Polyurethane Ionomers,a New Class of Block Polymers

Linear polyurethanes containing ionic centers at wide intervals are heteropolymers having a pronounced segment structure, i.e. ionomers. As a result of interactions between chains (Coulomb forces and hydrogen bonds), their properties are similar to those of crosslinked elastomers. They are strongly associated both in organic and in aqueous solutions. Polyurethane ionomers in polar organic solvents spontaneously form stable aqueous dispersions on addition of water, with the ionomer as the disperse phase. The particle size can be varied between 20 nm and 1 mm.     

Admissible and minimax multiparameter estimation in exponential families

Consider p independent distributions each belonging to the one parameter exponential family with distribution functions absolutely continuous with respect to Lebesgue measure. For estimating the natural parameter vector with p ≥ p₀ (p₀ is typically 2 or 3), a general class of estimators dominating the minimum variance unbiased estimator (MVUE) or an estimator which is a known constant multiple of the MVUE is produced under different weighted squared error losses. Included as special cases are some results of Hudson [13] and Berger [5]. Also, for a subfamily of the general exponential family, a class of estimators dominating the MVUE of the mean vector or an estimator which is a known constant multiple of the MVUE is produced. The major tool is to obtain a general solution to a basic differential inequality.     

Structure characterization and possible biogenesis of three new families of nortriterpenoids: schisanartane, schiartane, and 18-norschiartane

Four new, highly oxygenated nortriterpenoids with unique schisanartane skeletons, micrandilactones D-G (1-4), have been isolated from the leaves and stems of Schisandra micrantha, and their structures have been elucidated on the basis of extensive spectral studies. The postulated biogenetic sequences of sixteen highly oxygenated nortriterpenoids and bisnortriterpenoids with new skeletons from three Schisandra species are discussed and have been compared from a chemotaxonomic standpoint.