Novel alkoxo-titanium(IV) complexes with fluorinated 2-hydroxymethylphenol derivatives as catalysts for the formation of ultra-high molecular weight polyethylene nascent reactor powders

Article abstract of DOI:10.1016/j.ica.2019.119159

A series of titanium (IV) complexes 3a–g stabilized by fluorinated derivatives of 2-hydroxymethylphenol have been synthesized; their composition and structure have been confirmed by NMR, IR-spectroscopy and elemental analysis. The structures of compounds

Full text of DOI:10.1016/j.ica.2019.119159

InorganicaChimicaActa498(2019)119159
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Research paper
Novel alkoxo-titanium(IV) complexes with fluorinated 2-
hydroxymethylphenol derivatives as catalysts for the formation of ultra-high
molecular weight polyethylene nascent reactor powders
⁎
Vladislav A. Tuskaeva,b, , Svetlana Ch. Gagievaa,b, Dmitry A. Kurmaeva, Sergei V. Zubkevicha,
Pavel V. Dorovatovskiid, Victor N. Khrustalevd,e, Elena S. Mikhaylikb,c, Evgenii K. Golubevb,c
Mikhail I. Buzinb, Galina G. Nikiforovab, Viktor G. Vasil'evb, Tamara M. Zvukovaa,
Boris M. Bulycheva
,
a Department of Chemistry, M. V. Lomonosov Moscow State University, 1 Leninskie Gory, 119992 Moscow, Russian Federation
b A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 28 ul. Vavilova, 119991 Moscow, Russian Federation
c Enikolopov Institute of Synthetic Polymer Materials, Russian Academy of Sciences, Profsoyuznaya Str., 70, 117393 Moscow, Russian Federation
d National Research Center “Kurchatov Institute”, Acad. Kurchatov Sq., 1, Moscow 123182, Russian Federation
e Peoples’ Friendship, University of Russia (RUDN University), Miklukho-Maklay St., 6, Moscow 117198, Russian Federation
A R T I C L E I N F O
A B S T R A C T
Keywords:
Ziegler-Natta polymerization
Titanium
OO-ligands
UHMWPE
A series of titanium (IV) complexes 3a–g stabilized by fluorinated derivatives of 2-hydroxymethylphenol have
been synthesized; their composition and structure have been confirmed by NMR, IR-spectroscopy and elemental
analysis. The structures of compounds 3c, 3f and 3g have been unambiguously established by X-ray diffraction
study. The complexes in the presence of a binary cocatalysts {alkyl aluminum chloride + MgBu2} catalyze
ethylene polymerization to afford Ultra High Molecular Weight Polyethylene (UHMWPE). The effects of sub-
stituents in the ligands on the catalytic activity and properties of the obtained polymer – molecular weight, DSC
melting behavior, and morphology of nascent reactor powders have been investigated. UHMWPE samples were
processed by a solid-state uniaxial deformation into high-strength (up to 2.65 GPa) and high-modulus (over
140 GPa) oriented film tapes, which indirectly indicates a low degree of entanglements between the macro-
molecular chains.
1. Introduction
and films. At present, gel spinning technique with further stretching is
used for this purpose. However, this technology involves the use of
Ultra-high molecular weight polyethylene (UHMWPE) is a linear
(non-branching) semi-crystalline polymer which can be described as a
two phase composite consisting of crystalline and amorphous phases
[1]. The ultra-high molecular weight of UHMWPE (1–6 106 Da) results
in excellent mechanical properties such as high strength, resistance to
aggressive media, high wear resistance, low friction coefficient (self-
lubrication behavior), high toughness, very high resistance to low
temperatures. As a result, UHMWPE has found successful applications
in many industrial sectors [2]. On the other hand, the ultra-high mo-
lecular weight of this polymer determines its high melt viscosity and
lack of fluidity which greatly hinders its processing by standard
polymer processing methods, such as injection molding, ram extrusion,
etc. One of the most promising approaches to the processing of
UHMWPE is the production of high-modulus and high-strength tapes
highly diluted polymer solutions (3–5%), whereby necessity to re-
generate large volumes of high boiling solvents significantly increases
the cost of the final product. An alternative is a solvent-free solid-phase
monolithization of UHMWPE reactor powder with subsequent or-
ientation extraction. This methodology, introduced by Smith et al.,
[3–4] was further considerably improved by Rastogi et al. [5–6].
The microstructure of UHMWPE can be considered as a matrix of
heterogeneously distributed entanglements, where the disentangled
regions reside in the crystalline domains and the entangled regions in
the amorphous domains [7]. By reducing the entanglement density the
UHMWPE nascent reactor powders can be processed in solid-state
below its melting temperature, leading to the high-strength and high-
modulus oriented materials. The UHMWPE reactor powders of the re-
quired quality
– i.e. with reduced entanglement density of the
⁎ Corresponding author at: Department of Chemistry, M. V. Lomonosov Moscow State University, 1 Leninskie Gory, 119992 Moscow, Russian Federation.
E-mail address: tuskaev@yandex.ru (V.A. Tuskaev).
https://doi.org/10.1016/j.ica.2019.119159
Received 14 May 2019; Received in revised form 10 September 2019; Accepted 13 September 2019
Availableonline14September2019
0020-1693/©2019ElsevierB.V.Allrightsreserved.

V.A. Tuskaev, et al.
InorganicaChimicaActa498(2019)119159
Ti(OiPr)4
(CF3)2CO
1 a: R1 =R3= Cumyl, R2 = H;
1 b: R1 =R3= H, R2 = CH3;
1 c: R1 = Ad, R2= H, R3=t-Bu
1 d: R1=R3=t-Bu, R2=H
2a-d
3a-d
Ti(OiPr)4
2e-g
3e - R4 - CH3
3f - R4 - C6F5
3g - R4 - C6H5
Scheme 1. Synthetic procedures for complexes 3a–g.
molecular chains, can be obtained when homogeneous catalysts are
used in diluted systems and the temperature of polymerization is kept
low. Subject to these conditions, the polymer chains will begin to
crystallize during the polymerization, that facilitates the formation of
polymer with highly disentangled chains [5–8] (Scheme 1).
Previously, we proposed a new group of titanium complexes stabi-
lized by 2-hydroxymethylphenol derivatives capable to catalyze the
production of UHMWPE suitable for solvent-free processing into high-
strength and high-modulus films and film tapes [9–12] (examples of
such structures are shown in Fig. 1).
In the present work, ligands with perfluorinated substituents were
used to obtain titanium complexes. Replacement of hydrogen with
fluorine leads to an increase in the lipophilicity of ligand molecule and
in the acidity of hydroxyl groups, and probably in Lewis acidity the
central metal atom. In this case, the geometric parameters of the mo-
lecule change slightly (the van der Waals radii of the CH3 and CF3
groups are 1.29 A and 1.35 A, respectively). The high chemical stability
of C–F bonds should be noted, which is unattainable for other halogens
[13]. It is known that relatively more basic alkoxide ligands (compared
to phenoxides) often act as bridging ligands in the process of com-
plexation, which leads to the formation of highly agglomerated struc-
tures. Increasing the acidity of alcohol hydroxyl (as well as increasing
the steric bulk of alkyl substituents) partially suppresses this process
[14–16]. The interest in fluorinated precatalysts for olefin poly-
merization was also stimulated by the works of Fujita [17–20]. They
showed that group 4 metal complexes stabilized by partially or fully
fluorinated phenoxyimine ligands significantly outperform non-fluori-
nated analogs in activity and stereo-selectivity in the polymerization of
propylene and higher α-olefins and in the molecular weights of the
obtained polymers.
