It is well established that polymer chain architecture and the distribution of molecular weight play a key role in the flow behavior (processing) and performance of a given polymer material. Long-chain branching (LCB) in particular is known to strongly affect the processability and the material performance of polymers. Often branching is a result of the polymerization process and therefore must be quantified in every sample. We study four commercial high-density polyethylene (HDPE) samples with unknown degrees of polydispersity and LCB. We first use size-exclusion chromatography and linear shear rheology to identify differences in molecular weight, polydispersity, and LCB. Each material is then tested in constant rate and constant stress uniaxial extension using a filament stretching rheometer to quantify extensional viscosity and strain hardening. Correlations between nonlinear extensional rheology, LCB and polydispersity are discussed. We show that the combination of the van Gurp-Palmen plot and extensional rheology allows for a full characterization of the LCB fraction and their effect on extensional rheology.

中文翻译：

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通过线性粘弹性和拉伸流变学表征商业 HDPE 样品中的长链支化

众所周知，聚合物链结构和分子量分布在给定聚合物材料的流动行为（加工）和性能中起着关键作用。众所周知，长链支化 (LCB) 尤其会强烈影响聚合物的可加工性和材料性能。支化通常是聚合过程的结果，因此必须在每个样品中进行量化。我们研究了四种具有未知多分散度和 LCB 程度的商业高密度聚乙烯 (HDPE) 样品。我们首先使用尺寸排阻色谱和线性剪切流变学来确定分子量、多分散性和 LCB 的差异。然后使用长丝拉伸流变仪以恒定速率和恒定应力单轴拉伸测试每种材料，以量化拉伸粘度和应变硬化。讨论了非线性拉伸流变学、LCB 和多分散性之间的相关性。我们表明，van Gurp-Palmen 图和拉伸流变学的组合允许对 LCB 分数及其对拉伸流变学的影响进行全面表征。