"Schizophrenic" Self-Assembly of Block Copolymers Synthesized via Aqueous RAFT Polymerization: From Micelles to Vesicles

Dually responsive poly[(N,N-diethylaminoethyl methacrylate)-b-(N-isopropyl acrylamide)] is (P(DEAMA-b-NIPAM)s) capable of "schizophrenic" aggregation in aqueous solution were synthesized via aqueous reversible addition-fragmentation chain transfer (RAFT) polymerization. The nanoasembly 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 it hydrodynamic radii (R-h of 21 and 25 nm. respectively, at temperature below the lower critical solution temperature of PNIPAM and at solution pH values greater than the pK(a) of PDEAEMA. The two block copolymers, however, display quite different temperature-responsive behaviors at pH < 7.5. At elevated temperature (> 42 degrees C) P(DEAEMA(98)-b-NIPAM(209)) forms spherical micelles (R-h = 28 nm) with hydrophobic PNIPAM cores stabilized by it hydrophilic PDFAFMA shell. By contrast, P(DEAEMA(98)-b- assembles into vesicles (R-h = 99 nm) above 38 degrees C. The nanostructures were charactized by a combination of dynamic and static lighty scattering as well as transmission electron microscopy and are being investigated for their potential application as drug delivery vehicles.