Thin-Film Crystallization of Poly(butylene terephthalate) from the Anisotropic Amorphous State

Temperature-Dependent Triple Crystal Polymorphism of Poly(hexamethylene terephthalate): Long-Range Ordered Mesophase Formation and Crystal Structure–Property Relationships

“…Previous studies have reported that the metastable crystals with extremely small size can be formed in some semicrystalline polymers [ e.g. , isotactic polypropylene ( i PP), polyamide 6 (PA6), polyamide 6,6 (PA6,6), and polyamide 11 (PA11)] under an extremely low T c , which are often called as the mesophase. − These mesophases generally display the broad diffraction peak in WAXS profiles, which is somewhat similar to that of an amorphous phase. − However, DSC results confirmed that these mesophases have high crystallinity comparable to that of the stable crystal phase. , Besides, most of the reported mesophases show the nodular morphology with a smaller size of ∼10 nm. ,, In this study, the δ phase of PHT formed at a low T c is highly crystallized and has relatively high crystallinity (Figure ). Additionally, the δ phase shows a much smaller crystal size than the α and β phases.…”

“…Recent studies have demonstrated that the formation of a mesomorphic phase in terephthalic polyesters is related with the π–π interactions of phenylene groups, which can drive the layer organization of polymer chains in the initial stage of crystallization. Generally, the long-range ordered mesophase can be only acquired after stretching the amorphous phase of terephthalic polyesters such as PET, PPT, and PBT − ,, but not in the quiescent crystallization process. However, PHT can directly crystallize into the mesomorphic δ phase in the quiescent crystallization at a low T c (10–30 °C), without employing any external force.…”

“…Crystallization behaviors and physical properties of terephthalic polyesters have been extensively studied in the past decades. − Previous studies have found that PET and PTT can form a triclinic crystal phase in quiescent crystallization. , However, the chain conformations of CH 2 segments are different in the triclinic crystals of PET ( trans conformation) and PTT ( gauche conformation). , Interestingly, the flexible CH 2 segments in terephthalic polyesters can adopt diversified chain conformations and packing modes as the CH 2 segmental length increases, leading to the different crystal polymorphs. , For example, the medium-chain terephthalic polyesters of PBT and poly(1,5-pentylene terephthalate) (PPeT) with relatively longer CH 2 segments can form two types of crystal polymorphs (α and β phases) with the change of crystallization conditions . They crystallize into the triclinic α phase (containing both trans and gauche conformations in CH 2 segments) in the quiescent melt or cold crystallization but produce the triclinic β phase (with all- trans chain conformation in CH 2 segments) when the α phase is stretched. , …”