nCH2=CH-CH=CH2 + mCH2=CH-CN -> [-(CH2-CH=CH-CH2)n--(CH2=CH-CN)m-]
M butadienei = 54
M acrilonitril = 53
Masa cauciucului = 54n + 53m
54n + 53m grame cauciuc conţin..................14m grame N
100 grame ................................................. 8.7
=> 54n = 104m <=> n/m = 2/1