Supramolecular Elastomers with Movable Cross-Linkers

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Supramolecular Elastomers with Movable Cross-Linkers Showing High Fracture Energy Based on Stress Dispersion Ryohei Ikura,† Junsu Park,† Motofumi Osaki,† Hiroyasu Yamaguchi,† Akira Harada,*,‡ and Yoshinori Takashima*,§,† †

Department of Macromolecular Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan The Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan § Institute for Advanced Co-Creation Studies, Osaka University, Suita, Osaka 565-0871, Japan Downloaded via EASTERN KENTUCKY UNIV on September 6, 2019 at 11:43:02 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

‡

S Supporting Information *

ABSTRACT: Highly flexible and tough elastomers were obtained from the bulk copolymerization of a peracetylated cyclodextrin (CD) monomer and small alkyl acrylate main chain monomers without a guest monomer. The main chains penetrated the cavity of the CD units, and the CD units on the polymer chain acted as movable cross-linking points in the obtained elastomer. In contrast, the copolymerization using a bulky main chain monomer with bulky side groups gave linear polymers. The CD units with the bulky main chain polymer cannot serve as movable cross-linking points. Introducing movable cross-linking into poly(ethyl acrylate) resulted in a higher fracture energy comparable to that of conventional rubbers because of the stress-dispersion properties related to the sliding motion of the movable cross-linking points. The movable cross-linkers disperse applied external stresses more effectively than an elastomer with reversible cross-linking at a high Young’s modulus (150 MPa). Movable cross-linking can be introduced to enhance the fracture energy of polymeric materials.

1. INTRODUCTION Recently, polymeric materials that offer higher fracture energy, toughness, and durability have been of great interest for the preparation of polymeric materials with longer lifetimes.1−5 However, conventional polymeric materials are irreversibly deformed by concentrated external stress and break at a threshold minimum energy. To enhance the fracture energy of polymeric materials, materials scientists have investigated polymer network design using various approaches to avoid stress concentration.6,7 The addition of fillers to polymeric materials and the blending of dissimilar polymers can increase the elastic modulus and stress at break.8−10 However, increasing the fracture energy of polymeric materials is not easy because of the conflict between rupture stress and strain based on general polymer physics.11−13 Further new strategies for the design of novel polymeric materials should be proposed by not only polymer scientists but also supramolecular chemists.3,14,15 The cross-linked structures used to increase fracture energy when designing polymer networks fall into four broad categories: simple chemically cross-linking (permanent crosslinking),16,17 interpenetrating networks,18−21 reversible crosslinking,22−29 and movable cross-linking.30−32 Each of these improves the mechanical properties at the molecular level. Cyclic host molecules, crown ethers,33 cucurbit[n]uril,34,35 calixarenes,36 pillararenes,37 and cyclodextrins (CDs),38−40 © XXXX American Chemical Society

which selectively form inclusion complexes with suitable guest molecules depending on the molecular size matching with the guest molecules, have been widely used as functional crosslinking units to form reversible and movable cross-linking points. Notably, the preparation of topologically cross-linked materials without cyclic molecules is difficult; conversely, the complexation of cyclic molecules with linear guest molecules (as axes) through self-assembly should be used to prepare topologically cross-linked materials. We employed CDs to prepare polymeric materials with various properties, such as self-healing41−43 and stress dispersion, through method a in Figures 1 and 2.44,45 Previously, we reported a supramolecular elastomer crosslinked by a reversible noncovalent bond based on a host−guest interaction (Figure 1a).46 The supramolecular elastomer achieved stress-dispersion and self-healing properties based on the reversible bond formation. Previously, we reported a supramolecular elastomer based on poly(ethyl acrylate) (pEA) with cross-linking by a reversible noncovalent bond between peracetylated γ-cyclodextrin methylacrylamide monomer (PAcγCDAAmMe) and hydrophobic guest monomers (Figure 2a following Figure 1a).46 In Received: June 13, 2019 Revised: August 17, 2019

