New Titanium(IV)-Alkoxide Complexes Bearing Bidentate OO Ligand with the Camphyl Linker as Catalysts for High-Temperature Ethylene Polymerization and Ethylene/1-Octene Copolymerization

In order to increase the thermal stability of olefin polymerization precatalysts, new titanium(IV) complexes with diolate ligands differing in the degree of steric hindrances were synthesized from readily available precursor (±)camphor. The structures of the complexes 1–2 were established by X-ray diffraction. Complexes 1–4 in the presence of an activator {EtnAlCl3-n + Bu2Mg} catalyzed the synthesis of UHMWPE with an Mv up to 10 million and a productivity of up to 3300 kg/molTi·atm·h. The obtained polymers are obviously characterized by a low density of macromolecular entanglement, which makes it possible to use the solid-phase method for their processing. The mechanical characteristics of the oriented UHMWPE films had a breaking strength up to 2.7 GPa and an elastic modulus of up to 151 GPa. The precatalysts 1–4 were also active in ethylene/1-octene copolymerization. The comonomer content was in the range of 1.4–4.6 mol%. The use of a rigid linker and an increase in the steric load of the diolate complexes ensured the thermal stability of the catalytic system in the range of 50–70 °C.


Introduction
The development of catalysts for the (co)polymerization of olefins based on transition metal complexes is one of the most advanced areas of modern organometallic chemistry [1][2][3][4]. However, research in this field will undoubtedly continue due to the constant need for new polymer materials. The value of new catalytic systems is determined not only by their productivity and the properties of the resulting polymers, but also by the technological parameters of the polymerization process, including the ability to operate in an acceptable temperature range.
Titanium-alkoxide complexes are perhaps one of the most accessible and inexpensive precatalysts. We know that titanium alkoxides in the presence of organoaluminum compounds are capable of catalyzing the polymerization of conjugated dienes [5][6][7] as well An essential point limiting the possibility of the industrial implementation of this group of catalysts is their low thermal stability. As a rule, the maximum productivity of such systems is achieved at a temperature of 30 °С [15][16][17][18][19][20][21][22][23][24][25][26][27]; an increase in the polymerization temperature to 50-80 °С is accompanied by deactivation and a significant reduction in the polymer's molecular weight. The aim of this work is the structural modification of As was shown by Y. V. Kissin et al., the addition of the organomagnesium compound, e.g., Bu 2 Mg to the mixture Ti(OiPr) 4 -Et 2 AlCl results in active, cheap, and affordable catalytic systems suitable for the polymerization of propylene [13] and the copolymerization of ethylene with higher olefins [14].
Previously, we reported on the ability of various titanium(IV)-diolate complexes VII-X [15][16][17][18][19][20][21][22], including those with additional heteroatoms [23][24][25][26][27] (Chart 1), to catalyze the (co)polymerization of ethylene in the presence of such Al/Mg activators. This group of postmetallocene precatalysts is poorly studied, which is most likely due to the specifics of their activation: in the presence of trialkylaluminum derivatives, alkylaluminum chlorides, or alkylalumoxanes (traditional activators in Ziegler-Natta catalysis), and the activity of these systems is low or does not manifest itself at all. However, when using the Al/Mg activators Alk n AlCl 3-n +Bu 2 Mg (proposed by Yu. V. Kissin et al. [28,29]), their productivity in ethylene polymerization reached 4000 kg/mol·atm·h. It is important to note that, in most cases, these catalytic systems produce disentangled UHMWPE, which can be processed by the solid-phase method into high strength-oriented films and tapes, which are in high demand in various industries. In addition, such catalytic systems effectively catalyze the copolymerization of ethylene with higher olefins, and in some cases, even higher productivity is achieved ofup to 5 tons of copolymer /mol atm·h [20].
