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Morphology and molecular structure of three nascent ultra high molecular weight polyethylene (UHMWPE) powders synthesized on unsupported and supported Ziegler-Natta heterogeneous catalysts were studied with the help of electron microscopy and infrared (IR) spectroscopy. A synthesis was carried out in a slurry process in n-heptane at a temperature of about 70°C, which resulted in production of UHMWPE of one and the same molecular weight, approaching 10 6 g/mol. The morphology of the nascent particles dramatically differed, however, which is evidence of the important role of the catalytic system used. Nascent particles synthesized on unsupported TiCl 4 catalyst with EtAl as the cocatalyst had a globular structure, while those synthesized on supported TiCl 4 /Al 2 O 3 ؒSiO 2 and TiCl 3 ؒ0.3 AlCl 3 /MgCl 2 Ziegler-Natta catalysts with the same cocatalyst demonstrated fibrillar (cobweb) and spiral (wormlike) structures, respectively. As revealed by IR spectroscopy, there was a significant difference in the nature of the crystalline regions formed during the synthesis/crystallization process; in the amount of short trans sequences not included in crystallites (taut tie molecules); in the content of irregular conformers of various types, including typical point de-*Dedicated to Prof. Francisco J. Baltá Calleja on the occasion of his 65th 814 IVAN'KOVA ET AL.fects 2G1 kinks; and so on. The melt-crystallized films produced from the investigated reactor powders were markedly distinguished by their drawability and by the existence and the amount of different molecular conformations despite a sufficiently high recrystallization temperature and prolonged preheating. The difference in molecular structure of the drawn films was retained in a whole range of draw ratios. It is concluded that there is a well-pronounced "memory effect" and the morphology of the original nascent particles depending on the catalyst/synthesis conditions clearly play a role in the properties of the end product.

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