Polymerization-Induced Self-Assembly of Metallo-Polyelectrolyte Block Copolymers

Abstract

Cobaltocenium-containing polyelectrolyte block copolymer nanoparticles were prepared via polymerization-induced self-assembly (PISA) using aqueous dispersion RAFT polymerization. The cationic steric stabilizer was a macromolecular chain-transfer agent (macro-CTA) based on poly (2-cobaltocenium amidoethyl methacrylate chloride) (PCoAEMACl), and the core-forming block was poly(2-hydroxypropyl methacrylate) (PHPMA). Stable cationic spherical nanoparticles were formed in aqueous solution with low dispersity without adding any salts. The chain extension of macro-CTA with HPMA was efficient and fast. The effects of block copolymer compositions, solid content, charge density, and addition of salts were studied. It was found that the degree of polymerization of both the stabilizer PCoAEMACl and the core-forming PHPMA had a strong influence on the size of nanoparticles.

Keywords: block copolymer; metallopolymer; polyelectrolyte; self-assembly.

FIGURE 1

Schematic representation of polymerization induced self-assembly (PISA) of metallo-polyelectrolyte diblock copolymers.

FIGURE 2

Synthesis of diblock copolymers by aqueous dispersion RAFT polymerization.

FIGURE 3

(a) ¹H NMR spectra of macro-CTA and a diblock copolymer; (b) A plot of conversion versus time for aqueous dispersion RAFT polymerization of HPMA using macro-CTA at 70 °C; (c) A plot of particle’s hydrodynamic diameter (D_h) versus time.

FIGURE 4

Representative AFM (a, b, c) and TEM (d, e, f) images obtained for PCoAEMACl-b-PHPMA prepared by aqueous dispersion RAFT polymerization at 70 °C with a degree of polymerization for core-forming PHPMA block at (a, d) 250; (b, e) 500; and (c, f) 650. All scale bars are 500 nm.

FIGURE 5

(a) Hydrodynamic diameter versus DP of PHPMA by DLS; (b) Intensity-average particle size distribution curve by DLS; (c) AFM height images of PCoAEMACl₁₃-PHPMA₅₀₀, PCoAEMACl₂₆-PHPMA₅₀₀, and PCoAEMACl₅₂-PHPMA₅₀₀ with 12.5% w/w solid and PCoAEMACl₁₃-PHPMA₅₀₀ with 25% w/w solid content. All scale bars are 500 nm.

FIGURE 6

(a) DLS intensity-average particle size distribution curve of PCoAEMACl₂₆-PHPMA₄₅₀ in water and 0.2 M NaCl solution; (b) AFM images of PCoAEMACl₂₆-PHPMA₄₅₀ nanoparticles in water and in 0.2 M NaCl solution. All scale bars are 500 nm.