Thermo- and pH-responsive diblock copolymers synthesized via reversible addition-fragmentation chain transfer (RAFT) radical polymerization

Abstract

Well-defined poly (N-isopropylacrylamide)-block-poly (acrylic acid) (PNIPAM-b-PAA) was prepared via reversible addition-fragmentation chain transfer (RAFT) controlled radical polymerization. The "living" polymerization was evidenced by the fact that the molecular weight increased linearly with monomer conversion while the molecular weight distribution (Mw/Mn) remained reasonably narrow independent of the conversion. The thermo- and pH-responsive association behavior of the diblock copolymer was investigated by 1H NMR, transmittance (%T), and fluorescence probe techniques. The diblock copolymer indicated a cloud point (Tcp) in 0.1 M NaCl aqueous solutions. The Tcp value strongly depends on the solution pH because of an interaction between the pendent carboxyl group of the PAA block and the amide group of the PNIPAM block at pH <5. Above the Tcp, the 1H NMR peak intensity of the PNIPAM block and the %T value decreased. 8-Anilino-1-naphthalenesulfonic acid, an ammonium salt hydrate (ANS), a fluorescence probe, was confirmed to be incorporated into the hydrophobic domain formed from the polymer association above Tcp.