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Figure 1. Preparation of polymeric elastomers with reversible cross-linking points (a), with movable cross-linking points (b), and with linear polymers without cross-linking points (c). This study focuses on methods b and c. These polymeric elastomers have macrocyclic monomers, but the network structure and mechanical properties of the obtained elastomers are significantly different depending on the presence and size of guest monomers.

particular, the supramolecular elastomer, pEA-PAcγCD-F, which possesses a fluoroalkyl guest group (F), also showed self-healing and stress-dispersion properties (Figure 2c) due to the reversible bond.46 Here, we unintentionally obtained topological polymeric materials from the bulk copolymerization of PAcγCDAAmMe and acrylate monomers (Figure 2b). Initially, we expected the polymerization of PAcγCDAAmMe and ethyl acrylate (EA) to give linear polymers with no crosslinking points. However, the mechanical properties of the bulk copolymer from a mixture of the CD monomer and EA indicated it was highly flexible and had a desirable Young’s modulus (Figure 2b and 2c), and even in the absence of a guest, the fracture energy was similar to those of pEAPAcγCD-F. We hypothesized that the obtained elastomers had movable cross-linkers consisting of main chain-penetrating CD units, and the material was characterized by spectroscopic and mechanical tests. The narrow main chain monomer forms a movable cross-linking point with the penetrating CD units (Figure 1b); however, the bulky main chain monomer likely forms linear polymers, not movable cross-linked materials (Figure 1c). Herein, we clarify the relationship between the size of the main chain monomers and the formation of movable cross-linking points. This report proposes a new approach for preparing supramolecular polymeric materials with movable cross-linking points.

2. RESULTS AND DISCUSSION 2.1. Preparation of Poly(alkyl acrylate)s with Tethered CD Units as Side Chains. CDs having a vinyl group (γCDAAmMe and βCDAAmMe) were prepared by the reported method.42 To solubilize the CD monomers in the hydrophobic liquid monomers, peracetylated CD monomers (PAcγCDAAmMe and PAcβCDAAmMe) were prepared using acetic anhydride as the acetylation reagent (Schemes S1 and S2).46 PAcγCDAAmMe and PAcβCDAAmMe (Figure 3a) were characterized by 1H and 13C NMR spectroscopies, MALDI-TOF MS, and ESI-Qq-TOF MS (Figures S1−S8).

Figure 2. (a) Host−guest elastomer prepared by using host and guest monomers. (b) Material obtained from the copolymerization of a host monomer and main chain monomer exhibited high fracture energy. (c) Plots of fracture energy and Young’s modulus for the various materials; pEA-PAcγCD-F (1, 1) (blue filled circle), pEA-PAcγCD (1) (red filled circle), pEA-BDA (x) (x = 0.5, 1, 2, 3, 4, and 5) (black filled circle), and pEA (open circle).

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Figure 3. Chemical structures of (a) the main chain monomers (EA and BA), the CD monomers (PAcγCDAAmMe and PAcβCDAAmMe), and 1,4-butanediol diacrylate as the covalent cross-linking reagent (BDA). (b) Chemical structures of elastomers, elastomers with CDs (pR-PAcγCD (x) and pR-PAcβCD (x)), covalently cross-linked polymers (pR-BDA (x)), and linear polymers without cross-linking (pR).

Scheme 1. Preparation of the pEA-PAcγCD (x) Elastomer and pBA-PAcγCD (x) through Bulk Polymerizations

30 min. After photoinitiated polymerization, the elastomer was dried at 80 °C in vacuo to remove residual EA. The other elastomers, pR-BDA (x) (covalently cross-linked elastomer) and pR (poly(R); homopolymer of R without any cross-linking points), were prepared in the same manner (Schemes S3−S5 and Tables S1−S7). 1H NMR (Figures S9−S12) and FT-IR (Figures S13−S20) spectroscopies were used to characterize the pEA-PAcγCD (x) and pBA-PAcγCD (x) elastomers in Figure 3b. 2.2. Mechanical Properties of pEA-PAcγCD(x) vs Reference Elastomers with Different Cross-Linking Points. The mechanical properties of pEA-PAcγCD(x) were investigated by tensile tests. Figure 4b shows plots of the relation between the fracture energy (E) and the Young’s modulus of pEA-PAcγCD (x) (x = 0.5, 1, 2, 3, 4, and 5) and the control polymers (pEA-BDA (x) and pEA). E was evaluated as the integral of the strain−stress curve from the

