Doubly thermo-responsive nanoparticles constructed with two diblock copolymers prepared through the two macro-RAFT agents co-mediated dispersion RAFT polymerization

A new strategy to prepare doubly thermo-responsive nanoparticles constructed with the two diblock copolymers poly(N-isopropylacrylamide)-block-polystyrene (PNIPAM-b-PS) and poly[N,N-(dimethylamino) ethyl methacrylate]-block-polystyrene (PDMAEMA-b-PS) through the two macro-RAFT agents co-mediated dispersion polymerization is proposed. In this two macro-RAFT agents co-mediated dispersion polymerization, two macro-RAFT agents are simultaneously adopted, and the two in situ synthesized diblock copolymers PNIPAM-b-PS and PDMAEMA-b-PS co-assemble into nanoparticles containing a PNIPAM/PDMAEMA mixed corona and a common PS core. It is found that the molecular weight of PNIPAM-b-PS and PDMAEMA-b-PS in the mixed corona–core nanoparticles increases with the monomer conversion, and the size of the mixed corona–core nanoparticles increases with the PS block extension during the two macro-RAFT agents co-mediated dispersion polymerization. In water, the mixed corona–core nanoparticles exhibit two separate phase transition temperatures of 44 °C and 56 °C, corresponding to the PNIPAM and PDMAEMA blocks, respectively, which is confirmed by turbidity analysis, 1H NMR analysis and TEM observation. Our strategy named the two macro-RAFT agents co-mediated dispersion polymerization is believed to be a valid method to prepare multi-thermo-responsive nano-objects constructed with two or more than two thermo-responsive diblock copolymers.