# Fileset
[2024 - Self-healing amino acid-bearing acrylamides n-butyl acrylate copolymers via multiple noncovalent bonds.pdf](https://mdr.nims.go.jp/filesets/da08ebfe-238b-44b1-86c0-0be952fe8f7b/download)
## Creator
Ryo Kudo, [Sadaki Samitsu](https://orcid.org/0000-0002-4139-1656), Hideharu Mori
## Rights
## Other metadata
[Self-healing amino acid-bearing acrylamides/n-butyl acrylate copolymers via multiple noncovalent bonds](https://mdr.nims.go.jp/datasets/424390ce-de04-4f89-980a-e44a78f47399)
## Fulltext
Self-healing amino acid-bearing acrylamides/n-butyl acrylate copolymers via multiple noncovalent bondsRSC AdvancesPAPEROpen Access Article. Published on 06 March 2024. Downloaded on 5/8/2024 8:07:25 AM. This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article OnlineView Journal | View IssueSelf-healing aminaDepartment of Organic Material Science,Science, Yamagata University, 4-3-16, Jona992-8510, Japan. E-mail: h.mori@yz.yamagbNational Institute for Materials Science, 1-† Electronic supplementary informahttps://doi.org/10.1039/d4ra00800fCite this: RSC Adv., 2024, 14, 7850Received 31st January 2024Accepted 19th February 2024DOI: 10.1039/d4ra00800frsc.li/rsc-advances7850 | RSC Adv., 2024, 14, 7850–78o acid-bearing acrylamides/n-butyl acrylate copolymers viamultiple noncovalentbonds†Ryo Kudo,a Sadaki Samitsu b and Hideharu Mori *aFour amino acid-bearing acrylamides, N-acryloyl-L-threonine (AThrOH), N-acryloyl-L-glutamic acid(AGluOH), N-acryloyl-L-phenylalanine (APheOH), and N-acryloyl-L, L-diphenylalanine (APhePheOH), wereselected for copolymerization with n-butyl acrylate (nBA) to develop amino acid–based self-healablecopolymers. A series of copolymers comprising amino acid-bearing acrylamides and nBA with tunablecomonomer compositions and molecular weights were synthesized by free radical and reversibleaddition–fragmentation chain-transfer copolymerization. Self-healing and mechanical propertiesoriginated from the noncovalent bonds between the carboxyl, hydroxyl, and amide groups, and p–pstacking interactions among the amino acid residues in the side chains were evaluated. Among thesecopolymers, P(nBA-co-AGluOH) with suitable comonomer compositions and molecular weights (nBA :AGluOH = 82 : 18, Mn = 18 300, Mw/Mn = 2.58) exhibited good mechanical properties (modulus oftoughness = 17.3 MJ m−3) and self-healing under ambient conditions. The multiple noncovalent bondsof P(nBA-co-AGluOH)s were also efficient in improving the optical properties with an enhancedrefractive index and good transparency.IntroductionSelf-healing materials that can heal damages have emerged aspromising materials for sustainable societies and numerousindustrial applications.1–4 In addition to extrinsic self-healingmaterials utilizing a healing agent,5,6 a variety of intrinsic self-healing materials have been developed, which relied mainlyon covalent dynamic bonds (e.g., urea bond,7,8 trithiocarbonateunit,9 disulde bond,10,11 Diels–Alder reaction,12–14 and trans-esterication15,16) and noncovalent reversible interactions (e.g.,hydrogen bonds,17–19 ionic interactions,20 p–p interactions,21–23and metal–ligand coordination24–26). The incorporation of suchself-healing units into polymeric materials with sophisticateddesigns is crucial for achieving desirable self-healing proper-ties, mechanical properties, and targeted functions. Forinstance, various supramolecular hydrogels showing essentialfunctions, e.g., self-healing, stimuli-responsive, biocompatible,antibacterial, antioxidant, and tissue-adhesive functions, havebeen developed for biomedical and clinical applications.27,28The capability to utilize conventional and industriallyGraduate School of Organic Materialsn, Yonezawa City, Yamagata Prefectureata-u.ac.jp2-1, Sengen, Tsukuba, 305-0047, Japantion (ESI) available. See DOI:57applicable processes that can be extended to future large-scaleproduction is desirable.Self-healing can be found in living organisms, which origi-nated from physical and chemical changes in response toenvironmental change.4 Peptides and amino acids, which areconstitution units for proteins, have attracted considerableattention as bio-mimics and critical units for self-healingpolymers and gels, demonstrating various advantages, such asnontoxicity, biodegradability, and hydrophilicity.29 Thesesystems can be governed by abundant units, such as hydrogenbonds, electrostatic and hydrophobic interactions, leading tosupramolecular self-assembly (e.g., b-sheets). Because aminoacids with the general form RCH(NH2)COOH have an aminogroup, a carboxyl group, and other functional groups dependingon the structure of the R group, their derivatives have beenintensively employed as constituent units for various self-healing materials. For example, various self-healable hydro-gels and shape memory polymer networks have been developedutilizing amino acid derivatives and polymers, such as chitosan/acryloyl-phenylalanine,30 poly(aspartic acid),31 poly(g-glutamicacid),32,33 poly(L-glutamic acid)/ureido-pyrimidinone,34 acryloyl-6-aminocaproic acid,35 N-acryloyl glycinamide,36 N-acryloyl gly-cinamide/N-acryloyl serine methyl ester37 and N-acryloylalanine.38 These hydrogels and polymer networks mainly reliedon chemical crosslinking, occasionally combined with physicalcrosslinking originating from amino acid-derived hydrogenbonds. Interestingly, N-acryloyl glycinamide was found to formsupramolecular hydrogels directly via physical crosslinking© 2024 The Author(s). Published by the