Thermorheological effects of long-chain branching in entangled polymer melts

Carella, José M.; Gotro, J. T.; Graessley, William W.

doi:10.1021/ma00157a031

Cited by 136 publications

(169 citation statements)

References 14 publications

(33 reference statements)

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“…28 Experimental data corroborating eq 1 are problematic. Results for hydrogenated polyisoprene, polyethylene, 20,21 and 1,2-polybutadiene are qualitatively consistent with the predicted correlation between an excess temperature dependence for branched chains with their conformational energies. 19,20 On the other hand, the gauche conformers of 1,4-polyisoprene are lower in energy than the trans; 28,29 nevertheless, the presence of long branches gives rise to larger temperature coefficients than linear polyisoprene.…”

Section: Introductionsupporting

confidence: 77%

“…20 The resulting curves (Figure 8) have essentially zero slope, demonstrating that branching does not change the temperature dependence of PIB.…”

Section: Resultsmentioning

confidence: 92%

“…19,20,25,42 To better illustrate the degree of thermorheological simplicity found herein, the loss modulus measured at all temperatures for the higher molecular …”

Section: Resultsmentioning

confidence: 96%

“…19,20 On the other hand, the gauche conformers of 1,4-polyisoprene are lower in energy than the trans; 28,29 nevertheless, the presence of long branches gives rise to larger temperature coefficients than linear polyisoprene. [25][26][27] Branched 1,4-polybutadiene exhibits a similar anomalysstronger temperature dependence 20 even though the retracted configuration should be the lower energy state. 29 For polystyrene and hydrogenated 1,2-polybutadiene, the only available data were obtained on polymers too low in molecular weight to be a sensitive test of the arm retraction hypothesis.…”

Section: Introductionmentioning

confidence: 99%

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Rheology of Star-Branched Polyisobutylene

1999

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The rheology of high molecular weight, six-arm-star polyisobutylenes (PIB) was measured and compared to the behavior of linear PIB. The polymers had equivalent plateau moduli and conformed well in the terminal zone to the time-temperature superposition principle. Moreover, the temperature coefficients of the terminal relaxation times were identical for the star and linear polymers. Since the trans and gauche conformations in PIB have virtually the same energy, this absence of enhanced temperature sensitivity in star PIB, as well as the thermorheological simplicity, is consistent with an interpretation of the rheology of branched polymers based on an arm retraction mechanism.

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Section: Introductionsupporting

confidence: 77%

“…20 The resulting curves (Figure 8) have essentially zero slope, demonstrating that branching does not change the temperature dependence of PIB.…”

Section: Resultsmentioning

confidence: 92%

“…19,20,25,42 To better illustrate the degree of thermorheological simplicity found herein, the loss modulus measured at all temperatures for the higher molecular …”

Section: Resultsmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

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Rheology of Star-Branched Polyisobutylene

1999

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“…Graessley et al [68][69][70] and Raju et al (71) observed viscosity enhancement over that of linear polymers of equivalent molecular size in star and comb polyisoprene (PI), polystyrene (PS) and hydrogenated polybutadiene (HPB). In star HPB, considered to be a model of monodisperse branched PE, η o seems to depend exponentially on M b [71][72][73] but not on the number of arms [74]. Moreover, in blends of branched and linear HPB, this enhancement does not depend on the interaction between two branched species, but rather on the interaction of a branched chain with other entangled chains [75,76].…”

Section: Model Polymersmentioning

confidence: 99%

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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LLDPE/LDPE blends. I. Rheological, thermal, and mechanical properties

Yamaguchi

Abe

1999

J. Appl. Polym. Sci.

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Structure and mechanical properties were studied for the binary blends of a linear low density polyethylene (LLDPE) (ethylene-1-hexene copolymer; density ϭ 900 kg m Ϫ3 ) with narrow short chain branching distribution and a low density polyethylene (LDPE) which is characterized by the long chain branches. It was found by the rheological measurements that the LLDPE and the LDPE are miscible in the molten state. The steady-state rheological properties of the blends can be predicted using oscillatory shear moduli. Furthermore, the crystallization temperature of LDPE is higher than that of the LLDPE and is found to act as a nucleating agent for the crystallization of the LLDPE. Consequently, the melting temperature, degree of crystallinity, and hardness of the blend increase rapidly with increases in the LDPE content in the blend, even though the amount of the LDPE in the blend is small.

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Thermorheological effects of long-chain branching in entangled polymer melts

Cited by 136 publications

References 14 publications

Rheology of Star-Branched Polyisobutylene

Rheology of Star-Branched Polyisobutylene

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

LLDPE/LDPE blends. I. Rheological, thermal, and mechanical properties

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