PROCESS FOR PREPARING THE SAME

TECHNICAL FIELD

The present invention relates to a process for preparing olefin polymerization catalyst, and an olefin polymerization catalyst. Preferably, this olefin polymerization catalyst is used for the production of high density polyethylene (HDPE) with an improvement of comonomer response and comonomer distribution.

BACKGROUND OF THE INVENTION

Ziegler-Natta catalysts have been used for olefin polymerization such as polyethylene, polypropylene, etc. due to their benefits of providing a high molecular weight, high melting point, and controllable morphology of polymers. It's been known that the synthesis method and the catalyst compositions are important for the nature of active species and the performances of the catalyst. In general, the chemical route for preparation process of Ziegler- Natta catalyst comprises the step of: (i) preparation of magnesium compound suspension, (ii) titanation with ΤΚ¾, and (iii) pre-activation with aluminum alkyl at the elevated temperature.

In specific applications, it is necessary to use polymer having specific properties. For example, the high density polyolefin film produced by extrusion blow process requires polyolefin raw material with low gel content. Typically, factors affecting gel content are, for example, polymer's molecular weight, amount of unmelted particles (i.e. agglomeration of additives), degree of crosslinking, and so on. It's found that the titanium (Ti) oxidation state of the catalysts, especially Ti(II) and Ti(III), normally affects molecular weight of polyolefin fractions, i.e. greater percentage of Ti(II) and Ti(III) content providing higher molecular weight polyolefin fractions.

To obtain specific properties of polyolefin such as morphology, molecular weight, stereoregularity, and etc., the special steps, conditions, and chemicals are required for preparing the catalysts.

US Patent No. 5,292,837 discloses the process of Ziegler-Natta catalyst preparation and the process of (co)polymerization of ethylene to obtain a large particle size polyethylene with a narrow particle size distribution and high bulk density. The catalysts are prepared by reducing the fraction of Ti(III)-containing catalyst obtained from the reaction of magnesium alkoxide, tetravalent transition-metal compound, and organoalurninum compound with metal halides, in particular T1CI .

EP Patent No. 0 319 913 Bl discloses the process of olefin polymerization in the presence of a catalyst obtained from the specific components. The catalyst is obtained from a reaction of dialkoxymagnesium, organic acid ester, and silicon compound; then reacting the reaction product with titanium tetrahalide. The catalyst product consumes shorter time to reach a high polymerization activity and can produce the polyolefin with a high stereoregularity polypropylene.

EP 0 123 245 discloses the polymerization of olefins and catalyst. The catalyst can be prepared from the reaction of the first catalyst component, organoalurninum halide and halogenating agent comprised a titanium halide. The first catalyst component is obtained from the first mixing between a magnesium dihalide - alkanol adduct, and an alkoxytitanium compound (such as Ti(OR) ₄ ) under stirring at 90-100°C and then reacting the resulting product with benzoic acid ester or the combination of benzoic acid ester and phenol. SUMMARY OF THE INVENTION

In one aspect, this invention relates to a process for preparing a catalyst for olefin polymerization comprising

(a) preparing magnesium ethoxide (Mg(OEt) ₂ ) suspension in hydrocarbon medium;

(b) adding an electron donor in Mg(OEt) ₂ suspension and mixing at ambient temperature for utmost 24 hours;

(c) heating the mixture obtained from (b) to 70-90°C before adding a transition metal compound of one of transition metal groups IV to VI in the Periodic Table of Element with mixing for at least 4 hours;

(d) heating the reaction mixture obtained in step (c) to 100-120°C and mixing for 1-4 hours, then cooling said reaction mixture to 50-65°C; and

(e) adding aluminum alkyl or aluminum alkyl halide into said reaction mixture obtained in step (d), then heating said mixture to 80-100°C for 1-4 hours.

In some embodiments, transition metal compound is selected from titanium tetrachloride (TiC ), vanadium tetrachloride (VC ), zirconium tetrachloride (ZrC ) or hafnium tetrachloride (HfC ).

In some embodiments, said hydrocarbon medium is selected from hexane, heptane, octane, nonane, n-decane or white spirit. In some embodiments, said aluminum alkyl or aluminum alkyl halide is selected from a group consisting of ethyl aluminum chloride (EADC), diethylaluminum chloride (DEAC), ethyl aluminum sesquichloride (EASC), and triethyl aluminum chloride (TEA).

