Solvent effects on radical homo- and copolymerizations of methacryloyl fluroride

The effect of solvent in homo- and copolymerizations of methacryloyl fluoride (MAF) was investigated in various aromatic solvents. In these solvents, there is a significant effect on the rate of polymerization, on the tacticity of the resulting poly(methacryloyl fluoride), and on the copolymerization of MAF with methyl methacrylate (MMA). The equilibrium constants between MAF and aromatic solvents were determined from NMR spectroscopic measurements. These results indicated that the solvent effect on the MAF polymerization stems from changes in reactivity of MAF induced by the strong MAF–solvent interaction as well as stabilization of the MAF radical by solvents. Copolymerization of MAF with both p-methoxystyrene (MSt) and p-nitrostyrene (NSt) was also studied.     

Vibronic state symmetry,selection rule and transition probabilities for a molecular rearrangement process. The butadiene-cyclobutene rearrangement

Permutation-inversion group theory is applied to the classification of vibronic states, selection rules, and transition probabilities for a molecular rearrangement process in which the nuclear configuration of the molecule changes substantially. The advantage of the permutation-inversion group in this respect is that it is independent of any particular nuclear configuration.     

Correlation effects and 1.05 GeV p-He elastic scattering

Elastic proton-helium cross sections and polarizations at 1.05 GeV are calculated in the multiple diffraction approximation with inclusion of intermediate isobar states. Short-range correlation effects are shown to be small compared to intermediate isobar contributions and uncertainties in NN amplitudes.     

Solubility of uranium (IV) oxide in alkaline aqueous solutions to 300°C

The solubility of carefully characterized UO₂ in pOH 1.5 and pOH 2.5 aqueous solutions has been determined from 25°C to 300°C using a flow apparatus. Data were analyzed in terms of the reaction $$UO_2 + 2H_2 O + OH^ - \rightleftharpoons U(OH); log K = - 5.86 + 32/T$$ The extreme sensitivity of both the UO₂ surface and aqueous U(IV) to oxidation is discussed.     

Particle size analysis of polymer latexes by light scattering. V. The significance of an assumed distribution in the analysis of angular scattering data

In the analysis of light scattering data from polymer latex systems or other systems of spherical particles, it is necessary to assume a particle size distribution function. Theoretical angular scattering functions based on the assumed distribution and representing a wide range of size distribution parameters are compared to experimental data in order to obtain a best fit. In previous work, it has been shown that as the polydispersity increases beyond certain limits the uncertainty in the assignment of the size distribution parameters (i.e., the best fit) increases. This report is concerned with the analysis of angular scattering from unimodal systems and simulated cases where theoretical scattering functions for wide, negatively skewed distributions are used as “experimental data,” are analyzed by utilizing four different distribution functions. These functions represent different degrees of skewness and include negatively, positively, and normally skewed distributions. The results from the use of the various distribution functions are discussed with respect to the uncertainly in the assignment of distribution parameters resulting from the loss of structure in the angular scattering pattern due to increased polydispersity. Scattering data from the bimodal distribution are analyzed by assuming a unimodel distribution, and the consequences of this assumption are assessed.     

Carbon-13 NMR studies of naturally occurring maytansinoids

The ¹³C NMR spectra of the antileukemic ansa macrolide maytansine and eight naturally occurring homologues were recorded. Signals were assigned to specific carbon atoms of the ansa macrolide ring and C-3 ester side chain using data from off-resonance decoupling, single frequency decoupling, and 180°–τ–907° double pulse experiments. The assignment of each carbon is discussed for maytansine and tabulated for the other eight maytansinoids.