Fine structural features and proton conduction in zwitterionic poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC): Multinuclear solid-state NMR, impedance and FTIR spectroscopy study

Abstract

The poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), i.e. one of the most biocompatible synthetic polymer, was synthesized using radical addition-fragmentation chain transfer (RAFT) polymerization and characterized by a wide set of experimental techniques, the 1H, 13C, 15N, 31P NMR, impedance and FTIR spectroscopy among those. The optimized synthesis conditions ensured the high product yield, high purity and narrow molecular weight distribution. The stereochemical content was determined from the complex shaped 13C MAS signal of CH3 group, and the relative content of the adsorbed water - from the 1H MAS spectra. The 1H13C and 1H31P cross-polarization kinetics were measured and processed using the Hirschinger and Raya spin dynamics model. Fine structural details, such as the partial (ca 10%) protonation of the internal PO4− group, the local order and the flexibility of the main chain were deduced. The thermal activation of proton conduction in the wet PMPC was deduced by impedance spectroscopy. The thermal boosting of proton mobility is driven via breaking the cage-like structures of water. This was confirmed by 1H MAS and FTIR spectroscopy. The experimental data for poly[2-(methacryloyloxy)ethyl trimethylammonium chloride] (PMETAC), i.e. cationic proton conducting polymer, which structure is closely related to PMPC, were revisited, compared and discussed.