Structure Development during Crystallization of Homogeneous Copolymers of Ethene and 1-Octene:  Time-Resolved Synchrotron X-ray and SALS Measurements

Akpalu, Yvonne A.; Kielhorn, L.; Hsiao, B. S.; Stein, R. S.; Russell, T. P.; Egmond, J van; Muthukumar, Murugappan

doi:10.1021/ma9810114

Cited by 76 publications

(83 citation statements)

References 32 publications

(56 reference statements)

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“…12 It has also been reported that a small amount of chain branches appears to hinder the isothermal thickening process in polyethylene. 25 The argument of isothermal lamellar thickening is also consistent with the decrease in amorphous layer thickness with time [ Figs. 2(a) and (b)].…”

Section: Effect Of Miscible Polymer Diluents On Lamellar Morphologysupporting

confidence: 65%

“…The decrease in L at long times has recently been reported by time-resolved SAXS techniques in many polymers: poly(ethylene terephthalate) (PET), 20,21 poly(aryletheretherketone) (PEEK), 11,22,23 isotatic polypropylene (iPP), 24 and ethylene 1-octene copolymer. 25 This behavior again can be attributed to the secondary crystallization process (after spherulites impinge) through the lamellar stack-insertion mechanism. It is noted that the change in la in the above systems is relatively small during prolonged annealing; we thus believe that the lamellar stack insertion mechanism may be favored at this stage.…”

Section: Effect Of Miscible Polymer Diluents On Lamellar Morphologymentioning

confidence: 95%

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Effect of miscible polymer diluents on the development of lamellar morphology in poly(oxymethylene) blends

Yeh

Hsiao

Chu

et al. 1999

J. Polym. Sci. B Polym. Phys.

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Section: Effect Of Miscible Polymer Diluents On Lamellar Morphologysupporting

confidence: 65%

Section: Effect Of Miscible Polymer Diluents On Lamellar Morphologymentioning

confidence: 95%

Effect of miscible polymer diluents on the development of lamellar morphology in poly(oxymethylene) blends

Yeh

Hsiao

Chu

et al. 1999

J. Polym. Sci. B Polym. Phys.

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“…The crystallinity at the gel point, X c , was found to be about 3% at slow crystallization and slightly higher at increased rate of crystallization (higher undercooling, ∆T). The observations of Schwittay et al 1 were confirmed and, possibly, explained by recent experiments of Akpalu et al 6 who, for a crystallizing polyethylene (PE), found that spherulites reach their full size after very short times of crystallization and at very low crystallinity. This similarity in behavior is quite surprising in view of the very different crystal habit in PE and iPP.…”

Section: Introductionmentioning

confidence: 69%

Polypropylene Crystallization as a Physical Gelation Process

1998

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Early stages of crystallization of polymers may be viewed as physical gelation. This is shown with four commercial isotactic polypropylenes, which have been studied by dynamic mechanical experiments at low degrees of undercooling, ∆T ) 10-26 K, below their nominal melting temperature. The physical gel point is manifested by slow power law dynamics, which expresses itself in a shear relaxation modulus G(t) ) St -n at long times, λ0 < t < λpg, where S is the gel stiffness, n is the relaxation exponent, λ0 is the crossover to short time dynamics (entanglements, glass modes), and λpg is the longest relaxation time, which can be considered to be infinite for our experiments due to the long lifetime of the physical bonds. The time to reach the gel point (gel time tc) decreases exponentially with ∆T, and the critical gel becomes stiffer (smaller n, larger S) with increasing ∆T. The absolute critical crystallinity at the gel point, Xc, was found to be only about 2% or less. This value was determined from published DSC data which, however, needed to be extrapolated to tc, as measured by mechanical spectroscopy. This very low crystallinity suggests that only a few junctions are necessary to form a sample spanning network. The network in this case is "loosely" connected, and the critical gel is soft.

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“…There is considerable experimental evidence [9][10][11][12][13][14][15] for density fluctuations at very early times of crystallization before the full crystallographic features can be detected. What are the molecular origins of structural development in the primordial stage of polymer crystallization?…”

Section: B Nucleation In the Very Early Stagementioning

confidence: 99%