Effect of ligand backbone substituents of nickel α‐diimine complexes on livingness/controllability of olefin polymerization: Competition between monomer isomerization and propagation

Four α‐diimine nickel complexes [(Ar? N?C(R)? C(R)?N? Ar)NiBr₂; R?H, CH₃, cyclohexane‐1,2‐diyl, naphthalene‐1,8‐diyl, Ar?2,6‐i‐Pr₂‐C₆H₃‐) were investigated in propene and hex‐1‐ene polymerization to identify the limits of backbone substituent R size needed to provide living/controlled α‐olefins polymerization by the sufficient suppression of β–H elimination transfer. Propagation kinetics measurements, molar mass on monomer conversion dependencies and reinitiation tests were used to evaluate the livingness of hex‐1‐ene polymerization. Interestingly, living/controlled hex‐1‐ene polymerization was observed in the case of all diimine derivatives including the one bearing only hydrogen atom in backbone positions. Unexpectedly, in the case of catalysts bearing H and CH₃ backbone substituents, we observed the unusual isomerization of hex‐1‐ene into internal hexenes in parallel with its polymerization. Nevertheless, by subtracting the amount of monomer consumed in isomerization side reaction, polymerization still keeps the features of living/controlled process. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3193–3202     

Covalent attachment of a peptide to the surface of gallium nitride

The properties of GaN have made it not only an ideal material for high power and high frequency electronic devices, but also a semiconductor suitable for application in biosensing devices. The utilization of GaN in electronic biosensors has increased the importance of characterizing robust and easily implemented organic functionalization methods for GaN surfaces. This work demonstrates and characterizes a route to functionalize the GaN (0001) surface with two organic molecules, hexylamine and a peptide, through olefin cross-metathesis with Grubbs first generation catalyst. The GaN (0001) surface was chlorinated, functionalized with a terminal alkene group using a Grignard reaction, and then terminated with a carboxyl group using an olefin cross-metathesis reaction. With a condensation reaction, the final step in the reaction scheme bound hexylamine or a peptide to the carboxyl terminated GaN surface. Qualitative and quantitative X-ray photoelectron spectroscopy (XPS) data verified the success of each step in the reaction scheme. Surface element composition, adlayer coverages, and adlayer thicknesses were calculated based on the XPS data. At least a monolayer of surface molecules covered the GaN surface.     

Olefin metathesis reaction on GaN (0 0 0 1) surfaces

Proof-of-concept reactions were performed on GaN (0 0 0 1) surfaces to demonstrate surface termination with desired chemical groups using an olefin cross-metathesis reaction. To prepare the GaN surfaces for olefin metathesis, the surfaces were hydrogen terminated with hydrogen plasma, chlorine terminated with phosphorous pentachloride, and then terminated with an alkene group via a Grignard reaction. The olefin metathesis reaction then bound 7-bromo-1-heptene. The modified surfaces were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy, and water contact angle measurements following each step in the reaction scheme. The XPS data was used to qualitatively identify surface chemical species and to quantitatively determine molecular surface coverage. The bromine atom in 7-bromo-1-heptene served as a heteroatom for identification with XPS. The reaction scheme resulted in GaN substrates with a surface coverage of 0.10 monolayers and excellent stability towards oxidation when exposed to oxygen plasma.     

Synthesis of poly(10-undecene-1-ol) by metallocene-catalyzed polymerization

Poly(10-undecene-1-ol)s as precursors for potential polar macromonomers were synthesized by metallocene-catalyzed polymerization. For the use as macromonomers, polymerizable terminal double bonds are an important requirement and thus, the investigation of the end groups in the polymers was the main focus of this study. The influence of the catalyst and polymerization conditions on the chain length of the polymer backbone, the monomer conversion as well as the end group characteristics were analyzed. It was possible to find conditions for preparing poly(10-undecene-1-ol)s with terminal double bonds using the catalyst system Cp₂ZrCl₂/MAO. Two other chosen catalysts produced mainly internal double bonds. The poly(10-undecene-1-ol)s could be prepared as atactic or isotactic-rich materials depending on the catalyst used.     

