Dynamics of an Amorphous Polymer by an Improved NMR Approach Based on the Simultaneous Analysis of ¹H and ¹³C Relaxation Times

Abstract

A new approach to extract quantitative dynamic information from NMR relaxation data of amorphous polymers is presented, consisting of the simultaneous fitting of 1 H and 13 C T 1 vs temperature curves obtained at different frequencies by means of unified motional models. The reliability of the dynamic parameters obtained by this approach is substantially increased with respect to the single curve analysis because of the possibility of both investigating motions over a wide frequency range and combining relaxation times carrying either global ( 1 H nuclei) or local ( 13 C nuclei) dynamic information. Experimental data were obtained for an amorphous ethylenepropylene random copolymer over a wide temperature range above its glass-transition: 1 H spin-lattice relaxation times were measured by wide-line techniques at four Larmor frequencies, while high-resolution MAS techniques were used to get 13 C spin-lattice relaxation times at a single frequency. The experimental data were analyzed in terms of segmental main-chain motion, rotation of the methyl groups about their ternary symmetry axes, and librations of C-H bonds, described by suitable models. The results showed good agreement between experimental and calculated data and allowed a detailed characterization of the motions investigated to be obtained.

Dynamics by Solid-State NMR: Detailed Study of Ibuprofen Na Salt and Comparison with Ibuprofen

“…A similar behavior has been explained with the contribution to 13 C T 1 relaxation of CÀH bond librations. 32,33,30 Indeed, if librations are considered to be independent from and much faster than the main motion (the isobutyl rotation, in our case), then their contribution to the relaxation results in a simple reduction of the theoretical constant C C C exp C ¼ χC theor C with the scaling factor χ < 1. In our case, a scaling factor of 0.25 indicates a significant contribution of librations to relaxation.…”

“…The motions of isobutyl and methyl groups were assumed to be independent; consequently, their contributions to the relaxation rate of carbons m/n were considered to be additive. 30 However, the agreement between calculated and experimental curves was found to be good only when C C for the sole isobutyl motion was taken as a fitting parameter rather than calculated from eq 4. (See Figure 3.)…”

Proton conducting membranes in fully anhydrous conditions at elevated temperature: Effect of Nitrilotris(methylenephosphonic acid) incorporation into Nafion- and poly(styrenesulfonic acid)

“…where e is the fundamental charge and wherein ion displacement is enabled by the segmental motion of polymer chains (indeed, the polymer main chain motion itself, detected for instance by nuclear relaxation, is well described only by the VTF model [52,53]). Thus, the behavior observed in Fig.…”

Detailed Characterization of the Dynamics of Ibuprofen in the Solid State by a Multi‐Technique NMR Approach

“…This method is more robust and reliable than the separate fittings of single curves, which may bring biased results. [15] …”