ANIONIC SYNTHESIS OF MODEL IONOMERS - OMEGA-LITHIUM POLY(STYRENE)SULFONATES

The chain end sulfoalkylation of poly(styryl)lithium and poly(styrene-block-alpha-methylstyryl)-lithium using sultones, 1,3-propanesultone and 1,4-butanesultone, has been investigated by a combination of colorimetric titration with methylene blue, two-phase titration with Hyamine 1622, size-exclusion chromatography, TLC, column chromatography using annealed silica gel, infrared, and H-1 and C-13 NMR spectroscopic analyses. Low yields (< 53%) of omega-lithium poly(styrene)sulfonate are obtained from the direct sulfoalkylation reaction under a variety of conditions. In contrast, the direct reaction of poly(styrene-block-alpha-methylstyryl)lithium with 1,3-propanesultone in THF at-78-degrees-C produces the corresponding omega-sulfonated polymer in 94% yield; a yield of only 28% is obtained in toluene at-78-degrees-C. High yields (> 90%) of omega-sulfonated polystyrenes are produced by first reacting poly(styryl)lithium with ethylene oxide prior to reaction with 1,3-propanesultone or 1,4-butanesultone; however, this product is labile toward hydrolysis reactions. End capping of poly(styryl)lithium with 1,1-diphenylethylene prior to the functionalization reaction with excess 1,3-propanesultone at 30-degrees-C in THF/C6H6 produces the omega-sulfonated polymer in 93% yield; lower yields are obtained with 1,4-butanesultone. This end-capping procedure with 1,1-diphenylethylene is recommended as the best procedure for anionic functionalization with sultones since it is efficient and effected at room temperature.