Covalently Cross-Linked and Mechanochemiluminescent Polyolefins Capable of Self-Healing and Self-Reporting

Open AccessCCS ChemistryRESEARCH ARTICLE1 May 2021Covalently Cross-Linked and Mechanochemiluminescent Polyolefins Capable of Self-Healing Self-Reporting Yakui Deng, Yuan Yulan Chen Deng Tianjin Key Laboratory Molecular Optoelectronic Science, Department Chemistry, University, 300354. Google Scholar More articles by this author , *Corresponding author: E-mail Address: [email protected] https://doi.org/10.31635/ccschem.020.202000303 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesTrack Citations ShareFacebookTwitterLinked InEmail Compared with non-cross-linked dynamically covalent polymers, covalently cross-linked networks are irreplaceable in many areas; however, they difficult repair once fractured, due limited polymer chain diffusion after cross-linking. Herein, the authors have reported a new kind permanently polyolefin, which when attached amide side groups, yield mechanically robust yet readily repairable materials. A key is use low cross-linking density, enables satisfactory elasticity mobility for thermodynamically favored healing. Another incorporate dense hydrogen bonds that can undergo reversible associations. These factors jointly promise polyolefin good mechanical properties self-healing performance (recovered spontaneously up 96% its original tensile strength). importantly, means mechanochemiluminescence from 1,2-dioxetane, serves as cross-linker built-in self-reporting stress probe, microscopic evaluation how entanglement proceeds upon healing failure occurs network be obtained. Download figure PowerPoint Introduction Permanently polyolefins represent an important class engineering materials demanding applications, such aircraft industry, high-performance coatings, so on.1,2 They superior properties, dimensional stability, solvent resistance relative their linear counterparts.3,4 Besides, polyolefin-based elastomers unique concerning energy savings during production comparison other materials, cost easily available raw well versatility physical properties.5 advantages highlight aggressive growth tremendous potential. However, these polymeric inevitably irreversibly damaged formation propagation cracks. To improve safety features lifetime, it great significance develop intrinsic fully or partially heal following damage. Moreover, revealing events correlated process fundamental interest priori useful designing durable networks. Soft ductile polymers often exhibit performance, based on associations bonds6–8 supramolecular interactions,9–11 bonds.12–14 associations, relatively weak compared analogs, mostly, reorganize healing, external stimuli catalyst loading required.15,16 Introducing cross-links into improves but usually at expense poor efficiency. This because entropy changes small surroundings matrix confinements. In regard, promoting segmental flexibility introducing efficiently become critical, challenge, excellent minimum intervention Recent research efforts mechanochemistry witnessed development sensors enable situ monitoring clearly perceptible optical signal.17–22 One outstanding example was developed Sijbesma et al. using 1,2-dioxetane mechanophore.23 found molecular unit could broken concomitant light emission incorporated network.23–25 Such mechanochemiluminescent constitutes sensitive way probe mechanochemical bond scission translating invisible signal visible case sufficient entanglement. As recognized outcome regain via entanglement.26–28 turn, knowledge highlights further utility mechanoluminescent probe: we thereby envision if integrated healable systems, view behaviors networks, particular interpenetrating being recovered efficient force transduction, would Ring-opening metathesis polymerization (ROMP) versatile preparing tunable structures properties.29 availability bifunctional dioxetane precursor ROMP, mechanochemiluminescent, cyclooctene-based (Figure 1a). By exploring hydrogen-bonding functionality autonomously behavior realized nondynamically elastomers. Importantly, optomechanical studies samples provide detailed information regarding buildup fracture surface process, beyond capability conventional macroscopic techniques. Figure 1 | (a) Schematic representation self-healable HBM-Ad-COEU. (b) Synthesis HBM-Ad-COEU controls (N1, M1) study. Experimental Methods General All work involving air- and/or moisture-sensitive compounds carried out Etelux glovebox under nitrogen atmosphere standard Schlenk techniques unless otherwise noted. were obtained Sigma-Aldrich (St. Louis, Missouri, USA) Tokyo Chemical Industry (TCI) used without purification not mentioned otherwise. The bulky cyclic olefin monomer exo-1,4,4a,9,9a,10-hexahydro-9,10(1?,2?)