Formation of Polyion Complex Aggregate Formed from a Cationic Block Copolymer and Anionic Polysaccharide.

Block copolymers (P m M n ; P 20 M 101 and P 100 M 98 ) comprising poly(2-(methacryloyloxy)ethylphosphorylcholine) (PMPC, P) containing biocompatible phosphorylcholin pendants and cationic poly((3-acryloylaminopropyl) trimethylammonium chloride) (PMAPTAC, M) were synthesized via a controlled radical polymerization method. The degrees of polymerization of the PMPC and PMAPTAC segments are denoted by subscripts (P m M n ). The mixture of cationic P m M n and anionic sodium chondroitin sulfate C (CS) with the pendant anionic carboxylate and sulfonate groups formed polyion complex (PIC) aggregates in phosphate-buffered saline. A charge-neutralized mixture of P 20 M 101 with CS formed P 20 M 101 /CS PIC vesicles with a hydrodynamic radius ( R h ) of 97.2 nm, zeta potential of ca. 0 mV, and aggregation number ( N agg ) of 23,044. PMPC shells covered the surface of the PIC vesicles. The mixture of P 100 M 98 and CS formed PIC spherical micelles with the PIC core and hydrophilic PMPC shells. The R h , zeta potential, and N agg of the PIC micelles were 26.4 nm, ca. 0 mV, and 404, respectively. At pH < 4, the carboxylate anions in CS were protonated. Thus, the charge balance in the PIC micelles shifted to decrease the core density owing to the electrostatic repulsions of the excess cations in the core. The PIC micelles dissociated at a NaCl concentration ≥0.6 M owing to the charge screening effect. The positively charged PIC micelles with excess P 100 M 98 can encapsulate anionic dyes owing to electrostatic interaction.