Diagnosing long-chain branching in polyethylenes

Janzen, Jay; Colby, Ralph H.

doi:10.1016/s0022-2860(99)00097-6

Cited by 195 publications

(246 citation statements)

References 29 publications

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“…The difficulty in evaluating such a small degree of branching using classical methods such as size exclusion chromatography (SEC) and nuclear magnetic resonance ( 13 C NMR) is proverbial [157]. Levels of branching ranging from 0.1 to 1 LCB/10 4 C have been recorded in mPE [147,148], yet there is some controversy on the utility of these techniques [158]. Branching levels of around 2 branches per 10 4 C were determined by 13 C NMR in only one polymer of a wide branched series [136].…”

Section: State-of-the-artmentioning

confidence: 99%

“…Due to the limitations of spectroscopic and chromatographic methods, some authors have suggested regarding the rheological response as a probe of molecular structure since it is more sensitive to molecular and architectural features. Janzen and Colby [158] suggest the need to relegate classical analyses based on Zimm-Stockmayer predictions [40] to a secondary role and to address the problem through more modern concepts of polymer physics based on scaling and percolation arguments. These authors present a semiempirical method of determining the level of LCB almost entirely from η o values.…”

Section: State-of-the-artmentioning

confidence: 99%

“…This model is based on recent advances in branched polymer molecular theories on branch hierarchical relaxation by path arm fluctuations, arm collapse and reptation [84][85][86][87][88][89]. In his work, Larson discusses the limitations of Janzen and Colby's approach [158], and demonstrates that η o and the entire viscoelastic response depend not only on branching content, but also on the type and topology of branching.…”

Section: State-of-the-artmentioning

confidence: 99%

“…These authors found that the exponent in the relation between η o and M w could be higher or lower than 3.4, depending on the magnitude of M bb , i.e., the level of branching. Janzen and Colby [158] took advantage of these studies and presented a method of determining the level of LCB from η o values.…”

Section: Quantitative Prediction Of Lcb From Rheological Data: Rheolomentioning

confidence: 99%

“…The model has been successfully applied to predict the branching level in randomly cross-linked melts of linear chains and LDPEs [158]. Colby [158] and Bersted [47,50] for randomly branched PEs, as a function of LCB density for a weight-average molecular weight M w of 200 000…”

Section: Quantitative Prediction Of Lcb From Rheological Data: Rheolomentioning

confidence: 99%

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Effect of long chain branching on linear-viscoelastic melt properties of polyolefins

et al. 2002

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Abstract:The aim of this review is to provide evidence that rheological testing is a potent tool for characterising polymers in the melt. An effort has been made in order to gather results in conventional and model polyolefins, and correlating them with phenomena occurring at the molecular level. We have focused our interest on long chain branching (LCB). In the case of materials containing long side-chain branches, strong effects on viscosity, elastic character and activation energy of flow are general features. Literature results mostly indicate that the effect of polydispersity on these parameters could be very similar to that expected due to the presence of LCB -notwithstanding that the effects of LCB seem to be stronger than those due to polydispersity for a given molecular weight. Different relaxation processes appear as a consequence of the presence of LCB: slower terminal relaxation behaviour than of linear counterparts, and faster additional branch relaxation at higher frequencies, clearly distinguishable from polydispersity effects. To measure the amount of LCB from limited viscoelastic data and molecular properties seems to be a suitable instrument to explain the rheological features of the different polymers, but it fails when the results are compared with measured values of LCB density in model polymers. The actual framework leads us to say that the number of branches is less important than the topology itself. Therefore, the position and architecture of the branches along the polymer main chain are the main factors that control the rheology of the material.

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Section: State-of-the-artmentioning

confidence: 99%

Section: State-of-the-artmentioning

confidence: 99%

Section: State-of-the-artmentioning

confidence: 99%

Section: Quantitative Prediction Of Lcb From Rheological Data: Rheolomentioning

confidence: 99%

Section: Quantitative Prediction Of Lcb From Rheological Data: Rheolomentioning

confidence: 99%

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Effect of long chain branching on linear-viscoelastic melt properties of polyolefins

et al. 2002

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Polyethylene, High Density

Benham

McDaniel

2005

Kirk-Othmer Encyclopedia of Chemical Technology

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Polyethylene (PE) is the most widely used plastic throughout the world, and high density polyethylene (HDPE) is the most widely used type of polyethylene. It was invented independently in the early 1950s in three different laboratories across the world. Commercial catalytic processes were quickly developed based on three different transition metals: Cr, Mo, and Ti. Today, hundreds of different grades of HDPE are manufactured by dozens of different commercial processes worldwide to meet the demands of applications too numerous to describe completely. The properties of HDPE can be made to vary widely for these specialized applications by varying its molecular structure, such as the molecular weight (MW); the MW distribution; the amount; type, and placement of short‐chain branching; the end group composition; and the degree of long‐chain branching. These affect the stiffness of the polymer; the gloss or clarity; the impact, puncture, and tear resistance; chemical resistance; electrical insulation properties; molding characteristics; and tensile properties. Common uses for HDPE include food packaging, bottles, bags, medical applications, drums, fuel tanks and other automotive parts, pipe, film, geomembranes, toys, film, and filament.

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Ethylene Polymers,HDPE

Benham

McDaniel

2001

Encyclopedia of Polymer Science and Technology

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History of PEEarly Work. The history of HDPE (and polyolefins in general) actually began in the 1890s with the synthesis of "polymethylene" from the decomposition of diazomethane. Between 1897 and 1938, numerous reports of such polymers appeared in the literature (1-6). Catalysts such as unglazed china, amorphous boron, and boric acid esters were used for the decomposition. The empirical formula of such products was found to be CH 2 . Later reproductions of work (3,6) established Encyclopedia of Polymer Science and Technology.

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Diagnosing long-chain branching in polyethylenes

Cited by 195 publications

References 29 publications

Effect of long chain branching on linear-viscoelastic melt properties of polyolefins

Effect of long chain branching on linear-viscoelastic melt properties of polyolefins

Polyethylene, High Density

Ethylene Polymers,HDPE

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