Effect of novel amido ester internal donor on the performance of Ziegler-Natta catalyst for propylene polymerization

Abstract

Various classes of molecules like diethers, succinates, diesters, amido esters are currently being used as internal donors on MgCl₂ supported titanium catalysts for isotactic polypropylene as an alternative to phthalate donors owing to their potential health risk laid down by REACH legislation. In the present paper, design and synthesis of a few novel amido ester internal donors with single chiral center (7–11) by mimicking the model amido ester 3 having two chiral centers; and their catalyst preparation method were described. Further preliminary polymerization tests with newly synthesized donor molecules were investigated and results revealed that by structurally mimicking 3 with one chiral center and also with varied substitutional patterns in ester/amido moiety decline the polypropylene activity as well as isotacticity. These donor molecules are ineffective for appropriate coordination on MgCl₂ sites on inducing steric hindrance for improved isotacticity; nevertheless also induces poisoning effect for the active Ti centers leading to catalyst fouling in many cases.

Keywords

Ziegler-Natta catalyst internal donors isotactic polypropylene

1 Introduction

Ziegler Natta (ZN) catalyst with MgCl₂ support is one of the most demanding catalysts for the industrial production of polyolefins especially Polypropylene (PP) [1 –3]. PP considering the largest demanded polyolefin due to their varied characteristic features like stiffness, transparency, impact resistance are generally applied for market segments like packaging materials, automotive, moulded products etc [4 –6]. Despite considerable attention being paved by researchers towards their development by the homogenous system, the industrial production of polyolefin was mainly triggered by a heterogeneous system. Many reports were well documented that improved stiffness (measuring isotacticity) of PP which was brought by the introduction of electron donors in the supported ZN system with MgCl₂ as support and TiCl₄ as catalytic center [7 –10]. MgCl₂ surface has two unsaturated acidic sites; stereospecific 104 plane and also 110 plane, which is aspecific and imparts atacticity PP [11 –13]. Two types of Lewis base (LB) electron donors played a significant role in improving the PP isotacticity (from 40% to nearly 98–99%) for the supported ZN system. The LB acting as an internal donor (ID) is typically added during the catalyst preparation and it is well understood that these donors co-adsorb nearby to open surface Ti leading to sufficient steric hindrance to Ti centers for enhancing the isotacticity by discriminating two enantiofaces of propene molecule in the insertion step [14 –16]. The other LB acting as an external donor (ED) is added during the polymerization process to cover the MgCl₂ sites where the ID leached out with strongly acidic co-catalyst (trialkyl aluminium) [17 –19].

Currently, industrial research on ID is mainly focusing on developing phthalate-free type PP catalysts since the PP from the phthalate class of donors is carcinogenic. In this regard, many classes of non-phthalate based IDs covering succinate esters [20 –22], diethers [23 –25], amido esters [26 –28], malonates [29, 30], glutarates [31], silyl diol esters [32] etc. are explored. It is observed that the catalyst with a different class of IDs prevails with varied features on the polymer formed. For example, diether bonds typically on 110 planes of MgCl₂ by chelating mode, and in general exhibits narrow molecular weight distribution(MWD) while the diester class of molecules tend to bind to both unsaturated 104 and 110 sites through bridging mode leading to medium MWD [33, 34]. Among the ester classes, amido ester 1 and diol diester 2 (Fig. 1) class of IDs were well explored by Dow and China Petroleum and Chemical Corporation respectively generating isotactic PP with broad MWD [28, 35]. Our recent study on representative compound 3 (Fig. 1) from amido benzoate showed very promising features in terms of PP activity and also isotacticity [27]. However, 1, 2, and 3 also bring broad MWD. The most probable underlying reason for this behaviour is the existence of an increased number of isomeric species (Fig. 2) bringing different stereo specific centers. However, this might not be done very promptly too, as achiral molecule from class 2 is also exhibiting broad MWD and one could manifest that generic nature of amido ester moiety would probably be the critical limit for exhibiting broad MWD. Owing to our curiosity in understanding how ID 3 behaves by slightly altering its backbone structure with fewer chiral centers (Fig. 2), a series of molecules were synthesized and evaluated for isotactic polypropylene (iPP) synthesis.

Fig. 1

Representative structure of internal donors 1, 2 and 3.

Fig. 2

Isomeric species of internal donors 3 and 7.

