The curing reaction mechanism of epoxide groups and C/C double bonds was investigated by using sulfur (S) as curing agent

and liquid nitrile butadiene rubber (NBR)

phenyl glycidyl glycerol ether (GPE) and allyl phenyl glycidyl ether (APE) as model compounds.Differential scanning calorimetry (DSC)

Fourier transform infrared spectroscopy (FTIR)

X-ray photoelectron spectroscopy (XPS) and dynamic mechanical thermal analysis (DMA) were used to detect the variations of curing enthalpy

double bonds and the epoxy groups with reaction time.The experimental results showed that the chemical reactions between the nitrile rubber and epoxy model compounds were verified

and the curing reaction in NBR-Sulfur system is a one step reaction

and in that rubber/epoxy compounds/sulfur system is a two step reaction.Comparatively

the cured NBR-S shows the lowest glass transition temperature and the highest energy storage modulus and crosslinking density

while

NBR-APE-S presents the highest glass transition temperature and the lowest energy storage modulus and crosslinking density.Furthermore

the curing mechanism of the liquid rubber and epoxy compound is suggested as:sulfur can cleavage into sulfur radicals

which initiate the addition reaction of rubber double bonds to form mercapto groups.Finally

the resultant mercapto groups react further with epoxy groups through ring-opening reaction.Meanwhile

coupling reactions between different radicals occur.