Constraint Release Dynamics in Entangled Polymers

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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.