The dimensional characterization of ethylcellulose (cellulose ethyl ether, ECx, where x is the degree of substitution based on the number of hydroxyl groups in a repeating unit (in this study, x = 3.0 and 2.5)) with a weight-averaged molar mass (Mw) ranging from 6.32 × 103 to 3.83 × 105 g mol–1 and a relatively narrow molar mass distribution (Mw/Mn < 1.2) was studied in tetrahydrofuran (THF) at 25 °C using static light and small-angle X-ray scattering and intrinsic viscosity ([η]) measurements. Eleven fully substituted EC3.0 samples with Mw/Mn values ranging from 1.05 to 1.22 were prepared by reacting commercially available EC2.5 with ethyl iodide in THF at 55 °C in the presence of sodium hydride, followed by fractionation using recycling preparative size exclusion chromatography (SEC) in CHCl3. Furthermore, eight EC2.5 samples with Mw/Mn values ranging from 1.04 to 1.19 were obtained by applying the same fractionation technique to EC2.5. Afterward, the z-averaged root-mean-squared radius of gyration (< S2 > z1/2) and [η] for the isolated EC3.0 and EC2.5 chains were measured and tabulated as functions of Mw. Furthermore, their Mw dependencies were analyzed using cylindrical wormlike chain and wormlike touched-bead models. The chain stiffness parameter (Kuhn segment length, λ–1), molar mass per unit contour length (ML), and hydrodynamic bead diameter (dB) were determined to be 23.1 nm, 491 g mol–1 nm–1, and 1.8 nm for EC3.0 and 16.5 nm, 467 g mol–1 nm–1, and 1.1 nm for EC2.5, respectively. These results indicate that both EC3.0 and EC2.5 form semiflexible chains with moderate stiffness, primarily because of steric hindrance arising from the ethyl groups in the cellulose backbone. The monomer counter length (lM) was estimated to be 0.50 nm for both EC3.0 and EC2.5, suggesting that the local conformation of the EC chain remains largely unaffected by x between 2.5 and 3.0. In addition, the lM value was almost equal to that (0.51–0.52 nm) of crystalline cellulose but considerably greater than that (0.33 nm) of α-1,4-linked amylose derivatives. In contrast, λ–1 and dB were influenced by x, likely because of greater steric hindrance in the main chain and desolvation around the hydroxyl groups.

Dimensional characterization of isolated ethylcellulose in tetrahydrofuran

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2026年2月13日

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Kenji Fukuda,
Moriya Kikuchi,
Seigou Kawaguchi

摘要

The dimensional characterization of ethylcellulose (cellulose ethyl ether, EC_x, where x is the degree of substitution based on the number of hydroxyl groups in a repeating unit (in this study, x = 3.0 and 2.5)) with a weight-averaged molar mass (M_w) ranging from 6.32 × 10³ to 3.83 × 10⁵g mol^–1 and a relatively narrow molar mass distribution (M_w/M_n < 1.2) was studied in tetrahydrofuran (THF) at 25 °C using static light and small-angle X-ray scattering and intrinsic viscosity ([η]) measurements. Eleven fully substituted EC_3.0 samples with M_w/M_n values ranging from 1.05 to 1.22 were prepared by reacting commercially available EC_2.5 with ethyl iodide in THF at 55 °C in the presence of sodium hydride, followed by fractionation using recycling preparative size exclusion chromatography (SEC) in CHCl₃. Furthermore, eight EC_2.5 samples with M_w/M_n values ranging from 1.04 to 1.19 were obtained by applying the same fractionation technique to EC_2.5. Afterward, the z-averaged root-mean-squared radius of gyration (< S² > _z^1/2) and [η] for the isolated EC_3.0 and EC_2.5 chains were measured and tabulated as functions of M_w. Furthermore, their M_w dependencies were analyzed using cylindrical wormlike chain and wormlike touched-bead models. The chain stiffness parameter (Kuhn segment length, λ^–1), molar mass per unit contour length (M_L), and hydrodynamic bead diameter (d_B) were determined to be 23.1 nm, 491 g mol^–1 nm^–1, and 1.8 nm for EC_3.0 and 16.5 nm, 467 g mol^–1 nm^–1, and 1.1 nm for EC_2.5, respectively. These results indicate that both EC_3.0 and EC_2.5 form semiflexible chains with moderate stiffness, primarily because of steric hindrance arising from the ethyl groups in the cellulose backbone. The monomer counter length (l_M) was estimated to be 0.50 nm for both EC_3.0 and EC_2.5, suggesting that the local conformation of the EC chain remains largely unaffected by x between 2.5 and 3.0. In addition, the l_M value was almost equal to that (0.51–0.52 nm) of crystalline cellulose but considerably greater than that (0.33 nm) of α-1,4-linked amylose derivatives. In contrast, λ^–1 and d_B were influenced by x, likely because of greater steric hindrance in the main chain and desolvation around the hydroxyl groups.