Chain-End Effect for Intermediate Water Formation of Poly(2-Methoxyethyl Acrylate)

Abstract

Intermediate water (IW), which is formed not only by biocompatible polymers such as poly(2-methoxyethyl acrylate) (PMEA), but also by biomacromolecules, plays a key role in determining the biocompatibility of synthetic polymers. In this study, we compare the well-defined linear and cyclic PMEA using differential scanning calorimetry and atomic force microscopy. This study aims to clarify the role of the chain-end effect in IW formation to establish design guidelines for biomaterials.

Key words

intermediate water - hydration state - chain-end effect - poly(2-methoxyethyl acrylate) - cyclic polymers - interfacial structures

• References And Notes

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• 6 Synthetic procedure for compound 1: Ethylene glycol (dehydrated) 2.48 g (40 mmol) and pyridine 7.26 mL (90 mmol) were dissolved in dry THF 60 mL and cooled to 0 °C. Then, 2-bromopropanoyl bromide 9.43 mL (90 mmol) was diluted with dry THF 10 mL and added dropwise to the mixture and reacted at RT for 15 h. The resultant mixture was concentrated in vacuo and 100 mL of hexane/ethyl acetate (v/v = 1/1) mixture solution was added. The solution was washed with sat. sodium hydrogen carbonate aqueous solution 100 mL × 5, 1 M sodium hydrogen sulfate aqueous solution 100 mL × 3, and water 100 mL × 3. An organic layer was collected and dried over magnesium sulfate anhydrous. The solvents were removed in vacuo to give an objective ethane-1,2-diyl bis(2-bromopropanoate), 1, as a colorless oil (10.12 g, 76.2%). ¹ H NMR [400 MHz, CDCl₃, tetramethylsilane (TMS)] (Figure S1a): σ = 1.85 ppm ((–CH₂OC(=O)CH(CH ₃)Br)₂ d, 6H), 4.40 ppm ((–CH₂OC(=O)CH(CH₃)Br)₂ q, 2 H), 4.43 ppm ((–CH ₂OC(=O)CH(CH₃)Br)₂ s, 4 H). ¹³ C NMR [75 MHz, CDCl₃, TMS] (Figure S1b): σ = 21.6 ppm ((–CH₂OC(=O)CH(CH₃)Br)₂), 39.6 ppm ((–CH₂OC(=O)CH(CH₃)Br)₂), 63.3 ppm ((–CH₂OC(=O)CH(CH₃)Br)₂), 170.1 ppm ((–CH₂OC(=O)CH(CH₃)Br)₂
• 7 Synthetic procedure for compound 2: Sodium hydride 6.68 g (0.167 mol) was dispersed to dry diethyl ether 200 mL and cooled to 0 °C under an argon gas atmosphere. Ethanethiol 13.3 mL (0.185 mol) was added dropwise to the dispersion solution and its mixture was stirred for 15 min. Then, carbon disulfide 11.2 mL (0.185 mol) was added and reacted at RT for 1 h. After reaction, the reaction mixture was added n-pentane 100 mL to precipitate a resultant sodium salt of trithiocarbonate. The precipitation was collected by filtration and washed with n-pentane 400 mL to give an objective sodium ethyl carbonotrithioate, 2, as a yellow powder (25.0 g, 93.4%). ¹ H NMR [400 MHz, DMSO-d ₆, TMS] (Figure S2a): σ = 1.14 ppm (CH ₃CH₂SC(=S)SNa, t, 3 H), 2.96 ppm (CH₃CH ₂SC(=S)SNa, q, 2 H). ¹³ C NMR [100 MHz, DMSO-d ₆, TMS] (Figure S2b): σ = 14.6 ppm (CH₃CH₂SC(=S)SNa), 34.3 ppm (CH₃ CH₂SC(=S)SNa), 240.1 ppm (CH₃CH₂SC(=S)SNa)
