1,721,058 research outputs found
Tautomerism in Bis(oxazolines): an Experimental and Theoretical Study of Proton Transfer in 1,1-Bis[4,4-dimethyl-1,3-oxazolin-2-yl]ethane
No full textThe serendipitous isolation of an unusual protonated bis(oxazoline) prompted us to discuss the role of H+ on the kinetics and thermodynamics of the equilibrium between its ketimine and enamine forms. X-ray diffraction analysis revealed that the protonated bis(oxazoline) is in the Z-enamine form, the unipositive charge is counterbalanced by [(FeCl3)(2)O](2-) and [FeCl4](-) anions. DFT calculation at the BP86/TZVP level showed that relative stability of enamine tautomer versus ketimine tautomer increases with the protonation of the nitrogen atom of the oxazolidine ring. At the same time, the barrier energy of tautomerism decreases
Group IV complexes with nitrogen based ligands in the ring opening polymerization of cyclic esters
No full textSynthesis of group 4 metal alkyl complexes bearing heteroscorpionate ligands and their role as homogeneous olefin polymerisation catalysts
No full textEthylene Polymerization catalyzed by Group 4 Metal Complexes of Tridentate Heteroscorpionate Ligands based on Substituted bis(pyrazol-1-yl)methanes
No full textStereoselectivity in Butadiene Polymerization Promoted by Using Ziegler–Natta Catalysts Based on (Anilidomethyl)pyridine Group (IV) Complexes
No full textThe stereoselective polymerization of conjugated dienes promoted by using transition metal complexes has attracted much interest in both industrial and academic environments for the relevance of polydienes as synthetic rubbers and for the challenging reaction mechanisms. Among the different transition metal complexes, those based on group IV have been demonstrated to be versatile and efficient catalysts. Titanium complexes are generally more active than zirconium complexes. A rare exception to this trend is represented by a series of Zr(IV) complexes supported by (anilidomethyl)pyridine ligands that, after activation by using Al(iBu2H)/MAO, were found to be highly active affording exclusively cis-1,4-polybutadiene. To rationalize this unexpected trend and to obtain more insights into the parameters that control the reactivity of group IV complexes, a theoretical investigation of the entire polymerization mechanism, employing density functional methods, was undertaken. In the framework of the widely accepted polymerization scheme, the different intermediates featuring h4 (both cis and trans) coordination of the monomer and h1 or h3 (syn or anti)allyl coordination of the growing chain were scrutinized. Subsequently, the effects of the metal center on the free-energy profiles of the elementary steps involved in the reaction were examined. The results presented herein aim to achieve a better knowledge of the influence of the metal on the polymerization rates and on the stereoselectivity of the reaction
“Cationic Benzyl Zirconium Eteroscorpionates: Synthesis And Caracterization Of Novel Ethylene Polymerization Catalysts.”
No full textSYNTHESIS, CHARACTERIZATION AND OLEFIN POLYMERISATION ACTIVITY OF AMIDE VANADIUM (IV) COMPLEXES
No full text
Olefin Polymerization Catalyzed by Amide Vanadium (IV) complexes: Stereo and regiochemistry of Propene Insertion
No full textThe reaction of VCl3(THF)3 with 1 equiv of the lithium salt of ligand
ArNH(Me2SiCH2CH2SiMe2)NHAr or ArNH(SiMe3) (Ar = 2,6-Me2C6H3) afforded the corresponding V(IV) amide complexes, [1,2-CH2CH2(Me2SiNAr)2]VCl2 (3) and (Me3Si-NAr)2VCl2 (4). The activation of 3 and 4 with the alkyl aluminum compound Al2Et3Cl3 or AlEt2Cl produced active ethylene polymerization catalysts exhibiting productivity values among the highest reported for vanadium amide based catalysts. Moreover, syndiotactic specific propylene polymerization was successfully conducted at 40 °C in the presence of 3/Al2Et3Cl3 and 4/Al2Et3Cl3. Syndiotactic polypropylenes with moderate stereoregularity ([rr] = 0.66) and a concentration of regioirregular propylene
of 6.9 mol % were obtained. Monomodal molecular weight distributions and polydispersity indices lower than 2 were observed in the polymerization runs carried out in heptane solutions. Thus, ethylene–propylene copolymers with propylene concentrations up to 45 mol % were synthesized and characterized by 13C NMR and thermal analysis. Good alternation and random distribution of the two monomers were actually obtained. Samples with elevated concentrations of propylene were completely amorphous, with a glass-transition temperature of 50 °C. The properties and structure of the copolymers produced with amide vanadium catalysts 3 and 4 were similar
to those reported for ethylene–propylenes produced with industrial vanadium-based catalysts, suggesting the presence of the same active catalyst species
Thermoremendable Styrenic Polymers by Controlled Radical Copolymerization of Styrene with bioderived 2-vinylfuran
No full textThermoremendable Styrenic Polymers by Controlled Radical Copolymerization of Styrene with bioderived 2-vinylfuran
A. Grassi,* A. Buonerba, C. Capacchione, S. Milione
Department of Chemistry and Biology “Adolfo Zambelli”, University of Salerno – Italy
CIRCC - Interuniversity Consortium on Chemical Reactivity and Catalysis
*Corresponding author: [email protected]
Keywords: Biosourced olefins, functional olefin copolymer, furan-maleimide Diels Alder reaction.
Abstract
2-vinylfuran (2VF) is a bioderived olefin synthesized by Peterson methylenation of furfural, a cheap platform molecule resulting from acid catalyzed hydrolysis and dehydration of pentosanes from lignocellulosic biomass. Ideal ATR copolymerization of styrene with 2VF yielded random copolymers (S-co-2VFs) in a wide range of composition and high monomer conversion.[1] The S-co-2VFs are stable for years in solution and solid state at room temperature; radical oxidation of the furan moieties starts in air at temperature higher than 120°C whereas thermal degradation occurs at 380°C. Diels Alder (DA) cycloaddition reaction of S-co-2VFs with bismaleimide (BMI) produces thermorevesible crosslinks: the thermodynamic and kinetic parameters of this reaction were investigated by NMR and FT-IR spectroscopy to assess the optimal condition for high crosslink degree and self healing conditions. The mechanical properties of the S-co-2VFs, before and after reaction with BMI, were compared using INSTRON analysis and nanoidentation of polymeric thin films by Atomic Force Microscopy.[2] Moreover simple thermal treatment of mechanically fractured films of S-co-2VFs reacted with BMI allowed full repairing in 80 min (Figure 1).
Scheme. Diels Alder reaction of S-co-2VFs with BMI.
Figure 1. Fractured (a) and healed (b) polymer film of S-co-2VF crosslinked with BMI after thermal annealing at 150°C.
References
[1] S. Ortega Sáncheza, F. Marra, A. Dibenedetto, M. Aresta, A. GrassiMacromolecules 2014, 47, 7129−7137.
[2] A. Grassi, A. Buonerba, C. Capacchione, S. Milione ACS National Meeting San Diego (USA) 2016
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