No abstract

The carbon-13 chemical shifts of ethylene propylene copolymers were found to be very sensitive to monomer sequence distribution. Methylene resonances were interpreted in terms of methylene sequence length and tertiary carbon resonances were interpreted in terms of propylene centered pentad sequences. Propylene inversion was detected and measured quantitatively in the spectra. A formula was derived for calculating r1·r2, which is independent of monomer feed, and which is based on measuring contiguous and isolated propylene sequences in the copolymer. The interpretations are shown to be consistent for copolymers containing 26, 34, and 62 mole% propylene. The r1·r2 products were determined for each of these polymers. Calculation of copolymer composition based on the 13C chemical shift assignments gave excellent agreement with the compositions as determined by infrared and 1H NMR. A formula was derived, based on copolymerization theory, for calculating the reactivity ratio product, r1·r2, directly from the copolymer composition (% ethylene) and the ratio of contiguous to isolated propylene sequences. Using this formula an average value for r1·r2=0.42±0.02 was determined for the copolymers made with vanadium acetylacetonate-diethylaluminum chloride catalyst system.

The acquired immunodeficiency syndrome (AIDS) was first recognized among hemophiliacs in 1982. The authors have conducted investigations to determine the onset and incidence of AIDS among hemophiliacs and to determine trends in hemophilia mortality since the introduction of clotting-factor concentrates in the late 1960s. A survey of United States hemophilia treatment centers, supported by the Centers for Disease Control and the National Hemophilia Foundation, defined a population of hemophiliacs which was monitored for AIDS cases through June 1984. Death reports from the United States Vital Statistics System and from the hemophilia treatment center survey provided mortality trends for 1968-1979 and for 1978-1982, respectively. The results of these investigations demonstrate the following points. 1) The AIDS epidemic is a new and important cause of illness and mortality among hemophiliacs, although a very low incidence of AIDS among hemophiliacs prior to 1982 cannot be ruled out. 2) The AIDS cases who attended the surveyed hemophilia treatment centers were distributed throughout the United States and were older than hemophilia treatment center patients without AIDS. AIDS cases also used more lyophilized clotting-factor concentrate, but only a small number of cases were reported with this information. 3) Improved care for hemophilia, including the use of clotting-factor concentrates, dramatically reduced hemophilia mortality rates during the 1970s. 4) In 1982, hemorrhage was the major cause of death among hemophiliacs. Deaths from non-alcoholic liver disease were also increased. AIDS incidence among hemophilia treatment center attendees was stable at 0.6 cases per 1,000 hemophilia treatment center attendees per year during 1982 and 1983 but increased sharply to 5.4 cases per 1,000 during the first quarter of 1984.

Natural-abundance carbon-1 3 nuclear magnetic resonance spectra, with proton noise decoupling, have been obtained for pure meso-and rac-2,4-dichloropentane, pure meso-and rac-2,3-dichlorobutane, and two samples of poly(viny1 chloride) of different stereochemical configuration. The chemical shifts of the chlorinated hydrocarbon models are interpreted in terms of their rotational isomers. The sensitivity of 13C shifts to stereoisomers was found to be an order of magnitude greater than that of proton shifts. Triad sequences were easily distinguished for poly(viny1 chloride), but the diad, tetrad, or pentad structures may be more difficult to extract from

Electron spin resonance (esr) was used to characterize the electronic environment of Cr8+ ions in a series of polycrystalline -chromia-alumina solid solutions. The solid solutions were formed at 1350°and contained from 0.082 to 14.70 wt % Cr2Os. Esr resonances corresponding to electronically isolated Cra+ ions, Cra+ ions which are electronically coupled via weak exchange interactions, and Cr3+ ions which are electronically coupled via strong exchange interactions were found. Isolated Cr8+ ions predominate at low Cr203 concentration. The relative concentration of isolated to coupled Crs+ ions decreases with increasing Cr2Os concentration in a regular manner until all of the Cr3+ ions are strongly coupled. An explanation is proposed for the two resonances from coupled Cr8+ ions which occur at intermediate Cr203 concentrations. The results are compared to the esr studies of supported chromia-alumina catalysts which are reported in the literature.