Abstract:The nonpolar nature of polyolefins is one of their biggest limitations. Now, an efficient route to generate polar‐functionalized, crosslinkable, self‐healing, photoresponsive polyolefins with thermoplastic, elastomeric, and thermosetting properties is reported. Tunable amounts of carboxylic acid and a cyclic comonomer are installed onto polyolefins by palladium‐catalyzed terpolymerization reactions. The incorporated carboxylic acid unit can alter the surface properties of polyolefins. The subsequently introduc… Show more
“…According to the Ashby plot of UTS versus self-healing temperature for recently reported elastomers, previous tensile strengths did not exceed 20 MPa without the aid of light or a temperature above 40 °C (Fig. 2 and Supplementary Table 3 ) 9 , 21 – 24 , 34 – 40 , 42 , 43 , 47 – 51 . Fig.…”
Section: Resultsmentioning
confidence: 80%
“…However, the trade-off between mechanical and healing performance is the biggest hurdle that these materials face and need to overcome. The high chain rigidity, entanglement, and crystallinity required for mechanical strength conflict with the high diffusibility and exchange of dynamic bonds required for repairing damage 21 – 24 . Consequently, materials that autonomously heal at ambient temperature exhibit mechanical performance that is unsatisfactory for industrial commercialization.…”
Self-repairable materials strive to emulate curable and resilient biological tissue; however, their performance is currently insufficient for commercialization purposes because mending and toughening are mutually exclusive. Herein, we report a carbonate-type thermoplastic polyurethane elastomer that self-heals at 35 °C and exhibits a tensile strength of 43 MPa; this elastomer is as strong as the soles used in footwear. Distinctively, it has abundant carbonyl groups in soft-segments and is fully amorphous with negligible phase separation due to poor hard-segment stacking. It operates in dual mechano-responsive mode through a reversible disorder-to-order transition of its hydrogen-bonding array; it heals when static and toughens when dynamic. In static mode, non-crystalline hard segments promote the dynamic exchange of disordered carbonyl hydrogen-bonds for self-healing. The amorphous phase forms stiff crystals when stretched through a transition that orders inter-chain hydrogen bonding. The phase and strain fully return to the pre-stressed state after release to repeat the healing process.
“…According to the Ashby plot of UTS versus self-healing temperature for recently reported elastomers, previous tensile strengths did not exceed 20 MPa without the aid of light or a temperature above 40 °C (Fig. 2 and Supplementary Table 3 ) 9 , 21 – 24 , 34 – 40 , 42 , 43 , 47 – 51 . Fig.…”
Section: Resultsmentioning
confidence: 80%
“…However, the trade-off between mechanical and healing performance is the biggest hurdle that these materials face and need to overcome. The high chain rigidity, entanglement, and crystallinity required for mechanical strength conflict with the high diffusibility and exchange of dynamic bonds required for repairing damage 21 – 24 . Consequently, materials that autonomously heal at ambient temperature exhibit mechanical performance that is unsatisfactory for industrial commercialization.…”
Self-repairable materials strive to emulate curable and resilient biological tissue; however, their performance is currently insufficient for commercialization purposes because mending and toughening are mutually exclusive. Herein, we report a carbonate-type thermoplastic polyurethane elastomer that self-heals at 35 °C and exhibits a tensile strength of 43 MPa; this elastomer is as strong as the soles used in footwear. Distinctively, it has abundant carbonyl groups in soft-segments and is fully amorphous with negligible phase separation due to poor hard-segment stacking. It operates in dual mechano-responsive mode through a reversible disorder-to-order transition of its hydrogen-bonding array; it heals when static and toughens when dynamic. In static mode, non-crystalline hard segments promote the dynamic exchange of disordered carbonyl hydrogen-bonds for self-healing. The amorphous phase forms stiff crystals when stretched through a transition that orders inter-chain hydrogen bonding. The phase and strain fully return to the pre-stressed state after release to repeat the healing process.
“…[ 1 ] Late‐transition‐metal catalysts have been playing important roles in the field of catalytic olefin polymerization. [ 2‐11 ] Initially, nickel complexes were known as “poisons” for coordination polymerization of olefins, since Ziegler et al . observed the famous nickel effect.…”
Section: Background and Originality Contentmentioning
A series of dibenzhydryl-based iminopyridine-N-oxide ligands bearing a range of electron-donating or -withdrawing substituents (OMe, H, and NO 2 ) and corresponding nickel pre-catalysts are prepared and characterized. The substituents are installed at different positions on the ligand structure, including 4-position of the pyridine-N-oxide moiety (position X) and 4-position of the aniline moiety (position Y). These nickel pre-catalysts are highly active in ethylene polymerization with the addition of very little amount of aluminum cocatalysts, leading to the formation of polyethylenes with molecular weights of well above one million. Electron-donating substituents make the catalysts sensitive to polymerization temperature. In contrast, the catalysts bearing electron-withdrawing NO 2 substituents show relatively steady performances at different temperatures. Most importantly, we demonstrate that different substituents and different positions both play important roles in determining the properties of nickel catalysts. This provides an alternative strategy for the future design of high-performance polymerization catalyst.
“…With a biaryl‐ based phosphine sulfonate palladium catalyst (PO‐Pd), the group of Chen successfully installed polar functional units into polyethylenes by terpolymerization of ethylene with ethylidene norbornene (ENB) and 10‐undecenoate ( m ‐CO 2 Me) or 10‐undecenoic acid ( m ‐CO 2 H) (Scheme 3). [ 5 ] This system exhibits several appealing features: (a) good tolerance of ester or carboxylic acid functionalities; (b) very efficient ENB incorporation rate (i.r. up to 22.6%); (c) high molecular weight ( M n up to 17.6×10 4 g·mol –1 ).…”
Increasing demand for polar functionalized polyolefins has motivated the development of new polymerization chemistry to introduce functional groups into polyolefins, which is industrially important but scientifically challenging. Coordination-insertion copolymerization of ethylene and polar comonomers offers a direct and economic way to synthesize functionalized polyethylenes and great achievements have been gained by employing catalytic systems based on transition metals and rare earth metals. Continuous efforts have been devoted to developing novel catalytic systems and strategies to introduce chemically diverse functionalities at specific positions, control over the microstructures and get high molecular weight functionalized polyethylenes with high activity and good enchainment capacity. This article summarizes some important advances in the past three years in this field, focusing on the studies using chemically diverse polar comonomers to afford functionalized polyethylenes with novel microstructures.
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