Tuning supramolecular ring-opening polymerization by conformational design

Supramol. polymers, in which the monomer units are linked together by non-covalent interactions, provide unique opportunities to design responsive materials, as the system remains in const. equil. with its environment. One of the most interesting aspects is the equil. between linear and cyclic structures formed in soln. and in bulk material, as this strongly influences soln. and material properties. Bifunctional mols. based on the strongly quadruple hydrogen bonding 2-ureido-4[1H]-pyrimidinone moiety form long supramol. polymers as well as small cyclic oligomers in soln. The equil. between the different aggregates is dependent on external conditions such as temp., but also on the geometry of the monomers. Here we report that small changes in the structure of the spacer between the hydrogen bonding units have a striking effect on the tendency of the mol. to form cyclic structures and, with that, on soln. viscosity.