Terminal anhydride functionalization of polystyrene

Polystyrene chains with terminal anhydride groups were synthesized by direct chain transfer reaction between poly(styryl) lithium and trimellitic anhydride chloride (TMAC) and by the alkoxy-de-halogenation reaction between TMAC and hydroxy terminated polystyrene. Pyridine was used as a catalyst for these nucleophilic substitution reactions. For the direct reaction a poly(styryl) lithium with M?_n ～ 1000 (a low MW was used for characterization purposes) was prepared in an argon purged reactor and then introduced into an excess of trimellitic anhydride chloride. Due to the nature of our reaction system, the molecular weight distributions obtained were broader than those possible using more stringent high vacuum techniques. Hydroxy terminated polystyrenes with M?_n = 3,000 and 13,000 obtained elsewhere were used for the indirect addition of terminal anhydride groups. ¹H-NMR spectroscopy, gel permeation chromatography (GPC), and FTIR spectroscopy were used to characterize the reaction products. A maximum yield of 61% for the direct functionalization route and 85% for the indirect functionalization route using hydroxyl terminated polystyrene were achieved. The higher yield of the indirect method seems to be the result of the relatively mild reactivity of the hydroxyl group.