Binding of Hydrophobic Counterions by Polyelectrolyte and Their Hydrophobic Association around Polyion

Abstract

ABSTRACT:The binding of p-ethylbenzenesulfonate ions (EBS-'s) by poly(allylammonium) cation (PAAH+) and their hydrophobic association around PAAH+ have been investigated in aqueous solutions through 1 H NMR and c1-activity measurements. At a constant PAAH+c1-concentration, all 1 H NMR signals of EBS-exhibited up-field shift (ring current shift) with the increase in the NaEBS concentration. However, any chemical shift change did not observe in each signal of PAAH+. These results show that EBS-'s atmospherically bound to PAAH+ associate each other due to their hydrophobic interaction. The association of EBS-'s is depressed by the decrease in the charge density of the polyion and broken by the addition of another simple salt (NaCl) to the PAAH+c1-;NaEBS system. Moreover, it was found that the counterion exchange from CJ-'s to EBS-'s around PAAH+ is efficiently promoted by the association of EBS-'s.KEY WORDS Poly(allylammonium) Cation / Hydrophobic Counterion / Atmospherical Binding / Association of Hydrophobic Counterions / Counterion Exchange / The properties of polyelectrolyte solutions depend, very much, on the electrostatic interactions between charges fixed along the polymer backbone. These interactions are also very sensitive to the presence of counterions. The addition of electrolyte to the medium screens out the repulsive interactions between charges through the counterion binding and/or condensation around the polyion with a high electrostatic potential. This counterion binding (condensation) is an important feature of polyelectrolyte solutions. 1 Thus, the solution properties are considerably modified accompanying the changes in the chain conformation, water structure, degree of hydration around the polyion, and so on. On the one hand, when hydrophobic salt is used as an added electrolyte, z-4 the hydrophobic counterion, which has both hydrophilic and hydrophobic moieties, may have a different influence upon these electrostatic interactions. Especially, interactions among hydrophobic counterions should be also taken into account when polyion/hydrophobic counterion system is examined, although this interaction would be negligible in the absence of polyion. 5 In the previous work, 6 the interaction of three hydrophobic ions, i.e., benzenesulfonate (BS-), p-methylbenzenesulfonate (MBS-), pethylbenzenesulfonate (EBS-) with PAAH+ cation was investigated by 1 H NMR and viscosity measurements. It was found that EBS -'s accumulated electrostatically around the polyion can associate each other through their hydrophobic interaction. But, BS -and MBS-, which are slightly less hydrophobic than EBS -, did not show any sign of such hydrophobic association. This indicates that the hydrophobicity of counterion plays an important role in the association of counterions 545

Thermoresponsive polycations

“…For example, aqueous solutions of the cationic poly(allylammonium chloride) (PAAC) phase separate when introducing hydrophobic counterions like p -ethylbenzenesulfonate (EBS − ) ions. 24 This phenomenon was also investigated for solutions of the styrene-based polycation poly((vinylbenzyl)trimethylammonium chloride) (PVBTMAC) with hydrophobic fluorescent ions such as pyrene sulfonate (PSA − ). Excimer emission of PSA − ions in the presence of PVBTMAC confirmed the formation of hydrophobic domains.…”

Biohydrogels for medical applications: A short review

“…They show no self-healing behaviour but exhibit a high adhesive capability when in contact with one another. That property is attributed to the hydrogen bonding between the amide and carboxyl groups of the PAAm and PAAc, respectively 5 .…”

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“…Although these materials were initially obtained from natural resources, they were later synthesized as synthetic polymers and had a higher water absorption capacity, longer service life and larger spectra of chemical resources available 3 . Hydrogels are used in tissue engineering and tailored drug delivery mechanisms 4,5 . In soft tissue engineering, particularly, collagen, chitosan and bacterial cellulose are used in obtaining hydrogels that are able to speed up the healing process.…”