1,2 Enriched polymerization of isoprene by cobalt complex carrying aminophosphory fused (PN3) ligand

Metal-catalyzed selective isoprene polymerization has been a major entry toward cis-1,4, trans-1,4, and 3,4 isomers of polyisoprene, however, 1,2 selective polymerization of isoprene has not yet been achieved due to the steric problem. In this work, difluoro cobalt complexes carrying aminophosphory (-HN-P(=O) ^tBu₂-) fused pyrazol-pyridine ligand has been prepared and characterized. In combination with Mg^n-Bu₂, the formed catalyst unprecedentedly converts isoprene to polyisoprene with 1,2 enchainment up to 50 mol% in a molecular weight controlled polymerization mode. The resultant polymers are fully characterized by NMR, IR, DSC, and GPC. The 1,2 incorporation of polyisoprene is weakly dependent on feeding of Mg^n-Bu₂ and reaction temperature. The weak affinity between Mg²⁺ and allylic terminal of propagating chain is possible for the unique 1,2 irregular insertion and non-irreversible chain transfer and termination reactions throughout the chain propagation. The ability of current catalyst demonstrates a big advantage for application in the development of 1,2 selective polymerization of isoprene, and a potential for access to a new family of polyisoprene. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2286–2293     

Iminoimidazole‐based Co(II) and Fe(II) complexes: Syntheses,characterization, and catalytic behaviors for isoprene polymerization

A stereoselectivity switchable polymerization of isoprene has been developed, which is catalyzed by iminoimidazole‐Co(II) and ‐Fe(II) complexes. The influence of substituents ranging from electron donating to the electron withdrawing on the iminoimidazole‐Co(II) and ‐Fe(II) catalysts is investigated for isoprene polymerization. Two sets of iminoimidazole‐Co(II) and ‐Fe(II) complexes have been prepared and fully characterized. X‐ray crystallography analysis reveals that the complexes Co1 and Fe1 adopt distorted tetrahedral geometries. In the presence of AlEt₂Cl as co‐catalyst, all the Co(II) complexes are active and the catalytic activity is highly dependent on the molar ratio of Al/Co. All the Co(II) complexes exhibit higher activities at low Al/Co ratio. Compared with the Co(II) complexes, the Fe(II) complexes are essentially inactive under the identical condition. However, on activation with combination of AlEtCl₂ and [Ph₃C][B(C₆F₅)₄], both Co(II) and Fe(II) complexes display high activities with good conversions of isoprene (up to >99%). Additionally, low molecular weight and high trans‐1,4‐unit (>96%) selectivity are characteristics of the resultant polyisoprene. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 767–775     

Controlled isoprene polymerization mediated by iminopyridine‐iron (II) acetylacetonate pre‐catalysts

A ligand controlled stereoselective polymerization of isoprene has been developed. A series of (aryl/alkyl)‐iminopyridine iron (II) acetylacetonate complexes: (aryl = Ph Fe1 ; alkyl = CH₂Ph Fe2 , CH (Ph)₂ Fe3 , CH (Me)₂ Fe4 , C (Me)₃ Fe5 , C (Me)₂CH₂C(Me)₃ Fe6 ), has been prepared in which steric and electronic substituents systematically modified to investigate their influences for isoprene polymerization. The molecular structure of representative complex Fe2 was confirmed by single crystal X‐ray diffraction and, revealed a distorted octahedral geometry at iron center. On treatment with methylaluminoxane (MAO), Fe1 – Fe6 displayed low ( Fe5 & Fe6 ) to high activities ( Fe1 – Fe4 ) with quantitative monomer conversion (>99%) for isoprene polymerization producing polyisoprene of high molecular weight (up to 2.0 × 10⁵ g/mol) and unimodal molecular weight distribution (1.4–3.3). Specifically, complex Fe2 (alkyl = CH₂Ph) displayed the highest activity of 7.0 × 10⁶ g (mol of Fe)^?1 h^?1 with 85% conversion of monomer over run time of 10 min at 25 °C. While, Fe6 catalyzed polyisoprene possessed high content of trans‐1,4 unit (up to 87%). Furthermore, the influence of the reaction parameters and the nature of the ligands on the catalytic activities and microstructural properties of the polymer were investigated in detail.     