In some embodiments, said electron donor is selected from a group consisting of ethyl benzoate, propyl benzoate, butyl benzoate, pentyl benzoate, hexyl benzoate, and a combination thereof.

In another aspect, this invention relates to an olefin polymerization catalyst, which is prepared from the above-mentioned process, wherein the catalyst comprises titanium (Ti), magnesium (Mg), aluminum (Al), and electron donor.

In some embodiments, the olefin polymerization catalyst contains Ti content is in a range of 5-8%wt based on the total weight of catalyst.

In some embodiments, the olefin polymerization catalyst have the percentage of preactivation less than 80%, preferably in a range of 60-80%, more preferably in a range of 65-75%.

In some embodiments, the olefin polymerization catalyst contains electron donor content is in a range of 8-12%wt based on the total weight of catalyst.

In some embodiments, the olefin polymerization catalyst has a particle size in a range of 7-13 μπι.

The object of this present invention is to provide the catalyst for the production of olefin polymerization with an improvement of comonomer and hydrogen response, high catalytic activity, and comonomer distribution.

Another object of this present invention is to provide an efficient catalyst for producing olefin polymer, especially high density polyethylene (HDPE) with low gel content, and good chemical composition distribution. The high density polyethylene produced by this inventive catalyst is suitable for injection, extrusion, and blow moulding process.

Additionally, the object of the present invention is to provide a catalyst for olefin polymerization by using the specifically sequential step of preparation in order to control the titanium content with oxidation state of Ti(III) and reduce the dimeric form of transition metal compound such as TiC - This process is recognized as an environmental friendly process of catalyst production for producing olefin polymer. BRIEF DESCRIPTION OF THE DRAWINGS

DETAILED DESCRIPTION

In the first aspect, the present invention relates to a process for preparing a catalyst for olefin polymerization comprising

(a) preparing magnesium ethoxide (Mg(OEt) ₂ ) suspension in hydrocarbon medium;

(b) adding an electron donor in Mg(OEt) ₂ suspension and mixing at ambient temperature for utmost 24 hours;

(c) heating the mixture obtained from (b) to 70-90°C before adding a transition metal compound of one of transition metal groups IV to VI in the Periodic Table of Element with mixing for at least 4 hours;

(d) heating the reaction mixture obtained in step (c) to 100-120°C and mixing for 1-4 hours, then cooling said reaction mixture to 50-65°C; and

(e) adding aluminum alkyl or aluminum alkyl halide into said reaction mixture obtained in step (d), then heating said mixture to 80-100°C for 1-4 hours.

It is apparent that the specific step of mixing electron donor together with magnesium ethoxide suspension before the chemical reaction between the mixture and the transition compound as defined above results in better homogeneity of electron donor dispersion on magnesium ethoxide. This contributed to the specific of transition metal coordination. The specific coordination between electron donor and transition metal provided the longer mileage of catalyst and resulting in high yield.

In some embodiments, the magnesium ethoxide suspension was mixed with electron donor for hydrogen response as well as stereocontrol for higher alpha olefin polymerization at ambient temperature for utmost 24 hrs. The preferred time period is 10-24 hrs.

In some embodiments, the transition metal compound used in this invention is selected from titanium tetrachloride (TiCL _t ), vanadium tetrachloride (VC ), zirconium tetrachloride (ZrCLt) or hafnium tetrachloride (HfCk). The preferred transition metal compound is titanium tetrachloride (TiC ).

In some embodiments, the hydrocarbon medium used in this invention is selected from hexane, heptane, octane, nonane, n-decane, or white spirit. The preferred hydrocarbon medium is n-decane or white spirit (Exsol D80X). In some embodiments, the electron donor used in this invention is selected from a group consisting of ethyl benzoate, propyl benzoate, butyl benzoate, pentyl benzoate, hexyl benzoate, and a combination thereof. Preferably, the electron donor is propyl benzoate.

In the preferred embodiment, the advantage of propyl benzoate as electron donor is useful for the hydrogen response optimization of the catalyst. This parameter is very crucial for polymerization operating control and polymer properties consistency.

In some embodiments, the aluminum alkyl or aluminum alkyl halide is selected from a group consisting of ethyl aluminum chloride (EADC), diethylaluminum chloride (DEAC), ethyl aluminum sesquichloride (EASC), triethyl aluminum chloride (TEA), and a combination thereof. Preferably, the mi um alkyl or aluminum alkyl halide is ethyl alurninum sesquichloride.

