A POLYSTYRENE-OLIGOTHIOPHENE-POLYSTYRENE TRIBLOCK COPOLYMER

A well-defined triblock copolymer is synthesized by using a strategy i n which the alpha-coupling of 11 thiophene rings of the middle block a nd the monodispersity (DP = 30 and (M) over bar(w)/(M) over bar(n), = 1.1) of the two polystyrene outer blocks is ensured. Monofunctional po lystyrene 1 is first modified with an alpha-terthiophene unit 2 to for m 3, and two of these units are coupled in a double Stetter reaction o f 4 with a difunctional alpha-terthiophene 5 to yield a tetraketone 6 as the precursor of the triblock copolymer, which was formed with exce ss Lawesson's reagent. The polymer 7 is fully characterized with IR an d NMR spectroscopy and MALDI-TOF mass spectrometry. Size exclusion chr omatography, transmission electron microscopy, and scanning force micr oscopy show that 7 is self-assembled into spherical, micellar structur es with average diameters of 12 nm, which corresponds to about 60 bloc k copolymer molecules per aggregate. The optical properties of 7 are i n full agreement with an associated unsubstituted oligothiophene. Elec trochemical doping is hampered by the polystyrene shell; however, chem ical doping afforded small nanoscopic charged aggregates that are solu ble in organic solvents.