Role of polydispersity in the rheology of a branched polymer

自土井和爱德华兹提出的基于“管中分子”概念的缠结聚合物模型问世以来，我们对已知分子结构的熔融聚合物的流变行为进行定量预测的能力一直在稳步发展。Doi-Edward理论最初是为线性、单分散聚合物开发的，现在已被详细阐述以处理多分散线性聚合物和单分散支化体系。在对具有有限多分散度的支化体系进行建模方面也取得了一些进展。使用这些平均场分子理论来描述具有工业重要性的聚合物的最后障碍是缺乏每个分子具有至少两个分支点的广泛多分散支化聚合物的可靠模型。R. G.密歇根大学的Larson已经开发了解决该问题的分层方法，现在提出将该模型结合到能够预测在支链长度上具有多分散性的支化聚合物的流变行为的算法中。预测结果将与精确已知的具有分支结构和多分散性的样品的数据进行比较。接下来，将对样品进行准确的流变学表征，将数据与模型的预测进行比较，并解决任何明显的缺陷。该项目的成功完成将为聚合物科学家以及希望为特定应用开发新聚合物结构的公司提供感兴趣的信息。这也将是有趣的，研究如何模型可能被用来推断分子结构的流变学数据。

Since the advent of models for entangled polymers based on the concept of a "molecule in a tube", pioneered by Doi and Edwards, there has been a steady advance in our ability to make quantitative predictions of the rheological behavior of molten polymers of known molecular structure. Originally developed for linear, monodisperse polymers, the Doi-Edward theory has been elaborated to deal with polydisperse linear polymers and monodisperse, branched systems. There has also been some progress in the modeling of branched systems with a limited degree of polydispersity. A final barrier to the use of these mean-field molecular theories to describe polymers of industrial importance is the lack of a reliable model for broadly polydisperse branched polymers having at least two branch points per molecule. Prof. R. G. Larson of the University of Michigan has developed a hierarchical approach to this problem, and it is now proposed to incorporate this model into an algorithm capable of predicting the rheological behavior of branched polymer having polydispersity in the lengths of the branches. The predictions will be compared with data for samples having branching structures and polydispersities that are precisely known. Next, an accurate rheological characterization of the samples will be carried out, the data will be compared with the predictions of the model, and any deficiencies that become apparent will be addressed. The successful completion of the project will provide information of interest to polymer scientists as well as companies wishing to develop new polymer structures for specific applications. It will also be of interest to examine how the model might be used to infer molecular structure from rheological data.