Fluorine-Containing Styrenic Block Copolymers toward High χ and Perpendicular Lamellae in Thin Films

We propose a new approach to fluorine-containing, high-χ styrenic block copolymers (BCPs) via side-chain modification in one block. Polystyrene-b-poly(2,2,2-trifluoroethyl acrylate)s (PS-b-PTFEAs) were synthesized by high-conversion transesterification in acrylate units of polystyrene-b-poly(tert-butyl acrylate)s (PS-b-PtBAs) with the narrow dispersity being unchanged. A simple modification from PtBA into PTFEA block effectuates a remarkable increase in Flory-Huggins interaction parameter (χ) between the two blocks, which measures χ = 30.86/T + 0.160, where T (K) is absolute temperature. The smallest half-pitch feature size of lamellae was evaluated to be 5 nm in 6.3 kg/mol PS-b-PTFEA. For versatility in thin film application, our results also offer a rapid perpendicular orientation of lamellar microdomains in PS-b-PTFEA films supported on a neutral homopolymer mat (cross-linked poly(4-trifluoromethylstyrene)), in which the lamellar spacing (L₀) between the as-spun film and equilibrium bulk gets closer as the molecular weight of BCPs increases.