Solution‐grown lamellar crystals of thermally decomposed isotactic polypropylene

Kojima, Morio

doi:10.1002/pol.1967.110050307

Cited by 37 publications

(27 citation statements)

References 5 publications

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“…However, it can be obtained in large quantities by crystallization under high pressure 4-8 sat pressures above 200 MPa iPP crystallizes exclusively in the γ form. 8 The γ form was observed also in samples of a "defective" polypropylene crystallized at atmospheric pressure: either material of very low molecular weight (1000-3000 g/mol) [9][10][11] or PP demonstrating relatively short isotactic sequences due to copolymerization with a small amount of 1-olefine counits [12][13][14] or due to some stereo-and regioirregularities as those obtained in high molecular weight iPP prepared with metalocene catalyst. 15,16 The structure of γ-iPP crystal is unique since its orthorhombic unit cell is formed by bilayers, each composed of parallel helical chains, [5][6][7] while the direction of the chain axis in adjacent bilayers is tilted by ∼80°against each other and ∼40°with respect to the crystallographic b axis, which coincides with the lamella normal.…”

Section: Introductionmentioning

confidence: 88%

Plastic Deformation of the γ Phase Isotactic Polypropylene in Plane−Strain Compression at Elevated Temperatures

Łężak

Bartczak

2007

Macromolecules

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Plastic deformation behavior of iPP homopolymer crystallized exclusively in the γ modification was studied. Samples of γ-iPP were obtained by isothermal crystallization under pressure of 200 MPa. Deformation experiments in plane-strain compression were performed in the temperature range of 55-100°C. Samples of γ-iPP demonstrated higher modulus, higher yield stress, and flow stress, yet slightly lower ultimate strain comparing to R-iPP in the entire range of temperature studied. During plastic deformation numerous fine shear bands, initiated by the interlamellar shear of the amorphous layers, start to develop already at the yield point. Their propagation across the sample causes a limited destruction of γ lamellae oriented perpendicularly to the direction of the band. Destroyed fragments of crystallites partially reconstruct into either mesophase (smectic) domains or crystals of R phase, depending on the deformation temperature. Mesophase is produced upon deformation at room temperature, while at 55°C and above the crystalline R phase is formed instead. With increasing strain shear bands multiply and tilt toward the flow direction. Fragmented lamellae undergo kinking and rotation, which results in formation of a chevron-like lamellar morphology. This leads also to the development of a weak crystalline texture. Both crystalline texture and lamellae orientation emerge due to the same deformation mechanism of interlamellar slip, produced by the shear within interlamellar amorphous layers. The activity of any crystallographic deformation mechanism within the crystalline component was not detected at any temperature. The interlamellar amorphous shear appears to be the primary deformation mechanism of γ-iPP. The other identified mechanisms, i.e., γ-smectic and γ-R transformations, play a supplementary role in the deformation sequence.

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Section: Introductionmentioning

confidence: 88%

Plastic Deformation of the γ Phase Isotactic Polypropylene in Plane−Strain Compression at Elevated Temperatures

Łężak

Bartczak

2007

Macromolecules

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“…[13][14][15][16] Usually, the ␤ phase is observed only in a small amount, although in the presence of selective ␤-nucleating agents, 16 -20 the content of ␤ can be significantly increased. The ␥ modification occurs even more rarely but may form in degraded iPP, 10,21 in low molecular weight iPP, 7,[22][23][24] or under high-pressure conditions. [25][26][27][28] The self-nucleation and recrystallization of iPP synthesized with conventional Ziegler-Natta catalysts for the ␣ and ␤ phases were investigated by Fillon and coworkers 17,29,30 with differential scanning calorimetry (DSC), optical microscopy, and electron microscopy.…”

Section: Introductionmentioning

confidence: 99%

Thermal analysis and X‐ray scattering study of metallocene isotactic polypropylene prepared by partial melting

