Analytic Rheology of Polydisperse and Long-chain-branched Polymers

这是密歇根大学和流变学科学公司之间的一项GOALI奖项，由材料研究部和数学与物理科学理事会多学科活动办公室联合支持。最近茂金属催化聚合物的商业化发展极大地增加了分子质量分布（MWD）和长链分支（LCB）分布的分子定制的前景，以获得最佳的聚合物加工特性。然而，进展需要更详细地了解随钻测井和LCB对聚合物流变性能的影响。已经证明，线性流变学数据可以用来推断无支化聚合物的随钻距离。然而，推断LCB的特征要困难得多，并且不能单独使用线性粘弹性数据来完成，因为如果没有额外的信息，LCB就没有独特的线性粘弹性特征，这也不能解释为特殊的分子量分布。幸运的是，最近的理论进展开辟了使用非线性流变数据来量化缠绕熔融体和柔性聚合物浓缩溶液的随钻距离和LCB特性的可能性。为了开发和增强这些新功能，将进行一项实验计划，将流变仪器的最新进展与聚合物合成方法的可用性相结合。该小组将使用一种新的商用拉伸流变仪和无顺应性和修正顺应性的剪切流变仪来研究表征良好的线性聚合物、理想的、单分散的、星形的和“pom- pom”支链聚合物的共混物的随时间的非线性流变特性。非线性数据将与新发展的理论进行详细的比较。努力开发强大的方法来区分线性聚合物和支链聚合物的混合物，仅使用流变学方法将是目标。这种研究具有强大的潜在应用，因为它可以将流变仪变成测定聚合物随钻距离和LCB的分析仪器。此外，这个GOALI研究项目是一个重要的教育工具，因为它将使研究生与一个主要的商业仪器开发商密切接触，并将要求他们全面了解聚合物流变学领域最强大的实验工具和最新的理论思想。＊＊＊

9807262 Larson This is a GOALI award between the University of Michigan and Rheometric Scientific Co.,supported jointly by the Division of Materials Research and the Office of Multidisciplinary Activities of the Directorate for Mathematical and Physical Sciences. Recent commercial development of metallocene-catalyzed polymers greatly increases the prospects for molecular tailoring of molecular weight distribution (MWD) and long-chain branching (LCB) distributions for optimal polymer processing characteristics. However, progress requires a much more detailed understanding of the impact of MWD and LCB on the polymer rheological properties. It has already been shown that linear rheological data can be used to infer the MWD of unbranched polymers. Inferring LCB characteristics, however, is much more difficult, and cannot be done using linear viscoelastic data alone, since without additional information, there is no unique linear viscoelastic signature of LCB which could not also be interpreted as a peculiar molecular weight distribution. Fortunately, recent theoretical advances open up the possibility of using nonlinear rheological data to quantify both the MWD and LCB characteristics of entangled melts and concentrated solutions of flexible polymers. To exploit and enhance these new capabilities, an experimental program that combines recent advances in rheological instrumentation with the availability of polymer synthetic methods will be carried out. The group will use a new commercial extensional rheometer and compliance-free and compliance-corrected shear rheometers to study the time dependent nonlinear rheological properties of well characterized blends of linear polymers, and ideal, monodisperse, star and "pom- pom" branched polymers. The nonlinear data will be compared in detail with newly developed theories. Efforts to develop robust methods for distinguishing mixtures of linear polymers from branched polymers, using rheological methods alone will be targeted. %%% Such research has powerful potential applications, since it could turn rheometers into analytic instruments for determining polymer MWD and LCB. In addition, this GOALI research program is an important educational tool, since it will bring graduate students into close contact with a major commercial instrument developer, and will require of them a thorough knowledge both of the most powerful experimental tools and the most recent theoreticai ideas in the field of polymer rheology. ***