The paper also briefly described the supported ZN catalyst preparation with TiCl₄ and MgCl₂ support with the presented donors and subsequent evaluation for iPP.

2 Results and discussion

Our research on ID 3 was synthesized by three-step protocol [27] found to be existed in four different isomeric forms due to the presence of two chiral centers as revealed by analytical methods. These isomeric forms generate different stereogenic catalytic Ti centers, and more likely, these centers behave very different for polymer chain growth leading to broad MWD. Not every attempt to isolate isomeric species by laboratory method for understanding isomer’s behavioural pattern for propylene polymerization was successful. Being equipped with this underlying fact and hoping, if one could manifest with less number of chiral centers in amido benzoate structure, then more likely the candidate would generate less number of different stereospecific Ti centers; which in turn would probably help in narrowing MWD too. Thus, we remodified amido benzoate 3 with a single chiral center and five molecules were designed on this ground. In all the designed molecules, the chirality was placed at the carbon adjacent to the O-benzoate group, while keeping the second carbon adjacent to the amido group of propane as achiral. The effect of the introduction of substituents on the benzoyl group; typically with electron-donating/withdrawing groups (7–10) on 3⁰ amido benzoates and also on 2⁰ amido benzoate (11) towards isotacticity and activity were also taken into consideration.

All these molecules were synthesized by an easy two-step protocol starting from α-enone (mesityl oxide) as given in Scheme 1. Initially, enone was made to react with 1⁰ amines, without isolation of so formed keto amine, the attempts to reduce the keto functionality with sodium borohydride not led to the satisfying result. Further judicial choice of reducing agent; Ni-Al alloy resulted in the formation of the requisite amino alcohol (80–85% conversion). In all cases, final esterification was performed under mild conditions with the aid of bases like pyridine/triethylamine. So formed IDs (7–11) were isolated and characterized in detail by usual analytical methods (see the supporting information).

Scheme-1

Synthetic scheme for amido esters: i) RNH₂, –5°C-RT, 15 h ii) Ni/Al alloy, NaOH (25%) , 10°C-RT, 18 h iii) R₁COCl, DMAP, TEA, 10°C RT, 15 h.

These molecules were applied as ID for the catalyst preparation. The ID incorporated MgCl₂ support was prepared by reacting butyl magnesium support [36] with TiCl₄ and ID in chlorobenzene with the aid of activating agent N, N-dimethyl benzamide at 115°C by employing BA/Mg ratio and ID/Mg ratio as 0.1 mol/mol and 0.15 mol/mol respectively. After decanting the solvent, the TiCl₄ addition process was repeated three times.

All the prepared catalysts were evaluated for propylene polymerization with the aid of ED; diisobutyl dimethoxy silane (DiBDMS, Si/Ti: 11.3 mol/mol) and triethylaluminium as co-catalyst (Al/Ti: 160 mol/mol). It was found that only (11) showed relatively reasonable activity of 10.4 Kg/g catalyst (Table 1). The introduction of either electron releasing methyl in benzoyl moiety in (8) was found to have a slight increase in catalytic activity from 4.8 (naked benzoyl moiety (7) to 6.1 Kg/g catalyst. However, the introduction of the electron-withdrawing group in benzoyl moiety in (9) is relatively insignificant while considering the PP activity. The introduction of bulkier groups in N-alkyl moiety, the activity follows the order N-H > N-Me > N-Et and the movement of primary amido group to secondary N-methyl amido, the activity was found to be decreased by half (10.4 Kg/g catalyst (11) vs 4.8 Kg/g catalyst (7). This typified that primary amido benzoate from this class is the reasonable candidate for propylene polymerization.

Table 1

Gas-Phase propylene polymerization of prepared supported ZN catalyst

Catalyst^*	Internal donor	Activity (Kg/g.cat)	Xylene solubility
7’	7	4.8	14
8’	8	6.1	15
9’	9	5.3	15
10’	10	2.5	13
11’	11	10.4	14
3’	3	18.7	3

Polymerization temperature: 70°C, Polymerization time: 1.0 h, cocatalyst used: TEAL: Al/Ti: 160 mol/mol, ED used: DiBDMS: Si/Ti: 11.3 mol/mol, propylene pressure: 24 bar H₂/C3 (mol%) : 1.0%. ^*Weight of catalyst: 10 mg.