-benzeno-l,4-methanoanthracene (HBM) 5-norbornene-2-yl methyl 11-(2-ethylhexanamido)undecanoate (NMEU) prepared according literature procedures.12 Grubbs’ third-generation (G3) stored weighed glovebox. Dichloromethane (DCM) distilled argon over CaH2 prior use. reactions performed specified, all glassware oven dried before Detailed synthesis [cyclooct-4-en-1-yl-11-(2-ethylhexanamido)undecanoate (COEU), bis(adamantyl)-1,2-dioxetane (Ad), cyclooct-4-en-1-yl-11-(2-ethyl-N-methylhexanamido)undecanoate (COMU)], additional characterization data Supporting Information. Representative procedure Taking HBM-Ad-COEU-1 example, COEU (1188 mg), Ad (12 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole23 (6 mg) mixed 10 mL anhydrous DCM flask. Then removal oxygen accomplished applying least three freeze–pump–thaw cycles. G3 (3.8 dissolved 3 DCM. solution transferred another flask cooled ?10 °C. After stirred °C 5 min, HBM (64 added 30 min. solutions two flasks simultaneously poured Teflon mold mixing 72 h, followed removing 40 24 h vacuum. Optomechanical testing Tensile experiments TA Rheometrics, Discovery Hybrid Rheometer-2 (DHR-2) equipped Xpansion Instrument, Sentmanat Extensional Rheometer (SER3), extensional fixture. drums fixture colored black permanent marker eliminate reflecting light. transparent double-sided sticky tape put tightly fix film slippage. pco.edge (version 5.5; Kelheim, Free State Bayern, Germany) camera Nikon AF NIKKOR 50 mm 1?1.4 D lens record videos darkness. recorded rolling shutter color mode shooting rate 200 fps exposure time 5.0 ms. frames resulting video exported separate monochrome TIF files, intensity analyzed home-made program MATLAB literature.23 Results Discussion shown 1b, first, steric bulk monomer, HBM, subjected ROMP (G3), affording preoligomer (PHBM, Mn = 5.3 kDa, Information S1).12 construct “soft” block high segment introduce H-bonding association entities, second pendant groups prepared. Specifically, norbornene-modified ( Scheme S1) successfully developed, serve both skeleton. Subsequently, target loose HBM-Ad-COEUs through one-pot (0.60 mol % 0.74 HBM-Ad-COEU-2) Table S1). reveal role soft promote self-healing, rigid NMEU selected offer control sample N1.12 investigate effect hydrogen-bonding, synthesized M1 blocked Fourier transform infrared (FT-IR) spectra indicated characteristic peaks assignable HBM-Ad-COEU-1, HBM-Ad-COEU-2, N1. M1, disappearance N–H stretching in-plane bending bands proved S2).8,11 densities evaluated swelling experiments.30,31 With content increasing, ratio CHCl3 decreased, while gel increased instead S3). addition, thermal stability supported thermogravimetric analysis (TGA; S4). Differential scanning calorimetry (DSC) analyses demonstrated amorphous Tg below room temperature S5); therefore, rubbery temperature. Notably, N1, showed rather (e.g., ca. ?20 ?30 °C), essential achieve dynamics reversibility (Table 1).11,12 Mechanical Propertiesa Polymers Sample Strength (MPa) ?b (%) TgDSC (°C) 42 ± 4 243 ?30.7 HBM-Ad-COEU-2 116 2 249 15 ?20.9 N1 123 228 13 3.1 17 212 ?18.1 HBM-Ad-COEU-1(9 h)c 38 6 225 37 — HBM-Ad-COEU-1(11 41 230 aAll tests conducted Hencky strain 8 s?1. bMaximum break. cSelf-healed designated time. as-synthesized characterized static tests, rheometer Expansion Instruments SER Universal Testing Platform S6).32 geometry ensured uniform deformation facilitated stress–strain relationship luminescence (see below) measurements maintaining center stretch zone fixed location. First, incorporation labile did weaken network, seen results Ad-free material HBM-EG-COEU S7). Since our comparable documented secondary amide-containing polyolefins8,12,33 