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SynopsisSamples of industrial high-density polyethylenes (Liten Macro, Liten FB 29, and Hostalen GM 9255 F) were divided into fractions by precipitation fractionation. The original samples and their fractions were characterized by light scattering, GPC, and viscometry. For all samples the molecular weight distribution is of logarithmic-normal type. High-density polyethylenes under investigation contain also high-molecular-weight fractions of pronouncedly branched structure, the content of branched molecules being, of course, considerably smaller than that in low-density polyethylenes.

A simple and universal relation between the mutual change of weight and number average molecular weight at random degradation of polymers has been derived. A good agreement has been found between this relation and the experimental results obtained at peroxide initiated degradation of polypropylene. ZUSAMMENFASSUNG:Eine einfache und allgemeine Beziehung zwischen der gegenseitigen h d e r u n g des Gewichts-und Zahlenmittels des Molekulargewichts bei statistischem Abbau von Polymeren wurde abgeleitet. Es wurde eine gute Ubereinstimmung zwischen dieser Beziehung und den experimentellen Ergebnissen beim peroxidisch initiierten Polypropylenabbau gefunden.

Lower Badenian sediments were studied on the locality Hvozdíkova at the Diviš district, Brno. There were interpreted 4 lithofacies of Neogene (Lower Badenian) sediments (lithofacies M1, M2, Sl, and SGl). Occurrence of basal Lower Badenian clastics is connected with existence of coarse-grained delta (foreset). Overlying pelites document pelagic sedimentation of open sea. Garnet dominates in assemblage of heavy translucent minerals.Rich assemblages of foraminifers, molluscs, spines of echinoids, ostracods and shark fauna were discovered in sediments. Diversified assemblages are dominated by plankton specimens. Species Orbulina suturalis Brön., Praeorbulina glomerosa circularis (Blow) and Globigerinoides bisphericus Todd. indicate the Lower Badenian age.From the point of view of the shark fauna diversity the locality Hvozdíkova is unique; shark fauna is very rare in Lower Badenian clays, and the genera of Squaliolus and Paraetmopterus are identified for the first time. Oysters – especially species Neopycnodonte navicularis (Brocchi) – dominate in Lower Badenian sediments. Small gastropods (for example Cancellaria sp., ?Tornus sp., Rissoa sp., Alvania sp.) probably represent fossils reworked from shallow littoral area.

The relation between composition of the one‐phase titanium‐based silica supported catalysts for gas‐phase ethylene polymerization, and the ability of these catalysts to control the molecular weight of polymer using hydrogen has been studied. Halogen containing alkylaluminium compounds and alkoxy groups on titanium promote the chain transfer process. A significant polymerization rate lowering effect is caused by hydrogen. However, catalyst activity fully revives after hydrogen removal from the polymerization system. The proportion of active titanium was found to be 18±4% in the presence of hydrogen, and the value of propagation rate constant (kp) was calculated to be 190±45 L/mol.s. © 1993 John Wiley & Sons, Inc.