2. Experimental
2.1. Catalysts and synthetic methods
All manipulations with air-sensitive materials were performed with
rigorous exclusion of oxygen and moisture in oven-dried Schlenk
glassware on a dual manifold Schlenk line, interfaced to a high-vacuum
line. Argon and ethylene of special-purity grade (Linde gas) were dried
by purging through a Super Clean™ Gas Filters.
NMR spectra were recorded on Bruker Avance-400 instrument.
Deuterated solvents (CDCl3, THF-d8) were degassed by freeze-pump-
thaw vacuum cycles and stored over 3 Å molecular sieves. Chemical
shifts are reported in ppm vs. SiMe4 and were determined by reference
to the residual solvent peaks. All coupling constants are given in Hertz.
Air-sensitive NMR spectra were taken in J. Young tubes with Teflon
valve plugs. IR spectra were recorded on a Magna-IR 750 spectro-
photometer. Elemental analysis was performed by the microanalytical
laboratory at A. N. Nesmeyanov Institute of Organoelement
Compounds.
Toluene was distilled over Na/benzophenone ketyl and the water
content was periodically controlled by Karl-Fischer coulometry by using
a Methrom 756 KF apparatus. Diethylaluminum chloride, ethylalu-
minum sesquichloride and di-n-butylmagnesium (Aldrich) were used as
1.0 M solution in heptane. Ligands 2b, 2d and 2c were synthesized as
described [21,22], its 1H and 13C NMR spectra were found to match the
published data. Ligands 2d–f were obtained by the interaction of 1-(3,5-
di-tert-butyl-2-hydroxy-phenyl)-2,2,2-trifluoroethanone with the corre-
sponding organometallic compounds [23].
2.1.1. 2-(1,1,1,3,3,3-Hexafluoro-2-hydroxypropan-2-yl)-4,6-bis(1-
methyl-1-phenyl–ethyl)-phenol (2a)
Therefore, the main purpose of present work is the synthesis of new
titanium complexes stabilized by 2-hydroxymethylphenol derivatives
and studying the impact of both fluorinated fragments and bulky sub-
stituent in position 6 of the ligand on the catalytic activity in ethylene
polymerization and on the properties of the resulting polymers in-
cluding their ability to be processed by a solid-state solvent-free method
below melting temperature.
To a pre-dried ampule, 6.61 g (0.02 mol) of 2,4-bis(1-methyl-1-
phenyl-ethyl)-phenol and 25 mL of CCl4 were introduced under argon
flow. After the solution was degassed it was cooled down to −35 °C and
5.0 g (~0.03 M) of 1,1,1,3,3,3-hexafluoroacetone was added over a
period of 20 min. The ampule was sealed and incubated for 24 h at r.t.
Upon completion, the ampule was frozen, unsealed and the remaining
gas was removed by argon and trapped in a washing bottle. The organic
phase was concentrated under reduced pressure. The crude product was
purified by recrystallization from n-hexane to give the title compound
as colorless crystals. Yield: 6.16 g (62%). Anal. Calc. for C27H26F6O2
2

V.A. Tuskaev, et al.
InorganicaChimicaActa498(2019)119159
B
A
E
D
C
G
F
Fig. 1. Examples of Titanium(IV) complexes with 2-hydroxymethylphenole derivatives suitable for disentangled UHMWPE production.
(496.48): C, 65.32; H, 5.28; F, 22.96. Found (%): C, 65.30; H, 5.26; F,
22.94. 1H NMR (CDC13, 400 MHz): δ = 1.62 (s, 6H, CH3), 1.75 (s, 6H,
CH3), 5.17 (s, 1H, OH), 7.29–7.44 (m, 12H, Ar). 19F NMR (376 MHz,
CDCl3): δ = −75.34. l3C NMR (101 MHz, CDCl3): δ = 150.45, 149.88,
146.54, 143.89, 136.98, 129.90, 129.16, 128.14, 128.05, 127.05,
126.65, 125.93, 125.89, 125.72, 124.28, 121.41, 116.36, 42.85, 42.21,
31.07, 30.82, 29.61. ESI-MS: m/z (%): 496 [M+, 82.37], 481 [100], 403
[21.15], 377 [3.38].
61.01, 22.95, 22.84, 22.77, 22.64, 22.56, 22.44, 22.24, 22.04, 21.94,
18.09.
2.1.3. 2-(1,1,1,3,3,3-Hexafluoro-2-hydroxypropan-2-yl)-4-tert-butyl-6-
adamantylphenol (2c)
The title compound was prepared as described above for 2a, starting
from
a solution of 2-adamantyl-4-tert-butylphenol [24] (5.69 g,
0.02 mol) in tetrachloromethane (40 mL) and 1,1,1,3,3,3-hexa-
fluoroacetone (5.0 g; 0.03 M). Reaction was conducted for 48 h at r.t
Yield: 6.22 g (69%). Calculated (%) for C23H28F6O2 (438): C, 61.33; H,
6.27; F, 25.31. Found (%): C, 61.28; H, 6.23; F, 25.28. 1H NMR
(400 MHz, CDCl3): δ = 1.29 (s, 9H, CH3), 1.79 (s, 5H, CH), 2.14 (s,
10H, CH2), 5.40 (s, 1H, OH), 7.80 (s, 1H, Ar), 7.36 (s, 1H, Ar). 19F NMR
(376 MHz, CDCl3): δ = −75.13. 13C NMR (101 MHz, CDCl3):
δ = 153.69, 141.95, 137.57, 126.35, 124.17, 122.13, 121.36, 111.61,
80.80, 40.67, 40.46, 37.14, 31.27, 29.32, 29.10.
2.1.2. 2-(1,1,1,3,3,3-Hexafluoro-2-hydroxypropan-2-yl)-5-methylphenol
(2b)
This ligand was prepared as described above for 2a, starting from a
suspension of sodium m-cresolate (2.6 g, 0.02 mol) in tetrachloroethane
(40 mL) and 1,1,1,3,3,3-hexafluoroacetone (5.0 g; 0.03 M). Reaction
was conducted for 48 h at r.t and upon removing the unreacted gas, the
organic phase was washed by diluted HCl, water and brine. The organic
phase was concentrated under reduced pressure and the crude product
was purified by recrystallization from n-hexane to give the title com-
pound as colorless crystals. Yield: 4.49 g (82%). Calculated (%) for
2.1.4. 2-(1,1,1,3,3,3-Hexafluoro-2-hydroxypropan-2-yl)-4,6-di-tert-
butylphenol (2d)
C
10H8F6O2 (274): C, 43.81; H, 2.94; F, 41.58. Found (%): C, 43.78; H,
The title compound was prepared as described above for 2a, starting
2.92; F, 41.56. 1H NMR (400 MHz, CDC13): δ = 2.32 (s, 3H, CH3), 6.73
(s, 1H, Ar), 6.82 (d, J = 7.7 Hz, 1H, Ar), 7.32 (d, J = 8.2 Hz, 1H, Ar),
8.64 (s, 1H, OH). 19F NMR (376 MHz, d-THF): δ = −75.73. l3C NMR
(101 MHz, d-THF): δ = 154.59, 139.69, 138.58, 126.16, 126.13,
126.11, 126.09, 125.64, 125.16, 122.77, 119.90, 119.62, 119.16,
117.06, 116.27, 115.00, 109.98, 65.00, 64.78, 64.56, 64.34, 64.12,
from a solution of 2,4-di-tert-butylphenol. Yield: 5.22 g (75%).