Highly active and thermo-stable iminopyridyl vanadium oxychloride catalyzed isoprene polymerization

Stereoregular polymerizations are of high importance, which disclosing the relationships between microstructures and physical properties of polymers. In this contribution, a series of iminopyridyl vanadium oxychloride complexes V1 – V8 (R = H, R¹ = CH₂Ph for V1 ; R = H, R¹ = CHPh₂ for V2 ; R = H, R¹ = octamyl for V3 ; R = H, R¹ = Ph for V4 ; R = H, R¹ = 4-OMe-C₆H₄ for V5 ; R = H, R¹ = 4-CF₃ C₆H₄ for V6 ; R = H, R¹ = 2,4,6-Ph₃ C₆H₂ for V7 and R = Me, R¹ = Ph for V8 ) have been prepared, and were investigated for their catalytic capacity of isoprene polymerization. A single crystal structure of V7′ was reported, which was reduced from V(v) to V(iv) in the oxidation state of vanadium central atom. The catalytic activity was up to 408 kg (mol V)⁻¹ hr⁻¹, when V4 was used. The catalyst V6 was found to be highly thermo-stable with excellent activity even at 100°C. Most importantly, resultant polymers mainly possessed cis-1,4 units (up to 75%) with 25% side-chain 3,4 functional group, which is particularly important component to enhance the application of these synthetic rubbers.     

Rare-Earth-Metal Pentadienyl Half-Sandwich and Sandwich Tetramethylaluminates–Synthesis,Structure, Reactivity,and Performance in Isoprene Polymerization

Targeting the synthesis of rare-earth-metal pentadienyl half-sandwich tetramethylaluminate complexes, homoleptic [Ln(AlMe₄)₃] (Ln=Y, La, Ce, Pr, Nd, Lu) were treated with equimolar amounts of the potassium salts K(2,4-dmp) (2,4-dmp=2,4-dimethylpentadienyl), K(2,4-dipp) (2,4-dipp=2,4-diisopropylpentadienyl), and K(2,4-dtbp) (2,4-dtbp=2,4-di-tert-butylpentadienyl). The reactions involving the larger rare-earth-metal centers lanthanum, cerium, praseodymium, and neodymium gave selectively the desired half-sandwich complexes [(2,4-dmp)La(AlMe₄)₂], [(2,4-dipp)La(AlMe₄)₂], and [(2,4-dtbp)Ln(AlMe₄)₂] (Ln=La, Ce, Pr, Nd) in high crystalline yields. Smaller rare-earth-metal centers yielded preferentially the sandwich complexes [(2,4-dmp)₂Ln(AlMe₄)] (Ln=Y, Lu) and [(2,4-dipp)₂Y(AlMe₄)]. Activation with fluorinated borate/borane co-catalysts gave highly active catalyst systems for the fabrication of polyisoprene, displaying molecular weight distributions as low as M_w/M_n=1.09 and a maximum cis-1,4 selectivity of 90.4 %. The equimolar reaction of half-sandwich complex [(2,4-dtbp)La(AlMe₄)₂] with B(C₆F₅)₃ led to the isolation and full characterization of the single-component catalyst {{(2,4-dtbp)La[(μ-Me)₂AlMe(C₆F₅)]}[Me₂Al(C₆F₅)₂]}₂. The reaction of the latter complex with 10 equivalents of isoprene could be monitored by ¹H NMR spectroscopy. Also, a donor-induced aluminato/gallato exchange was achieved with [(2,4-dtbp)La(AlMe₄)₂] and GaMe₃(OEt₂) leading to [(2,4-dtbp)La(GaMe₄)₂].     

