CRYSTALLIZATION BEHAVIOR OF CHAIN-DISENTANGLED POLY(ETHYLENE TEREPHTHALATE)

Abstract

The chain-disentangled poly ( ethylene terephthalate) ( PET) samples were prepared by freeze-extracting PET solutions (with concentrations ranged from 0. 1 ～ 10 g /dL,in three types of solvent) and were characterized by Fourier transform infrared spectroscopy ( FTIR),wide-angle X-ray diffraction ( WAXD) and differential scanning calorimetry (DSC). WAXD curves showed that,compared with the chain interpenetrated and entangled PET sample quenched from the melt,chain-disentangled PET samples crystallized more easily. By FTIR spectra,it was found that the level of chain disentanglement and crystallinity increased with decreasing solution concentration. But at high dilution,distances between chains became too great to crystallize during the extracting process. For a solution concentration near the overlap concentration c* ,it's advantageous not only to chain disentanglement,but also to the formation of ordered structure and crystallization. Moreover crystallization behavior of PET was affected by solvent used to prepare samples due to the influences of solvent power on the interactions between coils and then the level of chain disentanglement of these samples. When the concentrations of the solutions are lower than the overlap concentration c* ,the PET samples prepared from the good solvent have more orderly structure due to much fewer interchain entanglements. While the concentrations of the solutions are higher than c* ,samples prepared from the bad solvents have more orderly structure. Furthermore,The DSC and WAXD analysis results indicated the samples prepared by freeze-extracting PET solutions were partially crystallized. It's not full disorder in amorphous regions and was a metastable state between order and diorder. After the same annealling,chain-disentangled PET samples were prone to form ordered structure and had a higher crystallinity compared with the chain-entangled PET samples.