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

关于具有多个支化点的缠绕聚合物熔体中的复杂支化结构的松弛，例如H-或梳状支化聚合物，或者具有不同长度的支化的聚合物，例如不对称星形和不对称H聚合物，或者超支化聚合物(即具有支化-支化拓扑结构)，人们的理解仍然不完整。为了解决这些在科学上和在商业聚合物制造中的应用都很重要的问题，我们正在执行以下任务的组合：1.合成具有相同或不同长度支化的高质量模型支化聚合物，这些支化聚合物经过精心设计以检验物理理论。2.仔细表征这些聚合物的相对分子质量和支化性能。3.在较宽的频率范围内测量线性流变性。4.将测量的粘弹性性质与各种不同的拟议理论的预测值进行了比较。我们计划通过一个合作框架来完成这些任务，合作伙伴Jimmy Mays将使用一种新的路线来合成1)不对称H聚合物；2)不对称星形聚合物，基于核心星形聚合物，其每个分支终止于两个不等长的分支；以及3)带有四官能团分支点的梳子。这些聚合物将通过凝胶渗透色谱和TGIC进行仔细的表征，并通过流变学测量进行研究，包括借助McGill大学合作者John Dealy教授的实验室提供的仪器和方法进行仔细的长期蠕变流变仪研究。现有的用于预测测量的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。非技术摘要：为了形成用于包装的高级塑料纤维或薄塑料板，熔融的塑料以极高的速度被拉伸或拉伸。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，以及它们如何逃脱这些纠缠。分支成多条长链的聚合物对工业特别有用，因为它们充当网状物，加强塑料，使其在吹塑成型时不会撕裂或破裂。拉森？S团队已经发现，在一百万个分支点中只有一个分支点的变化可以显著影响熔体的性质，这与其作为熔体的强度有关。这是因为支化聚合物与其他支化聚合物缠绕得非常好。为了摆脱这些纠缠，它们必须通过向分支点卷曲树枝来重新配置，就像胡迪尼为了躲避直筒夹克而使肩膀脱臼一样。因此，缠结是长期存在的，使塑料更容易成形。拉尔森？S团队正在化学合成特殊的支化聚合物，这种聚合物在确定支化聚合物如何实现其胡迪尼？以及如何对其进行优化以获得更高的性能。他们对聚合物脱离缠绕的速度的测量提供了陶氏化学公司和其他塑料制造公司的合作者非常感兴趣的知识。这项研究与田纳西大学、麦吉尔大学、利兹大学和陶氏化学公司的合作者进行了高度跨学科和国际化的研究。

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.