Thermosensitive poly(N-isopropylacrylamide)-grafted magnetic-cored dendrimers for benzene uptake.

A series of thermosensitive and magneto-responsive dendrimers was synthesized based on magnetic-cored dendrimers (MCD) and carboxylic end-capped poly(N-isopropylacrylamide) (PNIPAM) to obtain PNIPAM-g-MCD. Thermo-response profiles of the PNIPAM-g-MCD from dynamic light scattering within the temperature range of 25-45 °C indicated that the lower critical solution temperature (LCST) of the PNIPAM-g-MCD was 32 °C. The physical size of the PNIPAM-g-MCD decreased as the temperature increased above the LCST. The initial hydrodynamic size of the PNIPAM-g-MCDs at 25 °C was 298.6 nm and reached 226.4 nm at 45 °C upon heating. Adsorption of benzene onto the PNIPAM-g-MCD at 25 °C was assessed, and the results showed that hydrophobic benzene was included within the internal cavities of lipophilic PNIPAM-g-MCD to maintain a thermodynamically stable state. Entrapment effects of the PNIPAM-g-MCD were confirmed at 45 °C, and the removal efficiency of benzene increased considerably to 50% when benzene was adsorbed, and the entrapment process was added. The shrunken PNIPAM terminal groups aggregated and trapped benzenes within the cavities of PNIPAM-g-MCD to prevent escape into the aqueous solution. Un-trapped benzene was removed through coalescence with PNIPAM-g-MCD because hydrophobic interactions prevailed with increasing temperature. PNIPAM-g-MCD were also able to form emulsions below the LCST and disrupted emulsions above the LCST in oil-water emulsions.