Synthesis, characterization, and micellization of pH-responsive poly(4-vinylpyridine)-block-poly(methacrylic acid) four-armed star-shaped block copolymers

pH-sensitive poly(4-vinylpyridine)-block-poly(methacrylic acid) (P4VP-b-PMAA) four-armed star-shaped block copolymers were synthesized by two-step atom transfer radical polymerization (ATRP), followed by hydrolysis of P4VP-b-poly(tert-butyl methacrylate) (P4VP-b-PtBMA). The chemical structure and molecular weight of the as-synthesized block copolymers were characterized by Fourier transform infrared spectrometry (FTIR), nuclear magnetic resonance (H-1 and C-13 NMR), and gel permeation chromatography (GPC) determinations. The solution behavior was investigated by surface tension technique, ultraviolet visible (UV-vis) transmittance, transmission electron microscopy (TEM), dynamic light scattering (DLS), and zeta potentials measurements. The experimental results indicated that the copolymers can spontaneously assemble into spherical-shaped core-shell micelle aggregates, with a critical micelle concentration (CMC) about 200 mg L-1, hydrodynamic diameters from 90 to 210 nm, depending on the environmental pH values and compositional ratios. The transmittance measurements revealed that the block copolymers produce evident phase transition in aqueous solution at pH from 6.5 to 7.0. Zeta potential data revealed high micelle stability. The as-synthesized block copolymers are anticipated to find their applications in the realms of specific drug release, metal loading and heterogeneous catalysis.