Dextran-RAFT

Bernard et al. [105] used the same strategy to decorate polyVAc latex particles with a dithiocarbonate end-functionalized dextran (dextran-RAFT), well-suited for the CRP of non-activated vinyl esters such as VAc. Dextran-RAFT was obtained by Cu(I)-catalyzed Huisgen [3+2] dipolar cycloaddition [106] between an alkyne end-functionalized dextran and an azido-containing dithiocarbonate. The low functionalization yield (30%) was apparently not an impediment for the syntheses of stable poly VAc latex particles (diameters from 80 to 150 nm) via batch emulsion polymerization. The involvement of the dithiocarbonate end-group was corroborated by the retardation effect observed when the dextran-RAFT concentration was increased. In addition, a drastic effect on particle size was observed as compared to emulsion polymerization experiments performed with native or alkyne-functionalized dextran (particle diameter above 500 nm). 

Due to the relative ease of control, temperature is one of the most widely used external stimuli for the synthesis of stimulus-responsive bmshes. In this case, thermoresponsive polymer bmshes from poly(N-isopropylacrylamide) (PNIPAM) are the most intensively studied responsive bmshes that display a lower critical solution temperature (LOST) in a suitable solvent. Below the critical point, the polymer chains interact preferentially with the solvent and adopt a swollen, extended conformation. Above the critical point, the polymer chains collapse as they become more solvophobic. Jayachandran et reported the synthesis of PNIPAM homopolymer and block copolymer brushes on the surface of latex particles by aqueous ATRP. Urey demonstrated that PNIPAM brushes were sensitive to temperature and salt concentration. Zhu et synthesized Au-NPs stabilized with thiol-terminated PNIPAM via the grafting to approach. These thermosensitive Au-NPs exhibit a sharp, reversible, dear opaque transition in solution between 25 and 30 °C. Shan et al. prepared PNIPAM-coated Au-NPs using both grafting to and graft from approaches. Lv et al. prepared dual-sensitive polymer by reversible addition-fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide from trithiocarbonate groups linked to dextran and sucdnoylation of dextran after polymerization. Such dextran-based dual-sensitive polymer is employed to endow Au-NPs with stability and pH and temperature sensitivity. 

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