Sequestration of Ruthenium Residues via Efficient Fluorous-enyne Termination.

The creation of polymers without metal contamination remains a significant challenge for metathesis-based polymerization techniques and has complicated applications in biomedical and electronic applications. This communication reports a new approach for the removal of ruthenium byproducts through the design of an enyne terminator for metathesis polymerization that contains a fluorous tag. Upon reaction of a living polymer chain with the enyne, the ruthenium center is captured as a stable sulfur-chelated complex that can be efficiently removed after a single filtration through a fluorous cartridge. Levels of ruthenium residues as determined by ICP-MS were found to depend on the monomer structure, eluting solvent, and the degree of polymerization targeted. Ruthenium residues were minimized to low ppm levels (4-75 ppm) for most samples examined and also led to the improved thermal stability of the final materials. This represents the most efficient single method for removal of ruthenium residues from metathesis polymerization products.

Cascade Alternating Metathesis Cyclopolymerization of Diynes and Dihydrofuran.

Ruthenium alkoxymethylidene complexes have recently come into view as competent species for metathesis copolymerization reactions when coupled with appropriate comonomer targets. Here, we explore the ability of Fischer-type carbenes to participate in cascade alternating metathesis cyclopolymerization (CAMC) through facile terminal alkyne addition. The combination of diyne monomers and an equal feed ratio of low-strain dihydrofuran leads to a controlled chain-growth copolymerization with high degrees of alternation (>97% alternating diads) and produces degradable polymer materials with low dispersities and targetable molecular weights. When combined with enyne monomers, this method is amenable to the synthesis of alternating diblock copolymers that can be fully degraded to short oligomer fragments under aqueous acidic conditions. This work furthers the potential for the generation of functional metathesis materials via Fischer-type ruthenium alkylidenes.

Convergent Synthesis of Branched Metathesis Polymers with Enyne Reagents.

Branched polymers have found utility in an array of fields due to the high density of functional groups combined with unique physical properties. Despite the abundant methods reported to synthesize various branched structures, controlling parameters such as the location of branch points and molecular weight distribution still remains a challenge. This report explores the ability of enyne-containing branching agents to synthesize star and miktoarm star polymers through a convergent synthesis pathway using ring-opening metathesis polymerization (ROMP). The branching agents contain an enyne metathesis terminator covalently linked to a norbornene monomer. When these agents are introduced into a living ROMP, macromonomers are generated in situ that continue to propagate via a grafting-through process with the remaining living chains. This strategy permits control over the degree of polymerization of the star arms, control of the number of star arms, and chain-extension with additional monomer to produce functional asymmetric miktoarm star polymers.

Alternating Cascade Metathesis Polymerization of Enynes and Cyclic Enol Ethers with Active Ruthenium Fischer Carbenes.

Ruthenium alkoxymethylidene complexes have rarely been demonstrated as active species in metathesis reactions and are frequently regarded as inert. Herein, we highlight the ability of these Fischer-type carbenes to participate in cascade alternating ring-opening metathesis polymerization through their efficient alkyne addition reactions. When enyne monomers are combined with low-strain cyclic vinyl ethers, a controlled chain-growth copolymerization occurs that exhibits high degrees of alternation (>90% alternating diads) and produces degradable poly(vinyl ether) materials with low dispersities and targetable molecular weights. This new method is amenable to the synthesis of alternating diblock polymers that can be degraded to small-molecule fragments under aqueous acidic conditions. This work furthers the potential of Fischer-type ruthenium alkylidenes in polymerization strategies and presents new avenues for the generation of functional metathesis materials.

Modular Approach to Degradable Acetal Polymers Using Cascade Enyne Metathesis Polymerization.

A modular synthetic approach to degradable metathesis polymers is presented using acetal-containing enyne monomers. The monomers are prepared in a short and divergent synthetic sequence that features two points of modification to tune polymerization behavior and introduce molecular cargo. Steric and stereochemical elements are critical in the monomer design in order to provide rapid and living polymerizations capable of generating block polymers. The developed polyacetal materials readily undergo pH-dependent degradation in aqueous mixtures, and the rate of hydrolysis can be tuned through post-polymerization modification with triazolinedione click chemistry. This presents a new scaffold for responsive metathesis polymers that may find use in applications that requires controllable breakdown and release of small molecules.

