In addition to homodimers, heterodimers were observed to form in some instances from mixtures of cavitands, including when one of the components did not dimerise with itself. Narcissistic self-sorting behaviour of some cavitands was also observed, in which only homodimers self-assembled from mixtures of cavitands. Cram observed that dimer formation was highly dependent on both temperature and concentration. The nature of the solvent was also important, with more polar solvents (e.g. acetonitrile, methanol) promoting cavitand dimerization through solvophobic effects. A similar observation was made by Paek and co-workers, who determined the association constant for one homodimer in CDCl3 to be 4.9 × 10 -4 ; increasing the solvent polarity resulted in enhancement of the association constant by two orders of magnitude in 10% CD3OD. Within these systems, structural modifications to the cavitand could have profound effects on their self-assembly. Whilst larger resorcinol substituents, e.g. ethyl groups, still promoted the kite conformer, they prevented homodimerisation through steric hindrance. Dalcanale and coworkers observed that tethering groups on the lower rim of the cavitand also impeded dimerization through restricted conformational flexibility. Due to the difficulty of their design and fragility with respect to concentration, temperature and solvent, the host-guest chemistry of velcraplexes have not been studied. Although they have been investigated as supramolecular junctions within polymers, 178 their use remains extremely limited.