13C MAS NMR Study of Poly(methacrylic acid)-Polyether Complexes and Multilayers

Hydrogen-bonded interpolymer complexes are widely used as stimuli-responsive materials. This solid-state C-13 MAS NMR spectroscopy study examines the influence of water and temperature on the hydrogen bond structures of C-13-labeled poly(methacrylic acid) (PMAA) complexes with poly(ethylene oxide) (PEO) and poly(vinyl methyl ether) (PVME). The spatial variation of the inter- and intrapolymer hydrogen bonds in the dried bulk complexes and supported multilayers was measured by 2D C-13 exchange (EXSY) NMR. In contrast to earlier studies of PAA complexes, the cross-peak intensities of the PMAA complexes are primarily due to C-13 spin exchange rather than H-bond exchange due to the use of C-13-labeled PMAA and slower dynamics. The C-13-C-13 spin diffusion between the carbonyl groups with intra- versus interpolymer hydrogen bonds indicates interatomic distances of <7 angstrom, consistent with interpolymer and the different intra-PMAA hydrogen bonds occurring together along the PMAA chain segments or in nanodomains in close proximity rather than isolated clusters. The fractional population involved in the spin diffusion corresponded to the population of the stronger cyclic dimer, such that PMAA-PEO complex > PVME complex > PEO supported multilayers > PVME supported multilayers. For the multilayer films, there are fewer of the stronger, more ordered cyclic dimer hydrogen bonds due to the disordering effect of the interfaces.