Advanced NMR studies of fluoropolymers

The advanced NMR studies of fluoropolymers are focused on the Krytox RTM poly-(hexafluoropropylene oxide) (PHFPO) and poly(1-chloro-1-fluoroethylene) (PCFE).;2D NMR techniques were used to study the structures of PHFPO and its mechanism of polymerization. Model compounds K4, E4, and E2, containing four and two hexafluorpropylene oxide repeat units, respectively, were analyzed to interpret the patterns of the spectra from the polymers. Selective 19F-13C gradient HSQC experiments provided information about the C-F attachments within monomer units of the backbone and chain-ends. A series of selective 19F- 19F COSY 2D NMR experiments were performed. When selective experiments were combined with selective inversion pulses to remove most of the J FF couplings in the f1 dimension, greatly simplified 2D NMR spectra were obtained. This made it possible to resolve signals from various stereo sequences and monomer inversions present in the polymer. Resonances from all of the structures detected in the polymer have been identified and attributed to the various mechanisms for initiation and termination of the polymerization.;3D NMR techniques were used to study the structures and tacticities of PCFE. Higher resolution and higher intensity data were obtained with gradient coherence selected 1H/13C/19F 3D-NMR with single-quantum coherence transfer. Complex multiplet patterns, predicted due to the long range 19F-19F homonuclear couplings, were confirmed by careful examination of the 2D planes from the 3D-NMR data. Correlations were detected from methylene groups centered in twenty hexads, and fluorines centered in ten pentads. With an optimized constant evolution time version of the 3D pulse program, real fluorine resonance frequencies can be determined up to the pentad level.