Functional polymers

Summary Polymeric antioxidants prepared from 2,6-di-tertiary-butyl-4-vinyl (4-lsopropenyl)phenol and butadiene or isoprene, and their hydrogenated products (6-8 mol % of phenolic AO in the polymer) were tested by oxygen uptake studies for their effectiveness as antioxidants for polyolefins and polydienes. The polymeric antioxidants seem to be slightly less effective in short-term protection against oxidation at 150° C as compared to low molecular weight antioxidants, but more effective in long-term protection of the polymer samples at a level of 0.1 weight percent.Part 43: P. Grosso, O. Vogl: J. Macromol. Sci. Chem., in pressNow Chemical Company, Midland, MI 48674, USATo whom all correspondence should be addressed: Herman F. Mark Professor of Polymer Science, Polytechnic Institute of New York, Brooklyn, NY 11201, USA     

The Swedish approach to research and development in fire protection

Current Research Activities

The Swedish approach to research and development in fire protection     

Throughput of a satellite channel communication

Summary The throughput of a satellite channel communication is depending upon the link protocol. It is well known that the classical HDLC protocol is inadequate when applied to satellite links instead of short terrestrial links. Several modifications have been proposed to overcome this problem. The present paper gives an analysis and evaluation of a new class of protocols called Virtual Subchannel schemes which splits the satellite link into several components; these subchannels are assigned for transmission in cyclic order and are controlled independently of each other by the classical HDLC procedure.     

Finite canonical rewriting systems for congruences generated by concurrency relations

WhenC is a concurrency relation on alphabet , then ^*/= _C is a free partially commutative monoid. Here we show that it is decidable in polynomial time whether or not there exists a finite canonical rewriting systemR on such that the congruences _R ^* generated byR and = _C induced byC coincide. Further, in case such a systemR exists, one such system can be determined in polynomial time.     

Development and characterization of a biocompatible OH-modified copolymer based on polyurethane

Different polyurethanes were synthesized by varying the diol as well as the diisocyanate components and chain extenders. Polyurethanes with OH-groups were obtained by photo- and thermoinitiation of the radical polymerization of hydroxy alkyl acrylates in the presence of the polyurethanes. The polymers were evaluated with respect to their biocompatibility by measuring the cell spreading, the rates of DNA- and protein synthesis and the swelling behaviour. The differences in the surfaces and the bulks between the selected basic polyurethane and the functionalized modification were determined and characterized by XPS, FTIR-ATR and ¹³C-FT-NMR-spectroscopy. The mechanical data of Tecoflex EG 60D® and Pellethane 2363–80AE® were compared with the data of the synthesized polyurethanes.     

Chemisorption of alkenes on copper-exchanged ZSM-5 zeolite

On Cu-ZSM-5 zeolite at room temperature, propane is physisorbed, while propene shows characteristics of chemisorption. The chemisorption mode has certain advantages for the catalytic control of automotive emissions. Alkane and alkene adsorption equilibria and kinetics are compared on Cu-ZSM-5 and on ZSM-5 free of alumina. The results are discussed in terms of the Langmuir adsorption isotherm.     

The influence of sulfur dioxide on propane oxidation activity over supported platinum and palladium

Earlier studies have shown that sulfur dioxide and metal-support interaction can strongly influence propane oxidation over platinum. In particular, oxidation activity is enhanced when platinum is supported on sulfated -alumina or zirconia compared to -alumina. Therefore, it is of interest to compare the performance of palladium under the same experimental conditions. Four model catalysts were examined: Pt/-alumina, Pt/zirconia, Pd/-alumina and Pd/zirconia. The metal loading was kept at or below 0.05 wt% to emphasize changes in activity attributable to metal-support interaction. Reaction rates were measured with and without sulfur dioxide. Surface sulfation was analyzed by measuring acid strength and evaluating spectra obtained by Fourier-transform infrared spectroscopy. In contrast to platinum, sulfation does not promote propane oxidation on Pd/-alumina, and Pd/zirconia is less active than Pd/-alumina.     

In situ ellipsometric study of a palladium catalyst during the oxidation of methane

Ellipsometry is used to follow the growth of a PdO layer on the surface of a thick Pd-film catalyst during methane oxidation at 500°C. The oxide layer that develops under rich conditions (excess CH₄) is quite porous and roughens with time. Little CO is formed during this period, but the CO₂ formation rate increases until spontaneous oscillations develop, which correlate with changes in the ellipsometric data. These changes indicate that the porous oxide rapidly converts to a metal-rich state, which has decreased catalytic activity, and then slowly reoxidizes.     

Catalytic steam gasification of graphite: Effects of calcium,strontium, and barium with and without sulfur

Alkaline earths strongly catalyze steam gasification of graphite. The catalytic effect increases in the order Ca < Sr < Ba. Reaction rates of graphite impregnated with 0.3 at.% Ba are 500 times larger than those of pure graphite. Catalysis is due to the participation of additional reaction sites, not to a lowering of the true activation energy. It follows from kinetic data, electron microscopic observations, and theoretical considerations that the efficiency of the catalysts is closely related to their ability to coat a carbon surface and to continue contact with carbon atoms emerging from the bulk. In the presence of sulfur, severe, but not complete, catalyst deactivation occurs. This poisoning is to a large degree reversible.