Cellulose Research Unit, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu, Tokyo 183-8509, Japan.
Division of Natural Resources and Eco-materials, Graduate School of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwai-cho, Fuchu, Tokyo 183-8509, Japan.
Biomacromolecules. 2023 Sep 11;24(9):4199-4207. doi: 10.1021/acs.biomac.3c00517. Epub 2023 Aug 18.
The structure of hydroxypropylmethyl cellulose (HpMC) samples with a wide range of weight average molar masses () from 23 to 5000 kg mol, a controlled degree of substitution () of 1.9 by methyl groups, and a molar substitution number () 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 and the radius of gyration () showed the relationships ∝ and [η] ∝ in a range of < 100 kg mol, similar to rigid rod molecules in solution. However, exponents in the relationships decreased gradually with increasing and reached ∼0.5 in a high region, which is a typical value of flexible chain molecules for both and [η]. These observations suggest that the HpMC samples behave as semiflexible rods with a certain persistence length (). The ratios of the hydrodynamic radius via DLS measurements to also supported semiflexible rod behavior. Particle form factors and the average lengths () resulting from SLS and S-WANS experiments are well described with rigid rod particles in the range of < 100 kg mol and semiflexible rods with ∼ 100 nm in > 100 kg mol. Because the average contour length () calculated from is approximately twice as long as in the range < 100 kg mol, the formed HpMC particles possess a folded hairpin-like elongated rigid rod structure. However, the / value increases gradually in the range > 200 kg mol, 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 value, which showed rod-like behavior over a wide range. The addition of hydroxypropyl groups only at = 0.25 effectively changed the formed particle structure.
用静态光散射（SLS）、动态光散射（DLS）、小角-宽角中子散射（S-WANS）技术以及特性黏度（[η]）测量研究了羟丙基甲基纤维素（HpMC）样品的结构，这些样品的重均摩尔质量（Mw）范围很宽，从 23 到 5000kg/mol，甲基的取代度（DS）为 1.9，羟丙基的摩尔取代数（NS）为 0.25，并且溶解在水溶液中。测定的Mw 和回转半径（〈Rg〉）表现出在Mw < 100kg/mol 的范围内符合Mw∝〈Rg〉2和[η]∝Mw1.5 的关系，类似于溶液中的刚性棒状分子。然而，随着Mw 的增加，这些关系的指数逐渐减小，在高Mw 区域达到约 0.5，这是Mw 和[η]的柔性链分子的典型值。这些观察结果表明，HpMC 样品表现出具有一定持久性长度（lp）的半刚性棒状行为。通过 DLS 测量得到的水动力半径与〈Rg〉的比值也支持半刚性棒状行为。在 Mw < 100kg/mol 的范围内，SLS 和 S-WANS 实验得到的粒子形态因子和平均长度（〈L〉）与刚性棒状粒子很好地吻合，而在 Mw > 100kg/mol 的范围内，与具有约 100nm 的 lp 的半刚性棒状粒子很好地吻合。因为从〈L〉计算得到的平均轮廓长度（〈Lp〉）在 Mw < 100kg/mol 的范围内大约是〈Rg〉的两倍，所以形成的 HpMC 粒子具有折叠发夹状的刚性棒状伸长结构。然而，在 Mw > 200kg/mol 的范围内，〈Lp〉/〈Rg〉值逐渐增加，形成的 HpMC 粒子表现为半刚性棒状。形成的粒子结构与具有相似Mw 值的甲基纤维素样品的结构显著不同，后者在很宽的Mw 范围内表现出棒状行为。仅在 DS = 0.25 时添加羟丙基基团有效地改变了形成的粒子结构。
