SYNOPSISNascent high-molecular-weight (UHMW ) polyethylene ( PE ) samples of different origins show a rather high crystallinity of about 70-75% and contain both a major portion of orthorhombic extended chain crystallites and a minor portion of triclinic crystallites. The triclinic content is greater the higher the molecular weight of the sample and the higher the activity of the used catalyser. A melting/recooling treatment results in a reduction of crystallinity by about 15-25% and disappearance of the triclinic phase. Further, an irreversible conversion of nascent orthorhombic extended chain crystallites to orthorhombic folded chain crystallites of increased lateral dimensions and crystalline perfections takes place during the melting/recooling treatment. The results are compared to those obtained for lower-molecular-weight PE samples and for high-strength/modulus PE fibers of different origins.

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Zur Ethen-Loslichkeit in den fur die Suspensionspolymensation relevanten Losungsmitteln in entsprechenden Temperatur-und Druckbereichen existieren in der Literatur relativ wenige z.T. widerspruchliche Angaben. Im Rahmen dieser Arbeit wurde die Ethen-Loslichkeit in n-Pentan, n-Hexan, n-Heptan, n-Octan und einer technischen Hexan-Fraktion im Temperaturbereich von 20 bis 85°C bei Drucken von 0,l bis 1,0MPa untersucht und diskutiert. ExperimentellesFur die Geschwindigkeit der physikalischen Absorption eines Gases in eine Fliissigkeit konstanten Volumens und ohne chemische Reaktion gilt nach [l. 21'):Unter den Voraussetzungen, daB sich das Gleichgewicht in der Phasengrenze augenblicklich einstellt und daR die Konzentration c* in derselben mit der konstanten Konzentration im Innern der Gasphase im Gleichgewicht steht, ergibt sich nach Integration von G1. (1)

Polymerization of ethylene was carried out in a batch process under pressure with an optimized high-yield Ti/Mg-catalyst. It was shown through gas chromatography analysis as well as by educt/product mass balances that no side-reactions take place, and therefore, the monomer is quantitatively converted to polyethylene. It is demonstrated that influences of diffusion are excluded under the described experimental conditions. The dependence of the overall polymerization rate on time shows that the rate at constant pressure is constant from the beginning over a certain period of time. The rate of polymerization under isobaric as well as isochoric conditions was determined to be first order with respect to monomer concentration and catalyst concentration. The overall activation energy obtained for this catalytic system was determined to be 32 kJ . mol-'.