Mesoporous Silica Supported Multiple Single‐Site Catalysts and Polyethylene Reactor Blends with Tailor‐Made Trimodal and Ultra‐Broad Molecular Weight Distributions

Abstract

A ternary blend of the bisiminopyridine chromium (III) (Cr-1) with the bisiminopyridine iron (II) (Fe-2) post-metallocenes with the quinolylsilylcyclopentadienyl chromium (III) halfsandwich complex (Cr-3) was supported on mesoporous silica to produce novel multiple single-site catalysts and polyethylene reactor blends with tailor-made molecular weight distributions (MWDs). The preferred cosupporting sequence of this ternary blend on MAO-treated silica was Fe-2 followed by Cr-1 and Cr-3. Cosupporting does not impair the single-site nature of the blend components producing polyethylene fractions with $\overline M _{\rm w}$ = 10(4) g · mol(-1) on Cr-1, $\overline M _{\rm w}$ = 3 × 10(5) g · mol(-1) on Fe-2, and $\overline M _{\rm w}$ = 3 × 10(6) g · mol(-1) on Cr-3. As a function of the Fe-2/Cr-1/Cr-2 mixing ratio it is possible to control the weight ratio of these three polyethylenes without affecting the individual average molecular weights and narrow polydispersities of the three polyethylene fractions. Tailor-made polyethylene reactor blends with ultra-broad MWD and polydispersities varying between 10 and 420 were obtained. When the molar ratio of Fe-2/Cr-1 was constant, the ultra-high molecular polyethylene (UHMWPE, $\overline M _{\rm w}$ > 10(6) g · mol(-1) ) content was varied between 8 and 16 wt.-% as a function of the Cr-3 content without impairing the blend ratio of the other two polyethylene fractions and without sacrificing melt processability. When the molar ratio Fe-2/Cr-3 was constant, it was possible to selectively increase the content of the low molecular weight fraction by additional cosupporting of Cr-1. Due to the intimate mixing of low and ultra-high molecular weight polyethylenes (UHMPEs) produced on cosupported single-site catalysts a wide range of melt processable polyethylene reactor blends was obtained.

Characteristics of linear/branched polyethylene reactor blends synthesized by metallocene/late transitional metal hybrid catalysts

“…Mülhaupt et al have immobilized two bis(imino)pyridyl Fe catalysts with a half sandwich chromocene for production of polyethylene with very broad, trimodal MWD [30][31][32]. Likewise, Ahmadjo et al [33] have provided polyethylene with multimodal melting peaks using hybrid bis(imino)pyridine Fe/Ziegler-Natta catalysts.…”

UHMWPE/SBA-15 nanocomposites synthesized by in situ polymerization

“…Research papers published in recent years demonstrate the ability of these mesoporous silicas to produce nanometer scaled PE through space confined polymerization [20][21][22]. Dong et al produced PE nanofibers with Cp 2 ZrCl 2 fixed on MCM-41 and SBA-15 where the later fibers possess larger diameters due to the higher SBA-15 pore diameter [23].…”

Tailored bimodal ultra‐high molecular weight polyethylene particles

“…In recent decades, supported molecular catalysts have aroused a lot of interest due to the capability to produce polymers with narrow molar mass distributions of the high and low molecular weight fractions . Alternatively, a variety of studies were performed to generate a bimodal or a broad molar mass distributed polyethylene in a single reactor by using molecular precatalysts . In this process, the catalyst systems are a combination of two (or more) molecular precatalysts systems .…”

“…A dual site catalyst concept similar to the work of Chadwick et al . and Mülhaupt et al . was not deemed to be viable.…”