Excluded Volume Effects on the Orientation and Miscibility of Polymer Blends

几乎所有的分子，包括链状聚合物，在分子或链段水平上的形状都是各向异性的。形状各向异性导致分子间相互作用的各向异性，这导致在对称分子系统中无法观察到的各种合作现象。本研究从理论和实验两个方面研究了单轴拉伸对两种聚合物共混物链段取向和相容性的影响，基于晶格模型的理论预测，排斥体积效应会引起两种聚合物的额外取向，从而增加或降低相容性，聚苯乙烯（PS）/聚乙烯基甲基醚（PVME）和聚苯乙烯（PS）/聚乙烯基甲基醚（PVME）（α-甲基苯乙烯）（PMS）/PVME共混物作为两种柔性聚合物的混合物和EBBA的共混物的模型用红外二向色光谱、激光散射和荧光光谱研究了刚性聚合物/柔性聚合物共混物的结构模型。结果证实了理论预测。特别是，理论和实验普遍表明，当两种组分都是柔性聚合物时，单轴拉伸会导致共混物的不混溶，而单轴拉伸会增强柔性聚合物与刚性（高度不对称）分子的混溶性。这些结果强调了排除体积或熵的重要性相互作用在理解凝聚聚合物系统在变形下的行为方面。

Almost all molecules including chain polymers, are anisotropic in shape at a molecular or segmental level. Shape anisotropy brings about anisotropy in intermolecular interactions, and this causes various co-operative phenomena that cannot be observed in systems of symmetrical molecules. In this research project, we studied theoretically and experimentally the effects of a uniaxial stretch applied to a blend of two polymers on their segmental orientations and miscibility.The theory, based on a lattice model, predicted that the excluded volume effect would induce extra orientations of the two components and either increase or decrease miscibility, depending on the flexibility of the two polymers.Polystirene (PS) /polyvinylmethylether (PVME) and poly (alpha-methylstirene) (PMS) /PVME blends as models for a mixture of two flexible polymers and blends of EBBA (a liquid crystalline rigid molecule) and EPR ( ethylene propylene rubber) as models for a rigid polymer/flexible polymer mixture were studied by infrared dichroism spectroscopy, laser light scattering and fluorescence spectroscopy. The results confirmed the theoretical predictions. In particular, the theory and experiments commonly showed that when the two components are flexible polymers, a uniaxial stretch induces immiscibility of the blend, while it enhances miscibility of a flexible polymer with a rigid (highly asymmetric) molecule.These results stress the importance of excluded-volume or entropic interactions in understanding the behavior of condensed polymer systems under deformation.