• 8 Synthetic procedure for compound 3: 7.6 g of 1 (47.4 mmol) and freshly prepared 3.2 g of 2 (9.5 mmol) were dissolved to acetonitrile 30 mL and stirred at RT for 1.5 days. The reaction mixture was added diethyl ether 200 mL and washed with water 200 mL × 4. An organic layer was collected and dried over magnesium sulfate anhydrous. The solution was concentrated to give an objective ethane-1,2-diyl bis(2-(((ethylthio)carbonothioyl)thio)propanoate, 3, as an orange oil (3.6 g, 92.1%). ¹ H NMR [400 MHz, CDCl₃, TMS] (Figure S3a): σ = 1.26 ppm ((–CH₂OC(=O)CH(CH₃)SC(=S)S–CH₂CH _{3 2} t, 6 H), 1.54 ppm ((–CH₂OC(=O)CH(CH ₃)SC(=S)SCH₂CH_{3 2} t, 6 H), 3.29 ppm ((–CH₂OC(=O)CH(CH₃)SC(=S)SCH ₂CH_{3 2} q, 4 H), 4.28 ppm ((–CH ₂OC(=O)CH(CH₃)SC(=S)S–CH₂CH_{3 2} s, 4 H), 4.77 ppm ((–CH₂OC(=O)CH(CH₃)SC(=S)SCH₂CH_{3 2} q, 2 H). ¹³ C NMR [100 MHz, CDCl₃, TMS] (Figure S3b): σ = 12.7 ppm ((–CH₂OC(=O)CH(CH₃)SC(=S)S–CH₂ CH_{3 2}), 16.8 ppm ((–CH₂OC(=O)CH(CH₃)SC(=S)SCH₂CH_{3 2}), 31.6 ppm ((–CH₂OC(=O)CH–(CH₃)SC(=S)SCH₂CH_{3 2}), 47.9 ppm ((–CH₂OC(=O)CH(CH₃)SC(=S)SCH₂CH_{3 2}), 63.1 ppm ((–CH₂OC(=O)CH(CH₃)SC(=S)SCH₂CH_{3 2}), 170.9 ppm ((–CH₂OC(=O)CH(CH₃)SC(=S)SCH₂–CH_{3 2}), 221.9 ppm ((–CH₂OC(=O)CH(CH₃)SC(=S)SCH₂CH_{3 2}
• 9 Synthetic procedure for compound 4: MEA 5.00 g (38.40 mmol), 3 17.15 mg (3.48 µmol), and AIBN 5.50 mg (3.48 µmol) were dissolved to toluene (monomer concentration: 4 M), and the solution was degassed over freeze–pump–thaw cycles (three times) under an argon gas atmosphere. Then the reaction mixture was placed in a preheated oil bath at 60 °C. After polymerization for 1 h, the mixture was cooled to RT and poured into a large excess of hexane to precipitate the resulting polymer. The polymer was further purified by a reprecipitation method from the THF/hexane system. The solvents were removed in vacuo to give a pure telechelic PMEA, 4, as a yellow-colored viscosity liquid (Conv.: 77.6%). ¹ H NMR [400 MHz, CDCl₃, TMS] (Figure 1b, black): σ = 1.26–3.0 ppm (–SC(=S)SCH₂CH ₃ t, 6 H (both end); –(CH ₃)CH(=O)OCCH₂CH₂OC(=O)CH(CH ₃)–, t, 6H; PMEA, methylene (main chain), 2(1–x nH; PMEA, methine (main chain), (1–x nH), 3.26–3.47 ppm (–SC(=S)SCH ₂CH₃ q, 4 H (both end); –CO(=O)CH₂CH₂OCH ₃, 3(1–x nH), 3.48–3.70 ppm (–CO(=O)CH₂CH ₂OCH₃, 2(1–x nH), 4.00–4.47 ppm (–(CH₃)CH(=O)OCCH ₂CH ₂OC(=O)CH(CH₃)–, s, 4 H; –CO(=O)CH ₂CH₂O–CH₃, 2(1–x nH), 4.77 ppm (–(CH₃)CH(=O)OCCH₂CH₂OC(=O)CH(CH₃)–, q, 2 H). SEC [THF, 40 °C, PSt standard] (Figure 1a, black): M _n,SEC = 76,300 g mol ⁻¹, Ð M _w/M _n) = 1.06
