Thermoresponsive Nanohydrogels Cross-Linked by Gold Nanoparticles

'Thermoresponsive nanohydrogels cross-linked by gold nanoparticles (AuNPs) were prepared by 1,3-dipolar cycloaddition reactions and in situ reversible addition fragmentation chain-transfer (RAFT) polymerization. In order to synthesize thermoresponsive nanohydrogels, AuNPs decorated with azide groups (AuNPs-N3) were prepared through ligand exchange. Click reactions between AuNP5-N3and dialkynetrithiocarbonate yielded cross-linked AuNP aggregates. The size and cross-linking density of AuNP aggregates increased with the molar ratio of acetylene groups to azide groups. After click reactions, the absorption maximum of the plasmon band of AuNPs red-shifted to a long wavelength. Thermoresponsive nanohydrogels were prepared by in situ RAFT polymerization Of N-isopropylacrylamide (NIPAM) using trithiocarbonate in the cross-linked /kuNP agregates as chain-transfer agents. The thermor,e-. sponsive nanohydrogels- presented a low critical solution temperature at around 32 C due to the coil-to-globule transition of connecting PN1PAM -Chains in the 'nanohYdrogels. The size of the thermoresiionsive nanohydrogels was determined by the molar ratio of acetylene groups to azide groups.