Stacked Layer to Gyroid Structures in Partially Fluorinated PS-b-PtBMA Copolymer Films

Abstract

Partial fluorination of polystyrene-b-poly(tert-butyl methacrylate) (PS-b-PtBMA) copolymer was carried out to form PS-b-P(tBMA-r-TFEMA-r-MAA), where TFEMA and MAA denote 2,2,2-trifluoroethyl methacrylate and methacrylic anhydride units, respectively. Phase transitions of a partially (40%) fluorinated copolymer were investigated both in bulk and film using X-ray scattering techniques. The bulk transition pathways showed lamellae to hexagonally perforated layer (HPL) to gyroid (GYR) as temperature increases, although the volumetric ratio between the two blocks is still close to symmetric composition. Meanwhile in copolymer film, the interfacial interactions at air surface altered temperature-increasing transition pathways including HPL to hexagonally modulated layer (HML). However, the suppressed GYR was recovered in isothermal condition of HML at 240 ℃, while remaining the same HPL in isothermal condition at 140 ℃, indicating that a HML is less stable in thick films.