All the newly synthesized IDs 7–11 are not stereoselective for propylene polymerization as xylene solubility values obtained are very high compared to 3. Thus the preliminary investigation of these IDs revealed that a small twist in introducing methyl group in the backbone of 3, the ID became not sufficiently bonding enough for modifying atactic sites into isospecific ones and thus not imparting any benefit in improving the stereospecific sites on ZN system. This explains the high XS values of the resultant polymers with the tested donors 7–11. Thus modification in the original structure of 3 and reducing the chiral center does not influence tacticity, but it changes the alignment on the MgCl₂ surface and more likely behave like a non-bonding pattern. Such modifications do not exhibit any benefit to the catalyst in terms of activity/isotacticity.

3 General Experimental Details

3.1 Materials and methods

All reagents and solvents were laboratory grade chemicals purchased from Sigma Aldrich, SD Fine Chem and were used without additional purification. ¹H and ¹³C NMR spectra were recorded on Bruker 300 MHz (300 and 75 MHz, respectively) and Agilent 600 MHz (600 and 150 MHz respectively) spectrometers in CDCl₃ containing 0.05% Me₄Si as the internal standard. Column chromatography was carried out on silica gel (200–400 mesh). Purity analysis of intermediates was performed on GC (Agilent 7890) with FID detector using Agilent HP-5-, 30 m×0.320 mm (Internal diameter)×0.25μm thickness fused silica capillary column. Mass analysis of intermediates and final donors were performed on GCMS; Thermo scientific, ITQ 1100, Trace GC ultra with AI 3000 injector and LCMS; Waters 2695 separation module, with 2996 photodiode array detector, ESCi multimode ionization injector respectively. Xylene soluble measurement: reflux in xylene, cooled to 15°C, filtered, solvent evaporation (ASTM D5492 eq. to ISO 16152).

TiCl₄ was purchased from Alfa Aesar (99%) , chlorobenzene was purchased from Sigma Aldrich (99.9%) and dried with molecular sieves (4Å). Dry n-heptane was used as such from the solvent purification system and always degassed before use by bubbling dry nitrogen through the liquid. N, N-dimethyl benzamide was purchased from Alfa Aesar (98% purity).

Polymerization grade propene was obtained from the PP plant, (Sabic, Geleen, Netherland). The contents of critical impurities (CO, COS) were less than 10 ppb, water and oxygen levels were under 1 ppm. Triethyl aluminium (TEAL), a co-catalyst was purchased from Sigma Aldrich (99% purity). n-Heptane was purchased from Aldrich (99% spectrophotometric grade). Before the polymerization, the removal of water and oxygen was conducted inside the reactor by stripping. About 10% of the heptane was stripped-off by high-purity nitrogen (70°C, 40 min) to remove H₂O and O₂. The contents of O₂ and H₂O in the nitrogen were under 0.5 ppm. Butyl support was prepared according to the literature method [36].

3.2 Synthesis and Characterization

3.2.1 General procedure for the amino alcohol (4–6)

Mesityl oxide (1 eq) was cooled to 10°C To this, aq. solution of alkyl amine (1.1 to 1.45 eq.) was gradually added and stirred overnight at 20–25°C. To the aminoketone so formed, 25 wt% aq. NaOH solution (10.70 eq) was added at 10–15°C. Ni/Al alloy (2.85 eq) was gradually added to the resulting mass at 10–15°C in about 2–3 h. After the addition of Ni/Al alloy, the reaction mass was stirred at room temperature overnight. It was filtered over a high flow bed and the cake thus obtained was washed twice with dichloromethane (250 mL×2). Organic layers were separated and the combined organic layer was dried over anhydrous sodium sulphate and concentrated under reduced pressure to get the crude amino alcohol. Crude amino alcohol was further purified by fractional vacuum distillation (60–80°C, 0.5 bar) to obtain the pure product (4–6).

4-Methyl-4-(methylamino)pentane-2-ol (4). Mesityl oxide (30 gm, 0.3 mol), 40 wt% aq solution of methylamine (25.6 gm, 0.33 mol), 25 wt% aq. NaOH solution (513 mL), Ni/Al alloy (72.6 gm, 0.85 mol).

Yellow oil; Yield: 24.30 gm (60.59%) ; Purity: 87.60% (GC); GCMS (m/e): Calc. for C₇H₁₇NO: 131.22; found: 131.98 (M⁺).

