Study of Polyolefin Gel in Organic Solvents IX. Ethylene Sequence Distribution of Ethylene–Propylene Random Copolymer and Crystalline Junction Size in Its Thermoreversible Gel

Moteki, Yoshihiro; Okabe, Masaru; Takahashi, Masato; Matsuda, Hideomi

doi:10.1295/polymj.26.1002

Cited by 4 publications

(1 citation statement)

References 16 publications

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“…The propensity of ethylene−propylene (EP) random copolymers to form thermoreversible gels has been investigated in a variety of organic solvents . A number of studies have been published on EP copolymer gels. − These studies mainly focused on the influence of polymer concentration, molecular mass, ethylene content, and solvent type on the gel-melting temperature. The data obtained from these studies were also used to determine the average size of the crystalline junctions or crystallites formed by crystallizable ethylene sequences along EP copolymer chains.…”

Section: Introductionmentioning

confidence: 99%

Study of Ethylene−Propylene Copolymer Thermoreversible Gels

Daniel¹,

Jao²,

Bauer³

et al. 1999

Macromolecules

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Molecular structure and rheological properties of ethylene−propylene (EP) random copolymer gels formed in toluene and methylcyclohexane, respectively, have been investigated by small-angle neutron scattering (SANS) and oscillatory shear. In both solvents, SANS results are analyzed by considering a fiberlike structure with a radius cross-section distribution function expressed by w(r) ∼ r -λ. It is shown that a small change in the EP copolymer ethylene content has a large effect on the density of network connecting fibers but a much smaller effect on the diameter of the fibers. Oscillatory shear experiments reveal that the relaxation rate of the elastic modulus increases with decreasing EP copolymer ethylene content. This behavior indicates a decrease in the density of connections between fibers with decreasing ethylene content. The relationship between the elastic modulus and polymer concentration has also been examined. The results suggest, in light of the theory developed by Jones and Marques for rigid networks, that the rigidity of fibers formed in the gel is achieved only locally.

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Section: Introductionmentioning

confidence: 99%

Study of Ethylene−Propylene Copolymer Thermoreversible Gels

Daniel¹,

Jao²,

Bauer³

et al. 1999

Macromolecules

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Structural change of xanthan gum association in aqueous solutions

et al. 2000

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Estimation of Crystalline Junction Size of Linear High-Density Polyethylene Gel Comprised of Lamellae

Okabe

Takahashi

1998

Polym J

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ABSTRACT:A method for estimating junction point size in a thermoreversible gel made up of overlapping lamellae with disc-like morphology is proposed by combining the theory of melting temperature depression of copolymer-diluent system with the continuum percolation theory which takes account of the excluded volume of disc. According to our method, junction point size of gel can be estimated from measurement of gel-melting temperature Tmg* at the critical gelation concentration v,.This method was applied to linear high-density polyethylene (LHDPE)Ixylene gel. The junction point size estimated by the present method, i.e., diameter and thickness of disc-like lamellae in a LHDPE gel, was in reasonable agreement with measurement by scanning electron microscopy (SEM) and small-angle X-ray scattering (SAXS) measurement.KEY WORDS Thermoreversible Gel I Polyethylene I Linear High-Density Polyethylene I Continuum Percolation Theory I Junction Size of Lamella I Gel-Melting Temperature IThe sol-gel transition of polyolefin in organic solvents is well known. 1 • 2 Gelation of such crystalline polymer takes place through formation of a network structure with crystalline junctions. In the case of semi-crystalline polymer gels such as random copolymer gel of ethylene and propylene including high content of propylene units (i.e., lots of methyl branchings), fringed micelle-type crystallite was appropriate morphology for the junction point. 3 In the case of highly crystalline polymer gels such as linear high-density polyethylene (LHDPE) gel, junction points were disc-like lamellae with diameter 2r and thickness d, which were three-dimensionally in contact with the others at random array as shown in Figure 1. 4 Recently, site-bond percolation process was applied to gelation, because percolation has close similarity to sol-gel transition. Elastic behavior near the threshold ( C*) of gelatin or casein gel has been investigated 5 • 6 in detail by the bond percolation theory using the relation Eoc[(C-C*)/C*J and critical exponent (t) has been compared with that by the classical theory (i.e., the tree approximation), where E is the elastic modulus and C* is the critical gelation concentration.The site-bond percolation theory was developed basing upon a lattice model. Thus this theory cannot be applied directly to the system where particles such as lamellar or spherulitic crystals behave as junction points or loci, because the theory does not take the excluded volume effect of the particles into consideration. To such a system that contains the particles, application of the continuum percolation theory is more appropriate. In this theory, the excluded volume of the particles is taken into account.This study proposes a new method for estimating the size of lamellar junction in a thermoreversible gel by combining the theory of melting temperature depression of crystallites, formulated by Takahashi and co-workers, 7 with the continuum percolation theory. The present method is applied to the LHDPE/xylene gel in order to 1 To whom all corre...

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Study of Polyolefin Gel in Organic Solvents IX. Ethylene Sequence Distribution of Ethylene–Propylene Random Copolymer and Crystalline Junction Size in Its Thermoreversible Gel

Cited by 4 publications

References 16 publications

Study of Ethylene−Propylene Copolymer Thermoreversible Gels

Study of Ethylene−Propylene Copolymer Thermoreversible Gels

Structural change of xanthan gum association in aqueous solutions

Estimation of Crystalline Junction Size of Linear High-Density Polyethylene Gel Comprised of Lamellae

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