1H NMR spectroscopic studies of the structures of a series of pseudopolyrotaxanes formed by “threading”

Abstract

Introduction of the tetracationic cyclophane cyclobis(paraquat-p-phenylene) 2 into deuterioacetonitrile solutions of linear polymers with hydroquinol or resorcinol ether units linked by ethylene oxide sequences where, in several cases, the latter also contained carboxylic ester groups, led to the formation of pseudopolyrotaxanes. ¹H NMR spectroscopic analysis of these solutions at −40°C shows how the structures of the pseudopolyrotaxanes evolve as the amount of cyclophane introduced into the solution increases. In some cases the pseudopolyrotaxanes have about half the polymer repeat units threaded through cyclophane molecules and they adopt a ‘concertina’ type of structure as a result of π-stacking. In other cases more than 85% of the repeat units of the polymer are threaded through cyclophane molecules, so that most of the polymer repeat units which are threaded have adjacent repeat units which are also threaded, and to avoid interactions between the cyclophanes the polymer almost certainly exists mainly in an extended conformation.