Antiphase boundaries and ordering defects in syndiotactic polystyrene crystals

Pradère, P.; Thomas, Edwin L.

doi:10.1021/ma00225a013

Cited by 48 publications

(27 citation statements)

References 2 publications

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“…Syndiotactic polystyrene (sPS) has received considerable attention because of its high melting temperature, fast crystallization rate, low dielectric constant and permeability to gases, and good chemical resistance. Structural studies carried out with X‐ray diffraction,1–6 electron diffraction,7, 8 Raman spectroscopy,9, 10 Fourier transform infrared spectroscopy,11–16 and solid‐state nuclear magnetic resonance spectroscopy17–20 have revealed a complex polymorphic behavior. The various crystalline structures differ with respect to the chain conformation and the chain packing within a unit cell.…”

Section: Introductionmentioning

confidence: 99%

Polymorphic behavior in syndiotactic polystyrene/clay nanocomposites

Hsu

2002

J Polym Sci B Polym Phys

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X-ray diffraction methods were used in an investigation of the structural changes in syndiotactic polystyrene (sPS)/clay nanocomposites. sPS/clay was prepared by the intercalation of sPS polymer into layered montmorillonite. Both X-ray diffraction data and transmission electron microscopy micrographs of sPS/clay nanocomposites indicated that most of the swellable silicate layers were exfoliated and randomly dispersed in the sPS matrix. The X-ray diffraction data also showed the presence of polymorphism in the sPS/clay nanocomposites. This polymorphic behavior was strongly dependent on the thermal history of the sPS/clay nanocomposites from the melt and on the content of clay in the sPS/clay nanocomposites. Quenching from the melt induced crystallization into the ␣-crystalline form, and the addition of montmorillonite probably increased heterophase nucleation of the ␣-crystalline form. The effect of the melt crystallization of sPS and sPS/clay nanocomposites at different temperatures on the crystalline phases was also examined.

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Section: Introductionmentioning

confidence: 99%

Polymorphic behavior in syndiotactic polystyrene/clay nanocomposites

Hsu

2002

J Polym Sci B Polym Phys

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“…12, 16 Greis et al 12 have proposed, by electron diffraction on single crystals, a hexagonal unit cell with a ) 26.26 Å, c ) 5.04 Å, in which clusters of three chains are packed according to the space group P6 h2c.…”

Section: Introductionmentioning

confidence: 99%

Crystal Structure of the Trigonal Modification (α Form) of Syndiotactic Polystyrene

1996

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A model of packing for the ordered modification of the R form of syndiotactic polystyrene is suggested, through comparisons between calculated structure factors and experimental intensities observed in the X-ray fiber and electron diffraction patterns. The present analysis improves the preliminary model proposed in previous papers. Trans planar chains are arranged in triplets and packed in the unit cell with axes a ) b ) 26.26 Å, c ) 5.04 Å, according to a statistical rhombohedral symmetry for the disordered R′ modification and a trigonal, quasi-rhombohedral, symmetry for the ordered R′′ modification. The glide plane symmetry of the isolated chain is not maintained in the lattice; we suggest that the space group is R3 h for the statistically disordered R′ modification; it is P3 for the ordered R′′ modification (instead of R3 hc and P3c1 previously proposed). A rotation of nearly 7°of the triplets of chains with respect to the symmetric situation corresponding to the space group P3c1 for the R′′ modification, can account for the observed differences between the intensities of the hkl and khl reflections in the electron diffraction patterns of syndiotactic polystyrene. IntroductionSyndiotactic polystyrene (s-PS) presents a very complex polymorphic behavior. 1-7 Four different crystalline forms have been described so far. Following the nomenclature proposed in ref 3, the crystalline R and forms are characterized by chains in the trans planar conformation, whereas the crystalline γ and δ forms contain chains in the s(2/1)2 helical conformation. The term δ form has been used to indicate different clathrate structures, that is, compounds which include molecules of solvent. The general pattern is complicated by the fact that both R and forms can exist in different modifications having different degrees of structural order, so two limiting disordered modifications (R′ and ′) and two limiting ordered modifications (R′′ and ′′) have been described. [3][4][5] More recently, two mesomorphic modifications of s-PS, containing chains in the trans planar and in the s(2/1)2 helical conformations also have been described. [8][9][10][11] The crystal structures of R 4,12 and 5,13 forms, as well as those of molecular compounds containing molecules of solvent (clathrate structures) 14,15 have been described.As far as the R form is concerned, a detailed description of the morphology of thin films by transmission electron microscopy has been given. 12,16 Greis et al. 12 have proposed, by electron diffraction on single crystals, a hexagonal unit cell with a ) 26.26 Å, c ) 5.04 Å, in which clusters of three chains are packed according to the space group P6 h2c.We have pointed out 3,4 the absence, in the X-ray powder diffraction patterns of the R′ modification, of hkl reflections with -h + k + l * 3n, and their weakness in the powder diffraction patterns of the ordered R′′ modification. On the basis of this observation, we have suggested that alternative models for the molecular packing, characterized by a statistical rhombohedral symmet...

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“…However, the { 30) reflection (0.148 nm) falls in a positive peak of CTF, which results in a reverse contrast at this frequency. This coincidence of a strong CTF at a frequency greater than the resolution limit of the microscope has been repeatedly used to explain the presence of high frequency components in HREM images (e.g., 18,19). The intensity of the six { 30) reflections in Figure 2b are quite strong in comparison to that of other reflections.…”

Section: P Pmentioning

confidence: 90%

Direct imaging of smectic B phase of poly(p‐xylylene)

Zhang¹,

Thomas²

1992

J Polym Sci B Polym Phys

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Single crystals of poly(p‐xylylene) were grown in dilute α‐methylnaphthalene solution and studied by bright‐field and high‐resolution electron microscopy (HREM). The crystallization process was discussed in terms of the dependence of crystal form on crystallization conditions. A 0.15 nm resolution was achieved from high‐resolution images of a frozen liquid crystalline phase. High‐temperature electron diffraction patterns confirmed the existence of the liquid‐crystalline phase in agreement with previous work of Lieser. The HREM images show the molecular packing in the smectic B phase. © 1992 John Wiley & Sons, Inc.

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Antiphase boundaries and ordering defects in syndiotactic polystyrene crystals

Cited by 48 publications

References 2 publications

Polymorphic behavior in syndiotactic polystyrene/clay nanocomposites

Polymorphic behavior in syndiotactic polystyrene/clay nanocomposites

Crystal Structure of the Trigonal Modification (α Form) of Syndiotactic Polystyrene

Direct imaging of smectic B phase of poly(p‐xylylene)

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