WO2021105373A1

WO2021105373A1 - Catalyst composition for the polymerization of olefins

Info

Publication number: WO2021105373A1
Application number: PCT/EP2020/083644
Authority: WO
Inventors: Sikarin TAMIYAKUL; Phonpimol WONGMAHASIRIKHUN; Phairat Phiriyawirut
Original assignee: Thai Polyethylene Co., Ltd.; Kirsteen Gordon
Priority date: 2019-11-29
Filing date: 2020-11-27
Publication date: 2021-06-03
Also published as: CN114729068A; JP2023505758A; EP4065610A1

Abstract

The invention relates to a method for preparing a solid pro-catalyst suitable for use in a Zeigler-Natta type catalyst composition for polymerizing olefin monomers. The method is for preparing a pro-catalyst comprising a transition metal, Mg, a halogen, a modifier and an internal donor, and the method comprises reacting a halide of the transition metal with a magnesium alkoxide to provide a solid reaction product comprising the transition metal supported on a magnesium halide-based support, and contacting the solid reaction product with the internal donor and the modifier.

Description

CATALYST COMPOSITION FOR THE POLYMERIZATION OF OLEFINS

FIELD OF THE INVENTION

The invention relates to a method for preparing a solid pro-catalyst suitable for use in a Zeigler- Natta type catalyst composition for polymerizing olefin monomers. The invention also extends to the pro-catalyst, a Zeigler-Natta type catalyst composition comprising the pro-catalyst and the use of each of these to polymerize olefin monomers. The pro-catalyst or the catalyst composition can be used to produce phthalate-free polypropylene with high productivity, high melt flow rate and high stereo-regularity.

BACKGROUND OF THE INVENTION

Ziegler-Natta catalyst compositions/systems are well known in the art for the polymerization of olefins. Typically, a Ziegler-Natta catalyst composition/system comprises (I) a solid pro catalyst component which includes a transition metal such as titanium, magnesium, an electron donor compound, and a halogen atom, and (II) a co-catalyst component which is usually an organoaluminum compound. It is desirable to improve the activity and stereospecificity of Ziegler-Natta catalyst compositions and a widely used approach in this regard is that of using electron donating compounds. Normally, the electron donating compounds can be classified into two groups, (1) internal electron donors and (2) external electron donors, used with the solid Ziegler Natta pro-catalyst and co-catalyst component. Various polypropylene products can be produced by varying polymerization conditions, in particular, by utilizing an external electron donor. External electron donors include organic compounds containing O, Si, N, S, and/or P. Generally, external donor compounds are based on silanes, ketones, amides, amines, and thiols compounds etc., with the most common compounds being organosilicon compounds containing Si-O-C and/or Si-N-C bonds. With regard to internal donors, concerns relating to environmental issues have been raised recently about the use of phthalate derivatives as internal donors and also concerns relating to human contact, e.g. with polypropylene product containing the phthalate derivatives. Thus, it is highly desirable to provide alternative internal electron donors to phthalate compounds. WO 2018/059955A1 discloses a process for preparing a procatalyst for the polymerisation of olefins. The process involves a two step activation of a solid support Mg/OR^_xX^-_x (where 0 < x < 2 and, preferably R¹ is ethyl and X¹ is Cl) which results in an adduct of the solid support and at least two activating compounds. The process employs a Grignard reagent to prepare the solid support and this may make controlling the morphology of the catalyst difficult. An internal electron donor is a component of a Ziegler-Natta catalyst composition which is incorporated during the catalyst preparation. Well-known internal electron donors include ethers, esters, ketones, amines, alcohols, heterocyclic organic compounds, phenols, and phosphines. The structure of internal electron donor can influence catalyst activity, stereoregularity, hydrogen (melt flow rate of the polymer) and comonomer responses. Thus, the molecular weight, molecular weight distribution, and isotacticity of resultant polymer can significantly depend on the molecular structure of the internal electron donor (see, e.g. ACS Catal. 2017, 7, 4509-4518). Thus much effort has been dedicated to the development of new internal donors for Ziegler-Natta catalysts with a view to improving the properties of the polymers they can be used to produce. Common internal electron donor compounds which are suitable for incorporation into Ziegler Natta catalysts and that are known in the art, include esters, amines, alcohols, heterocyclic organic compounds, phthalates, diethers, and succinates compounds. It has been published that diether compounds have been developed for producing phthalate-free polypropylene (Journal of Applied Polymer Science, Vol. 99, 1399-1404 (2006)). One of the most broadly used is 9,9-bis(methoxymethyl)fluorene and its derivatives. This diether internal donor has been associated with a significant improvement in activity and hydrogen response when used in a Ziegler-Natta catalyst composition. However, it is also associated with moderate stereo-selectivity, and importantly, a stereo-selectivity which is poorer than that of phthalate-based catalysts, thus limiting the application of such internal donors in expanding the field of phthalate-free polypropylene production. Thus, it is desirable to improve the stereo-selectivity of diether-based Ziegler-Natta catalysts in efforts to produce phthalate- free polypropylene. It is especially desirable to improve the stereo-selectivity of diether-based Ziegler-Natta catalysts without compromising any of the other advantageous properties associated with these catalysts in efforts to produce phthalate-free polypropylene. There is a need to provide new Zeigler-Natta catalyst compositions that produce highly stereo -regular polypropylene.

The present invention seeks to solve one or more of the aforementioned problems or meet one or more of the aforementioned desires/needs.

SUMMARY OF THE INVENTION

In a first aspect, the invention provides a method for preparing a pro-catalyst comprising a transition metal, Mg, a halogen, a modifier and an internal donor, wherein the method comprises (i) contacting a halide of the transition metal and a magnesium alkoxide to provide a solid reaction product comprising the transition metal supported on a magnesium halide- based support, and (ii) contacting the solid reaction product with the internal donor and the modifier, wherein the modifier is of formula (I)

where Ri and R₂ are each independently hydrogen or an alkyl group having 1 to 6 carbon atoms, and R₃, R₄, R₅, R₆, and R₇ are each independently selected from hydrogen, a heteroatom or a hydrocarbyl group.

In another aspect, the invention provides a pro-catalyst comprising a transition metal, Mg, a halogen, a modifier and an internal donor obtained/obtainable by the method of the first aspect of the invention. For example, the pro-catalyst can be obtained/is obtainable by (i) contacting a halide of the transition metal and a magnesium alkoxide to provide a solid reaction product comprising the transition metal supported on a magnesium halide -based support, and (ii) contacting the solid reaction product with the internal donor and the modifier, wherein the modifier is of formula (I)

The pro-catalyst of the invention is suitable for use in a catalyst composition for the polymerization of olefin monomers. More specifically, the pro-catalyst is suitable for use along with an organoaluminum co-catalyst and, optionally, an external donor, in the polymerization of olefin monomers. The pro-catalyst can be free of any phthalates (phthalates are phthalic acid esters or phthalate esters, and derivatives thereof), i.e. in one embodiment, the pro-catalyst does not contain any phthalates. Advantageously, the pro-catalyst of the invention can be used in the polymerization of olefin monomers to produce highly isotactic polymers/copolymers, such as in the polymerization of polypropylene to produce highly isotactic polypropylene.

