TY - JOUR
T1 - Crystallization and morphological features of syndiotactic polystyrene induced from glassy state
AU - Wang, Chi
AU - Lin, Chang Chun
AU - Chu, Chia Ping
N1 - Funding Information:
Financial support by the National Science Council, ROC, under Grant NSC92-2216-E-006-016 is highly appreciated.
PY - 2005/12/12
Y1 - 2005/12/12
N2 - Spherulitic growth rates and microstructure of syndiotactic polystyrene (sPS) cold-crystallized isothermally at various temperatures, Tc (115-240 °C), have been investigated by small-angle light scattering (SALS), optical microscopy and transmission electron microscopy. The derived activation energy for sPS chain mobility at the crystal growing front is 5.4 kJ/mol, which is relatively lower than that of isotactic polystyrene, 6.5 kJ/mol. In addition, the Hv scattering invariant (QHv) measured by SALS on the crystallized sPS samples displays a pronounced minimum at ∼150 °C. Despite a wide range of Tc used, however, the sample crystallinity estimated by Fourier transformation infrared spectroscopy remains unchanged. Prior to crystallization, the correlation length derived from the Vv patterns on the basis of Debye-Bueche model is ca. 1.13 μm regardless of Tc used. Interconnected domains with a width of ca. 1.8±0.5 μm are readily observed in all the crystallized samples under phase contrast microscopy and the phase-separated structure is conserved within sPS spherulites whose diameters are increased with increasing Tc. Based on the above facts, we conclude that the presence of a QHv minimum is ascribed to the resultant events of the two competitive transitions i.e. liquid-solid crystallization, and liquid-liquid demixing resulting from the spinodal decomposition (SD). At lower Tc, the unstable SD transition overwhelms the crystallization. Despite the low chain mobility, the coarsening process driven by the interfacial energies has reached a certain level before crystalline nucleation takes place. At higher Tc, on the other hand, cold crystallization becomes the dominant process due to the enhanced chain mobility, leading to the suppression of ongoing SD coarsening process. At an intermediate Tc range, comparable competition of the phase separation and crystallization prohibits the development of ordered symmetry within spherulites, giving the presence of QHv minimum.
AB - Spherulitic growth rates and microstructure of syndiotactic polystyrene (sPS) cold-crystallized isothermally at various temperatures, Tc (115-240 °C), have been investigated by small-angle light scattering (SALS), optical microscopy and transmission electron microscopy. The derived activation energy for sPS chain mobility at the crystal growing front is 5.4 kJ/mol, which is relatively lower than that of isotactic polystyrene, 6.5 kJ/mol. In addition, the Hv scattering invariant (QHv) measured by SALS on the crystallized sPS samples displays a pronounced minimum at ∼150 °C. Despite a wide range of Tc used, however, the sample crystallinity estimated by Fourier transformation infrared spectroscopy remains unchanged. Prior to crystallization, the correlation length derived from the Vv patterns on the basis of Debye-Bueche model is ca. 1.13 μm regardless of Tc used. Interconnected domains with a width of ca. 1.8±0.5 μm are readily observed in all the crystallized samples under phase contrast microscopy and the phase-separated structure is conserved within sPS spherulites whose diameters are increased with increasing Tc. Based on the above facts, we conclude that the presence of a QHv minimum is ascribed to the resultant events of the two competitive transitions i.e. liquid-solid crystallization, and liquid-liquid demixing resulting from the spinodal decomposition (SD). At lower Tc, the unstable SD transition overwhelms the crystallization. Despite the low chain mobility, the coarsening process driven by the interfacial energies has reached a certain level before crystalline nucleation takes place. At higher Tc, on the other hand, cold crystallization becomes the dominant process due to the enhanced chain mobility, leading to the suppression of ongoing SD coarsening process. At an intermediate Tc range, comparable competition of the phase separation and crystallization prohibits the development of ordered symmetry within spherulites, giving the presence of QHv minimum.
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U2 - 10.1016/j.polymer.2005.10.122
DO - 10.1016/j.polymer.2005.10.122
M3 - Article
AN - SCOPUS:29144483596
VL - 46
SP - 12595
EP - 12606
JO - Polymer
JF - Polymer
SN - 0032-3861
IS - 26
ER -