Annealing of the delta form of syndiotactic polystyrene

Effect of Compressed CO2 on Phase Transitions and Polymorphism in Syndiotactic Polystyrene

“…9,13,14,[23][24][25] Consequently, as seen in Figure 8, the sample treated at 210°C and 57 atm gives a pattern typical of the R form. However, there is still a peak at 2θ ) 28.2°, reflecting the presence of a small amount of the γ form.…”

“…On heating, the δ form transforms to the helical mesophase around 90°C and then to the γ form around 120°C, which then transforms to the R form around 190°C. 9,13,[23][24][25] Under a tensile force of about 14 MPa, the transition from γ to R occurs at a much reduced temperature of 130°C. 26 There is also one report on the direct transition from δ to form brought about by rapidly heating the δ form to 160°C.…”

“…9 The T 4 -based mesophase can directly transform to R form on thermal annealing in the range 120-220°C, 20 whereas the T 2 G 2 -based mesophase first transforms to the γ form before giving the R form. 13,14 All these solidsolid transitions are irreversible due to the lower energy state of the T 4 conformation. A schematic representation of the main features of the polymorphism in sPS is given in Figure 1; a more detailed representation is reported elsewhere.…”

“…8 The latter form can also be obtained by rapid cooling from the melt state 8 or on heating the helical mesomorphic, δ,orγform. 9,13,14 The form can be obtained by slow cooling from the melt or by casting from a solution in o-dichlorobenzene at elevated temperatures. 15 Depending on the solvent type, crystal form δ or γ is obtained when amorphous sPS is immersed in liquid solvent and then dried under vacuum or directly exposed to solvent vapor.…”

“…[16][17][18] Generally, the δ form contains solvent molecules entrapped in the crystal structure whereas the γ form is free of solvent. 7,19 The mesophase with the helical conformation is obtained by removing the solvent molecules from the δ-form, 13,14 and the mesophase with the zigzag conformation is obtained by annealing 20 or stretching 21 amorphous sPS above its T g .…”