2,3-<i>exo</i>-Diheterotactic Dicyclopentadiene Oligomers: An X‑ray Powder Diffraction Study of a Challenging Multiphase Case

Cycloaliphatic polyolefins have attracted attention for use as functional materials, but they are rarely observed in the crystalline state. New semicrystalline dicyclopentadiene oligomers were obtained with an iminopyridine chromium complex in combination with methylaluminoxane. Fourier transform infrared and nuclear magnetic resonance measurements did not allow us to establish the chain stereochemistry, and size exclusion chromatography measurements merely revealed that the obtained sample contained oligomers of different molecular masses. The wide-angle X-ray diffraction (WAXS) powder pattern showed a remarkable crystalline character of the sample, and its study was considered the main route toward the comprehension of the obtained material. By analogy with the norbornene olefin, there was conjecture that the obtained dicyclopentadiene oligomers featured a 2,3-exo-diheterotactic stereoregularity. Then, different ad hoc computational techniques were implemented to describe the WAXS powder pattern in terms of a model mixture of perfect crystals of oligomers with different numbers of monomer units and with the mentioned stereoregularity. This modeling allowed us to shed light on the structures of crystals constituted by oligomers of different masses, to estimate their abundance in the sample, and to confirm the suggested chain stereochemistry, which has never been observed before in dicyclopentadiene macromolecules

2,3-<i>exo</i>-Diheterotactic Dicyclopentadiene Oligomers: An X‑ray Powder Diffraction Study of a Challenging Multiphase Case

Cycloaliphatic polyolefins have attracted attention for use as functional materials, but they are rarely observed in the crystalline state. New semicrystalline dicyclopentadiene oligomers were obtained with an iminopyridine chromium complex in combination with methylaluminoxane. Fourier transform infrared and nuclear magnetic resonance measurements did not allow us to establish the chain stereochemistry, and size exclusion chromatography measurements merely revealed that the obtained sample contained oligomers of different molecular masses. The wide-angle X-ray diffraction (WAXS) powder pattern showed a remarkable crystalline character of the sample, and its study was considered the main route toward the comprehension of the obtained material. By analogy with the norbornene olefin, there was conjecture that the obtained dicyclopentadiene oligomers featured a 2,3-exo-diheterotactic stereoregularity. Then, different ad hoc computational techniques were implemented to describe the WAXS powder pattern in terms of a model mixture of perfect crystals of oligomers with different numbers of monomer units and with the mentioned stereoregularity. This modeling allowed us to shed light on the structures of crystals constituted by oligomers of different masses, to estimate their abundance in the sample, and to confirm the suggested chain stereochemistry, which has never been observed before in dicyclopentadiene macromolecules

2,3-<i>exo</i>-Diheterotactic Dicyclopentadiene Oligomers: An X‑ray Powder Diffraction Study of a Challenging Multiphase Case

Cycloaliphatic polyolefins have attracted attention for use as functional materials, but they are rarely observed in the crystalline state. New semicrystalline dicyclopentadiene oligomers were obtained with an iminopyridine chromium complex in combination with methylaluminoxane. Fourier transform infrared and nuclear magnetic resonance measurements did not allow us to establish the chain stereochemistry, and size exclusion chromatography measurements merely revealed that the obtained sample contained oligomers of different molecular masses. The wide-angle X-ray diffraction (WAXS) powder pattern showed a remarkable crystalline character of the sample, and its study was considered the main route toward the comprehension of the obtained material. By analogy with the norbornene olefin, there was conjecture that the obtained dicyclopentadiene oligomers featured a 2,3-exo-diheterotactic stereoregularity. Then, different ad hoc computational techniques were implemented to describe the WAXS powder pattern in terms of a model mixture of perfect crystals of oligomers with different numbers of monomer units and with the mentioned stereoregularity. This modeling allowed us to shed light on the structures of crystals constituted by oligomers of different masses, to estimate their abundance in the sample, and to confirm the suggested chain stereochemistry, which has never been observed before in dicyclopentadiene macromolecules

Vanadium-Catalyzed Terpolymerization of α,ω-Dienes with Ethylene and Cyclic Olefins: Ready Access to Polar-Functionalized Polyolefins

α,ω-Dienes are an important class of monomers due to their utility in the synthesis of cyclopolyolefins and reactive polyolefin intermediates. In this contribution, the terpolymerization of two α,ω-dienes (i.e., 1,5-hexadiene and 1,7-octadiene) with ethylene and various cyclic olefins [i.e., norbornene (NB), 5-ethylidene-2-norbornene (ENB), and dicyclopentadiene (DCPD)] catalyzed by a chelated imido vanadium complex has been examined. The ENB and DCPD diene termonomers provide additional sites for post-polymerization functionalization. Vanadium-catalyzed terpolymerization of the investigated α,ω-dienes yields polyolefins with a high molecular weight (Mw up to 200 × 103 g mol–1), unimodal and narrow molecular weight distribution, subambient glass transition temperatures (−30 Tg °C < −3), and a proper content of CC bonds. Comprehensive NMR investigation of the obtained polymers revealed that subtle changes in the α,ω-diene size have important effects on the numerous combinations of insertion paths (ring closure vs ring opening), from which different repeating units with a CC bond in the side or main polymer chain and cyclic units are installed. Finally, the poly­(ethylene-ter-1,5-hexadiene-ter-NB) was subjected to thiol-ene addition using thioglycolic acid, methyl thioglycolate, and N-acetyl-l-cysteine to access polar-functionalized polyolefins with a degree of functionalization and properties dependent on the thiol substitution

