Morphological studies of polyphosphazenes and their nanocomposites using solid-state nuclear magnetic resonance spectroscopy
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Date
2014
Authors
Sun, Chuchu
University of Lethbridge. Faculty of Arts and Science
Journal Title
Journal ISSN
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Publisher
Lethbridge, Alta. : University of Lethbridge, Dept. of Chemistry and Biochemistry
Abstract
Solution state NMR of 'H, 19F and 3IP of poly[bis(trifluoroethoxy)] (PBFP) in THFd8
were acquired to study the polymer morphology in the solution state. Solid state high
resolution *H, I9F and 31P MAS DP NMR spectra were studied using a deconvolution
method to understand how each component proportion varies with synthetic approach and
processing methods, such as solvent casting, heat cycling, and inclusion of inorganic nanoparticles.
The l9F and 31P NMR relaxation time data were acquired at an MAS spinning rate of
10 kHz, over a temperature range from 20 to 80 °C for samples PBFP, annealed PBFP, NC
5% and annealed NC 5%. The l9F NMR spectra were deconvolved using a threecomponent
model for samples PBFP and NC 5% and a four-component model for samples
annealed PBFP and annealed NC 5% from 20 to 40 °C. A four-component model was used
for all four samples at high temperature range, from 50-80 °C. The 3IP NMR spectra were
deconvolved using a four-component model for all four samples from 20 to 40 °C. A fivecomponent
model was applied to all four samples over 50 to 80 °C. The models were
established and adjusted to be consistent for all the relaxation arrays over their
corresponding temperature ranges.
The relaxation time constants of each component were analyzed and compared
between samples and temperatures. All 31P Ti constants decrease with increasing
temperature and their T2 values increase, indicating the polymer backbone is in the slow
motion regime. For any particular component, the annealed PBFP always has the largest
Ti, the annealed NC 5% has the second longest Ti, followed by the PBFP and NC 5% has
the shortest Ti, suggesting that annealing increases the crystallite size and thus slows the
motion of the backbone; the filling of nano-TiCh suppresses the growth of the crystallites
and enhances the motion of the polymer backbone. The I9F Tj values increase with
temperature and their T2 also increase with temperature, suggesting the polymer sidechain
is in the slow motion regime. For any particular component, the NC 5% always has the
largest Ti and the PBFP has the second largest Ti, followed by the annealed NC 5% and
annealed PBFP has the shortest Ti; indicating that annealing increases the crystallite size
and thus slows the motion of the polymer sidechains; the nano-TiC>2 suppresses the growth
of the crystallite and enhances the motion of the polymer sidechain, similar effects as what
are observed for polymer backbone.
The lH to 31P and 19F to 31P NMR cross polarization results at 20 °C for all four
samples, indicated that there are two CP curves for JH to 31P. One has a much faster
building up and decay rate than the other. Only one CP curve for 19F to 3IP CP was observed.
This suggests that the protons from the middle of the polymer sidechains are more sensitive
to the motion of the polymer backbone than the fluorines near the terminal of the sidechains.
The model for 31P is further refined based on the CP curves and the relaxation data and
could be correlated to different phases of the polymer,
Description
Keywords
polymer morphology , solid state high resolution spectra , deconvolution method , solvent casting , heat cycling , inorganic nanoparticles , Polyphosphazenes -- Research , Nanocomposites (Materials) -- Research , Nuclear magnetic resonance spectroscopy , Quantum theory , Atomic orbitals , Dipole moments , Chemistry, Organic , Dissertations, Academic