NMR Measurement of Identical Polymer Samples by Round Robin Method II. Reliability of Spin-Lattice Relaxation Time and Nuclear Overhauser Enhancement Factor

Abstract

ABSTRACT:1 H and 13 C NMR spin-lattice relaxation times (T1) and 13 C nuclear Overhauser enhancement (NOE) of radically prepared poly(methyl methacrylate) (M.=28500) in CDC!3 were measured on 27 NMR spectrometers. Frequency range covered between 60 and 500 MHz for 1 H NMR. Precision of 1 H-T1 's of ix-CH3 and CH2 protons was less than 5%. The 1 H-T1 's of all sorts of protons increased linearly with increasing resonance frequency. The standard deviations for 13 C-T1 's were larger than those for 1 H-T1 'sand 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 13 C-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. KEY WORDS