Calculated (%) for C17H22F6O2 (372): C, 54.84; H, 5.96; F, 30.61. Found
(%): C, 54.81; H, 5.93; F, 30.57. 1H NMR (toluene‑d8), δ: 1.28 (s, 9H);
1.53 (s, 9H); 3.99 (br.s, 1H); 7.51 (s, 1H); 7.58 (s, 1H); 8.23 (br.s, 1H).
19F NMR (376 MHz, (benzene‑d6): δ = −75.11; 13C NMR (101 MHz,
CDCl3): δ = 154.55, 141.48, 138.19, 137.32, 128.94, 128.70, 128.47,
3

V.A. Tuskaev, et al.
InorganicaChimicaActa498(2019)119159
128.03, 127.80, 127.56, 126.48, 125.20, 124.96, 124.72, 124.57,
122.25, 121.69, 111.21, 81.64, 81.34, 81.04, 35.46, 34.26, 31.24,
29.71, 20.82, 20.63, 20.44, 20.25, 20.05, 19.86, 19.67.
atmosphere, followed by the addition of Ti(OiPr)4 (0.296 mL,
1.0 mmol) at 40 °C and the reaction mixture was kept at 40 °C for 12 h.
The red crystals that formed were filtered off, washed with toluene, and
dried in vacuo. Yield 0.82 g (62.0%). Calculated (%) for C66H76F12O8Ti2
(1321.0): C, 60.01; H, 5.80; F, 17.26; Ti, 7.25. Found (%): C, 59.99; H,
5.73; F, 17.20; Ti, 7.21. 1H NMR (CDC13): δ = 1.19 (d, 24H, CH3), 1.58
(s, 12H, CH3), 1.73 (s, 12H, CH3), 4.14 (s, 4H, CH), 7.11–7.47 (m, 24H,
Ar). 19F NMR (CDC13): δ = −75.34. l3C NMR (101 MHz, CDCl3):
δ = 157.49, 150.72, 141.45, 135.03, 129.37, 129.06, 128.08, 127.91,
127.32, 126.70, 126.00, 125.88, 125.77, 125.67, 125.56, 125.28,
124.94, 124.38, 122.05, 119.26, 67.22, 42.94, 42.81, 42.68, 42.32,
31.09, 30.79, 29.65, 29.58, 24.72. FT-IR (KBr): 600, 440 cm−1 ν(Ti-O).
2.1.5. 2-(1,1,1-Trifluoro-2-hydroxy-propan-2-yl)-4,6-di-tert-butyl-6-
phenol (2e)
To a solution of MeMgI (10 mmol) in Et2O, prepared from magne-
sium (0.29 g, 12 mmol) and MeI (0.62 mL, 10 mmol) was added drop-
wise an ethereal solution of 1-(2,4-di-tert-buthylphenyl)-2,2,2-tri-
fluoromethylethanone-1 (1.08 g, 3.6 mmol) at 0 °C. The reaction
mixture allowed to slowly warm to room temperature, stirred over-
night, quenched with HCl (1 M, 5 mL) and then and the product was
extracted by diethyl ether. The combined organic phase was dried over
Na2SO4, and the solvent was removed under reduced pressure.
Recrystallization of the crude product from hexane gave 0.78 g (69%)
of a colorless solid. Calculated (%) for C17H25F3O2 (318.38): C, 64.13;
H, 7.91; F, 17.90. Found: C, 64.10; H, 7.88; F, 17.84. 1H NMR
(400 MHz, CDCl3): δ = 1.28 (s, 9H), 1.42 (s, 9H), 1.90 (s, 3H), 3.29 (s,
1H) 7.04 (s, 1H), 7.44 (s, 1H), 8.66 (s, 1H). 19F NMR (CDCl3, 25 °C):
δ = −81.24 (s). 13C NMR (101 MHz, CDCl3): δ = 153.67, 140.82,
137.57, 126.95, 124.47, 122.46, 119.11, 35.22, 34.09, 31.53, 29.92,
24.11.
2.1.9. Di{2-[α,α-bis(trifluoromethyl)methanolato]-5-methylphenolato}di
(μ-isopropoxo)di-(isopropoxy) dititanium (3b)
This complex was prepared as described above for 3a, starting from
a solution of ligand 2b (0. 274 g, 1.0 mmol) in toluene (10 mL) and Ti
(OPri)4 (0.29 mL, 1.0 mmol). Reaction was conducted for 48 h at 50 °C
and workup afforded 3b as a red–orange powder. Yield 0.72 g (82.2%).
Calculated (%) for C32H40F12O8Ti2 (876.4): C, 43.86; H, 4.60; F, 26.01;
Ti, 10.92. Found (%): C, 43.75; H, 4.57; F, 25.96; Ti, 10.87. 1H NMR
(THF- d8): δ = 1.08 (s, 12H, CH3), 1.12 (s, 12H, CH3), 2.26 (s, 6H,
CH3), 3.70 (m, 4H, CH), 6.70 (m, 4H, Ar), 7.31 (d, 2H, Ar). 19F NMR
(CDC13): δ = −76.23. 13C NMR (101 MHz, d-THF): δ = 154.59,
139.69, 138.58, 126.16, 126.13, 126.11, 126.09, 125.64, 125.16,
122.77, 119.90, 119.62, 119.16, 117.06, 116.27, 115.00, 109.98,
77.68, 61.01, 18.09. δ FT-IR (KBr): 601, 533 cm−1 ν(Ti-O).
2.1.6. 2-[2,2,2-Trifluoro-1-hydroxy-1-pentafluorophenyl-ethyl]-4,6-di-
tert-butylphenol (2f)
A solution of 1.0 mL (8.1 mmol) of C6F5Br in 20 mL of Et2O was
cooled to 78 °C, and 3.24 mL of nBuLi (2.5 M solution in hexane,
8.1 mmol) was added dropwise. The reaction mixture was stirred at
78 °C for 30 min, and then a solution of 1-(2,4-di-tert-buthylphenyl)-
2,2,2-trifluoromethylethanone-1 (1.1 g, 3.64 mmol) in diethyl ether
was added dropwise. The resultant solution was stirred overnight at
room temperature, cooled to 0 °C, and then quenched with an aqueous
NH4Cl solution (50 mL) and extracted with ether. The combined or-
ganic phase was dried over Na2SO4, and the solvent was removed under
reduced pressure. Recrystallization of the crude product from hexane
gave 2.99 g (82%) of a colorless solid; mp 149–150 °C. Calculated (%)
for C22H22F8O2 (470.0): C, 56.17; H, 4.71; F, 32.31. Found (%): C,
56.12; H, 4.69; F, 32.28. 1H NMR (400 MHz, CDCl3): δ = 1.19 (s, 9H,
CH3), 1.25 (s, 9H, CH3), 4.39 (s, 1H, OH), 6.68 (s, 1H, Ar), 7.12 (m, 1H,
Ar). 19F NMR (376 MHz, CDCl3): δ = − 76.36, −137.53, −151.10,
−160.88. 13C NMR (101 MHz, CDCl3) δ 151.45, 142.04, 137.68,
125.44, 121.73, 80.14, 77.32, 76.68, 35.03, 34.44, 31.42, 29.83.