An essential point limiting the possibility of the industrial implementation of this group of catalysts is their low thermal stability. As a rule, the maximum productivity of such systems is achieved at a temperature of 30 • C [15][16][17][18][19][20][21][22][23][24][25][26][27]; an increase in the polymerization temperature to 50-80 • C is accompanied by deactivation and a significant reduction in the polymer's molecular weight. The aim of this work is the structural modification of the ligand environment of the metal, aimed at increasing the thermal stability of the considered precatalysts.

Experimental Section
All manipulations with air-sensitive materials were performed using standard Schlenk techniques. Argon and ethylene of a special purity grade (Linde gas) were dried by purging through Super Clean™ Gas Filters.
Toluene and nefras were 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, ethylaluminum sesquichloride, and di-n-butylmagnesium (Aldrich) were used without further purification. (±)-Camphorquinone was obtained by the method described in [30]. The preparation of the ligands L1 and L2 followed the procedure described in [31]; their properties corresponded to the literature data.
NMR spectra were recorded on a Bruker AMX-400 instrument (Mundelein, Illinois 60060 USA). Elemental analysis (C, H, Cl) was performed by the microanalytical laboratory at A. N. Nesmeyanov Institute of Organoelement Compounds on Carlo Erba-1106 and Carlo Erba-1108 instruments. The content of Ti was performed by X-ray fluorescence analysis on a VRA-30 device (Karl Zeiss, Germany).
[L 1 Ti(OiPr) 2 ] 2 (Complex 1). Ligand L1 (0.85 g, 5 mmol) and toluene (22 mL) were placed into a Schlenk tube equipped with a magnetic stirrer under an argon atmosphere, followed by the addition of Ti(OiPr) 4 (1.42 g, 1.48 mL, and 5 mmol) at room temperature. The resulting suspension was heated until all solids dissolved. The next day, the formed crystals were collected by filtration and dried in vacuo. Yield 1.41 g (81.5%). Calculated (%) for C 32 (Complex 3). In a 100 mL flame-dried Schlenk flask, ligand L1 (0.85 g, 5 mmol) was dissolved in anhydrous toluene (20 mL). A solution of TiCl 2 (OiPr) 2 (1.185 g, 0.05 mmol) in toluene (20 mL) was added to the resulting solution under stirring in an argon atmosphere. The solution was stirred for 14 h at room temperature, and the precipitated complex was filtered off, washed with hexane (5 mL), and dried in a vacuum. The yield was 1.4 g (69%). Calculated (%) for C 16

X-ray Crystal Structure Determination
X-ray diffraction experiments were carried out at 100 K for 1 and at 240 K for 2 (below this temperature, the crystals of 2 cracked) with a Bruker D8 Quest diffractometer, using graphite monochromated Mo-Kα radiation (λ = 0.71073 Å). Using Olex2 [32], the structures were solved with the ShelXT [33] structure solution program using Intrinsic Phasing and refined with the olex2.refine [34] refinement package using Least-Squares minimization against F 2 in anisotropic approximation for nonhydrogen atoms. Positions of hydrogen atoms were calculated, and they were refined in isotropic approximation within the riding model. Crystal data and structure refinement parameters for 1 and 2 are given in Table 1. CCDC 2189447 (for 1) and 2189448 (for 2) contain the supplementary crystallographic data for this paper.

Polymerization Experiments
The ethylene polymerization and ethylene/α-olefine copolymerization techniques are described in detail in [21].

Polymer Characterization Methods
DSC was performed by a differential scanning calorimeter DSC-822e (Mettler-Toledo, Switzerland) at a heating rate of 10 • C/min in argon.
Viscosity average molecular weight of synthesized UHMWPE samples was calculated with the Mark-Houwink equation [35].
The technique for manufacturing-oriented films from UHMWPE nascent reactor powder and determining their mechanical characteristics is described in detail in [36].
Scanning electron microscopy investigations of morphologies of nascent reactor powders were carried out with a high-resolution Tescan VEGA3 SEM operated at 5 kV. Aspolymerized particles were carefully deposited on SEM stubs, and the samples were coated with gold by a sputtering technique. 13 C NMR spectra of ethylene/octene-1 copolymers (~5 wt % solutions in dichlorobenzene) were recorded at 150 • C on a Bruker Avance-400 spectrometer at 101 MHz.
