Constraint Release Dynamics in Entangled Polymers

技术摘要：单分散线性聚合物与单分散“星形”支化聚合物的混合物代表了最简单的聚合物，它暴露了目前对“约束释放”--一个聚合物链的运动对其与其他链的纠缠的影响--的最大缺陷。这个问题将通过以下方式来解决：(1)获得一系列精心合成的星形1，4-聚丁二烯聚合物，然后通过可用的最先进的方法，即温度梯度相互作用层析(TGIC)对其进行彻底表征，(2)配制和测量覆盖一系列约束-释放条件的一组约40种具有星形支链和线形聚合物的混合物的流变性，(3)应用最先进的“管”理论来预测这些混合物和文献中已有的其它此类混合物的流变性，以及(4)通过国际网络进行合作，从而获得新的聚合物材料，利用顺式聚异戊二烯星形/线形共混物的介电松弛数据，并利用“滑链”和分子动力学聚合物模拟的结果来预测这些星形/线型共混物的流变学和介电松弛。非技术概述：聚合物是使用最广泛的合成材料之一；年产量超过3亿吨，用于汽车、医疗用品和设备、食品保鲜包装和许多其他应用。由于廉价而丰富的天然气来源，在美国制造这种聚合物现在越来越有吸引力，从天然气中可以获得聚烯烃等常见聚合物的起始化学品。为了节省所需的数量、加快聚合物成型并降低成本，必须对聚合物的流动性能进行优化。这通常涉及到在聚合物分子中添加控制量的长链支化。然而，支化策略的设计依赖于对聚合物动力学的透彻了解，而目前对一种称为“约束释放”的现象--一种聚合物链的运动对其与其他链的纠缠的影响--缺乏了解而受到限制。这一提议代表了对这一悬而未决的问题的直接攻击，使用了先进的聚合物合成工具和新发现的表征支化的方法，其准确度达到了前所未有的水平。通过与国际团队的合作，将极大地增进理解，国际团队包括世界上最有见识的科学家在问题的各个方面，包括合成(在沙特阿拉伯、韩国和美国)、表征(在韩国和日本)和计算建模(在美国和英国)。这项研究将在支化聚合物中建立最完整的实验工作体系，数据和理论将通过出版、基于网络的访问以及与工业研究人员的直接互动向工业研究人员提供。博士、本科生和高中生将在研究过程中接受培训。

TECHNICAL SUMMARY:Mixtures of a monodisperse linear polymer with a monodisperse "star"-branched polymer represent the simplest polymers that expose the greatest deficiencies in current understanding of "constraint release" -- the effect that motion of one polymer chain has on its entanglements with other chains. This problem will be attacked by (1) obtaining a series of carefully synthesized star 1,4-polybutadiene polymers, which are then thoroughly characterized by the most advanced method available, namely temperature gradient interaction chromatraphy, or TGIC, (2) formulating and measuring the rheology of a set of some 40 mixtures of "star"-branched and linear polymers covering a range of constraint-release conditions, (3) applying the most advanced "tube" theories to predict the rheology of these mixtures and other such mixtures already available in the literature, and (4) collaborating through an international network, thereby accessing new polymer materials, dielectric relaxation data on cis-polyisoprene star/linear mixtures, and accessing results from "slip-link" and molecular dynamics polymer simulations for the prediction of the rheology and dielectric relaxation of these star/linear blends. NON-TECHNICAL SUMMARY:Polymers are among the most widely used synthetic materials; over 300 million tons are produced annually, for use in automobiles, medical supplies and equipment, wrappings for food preservation, and many other applications. The manufacture of such polymers in the United States is now increasingly attractive, due to cheap and abundant sources of natural gas, from which the starting chemicals for common polymers, such as polyolefins, are obtained. To economize on the quantity needed and to speed and cost-reduce the shaping of polymers into products, the flow properties of polymers must be optimized. This often involves the strategic addition of controlled amounts of long-chain branching to the polymer molecules. However, design of branching strategies depends on a thorough knowledge of polymer dynamics, which is currently inhibited by lack of understanding of a phenomenon called "constraint release" -- the effect that motion of one polymer chain has on its entanglements with other chains. This proposal represents a direct attack on this unsolved problem, using advanced tools of polymer synthesis and newly discovered methods of characterization of branching at unprecedented levels of accuracy. Understanding will be greatly enhanced by collaborating with an international team, which includes the most knowledgeable scientists in the world on various aspects of the problem, including synthesis (in Saudi Arabia, Korea, and the U.S.), characterization (in Korea and Japan), and computational modeling (in the U.S. and United Kingdom). The research will create the most complete body of experimental work on "constraint release" in branched polymers, and the data and theories will be made available to industrial researchers through publication, web-based access, and direct interaction with industrial researchers. Ph.D., Undergraduate, and High School students will be trained in the course of the research.