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Lignin can be an important source of synthetic commodity materials owing to its abundance in nature and low production cost. The current use of lignin as a raw material, however, is very limited and focused only on cheap and poorly defined nonfunctional materials. Herein we report a new lignin-containing functional polymer, lignin-graft-poly(5-acetylaminopentyl acrylate) (lignin-graft-PAA), which has been prepared by the covalent linkage of chemically modified lignin with PAA, which is an end-group functionalized polymer. This work makes two significant advances in the study of lignin-containing polymers: (1) lignin-graft-PAA is the first example of lignin being modified by a polymer with sophisticated structure, and (2) lignin-graft-PAA shows a special performance, autonomic self-healing properties, which have not yet been seen in lignin-containing polymers. The key synthetic step in this process utilizes a copper-catalyzed azide-alkyne cycloaddition or "click" reaction in order to join together the lignin and polymer moieties. The polymer, PAA, was itself prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization of monomers containing multiple hydrogen-bonding sites on their pendants in the form of acetylamino functional groups. The selected RAFT agents also resulted in a polymer with an azide group at its terminus, which is necessary for the desired click reaction. Separately, biomass lignin was chemically modified by 5-hexynoic acid to introduce an alkyne functionality onto lignin. The azide terminus of the polymer was joined to the alkyne group of lignin to form a covalent bond. The lignin-graft-PAA possesses a well-dispersed multiphase nanostructure, a rigid lignin phase and a soft-PAA phase, which has a rubber-like flexibility. The mechanical properties of the newly synthesized lignin-graft-PAA can be readily controlled by the mass ratio of lignin and polymer during synthesis. In this study, the mass ratio was varied by either polymer length or weight percentage of lignin. It was revealed that a lignin-graft-PAA composite with 15-20 wt % lignin demonstrated the most optimal rubber-like, flexible property. Thanks to the high degree of hydrogen bonding from the acetylamino functionalities, lignin-graft-PAA also showed self-healing properties, recovering up to 93% of its original maximum stress before fracture. [ABSTRACT FROM AUTHOR]

Using principles inspired by the study of naturally occurring sticky systems such as the micro- and nanoscale fibers on the toes of geckos and the adhesive proteins secreted by marine animals such as mussels, this study describes the development and evaluation of a novel patterned and coated elastomeric microfibrillar material for enhanced repeatable adhesion and shear in wet environments. A multistep fabrication process consisting of optical lithography, micromolding, polymer synthesis, dipping, stamping, and photopolymerization is described to produce uniform arrays of polyurethane elastomeric microfibers with mushroom-shaped tips coated with a thin layer of lightly cross-linked p(DMA-co-MEA), an intrinsically adhesive synthetic polymer. Adhesion and shear force characterization of these arrays in contact with a glass hemisphere is demonstrated, and significant pull-off force, overall work of adhesion, and shear force enhancements in submerged aqueous environments are shown when compared to both unpatterned and uncoated samples, as well as previously evaluated patterned and coated arrays with differing geometry. Such materials may have potential value as repeatable adhesives for wet environments, such as for medical devices. [ABSTRACT FROM AUTHOR]

In this work, we take previously developed gecko-foot-hair-inspired elastomer microfiber arrays with film-terminated and mushroom-shaped tips that have demonstrated enhanced adhesion with respect to unpatterned materials under dry conditions and coat them with synthetic DOPA-containing mussel-inspired polymers to enhance adhesion repeatedly in fully submerged wet environments. A new protocol for the development of this hybrid patterned, coated adhesive, which is suitable for use in contact with both wet and dry nonflat surfaces, is described. The experimental evaluation of repeatable adhesion under both wet and dry conditions for these materials is described and compared with unpatterned and/or uncoated materials. Macroscale reversible fibrillar adhesion enhancement on a nonflat, smooth glass surface when compared with unpatterned materials under fully submerged conditions is demonstrated with no suction effect. [ABSTRACT FROM AUTHOR]

A highly removable N-heterocyclic carbene ligand for a transition-metal catalyst in aqueous media via host–guest interactions has been developed. Water-soluble adamantyl tethered ethylene glycol in the ligand leads a hydrophobic inclusion into the cavity of β-cyclodextrin. Ruthenium (Ru) olefin metathesis catalyst with this ligand demonstrated excellent performance in various metathesis reactions in water as well as in CH2Cl2, and removal of residual Ru was performed via filtration utilizing a host–guest interaction and extraction. [ABSTRACT FROM AUTHOR]