Poly(bis-2,2,2-trifluoroethoxymethyl oxetane): Multiple crystal phases, crystallization-induced surface topological complexity and enhanced hydrophobicity

Abstract

Semicrystalline poly(bis-trifluoroethoxymethyl)oxetane, P(B-3FOx), was prepared by cationic ring-opening polymerization at −5 °C with Mn up to 21 kDa. Differences in cooling rates from the melt have substantial effects on crystal phase, percent crystallinity, surface topography, and wetting behavior. DSC and WAXD show that cooling from the melt at slow rates (<5 °C/min) gives α-P(B-3FOx) with ΔHf = 22–27 J/g. Quenching from the melt results in β-P(B-3FOx) for which a mesophase structure is suggested. β-P(B-3FOx) melts at 53 °C followed by recrystallization to α-P(B-3FOx). Solution casting from THF results in third phase, γ-P(B-3FOx). TM-AFM and SEM imaging for α-P(B-3FOx) showed that cold crystallization at 25 °C brought about increased crystallinity and surface topologies characterized by sharp asperities and lath-shaped crystals. Spontaneous surface roughening of α-P(B-3FOx) results in a discontinuous three-phase contact line with water and an increase in water sessile drop contact angle from 106° to 136°. The ∼30° increase in water contact angle was attributed primarily to a topological change from a relatively smooth surface (Wenzel state) to an asperity-rich surface yielding a discontinuous three-phase contact line (composite of Wenzel and Cassie-Baxter state). The oleophobicity for this polymer, which contains only a single CF3 end group on each side chain, compares favorably with more highly fluorinated acrylates. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1022–1034, 2010