Polymer Modeling At ExxonMobil: Reaction Kinetics And Computational Rheology

Industrially produced polymers generally contain molecules with a wide range of architectures and sizes, which are responsible for their unique flow properties. For example, polyethylene (PE), despite its apparent chemical simplicity, is a complex mixture characterized by three distributions: (i) Molecular weight, (ii) Comonomer composition (e.g. butene or hexene), and (iii)Branching (long chain branching, where the branch length exceeds about 1,000 g/mol for PE). \\ \\ When developing a new plastic, it is essential to understand how to relate these various distributions to its melt flow performance. Recent theoretical advances in reaction kinetics and computational rheology have enabled the prediction of polymer melt flow performance from molecular structure. \\ \\ In this presentation, we describe a modeling platform which combines polymerization and computational rheology models in order to predict the flow of various branched polyolefins. In particular, we show how the polymer branching distribution controls the ultimate resin flow performance (e.g. extrudability and bubble stability for film blowing operations). This approach combines multiple characterization techniques such as gel permeation chromatography, nuclear magnetic resonance, or shear and extensional rheology, in order to establish a detailed inventory of branched species. Decoding the branching distribution is critical as rheology is highly sensitive to the molecular architecture and amount. In addition, there exists today no stand-alone experimental characterization tool capable of providing quantitative polymer branching information. In this context, this framework opens up unique opportunities for the design of resins with targeted flow performance.