Cover Picture: Macromol. Theory Simul. 7∕2014

Neuhaus, Eric; Herrmann, Thomas; Vittorias, Iakovos; Lilge, Dieter; Mannebach, Gerd; Gonioukh, Andrei; Busch, Markus

doi:10.1002/mats.201470019

Cited by 8 publications

(14 citation statements)

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“…With regard to the hypothesis proposed, it would be quite difficult to demonstrate that none of the previously published sets of kinetic parameters reproduce the observed trends of M n and PD in the multizone autoclave reactor; however, it can be argued that it would suffice to demonstrate that a set of kinetic parameters based on those used by Iedema et al (later called set I parameters) is not capable of reproducing the observed trends in M n , since this set and the one by Krallis et al are the only two parameter sets that predict realistic values of PD, and both works use very similar parameter values (largely based on those of Pladis and Kiparissides except for the scission reaction). Other recent stochastic models also predict broad MWDs for LDPE tank reactors, but they do not report PD values . Other recent works that also resort to stochastic models report similar results for tubular reactors …”

Section: Resultsmentioning

confidence: 86%

Some Factors Affecting the Molecular Weight Distribution (MWD) in Low Density Polyethylene Multizone Autoclave Polymerization Reactors

Saldívar‐Guerra

Ordaz-Quintero

Infante

et al. 2015

Macro Reaction Engineering

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Due to its complexity, free‐radical polymerization of ethylene at high pressure still remains to be fully understood. This paper investigates factors that contribute to shape the MWD, one of the main features of LDPE, such as the structure of primary chains and the reactor operation in one/two phases. Using plant data and different models, it is found that chain transfer to small species is the controlling chain termination step and it is explained why one‐phase operation leads to more branched polymer. Simulations with the Polyred software package provide a set of kinetic parameters that reproduce the observed trends in number average molecular weight and MWD dispersity in the reactor.

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Section: Resultsmentioning

confidence: 86%

Some Factors Affecting the Molecular Weight Distribution (MWD) in Low Density Polyethylene Multizone Autoclave Polymerization Reactors

Saldívar‐Guerra

Ordaz-Quintero

Infante

et al. 2015

Macro Reaction Engineering

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“…It is an individual macromolecule approach, which calculates topologies of an ensemble of macromolecules one after the other depending only on reaction conditions as implemented in the kinetic model. [10] A reaction frequency R i is calculated for each reaction i of the network by the deterministic model. The reaction frequency is defined as the corresponding reaction rate divided by considered moment of the respective polymeric species.…”

Section: Multiscale Modelingmentioning

confidence: 99%

Using a Multiscale Modeling Approach to Correlate Reaction Conditions with Polymer Microstructure and Rheology

Zentel

Degenkolb

Busch

2020

Macro Theory & Simulations

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are created-with molecular weight (MW), branching, and comonomer distribution being the most important parameters. This is the reason for the incredibly broad spectrum of polymer properties that can be tuned by adjusting a polymeric microstructure on a molecular level. As "polymers are products by process," their microstructure is-to a certain extent-directly controllable via process conditions. [1] This opens up a huge potential of process optimizations as well as aimed product designs for systems with interesting polymeric microstructures that are industrially relevant and fairly well understood. One of those processes is the high-pressure free-radical polymerization of ethylene to low-density polyethylene (LDPE) under supercritical conditions. It is a remarkable example not only because of its high industrial relevance, but mainly because of its complex random branching distribution. The short-and especially long-chain branches (LCBs) impact material properties drastically. [2,3] The LCBs are introduced by an intermolecular transfer reaction of a propagation macroradical to a polymer molecule. The resulting midchain radical can then either undergo a β-scission reaction or propagate further by monomer addition, which forms LCBs. This is shown schematically in Figure 1. Full kinetic schemes of the LDPE polymerization can be found in the literature. [4,5] LCBs are essential when it comes to polymer properties and processing behavior. They lead to effective size reduction of the polymer coil, which can be seen both analytically in light-scattering experiments [6] as well as by studying flow behavior. Rheological experiments show reduced viscosities for LDPE compared to linear high-density polyethylenes. [3,7] However, when the technically relevant strongly nonlinear flows in extension are investigated, LCBs lead to an increased network connectivity in the polymer melt and consequently reduce the rate of disentanglement, if an external force is applied. Thus, a pronounced increase of elongational viscosity with time is observed in extensional flows, which is referred to as strain hardening behavior and very beneficial in terms of processing operations such as blow molding, film blowing, foaming, or fiber spinning. [8] Following this argumentation, understanding structure-property relationships and how they can be manipulated by choosing appropriate reaction conditions is extremely beneficial in the LDPE context. A three-step multi-scale modeling strategy was recently introduced by Pflug and Busch, [4] which demonstrates Reaction conditions have a huge impact on the resulting polymer properties, but capturing this requires understanding the correlation of the underlying kinetics, the polymer architecture, and polymer flow behavior. Long-chain branched polymers created randomly by free-radical polymerization, such as low-density polyethylene (LDPE), show complex rheological behavior and are thus interesting in this context. A study applying a multiscale modeling approach is used to simulate varying reaction condition...

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“…Furthermore, the presented approaches are either suitable for modeling autoclave or tubular reactors. Therefore Neuhaus et al [13,14] developed a coupled deterministic and stochastic simulation approach to model the polymeric microstructure independent of the reactor type. Eckes [15,16] extended that model and validated it for homopolymerizations of ethene in autoclaves.…”

Section: Literature Reviewmentioning

confidence: 99%

Modeling of High‐Pressure Ethene Homo‐ and Copolymerization

Peikert

Pflug

Busch

2019

Chemie Ingenieur Technik

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While reaction engineering of low‐molecular weight compounds mainly focuses on equilibria and selectivities, polymer properties are tremendously influenced by molecular weight distribution as well as branching structure. In order to determine the branching structure of low‐density polyethylene (LDPE) copolymers in dependence on chosen process conditions, a Monte‐Carlo approach was developed. By modeling the topology as well as the comonomer distribution in the polymer chains a deeper insight in the process‐microstructure‐properties relationship is gained.

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Cover Picture: Macromol. Theory Simul. 7∕2014

Cited by 8 publications

References 0 publications

Some Factors Affecting the Molecular Weight Distribution (MWD) in Low Density Polyethylene Multizone Autoclave Polymerization Reactors

Some Factors Affecting the Molecular Weight Distribution (MWD) in Low Density Polyethylene Multizone Autoclave Polymerization Reactors

Using a Multiscale Modeling Approach to Correlate Reaction Conditions with Polymer Microstructure and Rheology

Modeling of High‐Pressure Ethene Homo‐ and Copolymerization

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