Gel permeation chromatographic (GPC) analysis of copolymers was carried out at 135 • C with a Waters GPCV-2000 chromatograph equipped with two columns (PLgel,

Results and Discussion
Commercially available (±) camphor was used as the initial compound for the synthesis of this group of ligands, the oxidation of which yielded camphoquinone (Scheme 1). Further, the reduction of camphoquinone with sodium borohydride or its interaction with methyl magnesium iodide yielded ligands L1-L2 (Scheme 1) differing in the steric load of hydroxyl groups.

Scheme 1. Synthesis of complexes 1-4.
Alkoxo-titanium(IV) complexes 1-2 were obtained by the reaction of the ligands L1-L2 with Ti(OiPr)4 in a toluene solution. All compounds were isolated in 69-82% yields as air-sensitive powders, which are soluble in aromatic hydrocarbons. Titanium-dichloride complexes 3-4 were synthesized by direct interaction of the ligands L1-L2 with one equivalent of TiCl2(OiPr)2 in toluene. The compositions and structures of complexes 1-4 were confirmed by elemental analysis and 1 H and 13 C NMR spectroscopies. The integration of the NMR signals confirmed the presence of two isopropoxy groups per ligand unit in the reaction product. The structures of the complexes 1-2 were unambiguously established by X-ray diffraction study and are shown in Figure 1 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. Alkoxo-titanium(IV) complexes 1-2 were obtained by the reaction of the ligands L1-L2 with Ti(OiPr) 4 in a toluene solution. All compounds were isolated in 69-82% yields as air-sensitive powders, which are soluble in aromatic hydrocarbons. Titaniumdichloride complexes 3-4 were synthesized by direct interaction of the ligands L1-L2 with one equivalent of TiCl 2 (OiPr) 2 in toluene. The compositions and structures of complexes 1-4 were confirmed by elemental analysis and 1 H and 13 C NMR spectroscopies. The integration of the NMR signals confirmed the presence of two isopropoxy groups per ligand unit in the reaction product. The structures of the complexes 1-2 were unambiguously established by X-ray diffraction study and are shown in Figure 1 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.
The complexes 1 and 2 crystallize in the triclinic space group P-1 with a half of the complex species being symmetry-independent; the appropriate symmetry element, the inversion center, is located in the geometric center of a Ti 2 O 2 cycle. Each titanium(IV) ion coordinates two isopropoxy groups and two camphorquinone ligands that act both as a bridging ligand and a chelate ligand ( Table 1). The resulting coordination polyhedron is a distorted square pyramid, as gauged by continuous symmetry measurements [37]. They measure how close the shape of the polyhedron is to a reference shape, such as an ideal square pyramid (SPY-5). The lower the value of an appropriate symmetry measurement, the better the fit is to a chosen polyhedron (Table S2). The complexes 1 and 2 crystallize in the triclinic space group P-1 with a half of the complex species being symmetry-independent; the appropriate symmetry element, the inversion center, is located in the geometric center of a Ti2O2 cycle. Each titanium(IV) ion coordinates two isopropoxy groups and two camphorquinone ligands that act both as a bridging ligand and a chelate ligand ( Table 1). The resulting coordination polyhedron is a distorted square pyramid, as gauged by continuous symmetry measurements [37]. They measure how close the shape of the polyhedron is to a reference shape, such as an ideal square pyramid (SPY-5). The lower the value of an appropriate symmetry measurement, the better the fit is to a chosen polyhedron (Table S2).