PAcγCDAAmMe and PAcβCDAAmMe are highly soluble in hydrophobic liquid monomers, such as ethyl acrylate (EA) or butyl acrylate (BA) (Figure 3a), indicating that the peracetylated CD monomers enable the bulk copolymerizations of these CD monomers with alkyl acrylates as the solvents. Scheme 1 shows the bulk copolymerization of EA with PAcγCDAAmMe to give poly(EA)-tethered CD units, abbreviated pEA-PAcγCD (x), where x is the mol % content of the CD units in the copolymers. To prepare pEA-PAcγCD (1), PAcγCDAAmMe was dissolved in EA, and the homogeneous mixture of monomers was sonicated for 1 h. Then 1-hydroxy-cyclohexylphenyl-ketone (Ciba IRGACURE184 as a photoinitiator) was added to the solution. When the bulk free-radical copolymerization was carried out by UV irradiation with a high-pressure Hg lamp (λ = 253 and 365 nm), a transparent elastomer formed in the solution within C

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Figure 4. (a) Chemical structures of pEA-PAcγCD (x), pEA-BDA (x), pEA, pEA-PAcγCD (1)/PHF, and PFH. (b) Plots of E and Young’s modulus for the pEA-PAcγCD (x) elastomers (red filled circle), pEA-BDA (x) elastomers (black filled circle), and pEA (open circle). (c) Swelling ratios of the pEA-PAcγCD (x) elastomers, pEA-BDA (x) elastomers, and pEA for chloroform. x values are 0.5, 1, 2, 3, 4, and 5. (d) Plots of E and Young’s modulus for pEA-PAcγCD (1) (red filled circle) and pEA-PAcγCD (1)/PHF (purple filled circle).

Figure 5. Stress−strain curves of (a) pEA-PAcγCD (1), pEA-PAcβCD (1), (b) pBA-PAcγCD (1), and pBA-PAcβCD (1). (c) Three-dimensional models (Chem3D) of PAcγCD, PAcβCD, BA, and EA.

2.3. Evaluation of the Cross-Linking Points by Swelling Tests. To prove the formation of cross-linking points we conducted swelling tests on the pEA-PAcγCD (x) elastomers using chloroform as the solvent (Figure 4c). The elastomers were swollen in chloroform to give organogels. The swelling ratios (W/W0; W is the weight of the swollen elastomer, and W0 is the initial weight of the elastomer before swelling) of these elastomers decreased as the mol % content of PAcγCD residues increased, indicating that the cross-linking density in pEA-PAcγCD (x) increases with increasing x. In contrast, the results of dissolving pEA-PAcγCD (0.5) and pEA in chloroform indicated that pEA-PAcγCD (0.5) and pEA did not have effective cross-linking points. In addition, pEAPAcγCD (x) (x = 1−5) exhibited a higher swelling ratio than pEA-BDA(x). These results support that the PAcγCD residues act as cross-linking points in the range of x = 1−5, generating

tensile tests. The Young’s modulus of pEA-PAcγCD (x) increased with increasing PAcγCD content, indicating that the PAcγCD residues act as cross-linking points in the polymer network. The E of pEA-PAcγCD (x) was higher than those of pEA and pEA-BDA(x) (x = 0.5, 1, 2, 3, 4, and 5) (Figure 3b). The E of pEA-BDA(x) decreased with increasing Young’s modulus, and these mechanical properties of pEA-BDA (x) are generally consistent with polymer physics, that is, hard materials with a high Young’s modulus are generally brittle and show a low E. On the other hand, the E of pEA-PAcγCD (x) increased with increasing Young’s modulus up to 150 MPa. pEA-PAcγCD (x) showed higher E values even when they had high Young’s modulus values. These results indicated that the modes of cross-linking in the pEA-PAcγCD (x) elastomers are different than that of the covalently cross-linked pEA-BDA(x). D

