Systematical Control of the Flory–Huggins Interaction Parameter of Poly(dimethylsiloxane)-<i>b</i>-Polyisoprene via Fluorination

The directed self-assembly (DSA) of block copolymers (BCPs) has been extensively studied as a highly scalable and cost-effective bottom-up approach for sub-20 nm patterning technology. The Flory–Huggins interaction parameter (χ) of BCP plays a crucial role in determining the properties of the self-assembled patterns, including defect density and pattern quality. Although the χ value of a BCP is determined by the inherent properties of the polymer and cannot be altered, we present an approach wherein the χ value of a BCP can be modulated through postpolymerization modification. In this study, the controlled synthesis of poly(dimethylsiloxane)-b-polyisoprene (DMSI) BCP via atom transfer radical polymerization and subsequent fluorination of the polyisoprene block in DMSI were attempted to prepare fluorinated DMSI (DMSI_F). The fluorination reaction of the DMSI block copolymer was successfully achieved by using hexafluoropropylene oxide. The nuclear magnetic resonance and size exclusion chromatography accurately characterized the quantitative fluorination. The impact of fluorination on the thermal properties and morphology of the DMSI was substantiated through thermogravimetric analysis, differential scanning calorimetry, and small-angle X-ray scattering (SAXS) measurements. In-depth SAXS analysis and Leibler’s mean field theory further confirmed that fluorination directly influences the χ value of DMSI. It was observed that the higher χ value of DMSI_F (0.0962 at 25 °C) compared to that of DMSI (0.0499 at 25 °C) was beneficial to the quality of the self-assembled patterns. The line edge roughness and line width roughness of DMSI_F were 1.78 ± 0.25 and 2.69 ± 0.33 nm, respectively. This postpolymerization modification provides an effective means of tuning the χ value of BCPs, thereby enabling the deliberate manipulation of self-assembled patterns with potential implications for advanced nanotechnology applications.