Biomedical Engineering Reference
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hesulfonated DPNR- graft -PS was stained with RuO 4 , in which the bright domains rep-
resent the DPNR and the gloomy domains represent polystyrene. The sulfonation of
DPNR- graft -PS-5.5made connecting the PS particles to form completely continuous
nanomatrix, since the PS particles were dissolved into chloroform before sulfonation
with chlorosulfonic acid, but the DPNR particles were not due to three-dimensional
network structure. Thickness of the connected nanomatrix is about 80 nm, reflecting
that several PS particles of about 60 nm in diameter fuse to each other after sulfona-
tion. A volume fraction of the resulting sulfonated PS is estimated by image-analysis
to be about 35 vol% in the sulfonated DPNR- graft -PS-5.5. The estimated value of
the volume fraction is quite similar to 36 vol% of fed styrene for graft copolymeriza-
tion, as expected from more than 90 mol% conversion and about 80 mol% grafting
efficiency of styrene.
Figure 15 shows solid state 13 C CP/MAS NMR spectra for (a) DPNR- graft -PS-5.5
and (b) DPNR- graft -PS-5.5 sulfonated with 0.8 N chlorosulfonic acid. As for the
DPNR- graft -PS-5.5 (Figure 15 (a)), signals at 23.4 (5), 26.5 (6) and 32.4 (7) ppm in
aliphatic region are assigned to methyl and methylene carbon atoms of cis -1,4-iso-
prene units, whereas the signals at 125.2 (9) and 134.8 (10) ppm in olefinic region are
assigned to C=C of cis -1,4-isoprene units. Furthermore, three signalssignals appeared
at 40.0 (8), 127.1 ppm (11) and 145.7 ppm (12), respectively, which are assigned to ali-
phatic carbon of methylene group and aromatic carbons of styrene unit, respectively.
After sulfonation, signals characteristic of DPNR and PS disappear, whereas broad
signals spectrum appear to overlap to each other in aliphatic region and new signal
appears in olefinic region, as shown in Figure 15 (b). The new signal at 139.5 ppm (3)
in Figure 15 (b), appears after sulfonation, which overlapped with the signals at 127.2
(2) and 149.4 (4) ppm. According to the previous literatures (Kawahara et al., 2003),
the signal at 139.5 ppm (3) is assigned to aromatic carbon substituted with sulfonic
acid group, whereas the broad signals in aliphatic region ranging from 10 ppm to 40
ppm were assigned to methyl and methylene carbons of cyclized cis -1,4-isoprene units
(Patterson et al., 1987). Therefore, the overlapped broad signals, marked as no.5 in
Figure 15 (b), are explained to be due to the cyclization of DPNR, which is supported
by a dramatic increase in glass transition temperature, T g , and gel content (Table 2).
Electrochemical properties of the sulfonated DPNR- graft -PS are summarized in
Table 2. A conversion of the sulfonation, estimated from a sulfur content (mol%) of
the sulfonated DPNR- graft -PS-5.5, is 75 mol% at 0.8 N chlorosulfonic acid. The value
of the ion exchange capacity (IEC) of the sulfonated DPNR- graft -PS-5.5 is 2.4 meq/g
at 75 mol% sulfur content, which is larger than the value of the IEC of sulfonated PS,
itself, and Nafion®117. ® 117. On the other hand, the value of the proton conductivity of the
sulfonated DPNR- graft -PS-5.5 was 9.5 × 10 -2 Scm -1 at 75 mol% sulfur content, which
was about third as large as that of the sulfonated PS. The large values of the IEC and
the proton conductivity may be attributed to the formation of the nanomatrix structure
as a channel for the ion-transpotation, since the well-connected nanomatrix of the sul-
fonated PS is formed between the cyclized DPNR particles.
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