In another aspect, the invention provides a catalyst composition for the polymerization of olefin monomers comprising the pro-catalyst of the invention and a co-catalyst. The co-catalyst comprises an organoaluminum compound.

In another aspect, the invention provides for the use of the pro-catalyst of the invention, or of the catalyst composition described above comprising the pro-catalyst of the invention, for the polymerization of olefin monomers. In particular, the invention provides for the use of the pro catalyst of the invention, or of the catalyst composition described above comprising the pro catalyst of the invention, for the preparation of highly stereo -regular polyolefins, such as polyolefins having an mmmm content of at least 95 %. In particular, it has surprisingly been found that the pro-catalyst of the invention or the catalyst composition of the invention can be used to prepare polypropylene having higher stereoselectivity (in terms of mmmm content) than polypropylene prepared using conventional diether catalysts.

In another aspect, the invention provides for a process for preparing a polyolefin comprising polymerizing olefin monomers in the presence of a catalyst composition comprising a pro catalyst according to the first aspect of the invention, a co-catalyst comprising an organoaluminum compound, and, optionally, an external donor. In another aspect, the invention provides for a polyolefin so obtained or obtainable by said process. The polyolefin can be a homopolymer or a copolymer, for example an impact copolymer polypropylene.

Definitions

As used herein the term “Ziegler-Natta (ZN) catalyst composition/system” refers to a pro catalyst that comprises a transition metal halide (e.g. titanium halide, chromium halide, hafnium halide, zirconium halide or vanadium halide) supported on a metal or metalloid compound (e.g. a magnesium compound or a silica compound), in combination with a co catalyst. The pro-catalyst is also referred to as the solid component of Ziegler-Natta (ZN) catalyst composition/system. The co-catalyst is typically an organoaluminum compound. As used herein the term “catalyst system” is interchangeable with the term “catalyst composition” and refers to the pro-catalyst, including any optional activators, internal electron donors and modifiers, in combination with the co-catalyst and any external electron donors.

As used herein the terms “internal electron donor”, “internal donor”, “ID” are interchangeable and refer to an electron donating compound containing one or more atoms of oxygen (O) and/or nitrogen (N) that is incorporated into the solid pro-catalyst during preparation of the pro catalyst. Suitable internal electron donors are commonly described in prior art for the preparation of solid pro-catalyst for a Ziegler Natta catalyst system useful for propylene polymerization.

As used herein the terms “external electron donor”, “external donor” and “ED” are interchangeable and refer to an electron donating compound which is used in combination with the pro-catalyst in the polymerization of olefin monomers. The external electron donor is not incorporated into the solid pro-catalyst during preparation of the pro-catalyst and is added independently of the pro-catalyst to the polymerization reaction. The external electron donor functions to donate electrons to another compound and may influence the properties of the catalyst composition/system.

As used herein the term “homopolymer” refers to a polymer which consists essentially of repeat units deriving from the same monomer. Homopolymer may, for example, comprise at least 99 %, more preferably at least 99.5 %, still more preferably at least 99.95 %, and yet more preferably at least 99.95 % e.g. 100%, by weight of repeat units deriving from the same monomer.

As used herein the term “propylene homopolymer” refers to a polymer which consists essentially of repeat units deriving from propylene. Homopolymer may, for example, comprise at least 99 %, more preferably at least 99.5 %, still more preferably at least 99.95 %, and yet more preferably at least 99.95 % e.g. 100%, by weight of repeat units deriving from propylene.

As used herein, “impact copolymer polypropylene” refers to a polymer comprising a propylene homopolymer or copolymer matrix and an ethylene propylene rubber phase dispersed in the matrix.

As used herein the term “propylene copolymer” refers to a polymer comprising repeat units deriving from propylene and at least one other comonomer. Typically, the propylene copolymer comprises at least 0.05 wt %, more preferably at least 0.1 wt % and, still more preferably, at least 0.4 wt % of a repeat unit derived from at least one other comonomer, where the wt % is based on the propylene copolymer. The propylene copolymer will normally not comprise more than 15 wt % of repeat units deriving from at least one other comonomer. Typically, the propylene copolymer comprises at least 85 wt % more preferably at least 90 wt % and, still more preferably, at least 95 wt % of propylene monomer repeat units.

As used herein the terms “modifier” and “M” are interchangeable and refer to an electron- donating compound containing one or more atoms of oxygen (O) and / or nitrogen (N) which is introduced into the pro-catalyst during the solid pro-catalyst preparation.

As used herein, the term “hydrocarbyl” or “hydrocarbyl group” refers to a univalent radical derived from a hydrocarbon. Hydrocarbyl groups include alkyl, alkenyl, aryl, aralkyl, arylalkenyl, alkoxycarbonyl and alkylaryl groups, for example.

As used herein “heteroatom” refers to atom selected from group 13, 14, 15, 16 or 17 of the IUPA Periodic Table of the Elements and can be described as a hetero atom selected from B, Al, Ga, In, Si, Ge Sn, N, P, As, O, S, Se, Te, F, Cl, Br and I.

As used herein the term “polypropylene” refers to a polymer of propylene.

As used herein the terms “XS”, “xylene solubles”, “xylene soluble fraction” are interchangeable and refer to the xylene soluble fraction in terms of percentage of polymer that does not precipitate out upon cooling of a polymer solution in xylene. The mentioned polymer solution is subjected to reflux conditions, and then cooled from the boiling point of xylene to 25 °C. The xylene soluble fraction is measured according to ASTM D5492-10 (Standard Test Method for Determination of Xylene Solubles in Propylene Plastics).

As used herein the term “Productivity” refers to the amount of kilogram of polymer produced per gram of solid pro-catalyst consumed in the polymerization reactor per one hour.

As used herein, the term “comprising”, which is inclusive or open-ended and does not exclude additional unrecited elements or method steps, is intended to encompass as alternative embodiments, the phrases “consisting essentially of’ and “consisting of’, where “consisting of’ excludes any element or step not specified and “consisting essentially of’ permits the inclusion of additional unrecited elements or steps that do not materially affect the essential or basic and novel characteristics of the composition or method under consideration. DETAILED DESCRIPTION OF THE INVENTION

According to a first aspect, the invention provides a method for preparing a pro-catalyst comprising a transition metal, Mg, a halogen, a modifier and an internal donor, wherein the method comprises (i) contacting a halide of the transition metal and a magnesium alkoxide to provide a solid reaction product comprising the transition metal supported on a magnesium halide-based support, and (ii) contacting the solid reaction product with the internal donor and the modifier, wherein the modifier is of formula (I)

The transition metal can be chosen from titanium, chromium, hafnium, zirconium and vanadium. Preferably, the transition metal is titanium. The halide of the transition metal is a halogenating agent, used to halogenate the magnesium alkoxide. The halide provides the halogen element of the pro-catalyst. The halide can be chosen from chloride, bromide and iodide. Preferably, the halide is chloride. Typically, the halide of the transition metal is titanium chloride. Preferably, the halide of the transition metal is titanium tetrachloride. For example, when the transition metal halide is titanium chloride, the pro-catalyst comprises titanium, Mg, chlorine, an internal donor and a modifier (also referred to as a modifying agent).

