LiCB11(CH3)12-Catalyzed Radical Polymerization of Isobutylene: Highly Branched Polyisobutylene and an Isobutylene−Ethyl Acrylate Copolymer

A Bibliometric Survey on Polyisobutylene Manufacture

Polyisobutylenes (PIB) constitute a versatile family of polymer materials that have been used mainly as fuel and lubricant additives. Particularly, the current commercial demand for highly reactive polyisobutylene (HR-PIB) products motivates the development of new processes and procedures to produce PIBs with high polymer yields, narrow molar mass distributions and high vinyl contents. For this reason, a bibliometric survey is presented here to map and discuss important technical aspects and technological trends in the field of solution cationic polymerization of isobutylenes. It is shown that investigations in this field are concentrated mainly on developed countries and that industrial initiatives indicate high commercial interest and significant investments in the field. It is also shown that use of catalyst systems based on AlCl3 and ether cocatalysts can be very beneficial for PIB and HR-PIB manufacture. Finally, it is shown that investigations search for cheaper and environmentally friendly catalysts and solvents that can be employed at moderate temperatures, particularly for the production of HR-PIB.

Extending the chemistry of weakly basic ligands: solvates of Ag+ and Cu+ stabilized by [Al{OC(CF3)3}4]- anion as model examples in the screening of useful weakly interacting solvents

Weakly Coordinating Anions (WCAs) facilitate the formation of exotic "naked" cationic species. However, the feasibility of the respective synthesis approaches may be limited by the basicity of the solvent utilized, as the latter is one of the most important factors determining the solvation ability. In this work, we focus on a series of novel complexes of Ag(i) and Cu(i) with weakly basic ligands such as CH₂Cl₂, Cl₃CCN and SO₂ stabilized by perfluorinated alkoxyaluminate, Al[(OR^F)₄]^-, R^F = C(CF₃)₃. The discussion includes their synthesis protocols, crystal structures, vibrational spectra and thermal stability (TGA/DSC/EGA). We show that the Cu-SO₂ adducts present exceptional stability in relation to other metal-SO₂ complexes. To broaden the scope of weakly basic ligands which could prove helpful in the development of chemistry with WCAs, the screening of potential candidates based on DFT calculations is presented.

Building blocks for the chemistry of perfluorinated alkoxyaluminates [Al{OC(CF3)3}4]-: simplified preparation and characterization of Li+-Cs+, Ag+, NH4+, N2H5+ and N2H7+ salts

Advanced weakly coordinating anions (WCAs) significantly facilitate synthesis of various exotic chemical compounds and novel, potentially useful materials. One of such anions - [Al{OC(CF₃)₃}₄]^-, denoted [Al(OR^F)₄]^-, appears particularly convenient, as it can be easily prepared from the commercially available alanates and HOC(CF₃)₃. Here we present a thorough characterization of a series of solvent-free M[Al(OR^F)₄] salts, M = Li-Cs, Ag, NH₄, N₂H₅ and N₂H₇, and related compounds of monovalent cations, which are crucial starting materials for further work with these species. Notably, the corresponding synthetic protocols are updated by an improved method for fast, facile and easily scalable synthesis of Li[Al(OR^F)₄], which remains the most useful primary source of the anion. The physico-chemical properties of these salts including crystal structures, thermal stability by TG/DSC, vibrational spectra as well as solubility are discussed in a systematic fashion.

Controlled Radical Homopolymerization of Representative Cationically Polymerizable Vinyl Ethers

Facile direct radical homopolymerization of vinyl ethers without a hydroxy group was achieved up to near full conversion. This polymerization was conducted in water suspension in the presence of lithium hydroxide using a thermally triggered azo-initiator of dimethyl 2,2'-azobis(2-methylpropionate). In the polymerization system, appropriate hydrogen bonding and cation-π interactions under basic conditions are keys to the successful direct radical homopolymerization. The hydrogen bonding between water and vinyl ether oxygen reduces the reactivity of the growing radical, thus suppressing unfavorable side reactions such as β-scission. In addition, Li⁺ interacts with the oxygen and the vinyl group of vinyl ethers. The vinyl ether tends to be "activated" and the polymerization can be facilitated. Based on the results of free radical polymerization of vinyl ethers, controlled polymerization was also accomplished using the appropriate dithiocarbamate RAFT agent in view of the solubilities of the radical leaving group.

Radical polymerization in the presence of a peroxide monomer: an approach to branched vinyl polymers

In this paper, we report radical polymerization in the presence of a peroxide monomer for the preparation of branched vinyl polymers.

Visible-Light-Induced Olefin Activation Using 3D Aromatic Boron-Rich Cluster Photooxidants

We report a discovery that perfunctionalized icosahedral dodecaborate clusters of the type B12(OCH2Ar)12 (Ar = Ph or C6F5) can undergo photo-excitation with visible light, leading to a new class of metal-free photooxidants. Excitation in these species occurs as a result of the charge transfer between low-lying orbitals located on the benzyl substituents and an unoccupied orbital delocalized throughout the boron cluster core. Here we show how these species, photo-excited with a benchtop blue LED source, can exhibit excited-state reduction potentials as high as 3 V and can participate in electron-transfer processes with a broad range of styrene monomers, initiating their polymerization. Initiation is observed in cases of both electron-rich and electron-deficient styrene monomers at cluster loadings as low as 0.005 mol%. Furthermore, photo-excitation of B12(OCH2C6F5)12 in the presence of a less activated olefin such as isobutylene results in the production of highly branched poly(isobutylene). This work introduces a new class of air-stable, metal-free photo-redox reagents capable of mediating chemical transformations.

Gas-phase lithium cation basicity: revisiting the high basicity range by experiment and theory

According to high level calculations, the upper part of the previously published FT-ICR lithium cation basicity (LiCB at 373 K) scale appeared to be biased by a systematic downward shift. The purpose of this work was to determine the source of this systematic difference. New experimental LiCB values at 373 K have been measured for 31 ligands by proton-transfer equilibrium techniques, ranging from tetrahydrofuran (137.2 kJ mol(-1)) to 1,2-dimethoxyethane (202.7 kJ mol(-1)). The relative basicities (ΔLiCB) were included in a single self-consistent ladder anchored to the absolute LiCB value of pyridine (146.7 kJ mol(-1)). This new LiCB scale exhibits a good agreement with theoretical values obtained at G2(MP2) level. By means of kinetic modeling, it was also shown that equilibrium measurements can be performed in spite of the formation of Li(+) bound dimers. The key feature for achieving accurate equilibrium measurements is the ion trapping time. The potential causes of discrepancies between the new data and previous experimental measurements were analyzed. It was concluded that the disagreement essentially finds its origin in the estimation of temperature and the calibration of Cook's kinetic method.