Synthesis and self-assembly of a series of π-conjugated triblock copolymers containing polyfluorene and poly(ethylene oxide)

A series of novel amphiphilic, conjugated triblock copolymers of poly(9,9-didodecylfluorene-2,7-diyl) (PF) were synthesized. The rod-like PF midblock was synthesized via a Yamamoto-type reaction of 2,7-dibromo-9,9-di-n-dodecylfluorene, and endcapped with 4-bromobenzyl alcohol to obtain the hydroxyl end-functionalized PF (PFOH). A series of α-monocarboxy-ω-mono-methoxy poly(ethylene glycol)s with various chain lengths were connected at both ends of PFOH to produce the triblock copolymers of poly(ethylene glycol)-b-polyfluorene-b-poly(ethylene glycol) (PEO-b-PF-b-PEO). The addition of PEO endblocks to the rod-like PF segment resulted in microphase separation between the component PF and PEO block, and suppressed the photo-oxidation and excimer formation of the PF molecules during high temperature annealing. These block copolymers were self-assembled into a micellar structure in a range of solvents, and the critical micelle concentration of the PEO-b-PF-b-PEOs decreased with decreasing molecular weight of the PEO endblock.