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We report the synthesis of gold nanoparticles protected with dithiol-fonctionalized LCST polymers in aqueous solution. The AuNPs assemble reversibly with temperature. The aggregation temperature Tagg of the AuNPs, corresponding to the phase transition temperature of the grafted polymer, can be easily tuned from 8 to 50 °C both by changing the proportion of hydrophilic polymer in the polymeric corona. The same polymers were used for the regioselective assembly of gold nanorods.
However, the aggregation of the LCST polymer-coated AuNPs leads to a macroscopic precipitation. We report an original strategy, which consists of finely and reversibly controlling the AuNP aggregation by using a Pluronic triblock copolymer. The presence of P123 prevents from the precipitation of the aggregated AuNPs in solution. The size, the colloidal stability and the optical properties of the AuNP aggregates are tuned as a function of the P123/AuNP ratio.
Finally, we study the thermosensibility in aqueous solution of AuNPs stabilized by UCST zwitteronic polymers, synthesized by RAFT controlled radical polymerization. The purified AuNPs are insensitive to the temperature and do not show any sign of aggregation whether in pure water or salt media. However, mixed with free PSPP solution, they present a thermosensitive and reversible aggregation behavior. The ionic strength, the free polymer quantity and molar weight influence the AuNP aggregation, which seems to come from a depletion mechanism.