Statistical copolymerization has been performed for five binary systems using 1-methoxy-2-methyl-1-trimethylsilyloxy propene (initiator) and tetrabutylammonium bibenzoate (catalyst) in tetrahydrofuran solution. The copolymer compositions were determined by elemental analysis for nitrogen and the results evaluated by the Kelen-Tudos method. The monomer pairs concerned are (1) acrylonitrile (AN) and methyl methacrylate (MMA), (2) AN and ethyl methacrylate (EMA), (3) AN and butyl methacrylate (BMA), (4) AN and butyl acrylate (BA), (5) AN and dibutyl maleate (DBM). The reactivity ratios determined in this study are : (1) gamma(AN) = 10.22, gamma(MMA) = 0.07; (2) gamma(AN) = 5.68, gamma(EMA) = 0.16; (3) gamma(AN) = 8.59, gamma(BMA) = 0.09 : (4) gamma(AN) = 4.08, gamma(BA) = 0.06; (5) gamma(AN) = 1.38, gamma(DBM) = 0.06. The copolymers were characterized by g.p.c., i.r. and H-1 n.m.r.