Isomeric Effect Enabled Thermally Driven Self-Assembly of Hydroxystyrene-Based Block Copolymers.

We demonstrate through isomeric effect the modulation of thermal properties of poly(hydroxystyrene) (PHS)-based block copolymers (BCPs). A minimal structural change of substituting 3HS for 4HS in the BCP results in a drastic decrease in , which in turn enables the thin film assembly of the BCP via thermal annealing. We synthesized a series of poly(3-hydroxystyrene---butylstyrene) [P(3HS--BuSt)] and poly(4-hydroxystyrene---butylstyrene) [P(4HS--BuSt)] BCPs by sequential anionic polymerization of protected 3HS/4HS monomer and BuSt followed by deprotection. Measured of P(3HS) was ∼20-30 °C lower than P(4HS) of comparable molecular weights. As a result, thermally driven self-assembly of P(3HS--tBuSt) BCPs in both bulk and thin film is demonstrated. For P(4HS--tBuSt) thermal annealing in thin-film at high temperatures results in poorly developed morphology due to cross-linking reaction of the 4HS block. The smallest periodicity observed for P(3HS--tBuSt) was 8.8 nm in lamellar and 11.5 nm in cylindrical morphologies. The functionality of the 3HS block was exploited to incorporate vapor phase metal oxide precursors to generate sub-10 nm alumina nanowires.