On the preparation and properties of CuZSM-5 catalysts for NO decomposition

Equilibrium exchange isotherms were determined for the exchange of Cu²⁺ with NaZSM-5 at varying Cu(Ac)₂ concentrations in solutions of constant volume and zeolite weight. At low Cu²⁺ levels the solid scavenged all the copper ions. When copper could be detected in the equilibrated solutions, overexchange was observed. The extent of overexchange was higher at pH 6 than at pH 4. These results were analyzed in relation to catalytic activity.On leave from the Central Institute for Chemistry, Hungarian Academy of Sciences, H1525 Budapest, Hungary.     

New telechelic polymers and sequential copolymers by polyfunctional initiator-transfer agents (inifers)

Summary Novel oxycarbonyl isocyanate telechelic polyisobutylenes have been prepared by conversion of hydroxylterminated polyisobutylenes with N-chlorocarbonyl isocyanate. This reaction is free from side-reactions and provides highly reactive isocyanate-terminated polyisobutylene prepolymers. Conversion of these prepolymers with glycol, urea, pentaerythritol, and polyethylene glycol led to linear chain extension, crosslinking, and multiblock copolymer formation, respectively.     

Living carbocationic polymerization

Summary The living synthesis of ,-di-tert.-chloropolyisobutylene ( ^t -Cl-telechelic PIB) has been accomplished by the use of the sterically hindered bifunctional initiator 1,3-di-(2-methoxy-2-propyl)-5-tert.-butylbenzene (tBu-m-DiCuOMe) in conjunction with BC1₃ coinitiator in CH₃Cl or CH₂Cl₂ diluents at –30°C and –10°C. The living nature of the polymerizations was demonstrated by linear ¯M_n versus W_PIB (g of PIB formed) plots starting at the origin and horizontal N (number of PIB moles) versus W_PIB plots. The molecular weight distributions are narrow (¯M_W/¯M_n < 2.0) and tend to decrease with increasing molecular weights. Number average end functionalities have been quantitated and found to be ¯F_n = 2.0±0.1.     

The influence of resin characteristics on the high speed melt spinning of isotactic polypropylene. II. On-line studies of diameter,birefringence, and temperature profiles

An investigation was carried out of the high speed melt spinning of three polypropylene resins with melt flow indices of 12, 35, and 300. On-line measurements were made of diameter, birefringence, and temperature as a function of distance from the spinneret for a range of spinning conditions for each polymer. A plateau (decrease of cooling rate) in the temperature profile was associated with the occurrence of crystallization in the spinline. The position of this plateau correlated with a rapid rise in the birefringence profile and a rapid decrease in the rate of drawdown in the diameter profile. The temperature and birefringence profiles were used to determine the temperature and position on the spinline at which the onset of crystallization occurred. It was found that the position and temperature of crystallization onset varied considerably with changes in take-up velocity, extrusion temperature, and resin melt index (weight average molecular weight). The crystallization onset occurred nearer the spinneret and at higher temperatures with (1) an increase of take-up velocity, (2) a decrease of extrusion temperature, or (3) a decrease of resin melt flow index. An analysis was carried out to estimate the rate of stress development with distance along the spinline; the results were also used to estimate the stress at the onset of crystallization for each spinning condition. It was concluded that the observed behavior could be attributed to the role of spinline stress in producing molecular orientation and consequent increase of crystallization rate.     

Reaction of pyritic sulphur in coal with lime and calcined dolomite during the coking process

Various reactions occur between pyrite (FeS₂) in coal and CaO to form CaS when a finely pulverized intimate mixture of coal and CaO is coked at 900 °C in an inert atmosphere. The effectiveness of lime and calcined dolomite (CaO.MgO) in promoting this reaction has been evaluated; calcined dolomite is somewhat more effective than lime over coal/ oxide weight ratios from 2.8 to 14. The degree of conversion of pyrite to calcium sulphide at a coal/calcined dolomite weight ratio of 7 has been determined as a function of time at 900 °C; coking time in excess of 2.5 h does not have a significant effect. It has been shown that the total sulphur lost on coking coal/lime mixtures decreases and the percentage of FeS, originating from the dissociation of pyrite, converted to CaS increases as the amount of lime added increases. But although the total sulphur content of coke produced in the presence of CaO is then higher than when the coal is coked without lime, the pyritic sulphur has been converted to CaS which is more amenable to chemical conversion to H₂S. A method is outlined for determining CaS in the coked mixture in the presence of FeS.     

Scandinavian Thins on Top of Cake: New and Improved Algorithms for Stacking and Packing

We show how to compute the smallest rectangle that can enclose any polygon, from a given set of polygons, in nearly linear time; we also present a PTAS for the problem, as well as a linear-time algorithm for the case when the polygons are rectangles themselves. We prove that finding a smallest convex polygon that encloses any of the given polygons is NP-hard, and give a PTAS for minimizing the perimeter of the convex enclosure. We also give efficient algorithms to find the smallest rectangle simultaneously enclosing a given pair of convex polygons.     

Hydrogels based on graft copolymers of collagen synthesis

Graft copolymerization of 2-hydroxyethyl methacrylate in combination with hydrophobic monomers onto soluble collagen was employed in the synthesis of hydrogels. The hydrogels were formed by simultaneous graft copolymerization and crosslinking. In order to study the effect of various crosslinking agents on the water retention character of the hydrogels, three different crosslinking agents, namely, N,N′-methylene bis acrylamide, 1,4-butanediol dimethacrylate, and hexamethylene urethanediacrylate were used. Hexamethylene urethanediacrylate crosslinked systems require a minimum amount of crosslinking agent to attain maximum water content in comparison to the other systems.     

Axial pressure profiles in non-newtonian flow: Part I: Theoretical and experimental considerations

The flow behavior of polymeric fluids in tubes can be determined from measurements of the radial stress profile in the flow direction. This subject, the focus of our research, will be examined in Part II of this communication. Part I describes a research designed to test the accuracy of stress measurement with pressure transducers in a variety of recess mount geometries. No mount geometry errors were detected for the fluids used in this work over a shear rate range of 1 to 2000 sec^?1. Part I also contains a survey of the literature and theoretical considerations pertinent to the entire work.