Nonconjugated α,ω-Diolefin/Propylene Copolymerization to Long Chain-Branched Polypropylene by Ziegler–Natta Catalyst: Overcoming Steric Hindrance by Introducing an Extra Electronic Pulling Effect

Abstract

Synthesis of long chain-branched polypropylene (LCB-PP) by propylene copolymerization with nonconjugated α,ω-diolefin is a steric hindrance-prevailing reaction process which involves in copolymerization not only α,ω-diolefin itself (α-olefin copolymerization) but also polymeric olefin intermediate derived from the first α-olefin copolymerization (ω-olefin copolymerization). This reaction mishap reaches its extreme when Ziegler−Natta catalysts based on MgCl 2supported TiCl 4 (MgCl 2 /TiCl 4 catalysts) are considered as catalyst, which produce active sites that are highly sensitive to olefin monomer's steric bulkiness. A proposition is put forward that such a steric difficulty may be overcome by functionalization of α,ω-diolefin with Lewis base functionality, which would usher in an extra electronic pulling effect to help with olefin coordination to the active center in both the α,ω-diolefin's monomeric α-olefin and the polymeric ω-olefin polymerization steps. Three model compounds, including di-n-hexyldiethoxysilane, di-5hexenyldiethoxysilane, and di-5-hexenyldimethylsilane, were synthesized and used to attest to the validity of the hypothesis. The experimental results evidently proved that the Lewis base functionality enabled the functionalized α,ω-diolefin to establish dynamic electron-donating interactions with MgCl 2 /TiCl 4 catalysts, making it far more effective in prompting LCB in copolymerization with propylene due to greatly enhanced polymerization reactivity of both its monomeric α-olefin and polymeric ω-olefin in their respective polymerization steps. The electronic promotion effect was found to be so robust that it could not be offset by reducing the initial α,ω-diolefin molecular steric hindrance. This approach is promising to solve the real issue of synthesizing LCB-PP by Ziegler−Natta catalyst.

Preparation of polypropylene with high melt strength by wet reaction blending of lignin

“…The double arc or low‐frequency warping is due to the coexistence of two relaxation processes with widely different relaxation times in the heterogeneous polymer system 24,25 . When a network structure was present in the polymer melt, it increased the elasticity of the PP matrix, which in turn lead to a low‐frequency relaxation behavior, increasing the relaxation time 26 . As the LS increased, the low‐frequency warping of the curve became more pronounced, indicating a more dense network structure with long‐time relaxation of the heterogeneous network structure Characteristics, occurring LTS.…”

Synergistic lignin construction of a long-chain branched polypropylene and its properties

“…From this information, the upward warping of the low- frequency region in the Cole-Cole diagram can be taken as a sign of the formation of a heterogeneous network structure. 43 It can be seen from Fig. 3D that when LS is introduced, the Cole-Cole diagram shows the phenomenon of low-frequency upwelling, indicating the formation of a heterogeneous network structure in the melt.…”

Industrial Adaptability of the Ziegler–Natta Catalyst-Friendly Synthesis of Long-Chain-Branched Polypropylene Based on ω-Alkenylmethyldichlorosilane-Assisted Propylene Polymerization

“…More importantly, though grouped into the traditional catalyst category, the latter family of catalysts is still constantly improving itself on all-round catalytic performance to meet the ever-growing consumer demands for PP properties by, for example, innovating on the electron donor (both internal and external) technology. − MgCl 2 /TiCl 4 containing 9,9-bis­(methoxymethyl)­fluorine (BMMF) as the internal electron donor is a mere example of the latest generation (fifth-generation) Ziegler–Natta catalysts, which has shown a set of exceptionally good catalytic properties for propylene polymerization including, but not limited to, high catalyst activity, high hydrogen response, and high comonomer (ethylene and higher α-olefins) incorporation rate and distribution homogeneity. − Unfortunately, for all the prevailingness and resilience of Ziegler–Natta catalysts in the PP industry, previously there have been no suitable chemistries for them to synthesize LCB-PP. The otherwise effective nonconjugated α,ω-diolefin/propylene copolymerization chemistry for both metallocene and nonmetallocene catalysts becomes dubious when it comes to Ziegler–Natta catalysts. , The task of industrial production of LCB-PP resins has to a great extent remained pending, not least with Ziegler–Natta catalysts.…”