Test of the reptation concept: crystal growth rate as a function of molecular weight in polyethylene crystallized from the melt

Hoffman, John D.; Miller, Robert L.

doi:10.1021/ma00188a024

Cited by 187 publications

(128 citation statements)

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“…An increase in crystallinity can lead to an increase in the lamellar thickness which leads to higher storage modulus and stiffiness values [2][3][4] . The effects of molecular weight [5][6][7][8] , molecular weight distribution [9] and tacticity [10][11][12][13] on the crystallization have been investigated by several authors. Cheng et al [6] showed that the linear growth rate of crystals decreases with the increase of molecular weight, but the overall crystallization rate might increase because an increasing number of intramolecular folded-chain nuclei could result in a higher nucleation density [7] .…”

Section: Introductionmentioning

confidence: 99%

Molecular weight and tacticity effect on morphological and mechanical properties of Ziegler–Natta catalyzed isotactic polypropylenes

2015

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SbstractThe morphological and mechanical properties of Ziegler-Natta catalyzed isotactic polypropylenes as influenced by the molecular weight and tacticity was investigated. Polypropylene samples were injection moulded into standard disks with a HAAKE MiniJet II injection moulder at 190 °C and 200 bar for morphological and mechanical tests. The morphological and mechanical properties of specimens were investigated by means of optical microscope (OM), scanning electron microscopy (SEM), microhardness (MH) and dynamic mechanical analysis (DMA). The samples exhibited a typical α-modification spherulite structure of isotactic polypropylenes crystallized from the melt. It was found that the most important factor affecting the structure and properties of these polymers is the isotacticity content. A clear molecular weight effect was also found for samples with low molecular weights. The microhardness and storage modulus values increased as crystallinity did. Accordingly, isotacticity degree is considered as the main parameter affecting the crystallinity of samples.

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Section: Introductionmentioning

confidence: 99%

Molecular weight and tacticity effect on morphological and mechanical properties of Ziegler–Natta catalyzed isotactic polypropylenes

2015

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“…This seemes plausible based on the current concept of polymer crystallization. 7 To understand blend-induced crystallization behavior, we have to clarify kinetic aspects of both crystallization and phase separation, especially the competitive situation of the two rate processes. Kinetic results will be presented in near future.…”

Section: Res Ul Ts and Discussionmentioning

confidence: 99%

Blend-Induced Crystallization of Aramid in Poly(ether-sulfone)/Aramid Blend

Nakata

Kakimoto

Imai

et al. 1990

Polym J

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KEY WORDSPoly(etlier sulfone}-Aramid Blend / Thermal Behavior / Phase Separation / Crystallization / Recently, much attention has been paid to a new family of high performance miscible blends based on aromatic polybenzimidazoles and aromatic polyimides. 1 -4 During the study on the synthesis of multiblock copolymers based on aramids and aromatic polyethers, 5 we discovered a new class of miscible blends of the constituent polymers. In addition, we found that a miscible blend of aramid with a commercially available poly(ether sulfone) (PES) exhibits interesting crystallization behavior: the aramid can crystallize in the miscible blend, while it has been believed to be an amorphous polymer. 6 Moreover, the annealed blend film was found to have high temperature resistance over 400°C. In this communication, we report preliminary results of the thermal analysis of the aramid-PES blend (Scheme I). PES EXPERIMENT AL MaterialsAromatic poly(ether sulfone) ("Victrex PES 300P") was supplied by Imperial Chemical Industries and used as received. Aramid PA44I was prepared by a low temperature solution polycondensation of bis( 4-aminophenyl) ether with isophthaloyl chloride in N-methyl-2-pyrrolidone. The intrinsic viscosities of PES and the aramid in N,N-dimethylacetamide (DMAc) at 30'C were 0.43 and l.60dl g-1 , respectively. Preparation of FilmsPES and PA44I were dissolved individually at a concentration of 15 wt 0 /,, in DMAc. Two solutions were mixed and a clear solution was obtained. The solution was cast on a glass plate. The cast film was dried under vacuum at room temperature for 24 h, then at 100°C for PA44I Scheme I. 80Polym.

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“…In the context of the LH secondary nucleation theory [1][2][3][4][5][6][7][8][9][10], the linear growth rate G of a crystalline aggregate (e.g. spherulite or axialite) for each regime is dependent on the degree of undercooling, DT, and is defined by the following equation:…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…the LH secondary nucleation theory) has been developed and revised repeatedly in subsequent publications essentially by Hoffman and his co-workers [4][5][6][7][8][9][10]. The theory suggests that polymers crystallize in three different regimes, as opposed to the classical theory of secondary nucleation in which the deposition of a single nucleus on a growth face is followed by a rapid lateral spreading process.…”

Section: Introductionmentioning

confidence: 99%

Regime crystallization in syndiotactic polypropylenes: re-evaluation of the literature data

Supaphol

Spruiell

2000

Polymer

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The Lauritzen and Hoffman secondary nucleation theory was applied to linear growth rate data of syndiotactic polypropylene taken from the literature. Observation of the distinctive upward change of slope in plots of log G ϩ U ‫ء‬ /2.303R(T c Ϫ T ∞ ) versus 1/2.303T c (DT)f suggested the regime II 3 III transition at the crystallization temperature of 110ЊC. Based on the input parameters judged to be the most accurate, the ratios of K g,III /K g,II were found to range from 1.7 to 2.2. Regardless of the crystal structure, if the growth is assumed to occur on the bc plane, the lateral surface free energy, s 11.3 erg cm Ϫ2 and the fold surface free energy s e 63.7^7.1 erg cm Ϫ2 were found. The latter leads to the average work of chain folding of q 7:4^0:8 kcal mol Ϫ1 . If the growth is assumed to occur on the ac plane, the fold surface free energy is found to be s e 82.4^9.1 erg cm Ϫ2 , while the lateral surface free energy is the same as previously noted. In this case, the work of chain folding of q 9:6^1:1 kcal mol Ϫ1 is found. These values are applicable to both regimes II and III. A detailed evaluation of the effects of changes in input parameters was also carried out. ᭧

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Test of the reptation concept: crystal growth rate as a function of molecular weight in polyethylene crystallized from the melt

Cited by 187 publications

References 20 publications

Molecular weight and tacticity effect on morphological and mechanical properties of Ziegler–Natta catalyzed isotactic polypropylenes

Molecular weight and tacticity effect on morphological and mechanical properties of Ziegler–Natta catalyzed isotactic polypropylenes

Blend-Induced Crystallization of Aramid in Poly(ether-sulfone)/Aramid Blend

Regime crystallization in syndiotactic polypropylenes: re-evaluation of the literature data

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