4-(Ethylamino)-4-methyl pentane-2-ol (5). Mesityl oxide (30 gm, 0.30 mol), 70 wt% aq solution of ethylamine (23.2 gm, 0.36 mol), 25 wt% aq. NaOH solution (513 ml), Ni/Al alloy (72.6 gm, 0.8 mol).

Yellow liquid; Yield: 26.6 gm (59.92%) ; Purity: 90.90% (GC); GCMS (m/e): Calc. for C₈H₁₉NO: 145.25; found: 145.97 (M⁺).

4-(Amino)-4-methyl pentane-2-ol (6). Mesityl oxide (30 gm, 0.30 mol), 25 wt% aq. solution of ammonia (29.6 gm, 0.43 mol), 25 wt% aq. NaOH solution (513 ml), Ni/Al alloy (72.6 gm, 0.85 mol).

Pale yellow liquid; Yield: 17.90 gm (49.98%) ; Purity: 87.72% (GC); GCMS (m/e): Calc. for C₆H₁₅NO: 117.19; found: 117.97 (M⁺).

3.2.2 General procedure for the synthesis of amido-esters (7–10)

To a stirred solution of amino alcohol (4–6) (1 eq) in dichloromethane at 0 to 5°C was added triethylamine (6 eq) and a catalytic amount of DMAP (0.2 eq). To this, a solution of substituted benzoyl chloride (2.1 eq) in dichloromethane (20 eq) was gradually added. The reaction mass was further stirred overnight at room temperature and diluted with water and dichloromethane. The organic layer was separated, washed with water, dried over anhydrous sodium sulphate. The solution was then concentrated under reduced pressure to give the crude product, purified by column chromatography using hexane/EtOAc as eluent gave pure amido-ester (7–10).

4-Methyl-4-(N-methylbenzamido)pentan-2-yl benzoate (7). 4 (6.3 gm, 0.048 mol), triethylamine (29.1gm, 0.28 mol), benzoyl chloride (14.16 gm, 0.10 mol) and dichloromethane (65 mL).

Pale Yellow liquid, Yield: 8.15 gm (49.93%) . ¹H NMR (300 MHz, CDCl₃) δ (ppm) 1.28 (3H, d, J = 6.2 Hz, CH-CH₃), 1.39 (3H, s, CH₃), 1.45 (3H, s, CH₃), 2.20–2.30 (1H, dd, J = 15.0 Hz, J = 9.3 Hz, CH₂), 2.66–2.71 (1H, dd, J = 15.0 Hz, J = 1.9 Hz, CH₂), 2.73 (3H, s, N-CH₃), 5.34–5.40 (1H, m, CH-CH₃), 7.25–7.27 (3H, m, ArH), 7.28–7.37 (4H, m, ArH), 7.44–7.47 (1H, m, ArH), 7.97 (2H, d, J = 9.0 Hz, ArH) ¹³C {¹H} NMR (75 MHz, CDCl₃) δ (ppm) 21.8, 26.8, 27.8, 35.8, 44.6, 58.4, 69.5, 127.0, 128.3, 128.3, 129.3, 129.5, 130.7, 132.8, 138.8, 166.1, 173.1 GCMS (m/e): Calc. for C₂₁H₂₅N0₃: 339.44; found: 340.05 (M⁺).

4-(N, 4-dimethylbenzamido)-4-methylpentan-2-yl 4-methylbenzoate (8). 4 (9.35 gm, 0.071 mol), triethylamine (43.2 gm, 0.42 mol), 4-methylbenzoyl chloride (23.0 gm, 0.14 mol) and dichloromethane (95 mL).

Pale Yellow oil, Yield: 14.38 gm (54.95%) . ¹H NMR (300 MHz, CDCl₃) δ (ppm) 1.26 (3H, d, J = 6.0 Hz, CH-CH₃), 1.37 (3H, s, CH₃), 1.43 (3H, s, CH₃), 2.21 (1H, d, J = 3.0 Hz, CH-CH₂), 2.26 (3H, s, ArCH₃), 2.32 (3H, s, ArCH₃), 2.68 (1H, d, J = 15.0 Hz, CH-CH₂), 2.74 (3H, s, N-CH₃), 5.32–5.36 (1H, m, CH-CH₃), 7.06 (2H, d, J = 6.0 Hz, ArH), 7.14 (2H, d, J = 6.0 Hz, ArH), 7.24 (2H, d, J = 6.0 Hz, ArH), 7.86 (2H, d, J = 9.0 Hz, ArH). ¹³C {¹H} NMR (75 MHz, CDCl₃) δ (ppm) 21.3, 21.6, 21.8, 26.8, 27.7, 35.9, 44.5, 58.3, 69.2, 127.2, 128.0, 128.9, 129.0, 129.6, 135.9, 139.4, 143.4, 166.2, 173.3. GCMS (m/e): Calc. for C₂₃H₂₉NO₃: 367.49; found: 367.97 (M⁺).

