Analytic Rheology of Long-Chain-Branched Polymers

新催化剂（包括顺丁烯）的开发使得广泛的新商业聚合物成为可能，包括具有受控水平的长链支化的聚合物。 现有的分析方法对长链支化的存在不够敏感，无法检测商业熔体中经常存在的非常低的支化水平。 然而，这种低支化水平对聚合物加工具有很大的影响，甚至在每100，000个主链碳原子小于1个长链分支的水平下。 流变学已经发展成为一种高灵敏度的分析工具，用于测定商业线性聚合物的分子量分布。 PI将使用流变学来推断商业聚乙烯聚合物的长链支化（LCB）特性。 最近的理论结合了爬行的影响，连续路径的波动，和约束释放到一个统一的理论松弛的聚合物的任意分支组成。 该理论已成功地预测了模型聚丁二烯的线性粘弹性，成功地预测了模型聚丁二烯线性、星星和H聚合物以及线性和星星与线性的双分散和多分散混合物的线性粘弹性。 然而，该理论是不太成功的更复杂的熔体，在很大程度上是因为不确定性的条件下，约束的释放应被认为是一个“管重组”与“管膨胀”的过程。 这里提出的下一个阶段是扩展这些理论思想，并通过获得更复杂的线性、星星和梳形聚丁二烯混合物的实验数据来测试它们，这些混合物旨在模拟商业熔体。 然后，这种方法将被用于氢化聚丁二烯，其化学性质与聚乙烯相同，但可以制成理想的，几乎单分散的形式。这项工作将开始的任务，推导出支化结构的商业聚乙烯从他们的流变。 在这个过程中，我们期望获得更深入和更彻底的基本理解的松弛过程中的聚合物。

The development of new catalysts, including metallocenes, has made possible a wide range of new commercial polymers, including polymers with controlled levels of long-chain branching. Existing analytic methods are not sufficiently sensitive the presence of long-chain branching to detect the very low branching levels that are often present in commercial melts. Yet such low branching levels have large effects on polymer processing, even at levels of less than 1 long-chain branch per 100,000 backbone carbon atoms. Rheology has already been developed as a highly sensitive analytic tool for determination of molecular weight distributions in commercial linear polymers. The PI will use rheology to infer the long-chain branching (LCB) characteristics of commercial polyethylene polymers. Recent theory combines the effects of reptation, primitive-path fluctuations, and constraint release into a unified theory of relaxation of polymers of arbitrary branch composition. The theory has successfully predicted the linear viscoelastic properties of model polybutadiene successfully predicted the linear viscoelastic properties of model polybutadiene linear, star, and H polymers, as well as bidisperse and polydisperse mixtures of linears and of stars with linears. However, the theory is less successful for more complex melts, in large part because of uncertainties about the conditions about the conditions under which constraint release should be thought of as a "tube reorganization" vs. "tube dilation" process. The next stage, proposed here, is to extend these theoretical ideas and test them by obtaining experimental data on more complex mixtures of linear, star, and comb polybutadienes designed to mimic commercial melts. Then, this approach will be carried over to hydrogenated polybutadienes, which are chemically identical to polyethylene, but can be made in ideal, nearly monodisperse form.%%%This work will begin the task of deducing the branching structure of commercial polyethylenes from their rheology. In the process, we expect to acquire a much deeper and more thorough fundamental understanding of relaxation processes in polymers.