Propylene Homopolymerization Research Articles

Synthesis of High-Molecular-Weight Polypropylene Elastomer by Propylene Polymerization Using α-Diimine Nickel Catalysts.

The α-diimine late transition metal catalyst represents a new strategy for the synthesis of atactic polypropylene elastomer. Taking into account the properties of the material, enhancing the molecular weight of polypropylene at an elevated temperature through modifying the catalyst structure, and further increasing the activity of α-diimine catalyst for propylene polymerization, are urgent problems to be solved. In this work, two α-diimine nickel(II) catalysts with multiple hydroxymethyl phenyl substituents were synthesized and used for propylene homopolymerization. The maximum catalytic activity was 5.40 × 105 gPP/molNi·h, and the activity was still maintained above 105 gPP/molNi·h at 50 °C. The large steric hindrance of catalysts inhibited the chain-walking and chain-transfer reactions, resulting in polypropylene with high molecular weights (407~1101 kg/mol) and low 1,3-enchainment content (3.57~16.96%) in toluene. The low tensile strength (0.3~1.0 MPa), high elongation at break (218~403%) and strain recovery properties (S.R. ~50%, 10 tension cycles) of the resulting polypropylenes, as well as the visible light transmittance of approximately 90%, indicate the characteristics of the transparent elastomer.

Propylene polymerization and copolymerization with polar monomers facilitated by flexible cycloalkyl substituents in α-diimine systems

The aryl substituents as well as backbones in the α-diimine catalysts have a significant influence on the olefin (co)polymerization. In this work, the effect of the cycloalkyl and dibenzhydryl substituents as well as backbones of the α-diimine Pd(II) catalysts on the propylene polymerization and copolymerization has been explored. The Pd(II) catalysts led to the moderate activities (level of 104 g mol−1 h−1), tunable molecular weights (5.6–125.2 kg/mol) and highly branched (155–249/1000C) polypropylene during homopolymerization. Among the catalysts, the catalyst Pd3 with the cyclopentyl substituents and dimethyl backbone resulted in the highest molecular weight and activity in the propylene polymerization. Moreover, during the copolymerization of polypropylene-MA, the Pd(II) catalysts showed low activities and yielded low to moderate molecular weight (Mn up to 39.8 kg/mol) polar functionalized copolymers with high branching density (134–217/1000C) and tunable incorporation ratios (1.0–11.5 mol%). Overall, the catalyst Pd3 was also observed to be optimal for the copolymerization reaction, owing to the excellent copolymerization ability of propylene with MA and some other acrylic derived monomers. Further, the rigid substituents with a high steric hindrance played an unfavorable role during the (co)polymerization, which was contrary to the ethylene polymerization. In summary, compared with the rigid bulky dibenzhydryl substituents, the cyclopentyl substituents not only endowed the propylene homopolymerization system with the highest molecular weight and activity, but also provided the copolymerization system with the highest activity, incorporation ratio, and molecular weight. In addition, the incorporation of polar functionalized units could notably change the surface properties of the polypropylene materials in this work.

Bottom-Up Synthesis of Multi-Grained Ziegler–Natta Catalyst Based on MgO/MgCl2/TiCl4 Core–Shell Catalyst

Morphology control plays a major role in the design of solid catalysts. Since the heterogeneous Ziegler–Natta catalyst (ZNC) is based on the in situ synthesis of MgCl2 support in a top-down manner, the individual control of the exterior and the interior structure of the catalyst macro-particles is challenging. In this study, we successfully prepared a ZNC with a multi-grain interior structure by the spray-drying of MgO nanoparticles, inspired by the fact that the MgO/MgCl2/TiCl4 core–shell catalyst can maintain the morphology of the raw MgO nanoparticles. This catalyst is the first example of the bottom-up preparation of MgCl2-supported ZNC. Here, we report its basic preparation method, characterization results, and performance in the homo-polymerization of ethylene and propylene, and copolymerization with 1-hexene.

Kinetic and Thermal Study of Ethylene and Propylene Homo Polymerization Catalyzed by ansa-Zirconocene Activated with Alkylaluminum/Borate: Effects of Alkylaluminum on Polymerization Kinetics and Polymer Structure.

