Crystallization of polyethylene from <i>o</i>‐xylene

Wunderlich, Bernhard; James, Edward; Shu, Tsao-Wen

doi:10.1002/pol.1964.100020626

Cited by 10 publications

(7 citation statements)

References 17 publications

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“…Below 80°C the angle of the crystal apex becomes increasingly sharpened with decreasing temperature, leading to a sharpened-apex lozenge at 75°C. At even lower temperature 35 trend was further confirmed by the observations of Kloos et al that truncated, faceted, and sharpened-apex lozenges were formed at 82, 75, and 45°C, respectively. 38 The transition from faceted habits to sharpened-apex lozenges and then to dendrites indicates a transition of underlying mechanism from nucleation-controlled to diffusion-limited growth.…”

Section: A Morphologysupporting

confidence: 83%

“…If shifting the thick line toward left, all morphologies along the thin lines are similar, implying that morphologies are functions of not only temperature but also concentration. This finding is not surprising because of the following experimental observations: hedgehog dendrites can be formed by either decreasing temperature 35 or increasing concentration; 36 and the axial ratio of lenticular crystals increases with either temperature or concentration. 43 Another feature in Fig.…”

Section: A Morphologymentioning

confidence: 52%

“…The study of Wunderlich et al 35 showed that polyethylene grows from dilute o-xylene in the form of faceted lozengelike crystals at 84°C ͓Fig. 2͑2͔͒.…”

Section: A Morphologymentioning

confidence: 99%

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Monte Carlo simulations of single crystals from polymer solutions

Zhang

Muthukumar

2007

The Journal of Chemical Physics

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A novel "anisotropic aggregation" model is proposed to simulate nucleation and growth of polymer single crystals as functions of temperature and polymer concentration in dilute solutions. Prefolded chains in a dilute solution are assumed to aggregate at a seed nucleus with an anisotropic interaction by a reversible adsorption/desorption mechanism, with temperature, concentration, and seed size being the control variables. The Monte Carlo results of this model resolve the long-standing dilemma regarding the kinetic and thermal roughenings, by producing a rough-flat-rough transition in the crystal morphology with increasing temperature. It is found that the crystal growth rate varies nonlinearly with temperature and concentration without any marked transitions among any regimes of polymer crystallization kinetics. The induction time increases with decreasing the seed nucleus size, increasing temperature, or decreasing concentration. The apparent critical nucleus size is found to increase exponentially with increasing temperature or decreasing concentration, leading to a critical nucleus diagram composed in the temperature-concentration plane with three regions of different nucleation barriers: no growth, nucleation and growth, and spontaneous growth. Melting temperatures as functions of the crystal size, heating rate, and concentration are also reported. The present model, falling in the same category of small molecular crystallization with anisotropic interactions, captures most of the phenomenology of polymer crystallization in dilute solutions.

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Section: A Morphologysupporting

confidence: 83%

Section: A Morphologymentioning

confidence: 52%

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Monte Carlo simulations of single crystals from polymer solutions

Zhang

Muthukumar

2007

The Journal of Chemical Physics

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“…The crystallization of long polymer chains induces drastic structural changes from random coils in the melt and solution states to folded polymer chains in thin crystalline layers with thicknesses of 5–20 nm. − Under relatively low supercooling, the crystal habits of single crystals reflect the symmetry of the crystal unit cell. For example, trigonally packed isotactic -poly(styrene) ( i PS) ,, and isotactic -poly(1-butene)( i PB1) form I , adopt hexagonal single crystals, whereas the orthorhombic form of polyethylene (PE) − and poly( l -lactic acid) (PLLA) α crystals , form lozenge-shaped structures. Tetragonally packed i PB1 form II and isotactic -poly(4-methyl-1-pentene) form III adopt square single crystals.…”

Section: Introductionmentioning

confidence: 99%

“…Tetragonally packed i PB1 form II and isotactic -poly(4-methyl-1-pentene) form III adopt square single crystals. Under large supercooling, the crystal habits commonly show dendritic ,,, or circular ,, morphologies, which have been widely accepted as a kinetics effect . The open questions regarding solution-grown crystals are (i) how longer polymer chains are embedded and (ii) how kinetics influence chain trajectory in single crystals.…”

Section: Introductionmentioning

confidence: 99%

Solid-State NMR Study of the Chain Trajectory and Crystallization Mechanism of Poly(l-lactic acid) in Dilute Solution

et al. 2017

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The nucleation and growth mechanisms of semicrystalline polymers are a controversial topic in polymer science. In this work, we investigate the chain-folding pattern, packing structure, and crystal habits of poly(l-lactic acid) (PLLA) with a relatively low molecular weight, ⟨M w⟩ = 46K g/mol, and PDI = 1.4 in single crystals formed from dilute amyl acetate (AA) solution (0.05 or 0.005 wt %) at a crystallization temperature (T c) of 90, 50, or ∼0 °C. The crystal habits drastically changed from a facet lozenge shape at T c = 90 °C to dendrites at ∼0 °C, whereas the chains adopt a thermodynamically stable α packing structure at both 90 and 0 °C. Comparing the experimental and simulated 13C–13C double quantum (DQ) buildup curves of 13C-labeled PLLA chains in crystals blended with nonlabeled chains at a mixing ratio of 1:9 indicates that the PLLA chains fold adjacently in multiple rows when the T c ranges from 90 to ∼0 °C. The results at different length scales suggest that (i) a majority of the chains self-fold in dilute solution and form baby nuclei (intramolecular nucleation) and (ii) the intermolecular aggregation process (secondary nucleation), which is dominated by kinetics, results in morphological differences.

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Structure of Polycrystalline Aggregates

Crist

2013

Handbook of Polymer Crystallization

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Crystallization of polyethylene from o‐xylene

Cited by 10 publications

References 17 publications

Monte Carlo simulations of single crystals from polymer solutions

Monte Carlo simulations of single crystals from polymer solutions

Solid-State NMR Study of the Chain Trajectory and Crystallization Mechanism of Poly(l-lactic acid) in Dilute Solution

Structure of Polycrystalline Aggregates

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