In the preferred embodiment, the mixing time in step (b) is in a range of 10-12 hours.

In the preferred embodiment, the heating temperature in step (c) is at 80-90°C.

In the preferred embodiment, the heating temperature and mixing time in step (d) is at 100-110°C, and 2-3 hours, respectively.

In the preferred embodiment, a molar ratio of Ti/Mg and electron donor/Mg is in a range of 0.22 - 0.27, and 0.10 - 0.30, respectively.

In some embodiment, a molar ratio of EASC/Ti is in a range of 1.50 - 2.50, preferably in a range of 1.80 - 2.00.

In the preferred embodiment, a molar ratio of electron donor/Ti is in a range of 0.5-1.0.

In the preferred embodiment, a particle size of said Mg(OEt) ₂ is in a range of 4 - 6 μι ^η .

In the second aspect, the present invention also relates to an olefin polymerization catalyst prepared from the above mentioned process comprising titanium (Ti), magnesium (Mg), aluminum (Al), and electron donor.

In some embodiments, the olefin polymerization catalyst contains Ti content is in a range of 5-8%wt based on the total weight of catalyst.

In some embodiments, the olefin polymerization catalyst have the % of preactivation is less than 80%, preferably in a range of 60-80%, more preferably in a range of 65-75%). The percentage of catalyst preactivation relates to a ratio of Ti(III) to total Ti content in catalyst.

In some embodiments, the electron donor used in this invention is selected from a group consisting of ethyl benzoate, propyl benzoate, butyl benzoate, pentyl benzoate, hexyl benzoate, and a combination thereof. Preferably, the electron donor is propyl benzoate. The preferred electron donor content in the olefin polymerization catalyst is in a range of 8-12%wt based on the total weight of catalyst.

In some embodiments, the olefin polymerization catalyst has a particle size in a range of 7 - 13 μηχ

The nature of catalyst is basically important for both olefin polymerization operation and polymer properties. Poor morphology of catalyst particles usually causes poor morphology of polymer powder and problems of polymerization processing control such as high fine powder content, drying process efficiency, powder transportation, etc. In addition, some catalyst may cause high wax content in mother liquor. Beside this invention, it is true that the synergy of specific electron donor and active species control of this catalytic system does not only minimize the gel formation of polyethylene by reducing high molecular weight fraction but also enhances the comonomer incorporation of copolymerization as well.

Other features of the invention will become apparent in the course of the following description of exemplary embodiments which are given for illustration of the invention and are not intended to be limiting thereof.

Example

Preparation of Catalyst

Example 1 - Preparation of the comparative catalyst C

28.5 g (0.25 mole) of magnesium ethoxide suspended in 450 ml of Exsol D80X was transferred into 1.5 liters glass reactor equipped with a two-blade impeller under inert gas blanketing. The suspension was stirred at ambient temperature with stirring speed of 150 rpm for 10 hours, and then allowed it to form a gel-liked magnesium ethoxide for 1 hour. The gel- liked magnesium ethoxide was heated up to a temperature of approximately 85°C under stirring at approximately 250 rpm. 8.25 ml (0.075 mole) of T1CI4 was added into the reaction over a duration of 4 hours. After that, the reaction mixture of TiC and gel-liked magnesium ethoxide was heated up to 110°C and stirred for further 2 hours before cooling down the reaction to 60-65 °C. Subsequently, the solution of 0.175 mole of ethyl aluminum sesquichloride (EASC) diluted in hexane was slowly added to the reaction mixture. The reaction mixture was then heated up to 100°C with stirring speed of approximately 250 rpm for 2 hours. Finally, the reaction mixture was cooled down to room temperature and drained to a conical flask under inert gas blanketing to collect the solid catalyst. Example 2 - Preparation of the catalyst Al

28.5 g (0.25 mole) of magnesium ethoxide suspended in 450 ml of Exsol D80X was transferred into 1.5 liters glass reactor equipped with a two-blade impeller under inert gas blanketing. The suspension was stirred at ambient temperature with stirring speed of 150 rpm for 10 hours, and then allowed it to form a gel-liked magnesium ethoxide for 1 hour. The gel- liked magnesium ethoxide was heated up to a temperature of approximately 85 °C under stirring at 250 rpm. 8.25 ml (0.075 mole) of T1CI4 was added into the reaction over 4 hours. After that, the reaction mixture of T1CI4 and gel-liked magnesium ethoxide was heated up to 110°C and stirred for further 2 hours before cooling down the reaction to 60-65°C. Subsequently, the solution of 0.175 mole of ethyl aluminum sesquichloride diluted in hexane (10 wt%) was slowly added to the reaction mixture. The reaction mixture was then heated up to 100°C and stirred at 250 rpm for 2 hours. Then, 5.4 ml (0.03 mole) of ethyl benzoate was added into to the reaction mixture, and heated to 60°C with stirring for 2 hours. Finally, the reaction mixture was cooled down to room temperature and the catalyst product was drained to a conical flask under nitrogen atmosphere blanketing.

