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Abstract
Why Rubber Trees Produce Polyisoprene – A Possible Role
of Natural Rubber in the Heavea Tree
A possible role of rubber in the Hevea brasiliensis
tree was presumed based on the analysis of structural changes of rubber
during storage in the rubber tree as latex. The rubber obtained from a previously
untapped mature-tree, a so-called virgin mature-tree (Vir-NR), contained
a gel fraction higher than 80%. The gel fraction showed almost the same
structure as a crosslinked rubber prepared from fresh latex in the presence
of peroxide, with the molecular weight of a primary segment between crosslinks
( Mc) of 3 x 103. The sol fraction from Vir-NR was
an oxidative degraded product containing aldehyde and epoxide groups. The
gel fraction from a regularly tapped mature-tree (Reg-NR) was less than
3% and was loosely crosslinked with hydrogen bondings and ester linkages,
having Mc of 7 x 105. These indicate that rubber accepts
radicals, to form C-C crosslinking and partly oxidative degradationproducts
in laticiferous tubes of Hevea tree during storage, suggesting a possible
role of rubber as a scavenger of hydroxy radicals in latex.
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