The kinetics of ethylene and propylene polymerization catalyzed by homogeneous metallocene were investigated using 2-thiophenecarbonyl chloride followed by quenched-flow methods. The studied metallocene catalysts are: rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2 (Mt-I), rac-Et(Ind)2ZrCl2 (Mt-II) activated with ([Me2NPh][B(C6F5)4] (Borate-I), [Ph3C][B(C6F5)4] (Borate-II), and were co-catalyzed with different molar ratios of alkylaluminum such as triethylaluminium (TEA) and triisobutylaluminium (TIBA). The change in molecular weight, molecular weight distribution, microstructure and thermal properties of the synthesized polymer are discussed in detail. Interestingly, both Mt-I and Mt-II showed high activity in polyethylene with productivities between 3.17 × 106 g/molMt·h to 5.06 × 106 g/molMt·h, activities were very close to each other with 100% TIBA, but Mt-II/borate-II became more active when TEA was more than 50% in cocatalyst. Similarly, Polypropylene showed the highest activity of 11.07 106 g /molMt·h with Mt-I/Borate-I/TIBA. The effects of alkylaluminum on PE molecular weight were much more complicated; MWD curve changed from mono-modal in Mt-I/borate-I/TIBA to bimodal type when TIBA was replaced by different amounts of TEA. In PE, the active center fractions [C*]/[Zr] of Mt-I/borate were higher than that of Mt-II/borate and average chain propagation rate constant (kp) value slightly decreased with the increase of TEA/TIBA ratio, but the Mt-II/borate systems showed higher kp 1007 kp (L/mol·s). In PP, the Mt-I/borate presented much higher [C*]/[Zr] and kp value than the Mt-II. This work also extend to investigate the mechanistic features of zirconocenes catalyzed olefin polymerizations that addressed the largely unknown issues in zirconocenes in the distribution of the catalyst, between species involved in polymer chain growth and dormant state. In both metallocene systems, chain transfer with alkylaluminum is the dominant way of chain termination. To understand the mechanism of cocatalyst effects on PE Mw and (MWD), the unsaturated chain ends formed via β-H transfer have been investigated by 1H NMR analysis.

Propylene homopolymerization and copolymerization with ethylene by acenaphthene-based α-diimine nickel complexes to access EPR-like elastomers

A series of acenaphthene-based α-diimine nickel complexes were synthesized and subsequently used for accessing branched EPR-like elastomers with different compositions and chain structures.

A Systematic Study of the Temperature-Induced Performance Decline of ansa-Metallocenes for iPP

Highly accurate high-throughput experimentation (HTE) data for a set of 21 silicon-bridged C2-symmetric ansa-zirconocenes in propene homopolymerization were collected and were used to develop quantitative structure – activity relationship (QSAR) models for several performance indicators at high polymerization temperature (Tp = 100 °C) by using chemically meaningful descriptors. Most notably, stereoselectivity is well described by a two-descriptor model linking the quadrant model for stereoselectivity (sterics) with the chain epimerization model (electronics). The catalysts show widely varying temperature responses, most notably on stereoselectivity and molar mass capability, while the regioselectivity response is uniformly weak. Soft conformational locks lose their performance rapidly while hard conformational locks offer enhanced performance even at high temperatures. The quest for high-temperature stable, well-performing ansa-zirconocenes will unquestionably lead to systems with enhanced rigidity.

Metallocene Catalyzed Homopolymerization of Propylene with a <i>C</i><sub>2</sub> Symmetric Isospecific Zirconecene/MMAO Catalysts under Different Polymerization Conditions

In this work, homopolymerization of propylene for synthesis of different molecular weights polypropylene was done using an isospecific metallocene catalyst by changing the polymerization conditions such as Al/Zr (Aluminium/Zirconium) ratio, temperature, pressure and polymerization time. The effects of the polymerization conditions on the molecular weight and other polymer properties have been discussed according to the results obtained. The results indicate that the activity of polymerization increased with increasing the Al/Zr mole ratio and reached a maximum value at a ratio of 2000. In relation to the mole ratio, the molecular weight also followed the same trend. The activity was also seen to increase with increase in temperature. The molecular weight increased with increasing the polymerization time at both 0°C and 25°C, but reduced with increase in time at 40°C. The increase of pressure also increased activity but lowered the molecular weight, indicating β-H elimination to the monomer.

