Study on the Anomalous Small-Angle X-Ray Scattering on Structural Change in pH-Responsive Polymer Micelles

Abstract

pH - triggered structural change of polymer micelles composed of poly ( methacrylic acid )- block - poly ( 2 - bromethyl methacrylate ) ( PMAA - b PBrEMA ) was investigated with anomalous small - angle X - ray scattering ( ASAXS ) near the Br K edge. ASAXS revealed that the size of the hydrophobic core and the aggregation number of PMAA - b - PBrEMA micelles drastically decreased with an increase in the pH from 4.8 to 12.5. It was concluded that the drastic reduction of the size of PMAA - b - PBrEMA micelles in alkaline conditions was caused by the reduced electrostatic repulsion between anionic PAA chains in the corona layer of the micelles.