How is the copolymerization of NBR latex different from that of SBR latex?
John Woon (Senior Latex Consultant):
Very briefly, the copolymerization of NBR (Acrylonitrile Butadiene) is similar to that of SBR (Styrene Butadiene) in the following:
1) Both acrylonitrile and styrene have similar effects on the final copolymers because both increase the Tg (Glass-Transition temperature), tensile modulus, hysteresis loss while reducing resilience and elongation of the respective copolymers.
2) Emulsion copolymerization of acrylonitrile and butadiene can be done using the same system for the copolymerization of styrene and butadiene.
However, they are different in the following manners:
1) NBR latex is normally used with its copolymer in rubbery and elastomeric form at ambient temperature. Hence the level of acrylonitrile is capped at about 50%. In the case of SBR latex, styrene level can be increased until the copolymer is no longer rubbery but stiff , brittle and non-film forming.
2) Copolymer with acrylonitrile is more polar than copolymer with styrene.
3) The effect of increased Tg of NBR by acrylonitrile is more due to the polarity rather than steric hindrance of the latter, unlike the case of styrene.
4) Needless to say, NBR when compared with SBR, as a result of the polarity of acrylonitrile, has higher adhesion to polar substrates and higher resistance against non-polar hydrocarbon liquids.