Abstract
1H and 13C NMR spin-lattice relaxation times (T1) and 13C nuclear Overhauser enhancement (NOE) of radically prepared poly(methyl methacrylate) (Mn=28500) in CDCl3 were measured on 27 NMR spectrometers. Frequency range covered between 60 and 500 MHz for 1H NMR. Precision of 1H-T1’s of α-CH3 and CH2 protons was less than 5%. The 1H-T1’s of all sorts of protons increased linearly with increasing resonance frequency. The standard deviations for 13C-T1’s were larger than those for 1H-T1’s and exceeded 10% in some cases. The T1’s of all carbons except for the carbonyl carbon increased with frequency. The contribution of chemical shift anisotropy to the relaxation of the carbonyl carbon became significant above 25 MHz. The protons and carbons in the sequence rich in meso dyad showed longer T1’s than those in the corresponding sequence rich in racemo dyad. The precision of NOE was as good as that of 13C-T1. The NOE’s decreased as the observing frequency increased and particularly the NOE for the carbonyl carbon became almost unity at 100 and 125 MHz.
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Chûjô, R., Hatada, K., Kitamaru, R. et al. NMR Measurement of Identical Polymer Samples by Round Robin Method II. Reliability of Spin-Lattice Relaxation Time and Nuclear Overhauser Enhancement Factor. Polym J 20, 627–638 (1988). https://doi.org/10.1295/polymj.20.627
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DOI: https://doi.org/10.1295/polymj.20.627