Synthesis and characterization of iPP‐sPP stereoblock produced by a binary metallocene system

Abstract

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How Chain Transfer Leads to a Uniform Polymer Particle Morphology and Prevents Reactor Fouling

“…Although it is clear that chain transfer to zinc takes place, the fact that the molecular weights do not increase proportional to the propylene consumption (Figure B) and that the polydispersity indices are greater than 2 indicates that the system is clearly not running under reversible, living CCTP conditions. − , Although this value should be treated with caution for a system in which the CTA-containing polymer precipitates, the k ct / k cg of 1.6 obtained from the Mayo plot (Figure B) clearly demonstrates that the rate constants for the chain transfer ( k ct ) and chain growth ( k cg ) are of the same order of magnitude. − This means that under the polymerization conditions applied, the actual rate of chain transfer is relatively low compared to the rate of polymerization. 1 H NMR analysis of the polymers qualitatively showed the existence of vinylidene and vinyl end groups indicating that competitive β-H and β-Me transfer is taking place as well (Figure S5).…”

“…The importance of the presence of DEZ in preventing reactor fouling and yielding a uniform polymer powder morphology encouraged us to further study the chain transfer to zinc during propylene polymerization and its effect on polymer particle morphology and reactor fouling. It was argued that the presence of DEZ during polymerization would initially result in a pseudo-living coordinative chain transfer polymerization (CCTP) system where the number of simultaneously growing chains would be proportional to the DEZ concentration, while the propagation rate of the individual growing chains would be inversely proportional to the DEZ concentration. − Depending on the DEZ concentration and the kinetics of chain propagation and chain transfer, tuning the k propagation / k crystallization ratio to lower values for such a CCTP system might allow the polymer to crystallize in a controlled manner from the solution. Subsequently, the thus formed polymer particles, the surface of which exceeds the surface of the reactor wall by several orders of magnitude, might function as seeds for newly formed polymer chains, produced under non-CCTP conditions, thereby avoiding reactor fouling and providing good morphology control. ,, …”

Correlation of Microstructure, Rheological and Morphological Characteristics of Synthesized Polypropylene (PP) Reactor Blends Using Homogeneous Binary Metallocene Catalyst

“…Therefore, some of the researchers used both homogeneous and heterogeneous binary metallocene silica-supported catalysts with different stereo-specificities to synthesize PPs with broad and bimodal MWD as well as stereoblock structures with different melting points [ 16 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ]. Numerous studies have been conducted on the microstructural characterization of PPs synthesized by binary or hybrid catalyst systems as well as the effects of type and composition of catalysts on their microstructures through different characterization techniques [ 15 , 35 , 36 , 37 ]. However, there exists limited literature on the morphological and rheological properties of these systems and their relationship with the microstructure of the synthesized PPs.…”

iPP–sPP Stereoblocks or Blends? Studies on the Synthesis of Isotactic–Syndiotactic Polypropylene Using Single C1‐Symmetric {Ph2C‐(Flu)(3‐Me3Si‐Cp)}ZrR2 Metallocene Precatalysts

“…Though essentially inseparable polypropylene blends composed of i PP, s PP, (or a PP) and a stereoblock component i PP– s PP (or i PP– a PP) have been reported, no unequivocal evidence on the stereoblock nature of the latter could be furnished. Recently, successful formation of low‐molecular‐weight stereoblock i PP− b − s PP polymers has been reported upon using mixtures of isoselective Me 2 Si{2‐Me‐4‐Ph‐Ind}ZrCl 2 and syndioselective Ph 2 C{(2,7‐ t Bu 2 Flu)(Cp)}ZrCl 2 precursors and Et 2 Zn as CTA . Different experimental techniques (NMR, crystallization analysis fractionation (CRYSTAF), high‐temperature HPLC (HT HPLC), DSC, successive self‐nucleation/annealing (SSA) and wide‐angle X‐ray diffraction (WAXD)) allowed clear authentication of these stereoblock materials.…”

“…Recently, successful formation of low-molecular-weight stereoblock i PP− b − s PP polymers has been reported upon using mixtures of isoselective Me 2 Si{2-Me-4-Ph-Ind}ZrCl 2 and syndioselective Ph 2 C{(2,7-t Bu 2 Flu)(Cp)}ZrCl 2 precursors and Et 2 Zn as CTA. [ 6 ] Different experimental techniques (NMR, crystallization analysis fractionation (CRYSTAF), high-temperature HPLC (HT HPLC), DSC, successive selfnucleation/annealing (SSA) and wide-angle X-ray diffraction (WAXD)) allowed clear authentication of these stereoblock materials.…”