Nitroxide‐mediated synthesis of styrenic‐based segmented and tapered block copolymers using poly(lactide)‐functionalized TEMPO macromediators

Poly(styrene)‐poly(lactide) (PS‐PLA), poly ( tert ‐butyl styrene)‐poly(lactide) (P t BuS‐PLA) diblocks, and poly( tert ‐butyl styrene)‐poly(styrene)‐poly(lactide) (P t BuS‐PS‐PLA) segmented and tapered triblocks of controlled segment lengths were synthesized using nitroxide‐mediated controlled radical polymerization. Well‐defined PLA‐functionalized macromediators derived from hydroxyl terminated TEMPO (PLA T ) of various molecular weights mediated polymerizations of the styrenic monomers in bulk and in dimethylformamide (DMF) solution at 120–130°C. PS‐PLA and P t BuS‐PLA diblocks were characterized by narrow molecular weight distributions (polydispersity index ( M w / M n ) < 1.3) when using the PLA T mediator with the lowest number average molecular weight M n = 6.1 kg/mol while broader molecular weight distributions were exhibited ( M w / M n = 1.47‐1.65) when using higher molecular weight mediators ( M n = 7.4 kg/mol and 11.3 kg/mol). Segmented P t BuS‐PS‐PLA triblocks were initiated cleanly from P t BuS‐PLA diblocks although polymerizations were very rapid with PS segments ∼ 5–10 kg/mol added within 3–10 min of polymerization at 130°C in 50 wt % DMF solution. Tapering from the P t BuS to the PS segment in semibatch mode at a lower temperature of 120°C and in 50 wt % DMF solution was effective in incorporating a short random segment of P t BuS‐ ran ‐PS while maintaining a relatively narrow monomodal molecular weight distribution ( M w / M n ≈ 1.5). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008