The catalytic activity of new titanium-diolate complexes 1-4 was studied in ethylene polymerization (Table 1). To activate precatalysts, binary activators {Et2AlCl or Et3Al2Cl3 +Bu2Mg} at a molar ratio of Al/Mg = 3/1 [28,29], were used. For the activator {Et-AlCl2+Bu2Mg}, a molar ratio of Al/Mg = 2/1 was used since according to [21], it is precisely this ratio of the activator components that makes it possible to achieve the maximum productivity of diolate-titanium complexes.
For complex 1, the effect of the nature of the organoaluminum compound (EtAlCl2, Et2AlCl, and Et3Al2Cl3) contained in the Al/Mg activator on the productivity of catalytic systems and the properties of the resulting polymer were studied (entries 1, 2, and 4; Table  1). The maximum activity was shown by the system containing EtAlCl2-a compound exhibiting the maximum Lewis acidity.
For the dichloride complex 3, this pattern changes slightly: in a row Et2AlCl, Et3Al2Cl3 and EtAlCl2 there is a consistent increase in both the productivity of the system and the molecular weight of polymers (entries 15-17, Table 1).
Comparing the effect of the nature of the organoaluminum component of the activator on the properties of the resulting polymer, it can be noted that for dichloride complexes 3-4, the replacement of Et2AlCl by Et3Al2Cl3 led to a very significant increase in molecular weight (by 2.3-2.6 times (entries 15 vs. 16 and 18 vs. 19, Table 1). In the case of alkoxide complexes 1-2, this effect also manifested itself, but to a much lesser extent (no more than 1.2 times, entries 1 vs. 2 and 10 vs. 11); a similar trend was seen previously [21,26].
Preactivation (holding the precatalyst with a small amount of activator in a Schlenk tube for 24 h) led to a significant drop in activity, from 2629 to 1600 kg/mol·h·atm, with a simultaneous significant increase in the molecular weight of the polymer (from 5.9 up to 7.7 × 10 6 Da). The replacement of the aromatic solvent toluene with the aliphatic one nefras The catalytic activity of new titanium-diolate complexes 1-4 was studied in ethylene polymerization (Table 1). To activate precatalysts, binary activators {Et 2 AlCl or Et 3 Al 2 Cl 3 +Bu 2 Mg} at a molar ratio of Al/Mg = 3/1 [28,29], were used. For the activator {EtAlCl 2 +Bu 2 Mg}, a molar ratio of Al/Mg = 2/1 was used since according to [21], it is precisely this ratio of the activator components that makes it possible to achieve the maximum productivity of diolate-titanium complexes.
For complex 1, the effect of the nature of the organoaluminum compound (EtAlCl 2 , Et 2 AlCl, and Et 3 Al 2 Cl 3 ) contained in the Al/Mg activator on the productivity of catalytic systems and the properties of the resulting polymer were studied (entries 1, 2, and 4; Table 1). The maximum activity was shown by the system containing EtAlCl 2 -a compound exhibiting the maximum Lewis acidity.
For the dichloride complex 3, this pattern changes slightly: in a row Et2AlCl, Et3Al2Cl3 and EtAlCl2 there is a consistent increase in both the productivity of the system and the molecular weight of polymers (entries 15-17, Table 1).
Comparing the effect of the nature of the organoaluminum component of the activator on the properties of the resulting polymer, it can be noted that for dichloride complexes 3-4, the replacement of Et 2 AlCl by Et 3 Al 2 Cl 3 led to a very significant increase in molecular weight (by 2.3-2.6 times (entries 15 vs. 16 and 18 vs. 19, Table 1). In the case of alkoxide complexes 1-2, this effect also manifested itself, but to a much lesser extent (no more than 1.2 times, entries 1 vs. 2 and 10 vs. 11); a similar trend was seen previously [21,26].
Preactivation (holding the precatalyst with a small amount of activator in a Schlenk tube for 24 h) led to a significant drop in activity, from 2629 to 1600 kg/mol·h·atm, with a simultaneous significant increase in the molecular weight of the polymer (from 5.9 up to 7.7 × 10 6 Da). The replacement of the aromatic solvent toluene with the aliphatic one nefras was accompanied by a very significant decrease in activity (from 2629 to 460 kg/mol·h·atm and an equally noticeable increase in M v from 5.9 to 8.5 × 10 6 , and the use of preactivation technique in aliphatic solvent made it possible to increase this value to 10.1 × 10 6 Da (entries 5 and 6, Table 1).