Example 3 - Preparation of the catalyst A2

28.5 g (0.25 mole) of magnesium ethoxide suspended in 450 ml of Exsol D80X was transferred into 1.5 liters glass reactor equipped with a two -blade impeller under inert gas blanketing. 5.4 ml (0.063 mole) of ethyl benzoate was added to the suspension followed by stirring speed of 150 rpm for approximately 10 hours at ambient temperature, and then allowed it to form a gel-liked magnesium ethoxide for 1 hour. The gel-liked magnesium ethoxide was heated up to a temperature of approximately 85 °C under stirring at approximately 250 rpm. 6.97 ml (0.063 mole) of TiC was added into the reaction over a duration of 4 hours in order to create the molar ratio of electron donor/Ti of 0.6. After that, the reaction mixture of TiC and gel-liked magnesium ethoxide was heated up to 100°C and stirred for further 2 hours before cooling down the reaction to 60-65°C. Subsequently, the solution of ethyl aluminum sesquichloride (EASC) diluted in hexane was slowly added to the reaction mixture. The molar ratio of EASC/Ti is 2.0. The reaction mixture was then heated up to 100°C with stirring speed of approximately 250 rpm for 2 hours. Finally, the reaction mixture was cooled down to room temperature and drained to a conical flask under inert gas blanketing to collect the solid catalyst. Example 4 - Preparation of the catalyst A3

The catalysts A3 was prepared by mean of the preparation of catalyst A2, with the exception that, 10 ml (0.07 mole) of ethyl benzoate and 6.97 ml (0.063 mole) of TiCU was used to create the molar ratio of electron donor/Ti of 1.1. Example 5 - Preparation of the catalyst A4

The catalysts A4 was prepared by mean of the preparation of catalyst A2, with the exception that, 8 ml (0.056 mole) of ethyl benzoate and 6.97 ml (0.063 mole) of TiCU was used to create the molar ratio of electron donor/Ti of 0.89.

Example 6 - Preparation of the catalyst A5

The catalysts A5 was prepared by mean of the preparation of catalyst A4, with the exception that, the preactivation with EASC was performed at 80°C.

Example 7 - Preparation of the catalyst A6

The catalysts A6 was prepared by mean of the preparation of catalyst A5, with the exception that, 6.02 ml (0.075 mole) of n-propyl benzoate and 7.25 ml (0.075 mole) of TiCU was used to create the molar ratio of electron donor/Ti of 1.0.

Example 8 - Preparation of the catalyst Bl

28.5 g (0.25 mole) of magnesium ethoxide suspended in 450 ml of Exsol D80X was transferred into 1.5 liters glass reactor equipped with a two-blade impeller under inert gas blanketing. 5.4 ml (0.063 mole) of ethyl benzoate was added to the suspension followed by stirring speed of 150 rpm for approximately 10 hours at ambient temperature, and then allowed it to form a gel-liked magnesium ethoxide for 1 hour. The gel-liked magnesium ethoxide was heated up to a temperature of approximately 85°C under stirring at approximately 250 rpm. 8.25 ml (0.075 mole) of TiCU was added into the reaction over a duration of 4 hours. After that, the reaction mixture of TiCU and gel-liked magnesium ethoxide was heated up to 110°C and stirred for further 2 hours before cooling down the reaction to 60-65°C. Subsequently, the solution of 0.175 mole of ethyl aluminum sesquichloride (EASC) diluted in hexane was slowly added to the reaction mixture. The reaction mixture was then heated up to 100°C with stirring speed of approximately 250 rpm for 2 hours. Finally, the reaction mixture was cooled down to room temperature and drained to a conical flask under inert gas blanketing to collect the solid catalyst. Example 9 - Preparation of the catalyst B2

The catalysts B2 was prepared by mean of the preparation of catalyst Bl, with the exception that, 6.1 ml (0.038 mole) of n-propyl benzoate and 0.15 mole of EASC was used.

