One-pot Near-ambient Condition AI-RAFT for Star Polymer Synthesis

A near-ambient and oxygen tolerant arm-first star polymer synthesis strategy was developed using alkylborane-initiated reversible addition-fragmentation chain transfer (AI-RAFT). An air stable alkylborane-amine complex was chemically deblocked with isocyanate functionalities in-situ to liberate a reactive alkylborane that consumes oxygen to generate radicals to drive the RAFT processes. The AI-RAFT system was optimized for oxygen and initiator concentration as well as reaction time to improve livingness and further improve star conversion. Crosslinking agents were injected at the conclusion of arm polymerizations to yield star polymers, which were evaluated by arm-conversion values, arm numbers, and dispersities. To assess the tunability of star morphology, systematic studies were performed to evaluate the influence of monomer concentration, crosslinker functionality, crosslinker concentration, and the degree of polymerization of the arms. Our experimentation revealed that the functionality of the crosslinker had little effect on conversion of arms to stars, but that the ratio of the alkene to the CTA caused significant changes in arm conversion and arm numbers. Last, the star polymers produced by AI-RAFT were converted into poly(acrylic acid) stars and evaluated for use as polyelectrolyte complexes.M.S., Materials Science and Engineering -- Drexel University, 201

Spontaneous delamination of affordable natural vermiculite as a high barrier filler for biodegradable food packaging

Expensive biodegradable packaging as a preventative measure against continued accumulation of plastic waste in our environment is often in conflict with the need for high performing packaging materials that prevent food waste. Compounding with delaminated vermiculite nanosheets is a compelling concept to simultaneously improve barrier properties through creation of a ‘tortuous path’ while also decreasing the price of the system due to its natural abundance. However, an effective delamination process that captures the full barrier improvement potential of this natural filler has been lacking. Here, we present a superior protocol for vermiculite delamination based on reducing the intrinsic hydrophobicity due to interlayer Mg2+ cations and the transfer of this osmotically swollen, liquid crystalline state into organic solvents. Nanocomposite coatings of degradable polyesters on nanocellulose exhibited oxygen and water transmission rates of 1.30 cm3 m−2 day−1 atm−1 and 1.74 g m−2 day−1, respectively, which competes with high-end, non-degradable poly(vinylidene dichloride) films.</p