Royal Society of Chemistryhttp://crossmark.crossref.org/dialog/?doi=10.1039/d4ra00800f&domain=pdf&date_stamp=2024-03-05http://orcid.org/0000-0002-4139-1656http://orcid.org/0000-0002-8123-1606https://doi.org/10.1039/d4ra00800fhttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d4ra00800fhttps://pubs.rsc.org/en/journals/journal/RAhttps://pubs.rsc.org/en/journals/journal/RA?issueid=RA014011Paper RSC AdvancesOpen Access Article. Published on 06 March 2024. Downloaded on 5/8/2024 8:07:25 AM. This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlineowing to dual amide motifs.36 In addition, side-chain type (e.g.,triblock and multiblock copolymers with N-acryloyl-L-phenylal-anine39) and main-chain type (e.g., multiblock copolymers witholigopeptides,40 polydimethylsiloxane with L-phenylalanineunit41) polymers have been explored, which have amino acid/peptide units that act as physical crosslinking motifs in theside chain and main chain. Furthermore, low-molecular-weightamino acid/peptide derivatives (e.g., phenylalanine,42 nucleo-tripeptides43) have been employed as self-healing gelators.44n-Butyl acrylate (nBA) is one of the most widely utilizedmonomers for producing rubbers and elastomers owing to thelow glass transition temperature (Tg) of the resulting poly(nBA).Hence, it has been widely employed as a exible component forself-healing elastomers, gels, and networks. For instance,carboxylic acid-containing monomers (e.g., acrylic acid45,46 andacrylic acid/vinylimidazole47) and hydroxyl group-containingmonomers (e.g., dopamine acrylamide48,49 and N-(hydrox-ymethyl)acrylamide50) have been copolymerized with nBA toform self-healable polymers. Their healing and physical prop-erties were mainly governed by noncovalent interactions (e.g.,hydrogen bonds, ionic interactions, and metal coordination)from the functional units and the exibility from nBA units. Thehydrophobic association of n-butyl groups of nBA units incopolymer chains has been occasionally utilized to forma physical hydrogel, depending on the environment (e.g., inaqueous solution).51 A variety of functional monomers, such as(2-acetoacetoxy)ethyl methacrylate,52 epoxy- and urea-containing methacrylates,53 1-vinylimidazole,54 2,2,2-tri-uoroethyl methacrylate,55 have also been utilized for nBA-based self-healable polymeric materials. Other attractivefeatures of nBA-containing copolymers include excellentbiocompatibility, stability, and good adhesion; therefore, nBAhas been utilized in biocompatible gels,56–58 networks,59,60 andcopolymers.61,62Here, we described a straightforward and efficient approachfor developing self-healing copolymers by incorporating aminoacid units into nBA-based elastomers via free-radical copoly-merization (Fig. 1). Four acrylamides bearing different aminoacids, N-acryloyl-L-threonine (AThrOH),63,64 N-acryloyl-L-Fig. 1 (a) Synthesis and (b) postulated healing process of amino acid–based random copolymers.© 2024 The Author(s). Published by the Royal Society of Chemistryglutamic acid (AGluOH),65,66 N-acryloyl-L-phenylalanine(APheOH)67 and N-acryloyl-L,L-diphenylalanine (APhePheOH)68were selected attempting to tune intra- and intermolecularnoncovalent interactions (e.g., hydrogen bonds, electrostaticinteractions, and p–p stacking) and their exibilities. AThrOHhas a hydroxyl group and a carboxyl group, AGluOH has twocarboxyl groups, and APheOH has a carboxyl group and a phenylgroup, in addition to an amide group in each monomer unit.APhePheOH contains two amide groups, two phenyl group, andone carboxyl groups. The core of our strategy is the selection ofsuitable amino acid-bearing acrylamides, which can act as self-healing sites via noncovalent interactions, combined with nBA,which can contribute to tuning the exibility. By exploiting thisunique combination of naturally originating hydrophilicbuilding blocks derived from amino acids and nonionic nBA asa hydrophobic unit, we demonstrated tunable physical, optical,and self-healing properties. The unique intrinsic features of thecopolymers, e.g., good transparency, tunable refractive indexesand soness, can be applied for ophthalmic optics in futureapplications. The introduction of chirality originated fromamino acid units is another attractive feature of the copolymers,which can extend to advanced materials, such as aggregation-induced circular dichroism and circularly polarized lumines-cence materials.69–71Results and discussionCopolymer synthesisAmino acid–based random copolymers were initially synthe-sized by free radical copolymerization of nBA and acrylamidesbearing different amino acids (AThrOH, AGluOH, APheOH, andAPhePheOH) with AIBN under the appropriate conditions(Table S1 and Scheme S1†). The chemical structure and como-nomer composition were veried via proton nuclear magneticresonance (1H NMR) spectroscopy (Fig. S1–S6†), and themolecular weight and dispersity were veried by size exclusionchromatography (SEC) measurement of the methylated sample(Fig. S7–S10†). For instance, the copolymerization of nBA andAThrOH was performed with various comonomer feed ratios[nBA]0/[AThrOH]0 = 50 : 150, 100 : 100, 150 : 50, 175 : 25 ata constant monomer-to-initiator ratio [nBA + AThrOH]0/[AIBN]0= 200 : 1 in ethanol at 60 °C for 24 h. Targeted P(nBA-co-AThrOH)s with various tunable comonomer compositions(AThrOH content = 10–65 mol%, as determined by 1H NMR,Fig. S4†) with similar molecular weights (Mn,SEC = 18 400–30800, Mw/Mn = 2.57–3.17, Fig. S8†) were obtained in good poly-mer yields of 81–90%, aer the reprecipitation from hexane.Similarly, P(nBA-co-AGluOH)s with tunable AGluOH contents(8–49 mol%) with reasonable molecular weights and polymeryields (Mn,SEC = 15 100–29 400, Mw/Mn = 2.06–2.60, yield = 74–98%), as illustrated in Fig. S7.