Lamellar Thickness Dependence of Crystal Modification Selection in the Syndiotactic Polystyrene γ-to-α/β Phase Transition Process

Abstract

The syndiotactic polystyrene (sPS) γ-to-α/β phase transition was investigated using temperature-dependent synchrotron wide-angle X-ray diffraction (WAXD) and smallangle X-ray scattering (SAXS) measurement. The sPS γ form samples, which were obtained from acetone solvent induced crystallization followed by annealing at various temperatures (T a ), exhibited a regular manner on the selection of the α or β crystal modification during the phase transition process. As the T a was increased from 25 to 150 °C, the weight fraction of β form in bulk sPS decreased from 55% to 0%, but that of the α form increased from 45% to 100%. In other words, the α form became the dominating crystalline modification at higher T a . The lamellar thickness (d c ) of the γ form at the initial state (before heating) ranged from 4.4 to 5.8 nm, and the weight crystallinity (X c ) was between 0.52 and 0.64. However, the d c values of the γ form at the final state (before γ-to-α/β phase transition) were very close for the samples pretreated at different T a s, which were in the range 7.0−7.4 nm. Therefore, the most plausible interpretation for the crystal modification selection during the γ-toα/β phase transition was that the nucleation of β form was suppressed totally in the γ form with higher initial d c value (>5.8 nm). With the elevated T a and increase of initial d c , the promoted nucleation of α form in the γ form resulted in the enhanced growth of the α crystalline phase during the γ-to-α/β phase transition. As a result, after the phase transition the crystalline phase in bulk sPS had a gradually increased weight fraction of the α form and turned out to be pure α form when T a was increased from 25 to 150 °C.

The Multilevel Structure of Sulfonated Syndiotactic-Polystyrene Model Polyelectrolyte Membranes Resolved by Extended Q-Range Contrast Variation SANS

“…The scattering was described by combining Equations (1) and (4)–(6), and was superimposed over the scattering from water domains (including the ionomer peak contribution), which is isotropic and is known from the model interpretation of the equatorial data. Assuming a very large lateral extension of the lamellae, R l > 1000 Å—thus out of the size domain that is covered by the SANS window—and a constant thickness of the crystalline lamellae d = 60 Å, which is an average value of what is reported in the literature for sPS crystals with different degrees of crystallinity and subjected to different treatments [63], only two free size parameters were used in the fitting procedure. These were, namely, the thickness of the interlamellar layer, L b , and the dispersion (smearing) parameter, σ D , of the interlamellar spacing, L D = d + L b .…”

The Multilevel Structure of Sulfonated Syndiotactic-Polystyrene Model Polyelectrolyte Membranes Resolved by Extended Q-range Contrast Variation SANS

“…1 and 4-6 and was superimposed over the scattering from water domains (including the ionomer peak contribution), which is isotropic and is known from the model interpretation of the equatorial data. Assuming a very large lateral extension of the lamellae, Rl > 1000 Å , thus out of the size domain that is covered by the SANS window, and a constant thickness of the crystalline lamellae d=60 Å , an average value of what is reported in literature for sPS crystals with different degrees of crystallinity and subjected to different treatments [56], only two free size parameters were used in the fitting procedure, namely the thickness of the inter-lamellar layer, Lb, and the dispersion (smearing) parameter, D, of the inter-lamellar spacing, LD=d+Lb. As discussed in Section 2.3, the SLD of the crystalline and inter-lamellar amorphous layers, lam and inter-lam, were considered free during the fitting procedure while that of the bulk region bulk was considered that of the amorphous sPS (Table 1) All three experimental curves in Figure 6b were modeled simultaneously.…”

Effect of Methoxy Side Groups on the Crystal Structures of a Series of Syndiotactic Polymethoxystyrenes as Studied by the X-ray Diffraction Data Analysis

“…The TTGG form can be obtained by the introduction of the solvent molecules to SPS samples. Besides, the TTGG to TTTT transition occurs during heating, [12][13][14][15][16]33 and the solvent effect is observed for the meta-OMe-SPS. It was found that the TTTT conformation in meta-OMe-SPS prepared from the uniaxially oriented glass sample changed easily to the TTGG form by supplying the organic solvents, forming the solvent/meta-OMe-SPS complexes.…”

“…The SPS exhibits various kinds of crystal modifications depending on the crystallization conditions: α, , β, , γ, δ, , δ e , and so on . The δ form having a TTGG chain conformation is unique in the point to form the complex with solvent molecules. , The heating of the δ form accelerates the evaporation of the solvent molecules to cause the transformation to the empty δ e form and to the γ form. − The further heating at a higher temperature results in the formation of the α and β forms with the all-trans zigzag chain conformations. − In this way, SPS is an interesting polymer to show the transformations among these various modifications. However, this polymer is a little weak in such a point that it consists of only C and H elements.…”