4-(4-Methoxy-n-methylbenzamido)-4-methylpentan-2-yl 4-methoxybenzoate (9). 4 (11.5 gm, 0.087mol), triethylamine (53.2 gm, 0.52 mol), 4-methoxybenzoyl chloride (31.2 gm, 0.18 mol) and dichloro-methane (115 mL).

White solid, Yield: 6.04 gm (17.25%) . ¹H NMR (600 MHz, CDCl₃) δ (ppm) 1.31 (3H, d, J = 3.0 Hz, CH-CH₃,), 1.43 (3H, s, CH₃), 1.49 (3H, s, CH₃), 2.30–2.34 (1H, dd, J = 7.5 Hz, J = 6.0 Hz, CH-CH₂), 2.66 (1H, d, J = 6.0 Hz, CH-CH₂), 2.83 (3H, s, N-CH₃), 3.79 (3H, s, -OCH₃), 3.83 (3H, s, -OCH₃), 5.37–5.39 (1H, m, CH-CH₃), 6.82 (2H, d, J = 6.0 Hz, ArH), 6.87 (2H, d, J = 3.0 Hz, ArH), 7.38 (2H, d, J = 6.0 Hz, ArH), 7.97 (2H, d, J = 3.0 Hz). ¹³C {¹H} NMR (150 MHz, CDCl₃) δ (ppm) 21.9, 26.7, 27.5, 35.9, 44.5, 55.2, 55.3, 58.2, 69.0, 113.4, 113.5, 123.2, 129.2, 131.5, 160.5, 163.2, 165.8, 173.0. LCMS (m/e): Calc. for C₂₃H₂₉NO₅: 399.49; found: 400.2 (M⁺).

4-(N-ethylbenzamido)-4-methylpentan-2-yl benzoate (10). 5 (8.9 gm, 0.061 mol), triethylamine (37.2 gm, 0.36 mol), benzoyl chloride (18 gm, 0.12 mol) and dichloromethane (90 mL).

Pale yellow low melting solid, Yield: 10.15 gm (46.88%) . ¹H NMR (300 MHz, CDCl₃) δ (ppm) 0.98 (3H, t, J = 15.0 Hz, N-CH₂-CH₃,), 1.38 (3H, d, J = 6.0 Hz, CH-CH₃), 1.53 (3H, s, CH₃), 1.61 (3H, s, CH₃), 2.19–2.27 (1H, dd, J = 15.0 Hz, J = 9.0 Hz, CH-CH₂), 2.90–2.96 (1H, dd, J = 15.0 Hz, J = 3.0, CH-CH₂), 3.12–3.24 (1H, m, N-CH₂-CH₃), 3.30–3.42 (1H, m, N-CH₂-CH₃), 5.40–5.49 (1H, m, CH-CH₃), 7.37–7.40 (5H, br, ArH,), 7.47 (2H, t, J = 6.0 Hz, ArH), 7.58 (1H, t, J = 9.0 Hz, ArH), 8.09 (2H, d, J = 9.0, ArH). ¹³C {¹H} NMR (75 MHz, CDCl₃) δ (ppm) 17.4, 21.8, 28.1, 28.2, 41.8, 45.2, 58.8, 69.7, 125.8, 128.3, 128.4, 128.4, 129.5, 130.8, 132.8, 139.5, 166.1, 173.3. GCMS (m/e): Calc. for C₂₂H₂₇NO₃: 353.46; found: 354.05 (M⁺).

