Collaborative Research: Synthesis and Theology of Strategically-Designed Long-Chain-Branched Polymers

技术总结：对于具有多个分支点的纠缠聚合物熔体中复杂分支结构的弛豫，如H型或梳状分支聚合物，或具有不同长度分支的聚合物，如不对称星型和不对称H型聚合物，或超支化聚合物（即具有支对支拓扑结构），人们的理解仍然不完整。为了解决这些在科学上和商业聚合物制造应用上都很重要的问题，我们正在执行以下任务的组合：合成具有相同或不同长度分支的高质量模型支化聚合物，精心设计以测试物理理论。2. 仔细表征这些聚合物的分子量和分支性质。3. 在宽频率范围内测量线性流变特性。4. 测量的粘弹性特性与从各种备选提出的理论推导出的预测的比较。我们计划通过一个合作框架来完成这些任务，合作者Jimmy Mays将使用一种新的途径来合成不对称H聚合物；2)不对称星对星聚合物，以一个核心星型聚合物为基础，每个分支末端有两个不等长的分支；3)具有四功能分支点的梳子。这些聚合物将通过凝胶渗透色谱和TGIC进行仔细的表征，并通过流变测量进行研究，包括在麦吉尔大学John Dealy教授实验室的仪器和方法的帮助下进行仔细的长时间蠕变流变测量。现有的预测测量流变学的计算模型将与利兹大学麦克利什小组的Chinmay Das合作使用。非技术概要：为了形成用于包装的高级塑料纤维或薄塑料片，熔融塑料以极高的速度被拉或拉伸。这一过程的性能取决于塑料中的聚合物分子如何相互纠缠，以及它们如何摆脱这些纠缠。分支成多条长链的聚合物在工业上特别有用，因为它们可以作为加强塑料的网，使塑料在定型时不会撕裂或破裂。拉森吗?S团队发现，在一百万个分支点中只要改变一个分支，就能显著影响熔体的特性，从而影响熔体的强度。其原因是支链聚合物与其他支链聚合物纠缠得非常好。为了摆脱这些纠缠，它们必须重新配置，将树枝缠绕到分支点，就像胡迪尼为了逃脱一件直夹克而脱臼了肩膀一样。因此，缠结是长期存在的，使塑料更容易成型。拉森吗?S团队正在化学合成特殊的支化聚合物，这些支化聚合物在确定支化聚合物如何发挥其作用方面非常有用。胡迪尼?行为以及如何优化它以获得高级性能。他们对聚合物脱离缠结速率的测量为陶氏化学公司和其他塑料制造公司的合作者提供了非常感兴趣的知识。田纳西大学、麦吉尔大学、利兹大学和陶氏化学公司都参与了这项高度跨学科和国际合作的研究。

TECHNICAL SUMMARY Understanding remains incomplete regarding the relaxation of complex branching structures in entangled polymer melts with multiple branch points, such as H- or comb-branched polymers, or for polymers with branches of differing lengths, such as asymmetric stars and asymmetric H polymers, or for hyperbranched polymers (i.e., with branch-on-branch topology). To address these issues, which are important both scientifically and for applications to commercial polymer manufacture, we are performing a combination of the following tasks: 1. Synthesis of high-quality model branched polymers with branches of the same or different length that are carefully designed to test physical theories. 2. Careful characterization of the molecular weight and branching properties of these polymers. 3. Measurement of the linear rheological properties over a wide frequency range. 4. Comparison of the measured viscoelastic properties with predictions derived from the various alternative proposed theories. We plan to accomplish these tasks through a collaborative framework, involving a collaborator, Jimmy Mays, who will use a novel route to synthesize 1) asymmetric H polymers; 2) asymmetric star-on-star polymers, based on a core star polymer, each branch of which terminates in two unequal length branches; and 3) combs with tetrafunctional branch points. These polymers will be carefully characterized by gel permeation chromatography and TGIC, and studied through rheological measurements, including careful long-time creep rheometry with the help of instrumentations and methods available in the laboratory of Prof. John Dealy, a collaborator at McGill University. Existing computational models for predicting the measured rheology will be employed in collaboration with Chinmay Das in the McLeish group at Leeds University. NON-TECHNICAL SUMMARY:To form advanced plastic fibers or thin plastic sheets used for packaging, molten plastic is pulled or stretched at extremely high speeds. The performance of this process depends on how the polymer molecules in the plastic are entangled with each other, and how they escape those entanglements. Polymers that branch into multiple long strands are exceptionally useful for industry, since they serve as netting that strengthens the plastic so that it does not rip or bursting when blown into shape. Larson?s team has found that changes to as few one branch in a million branch points can significantly impact the properties of the melt relevant to its strength as a melt. The reason for this is that branched polymers entangle extremely well with other branched polymers. To escape these entanglements, they must reconfigure by reeling branches towards the branch point, like Houdini dislocating his shoulder to escape a straight jacket. Therefore, the entanglements are long-lived and make the plastic easier to shape. Larson?s team is chemically synthesizing special branched polymers that are exceptionally useful in determining how branched polymers manage to perform their ?Houdini? acts and how to optimize this for advanced performance. Their measurements of the rates at which polymers escape entanglements is providing knowledge that is of great interest to collaborators at Dow Chemical Company and other plastics manufacturing companies. The research has been highly interdisciplinary and international with collaborators at the University of Tennessee, McGill University, the University of Leeds, and Dow Chemical Company.