Sulfonated poly(fluorenyl ether ketone) membrane prepared via direct polymerization for PEM fuel cell application

Sulfonated poly(fluorenyl ether ketone)s with inherent viscosity ranging from 0.68 to 0.93 dL/g were directly synthesized by aromatic nucleophilic polycondensation of bisphenol fluorene with various ratios of sulfonated difluorobenzophenone to difluorobenzophenone. The synthesized polymers were characterized by ¹H NMR method and elemental analysis. The polymers were tested to be soluble in dipolar aprotic solvents such as DMAc, DMF and DMSO and can be readily cast into tough films. These films showed highly thermal degradation temperature, glass transition temperature and excellent water affinity as well as excellent proton conductivity. The polymers showed a promising proton membrane material for PEM fuel cell application.     

Dimerization of functional pyrroloindolizines for the synthesis of complex myrmicarin alkaloids

The union of functionalized pyrroloindolizines for the synthesis of heterodimeric products relevant to myrmicarin alkaloids is described. Design and synthesis of tricyclic substrates and new methods for their union enable the investigation of late-stage cyclopentannulation strategies. The rapid assembly of dimeric structures using unique modes of pyrroloindolizine reactivity presents a concise approach to the dimeric myrmicarins and relevant derivatives.     

Oligomers and Polymers of Polyethers and Polyformals

Linear high molecular weight aromatic polyformals are readily obtained from biphenols and excess methylene chloride with solid sodium hydroxide or potassium hydroxide in the presence of a phase transfer catalyst or an aprotic dipolar solvent. By control of the stoichiometry bifunctional oligomers can be obtained which can subsequently be incorporated into a variety of block copolymers.     

Why the addition of neutral oxygen donor groups promotes selectivity for larger metal ions

Abstract

The origin of selectivity enhancement for large metal ions that occurs on the addition of neutral oxygen donors to existing ligands in such a way as to form additional five-membered chelate rings is analyzed in terms of inductive and steric effects. Molecular mechanics calculations are used to examine the degree of strain that develops in five-membered, aliphatic chelate rings of ethers and amines as a function of the size and charge of the metal ion. Although five-membered chelate rings that contain saturated neutral oxygen donors are found to exhibit an inherent steric preference for large metal ions, experimental evidence suggests that for the majority of cases where enhanced selectivity for larger metal ions has been observed after the addition of neutral oxygen donors, the selectivity enhancement is largely the result of steric and inductive changes to other donor groups in the ligand, e.g. amines, rather than the result of increasing the denticity of the ligand.     

Evaluation of Combustion Mechanisms Using Global Uncertainty and Sensitivity Analyses: A Case Study for Low‐Temperature Dimethyl Ether Oxidation

A global uncertainty analysis is performed for three current mechanisms describing the low‐temperature oxidation of dimethyl ether (Aramco Mech 1.3, Metcalfe et al., Int J Chem Kinet 2013, 45, 638–675; Zheng et al., Proc Combust Inst 2005, 30, 1101–1109; Liu et al., Combust Flame 2013, 160, 2654–2668) with application to simulations of species concentrations (CH₂O, H₂O₂, CH₃OCHO) corresponding to existing data from an atmospheric pressure flow reactor and high‐pressure ignition delays. When incorporating uncertainties in reaction rates within a global sampling approach, the distributions of predicted targets can span several orders of magnitude. The experimental profiles, however, fall within the predictive uncertainty limits. A variance‐based sensitivity analysis is then undertaken using high dimensional model representations. The main contributions to predictive uncertainties come from the CH₃OCH₂ + O₂ system, with isomerization, propagation, chain‐branching, secondary OH formation, and peroxy–peroxy reactions all playing a role. The response surface describing the relationship between sampled reaction rates and predicted outputs is complex in all cases. Higher order interactions between parameters contribute significantly to output variance, and no single reaction channel dominates for any of the conditions studied. Sensitivity scatter plots illustrate that many different parameter combinations could lead to good agreement with specific sets of experimental data. The Aramco scheme is then updated based on data from a recent study by Eskola et al. (J Phys Chem A, in press), which presents quite different temperature and pressure dependencies for the rates of CH₃OCH₂O₂ → CH₂OCH₂O₂H and CH₂OCH₂O₂H → OH+2CH₂O compared with currently used values and includes well skipping channels. The updates from Eskola worsen the agreement with experiments when used in isolation. However, if the rate of the CH₂OCH₂O₂H + O₂ channel is subsequently reduced, very good agreement can be achieved. Owing to the complex nature of the response surface, the tuning of this channel remains speculative. Further detailed studies of the temperature and pressure dependence of the CH₃OCH₂O₂ + O₂, CH₂OCH₂O₂H + O₂ system are recommended to reduce uncertainties within current dimethyl ether mechanisms for low‐temperature conditions.