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Figure 6. (a) Chemical structures of pEA-PAcγCD (x), pEA-PAcβCD (x), pBA-PAcγCD (x), and pBA-PAcβCD (x). (b) Plots of E and mol % contents of CD monomer units, and (c) plots of E and Young’s modulus for pEA-PAcγCD (x) elastomers (green filled circle) and pEA-PAcβCD (x) elastomers (yellow filled circle). (d) Proposed structure of pEA-PAcCDs with units. (e) Plots of E and mol % contents of CD monomer units, and (f) plots of E and Young’s modulus for pBA-PAcγCD (x) elastomers (green filled circle) and pBA-PAcβCD (x) elastomers (yellow filled circle). x values are 0.5, 1, 2, 3, 4, and 5. (g) Proposed structure of pBA-PAcCDs. PAcγCD and PAcβCD form some movable cross-linking points but fewer than those formed by pEA-PAcCDs. Young’s modulus of pBA-PAcCDs is lower than that of pEA-PAcCDs.

materials that are more flexible than those generated by covalent cross-linking. 2.4. Preparation of pEA-PAcγCD (x) in the Presence of Competitive Guest Molecules. To elucidate the formation of movable cross-linking points in these elastomers, we conducted the radical bulk copolymerization of the pEAPAcγCD (1) monomers in the presence of perfluorohexane (PFH) as competitive guest molecules (Figure 4d). PAcγCD strongly forms an inclusion complex with fluoroalkyl chains.46 The E of pEA-PAcγCD (1)/PFH decreased to 60% of that of pEA-PAcγCD (1), which was prepared without PFH. Additionally, the Young’s modulus of pEA-PAcγCD (1)/PFH was lower than that of pEA-PAcγCD (1), indicating that the addition of PFH decreases the cross-linking density of pEAPAcγCD (1) and inhibits the formation of the inclusion complex between PAcγCD and the poly(EA) main chain. The high E of pEA-PAcγCD (x) is thought to be due to the movable cross-linking points formed by the PAcγCD residues. The swelling ratio of pEA-PAcγCD (1)/PFH also increased to 2.4 times that of pEA-PAcγCD (1) in chloroform (Figure S26), indicating a decrease in the number of the cross-linking

point due to the addition of PFH. This result also supports the formation of movable cross-linking sites in pEA-PAcγCD (x) by the PAcγCD residues. To evaluate the effect of movable cross-linking, we also prepared CD-tethered poly(EA) without movable cross-linking point by solution copolymerization in chloroform. Chloroform acts as competitive guest and prevents from forming movable cross-linking, allowing us to evaluate the mechanical property derived from only entanglement of the polymer chain. The CD-tethered poly(EA) without any cross-linker dissolved in chloroform and exhibited much lower fracture energy than pEA-PAcγCD (x) with movable cross-linker (Figure S27). These result indicates that movable cross-linking plays an important role in enhancing the fracture energy. 2.5. Relation between the Size of the Main Chain and the Cavity Size of the CD. We investigated the relationship between the mechanical properties of the elastomers with various sizes of CD units (PAcγCD or PAcβCD) and the diameter of the polymers. Figure 5a and 5b show the stress− strain curves of the elastomers of poly(EA) or poly(BA) with the PAcγCD or PAcβCD units. In both the poly(EA) and the E

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Figure 7. Chemical structures and cyclic tensile tests of (a) pEA-PAcγCD (1), (b) pEA, and (c) pEA-BDA (1). (d) Plots of hysteresis (average of the last three cycles) and Young’s modulus for the pEA-PAcγCD (x) elastomers (red filled circle), pEA-BDA (1) (black filled circle), and pEA (open circle). Proposed structures of the pEA-PAcγCD elastomers (x) with (e) a low density of movable cross-linking points and (f) a high density of movable cross-linking points. x values are 0.5, 1, 2, 3, and 4.

