The Chemical World This Week RESEARCH & TECHNOLOGY
DECEMBER
16,
1963
CONCENTRATES
• A Sadder polymer, synthesis of polyphosphine oxide polymers, and degradation of some condensation polymers were among the highlights of the Battelle Symposium on Thermal Stability of Polymers, in Columbus, Ohio. Polymers of polyvinyl isocyanate or IV-vinyl-1nylon with a 90% ladder structure have been prepared by Dr. C. G. Overberger, Dr. S. Ozaki, and H. Mukamal of the Polytechnic Institute of Brooklyn. Vinyl isocyanate is first polymerized through the vinyl group to produce polyvinyl isocyanate, or through the isocyanate group to produce N-vinyl-1-nylon. The vinyl nylon is reactive and can be readily polymerized to a ladder polymer by heating at 80° C. with azobisisobutyronitrile, or by irradiation with ultraviolet light at room temperature. Gamma irradiation of polyvinyl isocyanate with cobalt-60 also gives a partial ladder polymer. Attempts to make a complete ladder structure result in an insoluble polymer. The partial ladder polymers are slightly soluble in organic solvents with high dielectric constant, although their average molecular weights are low. Thermal properties are not outstanding, with weight loss beginning at about 350° C. Polyphosphine oxide polymers with high aromatic group content and no beta-hydrogen atoms have a 10% weight-loss temperature up to 345° C., says Dr. Erwin Steininger, Battelle-Institut, Frankfurt, West Germany. While studying thermal stability, he and Dr. M. Sander prepared many polymers containing phosphorus linked to carbon. Both the Michaelis-Arbuzov reaction and the addition of phosphines to olefins were used. Diphosphinites and diphosphonites were synthesized as difunctional monomers to obtain two diphosphinites, which permit condensation to polyphosphine oxides containing no beta-hydrogen atoms. This lack, and the high content of aromatic groups, increases thermal stability. The results indicate that purely aromatic phosphine oxides carrying phenyl or methyl radicals as side chains and phenyl groups as bridge members would be the most stable polyphosphine oxides, Dr. Steininger says. But such polymers haven't been made yet. Phenol-, furan-, and urea-based condensation polymers degrade in oxygen or air primarily through activated methylene oxidation, says Dr. Robert T. Conley of Seton Hall University, South Orange, N.J. His studies range from phenol-formaldehyde and bisphenol-modified
phenolics to polybenzyl and polybenzyl ether polymers. In these materials (of interest in thermal protection systems such as ablation), oxidative degradation is studied by solid phase spectrometric examination and by continuous gas chromatographic monitoring of volatile products. Oxygen (or an oxygen source) makes the initial attack at the highly activated methylene linkage common to condensation polymers. High-temperature char formation stems from the initial oxidation products identified by Dr. Conley and coworkers. Data on activated methylene oxidation indicate that phenolics might be useful for oxidative stabilization of vinyl polymers. The data also allow predicting the course of char formation, and show that curing of phenolic resins by vacuum at high temperatures yields new phenolic polymers which resist oxidation. • A one-step synthesis of 2-pyrones and spectral studies of metailoporphyrins were among the topics covered at the ACS Southwest Regional Meeting in Houston, Tex. The one-step method to prepare naphthol[l,2-b]pyran-2-ones was developed by Dr. L. L. Woods of Texas Southern University, Houston. In the synthesis, naphthols are condensed with betaketoesters in the presence of trifluoroacetic acid to give the desired 2-pyrone in 80 to 90% yield. This synthesis of 2-pyrones (of interest because such compounds are pigments in flowers and other natural products, and are specialty chelating agents) is lower in cost than is the conventional Von Pechmann process, because it makes unnecessary a concurrent and competitive sulfonation with concentrated sulfuric acid. Studies of electronic spectra of metailoporphyrins show that there is no simple correlation between the atomic number of groups Ha and l i b (the closed-shell metals) and the interrelation of the yields and lifetimes of phosphorescence and fluorescence, as has been predicted, according to Dr. Ralph S. Becker and Jean B. Allison of the University of Houston. In addition, they find that no transition metal ion porphyrin will fluoresce. Increased spin orbit coupling within the molecular system may cause increased phosphorescence at the expense of fluorescence for some metailoporphyrins, but this is not always complementary (as would be expected). It depends on geometry, ionic size, electronic configuration, electronegativity, and the atomic number of the metal constituent. DEC
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