Zr-Containing 4,4'-ODA/PMDA Polyimide Composites

The objective of this research is to improve the atomic oxygen resistance of Kapton(TM), a polyimide (PI) made from pyromellitic acid dianhydride (PMDA) and 4,4'-oxydianiline (ODA), while retaining or enhancing the desirable properties of the pure polymer. Toward this end, zirconium-containing complexes and polymers were used to make composites and blends. Tetra(acetylacetonato)zirconium(IV), Zr(acac)4, which is commercially available, was identified as the best zirconium-containing complex for enhancing the atomic oxygen resistance of polyimide composites of the 10 complexes screened. Films prepared from the commercially available polyamic acid (PAA) of PMDA-ODA (DuPont) have good uniformity, flexibility, and tensile strength. A 24-layer 10% (mol) Zr(acac)4/PI composite film showed significant improvement (ca. 20 fold) of atomic oxygen resistance over the pure polyimide. However, 10% (mol) Zr(acac)4 represents an upper concentration limit, above which films undergo cracking upon thermal imidization. In order to increase the Zr complex concentration in PMDA-ODA PI films, while retaining good film properties, [Zr(adsp)2-PMDA]n coordination polymer [bis(4-amino-N,N'-disalicylidene- 1,2-phenylenediamino)zirconium(IV)-pyromellitic dianhydride] and [Zr(adsp)2-PMDA-ODA-PMDA]n terpolymer were synthesized and blended with commercial PAA, respectively. Several techniques were used to characterize the films made from the polymer containing Zr(acac)4. Plasma studies of films having 2% (mol) incremental concentrations of Zr in the Kapton up to 10% (mol) show that the overall rate of erosion is reduced about 75 percent

A Biopsychosocial Model of Normative and Problematic Pediatric Feeding

A comprehensive model is presented that (a) highlights factors that have been implicated in the development and maintenance of feeding problems in both normal and clinical populations; and (b) provides a framework for the prevention, management, and treatment of feeding problems across the range of physically healthy children to children with acute and chronic illnesses. Relevant literatures and feeding models were synthesized to present a comprehensive unified biopsychosocial model that may aid in the prediction and synthesis of information about feeding and eating in both normal and clinical populations and provide a framework for interdisciplinary research and intervention

Formation and Structure of a Platinum(II) Complex Containing Two trans Nonstabilized Phosphorus Ylide Ligands: Evidence for Reversible Ylide Dissociation

International audienceThe reaction of (nBu4P)2[PtBr4] with 2,2′-(C6H4Li)2 yields selectively (by 195Pt and 31P NMR) the compound trans-PtBr2[CH(nPr)(PnBu3)]2 as a mixture of meso (R,S) and dl (R,R + S,S) diastereoisomers. The initially formed 1:1 mixture slowly evolves toward a solution richer in the meso compound, which then crystallizes selectively. In addition to the NMR characterization, the meso isomer has also been characterized by a single-crystal X-ray diffraction analysis. DFT calculations in the gas phase and in solution (THF) confirm the slight thermodynamic preference for the meso isomer and reproduce the chemical shift difference of the 195Pt NMR resonances. They also suggest the likelihood of a dissociative mechanism for the slow diastereoisomer interconversion