Radically initiated copolymerization of N-allylmaleimide with electron-donor monomers – styrene and trans-stilbene has been carried out and investigated. It has been established by chemical, spectral and kinetic methods of analysis that copolymerization reaction proceeds on double bonds of imide cycle and allyl multiple bonds do not participate in the chain growth reaction. The formation of unsaturated copolymers of alternating composition has been confirmed by copolymerization constant values and probabilities of formation of alternating sequences in chain. The assumption about complex mechanism of alternation of links in macromolecules of copolymers has been suggested.