For the alkoxo complexes 1 and 2, the influence of the polymerization temperature on the activity and on the molecular weights of the resulting polyethylene was studied ( Figure 2). It was established that both complexes exhibited a sufficiently high thermal stability: for complex 1 with an increase in the polymerization temperature from 10 to was accompanied by a very significant decrease in activity (from 2629 to 460 kg/mol·h·atm and an equally noticeable increase in Mv from 5.9 to 8.5·10 6 , and the use of preactivation technique in aliphatic solvent made it possible to increase this value to 10.1·10 6 Da (entries 5 and 6, Table 1).
For the alkoxo complexes 1 and 2, the influence of the polymerization temperature on the activity and on the molecular weights of the resulting polyethylene was studied ( Figure 2). It was established that both complexes exhibited a sufficiently high thermal stability: for complex 1 with an increase in the polymerization temperature from 10 to 50 °C, the activity increased by 20%. At a temperature of 70 °C, the activity remained quite high at 2300 kg/molTi·atm·h. Complex 2 with the sterically more hindered ligands behaved somewhat differently: the maximum activity (3100 kg/molTi·atm·h.) appeared at 10 °C, and with an increase in the polymerization temperature, the activity consistently decreased to 1500 kg/molTi·atm·h. at 70 °C.
With an increase in the polymerization temperature, the processes of polymer chain termination were accelerated, which is reflected in a significant decrease in the molecular weights of the polymer. However, the polymers obtained at 50 °C and even 70 °C (for complex 2) were ultra-high molecular weight polyethylenes. Thus, the process temperature allowed us to control the molecular weight of the resulting polymers.
The morphology and molecular weight are important characteristics of UHMWPE nascent reactor powder, which determine the efficiency of its processing into high modulus-and high strength-oriented materials. To examine the morphologies of these powders, scanning electron microscope (SEM) observations were performed (Figure 3). At a low magnification (Figure 3, top), the UHMWPE powder particles do not have a spherical shape, typical for the polymer obtained on classical Ti/Mg catalysts. The irregular shape and porous structure of the powder particles determine the low bulk density (0.05-0.088 g/cm 3 ) of the obtained samples. Complex 2 with the sterically more hindered ligands behaved somewhat differently: the maximum activity (3100 kg/mol Ti ·atm·h.) appeared at 10 • C, and with an increase in the polymerization temperature, the activity consistently decreased to 1500 kg/mol Ti ·atm·h. at 70 • C.
With an increase in the polymerization temperature, the processes of polymer chain termination were accelerated, which is reflected in a significant decrease in the molecular weights of the polymer. However, the polymers obtained at 50 • C and even 70 • C (for complex 2) were ultra-high molecular weight polyethylenes. Thus, the process temperature allowed us to control the molecular weight of the resulting polymers.
The morphology and molecular weight are important characteristics of UHMWPE nascent reactor powder, which determine the efficiency of its processing into high modulusand high strength-oriented materials. To examine the morphologies of these powders, scanning electron microscope (SEM) observations were performed (Figure 3). At a low magnification (Figure 3, top), the UHMWPE powder particles do not have a spherical shape, typical for the polymer obtained on classical Ti/Mg catalysts. The irregular shape and porous structure of the powder particles determine the low bulk density (0.05-0.088 g/cm 3 ) of the obtained samples.
At high magnifications (Figure 3, bottom), the UHMWPE powder particles have a broccoli-like shape and differ in the number of fibrils connecting the globules.
