Recent advances in olefin polymerization

Abstract

Various metallocenes were tested for syndiotactic polymerization of propylene. Reduction in the amount of costly methylalumoxane (MAO) or replacement with the other components was accomplished. Small modifications in the metallocene ligands brought about remarkable differences in the resulting catalysts concerning their storage stability, H2 response as well as stereo‐specificity. Syndiotactic polypropylene (SPP) in the melt state behaves very differently compared to isotactic polypropylene (IPP). The notion that these polymers have different distributions of molecular entanglements are pursued, and verified for the first time. Excellent dispersibility of other olefin polymers in SPP matrix contributed to improve the usefulness of SPP.

Stereoregular Polymers

“…Ewen first reported syndiospecific propylene polymerization by C s -symmetric zirconocene catalyst (7) (41). Ph 2 C-bridged zirconocene (8) affords polypropylene with a slightly increased syndioselectivity (42,43), whereas those with ethylene or silylene bridges result in decreased syndioselectivity (44)(45)(46). The complexes with bulky substituents on the fluorenyl group such as 9 and 10 afford highly syndiotactic polypropylene with rrrr > 0.9 (43,47).…”

“…Ph 2 C-bridged zirconocene (8) affords polypropylene with a slightly increased syndioselectivity (42,43), whereas those with ethylene or silylene bridges result in decreased syndioselectivity (44)(45)(46). The complexes with bulky substituents on the fluorenyl group such as 9 and 10 afford highly syndiotactic polypropylene with rrrr > 0.9 (43,47). C s -symmetric zirconocenes with doubly-silylene bridges (11,12) are also effective for syndiospecific polymerization of propylene (48)(49)(50)(51).…”

Molecular weight dependence and stereoselective chain cleavage during the early stages of the isotactic polypropylene pyrolysis

“…The 1 H NMR spectra were previously recorded in the same spectrometer, at the same temperature, in order to accurately assess the relative content of chemical groups generated during the pyrolysis. This way, any transformation due to long residence times at high temperature in the 13 C NMR analysis is thus prevented.…”

“…molecular weight, tacticity and anomalous groups produced during the pyrolysis process, was analyzed by means of 13 C and 1 H NMR spectroscopy. In the former case, the spectra were obtained from 1,1,2,2-tetrachloroethane-d2 (10 wt%) in a Bruker Avance III HD (125 MHz) at 100ºC, using the solvent signal at 74.00 ppm as an internal reference.…”

“…The weight average molecular mass of both virgin PP films, as well as those ones of samples pyrolysed up to 330 ºC and 350 ºC, for HPP and LPP respectively, were estimated by means of the intrinsic viscosity in tetralin stabilized with Irganox 1010 (1 g/L), at 135 ºC, by using the relationship [] = 1.66·10 -4 · Mw 0.733 [13].…”