poly(BA) main chains the maximum stresses of the pRPAcγCD derivatives were higher than those of pR-PAcβCD. These results indicated that the cross-linking density of pRPAcγCD is higher than that of pR-PAcβCD. While pBA-PAcCDs showed lower E and plastic deformation, pEA-PAcCDs exhibited higher maximum stress and clear rupture points. These results indicate that the formation of movable cross-linking with CD is disfavored in pBA-PAcCDs. Moreover, the PAcγCD and PAcβCD derivatives of pEAPAcCDs showed a larger difference than those of pBAPAcCDs, suggesting that molecular recognition of the CD moiety with the main chain polymers plays an important role in the mechanical properties. Figure 5c shows 3D models of PAcγCD, PAcβCD, EA, and BA. The structures of the models were generated by minimizing the internal energy of each molecule by MM2 molecular dynamics calculations. The diameter of the PAcγCD cavity is larger than that of PAcβCD. The alkyl ester of EA is shorter than that of BA, suggesting that the diameter of poly(EA) is smaller than that of poly(BA). These models suggest that the larger cavity size of CD favors the formation of cross-linking points because of the lower steric hindrance. This coincides with the experimental observation that the elastomers generated from the poly(EA) main chains and PAcγCD unit form cross-links at a higher density. The appropriate CD units include the main chain, allowing the

formation of movable cross-linking points. The poly(EA) main chains can form movable cross-links with PAcγCD and PAcβCD, whereas the formation of cross-links with the poly(BA) main chains is difficult due to steric hindrance. The 2D NOESY NMR spectra of the model compounds support the complexation between the PAcγCD units and the pEA main chain (Figure S29). The spin−lattice relaxation time (T1) measurements also support that the poly(EA) main chain is included by the CD cavity (Table S8 and Figures S30−S32). 2.6. Relation of E with the Content of Functional Units and with the Young’s Modulus. Figure 6 shows the mechanical properties of the four elastomers (pEA-PAcγCD (x), pEA-PAcβCD (x), pBA-PAcγCD (x), and pBA-PAcβCD (x) in Figure 6a). E is closely related to the threading ratio (complex formation ratio), which is also related to Young’s modulus. We next sought to clarify the relationship between E and the cross-linking density as a function of CD cavity size/ diameter of the polymers. Figure 6b shows plots of E and the mol % contents of CD units for pEA-PAcγCD (x) and pEAPAcβCD (x). The maximum E of pEA-PAcγCD (x) was observed at a lower mol % content, and this E value was higher than that of pEA-PAcβCD (x). These results suggest that pEAPAcCDs with a higher mol % content of CD units have a higher density of movable cross-linking. Additionally, PAcγCD can more easily include a poly(EA) chain than can PAcβCD due to the larger cavity size of PAcγCD. F

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Figure 8. (a) Plots of E and Young’s modulus for pEA-PAcγCD (x) (red filled circle), pEA-PAcγCD-F (x, y) (blue filled circle), pEA (open circle), and various materials (black filled circle). x and y values are 0.5, 1, 2, 3, 4, and 5. (b) Photographs demonstrating the stab-resistant tests on sheets (size 30 × 30 × 1 mm3) of pEA-PAcγCD (1) using a cutter blade (Movie S1).

2.7. Characterization of the Movable Cross-Linking by Cyclic Tensile Tests. We investigated the effect of the movable cross-links with cyclic tensile tests of pEA-PAcγCD (x) (x = 0.5, 1, 2, 3, 4, and 5), pEA, and pEA-BDA (1) (Figure 7a−c). Test pieces were continuously stretched and recovered without interval. The maximum strains in the tests of pEAPAcγCD (x) and pEA were set to 100%, 200%, 300%, 400%, 500%, 600%, 700%, 800%, 900%, and 1000% with a deformation rate of 0.1 mm/s (Figures 7a and 7b). In the test of pEA-BDA (1), the strains were set to 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100% (Figure 7c). The maximum stress of pEA-PAcγCD (1) increased as the number of cycles increased (Figure 7a), while that of pEA decreased with increasing strain (Figure 7b). These results indicate that the movable cross-linking points influence the elastic properties. pEA-PAcγCD (1) exhibited larger hysteresis than pEA-BDA (1), which has covalent cross-links (Figure 7c), suggesting that the movable cross-linking dispersed the external stress into the polymer network through the sliding motion of the CD units along the pEA main chain, leading to the high fracture strain and E of pEA-PAcγCD (1). The tensile tests changing

