NMR studies of conformation and molecular motion of poly(methyl methacrylate) in solution

Abstract

NMR shift reagent, tris(dipivalomethanato)europium(III), was applied to the 'H NMR measurement of isotactic and syndiotactic poly(methy1 methacrylate) in solution in the temperature range 25580°C. The solvents used were benzene (C6D6), chloroform (CDC13), and carbon tetrachloride (CCI,). By comparing the observed values of paramagnetically induced shift with the values of geometric factor calculated for several kinds of conformational models hitherto proposed for these polymers, the possible conformations of the respective polymers in solution were eludicated. Furthermore the variation, as a function of temperature, of the carbon-1 3 spin-lattice relaxation times of individual carbons of isotactic and syndiotactic poly(methy1 methacrylate) in benzene and chloroform solutions were measured and the correlation between the molecular motion and the conformation is discussed. It is pointed out that the conformation depends both on the stereochemical configuration and the nature of solvent, and the molecular motion depends both on the conformation and the configuration.

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

“…Carbons in the sequence rich in meso dyad generally showed larger 13 C- - the carbons will be published in this Journal. 13 C-T 1 's for the carbonyl carbon decrease with increasing resonance frequencies above 25 MHz. The relaxation induced by chemical shift anisotropy is possible for the carbons in n-bond.…”

“…13 C Spin-Lattice Relaxation Times of PMMA 13 C-T/s for the PMMA in CDCl 3 were measured at 55°C on 27 instruments, whose resonance frequency ranged from 15.0 to 125 MHz. The individual data are collected in Table IV.…”

“…The relaxation parameters are also of essential importance in adjusting data acquisition conditions in FT NMR measurement to obtain quantitative data. Research group on NMR, Society of Polymer Science, Japan (SPSJ), collected 1 H and 13 C NMR spectra of two identical samples, poly(methyl methacrylate) and solanesol, from a number of NMR spectrometers. The results of assessment on the reliability of chemical shift and signal intensity were reported previously.…”

“…The results of assessment on the reliability of chemical shift and signal intensity were reported previously. 1 Insufficient agreement in the 13 C signal intensity urged us to assess the reliability of spin-lattice relaxation time {Ti) and nuclear Overhauser enhancement (NOE) factor which are required for proper setting of conditions of measurements. It is also important to know whether or not the precision of determination of these parameters allows us to treat them as one of the characteristics of a polymer.…”

“…The data were collected from spectrometers whose observing frequencies ranged from 60 to 500 MHz for 1 H NMR and from 15 to 125 MHz for 13 C NMR. As a result, frequency dependences of T 1 and NOE were obtained for a very wide range of frequencies.…”