Hollow polymer nanocapsules with a ferrocenyl copolymer shell

Abstract

Hollow polymer nanocapsules (HPN) consisting of a ferrocenyl shell have been developed by crosslinking the polymer chains grafted over silica nanoparticles (SiNP) which were synthesized via the one pot grafting from surface initiated reversible addition-fragmentation chain transfer (RAFT) approach followed by removal of the sacrificial silica template. Copolymer brushes composed of a ferrocene containing polymer, poly[2-(methacryloyloxy) ethyl ferrocenecarboxylate] (pFcMA) and an alkyne terminated polymer, poly(propargyl 4-vinylbenzyl ether) (pPVBE), were constructed in three different motifs on the SiNP surface as a shell. Two types of block copolymer grafted SiNP, p(FcMA-b-PVBE)-g-SiNP and p(PVBE-b-FcMA)-g-SiNP, and a random copolymer grafted SiNP, rp(FcMA-co-PVBE)-g-SiNP were chosen to investigate the influence of polymer architecture on the HPN morphology. Various structural characterization studies of all the copolymer grafted SiNP confirmed the brush morphology on the particle surface consisting of a core-shell structure. In order to bring robustness to the copolymer shell, crosslinking of the polymer chains was performed using a diazide crosslinker, 1,4-bis(azidomethyl)benzene and pPVBE via the copper-azide click reaction. Various microscopic studies showed that the incorporation of 30 wt% of cross-linker yielded sufficient structural stability leading to HPN formation with a ferrocenyl shell after etching away silica with HF treatment. A random copolymer skeleton was found to be the best choice for use as a polymer shell to engineer a successful HPN structure compared to a block copolymer shell. In addition, encapsulation of oxide free aluminum nanoparticles (Al-NP) inside the hollow cavity of both block and random copolymers was successfully carried out to make a composite material consisting of both Al and Fe.