† The nBA content in P(nBA-co-AGluOH)s (51–92%) is higher than the feed ratio ([nBA]0/[AGluOH]0 = 50 : 150–175 : 25), indicating a preferable insertionof nBA during the copolymerization. For the synthesis of P(nBA-co-APheOH) and P(nBA-co-APhePheOH), the copolymerizationwas conducted at [AIBN]/[nBA]/[amino acid-bearing monomer]at 1/150/50 at 60 °C in DMF, affording the copolymers withRSC Adv., 2024, 14, 7850–7857 | 7851http://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d4ra00800fRSC Advances PaperOpen Access Article. Published on 06 March 2024. Downloaded on 5/8/2024 8:07:25 AM. This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlinetargeted molecular weights and comonomer compositions(Mn,SEC = 27 200–46 400,Mw/Mn = 2.51–2.83, nBA content= 86–88 mol%, and yield = 68–73%).All copolymers bearing different amino acids (AThrOH,AGluOH, APheOH, and APhePheOH) were dissolved in DMFand DMSO (Tables S2–S4†). Owing to the amphiphilic nature,these copolymers were soluble in specic solvents (e.g., THF,chloroform, methanol, and basic water), dependent on thenature of the amino acid units and composition. For instance,P(nBA-co-AGluOH) with 82 mol% nBA content was soluble inTHF an methanol, while insoluble in neutral water. Thesecopolymers exhibited no detectable swelling and degradation(Fig. S11†), owing to the linear (Fig. 1) chain structures con-sisted of carbon–carbon backbone without cross-linking/network formation. Note that the threonine- and glutamicacid-based homopolymers (PAThrOH63 and PAGluOH65) weresoluble in water, independent of the pH value. In contrast, thephenylalanine- and diphenylalanine-based homopolymers(PAPheOH67 and PAPhePheOH68) were only soluble in basicwater (pH > 12) but insoluble in acidic and neutral water, owingto pH-dependent degree of the ionization.Fig. 2 shows attenuated total reection Fourier transforminfrared (ATR FT-IR) spectra of the copolymers with differentamino acid units. Characteristic absorption bands due to thecarbonyl (1730 cm−1) and C–H stretching vibrations (2775–3020 cm−1) are clearly observed for all copolymers. ATR FT-IRspectra of the copolymers reveal characteristic broad absorp-tion at 3100–3420 cm−1 (Fig. 2b), corresponding to an amidehydrogen bonded N–H.72,73 Among four copolymers, P(nBA-co-AGluOH) and P(nBA-co-AGluOH) exhibit remarkable broadabsorbance in the region below 3400 cm−1, suggesting thepresence of multiple hydrogen bonds. In all copolymers, char-acteristic absorption of the amide I is detected at approximately1650 cm−1, which reects the secondary structure.40 In additionto the clear peak attributed to ester carbonyl band at 1730 cm−1,a broad shoulder absorbance is detected at approximately1700 cm−1, depending on the copolymer. Similar tendency wasFig. 2 (a) ATR FT-IR spectra of amino acid-based copolymers (nBAcontent = approximately 80 mol%) and magnification in the region of(b) N–H band and (c) carbonyl band.7852 | RSC Adv., 2024, 14, 7850–7857observed for ATR FT-IR spectra of the homopolymers(PAThrOH, PAGluOH, PAPheOH, and PAPhePheOH, Fig. S12†).These results suggest the present of different intramolecular (orintermolecular) interactions, originated from the nature ofamino acids, which may affect the thermal, mechanical, andself-healing properties of the copolymers.Thermal and mechanical propertiesThe thermal properties of the P(nBA-co-AGluOH)s with differentnBA contents (52–92 mol%) were investigated by thermogravi-metric analysis (TGA) and differential scanning calorimetry(DSC). As illustrated in Fig. 3a, all P(nBA-co-AGluOH)s exhibitedhigh thermal stability (5% mass loss temperature Td5> 250 °Cunder nitrogen conditions), and the Td5 value increased withincreasing nBA content, e.g., Td5 = 280 °C for the copolymerwith highest nBA content (92 mol%). The glass transitiontemperature (Tg) value of P(nBA-co-AGluOH)s decreased from55.1 °C to −20.5 °C when the nBA content increased from 51 to92 mol% (Fig. 3b). The same trends were seen for P(nBA-co-AThrOH)s, which revealed an increase in the Td5 value from 187to 213 °C and a decrease in the Tg value from 134.1 to −37.8 °Cwith increasing nBA content from 35 to 90 mol% (Fig. S13 andTable S5†).The dog bone-shaped species were prepared from P(nBA-co-AGluOH)s having different comonomer compositions utilizinga Teon mold at 100–120 °C by hot-press for 1–3 min (TableS6†), followed by cooling at an ambient condition, for tensiletest. P(nBA-co-AGluOH) with 92 mol% nBA was viscous withuid properties, making it difficult to maintain the moldedshape (Fig. 3c). In contrast, rubbery samples were obtainedfrom P(nBA-co-AGluOH) with 82 mol% nBA content, which hassubstantial mechanical properties and exibility and was bentand twisted without breaking (Fig. 3d). A further decrease in thenBA content (e.g., less than 70 mol%) led to the formation ofglassy and fragile samples broken by shearing a small amountFig. 3 (a) TGA traces (b) DSC traces of P(nBA-co-AGluOH)s (nBAcontent = 51–92 mol%) and (c–e) appearance of P(nBA-co-AGluOH)(nBA content = 51–92 mol%).