The processing of the obtained UHMWPE reactor powders into high modulus-oriented films was carried out by preparing monolithic samples under pressure and shear deformation at an elevated temperature below the polymer melting point with a subsequent uniaxial drawing [36]. Mechanical tests were carried out for the samples oriented to the prefracture state, which varied for different samples (Table 2, Figure 4).  At high magnifications (Figure 3, bottom), the UHMWPE powder particles have a broccoli-like shape and differ in the number of fibrils connecting the globules.
The processing of the obtained UHMWPE reactor powders into high modulus-oriented films was carried out by preparing monolithic samples under pressure and shear deformation at an elevated temperature below the polymer melting point with a subsequent uniaxial drawing [36]. Mechanical tests were carried out for the samples oriented to the prefracture state, which varied for different samples (Table 2, Figure 4).   The UHMWPE nascent reactor powders obtained on bis-isopropoxo-titanium precatalysts 1 and 2 (entries 1,2,10, and 11) were processed into oriented films with approximately the same mechanical characteristics (Figure 4a). The nature of the organoaluminum compound (OAC) included in the Al/Mg activator did not significantly affect these parameters. The results obtained slightly exceeded those previously published for titanium complexes with diol ligands [17,18,21,[25][26][27]; however, the reason may be not only the structure of the precatalysts, but also the polymerization temperature (in the cited works, polymerization was carried out at 30 °C). For comparison, the modulus value for commercially available gel-spun UHMWPE fiber, produced by the gel-spinning process, is 113 GPa [38]. The replacement of toluene with an aliphatic solvent nefras was reflected in the morphology of the UHMWPE reactor powder, namely, in an increase in the number of fibrils (Figure 3b,c), while the degree of crystallinity of these two samples of UHMWPE was determined by DSC and was the same at 55%. The presence of fibrillated elements prevented a uniform distribution of stress in the sample during orientation drawing and, as a result, led to a deterioration in the strength characteristics of film tapes (entries 2 and 3, Table 2). For oriented films from polymers obtained on titanium dichloride complexes 3 and 4, the maximum values of the average tensile modulus were recorded when using an activator with Et3Al2Cl3.
An important condition for obtaining disentangled UHMWPE is to carry out the polymerization process at low temperatures, which allow to control the rates of polymer chain growth and its crystallization [39]. The fact that many samples obtained at elevated temperatures nevertheless turned out to be suitable for solid-phase processing (Figure 4b, curves 7 and 8) seems very promising to us.    The UHMWPE nascent reactor powders obtained on bis-isopropoxo-titanium precatalysts 1 and 2 (entries 1,2,10, and 11) were processed into oriented films with approximately the same mechanical characteristics (Figure 4a). The nature of the organoaluminum compound (OAC) included in the Al/Mg activator did not significantly affect these parameters. The results obtained slightly exceeded those previously published for titanium complexes with diol ligands [17,18,21,[25][26][27]; however, the reason may be not only the structure of the precatalysts, but also the polymerization temperature (in the cited works, polymerization was carried out at 30 • C). For comparison, the modulus value for commercially available gel-spun UHMWPE fiber, produced by the gel-spinning process, is 113 GPa [38]. The replacement of toluene with an aliphatic solvent nefras was reflected in the morphology of the UHMWPE reactor powder, namely, in an increase in the number of fibrils (Figure 3b,c), while the degree of crystallinity of these two samples of UHMWPE was determined by DSC and was the same at 55%. The presence of fibrillated elements prevented a uniform distribution of stress in the sample during orientation drawing and, as a result, led to a deterioration in the strength characteristics of film tapes (entries 2 and 3, Table 2). For oriented films from polymers obtained on titanium dichloride complexes 3 and 4, the maximum values of the average tensile modulus were recorded when using an activator with Et 3 Al 2 Cl 3 .
An important condition for obtaining disentangled UHMWPE is to carry out the polymerization process at low temperatures, which allow to control the rates of polymer chain growth and its crystallization [39]. The fact that many samples obtained at elevated temperatures nevertheless turned out to be suitable for solid-phase processing (Figure 4b, curves 7 and 8) seems very promising to us.
