Transition from Steric to Electrostatic Stabilization\nin Shell-Degradable Waterborne Particles Obtained by Photopolymerization-Induced\nSelf-Assembly

Semidegradable nanoparticles were synthesized in aqueous\nmedium\nby photoinitiated polymerization-induced self-assembly, using a cleavable\nhydrophilic copolymer as a steric stabilizer that also served as a\nmacromolecular chain transfer agent (mCTA) for the reversible addition–fragmentation\nchain transfer (RAFT) polymerization of 2-hydroxypropyl methacrylate\n(HPMA). This mCTA was obtained by modification of a pH-sensitive poly[(ethylene\ncarbonate)-<i>co</i>-(ethylene oxide)] (PECEO) random copolymer\nthat was end-fitted with a trithiocarbonate moiety. By adjusting the\ndegree of polymerization of HPMA through RAFT, we achieved the synthesis\nof a series of amphiphilic block copolymers that self-assembled in\nvarious morphologies, including spheres, worms, and vesicles. Through\ncharacterization by <sup>1</sup>H nuclear magnetic resonance, size\nexclusion chromatography, and transmission electron microscopy, it\ncould be demonstrated that the carbonate linkages of their hydrophilic\nblock and of their steric stabilizer undergo hydrolysis under alkaline\nconditions. The length of the PHPMA block and the balance between\nthe hydrophilic and hydrophobic blocks are two parameters that have\na significant impact on the self-assembly of these particles; a transition\nfrom steric to electrostatic stabilization of these nanoparticles\ncould be witnessed during degradation for short PHPMA blocks. In summary,\npH-sensitive nanoparticles sterically stabilized by degradable poly(ether-<i>co</i>-ether carbonate) copolymers gave rise under basic conditions\nto nanoparticles stabilized by electrostatic interaction.