text: A polycatenane is a chemical substance that, like polymers, is chemically constituted by a large number of units. These units are made up of concatenated rings into a chain-like structure.
  It consists of mechanically linked catenane structures, via topological Hopf links, resulting in a higher dimensionality than the repeating unit. They are a class of catenanes where the number of macrocycles is greater than two and as catenanes they belong to the big family of mechanically interlocked molecular architectures (MIMAs).
   The characteristic feature of a polycatenane compound, that distinguishes it from other polymers, is the presence of mechanical bonds in addition to covalent bonds. The rings in this chain-like structure can be separated only when high energy is provided to break at least a covalent bond of the macrocycle. [n]-Catenanes (for large n), which consist solely of the mechanically interlocked cyclic components, can be viewed as “optimized” polycatenanes. The main difference between poly-[2]-catenanes and poly-[n]-catenanes is the repeating unit, as a monomer is for the polymer. In the first case the monomer is made of two interlocked rings that repeat continuously in the final polycatenane, while in the latter case there is only one ring that repeat the interlocking process for a large number of times. If the rings of the polycatenane are all of the same type, it can be defined as a homocatenane while if the subunits are different it is defined as heterocatenane.
  As a chain, the degree of motion of these structures is very high, greater than the one of a usual polymer, because the rings possess a reciprocal rotational, elongational and rocking motion. This flexibility is retained even if the macrocycles themselves are very rigid units, because the mobility is given by the ability of the rings to move with respect to each other. This mobility influences the final properties of the material (mechanical, rheological and thermal), and provides a dynamic behavior.