Synthesis of Well-Defined Photo-Cross-Linked Polymeric Nanocapsules by Surface-Initiated RAFT Polymerization

Narrowly distributed hollow polymeric nanocapsules (PtBMA-co-PDMIPM-b-PHPMA), with the size of 450 or 900 nm, were first synthesized by surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization exploiting silica nanoparticles as sacrificial templates and 2,3-dimethylmaleic imidopropyl methacrylate (DMIPM) as a photo-cross-linker. First, silica nanoparticles were amino functionalized by aminosilane agents, and then the dithiocarbonate chain transfer agent (CTA) was anchored via activated R-groups to the amino-functionalized surface of silica nanoparticles. This surface layer of CTA groups was then used to grow linear copolymers and block copolymers by RAFT polymerization leading to a core-shell morphology. TEM and GPC results indicated that the thickness of the shell can be well governed by simply controlling the molecular weight of the grafted copolymer. Finally, after photo-cross-linking and etching the silica core with NH4F/HF buffer, hollow nanocapsules were obtained, of which the morphology and composition were confirmed by employing a range of techniques, such as TEM, cryo-TEM, DLS, SEM, XPS, TGA, FTIR, GPC, and UV-vis spectroscopy. Thus, robust and narrowly distributed polymeric nanocapsules with size of 450 nm and a wall thickness 10 nm based on the grafted block copolymer PtBMA-co-PDMIPM-b-PHPMA having M-n = 19 500 g/mol (GPC) could be prepared.