, 0.12 parts, 0.15 parts, 0.18 parts, 0.2 parts, 0.22 parts, 0.25 parts, 0.28 parts, 0.3 parts, 0.32 parts, 0.35 parts or 0.38 parts, based on 100 parts by mass of the polypropylene, and specific point values between the above point values are limited in length and for brevity, the present invention does not exhaustively list specific point values included in the range.

Preferably, the transparent nucleating agent comprises a sorbitol-based transparent nucleating agent.

Preferably, the sorbitol transparent nucleating agent is a commercially available product, such as NX8000K (meliken).

As a preferable technical scheme of the invention, the haze of the transparent polypropylene product obtained by granulating the polypropylene is less than or equal to 12 percent and can be 5.6-11.9 percent (1 mm).

Preferably, the notched Izod impact strength of the transparent polypropylene product is more than or equal to 6.6kJ/m ², and can be 6.6-7kJ/m ².

Compared with the prior art, the invention has the following beneficial effects:

(1) According to the olefin polymerization catalyst provided by the invention, through the design of the nano carrier and the alkyl magnesium mercaptide and the compounding of the nano carrier and other components, the catalyst has excellent catalytic activity, and can be fully fused with polypropylene in the preparation process of polypropylene, and is uniformly dispersed, so that the effect of a transparent nucleating agent is exerted, the spherulitic size of polypropylene is thinned, the crystallization is more perfect, the crystallization defect is reduced, the haze of a prepared polypropylene product is reduced, the transparency is greatly improved, the rigidity and toughness can be excellent, and the catalyst has better mechanical properties such as impact resistance and the like.

(2) The olefin polymerization catalyst provided by the invention is used for preparing polypropylene by using a Ziegler-Natta catalyst and catalyzing, a transparent polypropylene product with high transparency, low haze and excellent rigidity and toughness can be obtained without adding a nucleating agent, the haze is less than or equal to 12%, the notched impact strength of a cantilever beam is more than or equal to 6.6kJ/m ², and the catalyst can be widely applied to the injection molding fields of household appliances, automobiles, daily necessities and the like.

Detailed Description

The technical scheme of the invention is further described by the following specific embodiments. It will be apparent to those skilled in the art that the examples are merely to aid in understanding the invention and are not to be construed as a specific limitation thereof.

Synthesis example 1

Alkyl magnesium mercaptideBis (3, 4-dimethylbenzaldehyde) 1, 8-dioctyl magnesium mercaptide, and the preparation method is as follows:

(S1) adopting carbon tetrachloride and acetone as reaction media, wherein the mass ratio of the acetone to the carbon tetrachloride is 3:1; 1mol of 1, 8-dioctyl mercaptan and 2mol of 3, 4-dimethyl benzaldehyde are added into 1500mL of reaction medium to carry out aldol condensation reaction, the reaction temperature is 80 ℃, the reaction time is 12h, and the di (3, 4-dimethyl benzaldehyde) formal-1, 8-dioctyl mercaptan is obtained.

Structural characterization: ¹ H NMR (500 MHz, TMS, deuterated dimethyl sulfoxide DMSO-d ₆, ppm): delta 1.3-1.7 (12H, multiple multiplets, methylene H), 2.3-2.4 (12H, singlet, methyl H on benzene ring), 2.5-2.7 (4H, triplet, methylene H), 5.5-5.6 (2H, singlet, methylene H), 7.0-7.2 (6H, multiplet, hydrogen on benzene ring).

(S2) preparing the generated bis (3, 4-dimethylbenzaldehyde) 1, 8-dioctyl mercaptan into an alkaline aqueous solution, wherein the concentration of the bis (3, 4-dimethylbenzaldehyde) 1, 8-dioctyl mercaptan is 3.5%, the concentration of an alkaline substance is sodium hydroxide and 35%, and then adding magnesium powder and the prepared alkaline aqueous solution into a reaction kettle in a mass ratio of 4:1, and uniformly mixing. The mixture is heated to 85 ℃ and reacted for 3 hours to obtain the di (3, 4-dimethylbenzaldehyde) shrink-1, 8-dioctyl magnesium mercaptide.

