Cyclic Polymers and Olympic Gels
Michael Lang, Jens-Uwe Sommer, Ron Dockhorn and Marco Werner
The role of topology in polymers is a challenging topic for theory and not yet fully understood. Our current research focusses on understanding the properties of cyclic polymers in melts, solutions, and gels.
For melts of non-concatenated cyclic polymers („rings“), the topological restrictions among overlapping molecules force the rings to fold into compressed conformations. By comparing the conformations of concatenated rings and non-concatenated rings, we were able to construct a model that predicts the scaling of rings in concentrated solutions .
The dynamics of long linear and branched polymers shows a characteristic entanglement plateau and stress relaxes by chain reptation or branch retraction, respectively. In both mechanisms, the presence of chain ends is essential. But how do entangled polymers without ends relax their stress? Using properly purified high-molar-mass ring polymers, we showed that these materials exhibit self-similar dynamics, yielding a power-law stress relaxation that is unique for entangled molecules .
„Olympic gels“ are networks that are solely held together by the mutual concatenation of cyclic molecules. These materials exhibit unique swelling properties  that might be key to understand the role of entanglements during the swelling of a polymer network.
- M. Lang, J. Fischer, and J.-U. Sommer
The effect of topology on the conformations of ring polymers
Macromolecules 45 (2012) 7642-7648
- M. Kapnistos, M. Lang, D. Vlassopoulos, W. Pyckhout-Hintzen, D. Richter, D. Cho, T. Chang, J. Roovers, and M. Rubinstein
Unexpected power-law stress relaxation in entangled ring polymers
Nature Materials 7 (2008) 997-1002
- M. Lang, J. Fischer, M. Werner, and J.-U. Sommer
Swelling of Olympic gels
Physical Review Letters 112 (2014) 238001(5)