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Morphological effects on thermal transitions in immiscible polymer blends.

机译：不混溶的聚合物共混物对热转变的形态学影响。

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Polymer blend morphology and the interaction between component domains is a critical feature of immiscible blends that strongly influences physical properties. Lacking formal chemical bonding between the components, immiscible blends depend completely on the morphology and mechanical phase interaction developed through melt blending to achieve desirable properties. Even in the absence of chemical bonding, these mechanical interactions can alter the phase transitions of the blend components in significant and important ways. The primary objective of this thesis was to study the degree to which shifts in glass transitions and crystallization occur in selected binary blends and to deduce the mechanisms for these effects and their influence on mechanical properties.; In blends of polystyrene and polypropylene prepared by melt processing the polystyrene Tg revealed a sharp increase at high polypropylene content in the blend, an unexpected result because an invariant glass transition is the primary indicator of blend immiscibility. This novel and unexpected effect was confirmed in other polyolefin-containing blends melt processed in various ways. The variation in glass transition is attributed to the polymer domain interactions resulting from the different morphologies of various blend compositions and qualitative structural models are proposed based on physical interactions between the components. A size-dependent crystallization mechanism was observed in the semi-crystalline polymers in all the blends pairs.; Polycarbonate/polyethylene blends were prepared to alter the relationship between Tc of the semi-crystalline polymer and Tg of the amorphous polymer. Results show that the variation in amorphous component Tg with composition depends strongly on the physical state of the semi-crystalline domains.; Overall, the morphology of the immiscible polymer blends represents a composite structure in which three main effects have been identified in this work that influence the phase transition behaviors of the components: the resolved mechanical stresses that arise from differential contraction during cooling; the spatial pinning of domain structures, particularly in micro-dispersed blends; and the inter-diffusion of mobile modifying constituents that may be present in certain polymers but not formally bonded to the backbone. These effects are important to the evolving scientific understanding of polymer blend structures and are also critical to the fabrication of commercially important materials.
机译：聚合物共混物的形态和组分域之间的相互作用是不可混溶共混物的一个关键特征，它会严重影响物理性能。由于组分之间缺乏正式的化学键合，因此不混溶的共混物完全取决于通过熔融共混获得所需性能的形态和机械相相互作用。即使没有化学键合，这些机械相互作用也可以显着和重要的方式改变共混物组分的相变。本论文的主要目的是研究在选定的二元共混物中玻璃化转变和结晶发生的程度，并推论这些效应的机理及其对机械性能的影响。在通过熔融加工制备的聚苯乙烯和聚丙烯的共混物中，聚苯乙烯Tg在共混物中的高聚丙烯含量下显示出急剧增加，这是出乎意料的结果，因为不变的玻璃化转变是共混物不混溶的主要指标。在以各种方式熔融加工的其他含聚烯烃的共混物中，证实了这种新颖和出乎意料的效果。玻璃化转变的变化归因于各种共混物组成的不同形态所导致的聚合物域相互作用，并基于组分之间的物理相互作用提出了定性结构模型。在所有共混物对中的半结晶聚合物中都观察到了尺寸依赖性的结晶机理。制备聚碳酸酯/聚乙烯共混物以改变半结晶聚合物的Tc与无定形聚合物的Tg之间的关系。结果表明，非晶态组分Tg随组成的变化在很大程度上取决于半晶域的物理状态。总的来说，不混溶的聚合物共混物的形态代表了一种复合结构，在该复合结构中，已在这项工作中确定了三个主要影响因素，这些主要影响因素是各组分的相变行为。畴结构的空间固定，特别是在微分散共混物中；以及某些聚合物中可能存在但未正式键合到主链上的移动改性成分之间的相互扩散。这些效应对于不断发展的对聚合物共混物结构的科学理解至关重要，对于制造具有商业意义的材料也至关重要。

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