Solid-state nuclear magnetic resonance spectroscopy of phosphazene polymers
Borisov, Alexey S.
University of Lethbridge. Faculty of Arts and Science
Lethbridge, Alta. : University of Lethbridge, Dept. of Chemistry and Biochemistry, c2009
High-resolution one-dimensional 1H, 19F, 31P and 13C MAS NMR experiments were used in a morphological study of solvent-cast and heat-treated poly[bis(trifluoroethoxy)phosphazene] (PBFP). Deconvolution analyses performed on all Nuclear Magnetic Resonance (NMR) spectra are presented. These results suggest the presence of broad and narrow overlapping components at ambient temperature, which were assigned to the crystalline, amorphous and the mesophase regions within the polymer, respectively. The number of signals in the spectra was independently verified using 1H, 19F and 13C Discrimination Induced by Variable Amplitude Minipulses (DIVAM) nutation experiments. Deconvolution analyses showed that heat-treatment increases the overall crystallinity of the solvent-cast PBFP. Further studies conducted on two preparations of the polymer showed significant differences in crystallinity due to variations in the reaction conditions. Magic-Angle Spinning (MAS) NMR spectra of PBFP obtained via living cationic polymerization at ambient temperature indicated that the polymer contains mostly amorphous and mesophase regions with only a small contribution from the crystalline domain. Variable-temperature 31P NMR experiments suggested that the thermotropic transition occurs in a temperature range of 80ºC to 90ºC, where the crystalline signal disappears and a new signal due to a liquid crystalline phase emerges. Spin-lock 31P experiments provided rates of the transverse relaxation in the rotating frame for each signal, showing that the crystalline and the amorphous regions within the polymer are characterized by significantly different mobilities at ambient temperatures, while the v comparable degree of motion occurs between the amorphous and mesophase environments at temperatures above 90ºC. The process of thermal ring-opening polymerization of hexachlorocyclotriphosphazene was monitored using one-dimensional 31P MAS NMR at different stages of the reaction. The ratio between cyclic species and the high molecular weight poly(dichlorophosphazene) was seen to change over time. 31P NMR was seen to be a potentially valuable tool in monitoring rates of chain propagation, branching and cross-linking. Two-dimensional 31P homonuclear Radio-Frequency Driven Recoupling (RFDR) and Incredible Natural Abundance Double Quantum Transfer (INADEQUATE) MAS NMR experiments were first tested on the partially phenoxy-substituted hexachlorocyclotriphosphazene, and subsequently applied in the study of a preparation of the partially trifluoroethoxy-substituted poly(dichlorophosphazene). Very high resolution was obtained in the direct dimension due to the presence of low molecular weight species. Preliminary spectral assignments of all of the observed signals were made on the basis of both known chemical shifts of the related species, and the through-space and through-bond phosphorous-phosphorous connectivities.
xiii, 188 leaves : ill. ; 29 cm
Polyphosphazenes , Nuclear magnetic resonance spectroscopy , Polymerization , Ring-opening polymerization , Dissertations, Academic