Example 1

An olefin polymerization catalyst comprising a nano-carrier (nano-silica, particle size 150 nm) and a combination of titanium tetrachloride, magnesium bis (3, 4-dimethylbenzaldehyde) 1, 8-dioctyl mercaptide and an internal electron donor (diisobutyl phthalate) supported on the nano-carrier; wherein the mass ratio of the di (3, 4-dimethylbenzaldehyde) condensed-1, 8-dioctyl magnesium mercaptide to the nano-carrier is 2:1, the mass ratio of the diisobutyl phthalate to the nano-carrier is 1:2, and the mass ratio of the titanium tetrachloride to the nano-carrier is 1:6.

The preparation method of the olefin polymerization catalyst comprises the following steps:

Adding 50% of titanium tetrachloride in the formula amount into a reaction kettle according to the proportion of the components, cooling to 5 ℃, and adding nano silicon dioxide, bis (3, 4-dimethylbenzaldehyde) 1, 8-dioctyl magnesium mercaptide and 200mL of absolute ethyl alcohol at constant temperature; keeping a constant low-temperature environment at 5 ℃ to react with TiCl ₄ for 1.0h, heating to 40 ℃ at a heating rate of 5 ℃/h, adding diisobutyl phthalate as an internal electron donor, slowly heating to 150 ℃ within 1.5h, reacting at constant temperature for 2h, cooling to 70 ℃, settling for 1.5h, removing the upper liquid, adding the residual formula amount of titanium tetrachloride again, gradually heating to 150 ℃ and keeping the temperature for 2h, filtering, cooling to 60 ℃, washing for 4 times with 200mL of hexane to obtain the olefin polymerization catalyst, drying and sieving for later use.

The preparation method of polypropylene adopts the olefin polymerization catalyst provided by the embodiment, and comprises the following specific steps:

Diluting 15mg of the olefin polymerization catalyst with 50 times of hexane, adding triethylaluminum and external electron donor diisopropyl dimethoxy silane, wherein the mass ratio of di (3, 4-dimethylbenzaldehyde) shrink-1, 8-dioctyl magnesium mercaptide to diisopropyl dimethoxy silane is 1:2, the mass ratio of triethylaluminum to diisopropyl dimethoxy silane is 4:1, and the Al/Ti (molar ratio) of triethylaluminum to titanium tetrachloride is 420; the polymerization reaction is carried out under the conditions of liquid-phase propylene and gas-phase ethylene, and the specific parameters are as follows: the hydrogen adding amount is 25NL, the propylene adding amount is 3.0L, the ethylene adding amount is 60g, the temperature of the reaction kettle is 70 ℃, the pressure of the reaction kettle is 3.5MPa, and the reaction time lasts for 1.5h, so that polypropylene is obtained;

Adding 0.12 part of antioxidant 168, 0.06 part of antioxidant 1010 and 0.05 part of acid absorber calcium stearate into 100 parts of polypropylene by mass, mixing and extruding to pelletize by adopting a double-screw extruder (Hak parallel homodromous double-screw extruder EUROLAB), controlling the rotating speed of a screw to 270rpm, and obtaining transparent polypropylene products by 10 sections of barrels, wherein the temperatures of the sections 1-10 are 150 ℃, 190 ℃, 210 ℃, 220 ℃ and 200 ℃ respectively.

Example 2

An olefin polymerization catalyst comprising a nano-carrier (nano-silica, particle size 150 nm) and a combination of titanium tetrachloride, magnesium bis (3, 4-dimethylbenzaldehyde) 1, 8-dioctyl mercaptide and an internal electron donor (diisobutyl phthalate) supported on the nano-carrier; wherein the mass ratio of the di (3, 4-dimethylbenzaldehyde) condensed-1, 8-dioctyl magnesium mercaptide to the nano-carrier is 3:1, the mass ratio of the diisobutyl phthalate to the nano-carrier is 1:2, and the mass ratio of the titanium tetrachloride to the nano-carrier is 1:6. The preparation method of the olefin polymerization catalyst is the same as in example 1.

