Mechanism of interaction between hydroxypropyl cellulose and water in aqueous solutions: Importance of polymer chain length

The utilization of hydroxypropyl cellulose (HPC) can be regarded as unexpected with regard to certain applications, such as being employed as a solubility enhancer for poorly soluble drugs and as a solubilizing agent for nano-suspensions and amorphous solid dispersions. However, the best results were obtained for low-molecular weight (Mw) HPC grades with a short-chain structure.

Therefore, in this study, seven grades of HPC with different polymer chain lengths (Mw) are analyzed in various aqueous solutions by a combination of 1H quantitative NMR spectroscopy, diffusion NMR spectroscopy, and water ligand observed via gradient spectroscopy; these investigations provide insights into the remarkable solubilizing property of HPC at the molecular and supramolecular levels. Furthermore, the hydration and the water residence time are found to be strongly dependent on the polymer chain length of HPC. The quantitative results obtained herein indicate that HPCs with shorter chain lengths retain smaller amounts of water around their hydrated molecules, as compared to their counterparts with longer chain lengths.

Herein, the behavior of hydroxypropyl cellulose (HPC) with different polymer chain lengths in aqueous solutions is investigated by fragment-based screening via 1H-NMR. The results of the analysis reveal that in solution, short-chain HPCs associate with low amounts of water molecules around their chains, thus becoming more “hydrophobic.” Furthermore, diffusion-coefficient measurements confirm that the agglomeration ability of HPC in solution increases with augmentations in the chain length and molecular weight.

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About the article: Martin-Pastor, M, Stoyanov, E. Mechanism of interaction between hydroxypropyl cellulose and water in aqueous solutions: Importance of polymer chain length. J Polym Sci. 2020; 58: 1632-1641. https://doi.org/10.1002/pol.20200185

Materials: Seven HPC grades with average molecular weights of 2,500,000 (HPC-VH), 1,000,000 (HPC-H), 700,000 (HPC-M), 140,000 (HPC-L), 100,000 (HPC-SL), 40,000 (HPC-SSL), and 20,000 (HPC-UL) were procured from Nippon Soda (Japan), for this study.