Direct synthesis of light-emitting triblock copolymers from RAFT polymerization

Abstract

We introduce a straightforward and clean method to synthesize pi-conjugated triblockcopolymers (tri-BCPs) using RAFT polymerization. The strategy circumvents known disadvantages associated with transition metal- or nitroxide-mediated radical polymerizations. The method involves the synthesis of a conjugated macroinitiator, in this case based on poly(dioctylfluorene) (PFO), followed by a RAFT polymerization of styrene or methyl acrylate. The difference in chemistry and polarity between these monomers confirms the versatility of the method. As shown by NMR and GPC, the molecular weight of the obtained polystyrene-(PS-b-PFO-b-PS) and poly(methyl acrylate)-(PMA-b-PFO-b-PMA) tri-BCPs is well-controlled and exhibits a relatively low dispersity of Đ < 2. Thermally annealed films of the nonpolar PS-b-PFO-b-PS exhibit domains containing nanostructures with a lateral periodicity commensurate with classical BCP phase separated morphologies. PMA-b-PFO-b-PMA self-assembles in water, whereby the PFO blocks partly organize into the β-phase. The marked red-shift of the luminescence spectrum confirms complete energy transfer from the amorphous to the β-phase fraction, which can be fully barred by dissolving the nano-assemblies through titration of THF into the aqueous dispersion.