© 2024 The Author(s). Published by the Royal Society of Chemistryhttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d4ra00800fFig. 4 (a) TGA traces (b) DSC traces of amino acid-based copolymers(nBA content = approximately 80 mol%) and (c and d) stress–straincurves of the random copolymers (nBA content = approximately80 mol%) in (c) 0–1100% strain and (d) 0–10% strain.Paper RSC AdvancesOpen Access Article. Published on 06 March 2024. Downloaded on 5/8/2024 8:07:25 AM. This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlineof stress (Fig. 3e), implying that a higher AGluOH content led tohigher noncovalent interactions and lower nBA, which causedthe copolymer to behave as a brittle plastic. Hence, as expected,the comonomer composition signicantly inuenced thethermal and mechanical properties of P(nBA-co-AGluOH)s. Thisimplied that the noncovalent interactions of the amino acidunits (e.g., hydrogen bonds and electrostatic interactionsderived from the AGluOH unit in this case) were crucial factorsin manipulating the intermolecular interactions between thecopolymer chains.The thermal and physical properties of the four copolymersbearing different amino acids (AThrOH, AGluOH, APheOH, andAPhePheOH) were compared, and the results are summarized inTable 1. Copolymers with similar molecular weights and como-nomer compositions (Mn,SEC = 18 300–46400, and nBA content =80–88 mol%) were selected to clarify the effects of noncovalentinteractions derived from the amino acid unit. When the aromaticamino acid units were incorporated into the side chains, thermallystable copolymers were obtained (Td5 = 309 and 288 °C for thecopolymers with APheOH and APhePheOH), which were higherthan those with aliphatic amino acid units (Td5 = 200 and 270 °Cfor the copolymers with AThrOH and AGluOH), as illustrated inFig. 4a. The Tg values of the copolymers with AThrOH, AGluOH,and APhePheOH units ranged between 27.3–16.5 °C. In contrast,a lower Tg value (−5.1 °C) was seen for P(nBA-co-APheOH), asdepicted in Fig. 4b. Slightly lowerTg (16.5 °C) of P(nBA-co-AGluOH),compared to those of P(nBA-co-AThrOH) and P(nBA-co-APhe-PheOH) (27.3 and 21.5 °C) may be attributed to the presence ofexible alkyl chain in AGluOHunit. These copolymers possess easyprocessability that are moldable at a certain temperature, whichcan be tuned by selecting the nature of the amino acid units andtheir composition.The mechanical properties of four amino acid-based copol-ymers were evaluated by tensile stress–strain tests at roomtemperature (approximately 23–26 °C, Fig. 4c, d and Table 1).Young's moduli of the copolymers with AThrOH, AGluOH, andAPhePheOH units ranged between 97–148 MPa. In contrast,a lower value (5.1 MPa) was observed for P(nBA-co-APheOH),demonstrating the highest strain of more than 900% withoutfracture. P(nBA-co-AThrOH) exhibited the highest maximumstrength (11.0 MPa), whereas failure owing to brittleness wasTable 1 Characteristics of amino acid–based copolymers (nBA contentCopolymer Mna (SEC) n :mb Td5c (°C) Tgd (°C)YoumoP(nBA-co-AThrOH) 18 400 80 :20200 27.3 148P(nBA-co-AGluOH) 18 300 82 :18270 16.5 97P(nBA-co-APheOH) 46 400 88 :12309 −5.1 5.1P(nBA-co-APhePheOH)27 200 86 :14288 21.5 109a This was evaluated by SEC. b 1H NMR (Table S1). c 5 wt% loss temperatur(<5%). f Estimated by area under stress–strain until fracture point.© 2024 The Author(s). Published by the Royal Society of Chemistrydetected when the rupture strain reached 8.8%. Among the fourcopolymers, P(nBA-co-AGluOH) exhibited a good balance ofmoderate Young's modulus (97 MPa) and the highest modulusof toughness (17.3 MJ m−3) and was therefore utilized for theself-healing test.Self-healing propertiesFig. 5a illustrates a preliminary demonstration of the self-healing capability of P(nBA-co-AGluOH) with 82% nBAcontent. A dog bone-shaped specimen prepared by hot press at100 °C for 1 min can pull without breaking and then return tothe original shape, implying stretchable and good mechanicalproperties. The specimens were cut into two pieces andmanually pressed. The fractured surfaces of P(nBA-co-AGluOH)were rejoined aer being pressed together with the cut samplesfor approximately 30 s under ambient conditions (approxi-mately 25 °C). Similarly, the fractured surfaces of P(nBA-co-AThrOH) were rejoined by pressing at 40 °C for 30 min= approximately 80 mol%)ng'sduluse (MPa)Maximumstrength (MPa)Maximumstrain (%)Modulus of toughnessf(MJ m−3)11.0 8.8 0.545.2 385 17.300.40 997 3.955.0 350 14.08e. d Glass transition temperature. e Calculated from stress at slight strainRSC Adv., 2024, 14, 7850–7857 | 7853http://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d4ra00800fFig. 5 (a) Photos of original, stretched, and recovered P(nBA-co-AGluOH) sample and preliminary healing test. Stress–strain curves of(b and c) P(nBA-co-AGluOH) after healing in (b) 0–500% strain and (c)0–50% strain, and (d) P(nBA-co-AThrOH) after healing and (e) sche-matics of healing process of P(nBA-co-AGluOH).Fig. 6 (a) SEC, (b) TGA, and (c) DSC traces, and (d) stress–strain curvesof P(nBA-co-AGluOH)s (Mn = 9500–21 500) and (e and f) appearanceof P(nBA-co-AGluOH)s (Mn = 9500, 15 900).RSC Advances PaperOpen Access Article. Published on 06 March 2024. Downloaded on 5/8/2024 8:07:25 AM. This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Online(Fig. S14†), suggesting that the copolymer with AThrOHdemonstrated self-healable property. Still, the self-healableproperty was less than that with AGluOH. In contrast, P(nBA-co-APheOH) and P(nBA-co-APhePheOH) having aromatic aminoacids exhibited no healing capability, even if the healingtemperature increased up to 50–60 °C (Fig. S15 and Table S7†),which may be due to the interference of the