Bifunctional RAFT Agent Directed Preparation of Polymer/Graphene Oxide Composites.

Polymer/graphene oxide (GO) composites, which combine the physical properties of GO and the processability of polymers, are of increasing interest in a variety of applications ranging from conductive foams, sensors, to bioelectronics. However, the preparation of these composites through physical blending demands the polymers with functional groups that interact strongly with the GO. Here the design and synthesis of a new bifunctional reversible addition-fragmentation chain transfer (RAFT) agent are demonstrated, which allows the synthesis of polymers with predetermined molecular weights and low dispersibilities (Ð), while having functionalities at both polymer termini that allow strong binding to GO. To access polymers with diverse thermal and mechanical properties, acrylonitrile-styrene-acrylate (ASA) copolymers with different types of acrylates, both short and long side chains, are synthesized under the control of the bifunctional RAFT agent. Furthermore, the strong binding between GO and the synthesized polymers is verified and explored to prepare polymer/GO composites with diverse tensile strengths and conductivity in the range of semiconductors. Overall, this novel RAFT agent is expected to expand the utility of polymer/GO composites by providing well-defined polymers with tunable properties and strong binding with GO.

Self-assembled, optically-active {naphthalene diimide}U{cucurbit[8]uril} ensembles in an aqueous environment.

Naphthalene diimides (NDIs) are shown to arrange spontaneously co-facially with cucurbit[8]uril (CB[8]) in an aqueous environment through purely non-covalent interactions. The resultant 2 : 2 supramolecular complex of NDI and CB[8] is highly fluorescent (>30 times more than the constituent NDIs) due to the formation of NDI-NDI excimers within the supramolecular complex.

RAFT Polymer-Based Surfactants for Minerals Recovery.

Reagent consumption is an ongoing sustainability challenge for the mineral processing industry. There is a need to recover, regenerate, and reuse as many of the chemical inputs as possible. This study investigated the design and synthesis via reversible addition-fragmentation chain transfer (RAFT) polymerization of a novel polymer for use as a surfactant in a water-in-oil (w/o) emulsion system for ultrafine minerals recovery. The polymers were designed to hold a thermoresponsive moiety to allow for future recovery. The performance of the novel emulsion was tested for agglomeration of ultrafine talc mineral particles. A traditional emulsion containing sorbitan monooleate as the surfactant was used as a research benchmark to compare against the novel emulsion's stability and performance in minerals recovery. The novel RAFT polymer-based emulsions formed large and stable water droplets surrounded by a halo of smaller water droplets. Over time, the smaller droplets coalesced and a more uniform size distribution of droplets was formed, keeping the emulsion stable. Rheological testing of freshly made and aged emulsions showed both traditional and novel emulsions to have a high viscosity at a low shear rate. RAFT polymer B with a hydrophilic-lipophilic block ratio of 5:10 performed adequately as a surfactant replacement to stabilize w/o emulsions. The mineral recovery using the novel emulsion was on par with the traditional emulsions. The novel RAFT emulsion containing 2.5 wt % polymer B achieved 90% minerals recovery, a similar yield to the traditional emulsions. This study demonstrates that surfactants containing stimuli-responsive moieties can be synthesized via RAFT polymerization and successfully used in mineral processing applications to recover ultrafine particles. Work is ongoing to exploit the stimuli responsiveness to recover the polymer surfactant for reuse.

The Grob/Eschenmoser fragmentation of cycloalkanones bearing ß-electron withdrawing groups: a general strategy to acyclic synthetic intermediates.

Introduction of a ß-electron withdrawing group to cycloalkanones allows facile C-C bond fragmentation. The reaction has been demonstrated with a large range of ring sizes, bearing various leaving and electron withdrawing groups, and using a variety of nitrogen and oxygen containing nucleophiles (>30 examples). The application of fragmentation products to the preparation of substituted γ-lactones has been demonstrated. Mechanistic studies are reported which are suggestive of a Grob/Eschenmoser type reaction.