The method of the invention involves a step (i) whereby a halide of the transition metal and a magnesium alkoxide are contacted so that they react to provide a solid reaction product comprising the transition metal supported on a magnesium halide -based support. Further, the method involves a step (ii), whereby the solid reaction product is contacted with the internal donor and the modifier to provide a solid reaction product comprising the internal donor and the modifier. In the method of the invention, the transition metal halide and the magnesium alkoxide react together. The internal donor and the modifier are incorporated into the solid reaction product and do not partake in a chemical reaction as such. The method of the invention produces a solid pro-catalyst (the solid reaction product comprising the transition metal supported on a magnesium halide -based support and comprising the internal donor and the modifier). The method is preferably carried out in the absence of any phthalates and thus results in a solid pro-catalyst that does not contain any phthalates. The pro-catalyst can be considered as the solid component of a Ziegler-Natta catalyst composition (or a Ziegler-Natta catalyst system).

It has been found that, by using a magnesium alkoxide in the preparation of the support of the pro-catalyst of the invention, a pro-catalyst with a high porosity and a high surface area is obtained. In particular, it has been found that the morphology of the pro-catalyst of the invention is the same or similar to the morphology of the magnesium alkoxide used to prepare the pro-catalyst of the invention. For example, the particle size of the pro-catalyst can be within approximately within 10% of the particle size of the magnesium alkoxide. Clearly, there are advantages associated with having a pro-catalyst that has a high porosity and a high surface area. Further, it has been found that there are advantages in using the pro-catalyst of the invention in the preparation of impact copolymer polypropylene, in particular. For example, the pro-catalyst of the invention can be used to prepare impact copolymer polypropylene having high rubber phase content. Impact copolymer polypropylene having excellent mechanical property can be prepared using the pro-catalyst of the invention since the homopolymer part will have high stereoregularity and also a high content of rubber phase. With balancing this stereoregularity of the homopolypropylene part and the high content of rubber phase, impact copolymer polypropylene having excellent mechanical property can be obtained.

The magnesium alkoxide, also referred to herein as dialkyoxymagneisum, can have the formula MgORnOR where R12 and R13 are independently a hydrocarbyl group containing from 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms or more preferably 2 carbon atoms. The hydrocarbyl group can be an alkyl group. An exemplary magnesium alkoxide is magnesium ethoxide, i.e. MgORnOR where R12 and R13 are each an ethyl group. The magnesium alkoxide is solid and comprises particles (i.e. in particulate form). The magnesium alkoxide is preferably granular or powdery. It may comprise particles that are spherical or approximately spherical, for example, the particles do not necessarily have to have a true spherical shape, e.g. they can be potato-shaped. Preferably, the magnesium alkoxide comprises particles having a particle shape such that they have an average ratio (1/w) of the major axis diameter (1) to the minor axis diameter (w) is 3 or less, preferably 1 to 2, more preferably 1 to 1.5. The average particle diameter of the dialkoxymagnesium can be from 1 to 200 in terms of an average particle diameter D50 (i.e. the particle diameter at 50% in the cumulative particle diameter distribution) when measured using from SEM images taken over 500 particles. The particle diameter distribution is the number of particles that fall into each of the various diameter ranges given as a percentage of the total number of particles of all diameters in the sample. An average particle diameter D50 of 200 pm is preferable. This means that 50 % of the number of particles in the sample have a diameter greater than 200 pm and 50 % of the number of particles in the sample have a diameter smaller than 200 pm. An average particle diameter D50 of 5-150 micrometers is more preferable. In the case of dialkoxymagnesium, the average particle diameter D50 is preferably 1 to 100 pm, more preferably 5 to 80 or 50 pm, and even more preferably 10 to 40 pm. Further, a narrower particle size distribution with low amounts of fine powder and coarse powder is desirable. Preferably, the dialkoxymagnesium has a content of particles having a diameter of 5 pm or less of 20% or less, or more preferably 10% or less, when measured using from SEM images (these are percentages by number). Preferably, the dialkoxymagnesium has a content of particles having a diameter of 100 pm or more is 10% or less, more preferably 5% or less (these are percentages by number). Furthermore, the particle size distribution, ln(D90/D10) (where D90 is the particle size at 90 % in the cumulative particle size distribution, and D10 is the cumulative particle size at 10 % in the cumulative particle size distribution), is preferably 3 or less, more preferably 2 or less. Methods for producing dialkoxymagnesium as described above are described in JP-A-58-41832, JP-A-62-51633, JP- A-3-74341, JP-A-4-368391, and JP-A-8-73388, for example.

The modifier is of formula (I):

(I) where Ri and R₂ are each independently hydrogen or an alkyl group having 1 to 6 carbon atoms, and R₃, R₄, R₅, R₆, and R₇ are each independently selected from hydrogen, a heteroatom or a hydrocarbyl group. Ri and R₂ can be independently hydrogen or an alkyl group having 1 to 3 carbon atoms. Ri and R₂ can be independently hydrogen or a methyl group. Preferably, at least one of Ri and R₂ is an alkyl group (having 1 to 6 or 1 to 3 carbon atoms) and, more preferably, at least one of Ri and R₂ is a methyl group. R₃, R₄, Rs, R6, and R₇ are each independently selected from hydrogen, a heteroatom or a hydrocarbyl group. The heteroatom can be selected from B, Al, Ga, In, Si, Ge Sn, N, P, As, O, S, Se, Te, F, Cl, Br and I. Preferably, the heteroatom is a halide. Preferably, the hydrocarbyl group is chosen from alkyl, alkenyl, aryl, aralkyl, alkoxycarbonyl, or alkylaryl groups, and one or more combinations thereof. The hydrocarbyl group may be linear, branched or cyclic. The hydrocarbyl group may be substituted or unsubstituted, and may contain one or more heteroatoms. Preferably, the hydrocarbyl group has from 1 to 10 carbon atoms, more preferably from 1 to 8 carbon atoms, even more preferably from 1 to 6 carbon atoms. More preferably, R₃, R₄, Rs, R6, and R₇ are each hydrogen. Thus, in one embodiment, Ri and R₂ are each independently hydrogen or an alkyl group having 1 to 6 carbon atoms, and R₃, R₄, Rs, R6, and R₇ are each hydrogen.

Examples of modifiers include benzamide, methyl benzamide, and dimethylbenzaminde. Other examples include monoethylbenzamide, diethylbenzamide and methylethylbenzamide. An exemplary modifier is dimethylbenzamide.