2.1.10. Di{2-[α,α-bis(trifluoromethyl)methanolato]-4-tert-buthyl-6-(1-
adamantyl)phenolato}di(μ-isopropoxy)di-(isopropoxo) dititanium (3c)
This complex was prepared as described above for 3a, starting from
a solution of ligand 2c (0.438 g, 1.0 mmol) in toluene (15 mL) and Ti
(OPri)4 (0.29 mL, 1.0 mmol). Reaction was conducted for 24 h at 40 °C
and workup afforded 3c as an orange powder, yield 0.97 g (78.9%).
Calculated (%) for C58H80F12O8Ti2 (1228.96): C, 56.68; H, 6.56; F,
18.55; Ti, 7.79. Found (%): C, 56.61; H, 6.50; F, 18.51; Ti, 7.74. 1H
NMR (400 MHz, CDC13): δ = 1.21–1.31 (m, 54H), 2.12–2.25 (s, 18H),
4.15 (s, 4H, CH), 7.38 (s, 2H, Ar), 7.47 (s, 2H, Ar). 19F NMR (CDC13):
δ = -74.94. 13C NMR (101 MHz, CDCl3): δ = 13C NMR (101 MHz,
CDCl3): δ = 155.92, 147.35, 138.04, 132.90, 125.65, 123.78, 122.46,
121.74, 121.36, 34.61, 29.58, 24.82, 18.05. FT-IR (KBr): 600,
473 cm−1 ν(Ti-O).
2.1.7. 2-[2,2,2-Trifluoro-1-hydroxy-1-phenyl–ethyl]-4,6-di-tert-
butylphenol (2g)
2.1.11. Di{2-[α,α-bis(trifluoromethyl)methanolato]-4,6-di-tert-
buthylphenolato}di(μ-isopropoxy)di-(isopropoxo) dititanium (3d)
This complex was prepared as described above for 3a, starting from
a solution of ligand 2d (0.438 g, 1.0 mmol) in toluene (20 mL) and Ti
(OPri)4 (0.29 mL, 1.0 mmol). Reaction was conducted for 24 h at 40 °C
and workup afforded 3d as a red powder. The crystals that formed were
filtered off, washed with hexane, and dried in vacuo. Yield 0.83 g
(77.3%). Calculated (%) for C46H72F12O8Ti2 (1074.5): C, 51.50; H,
6.39; F, 21.25. Found (%): C, 51.45; H, 6.31; F, 21.18. 1H NMR
(400 MHz, CDCl3): δ = 1.32 (s, 18H, CH3), 1.45 (s, 18H, CH3), 1.47 (s,
24H, CH(CH3)2)), 4.84 (m, 4H, CH(CH3)2), 7.43 (s, 2H Ar-H), 7.59 (s,
2H Ar-H). 19F NMR (C6D6): δ = −80.28. 13C NMR (101 MHz, C6D6) δ
158.47, 143.19, 136.29, 128.04, 125.43, 122.90, 119.38, 35.70, 34.45,
34.38, 31.45, 30.65, 29.73, 24.48, 1.17.
To a stirred solution of PhMgBr (25 mmol) in ether (50 mL) was
added dropwise a solution of 1-(2,4-di-tert-buthylphenyl)-2,2,2-tri-
fluoromethylethanone-1 (2.17 g, 7.2 mmol) in ether (25 mL) at 0 °C in
1 h. After completion of the addition, the mixture was allowed to stand
at room temperature overnight. The resulting mixture was poured into
an aqueous NH4Cl solution and extracted with ether. The organic layer
was removed, dried (Na2SO4) and evaporated under reduced pressure.
Recrystallization of the crude product from hexane gave 2.21 g (81%)
of a colorless solid. Calculated (%) for C22H27F3O2 (380.44): C, 69.46;
H, 7.15; F, 14.98. Found (%): C, 69.41; H, 7.11; F, 14.67. 1H NMR
(400 MHz, CDCl3): δ = 1.29 (s, 9H, CH3), 1.40 (s, 9H, CH3), 3.52 (s, 1H,
OH), 7.12 (t, 1H, Ar), 7.39 (m, 2H, Ar), 7.42 (s, 1H, Ar), 7.52 (m, 2H,
Ar), 7.60 (s, 1H, Ar). 19F NMR (376 MHz, CDCl3): δ = −75.93. 13C
NMR (101 MHz, CDCl3) δ = 152.87, 140.66, 137.66, 137.53, 129.23,
128.32, 127.42, 127.40, 126.35, 125.11, 123.50, 123.19, 123.16,
123.13, 121.77, 82.04, 81.75, 81.46, 35.24, 34.32, 31.50, 29.69.
2.1.12. Di{2-[α-trifluoromethyl-α-methyl-methanolato]-4,6-di-tert-buthyl-
phenolato}di(μ-isopropoxy) di-(isopropoxo) dititanium (3e)
This complex was prepared as described above for 3a, starting from
a solution of ligand 2e (0.438 g, 1.0 mmol) in toluene (10 mL) and Ti
(OPri)4 (0.29 mL, 1.0 mmol). Reaction was conducted for 24 h at 40 °C
and workup afforded 3e as a dark red powder. The crystals that formed
were filtered off, washed with hexane, and dried in vacuo. Yield 0.85 g
(91.3%). Calculated (%) for C46H74F6O8Ti2 (964.8): C, 57.26; H, 7.73;
2.1.8. Di{2-[α,α-bis(trifluoromethyl)methanolato]-4,6-di-(1-methyl-1-
phenyl-ethyl)phenolato}- di(μ-isopropoxy)di-(isopropoxo) dititanium (3a)
Compound 2a (0.496 g, 1.0 mmol) and toluene (20 mL) were placed
into a Schlenk tube equipped with a magnetic stirrer under argon
4

V.A. Tuskaev, et al.
InorganicaChimicaActa498(2019)119159
F, 11.81; Ti, 9.92. Found (%): C, 57.19; H, 7.69; F, 11.78; Ti, 9.83. 1H
NMR (400 MHz, CDC13): δ = 1.47–1.53 (m, 42H, CH3), 1.69 (s, 18H,
CH3), 1.74 (s, 6H, CH3), 3.62 (m, 4H, CH), 7.13 (d, 4.2 Hz, 2H, Ar), 7.34
(d, 4.2 Hz, 2H, Ar). 19F NMR (CDC13): δ = −80.33. l3C NMR (101 MHz,
CDCl3): δ = 134.88, 125.70, 123.87, 123.33, 35.46, 35.33, 34.30,
34.21, 31.55, 30.74, 30.50, 30.45. FT-IR (KBr): 611, 594 cm−1 ν(Ti-O).
