High resolution /sup 1/H solid state NMR studies of polyethyleneterephthalate
Molecular motions and spatial properties of the solid polymer polyethyleneterephthalate have been investigated using high resolution /sup 1/H solid state NMR techniques. The longitudinal spin relaxation time T/sub 1/rho of protons (/sup 1/H) in the rotating frame was measured for a spin locking field ranging from 5 to 20 G. The decay of the /sup 1/H magnetization indicated the existence of two distinct T/sub 1rho/'s and their field dependence shows that they are associated with two mobile phases of the polymer. The /sup 1/H magnetization also relaxes under the dipolar narrowed Carr--Purcell (DNCP) multipulse sequence with two dintinct T/sub 1y/ relaxation times. The ratios T/sub 1y/'s and T/sub 1rho/'s deviate significantly from the expected theoretical values. The combined experiment with magic angle spinning and the DNCP sequence followed by homonuclear dipolar decoupling reveals the individual T/sub 1y/ relaxation of the resolved methylene and aromatic protons. These two species of protons were found to relax with the same T/sub 1y/'s, thus implying that spin diffusion must have taken place under the homonuclear dipolar decoupling multipulse. The qualitative description of spin diffusion under homonuclear decoupling is given. The combined experiment with spin locking and the DNCP sequence yields the correspondence between the two T/sub 1rho/'s and the two T/sub 1y/'s. The long T/sub 1rho/ corresponds to the short T/sub 1y/ whereas the short T/sub 1rho/ corresponds to the long T/sub 1y/. Communication between the two spatial phases via spin diffusion was also observed in this experiment by monitoring the recovery of the /sup 1/H magnitization associated with the short T/sub 1rho/ after it has been eliminated during the spin locking. The total /sup 1/H magnetization is allowed to equilibrate in the laboratory frame for a variable time much shorter than T/sub 1/ after the spin locking field has been turned off.
- Research Organization:
- Ames Laboratory and Department of Chemistry, Iowa State University, Ames, Iowa 50011
- OSTI ID:
- 6742843
- Journal Information:
- J. Chem. Phys.; (United States), Vol. 73:12
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
POLYESTERS
NMR SPECTRA
CARBOXYLIC ACID ESTERS
RELAXATION
RESOLUTION
SOLIDS
SPIN
TEREPHTHALIC ACID
ANGULAR MOMENTUM
CARBOXYLIC ACIDS
DICARBOXYLIC ACIDS
ESTERS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC POLYMERS
PARTICLE PROPERTIES
POLYMERS
SPECTRA
360404* - Materials- Polymers & Plastics- Physical Properties- (-1987)