Investigations of some polymers and electrooptical crystals by multiple pulse line narrowing NMR experiments (1H-resonance)

NMR line narrowing experiments (1H-resonance) were performed using a number of different solid samples. These samples were a series of polymers (enopentyl glycoldimethacrylates polyethylenes, copolymers of ethylene vinylacetate, polyformaldehydes, these materials prepared in different ways, and polystyrene, caprone, benzyl cellulose) and various electrooptical crystals (ADP, KDP, triglycine sulphate, triglycine selenate, ammonium oxalate). The NMR line width was determined by wide line spectra and T2-measurements. For line narrowing experiments the WHH-4 pulse sequence was used in all cases. Additionally, studies by means of the MW-4 method (sequence of identical π/2 pulses) were performed in all cases too, looking for the dependence on the cycle time in some polymers and ADP. The decay times attained by means of the WHH-4 programme are for the investigated substances in the range of 0,5 to 2,5 ms, using cycle times of 36 to 60 μs. The values of the narrowing factor depend to a high degree on experimental parameters (cycle time, resonance offset) and on properties of the material (internal motions, various phases in the NMR signal, heteronuclear dipole-dipole-interaction). Based upon this the values of residual line width are discussed. (author)