α‐keto‐β‐diimine nickel‐catalyzed olefin polymerization: Effect of ortho‐aryl substituents and preparation of stereoblock copolymers

A series of α‐keto‐β‐diimine nickel complexes (Ar‐N = C(CH₃)‐C(O)‐C(CH₃)=N‐Ar)NiBr₂; Ar = 2,6‐R‐C₆H₃‐, R = Me, Et, iPr, and Ar = 2,4,6‐Me₃‐C₆H₃‐) was prepared. All corresponding ligands are unstable even under an inert atmosphere and in a freezer. Stable copper complex intermediates of ligand synthesis and ethyl substituted nickel complex were isolated and characterized by X‐ray. All nickel complexes were used for the polymerization of ethene, propylene, and hex‐1‐ene to investigate their livingness and the extent of chain‐walking. Low‐temperature propene polymerization with less bulky ortho‐substituents was less isospecific than the one with isopropyl derivative. Propene stereoblock copolymers were prepared by iPr derivative combining the polymerization at low temperature to prepare isotactic polypropylene (PP) block and at a higher temperature, supporting chain‐walking, to obtain amorphous regioirregular PP block. Alternatively, a copolymerization of propene with ethene was used for the preparation of amorphous block. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2440–2449     

Amide-based molecular knots as platforms for fluorescent switches

A series of amide-based molecular knots equipped selectively with fluorescent dansyl and/or pyrenesulfonyl moieties were synthesized from the readily available tris(allyloxy)knotane. UV/Vis absorption spectra, emission spectra, and the emission lifetimes of the fluorescent knotanes were investigated in chloroform at 298 K. The absorption spectra of the knotanes correspond to those of mixtures of their UV-active constituents. The fluorescence quantum yields and lifetimes of the dansyl and pyrenesulfonyl moieties are partly quenched by the knotane platform. In the KN(Da)(2)(Py) species, the fluorescent excited state of the dansyl units (lambda(max)=510 nm) lies at lower energy than the fluorescent excited state of the pyrenesulfonyl unit (lambda(max)=385 nm), the emission of which is accordingly quenched with sensitization of the dansyl fluorescence. In the KN(Ao)(2)(Da), KN(Ao)(Da)(2), and KN(Da)(3) species, the addition of acids causes the protonation of their dansyl units with a consequent decrease in the intensity of the dansyl band at 510 nm and appearance of the emission band of the protonated dansyl unit (lambda(max)=340 nm). Each dansyl unit of KN(Ao)(Da)(2) and KN(Da)(3) undergoes the independent protonation. In these incompletely protonated knotanes the fluorescence of the protonated dansyl units is partly quenched by nonprotonated ones. These processes can be quantitatively reversed upon addition of a base. In KN(Da)(2)(Py), an increase of the fluorescence of its pyrenesulfonyl group is observed when the dansyl groups are protonated. The results obtained show that the readily available and easily functionalizable amide-knotanes can be used as an interesting scaffold to obtain fluorescent switches.     

Calibration possibilities and modifier use in ETV ICP OES determination of trace and minor elements in plant materials

The possibilities for universal calibration based on multi-element aqueous standard solutions and graphite laboratory reference materials (graphite standards) for the electrothermal vaporization inductively coupled plasma optical emission spectrometric (ETV ICP OES) determination of Al, B, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, P, Pb, S, Sr, Ti, V, and Zn in plant materials were investigated. A commercially available state-of-the-art ETV device was coupled with an Echelle ICP spectrometer equipped with a charge-injection-device (CID) camera for spectral detection. The transition area between transport tube and ETV graphite tube and the gas streams for inner gas, bypass gas, and modifier gas were optimized to achieve best transport efficiencies. The influence of four gaseous modifiers (CCl₄, CHCl₃, CCl₂F₂, and C₃H₈) added to the inner gas was studied. Five reference materials (RM P-Alfalfa, Lucerne; NIES CRM No.9 “Sargasso”; CTA-VTL-2 Virginia Tobacco Leaves; NIST SRM 1515 Apple Leaves; IAEA-V-10 Hay Powder) were used for method validation. If certified reference materials are not available, calibration against graphite standards or dried aqueous standard solutions is possible. Three carbonization procedures as sample pretreatment for the plant materials were investigated. Figure Picture of the ETV system (sample changer and graphite-tube furbace) used in this work Presented at the European Symposium on Atomic Spectrometry (ESAS) September 28-October 1, 2008, Weimar, Germany.