Dynamics of Model Long-Chain Branched Polymers

9816105Archer仅在美国，每个分子具有多个长侧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，但将它们成型为有用物品的最佳程序却很少显而易见。 复杂性来自于对侧支化长度如何影响聚烯烃流动性能以及流动性能如何反过来影响聚合物加工性缺乏基本理解。 因此，即使两种聚合物从标准剪切流变学测试中看起来相似，在真实的过程中也可以表现得非常不同。 拟议研究的目标是双重的。 首先，确定长链支化对具有多个缠结支链的柔性聚合物的松弛动力学的基本影响。 第二，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往往非常不同。 具体而言，支化的影响（例如，每个聚合物链的数量，长度和分支沿着链轮廓的分布）上的非线性剪切和拉伸流动性能的模型多臂聚合物将被解决。 这项研究将结合联合收割机聚合物的合成，纯化和表征程序，非线性剪切和拉伸流动流变仪，以及一些新的流动双折射测量，为聚合物的动力学提供新的见解。这项研究的结果将有助于指导新兴的多臂聚合物动力学理论，也应该有助于激励本构方程能够描述支化聚合物的行为在各种伸长率和聚合物加工中常见的混合流。

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.