BUTADIENA CH2=CH-CH=CH2 are M= 48gC+6gH= 54g/mol
STIRENUL C6H5-C(CH3)=CH2 are M= 108gC+10gH= 118g/mol
in polimer sunt x moli butadiena si y moli stiren
(54x+118y) cauciuc...................(48x+108y)g
100g................................................90g
100(48x+108y)=90(54x+118y)======. > x:y= 3:1