Quantitative Poly(vinyl alcohol) Modification in Ionic Liquids: Esterification and Urethanation with Low Surface Tension Producing Reagents

A method for rapid and quantitative chemical modification of poly(vinyl alcohol) (PVOH) is described using two different ionic liquids as reaction solvents. The quantitative modification of alcohol-containing polymers such as PVOH, cellulose, and other polysaccharides has been elusive due to solvent incompatibility with respect to alcohol-reactive reagents and to the limited solvent options for these polymers. Ionic liquids are ideally suited to address this problem as they are a diverse and extremely tunable class of solvents. Two ionic liquids that differ in both their cation and anion are demonstrated to dissolve and facilitate quantitative modification of PVOH under simple reaction conditions. Rapid esterification of PVOH using four different acid chlorides is demonstrated in both 1-butyl-3-methylimidazolium chloride (BMIM-Cl) and tri-n-butylethylphosphonium diethylphosphate (TBEP-DEP). Urethanation of PVOH was also demonstrated to be quantitative with the appropriate ionic liquid solvent. The reagents chosen for the modification of PVOH were selected based on their low surface tension. Controlling ionic liquid surface properties by the adsorption of partially modified PVOH to the ionic liquid/air interface was an initial objective. The surface tension and surface chemical composition of modified polymer/ionic liquid solutions demonstrate that polymer adsorption to the liquid/vapor interface occurs and that this is more prominent with increasing extent of PVOH modification.