The amount of modifier used in the method of the invention can be chosen so that the pro catalyst contains the modifier in an amount of from 0.15 to 8 wt % as measured by NMR and based on the total weight of the procatalyst. Preferably, the amount of modifier used in the reaction is such that the modifier is present in the pro-catalyst in an amount of 0.3 to 6 wt%, more preferably in an amount of 0.5 to 4 wt%. The amount of modifier used in the reaction can be such that the modifier is present in the pro-catalyst in an amount of 0.1 to 2.0 wt %, preferably in an amount of 0.1-0.4 wt%.

The internal donor can be a diether compound. Suitable diether compounds are those commonly known in the art as internal donors for Zeigler Natta catalyst systems. Suitable diether compounds are described in US2016/0311947, for example. Preferred diether internal donor compounds include 1,3 -diether compounds represented by the structure (I):

wherein: Rio and Rn are the same or different and are each selected from the group consisting of saturated or unsaturated aliphatic hydrocarbyl groups of from 1 to about 20 carbon atoms, and Rs and R₉ are the same or different and are each selected form the group consisting of linear, cyclic or branched hydrocarbyl groups having form 1 to about 40 carbon atoms. Preferably, Rio and Rn are each independently selected from alkyl groups of from 1 to about 10 carbon atoms. More preferably, Rio and Rn are each independently selected from alkyl groups of from 1 to 4 carbon atoms. Even more preferably, Rio and Rn are each independently selected from a methyl or ethyl group. Even more preferably, each of Rio and Rn is a methyl group. Preferably, Rs and R₉ are each independently selected from alkyl groups of from 1 to about 20 carbon atoms, an alkenyl group of from 2 to about 20 carbon atoms, an aryl group of from 6 to about 20 carbon atoms, an arylalkyl group of from 7 to about 40 carbon atoms, an alkylaryl group of from 7 to about 40 carbon atoms or an arylalkenyl group of from 8 to about 40 carbon atoms, and may contain one or more hetero atoms such as Si, B, Al, O, S, N or P, and/or may contain one or more halogen atoms such as F, Cl or Br, and/or Rs and R₉ may be joined together to form a hydrocarbon ring system (such as a fluorene). Thus, in one embodiment, Rio and Rn are each independently selected from alkyl groups of from 1 to about 10 carbon atoms, and Rs and R₉ are each independently selected from alkyl groups of from 1 to about 20 carbon atoms, an alkenyl group of from 2 to about 20 carbon atoms, an aryl group of from 6 to about 20 carbon atoms, an arylalkyl group of from 7 to about 40 carbon atoms, an alkylaryl group of from 7 to about 40 carbon atoms or an arylalkenyl group of from 8 to about 40 carbon atoms, and may contain one or more hetero atoms such as Si, B, Al, O, S, N or P, and/or may contain one or more halogen atoms such as F, Cl or Br, and/or Rs and R₉ may be joined together to form a hydrocarbon ring system (such as a fluorene).

Preferably, the diether internal donor compound is chosen from: 2, 2-di-isobutyl- 1,3- dimethoxypropane; 2.2-di-isopropyl- 1 ,3-dimethoxypropane; 2,2-di-cyclopentyl- 1 ,3 dimethoxypropane; 2-isopropyl-2-isopentyl- 1 ,3-dimethoxypropane; 2-isopropyl-2-isobutyl-

1.3-dimethoxypropane; 2-isopropyl-2-cyclopentyl-dimethoxypropane; 2-ethyl-2-tert-butyl-

1.3-dimethoxypropane or the corresponding 1,3-diethoxypropane analogues; 9,9- bis(methoxymethyl)fluorene; and 9,9-bis(ethoxymethyl)fluorene. The amount of the internal donor used in the method of the invention can be chosen so that the pro-catalyst contains the internal donor in an amount of from 10 to 30 wt % as measured by NMR and based on the total weight of the pro-catalyst. Preferably, the amount of internal donor used in the method of the invention is such that the internal donor is present in the pro catalyst in an amount of 15 to 28 wt% and, more preferably, in an amount of 20-28 wt% (e.g. 25 wt%). The amount of internal donor used in the method of the invention can be such that the internal donor is present in the pro-catalyst in an amount of 15 to 25 wt%.

The relative amounts of the modifier and the internal donor used in the method of the invention can be chosen so that the pro-catalyst contains the modifier of formula (I) and the internal donor in a molar ratio (M/ID) of from 0.04 to 0.50. Preferably, the molar ratio M/ID is from 0.04 to 0.18 or 0.17, 0.04 to 0.12, or 0.05 to 0.10. The molar ratio M/ID can be from 0.005 to 0.5 or 0.01 to 0.5 or 0.01-0.3. In particular, it has been found that, even at such low M/ID ratios, the resultant pro-catalyst can be used to obtain highly stereo-regular polymers, e.g. highly stereoregular polypropylene. Thus highly isotactic polypropylene can be obtained using relatively low levels of benzamide modifier. Further, it has been found that using lower amounts of benzamide modifier results in a pro-catalyst having improved morphology, e.g. the pro-catalyst will have lower amounts of fine particles and most of the catalyst particles will be of a similar size. Preferably, the pro-catalyst of the invention contains little or no fine particles (i.e. particles that are smaller than 5 micron). This can be determined qualitatively from SEM (Scanning Electron Microscope) images. A lower amount of fine particles in the pro-catalyst is preferred, since a high amount of fine particles in the pro-catalyst can cause flowability problems e.g. plugging in the reactor and can decrease heat removal efficiency.

The method of the invention for preparing a pro-catalyst comprising a transition metal, Mg, a halogen, a modifier and an internal donor comprises (i) contacting a halide of the transition metal and a magnesium alkoxide to provide a solid reaction product comprising the transition metal supported on a magnesium halide -based support, and (ii) contacting the solid reaction product with the internal donor and the modifier.

The method of the invention involves a step (i) of contacting a halide of a transition metal and a magnesium alkoxide so that they react to form a solid reaction product comprising the transition metal supported on a magnesium halide -based support. Typically, in this step, the halide of a transition metal and the magnesium alkoxide are mixed to form a reaction mixture. The magnesium alkoxide (which is solid) may be suspended in a hydrocarbon solvent and, in this case, the transition metal halide is added to the suspension to form the reaction mixture. Preferably, the transition metal halide is added to the magnesium alkoxide (or suspension containing the magnesium alkoxide) at a low temperature, for example, from -20 to 0 °C. The desired reaction between the transition metal halide and the magnesium alkoxide will occur at low temperatures but the mixture comprising the transition metal halide and the magnesium alkoxide is preferably heated (up to 110 C, for example) to complete the reaction.

