The NR-g-PMMA latex was diluted to ca. 20% DRC, stabilized
with 3 phr of a 10% solution of Teric N30 and then
placed into a 1000 mL glass reactor. Epoxidation was carried
out using performic acid generated in situ by the reaction
of formic acid and hydrogen peroxide at 60 C with a
controlled stirrer speed of 60 rpm [16]. The formic acid
was added dropwise and then the hydrogen peroxide was
slowly added under continuous stirring. The ratios of
reagents used were [HCOOH]/[H2O2] = 1 mol mol1 and
[H2O2]/[polyisoprene unit] = 0.25, 0.38 and 0.50 mol mol1.
The reaction was allowed to proceed for 24 h. The latex was
then neutralized by adding 25% aqueous solution of NH4-
OH, coagulated with acetone, washed several times with
distilled water and finally dried in a vacuum oven until a
constant weight was achieved. Before being subjected to
analysis, the epoxidized NR-g-PMMA; E(NR-g-PMMA),
samples were extracted by light petroleum ether and later
by acetone to remove free NR and free PMMA, respectively,
according to the method used for the purification of NR-g-
PMMA, as described above. The overall process from grafting
reaction to epoxidation is schematically displayed in
Scheme 1. In this study, epoxidized natural rubber (ENR)
with 30 mol% epoxide was also prepared directly from NR
latex, to be used for comparison purpose.