Halomethylated polysulfone: Reactive intermediates to neutral and ionic film-forming polymers

Halomethylation of polysulfone (PS) with C₈H₁₇OCH₂X (X = Cl, Br) in the presence of SnX₄ (X = Cl, Br) led to PS–CH₂X (X = Cl or Br or both) (Scheme 1). Under controlled conditions, PS–CH₂X could be isolated and retains the good film forming properties of PS itself. Interhalogen exchange reactions occur in the presence of SnX₄ (X = Cl, Br) under anhydrous conditions (Scheme 1), or a quaternary ammonium phase transfer catalyst R^*R₃N⁺X^?, under aqueous conditions (Scheme 2). The exchange reactions with R^*R₃N⁺X^?, are favored when R = C₈? C₁₀, and with R = C₄ only if n-octanol is added; otherwise gelation occurs. Exchange in CHCl₃ is attributed to dehydrohalogenation (and generation of dichlorocarbene) of the solvent in the presence of tetrabutyl ammonium hydroxide. Further chemical modifications of PS–CH₂X by reaction with strong nucleophiles, led to hydroxymethyl polysulfone, acetoxymethyl polysulfone, and t-butyl-oxymethyl polysulfone (Scheme 3). Hydroxymethyl polysulfone sometimes gels under basic hydrolytic conditions and is best obtained by methanolysis of PS–CH₂-OAc. Both PS? CH₂? OAc and PS? CH₂O-t-Bu are very stable, and provide a way to generate PS? CH₂Br on need by cleavage with HBr in acetic acid. Direct oxidations with DMSO or tetrabutyl ammonium dichromate (Scheme 4) or indirect oxidations (Scheme 5) produce polysulfone with pendent CHO, CO₂R and PO₃R groups. Finally, polysulfones with linker arms including, carboxy alkyl, hexaglycol or sulfonamido crowns are described (Scheme 6). The reaction products were characterized by ¹H- and ¹³C-NMR. Double irradiation experiments, proved unequivocally, that the first substitution occurred on the B ring of the bisphenol A moiety (see Table I); the second substitution occurs on the A ring in position a. Thermogravimetric analysis generally shows for all modified polysulfones an extra transition at a lower temperature. The area of this band agrees generally with the values expected from calculated substitution degrees.     

The imaging appearance of Creutzfeldt-Jakob disease caused by the E200K mutation

The E200K mutation on chromosome 20 can cause familial Creutzfeldt-Jakob disease (CJD). Patients with this mutation are clinically similar to those with sporadic CJD, but their imaging features are not well documented. We report here the quantitative and qualitative evaluation of the magnetic resonance (MR) imaging characteristics of this unique group of patients using three-dimensional spoiled gradient recalled (SPGR) echo images, diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) measurements, MR spectroscopy and a fluid-attenuated inversion recovery (FLAIR) sequence. The SPGR and ADC data were analyzed with SPM99. ANCOVA and regression models were used for a region-of-interest (ROI) analysis of ADC and metabolic ratios. CJD patients had a decreased fraction of gray matter and an increased fraction of cerebrospinal fluid (P=.001) in the cortex and cerebellum and increased ADC values in the cortex (P<.001). Focal decreases of ADC were found in the putamen via ROI analysis (548+/-83 vs. 709+/-9 microm(2)/s, P=.02). N-acetyl aspartate (NAA) was generally reduced, with the NAA/Cho ratio lowest in the cingulate gyrus. Qualitative assessment revealed hyperintensities on FLAIR, DWI or both in the putamen (three out of four patients), caudate (three out of four patients) and thalamus. These results provide a framework for future study of patients with genetically defined familial CJD.     

Top percentile network pricing and the economics of multi-homing

Top-Percentile pricing is a relatively new and increasingly popular pricing policy used by network providers to charge service providers. In contrast to fixed cost pricing and to pure per-usage pricing, top-percentile pricing has not been studied. Thus the efficient design and operation of networks under top-percentile pricing is not well understood yet. This work studies top-percentile pricing and provides an analysis of the expected costs it inflicts on a service provider. In particular we use our analysis framework to investigate the popular multi-homing architecture in which an Internet Service Provider (ISP) connects to the Internet via multiplicity of network providers. An ISP that uses multi-homing is subject to extra charges due to the use of multiple networks. Important questions that are faced by such an ISP are what is an efficient routing strategy (as to reduce costs) and how large the costs are. We provide a general formulation of this problem as well as its probabilistic analysis, and derive the expected cost faced by the ISP. We numerically examine several typical scenarios and demonstrate that despite the fact that this pricing aims at the peak traffic of the ISP (similarly to fixed cost), the expected bandwidth cost of multi-homing is not much higher than that of single-homing. Part of the results of this work was reported in Levy, Levy, and Kahana (2003). The work was done while J.Levy and Y. Kahana were with Comgates Ltd. and H. Levy was partially with Comgates Ltd.