The method of the invention involves a step (ii) of contacting the solid reaction product with the internal donor and the modifier, thus providing a pro-catalyst suitable for the polymerization of olefins. The pro-catalyst comprises the transition metal supported on a magnesium halide-based support, and the internal modifier and the modifier. Step (ii) can be include carrying out step (i) at least in part in the presence of the internal donor and, optionally, at least in part in the presence of the modifier. Thus, in this embodiment, the reaction of the transition metal halide with the magnesium alkoxide is carried out at least in part in the presence of the internal donor and at least in part in the presence of the modifier. The internal donor and the modifier can each be added to the reaction mixture comprising the magnesium alkoxide (e.g. the suspension containing the magnesium alkoxide) over a broad range of temperatures, e.g. from -20 to 110 °C. The internal donor and the modifier are each added independently, e.g. they can be added simultaneously or sequentially. The internal donor and/or the modifier can be added to the reaction mixture containing the magnesium alkoxide (e.g. the suspension containing the magnesium alkoxide) before transition metal halide is added. In this case, the internal donor and/or the modifier will be present during the reaction of the transition metal and the magnesium alkoxide. Also, the internal donor and/or the modifier can be added to the reaction mixture containing the magnesium alkoxide (e.g. the suspension containing the magnesium alkoxide) and the transition metal halide, i.e. after the transition metal halide has been added. For example, the internal donor and/or the modifier can be added during the heating of the reaction mixture. In this case, the internal donor and/or the modifier is added to the mixture before the reaction of the transition metal and the magnesium alkoxide is complete. Thus the reaction of step (i) takes place at least in part in the presence of the internal donor and/or at least in part in the presence of the modifier. Alternatively, the modifier can be added after the reaction of step (i) is complete. In one embodiment, step (i) is carried out at least in part in the presence of the internal donor and at least in part in the presence of the modifier. In one embodiment, step (i) is carried out at least in part in the presence of the internal donor and at least in part in the presence of the modifier and the modifier is contacted with solid reaction product after the reaction of step (i) is complete.

Preferably, the step of contacting a halide of a transition metal and a magnesium alkoxide so that they react to form a solid reaction product comprising the transition metal supported on a magnesium halide -based support is carried out at least in part in the presence of the internal donor. The internal donor can be added to the reaction mixture containing the magnesium alkoxide before or after the transition metal halide is added. The internal donor is added to the mixture before the reaction of the transition metal and the magnesium alkoxide is complete. The modifier can be added to the reaction mixture before or after the transition metal halide is added. The modifier may be added to the reaction after the reaction of the transition metal and the magnesium alkoxide is complete.

The method of the invention provides a solid pro-catalyst comprising the transition metal, a halogen, magnesium, the internal donor and the modifier. In one embodiment, the pro-catalyst resulting from steps (i) and (ii) discussed above has its activity increased by treatment with the halide of the transition metal. Typically, the solid reaction product comprising the transition metal supported on a magnesium halide -based support, and the internal modifier and the modifier, is washed with a hydrocarbon solvent and then brought into contact with the transition metal halide in the presence of the hydrocarbon solvent to obtain an activated pro catalyst. The activated pro-catalyst can then optionally be heat treated in the presence or absence of the hydrocarbon solvent. Suitable hydrocarbon solvents are known to those skilled in the art.

Thus the method of the invention can comprise contacting the solid reaction product of steps (i) and (ii) discussed above with the halide of a transition metal. This increases the activity of the pro-catalyst.

In another aspect, the invention provides a pro-catalyst obtained/obtainable by the method of the first of aspect of the invention. This includes all of the embodiments of the method of the first aspect of the invention described herein. Thus, for example, the invention provides for a pro-catalyst comprising a transition metal, magnesium, a halogen, a modifier and an internal donor, obtained/obtainable by a method comprising (i) contacting a halide of the transition metal and a magnesium alkoxide to provide a solid reaction product comprising the transition metal supported on a magnesium halide -based support, and (ii) contacting the solid reaction product with the internal donor and the modifier, wherein the modifier is of formula I

(I), where Ri and R₂ are each independently hydrogen or an alkyl group having 1 to 6 carbon atoms, and R₃, R₄, R₅, R₆, and R₇ are each independently selected from hydrogen, a heteroatom or a hydrocarbyl group. The transition metal, the transition metal halide, the halogen, the magnesium alkoxide, the internal donor and the modifier are as described for the method of the first aspect of the invention.

In particular, the morphology of the pro-catalyst is the same or similar to the morphology of the magnesium alkoxide from which it is prepared. The particles of the pro-catalyst can be spherical or spheroidal in shape and have a particle size which is within 10 % of the particle size of the magnesium alkoxide. The pro-catalyst particles can have a smooth surface. In particular, the pro-catalyst particles have an average ratio (1/w) of the major axis diameter (1) to the minor axis diameter w is 3 or less, preferably 1 to 2, more preferably 1 to 1.5. The average particle diameter D50 is preferably 5-80 micron, more preferably 10-60 micron, most preferably 20-40 micron.

The pro-catalyst of the invention can be used in combination with an organoaluminum co catalyst and, optionally, an external donor, for the polymerization of olefin monomers/preparation of polyolefins. Thus, the invention provides a catalyst composition for the polymerization of olefin monomers comprising: a pro-catalyst as described above; and a co-catalyst comprising an organoaluminum compound. Thus, the invention provides a catalyst composition for the polymerization of olefin monomers comprising:

(i) a pro-catalyst comprising a transition metal, Mg, a halogen, a modifier and an internal donor, wherein said pro-catalyst is obtainable/obtained by (i) contacting a halide of the transition metal and a magnesium alkoxide to provide a solid reaction product comprising the transition metal supported on a magnesium halide-based support, and (ii) contacting the solid reaction product with the internal donor and the modifier, wherein the modifier is of formula I

where Ri and R₂ are each independently hydrogen or an alkyl group having 1 to 6 carbon atoms, and R₃, R₄, Rs, R₆, and R₇ are each independently selected from hydrogen, a heteroatom or a hydrocarbyl group ; and

(ii) a co-catalyst comprising an organoaluminum compound.

The catalyst composition can be free of any phthalates.

The co-catalyst comprises an organoaluminum compound. The co-catalyst can be an organoaluminum compound. Typically the organoaluminum compound is an alkyl aluminum compound. The alkyl groups present in the alkyl aluminum compound can be linear or branched. Each of the alkyl groups in the alkyl aluminum compound can independently be a Cl to C8 alkyl group, or a C2 to C6 alkyl group. Preferred organoaluminum compounds include trialkyl aluminum, for example trimethyl aluminum, triethyl aluminum, triisopropyl aluminum, triisobutyl aluminum and mixtures thereof. Triethyl aluminum is preferred.

The co-catalyst is preferably used in excess relative to the transition metal, e.g. titanium. Preferably the molar ratio of the aluminum in the co-catalyst to the transition metal, e.g. titanium, in the catalyst composition is from 1 to 500, or 2 to 200.

Typically, in use, the pro-catalyst is contacted with the organoaluminum (co-catalyst) compound shortly before the resultant catalyst composition is used in a polymerization reaction. The purpose of adding co-catalyst is to activate the pro-catalyst, so that the pro catalyst will be active for the polymerization. Thus, in another aspect, the invention provides a process of the preparation of a catalyst composition for polymerizing olefin momoners comprising contacting the pro-catalyst of the invention with an organoaluminum compound. The process can involve a step of preparing the pro-catalyst as described above, prior to contacting the pro-catalyst with an organoaluminum compound.

