Thermal‐Induced Crystal/Conformation Transformations in Syndiotactic Polystyrene Films Treated with Different Solvents

Abstract

Solution‐crystallized or solvent‐induced crystal forms and transitions of these crystals upon post‐annealing in solvent‐treated syndiotactic polystyrene (sPS) (films cast from o‐dichlorobenzene or immersed in 1,2‐dichloroethane, respectively) were investigated via wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), and Fourier‐transform infrared (FTIR) spectroscopy. IR spectra in the frequency range of 720–820 cm−1, which is attributed to the CH out‐of‐plane bending of the phenyl ring for neat syndiotactic polystyrene (sPS) and their crystal/solvent complexes (sPS/o‐dichlorobenzene or sPS/1,2‐dichloroethane), were examined for the freshly as‐cast samples in comparison with those having been subjected to post‐annealing by heating to high temperatures. Three bands centered at approximately 779, 769, and 750 cm−1 were observed, the intensity and wavenumber being sensitive to the helical structural changes as a function of the annealing temperature. The band at 769 cm−1, being associated with the intramolecular interactions of the helical chains of the γ‐crystal, was used to confirm the formation of such a phase. The bands at 779 cm−1 and 769 cm−1 disappeared and the sharper band at 750 cm−1 remained upon further annealing above the γ → α′ transition temperature. Thus, by examining the temperature dependency as revealed in the IR spectra, the thermal‐induced phase transition from the δ‐ to an ordered γ‐ and then to an α′‐phase was successfully proven for the sPS/o‐dichlorobenzene complex. Similarly, the other sPS/1,2‐dichloroethane complex underwent transition (from a δ‐ to a disordered γ‐ and then to an α′‐phase) upon the same thermal treatments, except that the intermediate phase is a disordered γ‐phase.FTIR spectra in the frequency ranging from 720 to 820 cm−1 for the δ‐type sPS/o‐dichlorobenzene complex subjected to increase of the temperature by 5 °C steps in the range of 60–245 °C.magnified imageFTIR spectra in the frequency ranging from 720 to 820 cm−1 for the δ‐type sPS/o‐dichlorobenzene complex subjected to increase of the temperature by 5 °C steps in the range of 60–245 °C.

Syndiotactic Polystyrene Nanofibers Obtained from High-Temperature Solution Electrospinning Process

“…sPS is a polymorphic material possessing various crystal modifications, typically the α-form with hexagonal, the β-form with orthorhombic, and both γ- and δ-forms with monoclinic lattices. ,,− Both α- and β-forms are mainly derived from melt crystallization, whereas the γ- and δ-forms are obtained from solvent-induced crystallization. It has been demonstrated that the absorbance peak at 1222 cm −1 is associated with the crystalline phase, with TTTT chain conformation existing in the α- and β-form sPS.…”

“…Also included is the WAXD pattern of the as-spun fiber mats, which merely shows the amorphous halo. After vapor treatment, the diffraction peaks at 2θ = 8.4° and 2θ = 10.0° are the fingerprints of the δ-form sPS, ,, which correspond to the (010) and (2̅10) reflections, respectively. Additional broad diffraction peaks at 2θ = 15.8°, 19.5°, and 23.5° are also discernible.…”

Domino-like thermal phase transition of 2,3-bis(phenylethenyl)-5,6-dicyanopyrazine crystal

“…Theoretically this effect was explained by a model composed of the localized electrons and lattices. The polymorphology and crystal transition of polythiophene and polystylene on the solvent vapor and thermal treatment were also reported [14,15].…”

Poly(ethylene oxide) Crystallization and Gelation in Butanol Studied by In Situ SAXS/WAXD

“…Possible factors were further surveyed. A literature survey indicates that gelation/micellization, − phase separation, − and melting/reorganization − have been reported to interpret exotherms and endotherms in DSC. Except for reorganization, gelation and phase separation can produce turbid − or bluish solutions. − Turbid solutions are due to light scattering because of the formation of micro- and macroscale structures in solution.…”