链解缠结聚对苯二甲酸乙二酯的结晶行为研究

采用冷冻萃取聚对苯二甲酸乙二酯(PET)溶液(0.1～10g/dL7种不同浓度,3种不同性能溶剂)的方法制备了解缠结PET试样.与链相互穿透且缠结的熔体骤冷试样相比,解缠结PET试样的结晶能力明显增强,且随着制样溶液浓度的降低,链间解缠结程度增加,PET的结晶能力逐渐增强,有序结构含量明显增加,但是如果制样溶液浓度太低,溶液中链间距离太大,则又不利于萃取过程中链间的有序堆砌而结晶.采用接触浓度c*附近的溶液,既可确保链间的有效解缠结又有利于链间的有序堆砌而结晶.PET的结晶能力甚至还受制样所用溶剂性能的影响,这是因为溶剂性能影响了溶液中链间的相互作用以及链的解缠结程度.

CRYSTALLIZATION BEHAVIOR OF CHAIN\|DISENTANGLED POLY(ETHYLENE TEREPHTHALATE)

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.