Study On Crystalline Structure And Dielectric Relaxation Behavior Of Crystalline Polymer

As the amorphous phase plays an important role in the crystalline polymers. Therelaxation behavior of the amorphous phase and the affects of the crystallite phase onthe relaxation behavior of the amorphous phase were investigated in this paper, whichwould be helpful to understand the structure of the amorphous phase and therelationship between the structure and the property of semi-crystalline polymers.The relaxation behavior and the affects of the crystalline phase on the relaxationbehavior of the amorphous phase of PEO, PCL and PLLA were investigated.The dielectric relaxation behavior results of PEO indicate that the influence ofmolecular weight on the secondary relaxation dynamic of PEO is not obvious.However, the primary segmental relaxation dynamics of PEO slows down with theincrease of molecular weight. The crystallinity, the long period and the crystallinelayer thickness of PEO increase with increasing crystallization temperature. Theamorphous phase thickness and the relaxation dynamics of PEO are independent ofcrystallization temperature. The coordination of PEO with LiClO4increases theactivation temperature of the segmental relaxation of PEO, and accelerates thesegmental relaxation dynamics of PEO. During the isothermal crystallization process,the segmental relaxation frequency of PEO keeps constant, but the frequency of thedielectric normal relaxation which relates to the molecular chain relaxation shifts tolower frequency continuously as soon as the temperature cooled down to thecrystallization temperature.The dielectric relaxation spectroscopy results show that the relaxation peaks ofPCL both for pure PCL and PCL/LiClO4complexes shift to higher frequency with thetemperature increasing. The coordination of PCL with LiClO4can enhance thesegmental relaxation dynamics of PCL. The segmental relaxation dynamics of PCLand PCL/LiClO4complexes slow down with increasing crystallization temperature.The dielectric results imply that the relaxation dynamics for pure PCL andPCL/LiClO4complexes decrease continuously during the isothermal crystallizationprocess even at the crystallization induction stage.Both of the frequency and the maximum value of the dielectric loss peak of coldcrystallized and melting crystallized PLLA increase with temperature. With increasingcrystallization temperature, the segmental relaxation dynamic of cold crystallizedPLLA increases, but that of the melting crystallized PLLA slows down. The frequency of PLLA segmental relaxation peak keeps constant during the melting crystallizationprocess, and shifts to lower frequency region continuously during the coldcrystallization process. The crystalline morphology and thermal property of coldcrystallized and melting crystallized PLLA were investigated by using PolarizedOptical Microscope and Differential Scanning Calorimetry techniques. The resultsshowed that the crystalline morphology of cold crystallized and melting crystallizedPLLA differs significantly; however, the thermal property of cold crystallized andmelting crystallized PLLA is almost the same.