Lamellar morphology and equilibrium melting temperature of syndiotactic polystyrene in β‐crystalline form

Abstract

Lamellar morphology and thickness of syndiotactic polystyrene (sPS) samples melt-crystallized at various temperatures were probed using transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). In addition, the melting temperature and enthalpy of the crystallized samples were characterized with differential scanning calorimetry. Under appropriate thermal treatments, all the samples investigated in this study were crystallized into ␤Ј crystal modification, as revealed by wide-angle X-ray diffraction. From the SAXS intensity profiles, a scattering peak (or shoulder) associated with lamellar features as well as the presence of anomalous scattering at the zero-scattering vector were evidently observed. The peculiar zeroangle scattering was successfully described by the Debye-Bueche model, and subtraction of its contribution from the raw intensity profiles was carried out to deduce the intensity profile merely associated with the lamellar feature. The lamellar thickness obtained from Lorentz-corrected intensity profiles in this manner agrees with that measured from the TEM images, provided that the two-phase model is applied. On the basis of the Gibbs-Thomson equation, the modest estimations of equilibrium melting temperature and the surface free energy of the fold lamellar surface are 292.7 Ϯ 2.7°C and 20.2 Ϯ 2.6 erg/cm 2 , respectively, when lamellar thicknesses measured by TEM are applied.

Crystallization, Melting and Morphology of Syndiotactic/Atactic Polystyrene Blends: Molecular Weight Effects of Atactic Polystyrene

“…In a sPS/aPS blend, the equilibrium melting temperature of the blend ($T'_{\rm m}$ ) will be depressed due to the presence of aPS diluents. As the applicability of the Hoffman‐Weeks (or Gibbs‐Thomson) plot to determine $T'_{\rm m}$ of the blends was expected to be limited under certain circumstances,17,18 theoretical $T'_{\rm m}$ values were estimated in this work. According to Flory‐Huggins theory,19 the $T'_{\rm m}$ of a crystalline polymer in miscible crystalline/amorphous blends is estimated on the basis of the Nishi‐Wang expression,20 as given in Equation (2).…”

“…Previous studies have shown that the respective T for α ‐ and β ‐form sPS is ca. 281 and 291 °C, obtained from linear Hoffman‐Weeks plots 17,18. Based on Equation (2), $T'_{\rm m}$ of the blends can be deduced and plotted in Figure 4 as a function of aPS content after substituting the following parameters: V 1 = 99.0 cm 3 · mol −1 , V 2 = 92.9 cm 3 · mol −1 ,21,22 N 2 = 1 924 and N 1 = 12.5, 40.4 and 962 for aPS(L), aPS(M) and aPS(H), respectively.…”

Synthesis and characterization of sPS/montmorillonite nanocomposites

“…On the other hand, the annealing process favors the formation of crystalline forms within the polymer, as testified by the appearance of secondary peaks (additional information on identification of the characteristic peaks can be found in refs. [21][22][23][24]. Note that the crystalline form corresponding to the peak at 2 ϭ 5.0°-7.5°, which also was present in the neat polymer (but only after the annealing process), was strongly enhanced by the presence of the nanofiller, as the peak was present in the nanocomposite even before the annealing process (and did not seem to depend on the thermal history of the material).…”

Miscibility, thermal properties and polymorphism of syndiotactic polystyrene/poly(styrene-co-α-methyl styrene) blends

“…As pointed out by Alamo et al [39], if the experimental T m is measured at very low levels of crystallinity (where the thickening effect of lamellae is greatly limited), the conventional HW plot is applicable in determining the T 0 m : Therefore, despite the arguments, the HW plot is still commonly used to date. Also, we want to mention that the T 0 m value we determined for pure sPS is close to the value ð292:7^2:7 8CÞ determined based on the TEM results combined with the Gibbs -Thomson equation [40].…”