Mechanically linked polyrotaxanes: A stepwise approach

A new synthetic approach for the preparation of mechanically linked polyrotaxanes was developed. Two variations of rotaxane monomers were synthesized, based on diphenylmethane and tetraphenylmethane blocking groups. Both rotaxanes bear a protected phenol functionality in the dumbbell-shaped part and a protected carboxylic acid functionality in the cyclic component. Via a "stepwise" polymerization, a rotaxane dimer and a rotaxane tetramer have been obtained. The procedure involves selective deprotection of the two functional groups in separate batches and a subsequent coupling reaction of the produced monofunctional/monoprotected monomers so that a dimer is formed. Longer and monodisperse oligomers can easily be obtained by repetition of this procedure. In addition, deprotection of both functionalities in the dimer and subsequent esterification resulted in the formation of a polymer with a molecular weight of ca. 400 000. The molecules obtained were isolated and characterized by H-1 NMR and mass spectrometry.