1H Solid State NMR Study of Poly(methacrylic acid) Hydrogen-Bonded Complexes

The hydrogen bond structure of a series of poly(methacrylic acid) (PMAA) complexes was studied by solid-state NMR. 13C and 2H labeled PMAA samples were complexed with poly(ethylene oxide) (PEO), poly(vinyl methyl ether) (PVME), poly(acrylamide) (PAAM), poly(vinyl caprolactam) (PVCL) and poly(vinylpyrrolidone) (PVPon). The presence and relative strengths of PMAA’s hydrogen bonds with itself versus those with the complementary polymer was assessed by combining 13C CP-MAS NMR, 1H–13C HETCOR, 1D and 2D DQ 1H MAS NMR experiments. Analyses of 1H DQ spinning sideband patterns gave estimates of the proton–proton distances. Only the polyether–PMAA complexes, PEO and PVME, show resolved 13C and 1H resonances. This spectral resolution is proposed to be due to the selective disruption and stabilization of PMAA’s open and cyclic dimers, respectively. Residual PMAA dimers are detected by 1H NMR for the polylactam complexes, PVCL and PVPon, but both types dimers are weakened, reflecting the greater amount of interpolymer linkages. The PAAM–PMAA complex maintains more of the weaker hydrogen bonds. The role of the different hydrogen bond structures in the relative stabilities and dynamic properties within this series of PMAA complexes and multilayers is assessed.