Cationic copolymerizations of epichlorohydrin (ECH) (chloro-methyl oxirane) with styrene oxide (SO) (phenyl oxirane) and with 1,2-cyclohexene oxide (CO) (7-oxabicyclo [410] heptane) were carried out at 50°C by employing the salt triphenylmethyl hexachloro-antimonate (HC) (Ph3CSbCl6) as initiator. NMR spectra before and after attempted extractions of the polymeric products indicated that the resulting polymeric products were true copolymers and not mixtures of the respective homopolymers. Monomer reactivity ratios for both pairs of comonomers were determined; for one pair the values werer1(ECH) = 3.29,r2(CO) = 0.16 and for the second pairr1(ECH) = 0.57,r2(SO) = 0.16.