Aggregation behavior of poly(methacrylic acid) with cucurbit[7]uril and the effect of ammonia ions on aggregation

The interaction between poly(methacrylic acid) (PMAA) and cucurbit7]uril (CB7]) in aqueous solution were investigated by dynamic light scattering (DLS), fluorescence techniques, UV-spectrophotometer, and resonance light scattering (RLS). The experimental results show that the aggregates were formed between CB7] and H⁺ of PMAA by the hydrogen bonding interaction that increases with increasing the concentration of CB7], which leads to the formation of the larger aggregates. Interestingly, PMAA has temperature sensitivity with the addition of CB7] by UV-spectrophotometer and DLS. The pH of the solution of PMAA appears a inflection point with increasing the concentration of CB7] comparing with the increase of the electrical conductivity all the time with the addition of CB7]. In addition, in order to investigate the effect of cation on the size of the aggregates and avoid the effect of other anions at the same time, the dilute ammonia was added into the solution of PMAA. The experimental data show that the size of the aggregates increases with adding CB7] because CB7] could combine with both NH₄⁺ by the electrostatic and iondipole interactions and H⁺ by the hydrogen bonding interaction, and a possible model is proposed to explain the host-guest interactions between PMAA and CB7].