The catalyst composition can also comprise an external donor. In use, the external donor is added to the pro-catalyst at the same time as the organoaluminum co-catalyst. Examples of external electron donor compounds used in the polymerization herein include carboxylic esters, ketones, ethers, alcohols, lactones, organic phosphorus, and silicon compounds. The external donor can be an alkoxysilane. Preferred external donor compounds are organosilicon compounds e.g. dicyclopentyl dimethoxysilane, di-isopropyl dimethoxysilane, di-isobutyl dimethoxysilane, methylcyclohexyl dimethoxysilane, n-propyl trimethoxysilane, n- propyltriethoxysilane. An exemplary external donor is dicyclopentyldimethoxysilane.

Thus the pro-catalyst of the invention can be used to prepare a catalyst composition suitable for polymerizing olefin monomers comprising contacting the pro-catalyst of the invention with an organoaluminum compound, and, optionally, an external donor.

In another aspect, the invention provides for the use of the pro-catalyst of the invention for the polymerization of olefin monomers. Thus, the invention provides for the use of a pro-catalyst as described herein for the polymerization of olefin monomers. In particular, the invention provides for the use of the pro-catalyst of the invention in the preparation of highly stereo regular polypropylene in the polymerization of olefin monomers. For example the pro-catalyst can be used to prepare polypropylene having a mmmm content of at least 95 %.

Thus in another aspect, the invention provides for a process for preparing a polyolefin comprising polymerizing olefin monomers in the presence of a catalyst composition as described herein, i.e. a catalyst composition comprising the pro-catalyst of the invention, a co catalyst comprising an organoaluminum compound, and, optionally, an external donor.

The process maybe continuous, semi-continuous or batch, but it is preferably a continuous process. Preferably, the polymerization occurs in a bulk reactor, i.e. it is a bulk polymerization.

The polymerization can be carried out in a conventional manner using conventional conditions. Preferably the homopolymerisation of propylene occurs in a bulk reactor, i.e. in a bulk polymerisation. Optionally the bulk polymerisation is carried out in several reactors, e.g. 1, 2 or 3 reactors. The conditions may be the same or different in each reactor. Optionally, the process may also comprise a pre-polymerisation step which precedes the first polymerisation step. Any pre-polymerisation step is carried out in a conventional manner.

The polymerisation of the propylene homopolymer is preferably carried out at a temperature of 65-80 °C and more preferably about 70 °C. Preferably the polymerisation is carried out at a pressure of 0.1-4.5 MPa, more preferably 2.9-4.2 MPa and still more preferably 3.3-4.2 MPa. Preferably the polymerisation time is 5-240 minutes, more preferably 30-130 minutes and still more preferably 40-80 minutes. Hydrogen may be added to control the molar mass in a manner known in the art.

The polymerisation to prepare an impact copolymer polypropylene typically involves a multistage process. Each stage may be carried out in the same reactor or in a separate reactor. The process may be continuous, semi-continuous or batch but is preferably a continuous process. A preferred process for preparing the impact copolymer polypropylene of the present invention comprises (e.g. consists essentially of): (i) polymerising propylene and optionally an olefin monomer to obtain the propylene homopolymer or copolymer matrix; and (ii) polymerising propylene and ethylene in the presence of the propylene homopolymer or copolymer matrix to obtain the ethylene propylene rubber phase dispersed in the propylene homopolymer or copolymer matrix.

The polymerisation of the ethylene propylene rubber phase is preferably carried out at a temperature of 65-80 °C and more preferably about 70 °C. Preferably the polymerisation is carried out at a pressure of 0.1-2.2 MPa, more preferably 1-1.6 MPa and still more preferably 1-1.3 MPa.

Typically olefin monomers are selected from the group consisting of ethylene, propylene, butylene and isoprene monomers. A mixture of two or more different olefin monomers can be used, resulting in a copolymer. Preferably, the olefin monomers comprise propylene monomers.

Typically the polyolefin is selected from the group consisting of polyethylene, polypropylene, polybutylene and polyisoprene. Preferably the polyolefin is polypropylene. Preferably the polyolefin is a propylene homopolymer. In one embodiment, the polyolefin is a copolymer. The polyolefin can be an impact copolymer polypropylene. In the following section, further advantages and features of the invention are illustrated by way of examples.

EXAMPLES

Materials

All starting materials were commercially available.

Measurement method

The following describes the property testing of the catalyst composition/system of the present invention. The test methods and equipment employed are conventionally used and are not intended to limit the scope of the invention.

The amounts of internal donor (ID) and modifier (M) in the pro-catalyst are measured using H-NMR.

The amount of Ti and Mg in the pro-catalyst is measured using ICP (inductively coupled plasma) mass spectroscopy.

Productivity (kgPolymer/gCat) as used in the present description means: the amount of kilograms of polymer produced per gram of pro-catalyst consumed in the polymerization reactor per hour, unless stated otherwise. For polypropylene, the units of productivity are referred to as kgPP/gCat.

Melt flow rate (MFR) was determined according to ASTM D1238-13 at 230°C 2.16 kg. 2.16 kg is the load used when measuring the MFR.

Xylene solubles (XS) are measured according to ASTM D5492-10 (Standard Test Method for Determination of Xylene Solubles in Propylene Plastics). As used herein, the terms “xylene solubles”, “XS” and “xylene soluble fraction” are interchangeable. The xylene soluble fraction approximately correlates to the amorphous (atactic) fraction in the polypropylene. mmmm and mrrm are measured by ¹³C-NMR spectroscopy using a Bruker Ascend 500 NMR spectrometer, with a ¹³C resonance frequency of 100.4 MHz. mmmm represents the degree of isotacticity of the polypropylene and mrrm represents the degree of atacticity of the polypropylene. These are given as a % by mol of the polypropylene and represent the integrated area of the specific peak divided by the in integrated area of the total peaks mmmm and mrrm are determined according to the methods described in “High-Resolution ¹³C NMR Configurational Analysis of Polypropylene Made with MgCh- Supported Ziegler-Natta Catalysts. 1. The “Model” System MgCl2/TiCU-2,6-Dimethylpyridine/Al(C2H5)3”, Busico el ah, Macromolecules 1999, 32, 4173-4182.

The particle characteristics are defined by a DIO, D50 and D90 which are the cumulative number-based particle size at 10%, 50% and 90%, respectively. In this context the term “size” equates to diameter. The diameter measured is the largest diameter of the particles. These values were acquired from SEM images taken over 500 particles using image processing software.

The average ratio (1/w) of the major axis diameter (1) to the minor axis diameter (w) of magnesium alkoxide is obtained by photographing the magnesium alkoxide particles with a scanning electron microscope at a magnification such that 500 or more particles are displayed on one screen. After randomly extracting 500 particles from the photographed particles, and measuring the major axis diameter (1) and minor axis diameter (w) of each particle with image analysis processing software, the ratios of 1/w are calculated. The average 1/w is the average of the 1/w values measured for 500 particles.

