Macromolecular Engineering via Carbocationic Polymerization: Branched Structures,Block Copolymers and Nanostructures

This article features macromolecular engineering via carbocationic polymerization, the focus of research of the recently established Macromolecular Engineering Research Centre (MERC) at the University of Western Ontario. The fundamental philosophy of MERC is interdisciplinary research with a strong industrial orientation, while emphasizing the quest for fundamental understanding of polymerization processes and polymer structure‐property relationships. First, a brief overview of living polymerizations in general, and living carbocationic polymerizations in particular will be given. This latter technique is of interest because some monomers (e. g., isobutylene) can be polymerized by cationic techniques only, to yield polymers with unique properties (e. g., polyisobutylene with superior chemical and oxidative stability, low permeability and high damping). This will be followed by an overview of our research strategy and a summary of our latest results. These include the development of a fiber‐optic mid‐FTIR method for the real‐time monitoring of low temperature polymerization processes, the discovery that selected epoxides initiate effectively the living carbocationic polymerization of isobutylene, fundamental studies into the mechanism and kinetics of living carbocationic polymerization, and the design and synthesis of various polymer architectures (e. g., branched homo‐ and block copolymers) with improved properties and nanostructured phase morphologies.     

Das Scaling‐Down‐Problem bei der Zweistoff‐Gaszerstäubung von Metallschmelzen

The production capacities of plants for metal pulverisation are frequently rated according to the minimum throughput of melt flowing from the distributor crucible to pulverisation. Especially in the case of high‐melting point metals and their alloys deficiencies occur in the thermal balance of the crucible in the exit section as a result of gas expansion at the pulverisation gas jets, which act as heat sinks. Minimum throughputs and associated limiting values of the convective heat transfer of the melt are stipulated in order to prevent "freezing" (solidification of the melt) in the crucible. The pertinent situation is illustrated for copper and steel melts and technical possibilities for compensating for heat deficiencies by inductive heating of the distributor exit are presented. In addition, the demand for minimum throughputs can be abandoned, and there result possibilities of scaling‐down and energy conservation as well as improvement of powder discharge.     

Influence of the Metal Particle Size on the Ignition of Energetic Materials

A theoretical study of multi‐particle ignition uses a hot spot model which calculates the temperature evolution of individual hot spots in an energetic material. It indicated that ultra‐fine hot particles would be very effective in igniting energetic materials if impinging and penetrating the solid propellant. Igniting mixtures were prepared containing ultra‐fine Ti particles which react fastest compared with coarse particle mixtures, standard B/KNO₃ and black powder. The ultra‐fine particles, however, are obviously oxidized or gasified too fast as to reach the energetic material to be initiated and longer ignition delays are found mainly compared with coarse particle mixtures. An optimized mixture of coarse and ultra‐fine particles would give an improvement of ignition delay times.     

Preparation of Cyclobutyl Group Carrying Cyclobutanones and Related Synthetic Building Blocks

Compounds 3, 4, 10, 12, 16, 17, and 19 have been prepared as possible starting materials for liquid crystals containing two cyclobutyl moieties combined in a 1,3‐fashion. Further typical conversions of these have been tested giving 5, 7, and 14 for example. Useful intermediates 16 and 17 were also made.     

Heat shock transiently enhances the synthesis rate of Sis1p,a ribosome-associated DnaJ protein in the oleagenous yeast Apiotrichum curvatum

DnaJ proteins have been localized in different intracellular compartments of eukaryotes. In Apiotrichum curvatum, a fat-storing yeast, we found a DnaJ homolog associated with ribosomes and large cytosolic complexes as well. Using a plant DnaJ probe and a cDNA library constructed from poly(A)⁺ -RNA of A. curvatum grown on oleate we isolated a SIS1 cDNA coding for a 39·5 kDa protein. The putative protein contains neither a zinc finger motif nor a CAAX motif but is characterized by a J-domain at the N-terminal region and a large G-rich region in the middle part of the molecule. Heat shock applied for 1 h resulted in a pronounced but transient increase of the SIS1 mRNA. An antiserum was raised against the bacterially expressed protein. Cell fractions from A. curvatum were further separated by sedimentation centrifugation on sucrose gradients. Analysing the sub-fractions, we detected Sis1p mainly associated with ribosomes, and with particles sedimenting at approximately 200S. Hsp70 was found to be associated with the 200S fraction. The respective cytosolic A. curvatum Hsp70 cDNA was cloned and sequenced. High salt conditions caused the removal of Hsp70 and Sis1p from the 200S complexes. Mild RNase treatment of the 200S fraction afforded monosomes and 200S complexes unaffected by RNase. Heat shock led to a pronounced increase in the rate of de novo synthesis. However, due to the large pools of Sis1p on ribosomes and large cytosolic complexes, the increase in gene activation did not lead to a significant change of the total amount of Sis1p. Accession numbers are: Y12079 for ACHSP70 and Y12080 for ACSIS1. © 1998 John Wiley & Sons, Ltd.     

Kinetic Investigations on the Hydrogenation of 3-Ketosucrose

Sucrose can be converted to allosucrose by a sequence of a biotechnical oxidation and a hydrogenation. The second step was found to be highly stereoselective with high yield and without any side products. The kinetics of the hydrogenation was examined with respect to the influence of the starting materials and the catalyst. A quantitative correlation for the influence of the concentrations is given. Furthermore, the influence of mass transfer processes was considered. Under unfavorable conditions gas liquid mass transfer can be rate-limiting.