Connection of Stereoselectivity, Regioselectivity, and Molecular Weight Capability in rac-R′2Si(2-Me-4-R-indenyl)2ZrCl2 Type Catalysts

A set of 19 silicon-bridged C2-symmetric zirconocenes rac-R′2Si(2-Me-4-R-indenyl)2ZrCl2 of varying steric demand in position 4 were synthesized and screened in propene homopolymerization in a high-throughput experimental setup. The size and accuracy of the experimental data set allow to identify surprisingly good correlations among stereoselectivity, regioselectivity, and molecular weight capability (R2 ≈ 0.8–0.9) over a broad range. We rationalize this trend by assuming that steric tuning in the 4-position affects both preferred insertion and stereoerror formation similarly but leaves other barriers largely unaffected. A quantitative structure–activity relationship based on one single computational descriptor, Δ%VBur—using the difference in the percent of buried volume between the “blocked” and “open” quadrants of the catalyst precursor—is established. Provided that a large sphere of 5.0 Å is used, stereoselectivity can be predicted with unprecedented accuracy, i.e., a mean average deviation (MAD) of 0.18 kcal/mol (ΔΔG‡enantio), 0.0007 (σ, probability that the preferred propene enantioface is selected at an active site of given chirality), or 0.3% (mmmm pentads). On the basis of this empirical model, we predicted that the catalyst with R = o-tolyl is an ideal candidate for high stereoselectivity/high MW capability. Ad hoc synthesis and testing of the precursor confirmed the expectations: the catalyst shows the highest stereoselectivity reported so far (σ = 0.9999) for metallocenes at 60 °C, while maintaining a high MW capability (Mw > 1 MDa) and relatively high regioselectivity.

Trinuclear tris(ansa-metallocene) complexes of zirconium and hafnium for olefin polymerization

New platforms for trinuclear complexes, 1,3,5-tris(fluoren-2-yl-R)benzene (Ph{2-FluRH}3; R = H (2a), 6-tBu (2b), 7-tBu (2c), Tet (2d) (Tet = 2,2,5,5-tetramethyl-tetrahydrobenzofluorene), were synthesized via an acid-catalyzed cyclotrimerization of the corresponding substituted 2-acetylfluorenes. Subsequent nucleophilic addition of the [Ph{2-FluR}3]3− trianions onto 6,6,-dimethylfulvene afforded the corresponding isopropylidene-bridged pro-ligands Ph{Me2C(2-FluRH)(C5H5)}3 (3a-d). Discrete trinuclear tris(dichloro-ansa-zirconocene and hafnocene), Ph[{Me2C(2-FluR)(C5H4)}MX2]3 (X = Cl: 4b-d-Zr, 4c,d-Hf) were prepared by salt metathesis reactions. Some zirconium complexes were further alkylated towards the corresponding tris(dialkyls) (X = Me: 5c,d-Zr; X = CH2SiMe3: 6c-Zr). The structures of these metal complexes were determined by elemental analyses, and by 1D, inverse 2D heteronuclear correlation, and DOSY NMR spectroscopy, as well as by theoretical computations. Those studies revealed the existence of two isomers, of C3 and C1 symmetry respectively, originating from the mutual orientation of the three ansa-metallocene fragments. Preliminary studies on the catalytic performances of the dichloro complexes, upon activation with MAO, in ethylene and propylene homopolymerization and ethylene/1-hexene copolymerization were carried out and compared to those of the monometallic analogues under identical conditions.

Morphological Study of Nascent Growth of α‐Olefin Polymers on Spatially Unconstrained Silica Surfaces

AbstractThe experimental study of polymer growth on spatially unconstrained flat silica surfaces is presented for propylene and ethylene polymerization in liquid and gas phases with high activity metallocene catalyst (rac‐Et(Indenyl)2ZrCl2/ methylaluminoxane at 30–70 °C and 30–50 psig. The study shows a surprisingly rich spectrum of nascent morphologies for each polymer synthesized in two different reaction phases. In propylene polymerization in a liquid phase, polypropylene nanofibrils are first formed at the catalyst sites and quickly develop into microglobular morphology, whereas in ethylene polymerization in a liquid phase, polyethylene nanofibrils formed at the catalyst sites grow to a ribbon‐like morphology. In gas phase polymerization where polymerization rate is much lower due to low monomer concentration, both polymers grow to compact aggregates of globules. Unlike in liquid phase polymerization, no ribbon‐like structure is formed in ethylene polymerization. The sequential polymerization of these olefin monomers has also been carried out and the experimental data show two distinct regions of corresponding polymers as observed in separate ethylene and propylene homopolymerization experiments.

