Pulse and Multiple Pulse N.M.R. Studies of Crystallinity and Molecular Dynamics of Solid State Polymers

摘要

Pulse and multiple pulse N.M.R. techniques were used to study polypropylene and polyethylene. The degree of crystallinity of two polypropylene samples was investigated by analyzing the time decays of a simple pi /2 pulse and the more complex eight-pulse cycle. The single pulse experiment gives the superposition of two decays, the short component being attributed to the rigid region while the long component to the mobile region. Heating of the samples to 88 exp 0 Cproduced a situation where the rigid and mobile regions become synonymous with the crystalline and noncrystalline regions. The eight pulse cycle will only average the homonuclear dipole-dipole interactions, H/sub D/, only at observation times nt/sub c/, when the criteria t/sub c/ absolute value of H/sub D/ << 1 is met. With the selection of the appropriate cycle time, t/sub c/, of 72 mu s only the magnetization of the noncrystalline region will be monitored. The application of the eight pulse cycle, seventeen pulse cycle, -M/sub x/ phase pull sequence, and P/sub x/ - M/sub y/ phase pull sequence allowed for a variety of interaction Hamiltonians of polyethylene to be investigated. (ERA citation 04:053500)