Example 10 - Preparation of the catalyst B3

The catalysts B3 was prepared by mean of the preparation of catalyst Bl, with the exception that, 6.1 ml (0.038 mole) of n-propyl benzoate was used to create the molar ratio of electron donor/Ti of 0.5. The mixture of propyl benzoate and Mg(OEt) ₂ was stirred overnight at ambient temperature before the titanation step. The pre-activation with EASC (0.15 mole) was performed at 80 °C. The molar ratio of EASC/Ti is 2.0.

The obtained catalysts were characterized by redox titration with Ce(IV) sulfate for determining Ti contents; by Atomic Absorption Spectroscopy (AAS) for deterrnining Mg, Ti and Al content; by Fourier transform Infrared Spectroscopy (FTIR) for deterrnining the amount of an electron donor; and by laser scattering technique for determining particle size of each of the catalysts.

Table 1 shows the analytical results of the obtained catalysts.

Table 1

Based on the total weight of prepared catalyst For the same TiC _. loading, it is noticable that the addition of electron donor, ethyl benzoate, results in a decrease of Ti content from 10%wt (catalyst C) to approximately 7.5%wt (catalysts A2-A6) whereas the post-treatment with the electron donor did not affect the Ti content of the final catalyst Al. The electron donor also influences on the degree of catalyst preactivation, i.e. the catalyst prepared in the presence of electron donor exhibited the less preactivation compared to one of absence of electron donor in the same condition. Besides, the preactivated degree decreased by decreasing temperature from 100°C to 80°C as well as lower ratio of EASC/Ti. The advantage of electron donor treatment on catalyst support is also to promote the specific active species which is believed to enhance comonomer response in copolymerization.

In Table 1, the catalyst prepared using ethyl benzoate, particularly catalysts A2 to A6, shows the lower percentage of preactivated degree due to the higher Ti(IV) species than the catalyst prepared without using the electron donor (catalyst C). In other words, the comonomer incorporation of catalysts A2 to A6 was better because the Ti(IV) species was active for a- olefin polymerization, while Ti(III) and Ti(II) exhibited the lower performance.

Polymerization of Ethylene

The polymerization of ethylene was performed in the presence of each of prepared catalysts in the 20 liters stainless steel reactor under two-stages of condition polymerization. The polymerization was carried out by using 1-butene as comonomer, triethylalurninum (TEA) as cocatalyst, H ₂ gas as the molecular weight controller.

For example, in the 1 ^st stage, the polymerization was performed in 14 liters of hexane medium under the condition of using 0.8 mmol of prepared catalyst; 50:50 of ethylene ratio of low molecular weight and high molecular weight fraction (EE ratio); 100 of TEA/Ti molar ratio; 5 bars of H ₂ pressure at 84°C for 40 min. The total pressure of this reaction stage is 8 bars. Subsequently, the H ₂ content in the reactor was removed by flashing off the mixed gas after termination of the polymerization at 60°C. The ventilation was done by diluting the off- gas with 5 bars of N ₂ gas for 10 times. In the 2 ^nd stage, the polymerization was continued by using 100 g of 1-butene feed and 50:50 of EE ratio R1:R2 at 73°C for 40 min. The total pressure of this reaction stage is approximately 3 bars. After the completion of polymerization, the reaction was cooled down and drained out the suspended powder. Subsequently, the polymer product was separated and dried in vacuum oven at 80°C for 3 h. The condition of both stages of polymerization shows in the Table 2 The catalyst activity was determined in term of obtained polymer weight per mmol of Ti fed in the unit of g PE/mmol Ti. Particle size of polymer product was determined by light scattering technique. Molecular weights (i.e. weight average molecular weight (Mw), number average molecular weight (Mn), viscosity average molecular weight (Mv) and Z-average molecular weight (Mz)), and molecular weight distribution (MWD) of the polymer were determined by High temperature gel permeation chromatography (HT GPC-IR) under the condition of 4 mg of polymer dissolved in 8 ml of trichlorobenzene (TCB) at 160°C. The short chain branching (SCB) of polymer was determined by Infrared detector with composition sensor integrated.