Polypropylene and poly(ethylene-co -1-octene) effective synthesis with diamine-bis(phenolate) complexes: Effect of complex structure on catalyst activity and product microstructure

A series of group 4 metal complexes bearing amine-bis(phenolate) ligands with the amino side-arm donor: (μ-O)[Me2N(CH2)2N(CH2-2-O-3,5-tBu2-C6H2)2ZrCl]2 (1a), R2N(CH2)2N(CH2-2-O-3-R1-5-R2-C6H2)2TiCl2 (R = Me, R1, R2 = tBu (2a), R = iPr, R1, R2 = tBu (2b), R = iPr, R1 = tBu, R2 = OMe (2c)), and Me2N(CH2)2N(CH2-2-O-3,5-tBu2-C6H2)(CH2-2-O-C6H4)TiCl2 (2d) are used in ethylene and propylene homopolymerization, and ethylene/1-octene copolymerization. All complexes, upon their activation with Al(iBu)3/Ph3CB(C6F5)4, exhibit reasonable catalytic activity for ethylene homo- and copolymerization giving linear polyethylene with high to ultra-high molecular weight (600·× 103–3600·× 103 g/mol). The activity of 1a/Al(iBu)3/Ph3CB(C6F5)4 shows a positive comonomer effect, leading to over 400% increase of the polymer yield, while the addition of 1-octene causes a slight reduction of the activity of the complexes 2a-2d. The complexes with the NMe2 donor group (2a, 2d, 1a) display a high ability to incorporate a comonomer (up to 9–22 mol%), and the use of a bulkier donor group, N(iPr)2 (2b, 2c), results in a lower 1-octene incorporation. All the produced copolymers reveal a broad chemical composition distribution. In addition, the investigated complexes polymerized propylene with the moderate (1a, 2a) to low (2b-2d) activity, giving polymers with different microstructures, from purely atactic to isotactically enriched (mmmm = 28%). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017

Kinetics and mechanism of metallocene‐catalyzed olefin polymerization: Comparison of ethylene, propylene homopolymerizations, and their copolymerization

ABSTRACTA series of ethylene, propylene homopolymerizations, and ethylene/propylene copolymerization catalyzed withrac‐Et(Ind)2ZrCl2/modified methylaluminoxane (MMAO) were conducted under the same conditions for different duration ranging from 2.5 to 30 min, and quenched with 2‐thiophenecarbonyl chloride to label a 2‐thiophenecarbonyl on each propagation chain end. The change of active center ratio ([C*]/[Zr]) with polymerization time in each polymerization system was determined. Changes of polymerization rate, molecular weight, isotacticity (for propylene homopolymerization) and copolymer composition with time were also studied. [C*]/[Zr] strongly depended on type of monomer, with the propylene homopolymerization system presented much lower [C*]/[Zr] (ca. 25%) than the ethylene homopolymerization and ethylene–propylene copolymerization systems. In the copolymerization system, [C*]/[Zr] increased continuously in the reaction process until a maximum value of 98.7% was reached, which was much higher than the maximum [C*]/[Zr] of ethylene homopolymerization (ca. 70%). The chain propagation rate constant (kp) of propylene polymerization is very close to that of ethylene polymerization, but the propylene insertion rate constant is much smaller than the ethylene insertion rate constant in the copolymerization system, meaning that the active centers in the homopolymerization system are different from those in the copolymerization system. Ethylene insertion rate constant in the copolymerization system was much higher than that in the ethylene homopolymerization in the first 10 min of reaction. A mechanistic model was proposed to explain the observed activation of ethylene polymerization by propylene addition. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem.2017,55, 867–875

Effects of the Grafting of Lanthanum Complexes on a Silica Surface on the Reactivity: Influence on Ethylene, Propylene, and 1,3-Butadiene Homopolymerization.

