Cross‐polarization with magic‐angle spinning kinetics and impedance spectroscopy study of proton mobility, local disorder, and thermal equilibration in hydrogen‐bonded poly(methacrylic acid)

Abstract

The 1 H-13 C cross-polarization with magic-angle spinning (CP MAS) kinetics was studied in poly(methacrylic acid) (PMAA) having the purpose to track the links between the local order in the main chain and the proton dynamics in peripheral hydrogen bond networks. The experimental CP MAS kinetic curves were analyzed applying the models of isotropic and anisotropic spin-diffusion with thermal equilibration. The fractal dimension D p ≈ 3 was deduced that indicates that PMAA behaves as an isotropic 3D-system. No proton conductivity in the neat PMAA was deduced from the impedance spectroscopy data analyzing the frequency dependences of the complex dielectric permittivity. The value of local order parameter S = 0.70 for CH 2 in PMAA occupies an intermediate position between 0.63 and 0.85 deduced for CH 2 sites in the main chains of poly(vinyl phosphonic acid) and poly(2-hydroxyethyl methacrylate), that is, the true proton conductor and the polymer that contains the H-bond network, however, no proton conductivity, respectively.

Solid-State NMR and Impedance Spectroscopy Study of Spin Dynamics in Proton-Conducting Polymers: An Application of Anisotropic Relaxing Model

“…Poly[2-(methacryloyloxy)ethyltrimethylammonium chloride] (PMETAC), poly(methacrylic acid) (PMAA), and poly(2-hydroxyethyl methacrylate) (PHEMA) (see Figure 1 ) with narrow molecular weight distribution were synthesized via radical addition–fragmentation chain transfer (RAFT) polymerization. More details on synthesis and characterization of PMAA, PHEMA, and PMETAC are given in refs ( 14 ), ( 15 ), and ( 20 ). Detailed synthesis procedure of PMETAC is provided in the Supporting Information .…”

“…We have successfully demonstrated that anisotropic relaxation during cross-polarization and adapted CP models well-match the predictions of impedance spectroscopy. 15 , 17 − 19 Further, we have contrasted results with PMAA and PHEMA polymers, which are not proton conductors. 15 This signifies that combination of these two methods are sufficiently developed to be used for new series of polymer conductors.…”

“… 15 , 17 − 19 Further, we have contrasted results with PMAA and PHEMA polymers, which are not proton conductors. 15 This signifies that combination of these two methods are sufficiently developed to be used for new series of polymer conductors.…”

Secular and semi-nonsecular models of cross-polarization kinetics for remote spins: an application for nano-structured calcium hydroxyapatite

“…Finally, the extremely high anisotropy of spin diffusion in the nano-CaHA (R I dp /R I df ~ 100-200), never seen for other studied spin systems, e.g. glycine [17] or some polymers [30,31], is noteworthy. It can be a matter of the applied models, as the I-S interaction with environment is neglected in both models (R S df = 0).…”

“…The 1 H → 31 P CP MAS experiments were performed for the spinning sample at 5 kHz at the n = +1 Hartmann-Hahn (HH) matching condition. The CP contact was achieved with rectangular 71 and 76 kHz RF pulses for 31 P and 1 H, re-spectively. The sample temperature was set to 298 K and controlled by a Bruker BCU II temperature regulation system.…”