hydrogen bonds bybulky aromatic units in APheOH and APhePheOH. Furtherstudies were required to determine optimal comonomercompositions and sequences of these aromatic amino acid-based copolymers. Nevertheless, these results suggest thata suitable selection of the amino acid unit and its compositionwith nBA units are essential for achieving reasonable self-healing and mechanical properties of the nBA/amino acid–based copolymers by tuning suitable noncovalent interactions.The self-healing efficiencies of P(nBA-co-AGluOH) and P(nBA-co-AThrOH) were evaluated by comparing maximal strength ofthe pristine specimen and healed ones treated at 40 °C fordifferent compression time (Fig. 5 and Table S8†). Both copol-ymer samples demonstrated improved self-healing capabilitieswith increasing compression time. Notably, P(nBA-co-AGluOH)recovered 90% of the maximum strength of the pristine sampleaer 30 min compression (Fig. 5b and c). In contrast, P(nBA-co-AThrOH) recovered approximately 10%, even aer 3 h (Fig. 5d).These results suggest that intermolecular hydrogen bondsbetween two carboxylic acids in the AGluOH unit, in addition tocarboxylic acid/amide and amide/amide hydrogen bonds, areessential for achieving reasonable self-healing ability (Fig. 5e).Obviously, self-healing properties are affected by molecularmobility of the copolymer chain. Therefore, each copolymerhaving different Tg values possess suitable healing temperature.In this study, the self-healing behaviors of the copolymers7854 | RSC Adv., 2024, 14, 7850–7857having different animo acid units were compared at 40 °C,which are higher than those of Tg values of the copolymers(−5.1–27.3 °C). Further studies on the amino acid–basedcopolymers, such as the inuence on the healing temperatureon the healing properties and temperature-dependent rheo-logical behavior, will be reported separately.Effect of molecular weightP(nBA-co-AGluOH)s with different molecular weights andapproximately the same comonomer composition (nBA/AGluOHmolar ratio = approximately 8/2) were synthesized to evaluatethe effect of the molecular weight on the mechanical and self-healing properties (Table S9†). RAFT copolymerization of nBAand AGluOH utilizing a trithiocarbonate-type chain transfer agent(CTA) at different monomer-to-CTA ratios ([nBA + AGluOH]/[CTA]= 100–400) at a constant CTA-to-initiator and a comonomer feedratio ([CTA]0/[AIBN]0 = 2/1 and [nBA]/[AGluOH] = 3/1) producedP(nBA-co-AGluOH)s with adjustable molecular weights (Mn =9500–15 900). When RAFT copolymerization was conducted at[nBA]/[AGluOH]/[CTA]/[AIBN] = 150/50/2/1–300/100/2/1, P(nBA-co-AGluOH)s having relatively low disparities (Mw/Mn = 1.25–1.36)were obtained, while further increase in the monomer-to-CTAratio led to the broadening disparity (Mw/Mn = 1.79), as depic-ted in Fig. 6a. As comparisons, P(nBA-co-AGluOH)s having highermolecular weights (Mn = 18 300–21 500,Mw/Mn = 2.58–2.73) with(nBA/AGluOH = approximately 8/2 molar ratio) were prepared byfree radical copolymerization at different [nBA]/[AGluOH]/[AIBN]ratios (150/50/1 and 300/100/1). P(nBA-co-AGluOH) samples ofdifferent molecular weights were utilized to evaluate their thermaland mechanical properties (Table S9† and Fig. 6).© 2024 The Author(s). Published by the Royal Society of Chemistryhttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d4ra00800fFig. 7 (a) UV-vis transmittance spectra of P(nBA-co-AGluOH)s havingdifferent AGluOH contents (49–8 mol%) and (b) photographs ofP(nBA-co-AGluOH)s films utilized for transmittance measurements,(c) wavelength-dependent refractive indices determined by ellips-ometry, and (d) CD spectra of P(nBA-co-AGluOH) in HFIP (0.03 g L−1)and at the film state on a quartz plate.Paper RSC AdvancesOpen Access Article. Published on 06 March 2024. Downloaded on 5/8/2024 8:07:25 AM. This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article OnlineTGA results revealed that P(nBA-co-AGluOH)s displayedsimilar thermal stabilities (Td5 = 268–273 °C), regardless of themolecular weights. A substantial difference was observed in theTg values. For instance, the Tg values of P(nBA-co-AGluOH)ssynthesized by RAFT copolymerization decrease slightly from0.8 to −6.0 °C with increasing the molecular weights. Thistendency may be due to the higher content of the end-groupsand the absence of low-molecular-weight products, which areprobably removed during the purication process, resulting inlower polymer yield (e.g., 60% at [nBA]/[AGluOH]/[CTA]/[AIBN]= 150/50/2/1). P(nBA-co-AGluOH)s prepared by free radicalcopolymerization exhibited similar molecular weight-dependent tendency, demonstrating the higher Tg value(16.5 °C for Mn = 18 300) and lower one (−17.5 °C for Mn = 21500). RAFT-synthesized P(nBA-co-AGluOH) with relatively highmolecular weights (Mn = 14 700 and 15 900) was obtained asa rubbery sample with good stability and lm-forming ability.Low-molecular-weight P(nBA-co-AGluOH) (Mn = 9500) affordeda sample, but its mechanical properties were relatively poor(Fig. 6e). The RAFT-synthesized P(nBA-co-AGluOH)s (nBAcontent = approximately 80 mol%) with different molecularweights demonstrated moderate Young's moduli in the range of5.0–92 MPa. The strain of the RAFT-synthesized P(nBA-co-AGluOH)s increased with increasing molecular weight. Thesame tendency, where higher molecular weight led to higherstrain, was also observed for P(nBA-co-AGluOH) prepared by freeradical copolymerization. A substantial increase in the modulusof toughness was observed for P(nBA-co-AGluOH)s