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Structure and Conformation of Hydroxypropylmethyl Cellulose with a Wide Range of Molar Masses in Aqueous Solution─Effects of Hydroxypropyl Group Addition

回转半径 水溶液 静态光散射 化学 水动力半径 持续时间 羟丙基纤维素 摩尔质量 动态光散射 结晶学 分子 纤维素 散射 分析化学(期刊) 材料科学 光散射 物理化学 色谱法 聚合物 有机化学 光学 纳米技术 物理 医学 替代医学 病理 纳米颗粒 胶束
作者
Erika Saiki,Hiroki Iwase,Yoshiki Horikawa,Toshiyuki Shikata
出处
期刊:Biomacromolecules [American Chemical Society]
卷期号:24 (9): 4199-4207
标识
DOI:10.1021/acs.biomac.3c00517
摘要

The structure of hydroxypropylmethyl cellulose (HpMC) samples with a wide range of weight average molar masses (Mw) from 23 to 5000 kg mol–1, a controlled degree of substitution (DS) of 1.9 by methyl groups, and a molar substitution number (MS) of 0.25 by hydroxypropyl groups dissolved in aqueous solution was examined using static light scattering (SLS), dynamic light scattering (DLS), small-to-wide angle neutron scattering (S-WANS) techniques, and intrinsic viscosity ([η]) measurements. The determined Mw and the radius of gyration (Rg) showed the relationships Rg ∝ Mw1.0 and [η] ∝ Mw1.7 in a range of Mw < 100 kg mol–1, similar to rigid rod molecules in solution. However, exponents in the relationships decreased gradually with increasing Mw and reached ∼0.5 in a high Mw region, which is a typical value of flexible chain molecules for both Rg and [η]. These observations suggest that the HpMC samples behave as semiflexible rods with a certain persistence length (lp). The ratios of the hydrodynamic radius via DLS measurements to Rg also supported semiflexible rod behavior. Particle form factors and the average lengths (L) resulting from SLS and S-WANS experiments are well described with rigid rod particles in the range of Mw < 100 kg mol–1 and semiflexible rods with lp ∼ 100 nm in Mw > 100 kg mol–1. Because the average contour length (lc) calculated from Mw is approximately twice as long as L in the Mw range < 100 kg mol–1, the formed HpMC particles possess a folded hairpin-like elongated rigid rod structure. However, the lc/L value increases gradually in the range Mw > 200 kg mol–1, where the formed HpMC particles behave as semiflexible rods. The formed particle structure was substantially different from that found in methyl cellulose samples with a similar DS value, which showed rod-like behavior over a wide Mw range. The addition of hydroxypropyl groups only at MS = 0.25 effectively changed the formed particle structure.
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