Dynamics of Model Long-Chain Branched Polymers

仅在美国，每个分子具有多个长侧分支的聚烯烃的年产量就接近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方法却很少显而易见。这种复杂性来自于缺乏对长侧分支如何影响聚烯烃流动特性的基本理解，以及流动特性如何反过来影响聚合物的可加工性。因此，即使两种聚合物在标准剪切流变学测试中看起来相似，在实际过程中也可能表现完全不同。拟议研究的目的是双重的。首先，确定长链分支对具有多个侧支纠缠的柔性聚合物弛豫动力学的基本影响。其次，更清楚地了解为什么LCB聚合物在剪切和拉伸流动中流变性能经常非常不同。具体来说，分支（例如，每个聚合物链的数量，长度和分支沿链轮廓的分布）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得到解决。本研究将结合聚合物的合成、纯化和表征过程，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，为聚合物动力学提供新的见解。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，也应该有助于激发能够描述聚合物加工中常见的各种延伸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.