In this contribution, we report full details of the ethylene, 1,3-butadiene, and propylene homopolymerization processes mediated by alkylated bis(trimethyl)silylamide lanthanide-grafted complexes using a density functional theory (DFT) study of the initiation and first propagation steps. These systems allows us (i) to examine the role of the grafting mode on the kinetics and thermodynamics of the three processes considered, (ii) to confirm the catalytic behavior of these grafted complexes in ethylene polymerization, (iii) to rationalize the experimental preference for 1,4-cis polymerization of 1,3-butadiene, and (iv) to provide unprecedented information on the catalytic activity of the lanthanide-grafted complex as a propylene hompolymerization catalyst.

Crystalline Isotactic Polar Polypropylene from the Palladium-Catalyzed Copolymerization of Propylene and Polar Monomers.

Moderately isospecific homopolymerization of propylene and the copolymerization of propylene and polar monomers have been achieved with palladium complexes bearing a phosphine-sulfonate ligand. Optimization of substituents on the phosphorus atom of the ligand revealed that the presence of bulky alkyl groups (e.g. menthyl) is crucial for the generation of high-molecular-weight polypropylenes (Mw ≈10(4) ), and the substituent at the ortho-position relative to the sulfonate group influences the molecular weight and isotactic regularity of the obtained polypropylenes. Statistical analysis suggested that the introduction of substituents at the ortho-position relative to the sulfonate group favors enantiomorphic site control over chain end control in the chain propagation step. The triad isotacticity could be increased to mm=0.55-0.59, with formation of crystalline polar polypropylenes, as supported by the presence of melting points and sharp peaks in the corresponding X-ray diffraction patterns.

Crystalline Isotactic Polar Polypropylene from the Palladium‐Catalyzed Copolymerization of Propylene and Polar Monomers

AbstractModerately isospecific homopolymerization of propylene and the copolymerization of propylene and polar monomers have been achieved with palladium complexes bearing a phosphine‐sulfonate ligand. Optimization of substituents on the phosphorus atom of the ligand revealed that the presence of bulky alkyl groups (e.g. menthyl) is crucial for the generation of high‐molecular‐weight polypropylenes (Mw≈104), and the substituent at the ortho‐position relative to the sulfonate group influences the molecular weight and isotactic regularity of the obtained polypropylenes. Statistical analysis suggested that the introduction of substituents at the ortho‐position relative to the sulfonate group favors enantiomorphic site control over chain end control in the chain propagation step. The triad isotacticity could be increased to mm=0.55–0.59, with formation of crystalline polar polypropylenes, as supported by the presence of melting points and sharp peaks in the corresponding X‐ray diffraction patterns.

Preparation and characterization of spherical PP/PB alloys with MgCl2-supported Ziegler-Natta catalyst

Polypropylene (PP)/polybutene-1 (PB) alloys within reactor were prepared by MgCl2-supported Ziegler-Natta catalyst with sequential two-stage polymerization technology. First, propylene homo-polymerizations were carried out to form isotactic polypropylene (iPP) particles containing active catalyst. Then, butene-1 was subsequently polymerized to form polybutene-1 phase inside the iPP particles. Finally, iPP/PB alloys with spherical shape and adjustable PB content were synthesized. The catalytic activity and catalytic stereospecificity of the Z-N catalyst in the two-stage polymerization process are discussed. The composition and physical properties of the PP alloys were characterized by FT-IR, 13C-NMR, SEM, DSC and XRD. It was found that the in-reactor PP alloys are mainly composed of PP and PB with a little amount of poly(buteneco-propylene) random copolymers and poly(butene-block-propylene) block copolymers. SEM measurements verified that the PB phases with size in the range of 300–400 nm dispersed in the PP matrix uniformly. The incorporation of PB upon the PP matrix affects the properties of final products greatly.

Dynamic modeling of gas phase propylene homopolymerization in fluidized bed reactors

A new model with comprehensive kinetics for propylene homopolymerization in fluidized bed reactors was developed to investigate the effect of mixing, operating conditions, kinetic and hydrodynamic parameters on the reactor performance as well as polymer properties. Presence of the particles in the bubbles and the excess gas in the emulsion phase was considered to improve the two-phase model, thus, considering the polymerization reaction to take place in both the bubble and emulsion phases. It was shown that in the practical range of superficial gas velocity and catalyst feed rate, the ratio of produced polymer in the bubble phase to the total production rate is roughly between 10% and 13%, which is a substantial amount and cannot be ignored. Simulation studies were carried out to compare the results of the improved two-phase, conventional well-mixed and constant bubble size models. The improved two-phase and well mixed models predicted a narrower and safer window at the same running conditions compared with the constant bubble size model. The improved two-phase model showed close dynamic behavior to the conventional models at the beginning of polymerization, but starts to diverge with the evolution of time.