S8 S2), more cross-linkers much tougher than therefore concluded robustness mainly derived nature. reinforcement brought effective interactions played joint role, deduced study M1: going enhancement maximum breakage (ca. 2.5- 1.15-fold, respectively) observed. exhibited ambient conditions. Typically, (20 × 0.34 mm) cut pieces, conditions 11 self-repaired bear manual tearing 2a). Also, scratch recovery test illustrated became obviously shallow 2b). evaluate efficiencies quantitatively, films first (cut 70–90% width), then interfaces together any pressure, different periods. efficiency quantified (%stress) pristine sample, showing dependent (Figures 2c 2d; Figures S9–S11 samples, is, 96.2% achieved h. contrasts about 80.4% value same contrast, only partial (42.3% 25.2%). Their ascribed either rigidity stiffness backbone, bonds, suggested thermodynamic kinetic control.8,34 Images full-cut images scratched healed self-healed s?1: (c) (d) (%light), (e) total emitted straining films. %stress rupture sample. %light rare. Examples include olefin-containing Ru catalyst-mediated dynamic cross metathesis,8,33 hybrid elastomer 30% strength driven bonds.35 exceptionally supposed follow mechanisms. should noted despite similar skeleton Guan al.,8 self-repair metathetic way. adaptive potentially Ru-activated excluded, since return shape step S12).12,33,36 Next, relaxation surveyed series rheological indicators properties. frequency sweep varying 70 elastic solids wide range shear frequencies temperatures (storage modulus G? > loss G?; S13).37,38 Given loosely characteristics upward transition tested regions probably ease rearrangement dissipation sacrificial bonds.8 Based Information), calculated times (?) flow transitions (on order second).39 particular, best shorter lower those reflective chains greatly contributing S14).6 intercept plots square root G? against angular regarded measure stress.39 S15, has decreases increasing temperature, indicates highest amongst Then, probed set tests.8 Unlike bond-rich hysteresis loading–unloading cycle unremarkable 3a), elastomeric little dissipation.35 40% observed lost 2, continuing slight subsequent cycles (cycles 3–10), cannot relax equilibrium scales individual cycles, allowed min most performance. dissipated short period survival cross-links, prevent assist reformation bonds. Altogether, deduce nature dominates overall featured notable offers favorable thermodynamics fine-tuning cross-link density. Furthermore, play reinforcing 3b). Recovery HBM-Ad-COEU-1. specimens loaded (150%), unloaded, immediately reloaded (strain rate: 100 mm/min, 25 °C). Cycles 1, 3, 4, 5, 6, 7, 8, 9, 10, plotted clarity. Cycle took place no Bar graphs summarize percent each Proposed mechanism illustrating accounting capacity network. distinct feature Control bis(adamantanylidene) Ad, physically give light, confirming luminescence.23 Analysis representative taken demonstrates temporal spatial resolutions mechanoluminescence S16). That starts emit uniformly throughout stress, strongly luminescent pronounced localization location fracture. fracture, Similar transient stress-dependent also S11d). ability visualize distribution within space. Light s?1, displayed >2.1. Evolution versus HBM-Ad-COEU-2. region (Inset picture fracture.) question chemical recover understand resolution methods reach microscale.27 Again, benefiting enormously level. previously mentioned, transduction accumulation fractured proceed smoothly 1,2-dioxetanes activated accumulated. Therefore, terms (%light sample), %stress.40 findings recoverable reaching 60.5% 92.1% 9 respectively 2d 2e), mechanoluminesent 79.6% S10). early stage instance appeared S3), deviation %stress–%light gradually smaller proceeded. lags behind stress. reasonable earlier contributes experienced enough pull strands activate mechanophore. At later stages, coincide other, indicating reconstruction mechanotransduction, or, words, mostly 7 microscopically, far completed occurring stages. descriptions whose maintained level abilities, similarly, lagged property Thus, 1,2-dioxetane-based able precise insights origins Conclusions capable synthesized. 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