Fractionation of partly hydrolyzed polyvinyl acetate

Vinyl acetate–vinyl alcohol copolymers were fractionated in order to obtain their degree of hydrolysis distributions. In the method employed for fractionation, the differences in molecular weight of copolymer did not affect the fractional separation. Degree of hydrolysis distributions was found to be broad, with a pronounced maximum at a low degree of hydrolysis. Viscosity measurements were performed both for the precipitated fractions and unfractionated polymer. The Huggins constant was found to increase with a decrease in the degree of hydrolysis of polyvinyl acetate. These results were interpreted in terms of a polymer molecular association. From values of Huggins constants, comparative information about copolymer “blockiness” is also established.     

THEORETICAL ANALYSIS OF THE PHOTOPHYSICAL PROPERTIES OF ε-ADENINE AND THE RNAphe Y-BASE

Abstract— …An analysis of the photophysical and theoretical properties of e-adenine and the RNA Y-base shows that these materials have a closer conceptual relationship to the indolizines than the purines.     

ESR and chemical study of p-polyphenylene formed by using an AlCl3–CuCl2 catalyst

The free radicals in p-polyphenylene and the formation of free radicals in this polymer upon pyrolysis in vacuum have been studied by means of electron spin resonance. For an unpyrolyzed series of polymer samples, a linear relationship was observed between free radical concentration and increasing carbon content. The free radicals observed in the unpyrolyzed samples did not react with NO. When samples of polyphenylene were pyrolyzed, additional free radicals were produced which did react with NO. The growth of free radical concentration upon pyrolysis was observed to be closely related to the production of volatile products from the polymer. In the temperature range 250–600°C, HCl was the principal volatile species produced. Two mechanisms were involved in HCl production: a process with an activation energy of 7.1 kcal/mole which led to the production of stable free radicals; and a process involving 75 kcal/mole which was unconnected with the production of free radicals. From 600 to 700°C, H₂ was the principal volatile degradation product. The rate at which H₂ was evolved showed a second-order dependence on phenyl units bearing two or three substituents; this process had an activation energy of 79 kcal/mole. Electron spin resonance spectra indicated that this process led to the production of free radicals, and infrared spectra showed that a highly crosslinked product resulted.     

Magnetoresistivity of bismuth films in magnetic fields to 19 Tesla

The longitudinal and transverse magnetoresistance to fields of 19 Tesla and 4.2 K has been measured for bismuth films ranging in thickness from 0.01 to 2 m. We have observed a pronounced maximum in the longitudinal magnetoresistance which is thickness dependent. We compare these results with classical size effect theories for the longitudinal magnetoresistance in terms of magnetic-field-dependent electron scattering at grain and film boundaries. Measurements of the longitudinal magnetoresistance to 38 Tesla show a quenching of the classical size effect in the high field limit. This result strongly supports our analysis.Work supported by NSF grant #DMR 8113456Supported by the National Science Foundation     

Patterns of the Formation of Antimicrobial Micro/Nanocomposites during the Oxidation of Bimetallic Al/Zn Nanoparticles

Russian Journal of Physical Chemistry A - Porous composites of different phase composition are synthesized via oxidation in a water–ethanol mixture of bimetallic Al/Zn nanoparticles obtained...     

Reversible M−M Bonding by Alkaline Earth Metals (Mg,Ca, Sr,Ba) in Graphite Intercalation Compounds

The alkaline earth metals (M=Mg, Ca, Sr, and Ba) exhibit a +2 oxidation state in nearly all known stable compounds, but M^I dimeric complexes with M−M bonding, [M₂(en)₂]²⁺, (en=ethylenediamine) of all these metals can be stabilized within the galleries of donor-type graphite intercalation compounds (GICs). These metals can also form GICs with more conventional metal (II) ion complexes, [M(en)₂]²⁺. Here, the facile interconversion between dimeric-M^I and monomeric-M^II intercalates upon the addition/removal of en are reported. Thermogravimetry, powder X-ray diffraction, and pair distribution function analysis of total scattering data support the presence of either [M₂(en)₂]²⁺ or [M(en)₂]²⁺ guests. This phase conversion requires coupling graphene and metal redox centers, with associated reversible M−M bond formation within graphene galleries. This chemistry allows the facile isolation of unusual oxidation states, reveals M⁰→M²⁺ reaction pathways, and present new opportunities in the design of hybrid conversion/intercalation materials for applications such as charge storage.