Tunable Viscosity Modification by Hydrophobe-Modified, Water-Soluble Cellulose Ethers via a Facile Homogeneous Synthesis

Traditionally, hydrophobe-modified, water-soluble cellulose ethers are synthesized in a heterogeneous slurry process using ethylene oxide and long-chain alkyl halides or alkyl glycidyl ethers. In this work, water-soluble cellulose ethers were synthesized homogeneously from glycidyl reagents within a binary ionic liquid system in DMSO. The reaction solvent composition, temperature, and electrophile type were varied to understand the extent of etherification and the solubility of the cellulose ether products. A combination of the ionic liquids 1-ethyl-3-methyl imidazolium acetate (EmimAc) and chloride (EmimCl) resulted in the highest extent of etherification while maintaining an optically clear solution at 8.0 wt % cellulose; the reaction proceeded to completion in 30 min at 100 °C. Additionally, the dual role of weakly basic EmimAc as catalyst and solvent allowed for dissolution and modification of cellulose without the need for additional catalyst or acidic neutralization after the reaction. One-pot synthesis of hydrophobe-modified, water-soluble cellulose ethers exhibited a higher extent of etherification and higher efficiency than previously published heterogeneous reactions conducted with hydrophobic electrophiles of similar length. Rheological measurements of 3.0 wt % aqueous solutions of these cellulose ethers demonstrated a nearly four order-of-magnitude range of solution viscosity from 40 to 15,000 cP. Fully water-soluble cellulose ethers demonstrated an exponential dependence of solution viscosity on the degree of hydrophobe modification, allowing for tunability in a wide array of commercial products. This system demonstrates a versatile method for homogeneously synthesizing water-soluble, hydrophobically modified cellulose ethers in a single step.