Figure 6c shows plots of E and the Young’s modulus for pEA-PAcγCD and pEA-PAcβCD. The maximum E values of both pEA-PAcCDs were observed at similar Young’s modulus values (approximately 150 MPa), suggesting that the number of movable cross-linking points controlled the mechanical properties of these elastomers (Figure 6d). On the other hand, the pBA-PAcβCD and pBA-PAcγCD reached their maximum E values at the same mol % contents of the CD units, but they showed different Young’s moduli (Figure 6e and 6f). In bulk copolymerizations, steric hindrance is expected to hinder the formation of inclusion complexes with BA monomers and the main chain poly(BA) with CD units. pBA-PAcβCD and pBAPAcγCD form relatively few cross-linking points. The mechanical properties of pBA-PAcβCD and pBA-PAcγCD depend on the entanglement of the poly(BA) chain (Figure 6g). Swelling tests on the elastomers were performed using chloroform as the solvent. The swelling ratios of pEA-PAcCDs decreased with increasing content of CD residues (Figure S28). On the other hand, the pBA-PAcCDs were highly swollen, preventing the determination of their swelling ratio. This also indicates that the cross-linking points partly form in the pBA-PAcCDs. G

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PAcγCD (1) resisted the stress, indicating that pEA-PAcγCDs have an energy dissipation mechanism through their movable cross-linking points.

deformation rate also indicate the stress dispersion of movable cross-linking in pEA-PAcγCD (1) (Figure S34). We investigated the dependency of the hysteresis loss on the mol % content of CD monomer units. Figure 7d shows plots of hysteresis loss, which was calculated using the following equation

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CONCLUSION We conducted the free-radical copolymerization of peracetylated CD monomer (PAcγCDAAmMe and PAcβCDAAmMe) and alkyl acrylate main chain monomers. In the case of the small main chain monomers, the polymer main chains penetrate the CD units and act as movable cross-linking points in the obtained elastomer. In contrast, the copolymerization using a bulky main chain monomer gave linear polymers without movable cross-linking points. We believe that the selective preparation of polymer networks with movable cross-linking or linear polymers with free CD moieties will allow the design of new polymeric materials. Introducing movable cross-linking into poly(EA) resulted in a higher fracture energy compared with rubber because of the stressdispersion effect generated by the sliding of the cross-linking points. The materials with movable cross-links dispersed external stress more effectively than the elastomer with reversible cross-linking at high Young’s modulus (150 MPa). This simple method for introducing movable cross-links broadens the available strategies for enhancing the fracture energy of polymeric materials.

hysteresis loss (%) = (Win − Wout)/Win × 100 (%) Win: work added to the test piece during stretching Wout: work recovered from the test piece through the shrinking