Dynamically Cross-Linked Polyolefins via Hydrogen Bonds: Tough yet Soft Thermoplastic Elastomers with High Elastic Recovery

The fabrication of polyolefin thermoplastic elastomers (P-TPEs) with superior robustness (high strength and high toughness) is challenging. Integrating dynamic (reversible) noncovalent cross-links into P-TPEs may solve the trade-off between strength and toughness and permanent (irreversible) cross-linking and elasticity. Here, we report a two-step synthesis of P-TPEs that contain flexible polymer chains and different thiol branches (less than 2.0 mol %) that cross-link the polymer chains through dynamic hydrogen bonding. The cross-linked polymers exhibit negligible hysteresis after being circularly stretched 10 times at low strain, that is, few dynamic H-bonds break per cycle and delocalize the stress concentration to withstand load and delay premature fracture. At large deformation, the polymers dissipate vast stress energy by the sacrificial H-bond scission: the H-bonds break and reform to prevent failure and to dictate simultaneously high fracture strength (σ up to 10.2 MPa) and high toughness (UT up to 22.6 MJ/m3). Meanwhile, the resultant materials present low stiffness (E ≈ 2.5 MPa), good extensibility (ε > 600%), and elastic recovery of 90% even at 680% strain. The cross-linked polyolefins are readily (re)­processable, and tensile and elastic properties are largely recovered after being remolded at least twice

Homo- and Co-Polymerization of Ethylene with Cyclic Olefins Catalyzed by Phosphine Adducts of (Imido)vanadium(IV) Complexes

The synthesis and the characterization of a series of phosphine adducts of (imido)­vanadium­(IV) dichloride complexes of the type V­(NR)­Cl2(PMe2Ph)2 [R = 2,6-Cl2-Ph (1), 2,6-iPr2-Ph (2), and tBu (3)] and V­(NtBu)­Cl2(PMe3)2 (3′) are reported. The solid-state structures of 1 and 3′ were determined by X-ray crystallography. The complexes present a geometry around the metal center between a distorted trigonal-bipyramid and a square pyramid, with an almost linear N–V–C bond. Complexes 1–3 were evaluated as catalyst precursors for the polymerization of ethylene and ethylene copolymerization with various cyclic olefins (i.e., norbornene, dicyclopentadiene, 5-ethylidene-2-norbornene, and 5-vinyl-2-norbornene). In combination with Et2AlCl (500 equiv to V) and Cl3CCO2Et (ETA, 10 equiv to V), 1–3 are versatile and promising catalysts for the synthesis of high molecular weight linear poly­(ethylene)­s and alternating copolymers with efficient comonomer incorporation, unimodal molecular weight distributions, and uniform composition under mild conditions. Differences in the homo- and copolymerization of ethylene regarding the activity, stability over temperature, reactivity toward the target comonomers, and (co)­polymer chain growth were investigated to probe the effects of imido ligand substitution. The introduction of more electron-donating groups led to an increase in polymers molecular weight and provided increased stability over temperature to the catalysts, particularly for 3. Both of these effects are likely because the tert-butyl imido moiety in 3 strengthens the V–N bond, thus improving the stability of the active intermediate. The steric shielding of the tert-butyl group may also contribute to inhibit the associative chain transfer. Control over the molecular weight of the resultant copolymers proved to be possible also by varying the ETA loading. ETA acts as a reoxidant, restarting the catalytic cycle, but it behaves also like a chain transfer agent and to a different extent strongly depending on the type of imido ligand

Homo- and Co-Polymerization of Ethylene with Cyclic Olefins Catalyzed by Phosphine Adducts of (Imido)vanadium(IV) Complexes

The synthesis and the characterization of a series of phosphine adducts of (imido)­vanadium­(IV) dichloride complexes of the type V­(NR)­Cl2(PMe2Ph)2 [R = 2,6-Cl2-Ph (1), 2,6-iPr2-Ph (2), and tBu (3)] and V­(NtBu)­Cl2(PMe3)2 (3′) are reported. The solid-state structures of 1 and 3′ were determined by X-ray crystallography. The complexes present a geometry around the metal center between a distorted trigonal-bipyramid and a square pyramid, with an almost linear N–V–C bond. Complexes 1–3 were evaluated as catalyst precursors for the polymerization of ethylene and ethylene copolymerization with various cyclic olefins (i.e., norbornene, dicyclopentadiene, 5-ethylidene-2-norbornene, and 5-vinyl-2-norbornene). In combination with Et2AlCl (500 equiv to V) and Cl3CCO2Et (ETA, 10 equiv to V), 1–3 are versatile and promising catalysts for the synthesis of high molecular weight linear poly­(ethylene)­s and alternating copolymers with efficient comonomer incorporation, unimodal molecular weight distributions, and uniform composition under mild conditions. Differences in the homo- and copolymerization of ethylene regarding the activity, stability over temperature, reactivity toward the target comonomers, and (co)­polymer chain growth were investigated to probe the effects of imido ligand substitution. The introduction of more electron-donating groups led to an increase in polymers molecular weight and provided increased stability over temperature to the catalysts, particularly for 3. Both of these effects are likely because the tert-butyl imido moiety in 3 strengthens the V–N bond, thus improving the stability of the active intermediate. The steric shielding of the tert-butyl group may also contribute to inhibit the associative chain transfer. Control over the molecular weight of the resultant copolymers proved to be possible also by varying the ETA loading. ETA acts as a reoxidant, restarting the catalytic cycle, but it behaves also like a chain transfer agent and to a different extent strongly depending on the type of imido ligand

