A Novel Dynamic Polymer Synthesis via Chlorinated Solvent Quenched Depolymerization

Open AccessCCS ChemistryRESEARCH ARTICLES18 Oct 2022A Novel Dynamic Polymer Synthesis via Chlorinated Solvent Quenched Depolymerization Jiadeng Zhu, Sheng Zhao, Jiancheng Luo, Wei Niu, Joshua T. Damron, Zhen Zhang, Md Anisur Rahman, Mark A. Arnould, Tomonori Saito, Rigoberto Advincula, Alexei P. Sokolov, Bobby G. Sumpter and Peng-Fei Cao Jiadeng Zhu Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 , Sheng Zhao Departmnet of Chemistry, University of Tennessee, Knoxville, Tennessee 37996 , Jiancheng Luo Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 , Wei Niu Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee 37996 , Joshua T. Damron Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 , Zhen Zhang Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 , Md Anisur Rahman Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 , Mark A. Arnould Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 , Tomonori Saito Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 , Rigoberto Advincula Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee 37996 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 , Alexei P. Sokolov Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 Departmnet of Chemistry, University of Tennessee, Knoxville, Tennessee 37996 , Bobby G. Sumpter Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 and Peng-Fei Cao *Corresponding author: E-mail Address: [email protected] State Key Lab of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029 https://doi.org/10.31635/ccschem.022.202202362 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Dynamic polymers with both physical interactions and dynamic covalent bonds exhibit superior performance, but achieving such dry polymers in an efficient manner remains a challenge. Herein, we report a novel organic solvent quenched polymer synthesis using the natural molecule thioctic acid (TA), which has both a dynamic disulfide bond and carboxylic acid. The effects of the solvent type and concentration along with reaction times on the proposed reaction were thoroughly explored for polymer synthesis. Solid-state proton nuclear magnetic resonance (1H NMR) and first-principles simulations were carried out to investigate the reaction mechanism. They show that the chlorinated solvent can efficiently stabilize and mediate the depolymerization of poly(TA), which is more kinetically favorable upon lowering the temperature. Attributed to the numerous dynamic covalent disulfide bonds and noncovalent hydrogen bonds, the obtained poly(TA) shows high extensibility, self-healing, and reprocessable properties. It can also be employed as an efficient adhesive even on a Teflon surface and 3D printed using the fused deposition modeling technique. This new polymer synthesis approach of using organic solvents as catalysts along with the unique reaction mechanism provides a new pathway for efficient polymer synthesis, especially for multifunctional dynamic polymers. Download figure Download PowerPoint Introduction Dynamic polymers have been attracting significant attention due to their reprocessability and self-recovery after damage, which can prolong the lifetime of these materials.1–6 This is especially true for dynamic polymers with intrinsic self-healing ability that do not require a sequestered additive or trigger, allowing for multi-cycle healing.7–12 Generally, intrinsic self-healing polymers can be divided into three major categories based on the types of interaction: (1) physical bonds, such as ionic,13,14 metal-coordination,15,16 hydrogen bonding,17,18 host–guest,19 and van der Waals;20 (2) reversible chemical bonds, such as those formed by Diels–Alder reaction,21,22 free-radical reaction by acrylic monomers,23 disulfide exchange,24 and boronic ester bond;25,26 and (3) the combination of physical and chemical bonds.27 Due to the combined advantages from both physical and chemical interactions, the last category typically exhibits superior performance in terms of mechanical strength and extensibility, recyclability, self-healing rate, and efficiency. These advantages have recently led to intensive research; however, tedious, multistep synthetic routes under harsh conditions are generally required to create dynamic polymers with combined physical and chemical interactions. Preparation of such dynamic polymers via a low-cost, high-efficient approach from readily available raw materials is highly desired for sustainable materials development.28–33 With a carboxylic-acid tail and a dynamic covalent disulfide