Phosphorus in different forms is used in a variety of applications (catalysts, thermal stabilizers, flame retardants) in polymeric formulations. It is important to be able to determine its concentration in raw materials, intermediates and final products. The challenge of measuring low concentrations of P, combined with the volatility of the organic phosphorus compounds, has been solved through a novel analytical procedure with a method detection limit of 0.4 µg g−1 P (10σ). The volatilization of organic P compounds was prevented by pre-oxidation with periodic acid, which allows ashing in the presence of magnesium acetate while maximizing the weight to final volume ratio. Using factorial design of experiments, experimental factors including ashing temperature, time, and the amount of the reagents were optimized with respect to accuracy and precision of the technique. The influence of Ti when present in the samples was eliminated by complexing it with H2O2. Additional pre-treatment with NH4OH was found to improve recovery for some reactive samples. Comparison with other established methods was carried out and is discussed.

The structure of Gd-DTPA-polylysine, Gd-DOTA-polylysine, Gd-SCN-Bz-DOTA-polylysine, and Gd-DTPA-poly(glu:lys) was investigated with circular dichroism, gel permeation chromatography, low angle light scattering, and proton longitudinal relaxivity. Molecular modeling calculations were performed and predicted helical secondary structure for charged Gd-chelator residues, i.e., Gd-DTPA, when the DTPA conjugation levels reached 90% and higher. This helical secondary structure was observed with circular dichroism. The conformational transition from coiled to extended linear was observed also by gel permeation chromatography and by proton relaxivity measurements. The helical secondary structure was not observed when the chelator was changed to DOTA. The residue charge interactions were eliminated in this case since the Gd-DOTA complex had no net charge. For this construct, the gel permeation and relaxivity measurements indicated a coiled conformation. An extended linear conformation was regained when the chelator complex was changed to Gd-SCN-Bz-DOTA, which had a net negative charge. The functional aspects of these structures were investigated by MR imaging of an animal tumor model. The linear extended polymer constructs gave 10-fold higher tumor signals then the coiled-collapsed constructs, indicating a much higher degree of trans-endothelial transport in the tumors.

A method for measuring composition and sequence lengths in poly(dimethylsiloxane)/poly(tetramethyl-p-silphenylenesiloxane) copolymers by Si-29 NMR is presented. The technique has been used to study the relationship between the block length in the copolymer and the degree of oligomerization of the starting disiloxanol, and to study the redistribution reaction of the polymer. It has been shown from Si-29 NMR studies of the polymerization reaction that efficient water removal is necessary to minimize redistribution of siloxane bonds in the polymer.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCatalytic carbon-carbon bond formation via ortho-metalated complexesLarry N. Lewis and Joanne F. SmithCite this: J. Am. Chem. Soc. 1986, 108, 10, 2728–2735Publication Date (Print):May 1, 1986Publication History Published online1 May 2002Published inissue 1 May 1986https://doi.org/10.1021/ja00270a036RIGHTS & PERMISSIONSArticle Views2729Altmetric-Citations244LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (829 KB) Get e-Alerts Get e-Alerts

AbstractThere are two groups of A1 alkoxide (siloxide) β‐diketonate complexes, whose general properties and structures are quite different from each other.