Hydrogen bonded polymers

Control of polymeric structure is among the most important endeavours of modern macromolecular science. In particular, tailoring the positioning and strength of intermolecular forces within macromolecules by synthetic methods and thus gaining structural control over the final polymeric materials has become feasible, resulting in the field of supramolecular polymer science. Besides other intermolecular forces, hydrogen bonds are unique intermolecular forces enabling the tuning of material properties via self-assembly processes over a wide range of interactions strength ranging from several kJmol to several tens of kJmol . Central for the formation of these structures are precursor molecules of small molecular weight (usually lower than 10 000), which can assemble in solid or solution to aggregates of defined geometry.

Intermolecular hydrogen bonds at defined positions of these building blocks as well as their respective starting geometry and the initial size determine the mode of assembly into supramolecular polymers forming network-, rodlike-, fibrous-, disclike-, helical-, lamellar- and chainlike architectures. In all cases, weak to strong hydrogen-bonding interactions can act as the central structure-directing force for the organization of polymer chains and thus the final materials' properties. The important contribution of hydrogen bonds to the area of supramolecular polymer chemistry is definitely outstanding, most of all since the potency of hydrogen-bonding systems has been found to be unique in relation to other supramolecular interactions. Thus the high level of structural diversity of many hydrogen-bonding systems as well as their high level of directionality and specificity in recognition-phenomena is unbeaten in supramolecular chemistry.

The realization that their stability can be tuned over a wide range of binding strength is important for tuning the resulting material properties, ranging from elastomeric to thermoplastic and even highly crosslinked duroplastic structures and networks. On the basis of the thermal reversibility, new materials with highly tunable properties can now be prepared, being able to change their mechanical and optoelectronic properties with very small changes of external stimuli. Thus the field of hydrogen-bonded polymers forms the basis for stimuli responsive and adaptable materials of the future.