Lithiation of toluene by organolithium compounds activated by lithium polyether alkoxides

peer reviewedThe catalytic effect of polyether alkoxides (PEAs) on the activity of organolithium. compounds as metallating agent has been investigated. Toluene has been lithiated by using different organolithiums activated by various PEAs. It has been found that n-BuLi, yields higher conversion with 100% benzylic position metallation, whereas sec-BuLi gives some metallation at ring positions with the most reactive ligand, lithium 2-methoxy ethoxide (LiOEM). Optimum PEA to organolithium molar ratio for both sec- and n-BuLi activated by LiOEM where the amount of toluene being kept constant, was found to be as 3:1 with highest yield and regioselectivity. Substantial increment in yield was observed when the amount of substrate increased whereas regioselectivity stayed almost constant. It was also found that, for a constant reactant molar ratio (3:1:15) for which the optimum results were achieved, reaction began early and then yield values increased with time whereas upon increase in reaction temperature from -78 to 20degreesC, the benzylic metallation yield increased drastically while keeping the same regioselectivity high

Anionic polymerisation of methyl methacrylate with complex initiator system

Polymerisation of methyl methacrylate was conducted by using alkyl lithium/dimethylsulfoxide (DMSO) system as initiator in toluene. A special attention was focused on using some lithium polyetheralkoxides as polymerisation promoters at ambient temperatures. Poly(methyl methacrylate) samples were characterized with Gel Permeation Chromatography (GPC), Nuclear Magnetic Resonance Spectroscopy (H-1 NMR) and Differential Scanning Calorimetry (DSC). The positive effect of the mu/sigma type ligands such as lithium 2-(2-methoxyethoxy)ethoxide (LiOEEM), 2-(methoxy)ethoxide (LiOEM) on controlling the living character, molecular weight, stereo regularity and the yield of the produced polymers was demonstrated. It has been found that this approach provided high polymerisation yields and low polydispersity but low initiator efficiency

Synthesis of a new difunctional anionic initiator and ABA triblock copolymers

Ph.D. - Doctoral Progra

Ambient temperature anionic polymerization of methylmethacrylate by using alkyllithium/dimethylsulfoxide initiator system

peer reviewe

Lithiation of toluene by organolithium compounds activated by lithium polyether alkoxides

peer reviewedThe catalytic effect of polyether alkoxides (PEAs) on the activity of organolithium. compounds as metallating agent has been investigated. Toluene has been lithiated by using different organolithiums activated by various PEAs. It has been found that n-BuLi, yields higher conversion with 100% benzylic position metallation, whereas sec-BuLi gives some metallation at ring positions with the most reactive ligand, lithium 2-methoxy ethoxide (LiOEM). Optimum PEA to organolithium molar ratio for both sec- and n-BuLi activated by LiOEM where the amount of toluene being kept constant, was found to be as 3:1 with highest yield and regioselectivity. Substantial increment in yield was observed when the amount of substrate increased whereas regioselectivity stayed almost constant. It was also found that, for a constant reactant molar ratio (3:1:15) for which the optimum results were achieved, reaction began early and then yield values increased with time whereas upon increase in reaction temperature from -78 to 20degreesC, the benzylic metallation yield increased drastically while keeping the same regioselectivity high

Synthesis of High Molecular Weight and Strength Polyisobutylene-Based Polyurethane and Its Use for the Development of a Synthetic Heart Valve

Under optimized synthesis conditions we prepared, for the first time, polyisobutylene-based polyurethane (PIB-PU) with 70% PIB soft segment (i.e., a bioinert and calcification resistant PU) with Mn >100,000 Da, 32 MPa ultimate strength and 630 % elongation. The key parameters for this achievement were (a) the precise stoichiometry of the polyurethane forming reaction, specifically the use of highly purified diisocyanate (MDI), and (b) the increased the solid content of the synthesis solution to the limit beyond which increased viscosity prevents stirring. The shape of the stress-strain trace of PIB-PU indicates two-step failure starting with a reversible elastic (Hookean) region up to ~50 % yield, followed by a slower linearly increasing high modulus deformation region suggesting the strengthening of PIB soft segments by entanglement/catenation, and the hard segments by progressively ordering urethane domains. This PIB-PUs is a candidate for a fully synthetic bioprosthetic heart valve since preliminary studies show that PIB-PU has impressive fatigue life.Armstrong Trust and Vice Chancellor's Scholarshi

UV induced reversible chain extension of 1-(2-anthryl)-1-phenylethylene functionalized polyisobutylene

<p>The synthesis of novel 1-(2-anthryl)-1-phenylethylene (APE) di-telechelic polyisobutylenes is described. Utilization of a difunctional cationic initiator and the <i>in situ</i> addition of the non-homopolymerizable APE lead to the formation of di-anthryl telechelic polyisobutylenes. Products were characterized by ¹H NMR spectroscopy and Size Exclusion Chromatography. The polymers were UV irradiated at 365 and 254 nm and the reversible photocycloaddition of anthryl moieties was investigated. The chain extension of di-anthryl telechelic PIBs through photocoupling at 365 nm produced higher molecular weight products from low molecular weight precursors. The effect of precursor polymer concentration on the degree of chain extension was investigated, and intermolecular interactions leading to the formation of tetramers was observed. The photocoupled products were UV irradiated at 254 nm to induce the reversal of photocycloaddition of anthryl groups and to follow the consequent photoscission of polymers.</p

High Strength Bimodal Amphiphilic Conetworks for Immunoisolation Membranes: Synthesis, Characterization, and Properties

A strategy for the synthesis of new cross-linkable bimodal amphiphilic grafts (bAPGs) was developed. These grafts are of hydrophilic PDMAAm backbones carrying low (<i>M</i>_n ∼ 17 200 g/mol) and high (<i>M</i>_n ∼ 117 000 g/mol) molecular weight hydrophobic PDMS branches, each branch carrying a vinylsilyl end-group. The bAPGs were cross-linked by Karstedt catalyst to bimodal amphiphilic conetworks (bAPCNs) by the use of polyhydrosiloxane-<i>co</i>-PDMS as the cross-linker. Membranes prepared from bAPCNs exhibit mechanical properties surprisingly superior to earlier APCNs prepared with APGs with monomodal low molecular weight branches. Membrane bimodality controls surface morphology and topography by means of elastic wrinkling instability during film formation. Semipermeable bAPCN membranes with precisely controlled nanochannel dimensions were prepared so as to allow rapid insulin diffusion and prevent passage of IgG. bAPCN membranes were designed for immunoprotection of live pancreatic islets and are thus key components for a bioartificial pancreas