CHARACTERIZATION OF ABSORBED WATER IN PERDEUTERATED POLYCARBONATE BY RESIDUAL-PROTON NMR

The distance from the protons of water absorbed in a precipitated, perdeuterated polycarbonate powder to the C-13-labeled carbonyl carbon is 5 +/- 1 Angstrom. This distance was determined by magic-angle spinning rotational-echo double-resonance H-1 NMR with C-13 dephasing. As shown by rotor-synthesized Hahn-echo dephashing, translational motion of the absorbed water is restricted in a nominally dry powder but not in an annealed film. Water in both powder and film undergoes rapid, nearly isotropic rotational reorientation. Water in the powder shares motions with a structural unit in the polycarbonate that is large enough to have a correlation time comparable to the rotor period.