Insights into propylene/ω‐halo‐α‐alkenes copolymerization promoted by rac‐Et(Ind)₂ZrCl₂ and (pyridyl‐amido)hafnium catalysts

Abstract

This article discussed the root causes of the interesting differences between rac-Et(Ind) 2 ZrCl 2 and dimethyl (pyridyl-amido)hafnium in catalyzing the propylene/x-halo-a-alkene copolymerization. Confirmed by density functional theory (DFT) calculations, the larger spacial opening around the active center of rac-Et(Ind) 2 ZrCl 2 contributes to the coordination and insertion of the monomers, resulting in the higher catalytic activity, while the narrow spacial opening around the Hf center retards the chain transfer reaction, leading to the much higher molecular weights (M w s) of the copolymers. The superior tolerability of Zr catalyst toward halogen groups might be attributed to that the dormant species generated from halogen coordination could be promptly reactivated. DFT calculations indicated the higher probability for the x-halo-a-alkene vinyl to coordinate with the Hf catalyst leading to the better ability to incorporate halogenated monomers. The high M w s and the outstanding isotacticity achieved by the Hf catalyst determined the higher melting temperature values of the copolymers with a certain amount of halogen groups. In addition, the chain transfer schemes were employed to analyze why the presence of halogenated monomers greatly decreased the M w s of the copolymers when rac-Et(Ind) 2 ZrCl 2 was used, while had no or little effect upon the M w s in the copolymerization by the Hf catalyst.

Significant Polar Comonomer Enchainment in Zirconium‐Catalyzed, Masking Reagent‐Free, Ethylene Copolymerizations

“…Thus, overall polymerization activity is depressed due to this chelation. On passing to N(octenyl) n Pr 2 , the chelation effect is weakened due to the flexibility of long alkyl chain and unfavorable large ring conformation required for Zr⋅⋅⋅N coordination . Thus, amine coordination is less favorable (Δ G =+6.1 kcal mol −1 ).…”

Synthesis of Brominated Polyethylene by Copolymerization of Ethylene with ω–bromoalkene Catalyzed by a Metallocene and Methylaluminoxane System

“…The first consists of the direct introduction of a functional group into the polyolefin by using a radical. The second is functionalizing a polyolefin with a reactive site inside the polymer [1][2][3][4][5][6][7]. The third is the copolymerization of an olefin and a monomer with a functional group [8][9][10].…”

“…For example, the synthesis of homo-poly(11-chloro-1-undecene), a modified polymer, was carried out using highly reactive side-chain chlorine with a base, such as potassium carboxylate or potassium hydroxide [6]. The copolymerization of halogenated olefins and non-functionalized olefins has also been reported; rac-Et(Ind) 2 ZrCl 2 and (pyridine-amido)hafnium are used as catalysts, and halogen-containing isotactic polypropylene is obtained [6,7].…”

“…It was reported that the polymerization characteristics change based on the comonomer used for the copolymerization and the length of the methylene chain between the olefin and the halogen [6,7]. Comparing the copolymerization of 11-bromo-1-undecene and propylene with that of 4-bromo-1-butene and propylene, 4-bromo-1-butene could not be introduced into the synthesized polymer under the same conditions in which 4-bromo-1-butene was added, and only homo-polypropylene was formed.…”

Direct azidation of isotactic polypropylene and synthesis of ‘grafted to’ derivatives thereof using azide–alkyne cycloaddition chemistry

“…Unfortunately, both of the aforementioned methods are often challenging to apply to polyolefin‐based resins, such as isotactic polypropylene, largely due to the difficulties associated with finding a robust catalyst that features a combination of heteroatom resistance, sufficient activity and high selectivity. Although there has been some progress in the synthesis of halogen‐containing isotactic polypropylene, the subsequent azidation is hampered by the limited solubility of the requisite reagents (e.g. NaN 3 ).…”