A novel linear-dendron-like polyampholyte, poly(L-lysine)-b-D2-poly(L-glutamic acid) [PLL-b-D2-(PLGA)4], where D2 is the second generation of poly(amido amine), was prepared by hydrolyzing poly(ε-benzyloxycarbonyl-L-lysine)-b-D2-poly(γ-benzyl-L-glutamate) copolymer which was synthesized via a combination of ring-opening polymerization and click chemistry. The pH-responsive self-assembly behaviors of PLL-b-D2-(PLGA)4 were investigated in detail. It is found that PLL-b-D2-(PLGA)4 can self-assemble into PLGA-core aggregates at acidic pH and PLL-core aggregates at alkaline pH, which was accompanied with the coil-to-helix conformational transition of PLGA and PLL segments, respectively. The self-assembled aggregates with various morphologies, such as large compound micelles, worm-like micelles, large compound vesicles, simple vesicles, and rigid tubular structures have been obtained in "schizophrenic" aggregation process with simply increasing the solution pH. The hierarchical assembled fractal structures of PLL-b-D2-(PLGA)4 were observed during the solvent evaporation at high pH value.
The objective of the present work was to report the unprecedented cell structure variation in multilayered alternating polystyrene (PS)/PS−SiO 2 foams. The multilayered alternating PS/PS−SiO 2 foams were prepared via a coextrusion technique and a subsequent batch foaming process with high-pressure carbon dioxide (CO 2 ). The multilayered PS/PS−SiO 2 stacks were controlled of different layers (2, 4, 8, 16, 32, 64, and 128) using the layer-multiplying elements (LMEs). The PS−SiO 2 nanocomposite was prepared using a twin-screw extruder with 99 wt % PS resins and 1 wt % SiO 2 nanoparticles. With the increase of the layer number, three types of cell structures were observed: alternating big-cell/small-cell layers, a single big-cell layer in small-cell layers, and alternating film/small-cell layers. The original big cells were formed in the pure PS layer, and the small ones in the PS−SiO 2 layers. It was considered that the decrease in the thickness of the pure PS layer and the increase in the thickness of the PS−SiO 2 layer due to the interfacial mixing between the adjacent layers is the reason for the unprecedented cell structure variation. A possible mechanism was proposed for interpreting the cell structure variation in the preparation of multilayered PS/PS−SiO 2 foams. The interfacial mixing can be taken as the strategy to tune the cell structures for the purpose of end-use demands in preparing multilayered foams using the same polymer in adjacent layers.
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