Threading, growth and aggregation of pseudopolyrotaxanes

Pseudopolyrotaxanes are obtained by the threading of a polymeric guest through strings of cyclic host molecules. One typical example of pseudopolyrotaxanes (PPR) forms when a poly(ethylene glycol) (the guest) and cyclodextrins (CD, the hosts) are dissolved and mixed in water. We investigated the kinetics of the threading of linear poly(ethylene glycol) chains of different molecular weights and of a four-arm star-like polymer as a function of temperature. The aggregation and precipitation of pseudopolyrotaxanes are described in terms of the Avrami-Erofe’ev model, which provides relevant information on the mechanism of these processes. SAXS and TGA experiments confirm the structure and hydration of the final products obtained from the different polymers. A new hypothesis for the interaction between pseudopolyrotaxanes that leads to aggregation and precipitation, based on the spatial dielectric anisotropy, is proposed.