Bimodal molecular weight distribution formed in the emulsion polymerization of ethylene

Tobita, Hidetaka

doi:10.1002/pola.10439

Cited by 12 publications

(13 citation statements)

References 31 publications

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“…[19,29,30] For this kind of complex polymerization reactions, other mechanisms can also be considered to elucidate the formation of bimodal MWDs. I do not totally rule out other possibilities, however, the Monte Carlo simulation results agree reasonably well with the above experimental result, [31] without considering such complicated effects of particle size distribution, chainlength-dependent polymerization kinetics, and so on.…”

Section: Moments Of the Molecular Weight Distributionsupporting

confidence: 72%

Scale‐Free Power‐Law Distribution of Emulsion‐Polymerized Branched Polymers: Power Exponent of the Molecular Weight Distribution

Tobita

2005

Macro Materials & Eng

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Summary: The molecular weight distribution (MWD), formed in emulsion polymerization that involves the polymer transfer reaction during Interval II, may approach the power‐law distribution as polymerization proceeds. The power exponent, α, of the weight fraction distribution W(M) = M−α conforms to the relationship, α = 1/Pb, where Pb is the probability that the chain end is connected to a backbone chain. The MWD of emulsion‐polymerized polyethylene reported in literature agrees reasonably well with the relationship, W(M) = M−α with α = 1/Pb. This simple relationship could be used to estimate the Pb value from the MWD data, possibly leading to determining the polymer transfer constant under well‐designed experimental conditions. Because α > 1, the number‐average MW always approaches a finite value, but the weight‐ and higher order‐averages of MWD may continue to increase as the particle grows without limit depending on the magnitude of Pb. The power‐law distributions are self‐similar, possessing the nature of fractals and lacking a characteristic scale. The i‐th moment of the MWD for the present reaction system continues to increase without limit during Interval II for Pb ≥ 1/i.Molecular weight distribution of the emulsion‐polymerized polyethylene.magnified imageMolecular weight distribution of the emulsion‐polymerized polyethylene.

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Section: Moments Of the Molecular Weight Distributionsupporting

confidence: 72%

Scale‐Free Power‐Law Distribution of Emulsion‐Polymerized Branched Polymers: Power Exponent of the Molecular Weight Distribution

Tobita

2005

Macro Materials & Eng

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“…Recently, Tobita (2002) showed that the Monte Carlo (MC) simulation results, using parameters mostly reported in the literature, agree reasonably well with the experimental data. An example of comparison is shown in Figure 1.…”

Section: Introductionsupporting

confidence: 55%

“…In the earlier investigation for the emulsion-polymerized polyethylene (Tobita, 2002), a rather general model in which various kinetic mechanisms, such as the entry and exit of radicals and formation of polyradicals, are accounted for was used, although the polymer particles are assumed to be monodisperse. On the other hand, a more simplified model may be useful to clarify the necessary frequency of long-chain branching to form bimodal MWDs.…”

Section: Modelmentioning

confidence: 99%

Bimodal Molecular Weight Distribution Formed in Emulsion Polymerization with Long‐Chain Branching

Tobita¹

2003

Polymer Reaction Engineering

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It is known that the molecular weight distribution (MWD) formed in emulsion polymerization of ethylene can be bimodal. A simplified model is used to investigate the emulsion polymerization that involves chain transfer to polymer, aiming at finding necessary conditions to form a bimodal MWD. According to the present theoretical investigation, a bimodal MWD can be formed when the probability that the primary chain end is connected to a backbone chain, P b is larger than 0.5. The bimodality for these cases results from the limited volume effect, that is, the high molecular weight profiles are distorted by the small particle size, which is comparable to the size of the largest branched polymer molecule formed in a particle. During Interval II, the P b -value could be (1 À x c )] in usual emulsion polymerization without using the chain transfer agents, where C p and C m are transfer constants to polymer and to monomer, respectively, and x c is the conversion at which Interval II ends, and therefore, one can predict the possibility of obtaining a bimodal MWD on the basis of these reaction parameters. On the other hand, if the experimentally obtained MWDs are bimodal even when P b < 0.5, the origin of bimodality would be attributed to other reaction mechanisms, such as the chain-length dependent branching reactions and combination of two different MWDs formed in large and small polymer particles.

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“…It is reported recently that TiCl 4 (THF) 2 complex also give broad polyethylene but at low activity [39]. The broadness is also introduced not only by using disteromeric amido functionalized half sandwich Ti and Zr based catalysts [40] and also through emulsion polymerization of ethylene [41].…”

Section: Introductionmentioning

confidence: 98%

Immobilization of Titanium Tetrachloride on Mixed Support of MgCl2 · xEB/Poly(methyl acrylate-co-1-octene): Catalyst for Synthesis of Broad MWD Polyethylene

et al. 2009

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TiCl 4 immobilization on different compositions of mixed support of MgCl 2 Á xEB and poly(methyl acrylate-co-1-octene) (PMO; synthesized through ARGET ATRP) resulted in the formation of solid catalysts having variation in incorporation of titanium. The effect of mixed support composition onto the titanium immobilization, catalyst morphology and performance for ethylene polymerizations has been evaluated. The polyethylenes synthesized showed broad to bimodal MWD in GPC and DSC where the broadness was found to be dependent upon the ratio of mixed support MgCl 2 Á xEB/PMO. The morphological features of PE as elucidated using SEM lead to postulation of polymer formation mechanism.

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Bimodal molecular weight distribution formed in the emulsion polymerization of ethylene

Cited by 12 publications

References 31 publications

Scale‐Free Power‐Law Distribution of Emulsion‐Polymerized Branched Polymers: Power Exponent of the Molecular Weight Distribution

Scale‐Free Power‐Law Distribution of Emulsion‐Polymerized Branched Polymers: Power Exponent of the Molecular Weight Distribution

Bimodal Molecular Weight Distribution Formed in Emulsion Polymerization with Long‐Chain Branching

Immobilization of Titanium Tetrachloride on Mixed Support of MgCl2 · xEB/Poly(methyl acrylate-co-1-octene): Catalyst for Synthesis of Broad MWD Polyethylene

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