Tunable Thermosensitivity of Azo Polymers-Coated Gold Nanoparticles Achieved by Molecular Recognition

Abstract

Azo polymers-coated AuNPs (poly(DMA-co-PAPA)-coated AuNPs and poly(NIPAM-co-PAPA)-coated AuNPs) are prepared by the free radical “grafting through” copolymerization of MAEL-capped AuNPs, PAPA and DMA or NIPAM in THF solution using AIBN as initiator. The characterization of azo polymers-coated AuNPs is performed by UV-Vis, TEM, XPS, TGA, FT-IR and 1H-NMR spectroscopy. The influence of α-CD and α-CD derivatives (per-6-PDMA-α-CD and per-6-PNIPAM-α-CD) on the thermosensitivity of azo polymers-coated AuNPs aqueous solution is investigated. It is found that azo polymers-coated AuNPs aqueous solution barely exhibits any temperature sensitive properties. After the addition of α-CD or per-6-PDMA-α-CD, the thermosensitivity of azo polymers-coated AuNPs has been slightly enhanced due to the formation of inclusion complexes by molecular recognition of α-CD and azobenzene moiety. However, azo polymers-coated AuNPs exhibit excellent thermosensitivity with a narrow window of phase transition when the inclusion complexes are formed by molecular recognition between azo polymers-coated AuNPs and per-6-PNIPAM-α-CD after the addition of per-6-PNIPAM-α-CD. The lower critical solution temperature (LCST) is 29.8°C and 30.8°C for poly(DMA-co-PAPA)-coated AuNPs inclusion complexes of 2.5 g·L−1 and 1.25 g·L−1, respectively. For the poly(NIPAM-co-PAPA)-coated AuNPs system, the LCST is measured to be 25.4°C and 27.3°C corresponding to 2 g·L−1 and 1 g·L−1 inclusion complexes aqueous solution. These results indicate that the thermosensitivity of azo polymers-coated AuNPs can be controlled by molecular recognition between the azobenzene group in AuNPs and α-CD moiety.