Examples 1 and 2

Synthesis of Solid Pro-Catalyst Component - Pro-Catalyst 1

Magnesium ethoxide used for preparation of solid pro-catalyst has D50 of 35 micron and an average ratio (1/w) of the major axis diameter (1) to the minor axis diameter (w) of 1 - 1.5.

A flask with internal volume of 1000 mL and equipped with an overhead stirrer is thoroughly purged with anhydrous nitrogen. To this flask, 10 g of magnesium ethoxide, 60 mL of toluene, 40 mL of titanium tetrachloride, 3.6 g of 9,9-bis(methoxymethyl)fluorene and 0.64 g of N,N- dimethylbenzamide were introduced to form a suspension at -5 "C. Each component was added under the flow of anhydrous nitrogen. After all the components were added, all valves to the reactor were closed to keep the pressure in the reactor at a little bit higher than atmospheric pressure. The temperature of the suspension was gradually raised to 110 °C, and the suspension was maintained at this temperature for 2 hours with stirring. At this point the reaction had finished and the resulting solid was washed four times with 100 mL of toluene at 100 "C. Then, to a flask containing the resulting solid, 50 mL of toluene and 20 mL of titanium tetrachloride were added. The solid was heated to 110 "C and stirred at this temperature for 30 minutes. The resulting solid was allowed to settle and the supernatant was removed. The above operation was repeated twice and after that the solid was washed six times with 100 mL of toluene at 100 °C. The solid was further washed twice with 100 mL of hexane at 70 "C and the solid pro-catalyst was obtained by solid-liquid separation. The amounts of magnesium, 9,9- bis(methoxymethyl)fluorene and N,N dimethyl benzamide present in the pro-catalyst were determined according to the methods described above.

Propylene Bulk Polymerization

The pro-catalyst performance in propylene polymerization was tested in 2.4 L reactor. The reactor was preheated at 100 "C for 2 hours under nitrogen flow to remove contaminating moisture and oxygen. After that, the reactor was cooled to 25 °C, and 1000 g of liquid propylene was fed into the reactor. In a separate 10 mL stainless steel bomb, the solid pro-catalyst, Pro- Catalyst 1, was pre-contacted with triethylaluminum (1M in hexanes) with (Example 1), or without (Example 2), an external electron donor, dicyclopentyl dimethoxy silane (D donor). For Example 1, the mole ratio of Ti/Al = 1/200. For Example 2, the mole ratio of Ti/Al/Si = 1/200/20. The mixture in the 10 mL stainless steel bomb was flushed into the reactor using high pressure nitrogen. As a pre-polymerization step, the reactor was held at 25 "C for 10 minutes. After that the reaction temperature was increased to 70 "C and held at this temperature for 1 hour to complete the polymerization. The polymer was evaluated for melt flow rate (MFR), xylene solubles (XS%), and mmmm % using ¹³C NMR. The productivity of catalyst was measured. The results are reported in Table 1.

Examples 3 and 4

Synthesis of Solid Pro-Catalyst Component - Pro-Catalyst 2

The solid pro-catalyst preparation for Pro-Catalyst 2 was carried out in the same manner as for Pro-Catalyst 1 , except that 1.1 g of N,N-dimethylbenzamide was used instead of 0.64 g of N,N- dimethylbenzamide .

Propylene Bulk Polymerization

Propylene bulk polymerization for Examples 3 and 4 was carried out in the same manner as described for Examples 1 and 2, respectively, except that Pro-Catalyst 2 was used instead of Pro-Catalyst 1. The solid pro-catalyst, Pro-Catalyst 2 was pre-contacted with triethylaluminum (1M in hexanes) with (Example 3) or without (Example 4) an external electron donor, dicyclopentyl dimethoxysilane (D donor). For Example 3, the mole ratios of Ti/Al = 1/200. For Example 4, the mole ratios of Ti/Al/Si = 1/200/20. The results are summarized in Table 1.

Example 5

Synthesis of Solid Pro-Catalyst Component - Pro-Catalyst 3

The solid pro-catalyst preparation was carried out in the same manner as for Pro-Catalyst 1, except that 3 g of 9,9-bis(methoxymethyl)fluorene was used instead of 3.6 g of 9,9- bis(methoxymethyl)fluorene and 2.6 g of N,N-dimethylbenzamide was used instead of 0.64 g of N,N di methyl benzamide.

Propylene Bulk Polymerization

Propylene bulk polymerization was carried out in the same manner as described in Example 1 except that Pro-Catalyst 3 was used instead of Pro-Catalyst 1. The polymerization was carried out using an external electron donor, dicyclopentyl dimethoxysilane (D donor). The mole ratios of Ti/Al/Si = 1/200/20.

Example 6

Synthesis of Solid Pro-Catalyst Component - Pro-Catalyst 4

The solid pro-catalyst preparation was carried out in the same manner as for Pro-Catalyst 1 except that 2 g of 9,9-bis(methoxymethyl)fluorene was used instead of 3.6 g of 9,9- bis(methoxymethyl)fluorene and 2 g of N,N-dimethylbenzamide was used instead of 0.64 g of N,N di methyl benzamide.

Propylene Bulk Polymerization

Propylene bulk polymerization was carried out in the same manner as described in Example 1 except that Pro-Catalyst 4 was used instead of Pro-Catalyst 1. The polymerization was carried out using an external electron donor, dicyclopentyl dimethoxysilane (D donor). The mole ratios of Ti/Al/Si = 1/200/20.

Comparative Examples 1 and 2

Synthesis of Solid Pro-Catalyst Component - Comparative Pro-Catalyst 1

The solid pro-catalyst preparation was carried out in the same manner as for Pro-Catalyst 1, except that N,N-dimethylbenzamide was not introduced in to the reactor to make the solid catalyst component. Propylene Bulk Polymerization

Propylene bulk polymerization was carried out for Comparative Examples 1 and 2 in the same manner as described for Examples 1 and 2, respectively, except that Comparative Pro-Catalyst 1 was used instead of Pro-Catalyst 1. The results are summarized in Table 1.

Table 1

1. This M/ID is the molar ratio of the modifier N,N-dimethyIbenzamide to the internal donor 9,9-bis(methoxymethyl)fluorene in the mixture used to prepare the pro catalyst.

2. This M/ID ratio refers to the molar ratio of the components (M = N,N-dimethylbenzamide, ID = 9,9-bis(methoxymethyl)fluorene and Mg = magnesium) in the pro catalyst itself, determined using H-NMR.

The results of Table 1 show that pro-catalysts of the present invention, which are prepared using N,N-dimethylbenzamide as a modifier and 9,9-bis(methoxymethyl)fluorene as an internal donor, exhibit excellent stereoselectivity when used to polymerize propylene. Indeed, the results show that the use of the modifier and the internal donor in the pro-catalysts of the invention can result in an improvement in isotacticity of polypropylene prepared using the pro catalysts. In particular, a significant improvement in isotacticity of the polypropylene prepared was observed, while the productivity and MFR were still preserved at high values, due to the use of the benzamide modifier in the pro-catalyst.

