DETERMINATION OF PLATEAU MODULI AND ENTANGLEMENT MOLECULAR-WEIGHTS OFISOTACTIC, SYNDIOTACTIC, AND ATACTIC POLYPROPYLENES SYNTHESIZED WITH METALLOCENE CATALYSTS

Metallocene catalysis was employed to prepare model polypropylenes (PP ) with very high molecular weights and narrow molecular weight distrib utions (MWDs) of M-w/M-n approximate to 2, typical for ''single site'' metallocene catalysts. The viscoelastic properties of PP melts were i nvestigated by means of oscillatory rheometry. Arrhenius and WLF equat ions were applied to model the influence of temperature on PP theology . With very high molecular weight polypropylene samples it became poss ible to determine the onset of the plateau zone, reflecting the rubber -like properties of PP. For the first time plateau moduli G(N) degrees S and entanglement molecular weights M(e)s were determined and found to be depend upon stereoregularity. The entanglement molecular weights were found to be 6900 g/mol for isotactic PP, 7050 g/mol for atactic PP, and 2170 g/mol for syndiotactic PP. This influence of stereoregula rity was attributed to the different conformations of syndiotactic PP with respect to isotactic and atactic PP in PP melts.