Crystallographic data for 3c, 3f·CH3C6H5 and 3g have been de-
posited with the Cambridge Crystallographic Data Center, CCDC
1914946 (3c), CCDC 1902082 (3f), and CCDC 1914947 (3g). The
supplementary crystallographic data can be obtained free of charge
from the Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
2.1.13. Di{2-[α-trifluoromethyl-α-pentafluorophenyl-methanolato]-4,6-di-
tert-buthyl-phenolato}di(μ-isopropoxo)di-(isopropoxy) dititanium (3f)
This complex was prepared as described above for 3a, starting from
a solution of ligand 2f (0. 470 g, 1.0 mmol) in toluene (10 mL) and Ti
(OPri)4 (0.29 mL, 1.0 mmol). Reaction was conducted for 48 h at 40 °C
and workup afforded 3f as a red powder. The crystals that formed were
filtered off, washed with hexane, and dried in vacuo. Yield 0.79 g
(62.3%). Calculated (%) for C56H68F16O8Ti2 (1268.8): C, 53.01; H,
5.40; F, 23.96; Ti, 7.54. Found (%): C, 52.96; H, 5.32; F, 523.88; Ti,
7.51. 1H NMR (400 MHz, CDC13): δ = 1.19 (s, 12, CH3), 1.21 (s, 18,
CH3), 1.22 (s, 18, CH3), 1.24 (s, 12H, CH3), 4.13 (s, 4H, CH), 7.28 (d,
J = 2.5 Hz, 2H, Ar), 7.42 (d, J = 2.7 Hz, 2H, Ar). 19F NMR (CDC13):
δ = −76.36, −137.54, −151.54, −161.26. 13C NMR (101 MHz,
CDCl3): δ = 141.81, 141.58, 135.15, 134.95, 129.01, 128.20, 126.70,
125.00, 124.71, 124.61, 124.42, 123.78, 123.51, 123.13, 122.27,
83.51, 35.41, 35.26, 35.17, 34.32, 34.18, 34.13, 31.45, 31.36, 31.33,
30.60, 30.55, 30.11, 30.08, 29.99, 29.89, 29.70, 25.06, 24.09, 23.94. δ
155.92, 147.35, 138.04, 132.90, 125.65, 123.78, 122.46, 121.74,
121.36, 34.61, 29.58, 24.82, 18.05. FT-IR (KBr): 605, 437 cm−1 ν(Ti-
O).
2.3. Polymerization of ethylene
The ethylene polymerization was performed in a 450-mL reactor
(Parr Instrument Co.) equipped with a magnetic stirrer and inlets for
loading components of catalytic systems and ethylene at a total ethy-
lene and toluene vapors pressure of 1.7 atm. Toluene (100 mL) and the
necessary amount of a co-catalyst (Et2AlCl/Bu2Mg or Et3Al2Cl3/Bu2Mg)
were loaded in the reactor. The reactor was heated to a specified
temperature, and the reaction mixture was saturated with ethylene.
Polymerization was started by the addition of pre-catalyst to the reac-
tion mixture. The pressure of ethylene was maintained constant during
polymerization. Polymerization was stopped by addition of 20 mL of
isopropanol to the reactor. The polymer was filtered off placed in a
beaker and stirred with 10% HCl/isopropanol mixture for 30 min at
elevated temperature. Then the polymer was filtered off and washed
several times with water/isopropanol mixture and dried under vacuum
at 70 °C until a constant weight was achieved.
2.4. Polymer evaluation methods
DSC was performed by a differential scanning calorimeter DSC-822e
(Mettler-Toledo, Switzerland) at a heating rate 10 °C/min in air.
Viscosity-average molecular weight of synthesized UHMWPE sam-
ples was calculated with the Mark-Houwink equation: Mv = 5.37·104
[η]1.37 [1], where: Mv = viscosity-average molecular weight (g/mol);
[η] = intrinsic viscosity in decalin at 135 °C (dl/g); [η] = (2ηsp
−2lnηr)1/2/0.056 (ηsp – specific viscosity decalin at 135 °C; ηr – relative
viscosity in decalin at 135 °C; ηr = ηsp + 1.
The mechanical characteristics of the oriented materials prepared
from the synthesized polymers were evaluated using the oriented tapes
obtained by a solid state processing of UHMWPE nascent reactor
powders. The monolithic tapes uniform over the entire length (100 μm
in thickness and 10 mm in width) were formed at a pressure and shear
deformation below the polymer melting point (124–126 °C). The tapes
were subjected to uniaxial drawing while using a Spinline Daca
equipment. The drawing temperature was set 4 °C below the polymer
melting point. The mechanical characteristics of the tapes were mea-
sured with a Hounsfield H1KS machine at the gauge length of the tested
samples 120 mm with 2 mm/min initial deformation rate. The reported
values were the average of at least 8 samples.
2.1.14. Di{2-[α-trifluoromethyl-α-phenyl-methanolato]-4,6-di-tert-buthyl-
phenolato}di(μ-isopropoxy)di-(isopropoxo) dititanium (3g)
This complex was prepared as described above for 3a, starting from
a solution of ligand 2 g (0.380 g, 1.0 mmol) in toluene (20 mL) and Ti
(OPri)4 (0.29 mL, 1.0 mmol). Reaction was conducted for 24 h at 40 °C
and workup afforded 3g as a dark red powder. The crystals that formed
were filtered off, washed with toluene, and dried in vacuo. Yield 0.93 g
(85.4%). Calculated (%) for C56H78F6O8Ti2 (1088.9): C, 61.77; H, 7.22;
F, 10.47; Ti, 8.79. Found (%): C, 61.73; H, 7.15; F, 10.38; Ti, 8.72. 1H
NMR (400 MHz, d-THF): δ = 1.14 (d, 18H, CH3), 1.26 (s, 18H, CH3),
1.46 (s, 12H, CH3), 4.54 (s, 4H, CH), 7.26 (m, 10H, Ar), 7.49 (d, 4H,
Ar). 19F NMR (d-THF): δ = −74.44. 13C NMR (101 MHz, d-THF):
δ = 158.24, 143.58, 139.00, 135.07, 127.54, 127.32, 127.27, 126.46,
124.67, 123.26, 123.23, 122.68, 87.06, 86.78, 77.12, 75.85, 67.07,
66.94, 66.85, 66.72, 66.63, 66.50, 66.28, 66.06, 62.77, 35.02, 33.90,
31.05, 29.74, 25.99, 25.42, 25.03, 24.88, 24.75, 24.68, 24.55, 24.48,
24.35, 24.15, 23.95. FT-IR (KBr): 623, 461 cm−1 ν(Ti-O).
2.2. X-ray crystal structure determination
The single-crystal X-ray diffraction data for 3c, 3f and 3g were
collected on the ‘Belok’ beamLine of the Kurchatov Synchrotron
Radiation Source (National Research Center ‘Kurchatov Institute’,
Moscow, Russian Federation) using a Rayonix SX165 CCD detector. In
total, 480–720 frames were collected with an oscillation range of 1.0° in
the φ scanning mode using two different orientations for each crystal.
The semiempirical correction for absorption was applied using the Scala
program [25]. The data were indexed and integrated using the utility
iMOSFLM from the CCP4 software suite [26]. For details, see Table S1.
