Polydispersity-induced stabilization of a disordered bicontinuous morphology in ABA triblock copolymers

A study was conducted to demonstrate the formation of a disordered bicontinuous phase in weakly segregated, compositionally symmetric poly-(styrene-b-1,4-butadiene-b-styrene) (SBS) triblock copolymers with a polydisperse poly(1,4-butadiene) center segment and relatively monodisperse polystyrene end blocks. Polydisperse SBS triblock copolymers were prepared using an optimized variant of the tandem chain transfer ring-opening metathesis polymerization (ROMP-CT) and atom transfer radical polymerization (ATRP) synthesis. The themolecular weights and polydispersities of the end blocks were independently measured by SEC to be in the range M_w/M_n = 1.09-1.20 by using metathesis degradation of the polydiene segment with 1-hexene to isolate the PS end blocks. Polymer compositions were determined to be f _B = 0.48-0.53 from ¹HNMR composition analyses of the resulting block copolymers and the melt homopolymer densities at 140 °C for each block.