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11
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• 12 Synthetic procedure for compound 5: 4 1.0 g (13.1 µmol), TTMSS 65. 1 mg (262.0 µmol), and V-70 2.0 mg (6.5 µmol) were dissolved to toluene 5 mL. The colored solution was deoxygenated by freeze–pump–thaw cycles (three times). Then the reaction mixture was stirred at 40 °C for 12 h, resulting in a colorless solution. The solution was poured into a large excess of hexane to precipitate an objective polymer. The polymer was further purified by a reprecipitation method from the THF/hexane system to give a pure desulfurized-PMEA, 5, as a colorless viscosity liquid (0.88 g). ¹ H NMR [400 MHz, CDCl₃, TMS] (Figure 1b, red): σ = 1.30–3.0 ppm (–(CH ₃)CH(=O)OCCH₂–CH₂OC(=O)CH(CH ₃)–, t, 6 H; PMEA, methylene (main chain), 2(1–x nH; PMEA, methine (main chain), (1–x nH), 3.26–3.47 ppm (–CO(=O)CH₂CH₂OCH ₃, 3(1–x nH), 3.48–3.70 ppm (–CO(=O)CH₂CH ₂OCH₃, 2(1–x nH), 4.00–4.47 ppm (–(CH₃)CH(=O)OCCH ₂CH ₂OC(=O)CH–(CH₃)–, s, 4 H; –CO(=O)CH ₂CH₂OCH₃, 2(1–x nH), 4.77 ppm (–(CH₃)CH(=O)OCCH₂CH₂O–C(=O)CH(CH₃)–, q, 2 H). SEC [THF, 40 °C, PSt standard] (Figure 1a, red): M _n = 75,900 g mol ⁻¹, Ð = 1.09
• 13 Synthetic procedure for compounds 6 and 7: 4 1.0 g (13.1 µmol) and isobutylamine 95.9 mg (1.3 mmol) were dissolved in 20 mL THF and stirred at RT for 2 h, resulting in a colorless solution. The solution was poured into a large excess of hexane to precipitate an objective polymer. The polymer was further purified by a reprecipitation method from the THF/hexane system to give a pure thiol-terminated PMEA, 6, as a colorless viscous liquid (0. 67 g). Subsequently, 6 100 mg (1.31 µmol) was dissolved in 2 L of diethyl ether/THF (v/v = 3/1), and then iron(III) chloride 0.93 g (5.24 mmol) was added and stirred at RT for 1 month. The reaction mixture was concentrated in vacuo and poured into hexane to precipitate a resultant polymer as a yellowish viscous liquid. The polymer was passed through an alumina column using THF as an eluent. The solvents were removed in vacuo to obtain an objective cyclic PMEA, 7, as a colorless, viscous solid (38 mg). ¹ H NMR [400 MHz, CDCl₃, TMS] (Figure S5): σ = 1.30–3.0 ppm (–(CH ₃)CH(=O)OCCH₂–CH₂OC(=O)CH(CH ₃)–, t, 6 H; PMEA, methylene (main chain), 2(1–x nH; PMEA, methine (main chain), (1–x nH), 3.26–3.47 ppm (–CO(=O)CH₂CH₂OCH ₃, 3(1–x nH), 3.48–3.70 ppm (–CO(=O)CH₂CH ₂OCH₃, 2(1–x nH), 4.00–4.47 ppm (–(CH₃)CH(=O)OCCH ₂CH ₂OC(=O)CH–(CH₃)–, s, 4 H; –CO(=O)CH ₂CH₂OCH₃, 2(1–x nH), 4.77 ppm (–(CH₃)CH(=O)OCCH₂CH₂O–C(=O)CH(CH₃)–, q, 2 H). SEC [THF, 40 °C, PSt standard] (Figure 2, violet): M _p,L = 88,200 g mol ⁻¹, M _p,C = 63,500 g mol ⁻¹, Ð = 1.27
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