Amphiphilic Approach for Preparing Homopolyrotaxanes of Poly(ethylene oxide)

Abstract

A new concept was introduced for preparing homopolyrotaxanes that lack an enthalpic driving force for threading, and which are therefore truly a physical entrapment of non-interacting cyclic molecules and linear polymer chains. It is based on the ability of amphiphiles to form lamellae and columnar micelles in solvents that selectively solvate one of its components. An amphiphilic macrocrown ether (MC-12) with an average ring size of 42 atoms attached to a hydrophobic 12-carbon tail was prepared by formation of the macrocycle in the presence of multiple potassium template ions under pseudo-high dilution conditions. MC-12 is almost insoluble in aliphatic hydrocarbon solvents, but forms micelles in benzene and toluene in the presence of water. The micellar solutions of MC-12 macroscopically phase separate if water-soluble threads are added, but remain intact and solubilize less-water-soluble poly(ethylene glycol) (PEG) derivatives. PEG3350−bis(amine) threads do not react, or react incompletely, with tert-butyltrityl end-capping agents functionalized with benzaldehyde and acid chloride groups, respectively. The optimum end-capping reaction for PEG−bis(amine) threads in the water-induced micellar solutions of MC-12 is the addition reaction with 2-p-[tris(p-tert-butylphenyl)methyl]phenoxymethyl-4,4-dimethylazlactone.