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Confronting Molecular Complexity

Posted by: Amanda Barnard

August 22, 2016

Isotactic (left), syndiotactic (center) and atactic (right) configurations.
Isotactic (left), syndiotactic (center) and atactic (right) configurations.

Polymers are a ubiquitous part of modern life, but each application depends on the molecular structure on an individual and collective level.   Understanding these structure/property relations can lead to the development of better polymers, but development is hindered by our inability to control the ordering of monomers in each chain; a property known as tacticity.  The monomers in isotactic polymers align in one direction (right-handed or left-handed); in syndiotactic polymers they align in alternating directions (right-handed then left-handed), and atactic polymers are entirely randomly.  Most polymers are atactic, and so the challenge comes from making the impact of this randomness predictable, on both local and global scales.

The focus of this project is to develop computational methods for determining the properties of tactic polymers, such as methacrylate ester and chloroacrylate esters, with a current focus on the glass transition temperature and the mechanical properties. Both properties are heavily influenced by tacticity, as well as the surrounding  temperature.  We are using a data-driven approach, based on a representative dataset of polymer structure optimized using Density Functional Tight-Binding (DFTB) calculations, to identify correlations that lead to a better understanding of the impact structural complexity has performance.

Complex interactions between polymer chains are challenging to predict.
Complex interactions between polymer chains are challenging to predict.

Solubility of polymers is another challenge, particularly in cases where this property is intrinsically linked to temperature.  While this has been studied in the context of applications such drug delivery and biological separations, the impact of tacticity remains largely unknown.  In this project we are using MD simulations and advanced sampling methods such as metadynamics and umbrella sampling are being used to calculate the changes in free energy as the polymer agglomerates in water. Ultimately this will provide a more precise estimate of the temperature at which a polymer dissolves.

For more information, contact the Project Leader, Dr Brad Wells.