Intramolecular hydrophobic aggregation of amphiphilic polysulfobetaine with various hydrophobic groups in aqueous solution

The copolymers derived from zwitterionic DMAPAMAIPS and hydrophobic monomer (AdMAI or NaMAI) were studied in terms of the surface tension, viscometrics, and photophysical measurements. The surface tension of poly(DMAPAMAIPS) was shown to be larger than that of both the copolymer [poly(DMPAMAIPS/ NaMAI)] with an aromatic hydrophobic residue (naphthalene group) and [poly(DMAPAMAIPS/AdMAI)] with an aliphatic hydrophobic residue (adamantane group). The copolymer [poly( DMAPAMAIPS/NaMAI)] has a larger surface activity than that of [poly(DMAPAMAIPS/AdMAI)]. The reduced viscosity of the copolymers revealed that both zwitterionic and hydrophobic associations were important in polymer aggregation. The aromatic hydrophobic units of the copolymer [poly(DMAPAMAIPS/NaMAI)] were more strongly associated than the units of aliphatic hydrophobic copolymer [poly(DMAPAMAIPS/AdMAI)] due to the stronger hydrophobic aggregation of naphthyl groups. The fluorescence experiment showed that when the hydrophobic adamantyl group was incorporated into the polymer, the environmental polarity of the pyrene residue increases. Coil expansion was due to weaker hydrophobic associations of the adamantane moieties.