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 1H NMR spectroscopy, GPC, DSC, TGA, SAXS, and rheometry. The order-disorder transition temperatures (TODT) 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 (LS) 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.