Micellization of PAA-F108-PAA Block Copolymer Using NMR Spectroscopy

Abstract

Poly(acrylic acid)-F108-Poly(acrylic acid) copolymer(PAA-F108-PAA) was synthesized by atom transfer radical polymerization(ATRP), followed by the hydrolysis of tert-butyl groups from the tert-butyl acrylate. The effects of temperature, acrylic acid neutralization degree and salt concentration on the micellization behavior of PAA-F108-PAA block copolymer were investigated by H-1 NMR spectroscopy combined with nuclear Overhauser effect spectroscopy(2D NOE). The neutralization degree of carboxyl acid groups(alpha) had little influence on the critical micellization temperature(CMT) of PAA-F108-PAA. When alpha=0.14, the PAA-F108-PAA copolymer was in a collapsed state at low temperature, at high temperature the poly(propylene oxide) block (PPO) was dehydrated and associated into a hydrophobic micellar core, while PEO entangled with PAA and formed the micellar shell; when alpha=0.80, PAA-F108-PAA copolymer was in a stretched state at low temperature, while at high temperature the micellar core was still composed of the hydrophobic PPO, with PEO and PAA separating from each other and forming the micellar shell. Salt species and concentration had great influence on the CMT of PAA-F108-PAA copolymer, which The CMT of PAA-F108-PAA copolymer decreased significantly by increasing KCl concentration to 1 mol/L. KCl showed a dehydration effect for both PPO and PEO block. In contrast, 1 mol/L KI increased the CMT of PAA-F108-PAA to a slightly higher value, suggesting that KI weakened the interaction between PPO and water but enhanced the interaction between PEO and water.