designed byRAFT and free-radical copolymerization. Interestingly, P(nBA-co-AGluOH) having the highest molecular weight (Mn = 21 500,Mw/Mn = 2.73), exhibited relatively high tensile strength (4.8MPa) and modulus of toughness (22.28 MJ m−3), yet possesseda strain at break of 634%. In contrast, P(nBA-co-AGluOH) havinglowest molecular-weight (Mn= 7800), which was prepared usinga dithiocarbamate-type CTA, afforded viscous product with uidproperty, even if almost the same nBA content (82%, Table S10and Fig. S16†). These results imply that the molecular weighthas a remarkable effect on the mechanical properties, particu-larly the exibility and toughness.Optical propertiesIn addition to the mechanical and self-healing properties, inte-gration with additional functions is desirable for future applica-tions of self-healable materials (e.g., so robotics, sensors,electronic devices).74,75 Here, we focused on achieving good opticalproperties, including transparency and improved refractive index,because the simultaneous achievement of a high refractive indexwith good mechanical and self-healing properties remains a chal-lenge. Based on the Lorentz–Lorenz equation, molar refractionand molecular volume are crucial parameters to determinerefractive index.76Hydrogen bonds have been recently employed toincrease the refractive index via decreasing the free volume.77Here,P(nBA-co-AGluOH)s having different AGluOH contents (49–8 mol%) were employed to achieve good transparency and highrefractive indexes via tuning intermolecular hydrogen bonds. Asillustrated in Fig. 7, P(nBA-co-AGluOH)s demonstrated good lm-© 2024 The Author(s). Published by the Royal Society of Chemistryforming properties and good transparency in the visible region(>90% at 400 nm), regardless of the comonomer composition. Theellipsometry measurements of P(nBA-co-AGluOH)s indicatedtypical wavelength-dependent refractive indices (Fig. 7c), whichincreased from 1.4883 to 1.5089 with decreasing Abbe numbersfrom 63.5–56.7 by increasing AGluOH content (Table S11†). Thesevalues are comparable to those of poly(methyl methacrylate)(refractive index = 1.49 and Abbe number = 58),78 and silicon andacrylic intraocular lenses (refractive index = 1.41–1.55 and Abbenumber= 37–58).79 These results implied that the AGluOH havinghydrogen bonding ability can efficiently enhance the refractiveindex, while maintaining good transparency.Chiroptical properties of P(nBA-co-AGluOH) in solid and solu-tion states were evaluated by circular dichroism (CD) measure-ment. As shown in Fig. 7d, a positive CD peak at approximately215 nm appeared in the lm state, whereas no remarkable peakwas detected in the hexauoroisopropanol (HFIP) solution,showing aggregation-induced CD effect. The P(nBA-co-AGluOH)sexhibited good transparency, tunable refractive index,aggregation-induced CD effect, in addition to tunable exibilityand self-healing properties. This approach provides a practicaland efficient method for the preparation of self-healable polymerswith tunable properties by simple radical copolymerization ofamino acid-carrying monomers, which can open new avenues foradvanced optical materials, such as ophthalmic optics.ConclusionIn summary, we developed a series of amino acid-bearingacrylamide/nBA copolymers with good mechanical and self-healing properties under ambient conditions by selecting suit-able amino acid units, comonomer compositions, and molec-ular weights. Combining noncovalent interactions (e.g.,hydrogen bonds, electrostatic interactions, and p–p stacking)from the amino acid motifs and exibility from nBA can beRSC Adv., 2024, 14, 7850–7857 | 7855http://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d4ra00800fRSC Advances PaperOpen Access Article. Published on 06 March 2024. Downloaded on 5/8/2024 8:07:25 AM. This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Onlineachieved by copolymerizing charged monomers with a neutralmonomer under suitable conditions. The nature of the aminoacids (AThrOH, AGluOH, APheOH, and APhePheOH) andamino acid-bearing acrylamide/nBA content substantiallyaffected the thermal, mechanical, and self-healing properties.The molecular weight of the copolymers is also a crucial factorfor manipulating the mechanical strength. The AGluOHcontent in P(nBA-co-AGluOH) efficiently enhanced the refractiveindices while maintaining good transparency by tuning thenoncovalent interactions. This strategy is regarded as physicaland reversible crosslinking via noncovalent interactions derivedfrom naturally originating amino acid motifs, which cancontribute to the tuning of thermal, mechanical, and self-healing properties, as well as optical properties involvingtransparency and refractive index.Data availabilityThe data that support the ndings of this study are availablefrom the corresponding author upon reasonable request.Author contributionsRyo Kudo: investigation, methodology, writing – original dra.Sadaki Samitsu: investigation, validation, writing – review &editing. Hideharu Mori: conceptualization, supervision, vali-dation, writing – review & editing.Conflicts of interestThere are no conicts to declare.AcknowledgementsThis work was supported by Toshiaki Ogasawara MemorialFoundation. We thank MANA foundry at NIMS for instrumentalsupport for spectroscopic ellipsometry. We also thank RyoYonenuma and Kaori Morikawa at Yamagata University for thehelp in the monomer synthesis and ellipsometry measurement.Notes and references1 A. Campanella, D. Dohler