Homo- and Co-Polymerization of Ethylene with Cyclic Olefins Catalyzed by Phosphine Adducts of (Imido)vanadium(IV) Complexes

The synthesis and the characterization of a series of phosphine adducts of (imido)­vanadium­(IV) dichloride complexes of the type V­(NR)­Cl2(PMe2Ph)2 [R = 2,6-Cl2-Ph (1), 2,6-iPr2-Ph (2), and tBu (3)] and V­(NtBu)­Cl2(PMe3)2 (3′) are reported. The solid-state structures of 1 and 3′ were determined by X-ray crystallography. The complexes present a geometry around the metal center between a distorted trigonal-bipyramid and a square pyramid, with an almost linear N–V–C bond. Complexes 1–3 were evaluated as catalyst precursors for the polymerization of ethylene and ethylene copolymerization with various cyclic olefins (i.e., norbornene, dicyclopentadiene, 5-ethylidene-2-norbornene, and 5-vinyl-2-norbornene). In combination with Et2AlCl (500 equiv to V) and Cl3CCO2Et (ETA, 10 equiv to V), 1–3 are versatile and promising catalysts for the synthesis of high molecular weight linear poly­(ethylene)­s and alternating copolymers with efficient comonomer incorporation, unimodal molecular weight distributions, and uniform composition under mild conditions. Differences in the homo- and copolymerization of ethylene regarding the activity, stability over temperature, reactivity toward the target comonomers, and (co)­polymer chain growth were investigated to probe the effects of imido ligand substitution. The introduction of more electron-donating groups led to an increase in polymers molecular weight and provided increased stability over temperature to the catalysts, particularly for 3. Both of these effects are likely because the tert-butyl imido moiety in 3 strengthens the V–N bond, thus improving the stability of the active intermediate. The steric shielding of the tert-butyl group may also contribute to inhibit the associative chain transfer. Control over the molecular weight of the resultant copolymers proved to be possible also by varying the ETA loading. ETA acts as a reoxidant, restarting the catalytic cycle, but it behaves also like a chain transfer agent and to a different extent strongly depending on the type of imido ligand

Homo- and Co-Polymerization of Ethylene with Cyclic Olefins Catalyzed by Phosphine Adducts of (Imido)vanadium(IV) Complexes

The synthesis and the characterization of a series of phosphine adducts of (imido)­vanadium­(IV) dichloride complexes of the type V­(NR)­Cl2(PMe2Ph)2 [R = 2,6-Cl2-Ph (1), 2,6-iPr2-Ph (2), and tBu (3)] and V­(NtBu)­Cl2(PMe3)2 (3′) are reported. The solid-state structures of 1 and 3′ were determined by X-ray crystallography. The complexes present a geometry around the metal center between a distorted trigonal-bipyramid and a square pyramid, with an almost linear N–V–C bond. Complexes 1–3 were evaluated as catalyst precursors for the polymerization of ethylene and ethylene copolymerization with various cyclic olefins (i.e., norbornene, dicyclopentadiene, 5-ethylidene-2-norbornene, and 5-vinyl-2-norbornene). In combination with Et2AlCl (500 equiv to V) and Cl3CCO2Et (ETA, 10 equiv to V), 1–3 are versatile and promising catalysts for the synthesis of high molecular weight linear poly­(ethylene)­s and alternating copolymers with efficient comonomer incorporation, unimodal molecular weight distributions, and uniform composition under mild conditions. Differences in the homo- and copolymerization of ethylene regarding the activity, stability over temperature, reactivity toward the target comonomers, and (co)­polymer chain growth were investigated to probe the effects of imido ligand substitution. The introduction of more electron-donating groups led to an increase in polymers molecular weight and provided increased stability over temperature to the catalysts, particularly for 3. Both of these effects are likely because the tert-butyl imido moiety in 3 strengthens the V–N bond, thus improving the stability of the active intermediate. The steric shielding of the tert-butyl group may also contribute to inhibit the associative chain transfer. Control over the molecular weight of the resultant copolymers proved to be possible also by varying the ETA loading. ETA acts as a reoxidant, restarting the catalytic cycle, but it behaves also like a chain transfer agent and to a different extent strongly depending on the type of imido ligand