Diluting 15mg of the olefin polymerization catalyst with 50 times of hexane, adding triethylaluminum and external electron donor diisopropyl dimethoxy silane, wherein the mass ratio of di (3, 4-dimethylbenzaldehyde) shrink-1, 8-dioctyl magnesium mercaptide to diisopropyl dimethoxy silane is 1:2, the mass ratio of triethylaluminum to diisopropyl dimethoxy silane is 4:1, and the Al/Ti (molar ratio) of triethylaluminum to titanium tetrachloride is 420; carrying out polymerization under liquid-phase propylene and gas-phase ethylene, wherein specific parameters are the same as those of example 1, and polypropylene is obtained; the polypropylene was kneaded and extrusion-pelletized in the same manner as in example 1 to obtain a transparent polypropylene product.

Example 3

An olefin polymerization catalyst comprising a nano-carrier (nano-silica, particle size 150 nm) and a combination of titanium tetrachloride, magnesium bis (3, 4-dimethylbenzaldehyde) 1, 8-dioctyl mercaptide and an internal electron donor (diisobutyl phthalate) supported on the nano-carrier; wherein the mass ratio of the di (3, 4-dimethylbenzaldehyde) condensed-1, 8-dioctyl magnesium mercaptide to the nano-carrier is 4:1, the mass ratio of the diisobutyl phthalate to the nano-carrier is 1:2, and the mass ratio of the titanium tetrachloride to the nano-carrier is 1:6. The preparation method of the olefin polymerization catalyst is the same as in example 1.

Example 4

Diluting 15mg of the olefin polymerization catalyst with 50 times of hexane, adding triethylaluminum and external electron donor diisopropyl dimethoxy silane, wherein the mass ratio of di (3, 4-dimethylbenzaldehyde) shrink-1, 8-dioctyl magnesium mercaptide to diisopropyl dimethoxy silane is 1:3, the mass ratio of triethylaluminum to diisopropyl dimethoxy silane is 6:1, and the Al/Ti (molar ratio) of triethylaluminum to titanium tetrachloride is 420; carrying out polymerization under liquid-phase propylene and gas-phase ethylene, wherein specific parameters are the same as those of example 1, and polypropylene is obtained; the polypropylene was kneaded and extrusion-pelletized in the same manner as in example 1 to obtain a transparent polypropylene product.

Example 5

Diluting 15mg of the olefin polymerization catalyst with 50 times of hexane, adding triethylaluminum and external electron donor diisopropyl dimethoxy silane, wherein the mass ratio of di (3, 4-dimethylbenzaldehyde) shrink-1, 8-dioctyl magnesium mercaptide to diisopropyl dimethoxy silane is 1:3, the mass ratio of triethylaluminum to diisopropyl dimethoxy silane is 6:1, and the Al/Ti (molar ratio) of triethylaluminum to titanium tetrachloride is 420; carrying out polymerization under liquid-phase propylene and gas-phase ethylene, wherein specific parameters are the same as those of example 1, and polypropylene is obtained;

In terms of parts by mass, 0.12 part of antioxidant 168, 0.06 part of antioxidant 1010, 0.05 part of acid absorber calcium stearate and 0.20 part of transparent nucleating agent NX800K are added into 100 parts of polypropylene, and a double-screw extruder (Hak parallel homodromous double-screw extruder EUROLAB) is adopted for mixing and extrusion granulation, wherein specific parameters are the same as those of the example 1, so that a transparent polypropylene product is obtained.

Comparative example 1

An olefin polymerization catalyst differs from example 1 only in that magnesium bis (3, 4-dimethylbenzaldehyde) formal-1, 8-dioctyl mercaptan is replaced with an equal mass of nano-carrier (nano-silica), and the ratio of titanium tetrachloride to internal electron donor in the olefin polymerization catalyst is maintained the same as in example 1.