bond, the naturally derived organic molecule, thioctic acid (TA), is a promising candidate for the construction of robust dynamic polymers with combined physical and chemical interactions.34–41 By raising the temperature of TA above its melting point, the five-member ring containing disulfide bonds undergoes ring-opening polymerization, forming linear polymer chains with sulfur radicals at both termini.39 The terminal sulfur radicals initiate the reverse ring-closing depolymerization and revert to monomers after cooling, attesting to a more thermodynamically stable TA monomer.39 In recent years, several strategies report the synthesis of stabilized poly(TA) by quenching the terminal sulfur radicals.37–40 For example, Zhang et al.39 reacted 1,3-diisopropenylbenzene (DIB) with the terminal diradicals to form a chemically cross-linked polymer network. The molar ratio of Fe3+ to TA and reaction temperatures were tuned to enhance the Fe3+-carboxylate complexes, achieving a maximal tension strength of <60 kPa. Wang et al.40 recently prepared poly(TA)-based ionomer gel in the presence of 1-ethyl-3-methylimidazolium ethyl sulfate ([EMI][ES]), which stabilized the as-prepared poly(TA) with the aid of hydrogen bonds between [ES] and carboxylic acids. As an alternative approach, the deprotonated TA monomer, sodium thioctate (ST), was reported to self-organize and ring-opening polymerize during water evaporation process in a structurally ordered fashion. However, it exhibited a relatively low strain at low humidity (<10% elongation before breaks with relative humidity <10%).37 Very recently, the same group found that the poly(TA) could be stabilized with the addition of metal ions (i.e., Fe3+, Cu2+, etc.) as alternative ionic cross-linkers for polymer film formation in the absence of DIB, and the corresponding poly(TA) with metal ions can be recycled.38 According to these studies, extra cross-linkers (i.e., double bonds, ion-based, etc.) are normally required for dynamic elastic polymer poly(TA) synthesis, and although poly(ST) can be obtained without additional cross-linkers, they are a normally brittle, dry polymer that has lost the multifunctionalities including high stretchability and self-healing at ambient condition.42,43 Herein, we demonstrate a novel synthesis for a dynamic polymer that has the combined advantages of high stretchability, autonomous self-healing, excellent recyclability, high adhesion property, and 3D printability. Such design is inspired by some organic solvents with high chain transfer constant (e.g., chlorinated solvents) that react with and terminate the radical species.44–46 In contrast to regular reactions that require huge amounts of organic solvents (>90 wt. % solvent), a small amount of chlorinated solvent (<10 wt. %) is utilized here as a catalyst to produce dynamic polymers with a high monomer conversion. Different than previous studies on poly(TA) synthesis that use a double bond or ionic based cross-linker to interrupt the middle of the polymer chain, the chlorinated solvent herein acts as a "catalyst" that can stabilize and react with the sulfur radical terminated polymer chains at elevated temperatures, thereby preventing the kinetically favorable depolymerization of poly(TA) upon lowering the temperature. The insight of the solvent quenched depolymerization mechanism of the novel polymer synthesis approach, unraveled by solid-state NMR and first-principles simulations, may inspire other researchers to design different polymer synthetic routes via this unique reaction mechanism. Experimental Methods Synthesis of poly(TA) The TA (≥99%, Sigma-Aldrich, USA) was placed in a glass vial and melted at 120 °C in an oil bath. Then, a certain amount of dichloromethane (DCM) with a molar ratio of 0.25:1 to melted TA (anhydrous, ≥99.8%, Sigma-Aldrich, USA) was added during stirring. After 30 min reaction at 120 °C and cooling to room temperature, the obtained sample was dried in a vacuum oven. A sample without DCM was also obtained as a control following the same procedure. Meanwhile, other solvents, including MeOH, chloroform, and so on, with a molar ratio to TA of 0.25:1 were studied, and the corresponding results are summarized in Supporting Information Table S1. Characterizations Structure All NMR data were collected using a Bruker Avance III spectrometer (Bruker) operating at 400.3028 MHz 1H frequency. The monomer conversion was calculated by comparing integral ratios between vinyl peaks of poly(TA), described as follows: Monomer conversion ( % ) = [ Peak ( a ′ + c ′ ) / Peak ( a + c + a ′ + c ′ ) ] × 100 % Reaction mechanism