Procedure for the synthesis of 4-Benzamido-4-methyl pentane-2-yl benzoate (11). To a stirred solution of 4-amino-4-methyl pentane-2-ol (6) (10 gm, 0.085 mmol) in dichloromethane (70 mL) was added pyridine (20.2 gm, 0.25 mol), and the reaction mass was cooled to 0 to 5°C. To this, a solution of benzoyl chloride (25.0 gm, 0.18 mmol) in dichloromethane (30 mL) was slowly added in 15 min. After addition, the reaction mass temperature was slowly raised to room temperature and stirred for 15 hrs. The reaction mass was quenched in water (250 mL) and extracted with dichloromethane (100 mL). The organic layer was separated, washed with water (150 mL), dried over anhydrous sodium sulphate and concentrated on rota vapour under reduced pressure to give the crude material which was purified by column chromatography using hexane to hexane/EtOAc as eluent to obtain 11.

White solid, Yield: 3.12 gm (11.23%) . ¹H-NMR (300 MHz, CDCl₃) δ (ppm) 1.42 (3H, d, J = 6.0, CH-CH₃), 1.50 (3H, s, CH₃), 1.55 (3H, s, CH₃), 2.12 (1H, d, J = 15.0 Hz, CH-CH₂), 2.37–2.45 (1H, dd, J = 15.0 Hz, J = 9.0 Hz, CH-CH₂), 5.41 (1H, m, CH-CH₃), 6.51 (1H, s, NH-C=O), 7.28–7.31 (2H, m, ArH), 7.34–7.43 (3H, m, ArH), 7.53 (1H, t, J = 6.0 Hz, ArH), 7.68 (2H, d, J = 6.0 Hz, ArH), 7.98 (2H, d, J = 9.0 Hz). ¹³C {¹H} NMR (75 MHz, CDCl₃) δ (ppm) 22.0, 26.7, 28.1, 46.1, 53.2, 69.1, 126.7, 128.3, 129.5, 130.3, 131.0, 132.9, 135.4, 166.3, 166.9. GCMS (m/e): Calc. for C₂₀H₂₃NO₃: 325.41; found: 326.11 (M⁺).

3.2.3 Synthesis of supported ZN catalysts (3’, 7’-11’)

TiCl₄ (250 mL) was added to the reactor and heated to 100°C. Butyl-support [36] (5.5 gm) in heptane (30 mL) was added to the reactor while stirring. The temperature was raised to 110°C and N, N’-dimethyl benzamide (BA/Mg=0.15, 5.7 mmol, 1.71 gm) in 3 mL of chlorobenzene followed by ID (ID/Mg=0.10, 3.8 mmol) in 2 mL of chlorobenzene were added. 5) The temperature was raised to 115°C and was maintained for 90 min. The supernatant fluid was decanted after settling and the solid residue was washed with chlorobenzene (100 mL) at 100°C. The supernatant fluid was decanted after settling. A mixture of TiCl₄ (125 mL) and chlorobenzene (125 mL) was added and heated up to 115°C; the temperature was kept for 30 min under stirring. The supernatant fluid was decanted after settling and this operation was repeated two more times. The solid residue was washed with heptane (125 mL×6). The catalyst was dried and stored under nitrogen (Yield: 3.5–4.5 gm).

3.2.4 Propylene polymerization process

Solutions of both the co-catalyst (triethylaluminium (1.219 M in heptane); Al/Ti 160) and ED (DiBDMS (0.162 M in heptane), Si/Ti: 11.3) were added to the reactor with nitrogen-flushed pipettes at ambient temperature and ambient pressure. The amount of heptane was adjusted to be 3 mL in total. Then approx. 100 gm of propylene/hydrogen mixture (99 vol.% propylene, 1 vol.% hydrogen, viz. a 1 vol.% hydrogen pressure) was dosed to the reactor after which the reactor was heated to 50°C. A suspension of catalyst (5 mg of a 14.6 wt.% suspension in mineral oil) mixed with approx. 5 gm of inert homo-PP powder was dosed to the reactor by a 16 bar liquid propylene flow. After 1 min, the temperature and pressure were slowly increased to 70°C and 24 bar over 10 min. After this, all conditions were kept constant for one hour. After 1 h the reactor was vented to 15 bar within 2 min, the stirrer was turned off and the reactor was cooled down and vented to ambient conditions within 1–2 min. At ambient conditions, the reactor was opened and the polymer was collected.