A preparation method of polypropylene adopts the olefin polymerization catalyst provided by the comparative example, and comprises the following specific steps:

Diluting 15mg of the olefin polymerization catalyst with 50 times of hexane, and adding triethylaluminum and external electron donor diisopropyldimethoxy silane, wherein the mass ratio of triethylaluminum to diisopropyldimethoxy silane is 4:1, and the Al/Ti (molar ratio) of triethylaluminum to titanium tetrachloride is 420; carrying out polymerization under liquid-phase propylene and gas-phase ethylene, wherein specific parameters are the same as those of example 1, and polypropylene is obtained; the polypropylene was kneaded and extrusion-pelletized in the same manner as in example 1 to obtain a polypropylene product.

Comparative example 2

An olefin polymerization catalyst differs from example 2 only in that magnesium bis (3, 4-dimethylbenzaldehyde) formal-1, 8-dioctyl mercaptan is replaced with an equal mass of nano-carrier (nano-silica), and the ratio of titanium tetrachloride to internal electron donor in the olefin polymerization catalyst is maintained the same as in example 2.

Diluting 15mg of the olefin polymerization catalyst with 50 times of hexane, and adding triethylaluminum and external electron donor diisopropyldimethoxy silane, wherein the mass ratio of triethylaluminum to diisopropyldimethoxy silane is 4:1, and the Al/Ti (molar ratio) of triethylaluminum to titanium tetrachloride is 420; carrying out polymerization under liquid-phase propylene and gas-phase ethylene, wherein specific parameters are the same as those of example 2, and obtaining polypropylene; the polypropylene was kneaded and extrusion-pelletized in the same manner as in example 2 to obtain a polypropylene product.

Comparative example 3

An olefin polymerization catalyst differing from example 3 only in that magnesium bis (3, 4-dimethylbenzaldehyde) formal-1, 8-dioctyl mercaptan was replaced with an equal mass of nano-carrier (nano-silica) and the ratio of titanium tetrachloride to internal electron donor in the olefin polymerization catalyst was maintained as in example 3.

Diluting 15mg of the olefin polymerization catalyst with 50 times of hexane, and adding triethylaluminum and external electron donor diisopropyldimethoxy silane, wherein the mass ratio of triethylaluminum to diisopropyldimethoxy silane is 4:1, and the Al/Ti (molar ratio) of triethylaluminum to titanium tetrachloride is 420; carrying out polymerization under liquid-phase propylene and gas-phase ethylene, wherein specific parameters are the same as those of example 3, and polypropylene is obtained; the polypropylene was kneaded and extrusion-pelletized in the same manner as in example 3 to obtain a polypropylene product.

Comparative example 4

An olefin polymerization catalyst differing from example 4 only in that magnesium bis (3, 4-dimethylbenzaldehyde) formal-1, 8-dioctyl mercaptan was replaced with an equal mass of nano-carrier (nano-silica) and the ratio of titanium tetrachloride to internal electron donor in the olefin polymerization catalyst was maintained as in example 4.

diluting 15mg of the olefin polymerization catalyst with 50 times of hexane, and adding triethylaluminum and external electron donor diisopropyldimethoxy silane, wherein the mass ratio of triethylaluminum to diisopropyldimethoxy silane is 4:1, and the Al/Ti (molar ratio) of triethylaluminum to titanium tetrachloride is 420; carrying out polymerization under liquid-phase propylene and gas-phase ethylene, wherein specific parameters are the same as those of example 4, and polypropylene is obtained;

Comparative example 5

An olefin polymerization catalyst differing from example 1 only in that magnesium bis (3, 4-dimethylbenzaldehyde) formal-1, 8-dioctyl mercaptan was replaced with magnesium chloride of equal mass and the ratio of titanium tetrachloride to internal electron donor in the olefin polymerization catalyst was maintained as in example 1.

Comparative example 6

An olefin polymerization catalyst differing from example 1 only in that magnesium bis (3, 4-dimethylbenzaldehyde) formal-1, 8-dioctyl mercaptan was replaced with magnesium octyl butoxide of equal mass, and the ratio of titanium tetrachloride to internal electron donor in the olefin polymerization catalyst was maintained as in example 1.

