The fast developments in the synthetic chemistry during the last decades have made possible the preparation of large variety of macromolecular materials with controlled molecular weight, composition, topology and functionality. New classes of copolymers with complex architectures such as stars or bottle brushes have become available. We use a number of experimental techniques such as mechanical and dielectric spectroscopy, tensile tests, X-ray scattering, etc. to study the relations between molecular architecture, composition and processing on one hand and the morphology and thermo-mechanical properties of the materials on other.

For example, in close cooperation with the synthetic group of Prof. K. Matyjaszewski (Carnegi Mellon, Pittsburg) recently we studied poly(n-butyl acrylate)-based star polymers bearing a disulfide (SS) cross-linking agent on the end of each arm.

We found that these materials form weekly cross-linked polymer network that responds to reduction−oxidation conditions, indicating that the disulfide bonds between the arms can be cleaved and re-formed. If the material is stressed and deformed, some of the labile SS bonds can be broken, allowing the stars to slip and slide and then re-bond with new neighbors to reform a continuous film with self-healing properties. Further investigations and optimizations are currently underway.

In another project, again in cooperation with the synthetic group of K. Matyjaszewski, we explore the possibility to substitute the unsaturated middle segment of traditional thermoplastic elastomers such as polystyrene-b-polybutadiene-b-polystyrene or polystyrene-b-polyisoprene-b-polystyrene by acrylates and their hard segments by methacrylates or acrylonitrile based block copolymers. This would enable many benefits ranging from flexible glass transition temperatures (-60°C to 200°C), to better oxidation resistance and to resistance to hydrocarbons, opening new applications e.g. in automotive market. In particular we study systematically the effect of the composition and molecular architecture (e.g. linear ABA, 3-arm stars or multi-arm stars) on the phase separation behavior and the thermo mechanical properties of these new TPEs.

• J. Yoon, J. Kamada, K. Koynov, J. Mohin, R. Nicolaÿ, Y. Zhang, A. Balazs, T. Kowalewski, K. Matyjaszewski:
  Self-healing Polymer Films Based on Thiol-Disulfide Exchange Reactions and Self-healing Kinetics Measured Using Atomic Force Microscopy.
  Macromolecules, 45(1), 142–149 (2012)
• J. Kamada, K. Koynov, C. Corten, A. Juhari, J. Yoon, M. Urban, A. Balazs,K. Matyjaszewski:
  Redox Responsive Behavior of Thiol/Disulfide-Functionalized Star Polymers Synthesized via Atom Transfer Radical Polymerization.
  Macromolecules, 43, 4133-4139 (2010)
• A. Juhari, J. Mosnacek, J. Yoon, A. Nese, K. Koynov, T. Kowalewski, K. Matyjaszewski:
  Star-like poly(n-butyl acrylate)-b-poly(alpha-methylene-gamma-butyrolactone) block copolymers for high temperature thermoplastic elastomers applications.
  Polymer, 21, 4806-4813 (2010)
• A. Gitsas, G. Floudas, H.-J. Butt, T. Pakula, K. Matyjaszewski:
  Effect of nano-scale confinement and pressure on the dynamics of pODMA-b-ptBA-b-pODMA triblock copolymers.
  Macromolecules, 43, 2453 (2010)