Structure, Crystallization and Melting of Linear, Branched and Copolymerized Polyethylenes as Revealed by Fractionation Methods and DSC

Mathot, Vincent

doi:10.1007/978-1-4615-2992-7_10

Cited by 9 publications

(3 citation statements)

References 61 publications

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“…LLDPE samples M1 and ZN1 used in this study were characterized by TREF (temperature raising elution fractionation) at Exxon. TREF efficiency for LLDPEs characterization is well established by numerous studies. − TREF results confirm that the composition distribution for M1 is typical for metallocene LLDPEs, while composition of ZN1 is representative for Ziegler−Natta systems. M1 contains a variety of subfractions with branching varying from 0.9 to 9 mol %.…”

Section: Methodssupporting

confidence: 64%

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Effect of Branch Distribution on Rheology of LLDPE during Early Stages of Crystallization

Gelfer

Winter

1999

Macromolecules

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For a series of semicrystalline ethylene-R-olefin copolymers (linear low-density polyethylene, LLDPE) produced by metallocene and Ziegler-Natta polymerization, the effect of the copolymer composition on the morphology and the evolution of linear viscoelastic properties during isothermal crystallization was studied. The purpose of this study is to explore the extreme sensitivity of rheology and processing to small variations in molecular detail in LLDPE. The metallocene LLDPE sample contains fewer branched units (2.6 mol % C-6) than the Ziegler-Natta copolymer (3.8 mol % C-6), but still, it melts at lower temperatures than the more branched Ziegler-Natta LLDPE analogue. Physical gelation as observed by rheology occurs over a broader temperature region for the metallocene LLDPE than for the Ziegler-Natta copolymer. DSC and rheological observations indicate that the solidification behavior in LLDPEs is determined more by the composition distribution than by the overall content of branched units. A HDPE was included in the study for comparison purposes.

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Section: Methodssupporting

confidence: 64%

“…Linear low-density polyethylene (LLDPE) from Ziegler−Natta polymerization is highly heterogeneous , with broadly varying branch distributions. LLDPEs can be considered as blends of ethylene copolymers with variable branch contents.…”

Section: Introductionmentioning

confidence: 99%

Effect of Branch Distribution on Rheology of LLDPE during Early Stages of Crystallization

Gelfer

Winter

1999

Macromolecules

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“…The mass crystallinity at room temperature calculated from d = 896 kg m -3 is 32 %, which is slightly higher than the DSC value at room temperature. The difference in cooling rate (10~ min -1 vs. cooling rate during compression moulding) is unlikely to be of influence here [2]. From the SAXS intensity curve for EJ 207 the long period can be calculated, for there is a clear maximum in I(q, T).…”

Section: Co(t)mentioning

confidence: 99%

Dynamic DSC, SAXS and WAXS on homogeneous ethylene-propylene and ethylene-octene copolymers with high comonomer contents

Mathot

Scherrenberg

Pijpers

et al. 1996

Journal of Thermal Analysis

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Ethylene-propylene (EP) and ethylene-octene (EO) copolymers polymerized with the aid of homogeneous vanadium and metallocene catalysts were compared by DSC and time-resolved simultaneous SAXS-WAXS-DSC at scanning rates of 10 and 20~ rain -1 using synchrotron radiation. An EP eopolymer with a density of 896 kg m -3 (about 89 mol% ethylene) after compression moulding gave orthorhombic WAXS reflections. The crystallinity as a function of temperature [wC(7)] calculated from these reflections using the two-phase model was in good agreement with we(T) calculated from Cp measurements using DSC. The Cp measurements also enabled calculation of the baseline Cp and the excess Cp. The SAXS measurements revealed a strong change in the long period in cooling and in heating. The SAXS invariant as a function of temperature showed a maximum in both cooling and heating, which could be explained from the opposing influences of the crystallinity and the electron density difference between the two phases. Two EO eopolymers with densities of about 871 kg m -3 (about 87 mol% ethylene) no longer showed any clear WAXS reflections, although DSC and SAXS measurements showed that these eopolymers did crystallize. The similarity between the results led to the conclusion that the copolymers, though based on different catalyst systems -vanadium and metallocene -did not have strongly different sets of propagation probabilities of chain growth during polymerization. On the basis of a Monte Carlo simulation model of crystallization and morphology, based on detailed knowledge of the mierochain structure, the difference between WAXS on the one hand and DSC and SAXS on the other could be explained as being due to loosely packed cryz,tallized ethylene sequences in clusters. These do cause the density and the electron density of the cluster to increase (which is measurable by SAXS) and the enthalpy to decrease (which is measurable by DSC) but the clusters are too small and/or too imperfect to give constructive interference in the case of WAXS. Of an EP copolymer with an even lower ethylene content (about 69 mol%), the crystallization and melting processes could still be readily measured by DSC and SAXS, which proves that these techniques are eminently suitable for investigating the crystallization and melting behaviour of the copolymers studied.

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Short chain branching distribution and thermal behavior of high density polyethylene

Kim

Park

et al. 1996

J of Applied Polymer Sci

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In this paper, we have studied the effect of short branches on the thermal conductivity of a polyethylene (PE) chain. With a reverse non-equilibrium molecular dynamics method applied, thermal conductivities of the pristine PE chain and the PE-ethyl chain are simulated and compared. It shows that the branch has a positive effect to decrease the thermal conductivity of a PE chain. The thermal conductivity of the PE-ethyl chain decreases with the number density increase of the ethyl branches, until the density becomes larger than about 8 ethyl per 200 segments, where the thermal conductivity saturates to be only about 40% that of a pristine PE chain. Because of different weights, different types of branching chains will cause a different decrease of thermal conductivities, and a heavy branch will leads to a lower thermal conductivity than a light one. This study is expected to provide some fundamental guidance to obtain a polymer with a quite low thermal conductivity.

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Structure, Crystallization and Melting of Linear, Branched and Copolymerized Polyethylenes as Revealed by Fractionation Methods and DSC

Cited by 9 publications

References 61 publications

Effect of Branch Distribution on Rheology of LLDPE during Early Stages of Crystallization

Effect of Branch Distribution on Rheology of LLDPE during Early Stages of Crystallization

Dynamic DSC, SAXS and WAXS on homogeneous ethylene-propylene and ethylene-octene copolymers with high comonomer contents

Short chain branching distribution and thermal behavior of high density polyethylene

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