Co-reporter:Philip Wormald, Bruno Ameduri, Robin K. Harris, Paul Hazendonk
Solid State Nuclear Magnetic Resonance 2006 Volume 30(Issue 2) pp:114-123
Publication Date(Web):September 2006
DOI:10.1016/j.ssnmr.2006.05.003
Two fluoropolymers, poly(vinylidenefluoride) (PVDF) and a vinylidenefluoride telomer (VDFT), with molecular weights of 1×106 and 2×103 Da by GPC, respectively, have been analysed by 19F solid-state nuclear magnetic resonance (NMR) spectroscopy. Relaxation-filtered proton-decoupled magic-angle spinning (MAS) experiments, namely T1ρ filter, dipolar filter (DF), direct-polarisation delayed acquisition (DPDA) and discrimination induced by variable-amplitude minipulses (DIVAM), allowed signals in the direct polarisation (DP) spectra of PVDF and the VDFT to be discussed in terms of rigid and mobile domains. Both samples showed signals, which were multi-componential, but they differ in the nature of the crystalline form present. Thus, the Vinylidenefluoride (VDF) telomer exhibited a crystalline component corresponding to β PVDF, whereas the PVDF contained crystallites of the α form. Signals relating to end groups and reverse units, plus an anomalous signal displaying long-time transverse relaxation in the DPDA spectrum, were found for both polymers, though they showed diversity in chemical shift and content. Signals related to reverse units and/or end groups were seen between approximately −115 and approximately −117 ppm for both samples. High-speed MAS at higher magnetic field resulted in an increase in resolution so that signals previously attributed to single-phase characteristics are shown to indicate the possibility of several different mobilities. The results are debated with respect to molecular weight and relaxation parameters.
Co-reporter:Diego Carnevale ; Philip Wormald ; Bruno Ameduri ; Russell Tayouo ;Sharon E. Ashbrook
Macromolecules () pp:
Publication Date(Web):July 9, 2009
DOI:10.1021/ma900789t
Chlorotrifluoroethylene (CTFE) and ethyl vinyl ether (EVE) were reacted under radical conditions to produce the poly(CTFE-co-EVE) alternating copolymer, and a full 13C, 1H, and 19F NMR structural interpretation is offered. All spectra were characterized by broad signals resulting from the overlapping of different chemical shifts. This observation was rationalized by considering a complex mixture of diastereomerically related compounds, hence allowing an average assignment to be determined. A density functional theory (DFT) computational study of the isotropic magnetic shieldings with the GIAO and CSGT methods was performed to explore the diasteriomeric relationships between the single building blocks and their mutual influences along the polymer chain. The calculated results totally support the assignment of the experimental chemical shifts of two diasteriomeric sets of resonances indicating chiral center inversion, and not spin−spin J coupling interactions, as the main cause of spectral complexity.