Synthesis and characterization of novel fluorinated siloxane star-like copolymer with short perfluoroalkyl chain and used for modification the epoxy resin

Two series of fluorinated siloxane star-like copolymers, with different molecular weight of siloxane segments and large fluorinated segments at the tail, were synthesized from dicarboxyl terminated poly(2,2,3,4,4,4-hexafluorobutyl acrylate) (CTHFA) and dihydroxypropyl-terminated poly(dimethyl siloxane) (PDMS). The chemical structures of the star-like copolymer (CTHFA-PDMS) were measured by FT-IR, 1H NMR, 13C NMR and GPC. Long siloxane spacers were employed to increase the migration efficiency of the large fluorinated segments. The long siloxane spacers also played a part in toughening the epoxy resin. Then, the copolymers reacted with 4′4-diphenylmethane dissocyanate and were used as a surface modifier of cured commercial diglycidyl ether of bisphenol A (DGEBA) at different concentration (0.1–0.5 wt% with respect to DGEBA). For both kinds of the CTHFA-PDMS modified DGEBA, high water contact angles (122° and 110°) were obtained at very low concentration (0.2 wt%). The surface chemical composition was measured by X-ray photoelectron spectroscopy (XPS). It was found that the fluorine and silicon atoms selectively migrated toward the outermost surface of modified DGEBA resin. The surface enrichment factors of fluorine and silicon atoms (SmF and SmSi) of modified resin were up to 2.18 × 105 and 2.93 × 104 times than the theoretical value expected for the bulk formulations at very low concentration (0.2 wt%). Moreover, the surface of modified epoxy resins showed good chemical stability by immersing in acidic and salt solutions. Scanning electron microscopy (SEM) images observed many ridges and rough crack structures of the fracture surface of modified DGEBA resin, indicating the CTHFA-PDMS toughened the DGEBA network.