Ultrasoft thermoplastic elastomer synthesis

Hydrogels in the human body, such as cartilage and tendons, are soft and flexible; yet show incredibly toughness and extensibility. By contrast, man-made rubbers, have excellent mechanical toughness but are inherently stiff due to topological constraints known as entanglements, which prevent polymer chains from crossing and act as topological crosslinks (1,2). Thus, entanglements place a physical lower bound on how soft elastomers can be made without adding liquid fillers. As such, soft materials with Young’s moduli, E<1MPa are composed of multiple components and are not chemically pure substances. By introducing liquid fillers to polymeric materials, the stiffness may be decreased, however this swollen material is mechanically brittle and leaks the filler material upon deformation inhibiting their use in many biomedical applications. A Veni grant from NWO was recently awarded to investigate and solve this challenge. In your research, you will synthesize ultrasoft elastomers using controlled polymerization techniques to fabricate triblock co-polymers with a middle block of silicone polymers in a ‘bottlebrush’ architecture which eliminate entanglements making the material soft. Next you will add functional end blocks composed of thermoplastics, such as polystyrene, which undergo a glass transition upon cooling, allow this material to thermoset reversibly, see Figure. Combining these steps will yield a unique thermally-reversible elastically ultrasoft material. You will not only to synthesize these materials but also understand the physical chemistry underlying their unique behavior.

Molecular scale and self-assembled mesoscale representation of ultrasoft thermoplastic polymers; the dashed circles show microphase separated regions within the material that act as elastic crosslinks.
Molecular scale and self-assembled mesoscale representation of ultrasoft thermoplastic polymers; the dashed circles show microphase separated regions within the material that act as elastic crosslinks.

Tasks

  • Synthesize bottlebrush polymers from of liquid PDMS monomers
  • Functionalize these bottlebrushes with thermoplastic end block which will allow the material to be elastic at room temperature but liquid at elevated temperature
  • Depending on the time remaining, quantify their emergent and unique mechanical properties using rheology

Methods

  • Chemical synthesis
  • Gel Permeation Chromatography (GPC)
  • NMR
  • Rheology

References

  1. R. Pethrick. (2004), Polymer physics. Edited by M. Rubinstein and R. H. Colby, Oxford University Press, Oxford, 2003.
  2. L-H. Chai*, T. E. Kodger*, R. E. Guerra, A. F. Pegoraro, M. Rubinstein, D. A. Weitz, Advanced Materials, 2015, 27, 5132