“Schizophrenic” Self-Assembly of Block Copolymers Synthesized via Aqueous RAFT Polymerization: From Micelles to Vesicles†Paper number 143 in a series on Water-Soluble Polymers.

Abstract

Dually responsive poly[( N, N -diethylaminoethyl methacrylate)- b -( N -isopropyl acrylamide)]s (P(DEAEMA- b -NIPAM)s) capable of “schizophrenic” aggregation in aqueous solution were synthesized via aqueous reversible addition−fragmentation chain transfer (RAFT) polymerization. The nanoassembly morphologies, dictated by the hydrophilic mass fraction, can be controlled by the polymer block lengths, solution pH, and temperature. Both P(DEAEMA 98 - b -NIPAM 209 ) (52.5 wt % NIPAM) and P(DEAEMA 98 - b -NIPAM 392 ) (70.8 wt % NIPAM) self-assemble into PDEAEMA-core PNIPAM-shell spherical micelles with a hydrodynamic radii ( R h ) of 21 and 25 nm, respectively, at temperatures below the lower critical solution temperature of PNIPAM and at solution pH values greater than the p K a of PDEAEMA. The two block copolymers, however, display quite different temperature-responsive behaviors at pH < 7.5. At elevated temperatures (>42 °C) P(DEAEMA 98 - b -NIPAM 209 ) forms spherical micelles ( R h = 28 nm) with hydrophobic PNIPAM cores stabilized by a hydrophilic PDEAEMA shell. By contrast, P(DEAEMA 98 - b -NIPAM 392 ) assembles into vesicles ( R h = 99 nm) above 38 °C. The nanostructures were characterized by a combination of dynamic and static light scattering as well as transmission electron microscopy and are being investigated for their potential application as drug delivery vehicles.