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引言高聚物最明显的特点是它的分子量大,一般比小分子化合物的分子量大2到5个数量级。除某些天然聚合物以外,合成聚合物的分子量还有多分散性,这就是说,高聚物试样中的各个高分子之间的聚合度可以不相同,因而试样的分子量有一个分布。高聚物的分子量分布表征试样中不同分子量的分布情况。高聚物 相似文献
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Positron annihilation technique was used to study the micelle behaviors of two SBS triblock copolymers in MEK solvent at different temperatures. Annihilation lifetime τ_3 of ortho-positronium (o-Ps) exhibited an obvious transition from shorter lifetime to longer lifetime with temperature. It was attributed to the change of micelle behavior of SBS copolymer molecules in the solution. Experimental results of sedimentation velocity of ultracentrifuge were also reported. 相似文献
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Solution properties of ladder-like polymer polyphenylsilsesquioxane (PPS) were studied by measurement of intrinsic viscosity, small angle laser light scattering and gel permeation chromatography. It was found that PPS can be modeled with a wormlike continuous cylinder rather than a wormlike coil. A plot of (M~2/[η])~(1/3) vs. M~(1/2) was employed in obtaining the persistence length (2λ)~(-1) and effective hydrodynamic diameter. When MW≤5×10~5, Mark-Houwink equation is adequate in describing the relationship between MW and [η] with αabout unity. This implies that PPS chain is semi-stiff. For GPC experiments, it was shown that universal calibration can be applied in PPS. When molecular weights of PPS are sufficiently high, their molecular weight distributions are often very broad. 相似文献
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Infrared spectra at different temperatures have been studied for fractions ofa liquid crystal tormmg aromatic polyester. The molecular interactions in different phases and their changes duringthe transitions were discussed. Abrupt frequency shift was found for bands of groups both in mesogens and flexible spacers during fusion and isotropization transitions. It may imply that both the mesogens and the flexible spacers are included in the same crystalline phase and give their contributions to the formation of the mesophase. The splitting into doublet of the C—O stretching vibrations was observed for both the aromatic and aliphatic esters and was attributed to the existence of local regions for ester groups different in ordering. The more ordered regions do not disappear completely even in the isotropic liquid phase. 相似文献
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The kinetics of phase transitions including a transition between mesophases were studied for a main-chain thermotropic polyester by means of DSC and depolarizing transmittance techniques. The isothermal process of these transitions was found to be described by the Avrami equation to high conversions. The Avrami exponents n are about 2,4, 5.3 and 2.2 for liquid crystallization, transition between mesophases and crystallization from mesophase respectively. The liquid crystallization from isotropic liquid phase occurs at very low undercoolings with high transformation rate. This behavior is explained as the results of the smaller value of the surface free energy for mesophase than that for crystallites which is evidenced by the very weak temperature dependence of liquid crystallization rate. 相似文献