No abstract

A new class of poly(aryl ether) dendritic ligands containing a pyridine functionality at the focal point and the corresponding Ag(I) complexes through metal-ligand coordination were designed, synthesized, and fully characterized. Compared with the dendritic ligands, the corresponding dendritic complexes exhibited much better gelation ability for various organic solvents at very low critical gelation concentrations. The gel-sol phase transition temperatures and morphologies could be finely tuned by binding silver ion to the ligand. A preliminary study revealed that multiple noncovalent interactions, such as Ag(I) -pyridine coordination, solvophobic interaction, and π-π stacking, synergistically enable the formation of stable metallogels. Interestingly, these metallogels could intelligently respond to multiple external stimuli including temperature, chemicals, and shear stress, leading to gel-sol phase transitions. In addition, these dendritic metallogels were successfully applied as templates for the in situ formation and stabilization of silver nanoparticles without the use of any chemical reducing/stabilizing agents.

(2013) Well-defined poly(N-isopropylacrylamide) with a bifunctional end-group: synthesis, characterization, and thermoresponsive properties, Designed Monomers and Polymers, 16:5, 465-474, DOI: 10.1080/15685551.2012 In this study, well-defined poly(N-isopropylacrylamide) (PNIPAM) with a bisalkyne end-group was synthesized by reversible addition-fragmentation chain transfer polymerization using 2-(2-(ethylthiocarbonothioylthio)-2-methylpropanoyl-oxy)ethyl 3,5-bis(prop-2-ynyloxy) benzoate (EMEB) as the chain transfer agent. The molecular weight and polydispersity index of polymer was determined by gel permeation chromatography (GPC). The linear increase in molecular weight with conversion, unimodal, and almost symmetrical peak in GPC trace together with low polydispersity indicated the controlled polymerization process of NIPAM mediated by EMEB. Subsequently, the Cu(I)-catalyzed [3 + 2] Huisgen cycloaddition between the end-group of polymer and azide derivatives was carried out to produce PNIPAM, in which the bisfunctional end-group was modified with phenyl, octyl, amido, and hydroxyl groups. After completing the click reaction, the structure of the polymer was characterized carefully by Fourier transform infrared spectroscopy (FTIR), 1 H NMR, and Matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS), indicating the complete consumption of alkyne end-groups. In addition, almost no change in molecular weight as well as the polydispersity was observed by comparison with the GPC traces of polymers before and after click reaction. The cloud point temperatures (T cp s) of the resulting PNIPAM derivatives in aqueous solution were investigated in detail by dynamic light scattering. The results showed that the values of T cp were ranged from 22 to 38°C, which depended largely on end-groups as well as the polymer molecular weights.