Adsorption of bisphenol-A by pH-responsive polymer grafted on porous polyethylene vinyl acetate disk: Effect of the side-chain length of hydrophobic component in polymer on adsorption

• NaMmH and NaMmO were protonated at pH value lower than 7.
• Poly(NaAMPS-co-NaMmO) formed unimolecular micelles by the protonation of NaMmO.
• Micelle formation of poly(NaAMPS-co-NaMmH) was not observed at any pH.
• Poly(NaAMPS-co-NaMmO) encapsulated BPA stably within hydrophobic microdomains.
• The BPA adsorbed on poly(NaAMPS-co-NaMmH) easily desorbed.

Random copolymers of sodium 2-(acrylamido)-2-methylpropanesulfonate (NaAMPS) and sodium 6-methacrylamidohexanoate (NaMmH), [poly(NaAMPS-co-NaMmH)], and NaAMPS and 8-methacrylamidooctanoate (NaMmO), [poly(NaAMPS-co-NaMmO)], were grafted on the surface of a porous polyethylene vinyl acetate (PEVA) disk by peroxide plasma polymerization, respectively. By permeating the pH-adjusted bisphenol-A (BPA) solution through the disk, the adsorption behavior of BPA was examined. The pendant alkyl carboxyl groups in the hydrophobic components, i.e., NaMmH and NaMmO, were protonated at pH values lower than 7. The formation of polymer colloid composed of a single polymer chain, i.e., unimolecular micelle, by poly(NaAMPS-co-NaMmO) was observed according to the protonation of NaMmO. In contrast, polymer colloid formation by poly(NaAMPS-co-NaMmH) was not observed, even when NaMmH was protonated. The adsorption of BPA on the polymer-grafted PEVA disks increased abruptly at pH 10, although the protonation of NaMmH and NaMmO was not observed at this pH. Furthermore, the adsorption amount of BPA increased at pH 7, the pH at which the protonation of NaMmH and NaMmO occurred. In the case of poly(NaAMPS-co-NaMmO), BPA molecules were effectively and stably encapsulated in the hydrophobic microdomains in the micelles at pH values lower than 7. In contrast, in the case of poly(NaAMPS-co-NaMmH), BPA easily desorbed by permeation of an acidic solution through the disk.

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