Dynamics of Model Long-Chain Branched Polymers

9816105 Archer每个分子具有多个长侧支链的聚烯烃的年产量仅在美国就接近40亿磅。这些聚合物的合成成本很低，但将它们塑造成有用物品的最佳程序很少是显而易见的。这种复杂性来自于对侧枝长度对聚烯烃流动性能的影响以及流动性能如何反过来影响聚合物加工性缺乏基本了解。因此，即使是两种看起来与标准剪切流变学测试相似的聚合物，在实际工艺中的表现也可能截然不同。拟议研究的目的有两个。首先，确定长链支化对具有多个纠缠侧枝的柔性聚合物弛豫动力学的基本影响。其次，为了更清楚地了解为什么LCB聚合物的流变性能在剪切和拉伸流动中经常有很大的不同。具体地说，支化(例如，每个聚合物链的数量、长度和沿链轮廓的支化分布)对模型多臂聚合物的非线性剪切和拉伸流动特性的影响将被讨论。这项研究将结合聚合物的合成、提纯和表征过程、非线性剪切和拉伸流动流变学以及一些新的流动双折射测量，以提供对聚合物动力学的新见解。这项研究的结果将有助于指导多臂聚合物动力学的新兴理论，并有助于激励能够描述聚合物加工中常见的各种伸长和混合流动中支化聚合物行为的本构方程。

9816105ArcherAnnual production of polyolefins with multiple long side branches per molecule is close to 4 billion pounds in the United States alone. These polymers are inexpensively synthesized, but the best procedures for shaping them into useful articles are rarely obvious. The complexity comes from a lack of fundamental understanding of how long side branches affect polyolefin flow properties, and how flow properties in-turn affect polymer processibility. Thus, even two polymers that appear similar from standard shear rheology tests, can perform quite differently in a real process. The objective of the proposed research is two-fold. First, to determine the fundamental effect of long chain branching on relaxation dynamics of flexible polymers with multiple entangled side branches. Second, to develop a clearer understanding of why LCB polymer rheological properties are often very different in shear and extensional flows. Specifically, the effect of branching (e.g. number per polymer chain, length, and distribution of branches along the chain contour) on nonlinear shear and extensional flow properties of model multi-arm polymers will be addressed. This research will combine polymer synthesis, purification and characterization procedures, nonlinear shear and extensional flow rheometry, and some novel flow birefringence measurements to provide new insights into the dynamics of polymers.%%%Results from this study will help guide emerging theories for multi-arm polymer dynamics and should also help motivate constitutive equations capable of describing branched polymer behavior in various elongation and mixed flows common in polymer processing.