The structures were determined by direct methods and refined by full-
matrix least square technique on F2 in anisotropic approximation for
non-hydrogen atoms. The independent part of the unit cell of 3f con-
tained a toluene solvate molecule, which was disordered over two po-
sitions around the inversion center. The hydrogen atoms were placed in
calculated positions and refined within the riding model with fixed
isotropic displacement parameters [Uiso(H) = 1.5Ueq(C) for the methyl
groups and 1.2Ueq(C) for the other groups]. All calculations were car-
ried out using the SHELXTL program suite [27].
3. Results and discussion
3.1. Ligands and coordination compounds synthesis and structure
Ligands 2a–d were synthesized by uncatalyzed C-alkylation of
phenols 1a–d with hexafluoroacetone according to the general proce-
dure suggested in [28]. Ligands 2e–g were obtained by the interaction
of 1-(3,5-di-tert-butyl-2-hydroxy-phenyl)-2,2,2-trifluoroethanone with
the corresponding organometallic compounds [23]. The synthesis and
crystal structure of the complex 3d has been previously described in
[29].
Reactions of the diprotio ligands 2a-g with Ti(OPri)4 proceeded in
toluene solution at 40–50 °C, via isopropanol elimination, to afford the
corresponding alkoxo-titanium(IV) complexes 3a–g. All compounds
were isolated in 62–93% yields as red, air-sensitive powders, which are
almost insoluble in pentane, moderately soluble in aromatic hydro-
carbons, and soluble in dichloromethane and THF. The compositions
and structures of complexes 3a–g were confirmed by IR, 1H and 13C
5

V.A. Tuskaev, et al.
InorganicaChimicaActa498(2019)119159
Fig. 4. General view of molecule 3g in crystal in thermal ellipsoid re-
presentation (p = 50%).
Fig. 2. General view of molecule 3c in crystal in thermal ellipsoid representa-
tion (p = 50%).
as a distorted trigonal-bipyramidal, with the aryloxy and μ-isopropoxy
ligands being in the axial positions. Hence, each bridging μ-isopropoxy
group is apical with respect to one titanium atom and equatorial with
respect to the other titanium atom. The ancillary ligands are bidentate
and form the six-membered chelate rings to the metal atoms. The
chelate rings are non-planar and adopt a boat conformation, with the
O1 oxygen and C7 carbon atoms deviating by 0.195(2) and 0.151(2) Å
(3c), 0.232(2) and 0.343(3) Å (3f), 0.438(1) and 0.510(2) Å (3g), re-
spectively, from the mean plane passed through the other atoms of the
ring. Interestingly, the Ti1–O1 and Ti1–O2 distances are very close to
each other (Table S2), regardless the different types of the oxygen
atoms – axial aryloxy-O1 and equatorial alkoxy-O2. As expected, the
Ti1–O3 distance of the terminal isopropoxy ligand is significantly
shorter than those of the both bridging isopropoxy and bidentate che-
lating ligands.
NMR spectroscopies as well as by elemental analysis. The integration of
the NMR signals confirmed the presence of two isopropoxy groups per
ligand unit in the reaction product. Isopropanol, liberated during the
interaction of the ligand and Ti(OPri)4 was not coordinated with tita-
nium, as it takes place for complexes of the composition LTiCl2*2iPrOH
[29].
However, these data do not preclude aggregation of monomeric
units in order to increase coordination number.
The structures of the products 3c, 3f and 3g were unambiguously
established by X-ray diffraction study and are shown in Figs. 2–4 along
with the atomic numbering scheme. Experimental data for the X-ray
diffraction studies of compounds and selected bond lengths and angles
are given in Tables S1 and S2. Crystals suitable for X-ray diffraction
studies were obtained from concentrated solution of complexes in to-
luene.
Crystal packing of 3c, 3f and 3g is stacking along the crystal-
lographic b, c and c axis, respectively (Figs. S41–43). The molecules of
3c and 3g are arranged at van-der-Waals distances, whereas the mo-
lecules of 3f are linked within the stacks by weak non-valent F1⋅⋅⋅F2
(1 − x, 1 − y, 1 − z) [2.839(3) Å] interactions.
All complexes have dimeric structure consisting of two five-co-
ordinated mononuclear fragments shared the central four-membered
Ti–(μ-OPri)2–Ti cycle, and, in the crystal, occupy a special position on
the inversion center, i.e., the intrinsic symmetry of the complexes is Ci
¯
( ) and their mononuclear fragments are equivalent. The μ-isopropoxo
1
It is known that titanium alkoxides have a high tendency to increase
their coordination numbers. In the absence of an external Lewis base
the coordination number is increased by aggregation to larger units via
alkoxo bridges. It is known that the degree of association depends on
the steric bulk of the alkoxo ligands, for example, the titanium atoms in
the tetramer [Ti(OR)4]4 (R = Me, Et) reach their optimal coordination
number of 6 by formation of two µ3-OEt and four µ2-OEt ligands [30],
ligands are asymmetrically bridging [1.8983(11) and 2.1276(11) Å
(3c), 1.9378(17) and 2.0845(18) Å (3f), 1.9370(9) and 2.0945(9) Å
(3g), Table S2] between the titanium atoms, so the four-membered
cycles represent a rhombus with the non-bonding Ti⋯Ti separation.
The coordination geometry around the titanium atoms can be described
t
while bulkier Ti(OCH2 Bu)4 exists in the dimeric form with five-co-
ordinate titanium [31]. It is interesting, that in our case, even a ligand
2b that does not contain bulky substituents in the ortho-position to the
phenolic hydroxyl, also forms centrosymmetric dimer. However, the
use of 2-hydroxyphenole derivatives without substituents on benzylic
carbon atom, results in more complicated coordination compounds (for
example, complexes D, E, F and G (Fig. 1); their crystal structures are
described in [10,12]).
3.2. Catalytic properties of Ti(IV) complexes
Catalytic properties of compounds 3a–g in ethylene polymerization
are summarized in Table 1. To activate pre-catalysts, a binary activator
{3Et2AlCl + Bu2Mg}, proposed by Kissin et al. [32–33] or
{3Et3Al2Cl3 + Bu2Mg}, were used.
The maximum catalytic activity in this series − 2660 kg PE mol
(Ti)−1 h−1 atm−1, were demonstrated by complexes 3c and 3d, acti-
vated by the binary cocatalyst {1.5 Et3Al2Cl3 + MgBu2}. In most cases
(for complexes 3a, 3c, 3d and 3e) the use of Et3Al2Cl3 allows to achieve
higher activity (Table 1, Fig. 5A). According to T. Fujita classification
[20], most of these pre-catalysts can be classified as highly active.
Complexes stabilized by ligands containing bis-(trifluoromethyl)-
Fig. 3. General view of molecule 3f·CH3C6H5 in crystal in thermal ellipsoid
representation (p = 50%).
6

V.A. Tuskaev, et al.
