Table 4 Correlation coefficients between the CP dynamics parameters
–
H
CH
2
CF
2
–
–CF
H
2
CF
2
CF
2
–
–CF
H
2
CF
3
–CF
H
3
–CH
–CF
2
CF
2
–
CF
–CF
–CF
2
CF
2 2
CF –
2
F
2
2
–
2
CF
3
–
H
CF
2
2
3
CF
2
CF
2
–
À0.82
À0.03
À0.48
0.69
1
–CF
CF
3
0.02
0.02
1
H
–CF
À0.29
À0.04
À0.05
0.35
1
H
–CH
2
CF
CF
2
–
À0.93
À0.20
À0.03
À0.01
À0.05
À0.78
1
–CF
2
2
CF
2
2
–
–
–
CF
CF
2
2
CF
CF
2
CF
–
0.22
0.16
0.02
1
3
–
–
CF
CF
2
CF
3
0.06
0.05
3
T
1r(CF
ratio is larger, ranging between 3 and 4, suggesting that the
CF fluorines are more isolated than those in CF
3
)=T1r(CF
2
) of approximately 2. In the present case this
Conclusions
The theory of cross-polarization dynamics involving multiple
more than two) spin baths has been generalized using the spin-
3
2
.
(
Values of T1r(F) measured for Viton are shorter than for
copoly(I). However, the Viton measurements were taken at 200
MHz, at 297 K. They possibly indicate that the motion in the
Viton main chains is more restricted than for the copoly(I) side
temperature concept. It was implemented in the MATLAB
environment for up to six spin baths. The cross-polarization
dynamics for a fluoropolymer, copoly(I), was studied as a five-
spin-bath problem. Separate CP rates and T1r values were
obtained for each bath. The CP rates from the proton bath to the
fluorine baths reflect the side-chain structure. The T1r’s of the
proton bath measured via the fluorine signals show little differ-
entiation, indicating rapid H spin diffusion. Those of the
fluorine baths show significant variation, and are comparable to
those of PVDF. The long value for the CF
to rapid rotation about the C–CF bond and isolation from
1
9
chains. For copoly(I) in all cases, except for CF
are shorter than T1r(H). Similar trends were seen for the Viton
3
, the F values
1 19
T1 data of H and F. The T (F) and T (H) of copoly(I) are
r
very similar to those of the major component of the amorphous
1r
1r
1
1
3
signal of PVDF (2.9 ms and 5.8 ms respectively ).
The analysis of the CP dynamics was done by using the T1r
data for fluorine and proton as constraints to minimize the
number of parameters to be optimised. As mentioned pre-
viously, this system is treated as a five-spin-bath problem,
whilst strictly speaking there are more baths. Separate mea-
surements for three CF2 baths were not possible since the
resolution was inadequate. As a result, these had to be treated
as a single CF bath, referred to as the ‘‘internal’’ CF ’s. Thus
3
fluorines is attributed
3
other fluorines. The cross-polarization rates and the fluorine
spin-diffusion rates show significant statistical correlation.
2
2
Acknowledgements
an effective CP rate and relative population had to be used for
the ‘‘internal’’ CF2 spin bath. Consequently the relative
populations of the ‘‘internal’’ CF do not reflect the stoi-
2
chiometry of the system properly, being considerably smaller
than would be expected. The relative populations of the
remaining fluorine spin baths do reflect the stoichiometry of
the system, within the uncertainties that can be expected from
the deconvolution analysis.
The authors thank Professor C.A. Veracini for valuable dis-
cussions, the Italian MURST for partial financial support
within the framework of PRIN, and EPSRC for financial
support (grant GR=M73514). Access to the EPSRC Solid-state
NMR Research Service based at Durham is gratefully
acknowledged, as is the help in obtaining spectra by Dr. D.C.
Apperley and P. Wormald.
The cross-polarization rates from the proton to the fluorine
spin baths reflect the structure of the fluoroalkyl chain. The CP
À1
rate from H to CH
À1
2
CF
decreases to 120 s for the internal CF
2
is the most rapid at 258 s . This
À1
References
2
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1
2
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3 3
. The slower CP rate of the CF is in part due to the
1
3
3
Finite spin-diffusion rates between the fluorine spin baths
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3
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1
9,20
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7
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