Transition from Steric to Electrostatic Stabilization in Shell-Degradable Waterborne Particles Obtained by Photopolymerization-Induced Self-Assembly

Semidegradable nanoparticles were synthesized in aqueous medium by photoinitiated polymerization-induced self-assembly, using a cleavable hydrophilic copolymer as a steric stabilizer that also served as a macromolecular chain transfer agent (mCTA) for the reversible addition-fragmentation chain transfer (RAFT) polymerization of 2-hydroxypropyl methacrylate (HPMA). This mCTA was obtained by modification of a pH-sensitive poly[(ethylene carbonate)-co-(ethylene oxide)] (PECEO) random copolymer that was end-fitted with a trithiocarbonate moiety. By adjusting the degree of polymerization of HPMA through RAFT, we achieved the synthesis of a series of amphiphilic block copolymers that self-assembled in various morphologies, including spheres, worms, and vesicles. Through characterization by ¹H nuclear magnetic resonance, size exclusion chromatography, and transmission electron microscopy, it could be demonstrated that the carbonate linkages of their hydrophilic block and of their steric stabilizer undergo hydrolysis under alkaline conditions. The length of the PHPMA block and the balance between the hydrophilic and hydrophobic blocks are two parameters that have a significant impact on the self-assembly of these particles; a transition from steric to electrostatic stabilization of these nanoparticles could be witnessed during degradation for short PHPMA blocks. In summary, pH-sensitive nanoparticles sterically stabilized by degradable poly(ether-co-ether carbonate) copolymers gave rise under basic conditions to nanoparticles stabilized by electrostatic interaction.