andW. H. Binder,Macromol. RapidCommun., 2018, 39, e1700739.2 C. Kim and N. Yoshie, Polym. J., 2018, 50, 919–929.3 Y. Yang and M. W. Urban, Adv. Mater. Interfaces, 2018, 5,1800384.4 C. E. Diesendruck, N. R. Sottos, J. S. Moore and S. R. White,Angew. Chem., Int. Ed., 2015, 54, 10428–10447.5 S. R. White, N. R. Sottos, P. H. Geubelle, J. S. Moore,M. R. Kessler, S. R. Sriram, E. N. Brown andS. Viswanathan, Nature, 2001, 409, 794–797.6 M. Gragert, M. Schunack and W. H. Binder,Macromol. RapidCommun., 2011, 32, 419–425.7 H. Ying, Y. Zhang and J. Cheng, Nat. Commun., 2014, 5, 3218.8 Z. Wang, S. Gangarapu, J. Escorihuela, G. Fei, H. Zuilhof andH. Xia, J. Mater. Chem. A, 2019, 7, 15933–15943.7856 | RSC Adv., 2024, 14, 7850–78579 Y. Amamoto, J. Kamada, H. Otsuka, A. Takahara andK. Matyjaszewski, Angew Chem. Int. Ed. Engl., 2011, 50,1660–1663.10 J. Canadell, H. Goossens and B. Klumperman,Macromolecules, 2011, 44, 2536–2541.11 U. Lafont, H. van Zeijl and S. van der Zwaag, ACS Appl. Mater.Interfaces, 2012, 4, 6280–6288.12 J. Bai, H. Li, Z. Shi and J. Yin, Macromolecules, 2015, 48,3539–3546.13 J. Kötteritzsch, S. Stumpf, S. Hoeppener, J. Vitz, M. D. Hagerand U. S. Schubert, Macromol. Chem. Phys., 2013, 214, 1636–1649.14 K. K. Oehlenschlaeger, J. O. Mueller, J. Brandt, S. Hilf,A. Lederer, M. Wilhelm, R. Graf, M. L. Coote,F. G. Schmidt and C. Barner-Kowollik, Adv. Mater., 2014,26, 3561–3566.15 T. Liu, C. Hao, S. Zhang, X. Yang, L. Wang, J. Han, Y. Li, J. Xinand J. Zhang, Macromolecules, 2018, 51, 5577–5585.16 J. Tan, C. Li, K. De Bruycker, G. Zhang, J. Gu and Q. Zhang,RSC Adv., 2017, 7, 51763–51772.17 P. Cordier, F. Tournilhac, C. Soulie-Ziakovic and L. Leibler,Nature, 2008, 451, 977–980.18 D. Montarnal, P. Cordier, C. Soulié-Ziakovic, F. Tournilhacand L. Leibler, J. Polym. Sci., Part A: Polym. Chem., 2008,46, 7925–7936.19 D. Montarnal, F. Tournilhac, M. Hidalgo, J. L. Couturier andL. Leibler, J. Am. Chem. Soc., 2009, 131, 7966–7967.20 T. L. Sun, T. Kurokawa, S. Kuroda, A. Bin Ihsan, T. Akasaki,K. Sato, M. A. Haque, T. Nakajima and J. P. Gong, Nat.Mater., 2013, 12, 932–937.21 S. Burattini, B. W. Greenland, D. H. Merino, W. Weng,J. Seppala, H. M. Colquhoun, W. Hayes, M. E. Mackay,I. W. Hamley and S. J. Rowan, J. Am. Chem. Soc., 2010, 132,12051–12058.22 J. Fox, J. J. Wie, B. W. Greenland, S. Burattini, W. Hayes,H. M. Colquhoun, M. E. Mackay and S. J. Rowan, J. Am.Chem. Soc., 2012, 134, 5362–5368.23 L. R. Hart, J. H. Hunter, N. A. Nguyen, J. L. Harries,B. W. Greenland, M. E. Mackay, H. M. Colquhoun andW. Hayes, Polym. Chem., 2014, 5, 3680–3688.24 S. Bode, L. Zedler, F. H. Schacher, B. Dietzek, M. Schmitt,J. Popp, M. D. Hager and U. S. Schubert, Adv. Mater., 2013,25, 1634–1638.25 W. Weng, J. B. Beck, A. M. Jamieson and S. J. Rowan, J. Am.Chem. Soc., 2006, 128, 11663–11672.26 Y. Zhao, J. B. Beck, S. J. Rowan and A. M. Jamieson,Macromolecules, 2004, 37, 3529–3531.27 B. Guo, Y. Liang and R. Dong, Nat. Protoc., 2023, 18, 3322–3354.28 S. Zhuo, Y. Liang, Z. Wu, X. Zhao, Y. Han and B. Guo, Mater.Horiz., 2024, 11, 37–101.29 L. Cai, S. Liu, J. Guo and Y.-G. Jia, Acta Biomater., 2020, 113,84–100.30 S. Sharma, A. Kumar, Deepak, R. Kumar, N. K. Rana andB. Koch, Int. J. Biol. Macromol., 2018, 116, 37–44.31 H. An, L. Zhu, J. Shen, W. Li, Y. Wang and J. Qin, ColloidsSurf., B, 2020, 185, 110601.© 2024 The Author(s). Published by the Royal Society of Chemistryhttp://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d4ra00800fPaper RSC AdvancesOpen Access Article. Published on 06 March 2024. Downloaded on 5/8/2024 8:07:25 AM. This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence.View Article Online32 S. Dai, X. Zhou, S. Wang, J. Ding and N. Yuan, Nanoscale,2018, 10, 19360–19366.33 R. Yang, X. Liu, Y. Ren, W. Xue, S. Liu, P. Wang, M. Zhao,H. Xu and B. Chi, Acta Biomater., 2021, 127, 102–115.34 Q. Wang, Z. Shi, Y. Shou, K. Zhang, G. Li, P. Xia, S. Yan andJ. Yin, ACS Biomater. Sci. Eng., 2020, 6, 1715–1726.35 A. Phadke, C. Zhang, B. Arman, C.-C. Hsu, R. A. Mashelkar,A. K. Lele, M. J. Tauber, G. Arya and S. Varghese, Proc. Natl.Acad. Sci. U. S. A., 2012, 109, 4383–4388.36 X. Dai, Y. Zhang, L. Gao, T. Bai, W. Wang, Y. Cui and W. Liu,Adv. Mater., 2015, 27, 3566–3571.37 S.-n. Nishimura, D. Sato and T. Koga, Gels, 2023, 9, 829.38 T. Koga, K. Tomimori and N. Higashi, Macromol. RapidCommun., 2020, 41, 1900650.39 M. Hendrich, L. Lewerdomski and P. Vana, J. Polym. Sci., PartA: Polym. Chem., 2015, 53, 2809–2819.40 T. Koga, T. Morishita, Y. Harumoto, S.-n. Nishimura andN. Higashi, Mater. Adv., 2021, 2, 7851–7860.41 S. Tazawa, A. Shimojima, T. Maeda and A. Hotta, J. Appl.Polym. Sci., 2018, 135, 45419.42 D. Zaguri, S. Shaham-Niv, P. Chakraborty, Z. Arnon,P. Makam, S. Bera, S. Rencus-Lazar, P. R. Stoddart, E. Gazitand N. P. Reynolds, ACS Appl. Mater. Interfaces, 2020, 12,21992–22001.43 K. Baek, A. D. Noblett, P. Ren and L. J. Suggs, ACS Appl. BioMater., 2019, 2, 2812–2821.44 N. Zanna, A. Merlettini and C. Tomasini, Org. Chem. Front.,2016, 3, 1699–1704.45 W. Wang, Z. Liu, Z. Guo, J. Zhang, C. Li, S. Qiu, X. Lei andQ. Zhang, ACS Appl. Mater. Interfaces, 2020, 12, 50812–50822.46 R. K. Bose, N. Hohlbein, S. J. Garcia, A. M. Schmidt andS. van der Zwaag, Phys. Chem. Chem. Phys., 2015, 17, 1697–1704.47 Y. Hou, Y. Peng, P. Li, Q. Wu, J. Zhang, W. Li, G. Zhou andJ. Wu, ACS Appl. Mater. Interfaces, 2022, 14, 35097–35104.48 J. Li, H. Ejima and N. Yoshie, ACS Appl. Mater. Interfaces,2016, 8, 19047–19053.49 C. Kim, H. Ejima and N. Yoshie, RSC Adv., 2017, 19288–19295.50 L. Laysandra, C.