Casey L. Elkins

Introduction of Multiple Hydrogen Bonding for Enhanced Mechanical Performance of Polymer-Carbon Nanotube Composites

Due to their outstanding mechanical properties and high aspect ratios, carbon nanotubes (CNTs) are envisioned as attractive nanofillers in polymer composites. However, due to strong van der Waals interactions, deleterious aggregation of CNTs is typically observed in polymer nanocomposites. Moreover, due to low stress transfer between the matrix polymer and the nanotube filler, only limited reinforcement is obtained. We report here a novel functionalization strategy to obtain CNTs with pendant self-complementary hydrogen bonding groups in order to address these limitations. Multi-walled CNTs were functionalized with ureidopyrimidinone (UPy) groups, which display multiple hydrogen bonding. The functionalized CNTs were blended with acrylic copolymers containing pendant UPy moieties and significant enhancement in tensile performance of the nanocomposites was observed.

“Reversible Macromolecules” as Scaffolds for Adaptive Structures

Self-healing macromolecular structures, submicron capsules and fibers with molecular recognition, stimuliresponsive molecules, solvent-free rheological reversibility, multivalency in rational drug design, and the emergence of new fields of adaptive and evolutive chemistry will require a predictive synergy of tailored non-covalent and covalent bonding in molecular design. Supramolecular chemistry has emerged as a stimulating focal point that will enable these scientific and technological discoveries, and biorecognition and biomolecular organization often serve as the inspiration for the future design of supramolecular assemblies. Linear and branched macromolecules are conventionally prepared using unique combinations of step-growth and chain polymerization strategies wherein the repeating units are irreversibly connected using stable covalent bonds. Moreover, optimum physical properties and commercial success of macromolecules are derived from our ability to prepare exceptionally high molecular weights in a controlled fashion. Although high molecular weight linear macromolecules are desirable for the optimization of physical performance and commercial impact, high molecular weights often compromise future solvent-free manufacturing, melt processability, thermal stability, and recyclability of the final products. Our recent efforts have demonstrated the utility of living anionic polymerization techniques to place functionality at desired positions on the polymer backbone. This control allowed investigation of the relationship between topology and tailored functionality, a fundamental investigation that may lead to interesting adaptive and smart applications. Specifically, the synthesis of polyisoprene homopolymers in a variety of topologies was performed, as well as the introduction of complementary hydrogen bonding to diverse families of hydroxyl containing polymeric and monomeric precursors.Copyright