β‐Diketiminate‐supported magnesium alkyl: synthesis,structure and application as co‐catalyst for polymerizations mediated by a lanthanum half‐sandwich complex

Mg(n‐Bu){η²‐HC[C(Me)NMes]₂} ( 2 ) (Mes = mesityl, 2,4,6‐Me₃C₆H₂), a new β‐diketiminate‐supported magnesium alkyl, has been synthesized and structurally characterized. The X‐ray analysis of the lanthanum half‐sandwich complex Cp*La(BH₄)₂(THF)₂ ( 1 ) (Cp* = pentamethylcyclopentadienyl; THF = tetrahydrofuran) is also reported. Complex 2 has been assessed as both alkylating agent and chain transfer agent for the lanthanum‐catalysed polymerization and coordinative chain transfer polymerization of isoprene and styrene using 1 as the pre‐catalyst. The results are compared with those for n‐butylethylmagnesium (BEM) which is traditionally used for this purpose. The 1,4‐trans stereospecific polymerization of isoprene shows a more controlled character using 2 versus BEM, and higher activities are observed for the chain transfer polymerization of styrene when 2 is used as chain transfer agent. The activity is in turn lower than that observed using BEM when 1 equiv. of magnesium compound is used for the polymerization of styrene. The combination of 1 , 2 and Al(i‐Bu)₃ leads finally to a 1,4‐trans stereoselective coordinative chain transfer polymerization of isoprene, in a similar way to BEM. Copyright © 2015 John Wiley & Sons, Ltd.     

Propagation Kinetics of Isoprene–Glycidyl Methacrylate Copolymerizations Investigated via PLP–SEC

Pulsed‐laser polymerization combined with polymer analysis by NMR and size‐exclusion chromatography is used to study the radical copolymerization kinetics of isoprene (IP) with glycidyl methacrylate (GMA). The copolymer is characterized by a close‐to‐alternating microstructure, with the addition of IP leading to a significant decrease in the composition‐averaged propagation rate coefficient. A rigorous fitting strategy is developed to fit a mixed penultimate model to the data, with the selectivity of the IP, but not the GMA, macroradical dependent on the penultimate unit.

     

Simultaneous determination of the styrene unit content and assessment of molecular weight of triblock copolymers in adhesives by a size exclusion chromatography method

The content of styrene units in nonhydrogenated and hydrogenated styrene‐butadiene‐styrene and styrene‐isoprene‐styrene triblock copolymers significantly influences product performance. A size exclusion chromatography method was developed to determine the average styrene content of triblock copolymers blended with tackifier in adhesives. A complete separation of the triblock copolymer from the other additives was realized with size exclusion chromatography. The peak area ratio of the UV and refraction index signals of the copolymers at the same effective elution volume was correlated to the average styrene unit content using nuclear magnetic resonance spectroscopy with commercial copolymers as standards. The obtained calibration curves showed good linearity for both the hydrogenated and nonhydrogenated styrene‐butadiene‐styrene and styrene‐isoprene‐styrene triblock copolymers (r  = 0.974 for styrene contents of 19.3–46.3% for nonhydrogenated ones and r  = 0.970 for the styrene contents of 23–58.2% for hydrogenated ones). For copolymer blends, the developed method provided more accurate average styrene unit contents than nuclear magnetic resonance spectroscopy provided. These results were validated using two known copolymer blends consisting of either styrene‐isoprene‐styrene or hydrogenated styrene‐butadiene‐styrene and a hydrocarbon tackifying resin as well as an unknown adhesive with styrene‐butadiene‐styrene and an aromatic tackifying resin. The methodology can be readily applied to styrene‐containing polymers in blends such as poly(acrylonitrile‐butadiene styrene).     

A Catalyst Platform for Unique Cationic (Co)Polymerization in Aqueous Emulsion

Sodium dodecyl benzene sulfonate (DBSNa) surfactants, with a polydisperse and hyperbranched structure, combined with different rare earth metal salts generate highly water‐dispersible Lewis acid surfactant combined catalysts (LASCs). This platform of new complexes promotes fast, efficient cationic polymerization of industrially relevant monomers in direct emulsion at moderate temperature. The process described here does not require high shearing, long polymerization time, or large catalyst content. It allows the reproducible generation of high‐molar‐mass homopolymers of pMOS, styrene, and isoprene, as well as random or multiblock copolymers of the latter two, in a simple and straightforward one‐pot reaction.