4 Conclusion

A new family of amido esters with the single chiral center in the backbone was synthesized via the two-steps method by mimicking the structural motif of 3 having two chiral carbons with the anticipation of their behaviour towards isotacticity and activity of the catalyst. The influence of these donors on prepared MgCl₂ supported TiCl₄ catalysts for propylene polymerization was investigated. The results revealed; all the newly synthesized donors with varying electron releasing/withdrawing substituents and having one chiral center have far less activity/isotacticity concerning 3. It is concluded that these donor molecules are ineffective for appropriate coordination on MgCl₂ sites on inducing steric hindrance for improved isotacticity; nevertheless also induces poisoning effect for the active Ti centers leading to catalyst fouling in many cases. Further studies on structural modification of 3 and its related structures to be applied as ID are in the due course of our study.

Footnotes

Acknowledgments

The authors gratefully acknowledge Martin Zuideveld, Nicole Weekers (SABIC, Netherlands) for supporting catalyst preparation and polymerization studies.

Conflict of interest

The authors declare that there is no conflict of interest.

References

Soga

, Shiono

and Doi

, Influence of internal and external donors on activity and stereospecificity of Ziegler-Natta catalysts, Macromolecular Chemistry 189 (1988), 1531–1541.

Fisch

A.G.

, Ziegler-Natta Catalysts, Kirk-Othmer Encyclopedia of Chemical Technology 2019.

Soga

and Shiono

, Ziegler-Natta catalysts for olefin polymerizations, Progress in Polymer Science 22 (1977), 1503–1546.

Farrell

L.M.

, Polypropylene, PERP, Chem System PERP 2011-5.

Global Polypropylene in Transition-The Status Analysis of Phthalate-Free Catalysts (PFC), Townsend PFC Report 2015.

Maddah

H.A.

, Polypropylene as a Promising Plastic: A Review, American Journal of Polymer Science 6 (2016), 1–11.

Zhang

, Zhang

, Fu

, et al., Effect of internal electron donor on the active center distribution in MgCl₂-supported Ziegler-Natta catalyst, Catalysis Communications 69 (2015), 147–149.

Tanase

, Katayama

, Yabunouchi

, et al., Design of novel malonates as internal donors for MgCl₂-supported TiCl₄ type polypropylene catalysts and their mechanistic aspects, Part 1, Journal of Molecular Catalysis A: Chemical 273 (2007), 211–217.

Vestberg

, Denifl

, Parkinson

, et al., Effects of External Donors and Hydrogen Concentration on Oligomer Formation and Chain End Distribution in Propylene Polymerization with Ziegler-Natta Catalysts, Journal of Polymer Science: Part A: Polymer Chemistry 48 (2010), 351–358.

10.

Bukatov

G.D.

, Maslov

D.K.

, Sergeev

S.A.

, et al., Effect of internal donors on the performance of Ti-Mg catalysts in propylene polymerization: Donor introduction during or after MgCl₂ formation, Applied Catalysis A: General 577 (2019), 69–75.

11.

Busico

, Causa

, Cipullo

, et al., Periodic DFT and High-Resolution Magic-Angle-Spinning (HR-MAS) ¹H NMR Investigation of the Active Surfaces of MgCl₂-Supported Ziegler-Natta Catalysts. The MgCl₂ Matrix, Journal of Physical Chemistry C 112 (2008), 1081–1089.

12.

Chadwick

, Morini

, Balbontin

, et al., Theoretical Investigation of Active Sites at the Corners of MgCl₂ Crystallites in Supported Ziegler-Natta Catalysts, Macromolecular Chemistry and Physics 202 (2001), 1995–2002.

13.

Credendino

, Pater

J.T.M.

, Correa

, et al., Thermodynamics of Formation of Uncovered and Dimethyl Ether-Covered MgCl₂ Crystallites. Consequences in the Structure of Ziegler-Natta Heterogeneous Catalysts, The Journal of Physical Chemistry C 115 (2011), 13322–13328.

14.

Ratanasak

, Hasegawa

and Parasuk

, Roles of Salicylate Donors in Enhancement of Productivity and Isotacticity of Ziegler-Natta Catalyzed Propylene Polymerization, Polymers 12 (2020), 883.

15.

Dang

, Li

, et al., Ziegler-Natta catalysts with novel internal electron donors for propylene polymerization, Journal of Polymer Research 21 (2014), 619.

16.

Gao

, Xia

, Mao

, MgCl₂-Supported Catalyst Containing Mixed Internal Donors for Propylene Polymerization, Journal of Applied Polymer Science 120 (2011), 36–42.

17.

Zheng

, Zhou

, Li

, et al., Application of successive self-nucleation and annealing (SSA) to poly(1-butene) prepared by Ziegler-Natta catalysts with different external donors, Royal Society of Chemistry Advances 5 (2015), 9328–9336.

