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

We demonstrated the synthesis and directed self-assembly (DSA) of poly­(styrene-<i>b</i>-(lactic acid-<i>alt</i>-glycolic acid)) (PS-<i>b</i>-PLGA). Lamellae-forming PS-<i>b</i>-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 (<i>T</i>_ODT) of four PS-<i>b</i>-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-<i>b</i>-PLGA is twice as large as that of poly­(styrene-<i>b</i>-<i>racemic</i> lactide) (PS-<i>b</i>-PDLLA) at 150 °C, while the surface energies (γ) of PS and PLGA are nearly equal. Thin films of PS-<i>b</i>-PLGA were successfully directed to assemble on stripe chemical patterns with a range of pattern periods (<i>L</i>_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-<i>b</i>-PLGA as an attractive candidate for next-generation lithography with sub-10 nm resolution