Approaches to phthalimido and amino end-functional polystyrene by atom transfer radical polymerisation (ATRP)

Approaches to the synthesis of amine end-functional polystyrenes through intermediary phthalimido end-functional polystyrenes have been explored. Phthalimido groups can be quantitatively converted to amine groups by hydrazinolysis according to an Ing-Manske procedure. Approaches based on α- (functional initiator) and ω-functionalisation (end-group substitution) were examined. Thus, well defined, low molecular weight, ω-bromopolystyrenes, prepared by atom transfer radical polymerisation (ATRP) with copper(I) bromide, 4,4′-di-(nonyl)-2,2′ bipyridine (dNbpy) and 1-bromoethylbenzene initiator, were transformed into ω-phthalimidopolystyrenes by substitution with potassium phthalimide. However, elimination of the terminal bromine to form an unsaturated chain end was observed as a side reaction. Various α-phthalimidopolystyrenes were successfully prepared using phthalimido-functional initiators. Phthalimido-functional bromo isobutyrate derivatives proved very effective in yielding very low polydispersity polystyrene (M_w/M_n ∼ 1.1). However, the conversion of the derived α-phthalimidopolystyrense to an α-aminopolystyrene was problematic because of concomitant hydrazinolysis of the isobutyrate ester linkage and other side reactions. N-(Bromomethyl)phthalimide was successfully used as an ATRP initiator to prepare low polydispersity α-pthalimidopolystyrene (M_w/M_n ∼ 1.3) and thence α-aminopolystyrene with a high degree of end-group purity. End-group interconversions were followed by ¹H NMR.