Effect of changing molecular end groups on surface properties: Synthesis and characterization of poly(styrene-b-semifluorinated isoprene) block copolymers with -CF2H end groups

Poly(styrene-b-semifluorinated isoprene) block copolymers with -CF2H-termin ated side groups were synthesized by the esterification reaction of a poly( styrene-b-hydroxylated 1,2-/3,4-isoprene) block copolymer with semifluorina ted acid chlorides. Two distinct first-order transitions were observed by D SC measurements in the resulting block copolymers at temperatures below the glass transition of polystyrene. The transition temperatures of the longer fluorocarbon units (10 -CF2- units) were found to be higher than the short er fluorocarbon units (eight -CF2- units). By comparing the block copolymer s having -CF3 end groups with those with -CF2H end groups, it was found tha t both the thermal behavior and surface properties are significantly affect ed by the terminal group of the semifluorinated side chains in the block co polymer. NEXAFS spectroscopy reveals that, although the surface coverage by semifluorinated groups is roughly the same regardless of whether the ends are -CF2H or -CF3, the orientational order of the -CF2H surfaces is signifi cantly poorer than that of the -CF3 surfaces. After long-term water exposur e the -CF2H surfaces were observed to reconstruct to more hydrophilic ones even though the analogous polymers with -CF3-terminated semifluorinated sid e chains were quite stable. The ease of surface reconstruction is probably related to the relatively poor orientation order of the polymers with -CF2H end groups as determined by NEXAFS.