Clay Intercalation of Poly(styrene−ethylene oxide) Block Copolymers Studied by Two-Dimensional Solid-State NMR

Abstract

The intercalation of poly(styrene−ethylene oxide) block copolymers (PS-b-PEO) into a smectite clay, hectorite, has been studied by multinuclear solid-state nuclear magnetic resonance (NMR). The behaviors of two copolymers with similar PEO block lengths (7 and 8.4 kDa) but different PS block lengths (3.6 vs 30 kDa) were compared. Polymer intercalation is assessed by two-dimensional 1H−29Si heteronuclear correlation (HETCOR) NMR with spin diffusion and refocused 29Si detection for enhanced sensitivity. Hydroxyl protons in the smectite layers serve as crucial spin diffusion references and 1H magnetization relay points from the polymer to the 29Si in the silicate. Experiments with CRAMPS evolution, with 1H spin diffusion, and with detection of the sharp OH proton signal after a 1H T2 filter provide excellent sensitivity for spin diffusion studies with mixing-time series. Because of the mobility of PEO, in this homonuclear experiment we can observe PEO−PS and clay−polymer spin diffusion simultaneously. While t...