Synthesis and Characterization of Thermosensitive Nanosupports with Core–Shell Structure (PSt-PNIPAM) and Their Application with Silver Nanoparticles

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Abstract
The present study synthesized silver nanoparticles supported on a thermosensitive polymer with a core–shell structure, formed by a polystyrene (PS) core and a poly(N-isopropylacrylamide) (PNIPAM)/Poly(N, N-methylenebisacrylamide) (MBA) shell. The PS core was synthesized via semicontinuous heterophase polymerization at a flow of 0.073 g/min, enabling polystyrene nanoparticles with an average size (Dz) of 35.2 nm to be obtained. In the next stage, the conditions required for polymerization synthesis were established in seeded microemulsion using PS nanoparticles as seed and semicontinuously adding the thermosensitive shell monomer (PNIPAM/MBA) under monomer-flooded conditions to favor shell formation. The non-homopolymerization of PNIPAM/MBA was demonstrated by obtaining nanoparticles with a core–shell structure, with average particle sizes of 41 nm and extremely low and narrow polydispersity index (PDI) values (1.1). The thermosensitive behavior was analyzed by QLS, revealing an average shrinkage of 4.03 nm and a percentage of shrinkage of 23.7%. Finally, silver nanoparticles were synthesized on the core–shell heat-sensitive nanoparticles in a colloidal solution containing the latices, while silver nanoparticles were anchored onto the cross-linked heat-sensitive network via the formation of complexes between the Ag+ ions and the nitrogen contained in the PNIPAM/MBA network, favoring anchorage around the network and maintaining a size of 5 nm.

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