The gel content determination was performed by mixing the polymer powder with additives (0.2 phr of calcium stearate, 0.1 phr of Irganox 1010) and then melt mixing it in twin screw extruder (feed zone: 160°C, heating zone: 180-200°C, mixing zone: 200°C, screw conveying zone: 200°C, die zone 200°C). The polymer noodle was passed into the cooled water and pelletized. The gel content was evaluated after blow film extrusion at below 30 μηι film thickness. The film note value (FN) was determined by the in-house standard, whereas FN = 0-2 indicating the low gel content, FN= 3-4 indicating the high gel content, FN = 4-5 indicating the very high gel content and FN > 5 indicating the extremely high gel content.

Table 2 showed the activities of catalyst and analytical results of the prepared high density polyethylene (HDPE).

Table 2

Analytical results for Catalyst

prepared HDPE ³ C Al A2 A3 A4 A5 A6

Catalyst activity (g 10,000 12,000 10,000 10,000 10,000 12,000 10,000 PE/mmol Ti)

Mn (g/mol) 62,158 71,958 43,563 44,612 - - -

Mw (g/mol) 266,929 305,447 187,295 201,833 - - -

Mv (mol) 214,306 245,241 154,744 163,639 - - -

Mz (g/mol) 1,010,444 1,129,646 535,975 638,964 - - -

MWD 4.3 4.2 4.3 4.5 - - -

Density (g/cm ³ ) 0.945 0.942 0.945 - - 0.937 0.95

MFI ₅ (g/lOmin) ¹ 0.40 0.48 0.30 0.26 0.35 0.40 0.18

MFI5 (g/10min) ² 0.30 0.3.2 0.23 0.22 0.28 0.30 0.11 MFR 16.0 19.5 15.0 15.0 16.0 17.0 18.00

Comonomer content 2.70 2.79 2.78

(%wt)

FN number 4 1 1 2 1 1 1 powder

² pellet

³ The polymerization was performed in 14 liters of hexane medium under the condition of 0.8 mmol of Ti; Al/Ti ratio = 100; H ₂ = 5 bar; ethylene = 2 bar; blank pressure 1 bar; 1- butene fed ~ 100 g; total pressure of 1 ^st stage = 8 bar; total pressure of 2 ^nd stage= 3 bar; reaction time = 2 h.

In addition, the sequence of donor addition seemed to affect the polymer properties. The melt flow index ratio (MFI ₂₁ /MFIs, wherein MFI ₂₁ represents a melt flow index value using 2.16 kg of load and MFI ₅ represents a melt flow index value using 5 kg of load at 190 ^° C according to ASTM D1238) of polymer obtained from the catalyst prepared using ethyl benzoate before the titanation step (catalysts A2-A6) is in the range of 14-18, while the boarder value was found in the polymer obtained from the catalyst prepared using ethyl benzoate in the post-treatment (catalyst Al). The melt flow index (MFI ₅ ) of the polymer product obtained from all catalyst prepared by pre-treating with an electron donor before the titanation step is well- controlled in the range of polymer film grade.

The gel content in HDPE film was determined according to in-house standard method.

The results showed that the catalyst prepared by pre-treating with an electron donor before the titanation step can generate polymer product with low gel content (FN = 0-1) after conducting film application test. The excellence FN ranking indicated that the catalyst of this invention can improve the homogeneity of polymer compared to the unmodified one.

The high Mz value of the synthesized polymer represents a very high molecular weight fraction capable of forming unmelted polymer (gel formation). From the results, the HDPE obtained from the polymerization in the presence of catalysts A4 and A5 showed a significantly low Mz due to longer polymer chain length than others obtained from the catalysts C and Al . The effect of the molecular structure of electron donor on the chemical composition of catalyst and the properties of polymer product was observed as showed in Table 3. Table 3

Based on the total weight of prepared catalyst

² Based on the total weight of Ti species

³ The polymerization was performed under the condition of 0.01 mmol of Ti; Al/Ti ratio = 100; H ₂ = 0.2 bar; ethylene = 5.8 bar; 1-butene fed ~ 5 g; total pressure = 8 bar; reaction time = 2 h.

⁴ Powder

⁵ Pellet

The results showed the significant effect on the % preactivation and the content of Ti(III) species in the catalyst by propyl benzoate. This phenomenon might be caused by the molecular structure and bonding to catalyst and surface of catalyst precursor of different monoester. The lower content of Ti(III) species affected the gel content in the polymer film. Moreover, the activity of catalyst prepared by using propyl benzoate in the pre-treatment before the titanation step was also higher than one which prepared by using ethyl benzoate.