where r is the rubber density (r of NR ¼ 0.92 g/cm3), Vs is
the molar volume of the toluene (Vs ¼ 106.4 cm3/mol), Vr is
the volume fraction of the polymer in the swollen specimen,
Qm is the weight increase of the blends in toluene and
c is the interaction parameter of the rubber networksolvent
(c of NR ¼ 0.393). The degree of the crosslink
density is given by;