Influence of the Preparation Technique of MgCl2/TiCl4 Ziegler-Natta Catalyst on the Performance in Ethylene and Propylene Polymerization

Different methods to remove the alcohol of adduct MgCl2nEtOH were studied to obtain Ziegler-Natta catalysts for evaluation in ethylene and propylene polymerization. Thus, the adduct MgCl2nEtOH was submitted to thermal dealcoholation, as well as chemical dealcoholation with different substances: titanium tetrachloride, triethylaluminum, and dichloro-dimethylsilane. Thermogravimetric analyses (TGA) were performed to obtain information on the thermal characteristics of adducts and prepared supported catalysts. Ethylene and propylene homopolymerization were carried out with the prepared catalysts and the polymers were characterized.

Kinetic modeling of propylene homopolymerization in a gas-phase fluidized-bed reactor

A comprehensive mechanistic model describing gas-phase propylene polymerization is developed. The kinetics of polymerization is based on a multiple active site for Ziegler–Natta catalyst. The model considers the polymerization reaction to take place in both bubble and emulsion phases. The developed model was used to predict polymer production rate, number and weight average molecular weights, polydispersity index (PDI) and melt flow index (MFI). Results showed that by increasing the superficial gas velocity from 0.1 to 0.7 m/s the proportion of the polymer produced in the bubble phase increases from 7.92% to 13.14% which highlights the importance of considering the existence of catalyst in the bubble phase. Comparing the developed model with published models of the same reactor revealed that the polymer productivity will be higher using the new model at high catalyst feed rate.

Group 4 Post-metallocene Complexes Incorporating Tridentate Silyl-Substituted Bis(naphthoxy)pyridine and Bis(naphthoxy)thiophene Ligands: Probing Systems for “Oscillating” Olefin Polymerization Catalysis

New bulky silyl ortho-substituted tridentate 2,6-bis(naphthol)pyridine ({ONOSiR3}H2, SiR3 = SiPh3, SiMe2tBu) and 2,5-bis(naphthol)thiophene ({OSOSiPh3}H2) pro-ligands were synthesized via a four-step approach. The solid-state structures of pro-ligands {ONOSiPh3}H2 (3a) and {OSOSiPh3}H2 (3b) were established by X-ray diffraction analysis. Both types of ligands were introduced onto group 4 metal centers (M = Ti, Zr, Hf) using straightforward one-step alkane, amine, or alcohol elimination protocols. Dibenzyl {ONOSiPh3}M(CH2Ph)2 (M = Ti, 4a; Zr, 5a; Hf, 6a) and {ONOSiMe2tBu}M(CH2Ph)2 (M = Ti, 4b; Zr, 5b), diamido {ONOSiPh3}Hf(NMe2)2 (7a and 7a·(NHMe2)), and di(isopropoxy) {ONOSiPh3}Ti(OiPr)2 (8a) complexes were authenticated using NMR spectroscopy and X-ray crystallography methods for some of them. In the solid state, complexes 4a, 4b, and 6a feature rac-like binding of the ligand, while ligands in complexes 5b and 7a·(NHMe2) are meso-like coordinated. The solution structures of 4b and 5b were investigated by VT NMR spectroscopy, which revealed that both complexes exist as rac and meso stereoisomers, which interconvert (activation parameters: 4b, ΔH⧧ = 12.9(7) kcal·mol−1 and ΔS⧧ = −3(1) cal·mol−1·K−1; 5b, ΔH⧧ = 13.4(8) kcal·mol−1 and ΔS⧧ = −7(1) cal·mol−1·K−1). A mechanism for this interconversion process, implying straightforward racemization, was proposed on the basis of DFT computations at the B3LYP (BP86) level, with computed activation barriers for Ti, Zr, and Hf complexes of 11.4 (10.1), 12.5 (11.2), and 12.2 (11.1) kcal·mol−1, respectively. The catalytic activity of dibenzyl and diamido precursors in homopolymerization of propylene and ethylene, upon activation with MAO, “dried-MAO”, and [Ph3C](B(C6F5)4]/Al(iBu)3, has been explored as well.