Robert W. Graff

Core-Double-Shell Fe3O4@Carbon@Poly(InIII-carboxylate) Microspheres: Cycloaddition of CO2 and Epoxides on Coordination Polymer Shells Constituted by Imidazolium-Derived AlIII−Salen Bifunctional Catalysts

A hydrid microsphere Fe3O4@carbon@poly(In(III)-carboxylate) consisting of a cluster of Fe3O4 nanoparticles as the core, a carbon layer as the inner shell and a porous In(III)-carboxylate coordination polymer as the outer shell was prepared and applied as a recyclable catalyst for the cycloaddition reaction of CO2 and epoxides. Construction of this hybrid microsphere was achieved in the two steps, including (1) the one-pot solvothermal synthesis of Fe3O4@C particles with the abundant carboxylic groups on the carbon surface and (2) the subsequent growth of the outer shell polymers based on the precipitation coordination polymerization. Imidazolium-substituted Salen ligands were synthesized and chelated with the In(III) ions using the terminal carboxylic groups. The coordination polymer shell was formed on the Fe3O4@C particles, and the structures including shell thickness, surface area and porosity could be varied by tuning the feeding ratios of the In(III) ions and the ligands. The optimal structure of the coordination polymers showed a shell thickness of ca. 45 nm with ∼5 nm of mesopore, 174.7 m(2)/g of surface area and 0.2175 cm(3)/g of pore volume. In light of gas uptake capability, catalytic activity and magnetic susceptibility, cycloaddition of CO2 with a series of epoxides were studied by using Al-complexed Fe3O4@C@In(III)-[IL-Salen] microspheres. The results validated that the self-supporting catalytic layer with high surface area was of remarkable advantages, which were attributed from great increment of effective active sites and combination of nucleophilic/electrophilic synergistic property and CO2 uptake capability. Therefore, these hybrid microspheres provided excellent catalytic activity, prominent selectivity to cyclic carbonates and outstanding recyclability with the assistance of an applied magnetic field.

One-pot synthesis of hyperstar polymers via sequential ATRP of inimers and functional monomers in aqueous dispersed media

Core–shell structured hyperstar polymers that contained a hyperbranched core and hundreds of radiating arms were synthesized in a one-pot process without worrying about the hyperstar–hyperstar coupling reactions. The synthesis started with the atom transfer radical polymerization of an inimer in a microemulsion to produce hyperbranched polymers with high molecular weight, low polydispersity, and a high density of bromine initiating groups. After the complete conversion of the inimer, a second batch of monovinyl monomers was added in situ without destabilizing the microemulsion to subsequently grow radiating arms from these hyperbranched polymer macroinitiators (MIs). Two scenarios of arm growth were presented to demonstrate the efficient synthesis of hyperstar polymers. The hydrophobic n-butyl acrylate (nBA) monomer diffused into the latexes and swelled the hyperbranched polymers to form a seeded emulsion, which protected the growth of PnBA arms from each individual hyperbranched MI with no hyperstar–hyperstar coupling product even at >90% nBA conversion. The use of the zwitterionic cysteine methacrylate (CysMA) monomer caused the growth of arms out of the micelles and stabilized the hyperstar polymers in the aqueous phase, benefiting from the electrostatic repulsion between the charged arms and stars, which also avoided the hyperstar–hyperstar coupling at high conversion. When inimers containing a disulfide linker group were used in the synthesis of hyperbranched MIs, the produced hyperstar polymers exhibited rapid core degradation in a reducing environment and produced linear polymers as the degradation product.

Combinatorial therapy for triple negative breast cancer using hyperstar polymer-based nanoparticles

We report the ability of a novel combinatorial therapy obtained from nanoparticles of hyperstar polymers encompassing drugs to selectively target triple negative breast cancer (TNBC) cell proliferation through STAT3 and topoisomerase-II pathways. This nano-cocktail was at least two to four fold better than the individual drugs and 6-20 times more selective than the parent drugs.

Synthesis of acid-degradable hyperbranched polymers by chain-growth CuAAC polymerization of an AB3 monomer

A tetrafunctional AB3 monomer that was composed of one alkynyl group, three azido groups and one acetal linker was used in the one-pot copper-catalyzed azide–alkyne cycloaddition (CuAAC) polymerization for producing acid-degradable hyperbranched polymers (HBPs). In various feed ratios of the AB3 monomer to a B3 core, the polymerizations demonstrated a chain-growth mechanism with a linear increase of molecular weight versus conversion, low polydispersity and a high degree of branching (DB). The large amount of terminal azido groups on the HBPs periphery were further modified via reaction with an alkynyl-terminated poly(ethylene glycol) (PEG) to produce water-soluble PEGylated HBPs. Under acidic conditions, both the HBPs and the PEGylated HBPs exhibited clean and fast degradation into low-molecular weight compounds, confirming the labile acetal linkers in the backbone of HBPs.