InorganicaChimicaActa498(2019)119159
Table 1
Ethylene Polymerization by complexes 3a–f.a
c
Run
Complex
Cocatalyst,
[Al]/[Mg]
Ab
Bulk density, g/cm3
Mv, 106
D
Deg. of crystald
%
Tm
°C
1
2
3
4
5
6
7
8
3a
3a
3b
3b
3c
3c
3d
3d
3e
3e
3f
3g
Et2AlCl/Bu2Mg 300/100
Et3Al2Cl3/Bu2Mg 300/100
Et2AlCl/Bu2Mg 300/100
Et3Al2Cl3/Bu2Mg 300/100
Et2AlCl/Bu2Mg 300/100
Et3Al2Cl3/Bu2Mg 300/100
Et2AlCl/Bu2Mg 300/100
Et3Al2Cl3/Bu2Mg 300/100
Et2AlCl/Bu2Mg 300/100
Et3Al2Cl3/Bu2Mg 300/100
Et2AlCl/Bu2Mg 300/100
Et2AlCl/Bu2Mg 300/100
Et3Al2Cl3/Bu2Mg 300/100
Et2AlCl/MgBu2 300/100
Et3Al2Cl3/MgBu2 300/100e
1580
2090
2540
2345
2340
2660
2290
2660
1490
1543
743
0.049
0.060
0.039
0.060
0.044
0.095
0.046
0.072
0.054
0.071
0.031
0.053
0.06
3.1
2.8
1.8
2.1
1.0
2.9
1.6
3.6
2.2
2.2
2.4
1.8
2.7
1.66
3.34
74.7/49.2
69.4/47.1
73.8/50.9
69.1/48.2
70.3/57.8
67.7/48.2
59.72/40.9
75.45/43.2
75.8/49.5
69.8/39.9
75.0/50.6
80.4/52.1
76.0/45.0
68.4/52.8
75.1/47.2
141/137
139/132
140/133
140/135
138/134
140/133
139.1/136.4
140.6/134.8
140/136
140/135
139/136
138/136
143/137
138/133
140/135
9
10
11
12
13
14e
15e
1060
540
2914
2971
3g
Ti(OiPr)4
Ti(OiPr)4
0.049
0.053
a
Polymerizations were carried out in 100 mL of toluene with 5·10−6 mol of precatalyst at a constant 0.7 atm excessive ethylene pressure for 30 min, temperature
30 °C.
b
c
Activity, kg of PE·mol−1 h−1 atm−1
.
Melting points were determined by DSC, the values for the first and second heating runs are given.
Degree of crystallinity was calculated by use of value ΔHm100% = 288 J/g; the values for the first and second heating runs are given.
According to the results [35].
d
e
carbinol fragment (3a–d) showed the greatest activity. Comparing the
activity of complexes 3d–g (having the same substituents in the aro-
matic fragment), it can be noted that replacing one of the tri-
fluoromethyl groups with a methyl, phenyl or perfluorophenyl group
(3e–g) is accompanied by a significant decrease in activity (Table 1,
Fig. 5A).
respectively (Table 1).
It is well known [36,37] that drawability of UHMWPE highly de-
pends on its supramolecular structure. To examine the morphologies of
these powders, SEM observations have been made (Fig. 6). All of these
micrographs are of the same magnification for comparative purposes.
As can be seen from the scanning electron micrographs at low magni-
fication, the polymer particles have the irregular shape and porous
structure, which determines the low bulk density (0.031–0.095 g/cm3)
of the obtained samples.
At high magnification most samples, regardless of the nature of the
organoaluminum activator, have nodular type microstructures (eg,
polymer prepared on 3a/Et2AlCl + Bu2Mg, Fig. 6, top). However, in
some cases (polymer prepared on 3f/Et3Al2Cl3/Bu2Mg, Fig. 6, bottom)
there are no zones with a dense packing of spherical particles on the
surface; the particles look fused and connected by a large number of
fibrils, forming a “cobweb” structure.
The processing of reactor powders of UHMWPE obtained with
complexes 3a–g into high-modulus oriented films was carried out by
preparing monolithic samples under pressure and shear deformation at
an elevated temperature below polymer melting point with subsequent
uniaxial drawing [8]. Criteria for the quality of the resulting oriented
film tapes were: homogeneity of the resulting filament along the width
and homogeneity of the samples masses within one multiplicity at one
length.
To reveal the role of the ancillary ligands, we previously conducted
a series of ethylene polymerizations using {Ti(OPri)4/3Et2AlCl/Bu2Mg}
and {Ti(OPri)4/1.5Et3Al2Cl3/Bu2Mg} catalytic systems [35]. All the
conditions of the polymerization process – time and temperature,
The size of the substituent in the ortho-position to the phenolic
hydroxyl practically does not affect the productivity of catalytic systems
(complex 3b with no bulky hydrocarbon substituent in the 6th position,
was one of the most active), but the absence of shielding of the metal
center leads to a decrease in the molecular weight of the polymer. A
similar trend is typical for most non-metallocene catalysts with phenol-
containing ligands - the presence of bulky substituents in the ortho-
position to phenolic hydroxyl generally increases the molecular weight
of the polymer [17–20] due to increase of the propagation rate con-
stant. To our surprise, the molecular weight of the polymer obtained on
the adamantyl-containing complex 3c activated with Et2AlCl was un-
expectedly low (1.02 106 D). It is obvious that in the considered series
of pre-catalysts both the absence of steric shielding of the phenolic
hydroxyl and the presence of rigid cyclic substituents with a large steric
volume (e.g., adamantyl) is accompanied by a decrease in the molecular
weight of the polymer.
In some cases, the replacement of Et2AlCl with Et3Al2Cl3 leads to a
significant increase in the molecular weight of the polymer (Table 1,
Fig. 5B). A similar trend was observed for titanium complexes stabilized
with 1,4- and 1,2-diolate ligands [34,35].
The melting point and degree of crystallinity are typical for
UHMWPE [1,36] and are in the range of 139–143 °C and 68–75%
Fig. 5. Activities of the catalytic systems (A) and molecular weight of the obtained UHMWPE samples (B) versus the composition of catalytic system.
7

V.A. Tuskaev, et al.
InorganicaChimicaActa498(2019)119159
Fig. 6. Scanning electron micrographs of a series of nascent reactor powders, prepared on 3a/Et2AlCl + Bu2Mg (top) and 3f/Et3Al2Cl3/Bu2Mg (bottom).
Table 2
Mechanical properties of UHMWPE oriented film tapes.
(44) in this series was observed for UHMWPE, obtained on pre-catalyst
3a, activated by Et2AlCl/Bu2Mg. UHMWPE powders synthesized with
complexes 3a, 3b and 3e activated by Et2AlCl, allowed to achieve
larger values of drawing ratio compared with samples synthesized using
Et3Al2Cl3. The obtained results suggest that the volume of substituents
in the benzylic position of the ligand has a more significant effect on the
mechanical properties of oriented films than the substituent in the
ortho-position to the phenolic hydroxyl. The films produced from
powders obtained with the pre-catalyst 3e (containing a methyl group
instead of trifluoromethyl) have the greatest value of Young's modulus
in this series – 143 GPa. Replacing one of the trifluoromethyl groups
with bulkier phenyl or perfluorophenyl groups negatively affects the
mechanical parameters of oriented films (entries 11–12).
