Thiol–Ene Reactions Enable Precise Control over Water-Soluble Cellulosics

Cellulose ethers are a diverse class of materials typically used as rheology modifiers in aqueous applications, ranging from personal care products to construction materials. Hydrophobe-modified cellulose ethers provide excellent viscosity enhancement at low polymer loadings due to intermolecular associations of the hydrophobic and hydrophilic regions of the polymer. However, the synthesis of hydrophobe-modified cellulose ethers relies on inefficient heterogeneous etherification reactions between a hydrophilic cellulose derivative and hydrophobic reagents. In the present work, we synthesized a library of hydrophobe-modified cellulose ethers from a lightly allylated (MS 0.007–0.043) intermediate that is structurally similar to 2,3-dihydroxypropylcellulose (DHPC). Allylated DHPC (allylDHPC) was synthesized by the reaction of cellulose with glycidol and either allyl bromide or allyl glycidyl ether under heterogeneous conditions. AllylDHPC was characterized and used as a scaffold to synthesize a library of hydrophobe-modified DHPC (hmDHPC) materials via thiol–ene reactions with linear alkyl thiols ranging from six to 18 carbons in length. This two-step process allows a direct comparison between hmDHPC derivatives of various alkyl lengths with the exact same pattern of substitution across the cellulose backbone. Precise control over the structure of hmDHPC allows for a product with tunable solubility and viscosity in water over several orders of magnitude at the same molecular weight. We expanded the scope of the reaction to include the hydrophilic tripeptide glutathione, which resulted in an ionic polymer with high solubility and high viscosity in water. A representative subset of the polymer library was shown to be hydrolytically stable under neutral conditions but to be highly degradable in the presence of cellulase enzymes.