Theta Temperature Depression of Mechanically Interlocked Polymers: [2]catenane as a Model Polymer

Polycatenanes have recently attracted considerable attention due to their potential for many applications and as model systems for understanding the role of mechanical interlocking in the physical properties of mechanically interlocked polymers. We used molecular dynamics simulations to investigate the conformational properties of [2]catenane polymers in solution as a function of the solvent quality and molecular weight. We found the theta-temperature of [2]catenane polymers to be depressed compared to their linear and ring counterparts and follow the relationship theta([2]catenane) < theta(ring) < theta(linear). The conformation of the two rings in [2]catenane is found to be strongly dependent on the solvent quality. In a good solvent, their conformation is similar to that of an analogous free ring polymer, while, in a poor solvent, their conformation significantly deviates from an analogous ring polymer. Furthermore, the thermal blob size (N-blob) follows the theoretical prediction of the linear relation between N-blob and 1/v(2), where v is the excluded volume, and is found to be strongly dependent on polymer topology in a poor solvent condition than in a good solvent condition.