For example, it can be seen from Table 1 that the xylene soluble fraction decreases from 8.49 wt% for Comparative Example 1, to 2.47 wt% for Example 1, and to 2.15 wt% for Example 3. This correlates with an increase in the amount of N,N-dimethyl benzamide modifier loading of 0 for the catalyst of Comparative Example 1, to that which gives an M/ID value of 0.059 for the pro-catalyst of Example 1 and 0.095 for the pro-catalyst of Example 3. The results also show that this improvement in isotacticity of the polypropylene is not due to the use of the external donor in the polymerization reaction. Even when an external donor is used, an increase in isotacticity is observed that can be attributed to the N,N-dimethyl benzamide modifier. The xylene soluble fraction decreases from 3.31 wt% for Comparative Example 2, to 1.95 wt% for Example 2, and to 1.83 wt% for Example 4. This correlates with an increase in the amount of N,N-dimethyl benzamide modifier loading of 0 for the pro-catalyst of Comparative Example 2, to that which gives an M/ID value of 0.059 for the pro-catalyst of Example 2 and 0.095 for the pro-catalyst of Example 4.

In contrast, further increasing the N, N dimethyl benzamide modifier content to give an M/ID value of 0.441 for the pro-catalyst of Example 6 leads to a lower isotacticity. The xylene soluble fraction increases to 2.79 wt%. Not wishing to be bound to any theory, fine particles were found in this polymer and it is believed that they might be caused from a part of the Mg alkoxide support dissolving in N, N dimethyl benzamide.

Therefore, this invention relates to the development of a Ziegler-Natta pro-catalyst which has a diether as an internal donor and which can be used to obtain highly isotactic polypropylene. In particular, it has been found that N,N dimethyl benzamide can be used to improve and optimize the isotacticity obtained, while catalyst productivity and MFR is preserved at the high values found for the diether-based pro-catalyst.

Claims

1. A method for preparing a pro-catalyst comprising a transition metal, Mg, a halogen, a modifier and an internal donor, wherein the method comprises (i) contacting a halide of the transition metal and a magnesium alkoxide to provide a solid reaction product comprising the transition metal supported on a magnesium halide -based support, and (ii) contacting the solid reaction product with the internal donor and the modifier, wherein the modifier is of formula (I)

where Ri and R₂ are each independently hydrogen or an alkyl group having 1 to 6 carbon atoms, and R₃, R₄, Rs, R₆, and R₇ are each independently selected from hydrogen, a heteroatom or a hydrocarbyl group.

2. The method according to claim 1, wherein the contacting of the halide of the transition metal with the magnesium alkoxide to provide a solid reaction product is carried out at least in part in the presence of the internal donor and, optionally, at least in part in the presence of the modifier.

3. The method according to claim 1 or claim 2, wherein the method comprises a further step of contacting the solid reaction product comprising the internal donor and the modifier obtained from (i) and (ii) with the halide of the transition metal.

4. The method according to any one of the preceding claims, wherein the magnesium alkoxide comprises particles having an average ratio (1/w) of the major axis diameter (1) to the minor axis diameter w of 3 or less.

5. The method according to any one of the preceding claims, wherein the magnesium alkoxide comprises particle having an average particle diameter D50 of 1 to 100 or 5 to 80 micron.

6. The method according to any one of the preceding claims, wherein the magnesium alkoxide has the formula MgORnORn, where Rn and Rn are independently a hydrocarbyl group containing from 1 to 6 carbon atoms.

7. The method according to any one of the preceding claims, wherein the transition metal is chosen from titanium, chromium, hafnium, zirconium and vanadium and/or the halide is chosen from chloride, bromide and iodide.

8. The method according to any one of the preceding claims, wherein the halide of the transition metal is a titanium chloride.

9. The method according to any one of the preceding claims, wherein the internal donor is a di-ether compound.

10. The method according to any one of the preceding claims, wherein the amounts of internal donor and modifier used are chosen so as to provide a molar ratio of modifier of formula (I) to internal donor of from 0.01 to 0.5 or 0.04 to 0.50 in the pro-catalyst.

11. A pro-catalyst comprising a transition metal, Mg, a halogen, a modifier and an internal donor, obtained or obtainable by the method of any one of claims 1 to 10.

12. The pro-catalyst according to claim 11, wherein the catalyst comprises particles having an average particle diameter D50 of 1 to 100 or 5 to 80 micron.

13. The pro-catalyst according to claim 11 or claim 12, wherein the molar ratio of the modifier of formula (I) to internal donor in the pro-catalyst is from 0.04 to 0.50, 0.04 to 0.18 or 0.17, 0.04 to 0.12 or 0.05 to 0.10 or 0.01 to 0.5.

14. The pro-catalyst according to any one of claims 11 to 13, wherein the modifier is present in an amount of 0.25 to 2.0 wt% based on the total weight of the pro-catalyst and/or the internal donor is present in an amount of 15 to 25 wt% based on the total weight of the pro-catalyst, or the modifier is present in an amount of 0.1 to 2.0 wt% based on the total weight of the pro-catalyst and/or the internal donor is present in an amount of 15 to 28 wt% based on the total weight of the pro-catalyst..

15. The pro-catalyst according to any one of claims 11 to 14, wherein the magnesium alkoxide is magnesium ethoxide, the modifier is N,N-dimethylbenzamide, the internal donor is 9,9- bis(methoxymethyl)fluorene and the molar ratio of modifier to internal donor is from 0.05 to 0.10.

16. A catalyst composition for the polymerization of polyolefins comprising: the pro-catalyst according to any one of claims 11 to 15; and a co-catalyst, wherein the co-catalyst comprises an organoaluminum compound.

17. The catalyst composition according to claim 16, wherein the organoaluminum compound is chosen from trimethylaluminum, triethylaluminum, triisobutylaluminum, trioctylaluminum and methyldiethylaluminum.

18. The catalyst composition according to claim 16 or claim 17, further comprising an external donor, preferably chosen from carboxylic esters, ketones, ethers, alcohols, lactones, as well as organic phosphorous and silicon compounds.

19. The catalyst composition according to any one of claims 16 to 18, wherein the pro-catalyst is according to claim 15, the organoaluminum compound is trialkyl aluminum and wherein the composition comprises dicyclopentyl dimethoxysilane.

20. Use of a pro-catalyst according to any one of claims 11 to 15 or a catalyst composition according to any one of claims 16 to 19, for polymerizing olefin monomers.

21. A process for preparing a polyolefin comprising polymerizing olefin monomers in the presence of a catalyst composition according to any one of claims 16 to 19.

22. The use of claim 20 or the process of claim 21, wherein the olefin monomers comprise propylene monomers.

23. The process of claim 21, wherein the polyolefin is polypropylene or impact copolymer polypropylene.