The productivity of systems 1 and 2/Et 3 Al 2 Cl 3 +Bu 2 Mg in the ethylene /1-octene copolymerization was noticeably lower than for the homopolymerization of ethylene; i.e., in this case, no positive effect of the comonomer was observed. The molecular weights of the copolymers (1.1-8.9 × 10 5 Da) were also significantly lower than for the polyethylene samples (4.8 × 10 5 -1.01 × 10 7 Da) (we can compare these data only at a qualitative level, since different methods of their determination were used).
The percentage of comonomer incorporation was low (1.4-4.6 mol% for precatalyst 1), and it was obvious that an increase in the steric load at the metal center made it difficult for the bulk comonomer, 1-octene, to approach the reaction center. For complex 2, this trend was more pronounced.
The ethylene/1-octene copolymerization process even more clearly demonstrated the increased thermal stability of complexes 1-2: with an increase in the polymerization temperature from 10 to 50 • C, a noticeable increase in productivity was observed, which remains quite acceptable even at a temperature of 70 • C ( Figure 5, Table 3). To our surprise, with increasing temperature, the molecular weight of the copolymers increased significantly, reaching a maximum at 50 • C. The productivity of systems 1 and 2/Et3Al2Cl3+Bu2Mg in the ethylene /1-octene copolymerization was noticeably lower than for the homopolymerization of ethylene; i.e., in this case, no positive effect of the comonomer was observed. The molecular weights of the copolymers (1.1-8.9 × 10 5 Da) were also significantly lower than for the polyethylene samples (4.8 × 10 5 -1.01 × 10 7 Da) (we can compare these data only at a qualitative level, since different methods of their determination were used).
The percentage of comonomer incorporation was low (1.4-4.6 mol% for precatalyst 1), and it was obvious that an increase in the steric load at the metal center made it difficult for the bulk comonomer, 1-octene, to approach the reaction center. For complex 2, this trend was more pronounced.
The ethylene/1-octene copolymerization process even more clearly demonstrated the increased thermal stability of complexes 1-2: with an increase in the polymerization temperature from 10 to 50 °C, a noticeable increase in productivity was observed, which remains quite acceptable even at a temperature of 70 °C ( Figure 5, Table 3). To our surprise, with increasing temperature, the molecular weight of the copolymers increased significantly, reaching a maximum at 50 °C.  a Copolymerization was carried out in 100 mL of toluene with 5 × 10 −6 mol of precatalyst at a constant excessive ethylene pressure of 1.7 atm for 30 min; the activator was 1.5 Et3Al2Cl3+Bu2Mg, and the amount of 1-octene was 10 mL.  a Copolymerization was carried out in 100 mL of toluene with 5 × 10 −6 mol of precatalyst at a constant excessive ethylene pressure of 1.7 atm for 30 min; the activator was 1.5 Et 3 Al 2 Cl 3 +Bu 2 Mg, and the amount of 1-octene was 10 mL.

Conclusions
In summary, new titanium(IV) complexes with OO 2− -type diolate ligands in the presence of a binary cocatalysts {3Et 2 AlCl + Bu 2 Mg} or {1.5Et 3 Al 2 Cl 3 + Bu 2 Mg} exhibited moderate to high activities toward ethylene polymerization (460-3260 kg/mol·h·atm). The M v of the obtained polymer samples reached 10 million Da.
Compared to previously obtained titanium complexes with flexible aliphatic diolate ligands [15][16][17][18][19][20][21][22], complexes 1-4 with a rigid camphane framework were characterized by increased thermal stability. Complex 2 with an increased steric load at hydroxyl groups was able to produce UHMWPE even at a temperature of 70 • C. This UHMWPE sample was processed into an oriented film with a tensile strength of 1.6-2.0 GPa and an average tensile modulus of 108-123 GPa. Films obtained on the same precatalysts at a temperature of 10 • C were characterized by higher values of breaking strength up to 2.7 GPa and modulus up to 151 GPa.