Thermo-sensitive Microgels Supported Gold Nanoparticles as Temperature-mediated Catalyst

Microgels with a thermo-sensitive poly(N-isopropylacrylamide)(polyNIPAm) backbone and bis-imidazolium(VIM) ionic cross-links, denoted as poly(NIPAm-co-VIM), were successfully prepared. The as-synthesized ionic microgels were converted to nanoreactors, denoted as Au@PNI MGs, upon generation and immobilization of gold nanoparticles(Au NPs) of 5–8 nm in size into poly(NIPAm-co-VIM). The content of Au NPs in microgels could be regulated by controlling the 1,6-dibromohexane/vinylimidazole molar ratio in the quaternization reaction. The microgel-based nanoreactors were morphologically spherical and uniform in size, and presented reversible thermo-sensitive behavior with volume phase transition temperatures(VPTTs) at 39–40 °C. The Au@PNI MGs were used for the reduction of 4-nitrophenol, of which the catalytic activity could be modulated by temperature.

Influence of Different Inorganic Salts on Crystallization-driven Morphological Transformation of PCL-b-PEO Micelles in Aqueous Solutions

Different inorganic salts, including NaSCN, NaCl, MgCl2 and Na2SO4, were added into the aqueous solution containing poly（ε-caprolactone）-b-poly（ethylene oxide） （PCL-b-PEO） semicrystalline mieelles. The effects of inorganic salt on the micellar size and morphology were investigated with TEM and DLS. It is found that addition of NaSCN leads to increase of the micellar size, but the micelles remain to be spherical. By contrast, the other three inorganic salts can induce sphere-to-cylinder or sphere-to-lamella transformations of the PCL-b-PEO semicrystalline mieelles. The alteration rate of the micellar size with the time after addition of the inorganic salts decreases in the following order： NazSO4 〉 NaCl ≈ MgCl2〉 NaSCN. These results were interpreted in terms of the ＂salting-out＂ ability of the cations and anions. The anions SO42- and Cl- have a stronger ＂salting-out＂ ability, driving the morphological transformations of the micelles and leading to a rapid change in micellar size. By contrast, SCN- has a weaker salting-out＂ ability. The cations Na＋ and Mg2＋ may associate with the PEO blocks, leading to a ＂salting-out＂ effect as well. However, the ＂salting-out＂ ability of cations is weaker than that of SO42- and Cl- anions, and the ＂salting-out＂ abilities ofNa＋ and Mg2＋ are similar.

Morphology and Thermoresponsive Behavior of Hybrid Micelles of Polystyrene-b-Poly((N-isopropyl acrylamide)-co-(4-vinylbenzyl chloride)) with Prussian Blue

The hybrid micelles of polystyrene-b-poly（（N-isopropyl acrylamide）-co-（4-vinylbenzyl chloride）） block copolymer（PS-b-P（NIPAM-co-VBC）） with Prussian blue（PB） in the corona were prepared by reaction of pentacyano（4-（dimethylamino）-pyridine）ferrate（Fe-DMAP）-attached PS-b-P（NIPAM-co-VBC） with Fe Cl3. The formation of the PB framework inside the micelles was verified by UV-Vis, FTIR and TGA. The morphology of the hybrid micelles was studied by TEM and compared with that of the neat and Fe-DMAP-attached PS-b-P（NIPAM-co-VBC）. It is found that attachment of Fe-DMAP may change the short rod-like micelles of the neat PS-b-P（NIPAM-co-VBC） into spherical ones and lead to a smaller micelle size. The morphology of the hybrid micelles may be altered or remain unchanged after formation of the PB framework, depending on the chain structure of PS-b-P（NIPAM-co-VBC） and starting concentration. The thermoresponsive behavior of different micelles was studied using DLS. It is observed that attachment of Fe-DMAP can improve the hydrophilicity of the P（NIPAM-co-VBC） block, leading to weaker hysteresis of the micelle size during the heating and cooling cycle. However, the crosslinked PB framework in the micellar corona may result in a more evident hysteresis phenomenon and blur the two-stepwise change of the micellar size with temperature.