Entrya
Catalytic system
Draw ratio
σ,
GPa
E,
GPa
ε,
%
1
2
3
4
6
8
9
10
11
12
15
3a/Et2AlCl/Bu2Mg
3a/Et3Al2Cl3/Bu2Mg
3b/Et2AlCl/Bu2Mg
3b/Et3Al2Cl3/Bu2Mg
3c/Et3Al2Cl3/Bu2Mg
3d/Et3Al2Cl3/Bu2Mg
3e/Et2AlCl/Bu2Mg
3e/Et3Al2Cl3/Bu2Mg
3f/Et2AlCl/Bu2Mg
44
24
32
28
24
24
40
28
28
20
20
2.65
2.00
2.15
2.25
1.83
2.34
2.54
2.37
2.18
2.10
1.99
127
121
141
115
118
85
143
113
105
86
2.56
2.35
2.14
2.58
1.96
3.09
2.23
2.67
2.75
3.00
2.12
3g/Et2AlCl/Bu2Mg
Ti(OiPr)4/Et3Al2Cl3/MgBu2
105
A single-stage character of film rupture is observed in a number of
cases, indicating uniformity of the samples. Close values of elongations
and elastic modulus for a series of samples with the same drawing ratio
confirm the high quality of UHMWPE reactor powder,
a
Numbering corresponds to Table 1.
ethylene pressure, molar ratios Ti/Al/Mg were identical. According to
the results of the experiments, the model systems showed high activity
~2.9 103 kg of PE mol−1 h−1 atm−1 regardless of the composition of
the activator (Table 1, runs 14–15). Differences are manifested in the
properties of the polymer – the use of Et3Al2Cl3 instead of Et2AlCl re-
sults in obtaining UHMWPE with a significantly higher molecular
weight (3.3·106 and 1.7·106, respectively). The oriented film tapes,
obtained from these UHMWPE powders, are characterized by low va-
lues of average tensile modulus (~105 GPa, Table 2, runs 14–15).
Table 2 shows the mechanical characteristics of film tapes prepared
from reactor powders obtained in runs 1–4, 6 and 8–12 (Table 1).
Unfortunately, not all compacted films turned out to be suitable for
orientational drawing – samples 5, 7 and 9 (Table 1) could not be
converted to tapes by this method. The morphology of these reactor
powders is characterized by the presence of “melted” spherical particles
forming a stretched fibrillar grid. The polymer obtained in run 5, was
not tested due to the low molecular weight. Stress-strain curves of
UHMWPE orientated film tapes are shown in Fig. 7.
Comparing these results with those previously obtained, it can be
stated that this group of pre-catalysts showed the best results in a series
of titanium complexes stabilized by 2-hydroxymethylphenol deriva-
tives. Thus, tetrameric Ti-methoxo complex A, as well as dimeric Ti-
chloro(methoxo) complex B (Fig. 1) with the same ancillary ligand as in
complex 3d, are very effective catalysts for UHMWPE production,
however, oriented materials obtained from these polymers are char-
acterized by rather low values of breaking strength (~1.5 GPa) and
elastic modulus (60 GPa) [10]. UHMWPE samples obtained on hexa-
nuclear complex C were processed into oriented films with tensile
strength values in the range 1.9–2.5 GPa, but the values of elastic
modulus did not exceed 105 GPa [11].
The oriented films obtained with pre-catalyst without substituents
in the benzylic position (complexes D, E, F and G (Fig. 1) are inferior to
the best samples obtained in the present work and have tensile strength
in the range 1.9–2.1 GPa and elastic modulus 90–110 GPa. Among
them, the most interesting is the dichlorotitanium complex F, com-
bining high activity (2740 kg of PE mol−1 h−1 atm−1) and good me-
chanical characteristics of the oriented films (tensile strength
The maximum value of tensile strength (2.65 GPa), with an average
tensile modulus (127 GPa) and the highest value of the drawing ratio
8

V.A. Tuskaev, et al.
InorganicaChimicaActa498(2019)119159
3000
2000
1000
0
3000
2000
1000
0
3a
3a
3b
3b
3c
3d
3d
3e
3f
3g
0
1
2
3
0
1
2
3
Strain, %
Strain, %
Fig. 7. Stress-elongation curves for UHMWPE orientated tapes (the samples obtained on catalytic systems with Et2AlCl are indicated by the solid lines and with
Et3Al2Cl3 – by dotted lines).
−2.4 GPa, elongation – 2.67%). Unlike all previously considered
structures, complex F contains free hydroxymethyl groups. In the fu-
ture, we plan to investigate in more detail the effect of this structural
fragment on the activity of catalytic systems and the properties of the
obtained polymers.
but the absence of a substitute significantly reduces the molecular
weight of the resulting polymer.
Viscosity-average molecular weights of obtained polymer samples
were in the range 1.02–3.1·106 Da. The UHMWPE nascent reactor
powders were processed by a solvent-free method into high-strength
(up to 2.65 GPa) and high-modulus (over 140 GPa) oriented film tapes.
To obtain disentangled UHMWPE suitable for solution-free proces-
sing, it is preferable to activate pre-catalysts with mixtures Et2AlCl and
Bu2Mg (despite the fact that using of Et3Al2Cl3 allows to obtain poly-
mers with a higher yields and higher molecular weights).
The present publication is a part of the screening program of a large
group of transition metals coordination compounds, aimed at identi-
fying the most promising pre-catalysts for the synthesis of disentangled
UHMWPE. At this stage of research, achieving the maximum values of
mechanical characteristics was not our goal, since optimization of the
synthesis of UHMWPE reactor nascent powder and its solid-phase
processing (eg, multistage drawing [38] or orientational drawing in the
zone-drawing regime [39]) allows to significantly improve the me-
chanical properties of oriented materials. For example, the value of the
module for UHMWE films manufactured by a similar technology by
Teijin Aramid under the trade name Endumax®, is 170 GPa; and con-
ventional UHMWPE yarn, obtained by gel spinning are characterized by
the module values of 113 GPa [40].
We have previously shown that the catalysts formed upon activation
of titanium complexes with OO-type ligands by a mixture of alkylalu-
minum chlorides and dibutylmagnesium are not single-site. In cases
where the molecular weight of the polymer was not too high, which
allowed applying GPC, the values of Mw/Mn were in the range
2.5–11.5 [23]. The multisite nature of such catalytic systems was also
noted by Kissin et al. who proposed combinations of AlR2Cl/MgR2 as
cocatalysts for Ziegler–Natta, Metallocene, and Post-Metallocene Cata-
lysts [33]. On the other hand, it is known that in order to improve the
processability of UHMWPE, its mixtures with low molecular weight
polyethylene are used [41–43]. The main method for obtaining such
blends is mixing the melts of the components in the extruder, which is
rather difficult process due to significant differences in the viscosity of
components. It is likely that a broad molecular weight distribution of
UHMWPE samples obtained on titanium complexes activated by com-
binations of AlR2Cl/MgBu2 facilitates the solid-phase processing.
Acknowledgments
This work was financially supported by the Russian Science
Foundation (Project No 16-13-10502). Synthesis of the complexes 3a
and 3c was supported by Russian Foundation for Basic Research
(Project no. 17-03-00234). Synchrotron radiation-based single-crystal
X-ray diffraction measurements were performed at the unique scientific
facility Kurchatov Synchrotron Radiation Source supported by the
RUDN University Program “5-100”. NMR was performed with the fi-
nancial support from Ministry of Science and Higher Education of the
Russian Federation using the equipment of Center for molecular com-
position studies of INEOS RAS.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.ica.2019.119159.
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