investigation Magic angle spinning (MAS) experiments were performed in a 3.2 mm triple resonance Bruker probe. All experiments were performed at 14 kHz except for the DCM treated material, which became gel-like making the faster MAS unstable. This sample was spun at 8 kHz MAS. 1H T1 relaxation times were estimated from the null point of an inversion recovery curve and ranged from 0.75 to 11 s depending on the sample treatment. Cross polarization (CP) experiments were performed using a 10% ramp CP under Hartmann–Hahn matching conditions and a contact time of 4 ms. SPINAL-64 decoupling was used for decoupling during 13C acquisition.47 The 13C multi-CP experiments were performed using 18–20 CP blocks lasting 400–500 μs with 1–1.5 s 1H repolarization times and a relaxation delay of 1 s.48 For the DCM treated material, an excess of DCM was introduced to the NMR rotor with TA powder. The rotor was then heated in an oven to 120 °C for 30 min. Afterward, the rotor was kept in the oven at 70 °C for 1.5 days to drive off excess DCM. A control experiment where CP spectra were collected on as received TA, which was subsequently heated to 120 °C and cooled without DCM, was performed. Ab initio simulations Geometry optimizations of the TA monomer and poly(TA) were carried out in a vacuum and a model aqueous solution phase without imposing geometrical restrictions by using the NWChem suite of programs (version 7.0.2).49 All calculations were optimized using hybrid meta-functionals50 at the M06-2X/6-311++G** level. The solvent effects were accounted for by using both an explicit model (single solvent shell) and implicitly using the Solvation Model Based on Density.51 Following geometry optimization, ab initio molecular dynamics was performed at the same level of theory using a stochastic velocity rescaling thermostat to control the temperature at 400 K to examine TA polymerization or at room temperature to study depolymerization of poly(TA).52 Simulations were performed up to 1 ns and the trajectories were analyzed for geometric evolution, for example, if bonds cleaved or formed. Molecular weight The molecular weight (MW) and polydispersity (PDI) of each sample were measured with a Malvern OMNISEC GPC system (Malvern Panalytical Ltd.) equipped with OMNISEC RESOLVE and OMNISEC REVEAL (Malvern Panalytical Ltd.). The sample concentrations were 5 mg mL−1 and each was filtered through 30 mm 0.2 μm polytetrafluoroethylene (PTFE) filters prior to analysis. The analysis was carried out using two PLgel 5 μm mixed-C columns (7.5 mm ID × 300 mm) and one PLgel 5 μm guard column (7.5 mm ID × 50 mm) in series. Tetrahydrofuran (THF) was utilized as the eluent (1 mL min−1, with the entire system at 30 °C). Absolute molar masses were calculated relative to polystyrene standards in the OMNISEC software v11.21. The chromatogram of each sample was split into three regions during analysis, the main distribution at higher MW, a lower MW tail, and low mass peaks at the end of the separation. The approximate ratio in each section was calculated based on peak area. Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectra were acquired on a Bruker autoflex speed in positive ion reflection mode. The sample solutions were prepared at 10 mg mL−1, the sodium trifluoroacetate salt (NaTFA) at 3 mg mL−1, and the matrix (Super-DHB) at 60 mg mL−1. The solutions were mixed in a 10:1:10 (matrix:salt:sample) ratio and 1 μL was deposited on the ground stainless steel target for analysis. The samples, matrix, and salt were dissolved in 50:50 THF:chloroform after repeated vortex mixing to ensure dissolution. The spectra were obtained by summing at least 5000 shots into the sum buffer prior to analysis. The mass spectra were analyzed in Bruker FlexAnalysis software. The absolute MW could not be provided due to the high PDI of the obtained sample; therefore, the lower MW species in the "ski-slope" distribution were targeted. Morphology and thermal properties The scanning electron microscopy (SEM) images were recorded in a Carl Zeiss Merlin scanning electron microscope. The energy-dispersive X-ray spectroscopy (EDS) results were obtained with a system from Bruker Nano GmbH using a XFlash detector 5030 (Bruker, Berlin, Germany). Differential scanning calorimetry (DSC) measurements were performed on a DSC2500 (TA instruments) with ca. 10 mg sample at a scan rate of 5 °C min−1. Thermogravimetric analysis (TGA) was measured on a TA instrument Q-50 TGA for thermal stability of the samples. Samples of 5 –10 mg were placed in a platinum pan. The measurements were conducted from room temperature to 800 °C