Win and Wout were determined from the stress−strain curve in the cyclic tensile tests. The hysteresis loss values in Figure 7d show the averages of the last three cycles against Young’s modulus for pEA-PAcγCD (x) (x = 0.5, 1, 2, 3, and 4), pEA, and pEA-BDA (1). The hysteresis loss of the pEA-PAcγCD (x) elastomers increased with increasing Young’s modulus. pEAPAcγCD (x) with high x (x = 3 and 4) exhibited higher hysteresis loss than pEA, indicating that excess movable crosslinking prevents recovery of the initial sample form. These results suggest the following proposed structures of pEAPAcγCD (x). In pEA-PAcγCD (x) with low movable crosslinking density, the PAcγCD units have more space to slide along the long poly(EA) main chain (Figure 7e). The PAcγCD units cannot pass over another CD unit on the poly(EA) main chain. Therefore, the area over which the PAcγCD unit can slide is determined by the mol % content of PAcγCD units. Consequently, pEA-PAcγCD (x) recovers its original form with low hysteresis loss due to the elasticity of the entropic spring of the polymer chain when the external stress is removed. However, in the case of pEA-PAcγCD (x) with high movable cross-linking density, a large number of CD units tethered to the poly(EA) main chain prevents sliding (Figure 7f), leading to deformation with large hysteresis loss and high Young’s modulus through the cyclic tensile tests. This result confirms that the E of pEA-PAcγCD (x) (x = 3 and 4) are very high compared with that of pEA-PAcγCD (5) (Figure 6b) due to its effective stress-dispersion properties. 2.8. Mechanical Properties of pR-CDs with Movable Cross-Linking vs pEA-PAcγCD-F with Reversible CrossLinking and Other Polymeric Materials (Figure 8). The mechanical properties of other polymeric materials were also evaluated by tensile tests. Figure 8 shows the plots of E and Young’s modulus for pEA-PAcγCD (x) (x = 0.5, 1, 2, 3, 4, and 5), pEA-PAcγCD-F (x, y)46 (x, y = 0.5, 1, 2, 3, 4, and 5; x and y are the mol % contents of the PAcγCD and F units in the copolymer), and various conventional materials. Introducing movable cross-links into poly(EA) resulted in higher E values compared with rubber and crystalline polymers with similar Young’s moduli. pEA-PAcγCD (4) exhibited an E value 1.6 times higher than that of pEA-PAcγCD-F (5, 5) at a Young’s modulus of 150 MPa, suggesting that movable cross-linking more effectively dispersed stress at a high Young’s modulus. Unfortunately, pEA-PAcγCD (x) does not have the molecular adhesion properties that pEA-PAcγCD-F (x, y) has, but a higher E can easily be achieved by choosing a suitable main chain polymer. Movies S1and S2 show the stab resistance of pEA-PAcγCD (1) and pEA-BDA (1). The results show that a cutter blade easily penetrated through a sheet (size 30 × 30 × 1 mm3) of pEA-BDA(1). On the other hand, a sheet of pEA-

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.9b01198. Experimental details and supporting data (PDF) Stab resistance testing of pEA-PAcγCD (1) (MP4) Stab resistance testing of pEA-BDA (1) (MP4)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Ryohei Ikura: 0000-0002-3850-4533 Junsu Park: 0000-0003-2557-904X Motofumi Osaki: 0000-0003-2874-9382 Hiroyasu Yamaguchi: 0000-0002-4801-5071 Akira Harada: 0000-0001-6177-1173 Yoshinori Takashima: 0000-0002-2620-3266 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was funded by a Grant-in-Aid for Scientific Research (B) (No. 18H02035) from MEXT of Japan, a Grantin-Aid from Iketani Science and Technology Foundation, the Ogasawara Foundation for the Promotion of Science & Engineering, and JST-Mirai Program Grant Number JPMJMI18E3, Japan.

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ABBREVIATIONS CD, cyclodextrin Ad, adamantane EA, ethyl acrylate

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BA, butyl acrylate BDA, 1,4-butanediol diacrylate γCDAAmMe, 6-acrylamido methyl ether-γCD βCDAAmMe, 6-acrylamido methyl ether-βCD CDAAmMe, 6-acrylamido methyl ether-CDs PAcγCDAAmMe, peracetylated 6-acrylamidomethyl etherγCD PAcβCDAAmMe, peracetylated 6-acrylamidomethyl etherβCD PAcCDAAmMe, peracetylated 6-acrylamidomethyl etherCDs F, 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl acrylate PFH, perfluorohexane PAcγCD, peracetylated γCD PAcβCD, peracetylated βCD DA, dodecyl acrylate MALDI-TOF MS, matrix-assisted laser desorption ionization-time-of-flight mass spectrometry NOESY, nuclear Overhauser effect spectroscopy FGMAS, field gradient magic angle spinning PET, polyethylene terephthalate PTFE, polytetrafluoroethylene

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DOI: 10.1021/acs.macromol.9b01198 Macromolecules XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.macromol.9b01198 Macromolecules XXXX, XXX, XXX−XXX