Ordering Process of Polymers during the Induction Period of Crystallization Observed by the Simultaneous Thermal Analysis and Molecular Vibration Spectroscopy

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The crystallization mechanism of polymers, especially the ordering process during the induction period of crystallization was investigated by the simultaneous differential scanning calorimeter and Fourie transform infrared spectroscopy (DSC-FTIR). The time resolutions of DSC and FTIR were 1 sec. Phase transition behavior of poly(vinylidene fluoride) (PVDF), syndiotactic polystyrene (sPS), poly(ethylene terephthalate) (PET) and n-alkanes were investigated by DSC-FTIR and DSC-XRD.The conformational ordering from random to trance-gauche proceeded before the positional ordering of α-form for the crystallization of PVDF from the molten state. Similar conformational ordering was observed for sPS and PET during the induction period of crystallization.The crystallization process of PET from the glassy state and the molten state were observed by DSC-XRD and DSC-FTIR. Molecular mechanism of crystallization process was discussed from conformational and structural viewpoint. The stacking of aromatic rings due to π-electron interaction caused the nucleation process. Conformational ordering of aromatic part and ethylene part proceeding individually and positional ordering contributed to crystallization enthalpy. The pre-melt crystallization and secondary crystallization process were occurred by the compensation of dis-orders between conformational ordering of aromatic part and ethylene part.