Self-healing thermoset polyurethanes utilizing host‒guest interaction of cyclodextrin and adamantane

Self-Healing Thermoset Polyurethanes Driven by Host-Guest Interactions Between α-Cyclodextrin and Poly(ethylene glycol) Monomethyl Ether or Dodecanol Moieties

Self-healing thermoset polymers have attracted significant attention because they contribute to resource and energy savings by extending their service life. The reactions between glycerol ethoxylate (GCE), α-cyclodextrin (α-CD), poly(ethylene glycol) monomethyl ether (MPEG), and hexamethylene diisocyanate (HDI) at molar ratios of GCE:α-CD:MPEG = a:b:c produced polyurethane networks (GCM-abc, abc = 311, 411, and 511) containing α-CD and MPEG as host and guest moieties, respectively. To compare this with GCM-411, 1-dodecanol (DN) was used instead of MPEG as a guest molecule to yield a polyurethane network (GCD-411). Dynamic mechanical analysis revealed the formation of a polymer network, and the loss tangent (tan δ) peak temperature (Tα) and crosslinking density (νe) decreased with increasing GCE fraction for GCMs, and the Tα and νe values of GCD were slightly higher than those of GCM-411. The tensile strength of the GCMs decreased with increasing GCE fraction, and the tensile strength of GCD-411 was slightly higher than that of GCM-411. All cured films were healed at room temperature for 24 h, and the healing efficiency (ησ), based on tensile strength, increased in the order of GCM-311 < GCM-411 < GCM-511 < GCD-411. When the healing temperature increased from room temperature to 80 °C, ησ increased from 24-38% to 45-62%. GCM-411 and GCD-411 were self-healed thrice by treatment at 80 °C, and ησ gradually decreased with each healing cycle.

Host-guest-induced electronic state triggers two-electron oxygen reduction electrocatalysis

Supramolecular polymers possess great potential in catalysis owing to their distinctive molecular recognition and dynamic crosslinking features. However, investigating supramolecular electrocatalysts with high efficiency in oxygen reduction reaction to hydrogen peroxide (ORHP) remains an unexplored frontier. Herein, we present organic polymers for ORHP by introducing cyclodextrin-containing noncovalent building blocks, affording these supramolecules with abundant dynamic bonds. The electronic states and reaction kinetics are further well-modulated via a host-guest strategy, resulting in appropriate regional electron binding force and controllable chemical activity. Notably, integrating supramolecular units into phenyl group-containing model covalent polymer achieves a production rate of 9.14 mol g-1 cat h-1, with 98.01% Faraday efficiency, surpassing most reported metal-free electrocatalysts. Moreover, the dynamic bonds in supramolecular catalysts can effectively regulate the binding ability of oxygen intermediates, leading to high reactivity and selectivity for the 2e- pathway. Supported by theory calculation and in situ experiment, C atoms (site-1) adjacent to the -C = N (N) group are potential active sites. This work pioneers host-guest strategy and provides inspiring ideas for the ORHP process.

Interfacial Rheological and Emulsion Properties of Self-Assembled Cyclodextrin-Oil Inclusion Complexes

To investigate the effect of the molecular size of alkanes and the cavity size of cyclodextrins (CDs) on the formation of interfacial host-guest inclusion complexes, the interfacial tension (IFT) of CD (α-CD, β-CD, γ-CD) solutions against oils (hexadecane, dodecylbenzene) was determined by interfacial dilational rheology measurements. The results show that the "space compatibility" between CDs and oil molecules is crucial for the formation of interface host-guest inclusion complexes. Hexadecane with a smaller molecular size can form host-guest inclusion complexes with small cavities of α-CD and β-CD, dodecylbenzene with a larger molecular size can form interfacial aggregates with the medium-sized cavity of β-CD easily, and the polycyclic aromatic hydrocarbon molecules in kerosene can form inclusion complexes with the large cavity of γ-CD. The formation of interfacial inclusion complexes leads to lower IFT values, higher interfacial dilational modulus, nonlinear IFT responses to the interface area oscillating, and skin-like films at the oil-water interface. What's more, the phase behavior of Pickering emulsions formed by CDs with different oils is explored, and the phenomena in alkane-CD emulsions are in line with the results in dilatation rheology. The interfacial active host-guest structure in the kerosene-γ-CD system improves the stability of the Pickering emulsion, which results in smaller emulsion droplets. This unique space compatibility characteristic is of great significance for the application of CDs in selective host-guest recognition, sensors, enhanced oil recovery, food industries, and local drug delivery.

Bio-Based Healable 2K PU Textile Coating for Durable Applications

A biobased healable 2K polyurethane (PU) coating incorporating a Schiff base was synthesized and applied as a thin coating on textiles. The Schiff base, made out of cystine and vanillin, contained reversible imine and disulfide bonds and was used as a chain extender in PU synthesis. The FT-IR analysis indicated the successful incorporation of the Schiff base in the PU backbone. Compared with control PU coatings, the healable bio-based PU coating with the Schiff base showed very good healing properties using heat as external stimuli: a healing recovery of 75% was obtained after applying a 2 N scratch and complete recovery of the resistance to hydrostatic pressure. SEM analysis revealed complete closure of the scratch after healing for 30 min at 90 °C. The healing properties are attributed to the synergy of the dual-dynamic metatheses of the imine and disulfide bonds.