The polypropylene products provided in examples 1-5 and comparative examples 1-6 were subjected to performance testing as follows:

(1) Melt index: measured according to GB/T3682.1 measurement standards for thermoplastic melt mass flow rate and melt volume flow rate.

(2) Haze: haze panels with a thickness of 1mm were prepared and measured according to the measurement standards of light transmittance and haze for GBT 2410-2008 clear plastics.

(3) Notched Izod impact Strength: and testing according to the measuring standard of the national standard GBT 1843-2008 cantilever beam impact strength.

The test results are shown in table 1:

TABLE 1

From the test data in Table 1, it can be seen that the olefin polymerization catalyst provided by the present invention is used in Ziegler-Natta catalysts and catalyzes the preparation of polypropylene, and the transparency of the resulting polypropylene product is comparable to that of a transparent polypropylene product incorporating a transparent nucleating agent (comparative example 4) at the same ethylene content. Compared with the polypropylene products (comparative examples 1-3) without the transparent nucleating agent, the polypropylene products prepared by using the olefin polymerization catalyst provided by the invention have obviously improved transparency and impact resistance, the haze is 9.8-11.9%, and the notched Izod impact strength is 6.6-7.0kJ/m ². Therefore, the olefin polymerization catalyst provided by the invention has excellent catalytic activity and can replace a transparent nucleating agent to produce polypropylene transparent material. In addition, if the transparent nucleating agent is added to the polypropylene product produced by using the olefin polymerization catalyst (example 5), the transparency of the product is obviously improved compared with that of common transparent polypropylene, and the ultra-high transparent polypropylene can be produced under the condition of the same dosage of the transparent nucleating agent.

According to the invention, through the design of the nano carrier and the alkyl magnesium mercaptide and the compounding of the nano carrier and other components, the olefin polymerization catalyst has excellent catalytic activity, and can play the role of a transparent nucleating agent, so that a polypropylene product with greatly improved transparency and excellent rigidity and toughness can be obtained. If the olefin polymerization catalyst does not contain the alkyl magnesium mercaptide with the structure shown in the formula I, for example, the magnesium chloride carrier is adopted in the comparative example 5, and the octyl magnesium butoxide is adopted in the comparative example 6, the olefin polymerization catalyst does not have the function of a transparent nucleating agent, and the obtained polypropylene product has higher haze, insufficient transparency and reduced shock resistance.

The applicant states that the present invention is illustrated by the above examples for the olefin polymerization catalyst of the present invention and its use, and the process for the preparation of polypropylene, but the present invention is not limited to the above examples, i.e. it is not meant that the present invention must be practiced by means of the above examples. It should be apparent to those skilled in the art that any modification of the present invention, equivalent substitution of raw materials for the product of the present invention, addition of auxiliary components, selection of specific modes, etc., falls within the scope of the present invention and the scope of disclosure.

Claims

1. An olefin polymerization catalyst, characterized in that the olefin polymerization catalyst comprises a nano-carrier and a combination of titanium halide, alkyl magnesium mercaptide and an internal electron donor supported on the nano-carrier;

the alkyl magnesium mercaptide has a structure shown in a formula I:

Wherein R is selected from any one of C1-C3 straight-chain or branched-chain alkyl;

m is selected from integers from 0 to 4;

n is an integer from 6 to 12.

2. The olefin polymerization catalyst according to claim 1, wherein R is methyl;

preferably, m is selected from integers from 1 to 3;

3. The olefin polymerization catalyst according to claim 1 or 2, characterized in that the alkyl magnesium mercaptide is prepared by a process comprising the steps of:

wherein R, m and n have the same defined ranges as in formula I;

(S2) reacting an alkaline aqueous solution comprising the intermediate with magnesium to obtain the magnesium alkyl mercaptide of the structure shown in formula I;

preferably, the temperature of the condensation reaction of step (S1) is 60-120 ℃;

preferably, the time of the condensation reaction of step (S1) is 6-24 hours;

preferably, the mass percentage of the intermediate in the alkaline aqueous solution is 1-80%;

preferably, the mass ratio of the alkaline aqueous solution to magnesium is 1 (3-5);

preferably, the temperature of the reaction of step (S2) is 70-95 ℃, further preferably 80-90 ℃;

preferably, the reaction time in step (S2) is 1-5 hours, more preferably 2-4 hours.

