Synthesis of star-shaped poly(N-isopropylacrylamide) via atom transfer radical polymerization and its photocatalytic oxidation of Rhodamine B

Zinc(II) tetra-(2-chloropropionylamido) phthalocyanine (TAPcCl) was synthesized as the initiator for atom transfer radical polymerization (ATRP). Using CuBr/tris(2-dimethylaminoethyl)amine as the catalyst system, ATRP of N-isopropylacrylamide (NIPAM) was performed to create a new star-shaped poly(N-isopropylacrylamide) (PNIPAM) with a zinc phthalocyanine core and PNIPAM arms (TAPc-PAM). The structures of the initiator and the polymers were characterized by means of Fourier transform infrared spectroscopy and proton nuclear magnetic resonance. The polydispersity index obtained by gel permeation chromatography indicated that the molecular weight distribution was narrow. The lower critical solution temperatures (LCST) for the TAPc-PAM aqueous solutions measured using the turbidimetry method were increased due to incorporation of the phthalocyanine core and decreased as molecular weight increased. TAPc-PAM possessed photocatalytic activity, a finding that was verified by Rhodamine B degradation in the presence of hydrogen peroxide under visible light. Moreover, the catalytic efficiency was higher at its LCST, which encouraged reuse of the photocatalyst.