-H. Chuang, S. Kobayashi, A.-N. Au-Duong,Y.-H. Cheng, Y.-T. Li, M. M. Mburu, T. sono, T. Satoh andY.-C. Chiu, ACS Appl. Polym. Mater., 2020, 2, 5432–5443.51 S. Chen, G. Ma, X. Duan, H. Zhuo, J. Xu and H. Chen, ACSAppl. Polym. Mater., 2023, 5, 6390–6398.52 S. Wang, L. Li, Q. Liu and M. W. Urban, Macromolecules,2022, 55, 4703–4709.53 Y. Zhou, G. Chen, S. Yan, C. Ni, L. Yu and X. Li, Prog. Org.Coat., 2022, 172, 107098.54 W. Wang, F. Wang, C. Zhang, J. Tang, X. Zeng and X. Wan,Chem. Eng. J., 2021, 404, 126358.55 S. Wang and M. W. Urban, Adv. Sci., 2021, 8, 2101399.56 S. S. Halacheva, D. J. Adlam, E. K. Hendow, T. J. Freemont,J. Hoyland and B. R. Saunders, Biomacromolecules, 2014,15, 1814–1827.© 2024 The Author(s). Published by the Royal Society of Chemistry57 D. Cao, Y. Zhang, Z. Cui, Y. Du and Z. Shi,Mater. Sci. Eng., C,2017, 70, 665–672.58 M. Prasitsilp, T. Siriwittayakorn, R. Molloy, N. Suebsanit,P. Siriwittayakorn and S. Veeranondha, J. Mater. Sci.:Mater. Med., 2003, 14, 595–600.59 C. A. Schoener, H. N. Hutson and N. A. Peppas, AIChE J.,2013, 59, 1472–1478.60 A. Mayer, T. Roch, K. Kratz, A. Lendlein and F. Jung, ActaBiomater., 2012, 8, 4253–4259.61 G. Rodriguez, M. Fernandez-Gutierrez, J. Parra, A. Lopez-Bravo, N. G. Honduvilla, J. Bujan, M. Molina,L. Duocastella and J. San Roman, Biomacromolecules, 2010,11, 2740–2747.62 J. Cui, K. Trescher, K. Kratz, F. Jung, B. Hiebl andA. Lendlein, Clin. Hemorheol. Microcirc., 2010, 45, 401–411.63 K. Shoji, M. Nakayama, T. Koseki, K. Nakabayashi andH. Mori, Polymer, 2016, 97, 20–30.64 M. P. Bueno, C. A. Cativiela, J. A. Mayoral and A. Avenoza, J.Org. Chem., 1991, 56, 6551–6555.65 T. Koseki, R. Kanto, R. Yonenuma, K. Nakabayashi,H. Furusawa, S. Yano and H. Mori, React. Funct. Polym.,2020, 150, 104540.66 S. Y. Park, S.-Y. Kim, T. Kim, H. Ahn and I. Chung, Polym.Adv. Technol., 2019, 30, 872–878.67 H. Mori, M. Matsuyama, K. Sutoh and T. Endo,Macromolecules, 2006, 39, 4351–4360.68 R. Yonenuma, A. Ishizuki, K. Nakabayashi and H. Mori, J.Polym. Sci., Part A: Polym. Chem., 2019, 57, 2562–2574.69 J. Liu, H. Su, L. Meng, Y. Zhao, C. Deng, J. C. Y. Ng, P. Lu,M. Faisal, J. W. Y. Lam, X. Huang, K. S. Wong andB. Z. Tang, Chem. Sci., 2012, 3, 2737–2747.70 H. Tanaka, Y. Inoue and T. Mori, ChemPhotoChem, 2018, 2,386–402.71 Y. Sang, J. Han, T. Zhao, P. Duan and M. Liu, Adv. Mater.,2020, 32, 1900110.72 G. Dado and S. Gellman, J. Am. Chem. Soc., 1994, 116, 1054–1062.73 K. Tsang, H. Diaz, N. Graciani and J. Kelly, J. Am. Chem. Soc.,1994, 116, 3988–4005.74 W. Zhang, H. Jiang, Z. Chang, W. Wu, G. WWu, R. Wu andJ. Li, J. Mater. Sci., 2020, 55, 13543–13558.75 Y. J. Tan, G. J. Susanto, H. P. Anwar Ali and B. C. K. Tee, Adv.Mater., 2021, 33, 2002800.76 J.-g. Liu and M. Ueda, J. Mater. Chem., 2009, 19, 8907–8919.77 S. Watanabe, H. Nishio, T. Takayama and K. Oyaizu, ACSAppl. Polym. Mater., 2023, 5, 2307–2311.78 G. S. Jha, G. Seshadri, A. Mohan and R. K. Khandal, e-Polymers, 2007, 120.79 M. Vacalebre, R. Frison, C. Corsaro, F. Neri, A. Santoro,S. Conoci, E. Anastasi, M. C. Curatolo and E. Fazio,Polymers, 2023, 15, 1590.RSC Adv., 2024, 14, 7850–7857 | 7857http://creativecommons.org/licenses/by-nc/3.0/http://creativecommons.org/licenses/by-nc/3.0/https://doi.org/10.1039/d4ra00800f Self-healing amino acid-bearing acrylamides/n-butyl acrylate copolymers via multiple noncovalent bondsElectronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4ra00800f Self-healing amino acid-bearing acrylamides/n-butyl acrylate copolymers via multiple noncovalent bondsElectronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4ra00800f Self-healing amino acid-bearing acrylamides/n-butyl acrylate copolymers via multiple noncovalent bondsElectronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4ra00800f Self-healing amino acid-bearing acrylamides/n-butyl acrylate copolymers via multiple noncovalent bondsElectronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4ra00800f Self-healing amino acid-bearing acrylamides/n-butyl acrylate copolymers via multiple noncovalent bondsElectronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4ra00800f Self-healing amino acid-bearing acrylamides/n-butyl acrylate copolymers via multiple noncovalent bondsElectronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4ra00800f Self-healing amino acid-bearing acrylamides/n-butyl acrylate copolymers via multiple noncovalent bondsElectronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4ra00800f Self-healing amino acid-bearing acrylamides/n-butyl acrylate copolymers via multiple noncovalent bondsElectronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4ra00800f Self-healing amino acid-bearing acrylamides/n-butyl acrylate copolymers via multiple noncovalent bondsElectronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4ra00800f Self-healing amino acid-bearing acrylamides/n-butyl acrylate copolymers via multiple noncovalent bondsElectronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4ra00800f Self-healing amino acid-bearing acrylamides/n-butyl acrylate copolymers via multiple noncovalent bondsElectronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4ra00800f Self-healing amino acid-bearing acrylamides/n-butyl acrylate copolymers via multiple noncovalent bondsElectronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4ra00800f Self-healing amino acid-bearing acrylamides/n-butyl acrylate copolymers via multiple noncovalent bondsElectronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d4ra00800f