Copolymer crystallization: Approaching equilibrium

Crist, Buckley; Finerman, Terry M.

doi:10.1016/j.polymer.2005.03.124

Cited by 6 publications

(7 citation statements)

References 22 publications

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“…Even though the two‐phase model may underestimate the lamellar thickness because of the possible existence of the transition layer, this value is still very small as compared with the typical lamellar thickness for i‐PP homopolymer (∼100 Å). Some recent studies for random ethylene‐based copolymer system7, 9–11, 29 reported the existence of thin lamellar structure because of the lower melting temperature, which is consistent with our findings. These results are different from Flory's model,30 which prohibits chain folding in random copolymer.…”

Section: Resultssupporting

confidence: 93%

“…Second, the sequence length of the crystallizable component in random copolymer also decreases, which would lead to shorter lamellar thickness. As a result, crystalline in random copolymers always shows a lower melting temperature and broader enthalpy change in differential scanning calorimetry (DSC) measurement as compared with those of homopolymers 7, 9–11. These features make the properties of crystallizable random copolymers very different from homopolymers, and thus provide considerable commercial potential 12, 13…”

Section: Introductionmentioning

confidence: 99%

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Crystallization behavior of isotactic propylene‐1‐hexene random copolymer revealed by time‐resolved SAXS/WAXD techniques

Mao¹,

Zuo²,

Keum³

et al. 2009

J Polym Sci B Polym Phys

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The crystallization behavior of isotactic propylene-1-hexene (PH) random copolymer having 5.7% mole fraction of hexene content was investigated using simultaneous timeresolved small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) techniques. For this copolymer, the hexene component cannot be incorporated into the unit cell structure of isotactic polypropylene (iPP). Only a-phase crystal form of iPP was observed when samples were melt crystallized at temperatures of 40 C, 60 C, 80 C, and 100 C. Comprehensive analysis of SAXS and WAXD profiles indicated that the crystalline morphology is correlated with crystallization temperature. At high temperatures (e.g., 100 C) the dominant morphology is the lamellar structure; while at low temperatures (e.g., 40 C) only highly disordered small crystal blocks can be formed. These morphologies are kinetically controlled. Under a small degree of supercooling (the corresponding iPP crystallization rate is slow), a segmental segregation between iPP and hexene components probably takes place, leading to the formation of iPP lamellar crystals with a higher degree of order. In contrast, under a large degree of supercooling (the corresponding iPP crystallization rate is fast), defective small crystal blocks are favored due to the large thermodynamic driving force and low chain mobility.

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Section: Resultssupporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Crystallization behavior of isotactic propylene‐1‐hexene random copolymer revealed by time‐resolved SAXS/WAXD techniques

Mao¹,

Zuo²,

Keum³

et al. 2009

J Polym Sci B Polym Phys

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“…17 The alternative, and currently more standard, interpretation is that broad and multimodal melting endotherms observed for polyethylene copolymers with narrow copolymer composition distribution (CCD) are due to the intrachain sequence length distribution, and this explanation has continued to be invoked in recent publications. [18][19][20][21][22] This approach is based on the equilibrium theory of Flory 23 and the classical G-T theory. Using this approach, it has been argued that a thicker crystal population arises in a primary crystallization step, during isothermal, bulk crystallization, from the longer ethylene sequences, which create a network structure that constrains shorter sequences to crystallize in a secondary step to form a thinner crystal population.…”

mentioning

confidence: 99%

Crystallization and melting of polyethylene copolymers: Differential scanning calorimetry and atomic force microscopy studies

Mirabella

2006

J Polym Sci B Polym Phys

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ABSTRACT:The HoffmanLauritzen theory of secondary, surface nucleation and growth was primarily relied upon for about 40 years after its introduction in about 1960 to rationalize the crystallization of flexible chain polymers into lamellar crystals. However, in about 1998, Strobl and coworkers introduced a different model for crystallization, based on the stagewise formation of lamellae. Two major components of this model were as follows: (1) the concept of the formation of a mesomorphic melt as a precursor to crystallization and (2) the control of the melting temperature range of lamellar crystals of homogeneous polyolefin copolymers by an inner degree of order or perfection rather than on the crystal thickness. The first concept is in disagreement with the HL theory and the second with the Gibbs-Thomson theory, which associates melting temperature with lamella thickness. In the present study, differential scanning calorimetry and atomic force microscopy were successfully employed to monitor the in situ quiescent crystallization of polyethylene homopolymer and copolymer. In the present study, evidence was not found to support the concept of lamellae with equal thickness melting over a broad temperature range. Some evidence was found that might be interpreted to support the concept of a mesomorphic melt as a precursor to crystallization. At present, the model promoted by Strobl and coworkers appears to be at an uncertain stage at which strong proof or disproof are not available. However, this alternative model has injected a new vitality into the study of crystallization of flexible chain polymers.

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“…The predicted crystallinity difference (with respect to f c ¼ 1) may be attributed to the topology and the eventual kinetic restraint with reference to Flory's equilibrium theory. 16,[61][62][63][64] Therefore, crystallinity may be improved by decreasing the kinetic and topological restraints. By topology, we mean the crystallizable isotactic polypropylene sequence length distribution SLD (due to stereodefects), the density of chain entanglement, and the conguration of the folding lamellae.…”

Section: Melting Behavior and Crystallization Of I-pp: Flory's Equilimentioning

confidence: 99%

Crystallization and melting behavior of i-PP: a perspective from Flory's thermodynamic equilibrium theory and DSC experiment

et al. 2017

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Copolymer crystallization: Approaching equilibrium

Cited by 6 publications

References 22 publications

Crystallization behavior of isotactic propylene‐1‐hexene random copolymer revealed by time‐resolved SAXS/WAXD techniques

Crystallization behavior of isotactic propylene‐1‐hexene random copolymer revealed by time‐resolved SAXS/WAXD techniques

Crystallization and melting of polyethylene copolymers: Differential scanning calorimetry and atomic force microscopy studies

Crystallization and melting behavior of i-PP: a perspective from Flory's thermodynamic equilibrium theory and DSC experiment

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