with a heating rate of 10 °C min−1 rate in a N2 atmosphere. Mechanical tests Dynamic mechanical analysis (DMA) was performed on a TA Discovery DMA850 (TA Instruments, New Castle, Delaware, U.S.A.). Specimens with a dimension of 20 mm length, 10 mm width, and 1 mm thickness were used for temperature ramp measurements. The amplitude and frequency in oscillation mode were set to 20 μm and 1 Hz, respectively. The samples were ramped from −50 to 50 °C, with a ramp rate of 3.0 °C min−1. Small-amplitude oscillatory shear measurements were performed on an AR2000ex rheometer (TA Instruments, New Castle, Delaware, U.S.A.). The experiments were performed between two 4 mm parallel steel plates. The temperature was controlled by a system using nitrogen as the gas source. All the samples were loaded between the plates, equilibrated at 60 °C for 30 min before the measurement, and measured at different temperatures with the angular frequency sweep from 100 to 0.1 rad s−1. The master curve at reference temperature could be built by applying time temperature superposition. An Instron 3343 universal testing system following the ASTM D1708 standard was used to test the mechanical properties, and at least three specimens were prepared for each test. Hysteresis curves were measured from 0% to 100% strain at 0.1 mm s−1 rate. Lap shear adhesion measurements for aluminum, steel, and PTFE were measured using Instron 3343 universal testing system equipped with 1 kN cell at 2 mm min−1 crosshead speed rate. Samples were spread onto the substrates and hot-pressed at 80 °C for 30 min. The adherends were overlapped (12 × 12 mm) in a single lap-shear configuration. After cooling to room temperature, the lap shear strength was measured and average results with standard deviation of three specimens were reported. Lap shear adhesion is defined as the maximum force (in N) of the adhesive joint obtained from the lap shear test divided by the overlap area (in mm2) of adhesives. 3D printing 3D printing of the synthesized poly(TA) was conducted with a Hyrel Engine SR. A Hyrel Tambora printing head composed of heating devices and a stainless-steel cartridge was employed in the printing, where the material was melted, extruded, and deposited on the build plate. Teflon paper and plates were chosen as the build plate for easy removal of the printed parts. The original synthesized materials were loaded in the printing cartridge with 0.5 mm nozzle and heated reversely to remove the bubbles. The printing head was then heated to 110 °C for 3D printing. Printing speed was set at 15 mm s−1. Consistent ink extrusion was achieved during printing. Details of the printing parameters are shown in Supporting Information Table S2. Results and Discussion Synthesis of poly(TA) TA has a unique chemical structure containing two types of dynamic bonds: covalent disulfide bonds and noncovalent hydrogen bonds.38–40 The thermodynamic controlled ring-opening polymerization of TA (Tm = 63 °C, Supporting Information Figure S1) is initiated by thermal treatment to form a linear polymer chain with two sulfur radicals, one at each end (Scheme 1a). However, as demonstrated by the digital images (Scheme 1b) and proton nuclear magnetic resonance (1H NMR, Figure 1b), upon cooling the reaction mixture, the semicrystalline TA monomer is reformed spontaneously due to the reverse ring-closing depolymerization process initiated by the terminal radicals.39 This is consistent with our ab initio quantum calculations showing the dissociation of disulfide bond in the sulfur radical-terminated poly(TA) in the absence of a chlorinated solvent, resulting in the reformation of TA monomers upon cooling. Scheme 1 | Illustration (a) and digital images (b) of reversible reaction between TA)monomer and poly(TA) upon heating and cooling. Illustration (c) and digital images (d) of DCM)solvent-enabled synthesis of poly(TA), a transparent film. Snapshots from ab initio quantum calculations results showing: bond dissociation of disulfide in poly(TA) without DCM (e); firm association of DCM with the sulfur radical end at 400 K over 1 s (f) and 5 s (g); a stable structure of poly(TA) with bonded DCM fragment (h). Download figure Download PowerPoint The key knowledge gained is that the kinetic-controlled depolymerization of poly(TA) is initiated by the terminal sulfur radicals.39 Therefore, we hypothesized that addition of small molecules that react with the terminal radicals may prevent the depolymerization of poly(TA) and afford a linear polymer even after cooling (Scheme 1c and Figure 1a). Drawing inspiration from the termination of radical