Dai

Cebe

Capel

2002

J Polym Sci B Polym Phys

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In this study, we examine the effects of heating, nucleation, cooling, and reheating on the thermal properties and structure of metallocene isotactic polypropylene (m-iPP) that had been prepared initially in a standard state containing nearly equal amounts of the crystallographic ␣ and ␥ phases. Heat treatment was achieved through partial melting and annealing by the heating of samples to self-nucleation temperatures (T n 's) that spanned and exceeded the entire range of melting of the standard state, from 122 to 160°C. The relative amounts of ␣ and ␥ crystals are determined from the area under the unique wide-angle X-ray reflections. The lower and upper endotherms are caused by the melting of ␥ and ␣ crystals, respectively. Four distinct regions of T n were identified on the basis of the thermal and structural parameters of m-iPP. In region I, T n is below the peak melting temperature of the ␥ phase. Here, ␥ crystals are annealed and ␣ crystals are barely affected by T n . In region II, T n is above the peak of the lower endotherm but below the peak of the upper endotherm. ␥ crystals melt, and ␣ crystals anneal. In both regions I and II, the portion of the sample melted at T n recrystallizes epitaxially with existing parent ␣ lamellae as the substrates, and the amount of ␣ always exceeds the amount of ␥. In region III, T n is above the peak of the upper endotherm, and all ␥ crystals and some or all ␣ crystals are melted at T n . The number of ␣-crystal nuclei steadily decreases as T n increases, causing systematic depression of the crystallization and melting temperatures seen during cooling. Finally, in region IV, T n exceeds the upper endotherm, and only small self-nuclei or heterogeneous nuclei remain. Recrystallization is now suppressed to lower temperatures. For regions III and IV, a crossover behavior in the relative amounts of ␣ and ␥ is observed during cooling from T n . Because of the effective nucleating ability of ␣ toward ␥, as the temperature drops, the amount of ␥ increases and then exceeds the amount of ␣. With subsequent reheating, the reverse crossover occurs because of the lower melting point of ␥.

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“…Hg in the apparatus described in a previous publication. 6 The materials thus decomposed were examined by infrared analysis. The spectra showed the characteristic absorption bands of isotactic polypropylene including vinylidenic terminal groups, and were similar to spectra previously reported by Natta et a1.…”

Section: Methodsmentioning

confidence: 99%

Morphology of polypropylene crystals. III. Lamellar crystals of thermally decomposed polypropylene

Kojima

1968

J. Polym. Sci. A‐2 Polym. Phys.

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SynopsisMorphology and crystal structure of solution-grown and melt-grown crystals of thermally decomposed polypropylene have been studied by electron microscopy and x-ray diffraction. By crystallization from dilute a-chloronaphthalene or carbitol solutions well-defined lamellar crystals about 100-150 A. in thickness are obtained from fractions (number-average molecular weights 1600-2100) of thermally decomposed crystalline polypropylene. The structure is monoclinic as crystallized from very dilute a-chloronaphthalene or carbitol solutions (0.024.005 wt.-%). However crystals of the triclinic as well as of the monoclinic forms are precipitated from carbitol solutions of higher concentrations (0.05-1 wt.-%). On the other hand, the separated triclinic form has been obtained from the melt,.I n addition, the chain molecules cannot be expected to fold, within the thickness of lamellae in crystals of either modification prepared from the low molecular weight fractions used in this study.Crystals of both modifications have similar morphology.

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Solution‐grown lamellar crystals of thermally decomposed isotactic polypropylene

Cited by 37 publications

References 5 publications

Plastic Deformation of the γ Phase Isotactic Polypropylene in Plane−Strain Compression at Elevated Temperatures

Plastic Deformation of the γ Phase Isotactic Polypropylene in Plane−Strain Compression at Elevated Temperatures

Thermal analysis and X‐ray scattering study of metallocene isotactic polypropylene prepared by partial melting

Morphology of polypropylene crystals. III. Lamellar crystals of thermally decomposed polypropylene

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