4. The olefin polymerization catalyst according to any one of claims 1-3, wherein the nano-carrier comprises any one or a combination of at least two of nano-silica, nano-titania, nano-alumina, nano-calcia, preferably nano-silica;

Preferably, the particle size of the nano-carrier is 10-500nm, more preferably 50-200nm;

preferably, the titanium halide comprises titanium tetrachloride and/or titanium trichloride, more preferably titanium tetrachloride;

Preferably, the mass ratio of the titanium halide to the nano-carrier is 1 (4-8);

preferably, the mass ratio of the alkyl magnesium mercaptide to the nano-carrier is (2-4): 1.

5. The olefin polymerization catalyst of any one of claims 1-4, wherein the internal electron donor comprises any one or a combination of at least two of diisobutyl phthalate, di-n-butyl phthalate, diethyl 2-methyl-2-isopropyl malonate;

Preferably, the mass ratio of the internal electron donor to the nano-carrier is 1 (1-3).

6. A process for preparing an olefin polymerization catalyst according to any one of claims 1 to 5, comprising:

7. The method of manufacturing according to claim 6, characterized in that the method of manufacturing comprises:

mixing nano carrier, alkyl magnesium mercaptan, 20-80% of formula amount of titanium halide and solvent, performing a first-stage reaction, adding an internal electron donor to perform a second-stage reaction, and adding the rest of titanium halide to perform a third-stage reaction to obtain the olefin polymerization catalyst;

Preferably, the solvent comprises an alcoholic solvent;

preferably, the temperature of the first stage reaction is from 2 to 15 ℃, further preferably from 5 to 10 ℃;

preferably, the time of the first stage reaction is from 0.2 to 2 hours, further preferably from 0.5 to 1 hour;

preferably, the adding temperature of the internal electron donor is 20-50 ℃;

preferably, the temperature of the second stage reaction is 120-180 ℃;

Preferably, the second stage reaction time is from 0.5 to 4 hours, more preferably from 1 to 3 hours;

Preferably, the second stage reaction and the third stage reaction further comprise the steps of settling and removing the supernatant;

Preferably, the sedimentation temperature is 60-80 ℃;

preferably, the sedimentation time is 0.5-3 hours;

Preferably, the temperature of the third stage reaction is 120-180 ℃;

preferably, the time of the third reaction is 0.5 to 4 hours, further preferably 1 to 3 hours;

8. A Ziegler-Natta catalyst comprising a combination of an olefin polymerization catalyst according to any of claims 1-5, an organoaluminum and an external electron donor;

Preferably, the organic aluminum comprises alkyl aluminum and/or alkyl aluminum chloride, further preferably any one or a combination of at least two of trimethyl aluminum, triethyl aluminum, triisobutyl aluminum, diethyl aluminum monochloride, diisobutyl aluminum monochloride;

Preferably, the molar ratio of Al in the organoaluminum to Ti in the olefin polymerization catalyst is (400-500): 1;

Preferably, the external electron donor includes silane external electron donors, and more preferably any one or a combination of at least two of diisopropyl dimethoxy silane, dimethyl dimethoxy silane, dibutyl dimethoxy silane and diphenyl dimethoxy silane;

Preferably, the mass ratio of the external electron donor to the alkyl magnesium mercaptide is (1-4): 1;

Preferably, the mass ratio of the external electron donor to the organic aluminum is 1 (3-7).

9. Use of the olefin polymerization catalyst according to any one of claims 1-5, the Ziegler-Natta catalyst according to claim 8 in olefin polymerization;

10. A method for preparing polypropylene, comprising: polymerizing propylene and optionally ethylene in the presence of a Ziegler-Natta catalyst according to claim 8 to obtain the polypropylene;

preferably, the temperature of the polymerization reaction is 0-100 ℃;

Preferably, the pressure of the polymerization reaction is 0.1 to 5MPa, more preferably 3 to 5MPa.