Properties and Nano-observation of Natural Rubber with Nanomatrix Structure - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 320

FormatioN oF NaNomatriX struCture
Nanomatrix structure was formed by graft-copolymerization of styrene onto deprot-
einized natural rubber. To form the nanomatrix structure, 1.5 mol/kg-rubber of styrene
is fed into natural rubber latex after adding an initiator (Akabori et al., 2009; Kawahara
et al., 2008, 2007, 2003; Pukkate et al., 2007; Suksawad et al., 2009, in press; Yusof et
al., 2008). The resulting graft-copolymer, DPNR- graft -PS, was characterized through
1 H-NMR spectroscopy. A typical 1 H-NMR spectrum of DPNR- graft -PS, is shown in
Figure 5. Signals characteristic of cis- 1,4-isoprene units appeared at 1.76, 2.10, and
5.13 ppm, which were assigned to methyl, methylene and unsaturated methyne pro-
tons of isoprene units, respectively. Broad signals at 6-7 ppm were assigned to phenyl
proton of styrene units, whose intensity was dependent upon the feed of styrene as a
monomer. Thus, we estimated a content of styrene units in the DPNR- graft -PS and
conversion of styrene from a ratio of signal intensity of phenyl proton to methyl proton
and the feed of styrene.
Figure 5. Typical 1H-NMR spectrum for DPNR-graft-PS.
The estimated content of styrene units and conversion of styrene are shown in
Figure 6. Both of the content and conversion were dependent upon the feed of styrene;
for instance, the higher the feed of styrene, the higher is the content of styrene units. In
contrast, a locus of convex curve was drawn for the conversion, in which a maximum
is shown at 1.5 mol/kg-rubberstyrene-feed. This suggests that the most significant
feed of styrene is 1.5 mol/kg-rubber in the case of graft-copolymerization of styrene
onto DPNR with tert- butyl hydroperoxide of 3.3×10 -5 mol/g-rubber with tetraethylene
pentamine at 30°C.