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

• Published in: ACS macro letters Vol. 5; no. 7; pp. 833 - 838
• Main Authors: Kanimozhi, Catherine, Kim, Myungwoong, Larson, Steven R, Choi, Jonathan W, Choo, Youngwoo, Sweat, Daniel P, Osuji, Chinedum O, Gopalan, Padma
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 19.07.2016
• ISSN: 2161-1653; 2161-1653
• DOI: 10.1021/acsmacrolett.6b00376

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 T g, which in turn enables the thin film assembly of the BCP via thermal annealing. We synthesized a series of poly­(3-hydroxystyrene-b-tert-butylstyrene) [P­(3HS-b-tBuSt)] and poly­(4-hydroxystyrene-b-tert-butylstyrene) [P­(4HS-b-tBuSt)] BCPs by sequential anionic polymerization of protected 3HS/4HS monomer and tBuSt followed by deprotection. Measured T g 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-b-tBuSt) BCPs in both bulk and thin film is demonstrated. For P­(4HS-b-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-b-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.