The influence of the catalytic system and synthesis conditions on the reactor powder morphology and the molecular packing in the nascent UHMWPE is studied with the help of various electron microscopic methods. The potentiality of different morphologies for producing strong consolidated material by sintering at temperature lower than the melting temperature is considered. It is shown that the small catalytic particles of colloidal sizes (reactor powders of M-series) produce homogeneous broccoli type morphology consisting of small nodules with the sizes less than 0.2-0.5 mu m, which in turn, comprise crystalline domains and disordered regions. Comparison analysis of transmission electron microscopic data with the DSC and NMR results enabled to conclude that the disordered regions are predominantly comprised of tie molecules with low degree of coiling, taut tie molecules, and a number of tight folds. This type of morphology best fits for compaction and sintering. Reactor powder morphology arising upon synthesis lab-scale and commercial UHMWPE on supported catalysts is not so homogeneous, and consists of miscellaneous morphological units, such as spirals, flakes, secondary fibrils, interconnecting the subparticles, large and small lamellae in depending of the catalyst system. The density of disordered regions in these reactor powders is less than that in the particles of M-series. The tensile strength of the samples obtained by sintering of the M-powders is higher than the strength of the other ones by a factor 2.5, which makes them good precursors for orientation drawing. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 866-875, 2010