Role of polydispersity in the rheology of a branched polymer

自从Doi和Edwards率先提出了基于“管中分子”概念的纠缠聚合物模型以来，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，现已详细阐述，用于处理多分散线性聚合物和单分散、支化体系。在模拟具有有限多分散度的支化体系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意义的聚合物的最后一个障碍是，对于每个分子至少具有两个支化点的广泛多分散的支化聚合物，缺乏可靠的模型。密歇根大学的R.G.Larson教授发展了一种分层方法来解决这个问题，现在建议将这个模型结合到一个算法中，该算法能够预测支链长度上具有多分散性的支化聚合物的流变行为。这些预测将与具有精确已知的分支结构和多分散性的样本的数据进行比较。下一步，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的聚合物结构的公司提供感兴趣的信息。研究如何使用该模型从流变学数据中推断分子结构也将是很有意义的。

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.