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Novel thermoresponsive copolymers of zwitterionic sulfobetaine methacrylate(SBMA)-and N,N-dimethylaminoethyl methacrylate(DMAEMA)-grafted silica nanoparticles were prepared via surface-initiated atom transfer radical polymerization.The phase behavior of the above nanoparticles was investigated through dynamic light scattering,nano-differential scanning calorimetry and zeta-potential measurements.The hybrid nanoparticles exhibit tunable phase transition temperature between upper critical solution temperature(UCST)and lower critical solution temperature(LCST)in aqueous solution.High PSBMA content in P(SBMA-co-DMAEMA)copolymer in hybrid nanoparticles leads to aggregation at low temperatures because of dominant electrostatic interactions of ionic pairs,whereas relatively low PSBMA content in hybrid nanoparticles results in phase transition at high temperatures as a result of predominant hydrophobic interactions of PDMAEMA.Interestingly,hybrid nanoparticles with a suitable molar ratio of SBMA/DMAEMA exhibit both UCST and LCST in aqueous solution where the water-insoluble microdomains of hybrid nanoparticles are generated by the PSBMA or PDMAEMA region depending on temperature.The above dual-thermoresponsive phase transition is also controllable in salt solution.A facile change in the molar content of copolymer grafted on silica nanoparticles will tune the UCST and LCST readily.