Synthesis of single chain thermoresponsive polymer nanoparticles

Poly(N-isopropylacrylamide) (pNIPAM) is a thermoresponsive polymer of great interest in biomedical applications. In this work we combine RAFT polymerization and click chemistry'' for the synthesis of well defined single chain pNIPAM nanoparticles below 10 nm size with increasing degree of cross-linking. The method consists of the synthesis of NIPAM based terpolymers containing alkyne and azide functional groups by RAFT polymerization. Using this procedure terpolymers with polydispersity values below 1.2 were obtained. The terpolymers were collapsed by intramolecular click'' cycloaddition for the synthesis of the corresponding nanoparticles. Thermal phase transition behaviour has been studied for single-chain polymer nanoparticles (PNPs) and linear polymers. Temperature-dependent turbidimetry experiments showed a gradual decrease of transmittance for NPs compared to linear precursors, which presented a sharp decrease of transmittance. In the case of collapsed polymers, this effect was highly affected by the pH, exhibiting significant pH dependency in comparison to their linear precursors.