Directed Self-Assembly of High χ Poly(styrene-b-(lactic acid-alt-glycolic acid)) Block Copolymers on Chemical Patterns via Thermal Annealing

We demonstrated the synthesis and directed self-assembly (DSA) of poly(styrene- b -(lactic acid- alt -glycolic acid)) (PS- b -PLGA). Lamellae-forming PS- b -PLGAs with a range of molecular weights were synthesized by ring-opening polymerization (ROP) of LGA ( d, l -3-methyl-1,4-dioxane-2,5-dione) from hydroxy-terminated polystyrene (PS–OH) with stannous octoate as the catalyst and characterized by 1 H NMR spectroscopy, GPC, DSC, TGA, SAXS, and rheometry. The order–disorder transition temperatures ( T ODT ) of four PS- b -PLGA block copolymers were determined by temperature sweep measurements and verified by variable-temperature SAXS, which were used to determine the temperature dependence of χ. The χ value of PS- b -PLGA is twice as large as that of poly(styrene- b - racemic lactide) (PS- b -PDLLA) at 150 °C, while the surface energies (γ) of PS and PLGA are nearly equal. Thin films of PS- b -PLGA were successfully directed to assemble on stripe chemical patterns with a range of pattern periods ( L S ) upon thermal annealing. SEM analysis of the assembled films revealed that long-range ordered perpendicularly oriented lamellae were registered on chemical patterns with 2× density multiplication. These results qualify PS- b -PLGA as an attractive candidate for next-generation lithography with sub-10 nm resolution.