ABSTRACT
Elastomers with high strength and toughness are in great demand. Previous research on elastomers focused mainly on the design of new chemical structures, but their complicated synthesis process and expensive monomers have restricted the practical application of these materials. Inspired by general filler effects, a strategy is proposed to remarkably enhance the mechanical properties of thermoplastic polyurethane (TPU) elastomers by designing the arrangement of hard/soft segments using traditional chemical compositions. By utilizing the synergetic effect of weak hard segments, normal TPU elastomers are upgraded into advanced elastomers. Combining experiments and simulations, it is demonstrated that a suitable sequence length can achieve considerably enhanced strength and toughness by maximizing the relative surface area of hard domains. Mixing the obtained elastomer with an ionic liquid can result in a durable ionogel sensor with balanced mechanical strength and ionic conductivity. This easy-to-implement strategy offers a new dimension for the development of high-performance elastomers.
ABSTRACT
A copper-catalyzed atroposelective ring-opening reaction of cyclic diaryliodoniums, sodium cyanate (NaOCN) and phenols is reported. The reaction chemoselectively affords axially chiral carbamates by sequential coupling of cyclic diaryliodonium and NaOCN, followed by phenol. Mechanistic investigations revealed that phenol is not only a reagent to trap highly active intermediate isocyanates, but it also activates the copper catalyst as a standby ligand. The carbamates were readily transformed into highly functionalized urea derivatives within a simple nucleophilic substitution reaction.
ABSTRACT
Flexible polymers are widely used in the fields of wearable devices, soft robots, sensors, and other flexible electronics. Combining high strength and elasticity, electrical conductivity, self-healability, and surface tunable properties in one material becomes a challenge for designing polymeric materials for these applications, especially in flexible electronics. Herein, we propose a "two birds with one stone" strategy to synthesize thermal and UV light adaptive polyurethane elastomers with high-strength, self-healable, surface-modifiable and patternable functions for photolithography-transfer printing flexible circuits. The "stone", dihydroxybenzophenone, plays two roles in the synthesized polyurethanes as both a dynamic covalent bond and a UV-sensitive unit. On one hand, the phenolic group reacts with isocyanate to form a dynamic covalent phenol-carbamate bond, making the polymer self-healable, processable, and surface-embeddable with conductive fillers utilizing dynamic network rearrangement. On the other hand, the benzophenone group acts as a UV-sensitive unit to graft other functional groups to the polymer surface or self-crosslink on the surface under UV irradiation. Based on the dynamic covalent network and UV self-crosslinking properties, self-healable patterned flexible circuits can be obtained by photolithography-transfer printing. The flexible circuits prepared by loading silver nanowires on the dynamically crosslinked polyurethane substrate show little change of electric resistance when stretched up to 125% and can withstand thousands of stretching cycles.
Subject(s)
Elastomers , Printing , Elastomers/chemistry , Nanowires , Polymers/chemistry , Polyurethanes/chemistry , Silver , Ultraviolet RaysABSTRACT
Four linear polyurea elastomers synthesized from two different diisocyanates, two different chain extenders and a common aliphatic amine-terminated polyether were used as models to investigate the effects of both diisocyanate structure and aromatic disulfide chain extender on hard segmental packing and self-healing ability. Both direct investigation on hard segments and indirect investigation on chain mobility and soft segmental dynamics were carried out to compare the levels of hard segmental packing, leading to agreed conclusions that correlated well with the self-healing abilities of the polyureas. Both diisocyanate structure and disulfide bonds had significant effects on hard segmental packing and self-healing property. Diisocyanate structure had more pronounced effect than disulfide bonds. Bulky alicyclic isophorone diisocyanate (IPDI) resulted in looser hard segmental packing than linear aliphatic hexamethylene diisocyanate (HDI), whereas a disulfide chain extender also promoted self-healing ability through loosening of hard segmental packing compared to its C-C counterpart. The polyurea synthesized from IPDI and the disulfide chain extender exhibited the best self-healing ability among the four polyureas because it had the highest chain mobility ascribed to the loosest hard segmental packing. Therefore, a combination of bulky alicyclic diisocyanate and disulfide chain extender is recommended for the design of self-healing polyurea elastomers.
