Kinetics of Styrene Polymerization to Syndiotactic Polystyrene over Metallocene Catalyst on Flat Surface, Silica Nanotube Reactors and Porous Silica Particles

Polymer Engineering & Sci

Choi

2020

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Styrene has been polymerized to syndiotactic polystyrene (sPS) over a layer of heterogeneous Cp*Ti(OCH3)3/MAO catalyst immobilized onto the surfaces of silica nanotube reactor (SNTR) arrays of 60–200 nm in diameter. The polymer produced in the SNTR arrays has been found to have the molecular weights much larger than the polymers synthesized by a liquid slurry polymerization over silica‐supported catalysts. A dynamic reactor model that consists of diffusion and reaction terms has been derived and solved to quantify the kinetics of styrene polymerization in a single nanotube reactor. The two‐site kinetic model applied to the silica nanotube reactor model shows that the experimentally observed high polymer molecular weight can be fitted if the chain transfer rate constants for monomer and β‐hydride elimination are reduced significantly. The simulation results suggest that the presence of dense crystalline sPS nanofibrils filling the nanotubes constrain the molecular movements of polymer chain ends in the proximity of catalyst sites to limit the chain transfer reactions. POLYM. ENG. SCI., 60:700–709, 2020. © 2020 Society of Plastics Engineers

Section: Resultssupporting

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Geometrically Constrained Polymerization of Styrene Over Heterogeneous Catalyst Layer in Silica Nanotube Reactors

Han

Polymer Engineering & Sci

Choi

2020

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“…And if a straight line is obtained, the above model can be considered as a reasonably good representation of the kinetic behavior of the catalytic polymerization. [11,12] In what follows, we shall test Equation (6) for the ethylene polymerization with different silica support materials used in our experiments. Figure 5 shows the test of Equation (6) for the polymerization data with four different silica-supported catalysts, and Table 3 summarizes the parameter values in Equation (6).…”

Section: Resultsmentioning

confidence: 99%

Metallocene Catalyzed Ethylene Polymerization with Specially Designed Catalyst Supports and Reaction Systems

Kim

Macromolecular Symposia

et al. 2013

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Summary:In heterogeneously catalyzed polymerization of a-olefins, the characteristics of a solid support material impact the catalyst activity, polymer particle morphology, and resulting polymer properties. Silica is the most widely used support for metallocene catalysts in a-olefin polymerization processes because of its large surface area and favorable surface properties for catalyst anchoring. Understanding the kinetics of heterogeneous olefin polymerization over a solidsupported catalyst is often quite complicated because of mass transfer effects and catalyst particle fragmentation during the polymerization. Incomplete or premature fragmentation of support material results in a large fraction of catalyst sites left unavailable for the polymerization, causing some inconsistencies in the performance of the catalyst. Silica-supported metallocene catalysts for a-olefin polymerization are known to follow the layer-by-layer fragmentation mechanism where the fracture of the silica/polymer layer begins from the surface region of a silica particle and it gradually continues into the center of the particle as fragmentation is complete. In this paper, we present new experimental results on ethylene polymerization with rac-Et(indenyl) 2 ZrCl 2 /MAO catalyst using different types of silica supports to quantitatively assess the effects of support geometry on intrinsic catalytic activity. Flat surface silica, nano-sized spherical silica, straight cylindrical pore silica, and conventional silica are used as supports. The presence or absence of intraparticle monomer diffusion resistance and particle fragmentation has been shown to have significant effects on the catalytic activity.

“…These pores are large enough for the diffusion of MAO and catalyst molecules. For example, the most frequently observed oligomeric MAO‐12 ([AlOMe] 12 ) structure has a dimension of about 0.96 nm . However, the pores are quite tortuous and it is quite possible that some fraction of pores or surfaces may not be fully accessible by monomer and cocatalyst (MAO) molecules if silica fragmentation is incomplete to expose the entire active sites available for polymerization.…”

Section: Introductionmentioning

confidence: 99%

“…For the polymerization of ethylene, a metallocene catalyst can be supported onto the surface of silica inside the nanochannels of an AAO film. The thickness of a typical silica layer inside a silica nanotube surface is about 10–15 nm, which is about the same dimension of the smallest unit of the silica gels synthesized by sol–gel techniques for industrial silica micro–particles . When SNTs are loaded with active metallocene catalyst, olefin polymers can be synthesized inside the nanochannels.…”

Section: Introductionmentioning

confidence: 99%

Growth of Polyethylene Nanofibrils Over rac‐Et(Indenyl)₂ZrCl₂/MAO Catalyst Supported on Silica Nanotubes

Han²,

Macro Reaction Engineering

et al. 2015

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The morphology of polyethylene synthesized over rac-Et(indenyl) 2 ZrCl 2 /MAO catalyst supported on silica nanotubes of anodized aluminum oxide (AAO) template and on liberated silica nanotubes have been studied. A silica nanotube is quickly filled up with polymer, which extrudes out to the bulk liquid phase as nanofibrils of 30-35 nm diameter with high crystallinity. When silica nanotubes are liberated from the AAO template and deposited with catalysts, the polyethylene nanofibrils formed at the outer surface of the silica nanotubes also grow as 30-35 nm diameter fibrils and they quickly entangle to a mass of polymers in the liquid phase. The liberated silica nanotube reactors showed much higher ethylene polymerization activity than the micro silica particle-supported catalyst.