Structure investigations by P.A.C.

The perturbed angular correlation /P.A.C./ technique is employed to investigate the structures of barium ferrite and barium hexaferrite using radioactive¹³³Ba /10.7 Y/ as a probe. The quadrupole interaction frequencies /W_Q'S/ are found to be 9.68 and 12.02 Mrad sec^–1 for barium ferrite and barium hexaferrite, respectively, showing a drift from usual cubic structure.     

Properties of PVC. I. Properties of PVC films prepared by casting and by precipitation

This investigation compares the properties of PVC films prepared both by casting from tetrahydrofuran solution and from samples obtained by precipitation with properties of samples from the original PVC. The differences in properties are explained on the basis of solvent residues remaining in the samples even after tempering at higher temperatures and after extremely long times of drying. Attention was given to the difficulties caused by this fact, namely, in observing the influence of molecular weight and of distribution of molecular weights of fractions on PVC properties. Reasons were given for the retention of the tetrahydrofuran by PVC.     

Characterization of proteins by mass spectrometry. Invited lecture.

Plasma desorption and fast atom bombardment mass spectrometry have in the last decade demonstrated the potential of mass spectrometry for protein studies. The recently developed matrix-assisted laser desorption and electrospray mass spectrometry have expanded the analytical potential of mass spectrometry to cover nearly all proteins. The type of information obtained with the four methods is described and their performances are compared. The potential of combining mass spectrometric relative molecular mass information on proteins with the information contained in protein sequence databases is outlined and some typical fields of application of mass spectrometry in protein chemistry are described. The need for the full integration of mass spectrometry in the protein laboratory is discussed.     

Inhibition of acrylic acid polymerization by phenothiazine and p-methoxyphenol. II. Catalytic inhibition by phenothiazine

Inhibition of acrylic acid by p-methoxyphenol fits a conventional stoichiometric mechanism but phenothiazine inhibits acrylic acid via a completely different, catalytic cycle which does not depend on the presence of oxygen. We propose that this mechanism may involve a pair of single electron transfer reactions between free radicals, phenothiazine N-radicalcation, and phenothiazine itself, the latter being cyclically regenerated. Arrhenius equations were derived for the rates of disappearance of inhibitor and oxygen in acrylic acid stabilized with phenothiazine and with p-methoxyphenol and also with phenothiazine in the absence of oxygen. The practical implication of high oxygen to p-methoxyphenol consumption ratios is quite important: if commercial acrylic acid (usually stabilized with p-methoxyphenol) is inadvertently heated during storage, the limiting substance determining the onset of polymerization will be the dissolved oxygen and not p-methoxyphenol unless oxygen (air) is being supplied to and dissolved in the liquid at a rate sufficient to overcome the rate of its consumption.     

Vinyl Polymerization Initiated by Peroxydiphosphate. IV. Polymerization of Acrylonitrile Initiated by Peroxydiphosphate-Thioacetamide Redox System

Abstract

The kinetics of the aqueous polymerization of acrylonitrile initiated by the peroxydiphosphate-thioacetamide redox system was investigated at 35, 40, and 50°C. The rates of polymerization were measured at different concentrations of oxidant, activator, and monomer. Peroxydiphosphate alone did not initiate polymerization under deaerated and undeaerated conditions. Addition of certain water-miscible organic solvents and neutral salts depress the rate and conversion. On the basis of experimental observations of the dependence of the rate of polymerization on various variables, a suitable kinetic scheme has been proposed.     

Polymerization photoinitiated by carbonyl compounds. XI. Styrene polymerization photoinitiated by cyclododecanones

To establish their potential as source of biradicals to initiate free-radical polymerization, 2-methyl- and 2,2,12-trimethylcyclododecanones were photolyzed in the presence of styrene. The initiation efficiency of both ketones is low—0.03. The molecular weight of the obtained polymer is ca. 25% higher than that obtained employing photoinitiators that produce monoradicals. This difference is explained in terms of a mixed polymerization mechanism comprising mono- and biradicals. © 1996 John Wiley & Sons, Inc.     

Comment on "Dynamic wetting by liquids of different viscosity," by T.D. Blake and Y.D. Shikhmurzaev

We comment on a recent theory of dynamic wetting that is based directly upon a model for interface formation, introduced by Shikhmurzaev. We argue that the treatment of surface tension and its relaxation, inherent in the original model, is physically flawed.