Phosphine phosphonic amide nickel catalyzed ethylene polymerization and copolymerization with polar monomers.

The phosphine phosphonic amide ligand platform is highly versatile, with three positions that can be independently tuned. In this contribution, we wish to study the nickel complexes based on this ligand system. Interestingly, the nickel dibromide and nickel allyl complexes are not active in ethylene polymerization. In contrast, the nickel phenyl chloride complexes are highly active in ethylene polymerization in the presence of a sodium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate cocatalyst. In addition, these nickel complexes can initiate ethylene copolymerizations with polar functionalized comonomers including methyl 10-undecenoate, 6-chloro-1-hexene and 5-acetoxy-1-pentene. More interestingly, these nickel complexes can oligomerize 1-hexene and 6-chloro-1-hexene.

Synthesis of high molecular weight polyethylene using iminopyridyl nickel catalysts.

A series of iminopyridyl Ni(ii) catalysts containing both the dibenzhydryl and the naphthyl moieties can polymerize ethylene with high activity and high thermal stability, generating polyethylene with a molecular weight of up to one million. In α-olefin polymerization, semicrystalline polymers with high melting temperatures are generated.

Highly Robust Palladium(II) α-Diimine Catalysts for Slow-Chain-Walking Polymerization of Ethylene and Copolymerization with Methyl Acrylate.

A series of sterically demanding α-diimine ligands bearing electron-donating and electron-withdrawing substituents were synthesized by an improved synthetic procedure in high yield. Subsequently, the corresponding Pd complexes were prepared and isolated by column chromatography. These Pd complexes demonstrated unique properties in ethylene polymerization, including high thermal stability and high activity, thus generating polyethylene with a high molecular weight and very low branching density. Similar properties were observed for ethylene/methyl acrylate copolymerization. Because of the high molecular weight and low branching density, the generated polyethylene and ethylene/methyl acrylate copolymer were semicrystalline solids. The (co)polymers had unique microstructures originating from the unique slow-chain-walking activity of these Pd complexes.

Conversion of chicken feather waste to N-doped carbon nanotubes for the catalytic reduction of 4-nitrophenol.

Poultry feather is renewable, inexpensive and abundantly available. It holds great business potentials if poultry feather can be converted into valuable functional materials. Herein, we describe a strategy for the catalytic conversion of chicken feather waste to Ni3S2-carbon coaxial nanofibers (Ni3S2@C) which can be further converted to nitrogen doped carbon nanotubes (N-CNTs). Both Ni3S2@C and N-CNTs exhibit high catalytic activity and good reusability in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by NaBH4 with a first-order rate constant (k) of 0.9 × 10(-3) s(-1) and 2.1 × 10(-3) s(-1), respectively. The catalytic activity of N-CNTs is better than that of N-doped graphene and comparable to commonly used noble metal catalysts. The N content in N-CNTs reaches as high as 6.43%, which is responsible for the excellent catalytic performance. This strategy provides an efficient and low-cost method for the comprehensive utilization of chicken feathers. Moreover, this study provides a new direction for the application of N-CNTs.

One for two: conversion of waste chicken feathers to carbon microspheres and (NH4)HCO3.

Pyrolysis of 1 g of waste chicken feathers (quills and barbs) in supercritical carbon dioxide (sc-CO2) system at 600 °C for 3 h leads to the formation of 0.25 g well-shaped carbon microspheres with diameters of 1-5 µm and 0.26 g ammonium bicarbonate ((NH4)HCO3). The products were characterized by powder X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Raman spectroscopic, FT-IR spectrum, X-ray electron spectroscopy (XPS), and N2 adsorption/desorption measurements. The obtained carbon microspheres displayed great superhydrophobicity as fabric coatings materials, with the water contact angle of up to 165.2±2.5°. The strategy is simple, efficient, does not require any toxic chemicals or catalysts, and generates two valuable materials at the same time. Moreover, other nitrogen-containing materials (such as nylon and amino acids) can also be converted to carbon microspheres and (NH4)HCO3 in the sc-CO2 system. This provides a simple strategy to extract the nitrogen content from natural and man-made waste materials and generate (NH4)HCO3 as fertilizer.