Molecular self-assembly of dendrimers, non-covalent polymers and polypseudorotaxanes

The formation of pseudorotaxanes from dibenzo-24-crown-8 (DB24C8) and secondary aliphatic ammonium ions was reported by Stoddart et al. Based on that molecular recognition motif several systems have been examined as prototypical examples of (1) self-assembly of dendrimers via pseudorotaxane formation, (2) self-assembly of linear non-covalent polymers of the pseudo- rotaxane type and (3) control of properties of a polymer by pseudorotaxane formation. Attachment of a DB24C8 moiety to the “focal point” of first, second and third generation benzyl ether dendrons (Fréchet type) allowed solution phase self-assembly with a core unit consisting of 1,3,5-tris[p-(N-benzylammoniomethyl)phenyl]benzene to produce the corresponding dendritic pseudoro-rotaxane structures, which are of nanometer scale. Ditopic hosts were prepared by coupling DB24C8 units with difunctional linear species; ditopic guests were similarly constructed by linking two dibenzylammonium ion moieties. At high concentrations in relatively non-polar solvents these complementary building blocks self-assembled into non-covalently bonded (pseudorotaxane) linear arrays, with high viscosity and fiber forming ability. Treatment of polymethacrylates bearing pendant DB24C8 units with dibenzylammonium resulted in changes in properties as a result of formation of side-chain pseudorotaxane units.