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都是各向异性的。形状各向异性导致了分子间相互作用的各向异性，这导致了在对称分子体系中不能观察到的各种合作现象。在这个研究项目中，我们从理论和实验上研究了单轴拉伸对两种聚合物共混物的链段取向和相容的影响。基于晶格模型的理论预测，排除体积效应将导致两个组分的额外取向，并增加或减少相容，分别以聚苯乙烯(PS)/聚乙烯基甲基醚(PVME)和聚α-甲基苯乙烯(PMS)/PVME作为两种柔性聚合物混合物的模型，以及EBBA(液晶刚性分子)和EPR(乙丙橡胶)作为刚性聚合物/柔性聚合物混合物的模型，用红外光谱、激光散射和荧光光谱研究了这两种聚合物的柔性。结果证实了理论预测。特别是，理论和实验通常表明，当两个组分都是柔性聚合物时，单轴拉伸导致了共混物的不相容，而它增加了柔性聚合物与刚性(高度不对称)分子的相容性。这些结果强调了排除体积或熵相互作用对于理解凝聚聚合物体系在变形下行为的重要性。

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.