Kinetics Of Olefin Polymerization Research Articles

Polyolefin microstructural deconvolution methods: The good, the bad, and the ugly

AbstractThe deconvolution of the molecular weight distribution (MWD) of polyolefins into Schultz–Flory most probable distributions has become the standard method to identify the number of site types on multiple‐site‐type olefin polymerization catalysts such as Ziegler–Natta, Phillips, and some supported metallocenes. This method has been used to quantify the effect of polymerization conditions and catalyst formulations on polyolefin MWD and olefin polymerization kinetics. Related methods have also been developed to deconvolute other polyolefin microstructure features, such as the chemical composition and comonomer sequence length distributions. In this paper, I explain the premises behind these deconvolution models and review the publications in this area, highlighting the advantages, disadvantages, and misuses of these methods. I also propose a revised formulation on how to model the MWD of polyolefins made with multiple‐site‐type catalysts using ratio distributions for propagation and chain transfer frequencies. The main objective of this overview article is to highlight the strengths, but also show the pitfalls, of polyolefin microstructure deconvolution methods.

Development of Large-Scale Stopped-Flow Technique and its Application in Elucidation of Initial Ziegler-Natta Olefin Polymerization Kinetics.

The stopped-flow (SF) technique has been extensively applied to study Ziegler–Natta (ZN) olefin polymerization kinetics within an extremely short period (typically <0.2 s) for understanding the nature of the active sites as well as the polymerization mechanisms through microstructure analyses of obtained polymers. In spite of its great applicability, a small amount of polymer that is yielded in a short-time polymerization has been a major bottleneck for polymer characterizations. In order to overcome this limitation, a large-scale SF (LSF) system has been developed, which offers stable and scalable polymerization over an expanded time range from a few tens milliseconds to several seconds. The scalability of the LSF technique has been further improved by introducing a new quenching protocol. With these advantages, the LSF technique has been effectively applied to address several unknown issues in ZN catalysis, such as the role of physical and chemical transformations of a catalyst on the initial polymerization kinetics, and regiochemistry of ZN propylene polymerization. Here, we review the development of the LSF technique and recent efforts for understanding heterogeneous ZN olefin polymerization catalysis with this new system.

Catalytic Olefin Polymerization Process Modeling: Multi‐Scale Approach and Modeling Guidelines for Micro‐Scale/Kinetic Modeling

AbstractThe scope of this work is to explain the multi‐scale polymerization process modeling framework, comprising of polymerization kinetics (micro‐scale), system thermodynamics (meso‐scale), and reactor performance (macro‐scale) as well as to present the methodology for developing a mathematical model for catalytic olefin polymerization. Guidelines for tuning the kinetic model parameters are proposed. This review aims to provide basic knowledge and understanding regarding catalytic olefin polymerization kinetics and offers the starter‐kit tools for developing similar works.

Site count: is a high-pressure quenched-flow reactor suitable for kinetic studies of molecular catalysts in ethylene polymerization?

Understanding the kinetics of olefin polymerization with Ziegler-Natta and related catalysts means identifying the main kinetic parameters such as k(p) and concentration of active sites. The high-pressure quenched-flow technique could be an absolute method for counting active sites and for activation studies of molecular catalysts. A kinetic study of metallocene catalysts and a phenoxy-imine titanium catalyst in the first instants of polymerization is presented in this paper.

Development of a Large‐Scale Stopped‐Flow System for Heterogeneous Olefin Polymerization Kinetics

AbstractStopped‐flow (SF) polymerization is a powerful tool to investigate the nature of the active site of heterogeneous Ziegler‐Natta catalysts, but poor polymer yields due to short polymerization times limit detailed structural analyses of the obtained polymer. A new large‐scale SF polymerization system is described in which an arbitrary volume of slurry can be transferred to obtain a polymer yield sufficient for a variety of analytic purposes. The developed LSF system is proven to be highly scalable and stable, leading to reproducible polymerization in an expanded time range from 0.03 s to a few seconds. The accurate polymerization below 0.1 s is promising for future studies to evaluate accurate kinetics as well as dormant processes in Ziegler‐Natta olefin polymerization. magnified image

GPC and ESI-MS Analysis of Labeled Poly(1-Hexene): Rapid Determination of Initiated Site Counts during Catalytic Alkene Polymerization Reactions

Accurate active-site counts are necessary for the establishment of olefin polymerization kinetics, yet current techniques are often tedious and limited in sensitivity. Herein, we describe the development of a novel method for determining the fraction of initiated catalyst using standard gel-permeation chromatography (GPC). The first insertion of monomer into the chromophore-bearing zirconocene 1 generates a single equivalent of a labeled polymer chain. The polymer-bound label can be quantified as a function of polymer molecular weight using a GPC with a UV detector; simultaneous RI detection allows both the extent of monomer conversion and the molecular-weight distribution to also be established. We estimate that monomer to catalyst ratios of as high as 10,000:1 can be measured using this technique.

Application of Fractionation Techniques to the Study of Olefin Polymerization Kinetics and Polymer Degradation

AbstractSummary: Temperature rising elution fractionation (TREF) has been regarded as a powerful technique for study of semicrystalline polymers. In this paper, two examples of unique applications of TREF were introduced. One was the study on the influence of extraction of internal donor on the variation of isospecific active sites of a MgCl2‐ supported Ziegler catalyst, and the other was the estimation of the relationship between polymer micro‐tacticity and degradation rate of isotactic polypropylene (iPP). The former example revealed the conversion from high to low isospecific site by the extraction of internal donors, whereas the latter showed a negative correlation between the level of isotacticity and the degradation rate. These results demonstrated that TREF was useful in these research applications.

Kinetics of olefin polymerization catalysed by various zirconocene/aluminoxane systems at low Al/Zr ratios

Ethylene, propylene and 1-butene polymerization kinetics have been investigated in the presence of 16 zirconocene and ethylalumoxane derivatives with various molecular masses and a molar ratio of Al/Zr = 23–26. It was found that zirconocene activity in combination with ethylalumoxanes with molecular weight MW = 880 (an oligomer with -[OAl(C 2H 5)]- unit number equal to 10) increases in series: Cp(Acac) 2ZrCl < (Fulv) 2Cp 2Zr 2Cl 2 < Cp 2ZrMe 2 < (Fulv) 2Cp 2Zr 2(O)Cl 2 < (Ind) 2ZrCl 2 < ( t-Bu 2Cp) 2ZrCl 2 < Cp 2ZrCl 2 < ( t-BuCp) 2ZrCl 2 < (MeCp) 2ZrCl 2 < (i-PrCp) 2ZrCl 2, where Fulv - fulvalene. With methylalumoxane (MW = 1930, (-[OAl(CH 3)]- unit number 31) the following series of zirconocene activity was established: (MeCp) 2ZrCl 2 < (EtCp) 2ZrCl 2 < (PrCp) 2ZrCl 2 < (BuCp 2ZrCl 2 < (i-PrCp) 2ZrCl 2 < (Cyclo-HexCp) 2ZrCl 2.