18.

Zhou

, Zheng

, Li

, et al., Effects of Some New Alkoxysilane External Donors on Propylene Polymerization in MgCl₂ Supported Ziegler-Natta Catalysis, Industrial & Engineering Chemistry Research 53 (2014), 17929–17936.

19.

Sacchi

M.C.

, Forlini

, Tritto

, et al., Activation Effect of Alkoxysilanes as External Donors in MgCl₂-Supported Ziegler-Natta Catalysts, Macromolecules 25 (1992), 5914–5918.

20.

Cavallo

, Del Piero

, Ducere

J.M.

, et al., Key Interactions in Heterogeneous Ziegler-Natta Catalytic Systems: Structure and Energetics of TiCl₄-Lewis Base Complexes, Journal of Physical Chemistry C 111 (2007), 4412–4419.

21.

Zaccaria

, Vittoria

, Correa

, et al., Internal Donors in Ziegler-Natta Systems: is Reduction by AlR₃ a Requirement for Donor Clean-Up? ChemCatChem 10 (2018), 984–988.

22.

Wen

, Ji

, Yi

, et al., Magnesium Chloride Supported Ziegler-Natta Catalysts Containing Succinate Internal Electron Donors for the Polymerization of Propylene, Journal of Applied Polymer Science 118 (2010), 1853–1858.

23.

Song

B.G.

and Ihm

S.K.

, The Role of Two Different Internal Donors (Phthalate and 1,3-Diether) on the Formation of Surface Structure in MgCl₂-Supported Ziegler–Natta Catalysts and Their Catalytic Performance of Propylene Polymerization, Journal of Applied Polymer Science (2014), 40536.

24.

Cui

, Ke

, Li

, et al., Effect of Diether as Internal Donor on MgCl₂-Supported Ziegler-Natta Catalyst for Propylene Polymerization, Journal of Applied Polymer Science 99 (2006), 1399–1404.

25.

Morini

, Albizzati

, Balbontin

, et al., Microstructure Distribution of Polypropylenes Obtained in the Presence of Traditional Phthalate/Silane and Novel Diether Donors: A Tool for Understanding the Role of Electron Donors in MgCl₂-Supported Ziegler-Natta Catalysts, Macromolecules 29 (1996), 5770–5776.

26.

Chen

, Leung

T.W.

, Tao

, et al., Procatalyst composition with substituted amide ester internal electron donor, Patent 2545087 B1, EP, (2016).

27.

Taftaf

, Sainani

, Zakharov

, et al., Catalyst composition for polymerization of olefins, Patent 10059656 B2, US, (2018).

28.

Chen

, Leung

T.W.

, Tao

, et al., Amide ester internal electron donor and process, Patent 106500, WO, (2011).

29.

Guo

, Hu

and Chen

, Synthesis of Novel Electron Donors and Their Application to Propylene Polymerization, Transactions of Tianjin University 18 (2012), 8–14.

30.

Morini

, Balbontin

, Cristofori

, et al., Components and catalysts for the polymerization of olefins, Patent 6313238 B1, US, (2001).

31.

Morini

and Balbontin

, Components and catalysts for the polymerization of olefins Patent 55215, WO, 2000.

32.

Chen

, Leung

T.W.

and Tao

, Procatalyst composition including silyl ester internal donor and method, Patent 8088872 B2, US (2012).

33.

Blaakmeer

E.S.M.

, Antinucci

, Correa

, et al., Structural Characterization of Electron Donors in Ziegler-Natta Catalysts, The Journal of Physical Chemistry C 122 (2018), 5525–5536.

34.

Brambilla

, Zerbi

, Piemontesi

, et al., Structure of Donor Molecule 9,9-Bis(Methoxymethyl)-Fluorene in Ziegler-Natta Catalyst by Infrared Spectroscopy and Quantum Chemical Calculation, The Journal of Physical chemistry C 114 (2010), 11475–11484.

35.

Gao

, Liu

, Li

, et al., Solid catalyst component for polymerization of olefins, a catalyst comprising the same and use thereof, Patent 068828 A1, WO (2003).

36.

Zakharov

V.A.

, Bukatov

G.D.

and Sergeev

S.A.

, Process for the preparation of a catalyst component for the polymerization of an olefin, Patent 1222214 B1, EP (2004).