Thermosensitive poly(allylamine)-g-poly(N-isopropylacrylamide) copolymers: Salt-tuned phase separation, particle formation and their applicability on curved surface

Salt and pH-tuned phase separation behaviors of poly(allylamine)-g-poly(N-isopropylacrylamide) (PAH-g-PNIPAA) copolymers have been studied by dynamic light scattering (DLS). The lower critical solution temperature (LCST) of the copolymers decreased linearly as a function of NaCl concentration ascribed to the “salt out effect”. The variation of the particle radius showed a sigmoidal plot as a function of temperature regardless of the salt concentration. A similar decrease of the LCST was found for PNIPAAm–COOH oligomers, except that the radius of the larger particles increased with temperature increase in the investigated temperature range. pH variation in a range of 2–11.3, however, did not affect the LCST of the copolymers. The applicability of the PAH-g-PNIPAA copolymers on curved surface was demonstrated by adsorption on pre-formed (PSS/PAH)4PSS hollow capsules. Confocal microscopy observed that the intact (PSS/PAH)4PSS/PAH-g-PNIPAA capsules were impermeable to positively charged rhodamine (Rd), but could induce selective deposition of fluorescein isothiocyanate-labeled dextran (mw 2 millions). This phenomenon is believed the effect of charge-controlled permeability.