polymerization, low-cost, normally unfavorable in polymer synthesis, chlorinated solvents,44,45 such as DCM, chloroform, and benzyl chloride, were with a molar ratio of solvent to TA being 0.25:1 employed to investigate their effect on stabilizing the reactive polymer chains. To better understand the effect, 1H NMR characterization of the unpurified reaction mixture was performed to calculate the monomer conversion by comparing the integral ratios of proton peaks adjacent to the disulfide bond in poly(TA) and TA, and the results are summarized in Supporting Information Table S1 and Figures S2–S11. As expected, many organic solvents can act as a "catalyst" to assist in the formation of poly(TA) after cooling the mixture as evidenced by the 1H NMR spectra analysis. For example, with DCM, the appearance of a new broad peak at ∼2.75 ppm corresponds to the polymeric structure, indicating efficient polymerization with a high monomer conversion of ∼77% (Figure 1c). As can be seen in Supporting Information Table S1, the chemical reaction with a small amount of DCM has relatively higher monomer conversion compared to other solvents, which produces a transparent polymer film. Based on the low cost and common use of DCM, dynamic polymer poly(TA) synthesized from the DCM "catalyzed" route was selected as the basic recipe for the remainder of the work. Figure 1 | (a) Schematic illustration of the reaction mechanism in the presence of DCM. 1H NMR spectra of heated and cooled TA sample without DCM (b), and with DCM (c). (d) MALDI results of the prepared poly(TA). (e) Expansion of the mass spectrum of poly(TA) from approximately 1050–1060 Da. Download figure Download PowerPoint The resultant poly(TA) film is highly transparent (Scheme 1d), whereas the sample produced under the same conditions without DCM is opaque because of the reversible reaction that forms crystalline TA monomers (Scheme 1b). The formation of poly(TA) is further confirmed by MALDI-TOF mass spectrometry (MS, Figure 1d,e). The sample generates an overall ski-slope distribution indicating a relatively broad PDI typical for free radical and condensation polymerizations. The spacing between the peaks in the mass spectrum is 206.1 Da, on average, consistent with the theoretical repeat unit mass, that is, 206.0 Da. The MALDI spectrum suggests that the products detected at low MWs are a cyclic species and/or linear chain possessing a double bond to a sulfur on one end and a proton on the other observed at 1053 Da and a second linear species 2 Da higher in mass with hydrogen on both ends (Figure 1e). The formation of these end groups can be explained by either dehydrochlorination (double bond formation) or radical loss of the original terminal groups and the substitution of hydrogen during the MALDI process. It is believed that both products are present due to the isotopic enrichment of the peak at 1055 Da over the naturally occurring isotopic envelope. It can also be seen that the low-mass oligomers have a bimodal distribution with an apex at approximately 1500 Da. The spectrum shows the disappearance of the cyclic species and the dominance of linear species (+2 Da) as mass increases. This suggests that the linear species will dominate chain structure at high MWs which is consistent with previous observations for the low MW oligomers of condensation polymers. MS/MS data seems to support this interpretation of a mixture of a cyclic and linear species and a second linear species 2 Da higher in mass. Other minor peaks in the spectrum arise from H and Na exchange on the carboxylic acid functionality of the repeat unit or matrix cluster formation. Meanwhile, gel permeation chromatography (GPC) measurements also demonstrate the formation of polymers, and the peaks at low retention volume can be attributed to the physical aggregation of polymer chains ( Supporting Information Figure S12). To optimize the reaction conditions, we explored the dynamic polymer synthesis at different reaction times and chlorinated solvent concentrations. As summarized in Figure 2a,b, the monomer conversion of poly(TA) in the presence of DCM is comparable with the different reaction times (from 30 min to 8 h, Supporting Information Figures S13–S16) and various molar ratios between DCM and TA (from 0.125 to 8, Supporting Information Figures S17–S22). Therefore, we simplified the reaction by using a short reaction time and decent "catalyst" quantity, that is, 120 °C for 30 min with a molar ratio of DCM to TA of 0.25:1 (around 9.3 wt. % DCM). The solid-state 13C NMR characterization of the as-received TA monomers (top), heated TA (middle), and heated TA with DCM (bottom) were also used to monitor the polymerization process (Figure 2c,d). No chemical shift changes were observed for the original TA and heated TA sample, indicating that the heating process without DCM does not render chemical changes in the system. The proton T1 relaxation time, however, drops from ∼11 to 1 s for heated TA, indicating decreased crystallinity of TA after the thermal process ( Supporting Information Figure S23),48 because the sample after the same heating process in the presence of DCM transforms the powder to a highly viscous liquid restricting the MAS rate of the semisolid-like sample.47 Therefore, the product spectrum generated in the presence of DCM was spun at a lower MAS rate as compared to the as-received TA (8 kHz vs 14 kHz). Nevertheless, the clear differences of 13C chemical shift observed for the DCM added TA polymerization indicates the chemical transformation. Figure 2 | Summary of the effect of (a) different reaction time and (b) DCM ratios on the monomer conversions of dynamic polymer synthesis. The inserts are the corresponding digital images. (c and d) Solid-state 13C NMR spectra of TA monomer (top), heated TA sample (middle), and heated TA with DCM (bottom). (e) Cl 2p XPS spectra of the TA monomer and prepared poly(TA). Download figure Download PowerPoint The reaction mechanism of DCM-assist poly(TA) synthesis was further investigated by physical analysis, ab initio calculations, and molecular dynamics simulations. The ring-opening polymerization of a disulfide containing five-member ring creates the reactive polymer chain as a fluidic liquid at an elevated temperature. The free-radical terminated polymer chains are stabilized and react with DCM molecules leading to a transparent yellowish poly(TA) (Scheme 1d). The presence of chlorine detected by X-ray photoelectron spectroscopy (XPS) (Figure 2e and Supporting Information Figure S24) and EDS ( Supporting Information Figure S25) confirms the existence of DCM fragments in the resultant polymers after the purification and drying process. Also, a smooth surface morphology is observed from the SEM image, and the corresponding elemental mapping indicates the homogeneity of poly(TA). However, it is difficult to determine the location of attachment of ·CH2Cl to the polymer chain from the 1H NMR spectrum since the proton signal on the DCM fragment is hard to detect. Therefore, two model molecules with a benzene ring, C6H5CH2Cl and ClCH2C6H4CH2Cl ( Supporting Information Figures S5 and S6), were also selected as the "catalyst" to perform the same reaction to help elucidate the structure of the terminated chains. The corresponding 1H NMR results of the obtained polymer indicate the presence of benzyl ring at ∼7.5 ppm after the reaction and purification, supporting the proposed mechanism. Ab initio calculations and molecular dynamics simulations were also employed to validate the proposed mechanism as illustrated in Scheme 1e–h. The results show that, without DCM, the disulfide in poly(TA) tends to dissociate to sulfur radicals, which initiates the depolymerization process. At an elevated temperature around 125 °C, DCM molecules tend to strongly associate and stabilize the sulfur radicals at the ends of polymer chains as exhibited in Scheme 1f,g. Moreover, the reactive polymer chains can also be terminated with a DCM fragment, generating a stable poly(TA) product. These experimental and computational results support the mechanism where the polymer chains with terminal sulfur radicals can react with DCM molecules, preventing the kinetically controlled depolymerization of poly(TA) after cooling to ambient temperature. Thermomechanical property evaluation The thermal properties of the prepared dynamic polymer were evaluated due to their significant influence on the polymeric materials' processability and other physical properties. The poly(TA) exhibits good thermal stability with no significant weight loss until 190 °C as shown in the TGA curve ( Supporting Information Figure S26), which is much higher than that of TA (169 °C). As illustrated in the DSC results in Figure 3a, the absence of the characteristic melting temperature (Tm) corresponding to TA monomer (63 °C, Supporting Information Figure S1) also suggests the successful conversion of TA monomer to polymer. The low glass-transition temperature (Tg = −14.0 °C) of poly(TA) demonstrates its rubbery nature and fast segmental dynamics at ambient temperature, which is important for its self-healing ability (vide infra). The amorphous nature of poly(TA) is further confirmed by the la